Merge pull request #1843 from kacpherek/fix/1504-hardcore-spectator

🤖 Agent: thank you! Merged after the contribution gate (checked against vanilla 26.3; one integration branch of main + all 14 of your PRs: fmt, clippy -D warnings, horizon-client/world tests, horizon-ctl scenarios on the server thread and in-frame, lan_e2e in both host modes, and the 30 harnesses covering these changes: 29 pass, the 30th is /help listing /pregen from #1805) and this head's verify.

.githooks/pre-push

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec python3 tools/check_public_tree.py --history
+exec python3 tools/check_public_tree.py --pre-push

.github/workflows/mod-registry.yml

@@ -0,0 +1,34 @@
+name: mod-registry
+# The submission service is its own workspace (crates/horizon-mod-registry), so the checks job doesn't build
+# it: this one does, when it or horizon-mods (the checks it shares with the launcher and the game) changes.
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'crates/horizon-mods/**'
+      - 'crates/horizon-mod-registry/**'
+      - '.github/workflows/mod-registry.yml'
+  pull_request:
+    paths:
+      - 'crates/horizon-mods/**'
+      - 'crates/horizon-mod-registry/**'
+      - '.github/workflows/mod-registry.yml'
+permissions:
+  contents: read
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    defaults:
+      run:
+        working-directory: crates/horizon-mod-registry
+    steps:
+      - uses: actions/checkout@v4
+      - run: rustup toolchain install stable --profile minimal --component rustfmt --component clippy
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: crates/horizon-mod-registry
+          save-if: ${{ github.ref == 'refs/heads/main' }}
+      - run: cargo +stable fmt --check
+      - run: cargo +stable clippy --all-targets --locked -- -D warnings
+      - run: cargo +stable test --locked

AGENTS.md

@@ -45,6 +45,7 @@ Game workspace (root `Cargo.toml`); `launcher/` and `crates/horizon-telemetry-se
 | `horizon-friends`, `horizon-relay` | Play with Friends: invite codes, encrypted tunnel, the relay ([docs/play-with-friends.md](docs/play-with-friends.md)) |
 | `horizon-mods`, `horizon-mod-sdk`, `cargo-horizon-mod` | Sandboxed WebAssembly mods: runtime, SDK + WIT, `cargo horizon-mod` ([docs/mods.md](docs/mods.md)) |
 | `horizon-port-pack` | Porting Java modpacks ([docs/modpacks.md](docs/modpacks.md)) |
+| `horizon-shader-api` | Horizon's own WGSL shader packs ([docs/api/shaders.md](docs/api/shaders.md)): `horizon-shaders.toml`, the `.hshader` package; shared by the game, the launcher and the registry |
 | `horizon-shaders` | Shader packs (the `shaders/` folder format), rebuilt clean-room from a written spec of the format; no wgpu |
 | `horizon-theme` | Design tokens and fonts for the launcher, the game's own menus and the website |
 | `horizon-telemetry`, `horizon-telemetry-server`, `horizon-bench` | Opt-in data collection, its ingest server, the benchmark report format |

CONTRIBUTING.md

@@ -7,6 +7,11 @@ welcome on [Discord](https://discord.gg/HcTeMZxe5E).
 This repository holds the game, the launcher and the website, plus the tools, tests and docs that build, check and
 release them. Anything else (videos, Discord and other community material) lives elsewhere.
 
+**Where to start: [playhorizon.dev/hub](https://playhorizon.dev/hub).** It shows what is being done now and next
+([ROADMAP.md](ROADMAP.md) in the repository), the work board, good first tasks, and the forms to report a bug or
+suggest something. A pull request for a roadmap item carries its `roadmap:<id>` label; ideas go to the suggestion
+queue (the hub, or `/suggest` on Discord) rather than to issues, which are for bugs.
+
 ## Build it
 
 You need Rust (stable), Python 3.10+, JDK 25, and on Linux the ALSA and udev headers (`libasound2-dev libudev-dev`).
@@ -39,6 +44,8 @@ probe against Horizon, and compares their outputs. There are about 290 of them.
 
 Never commit game files, decompiled source or prepared resources (`.local/`): `tools/check_public_tree.py` rejects
 them (`git config core.hooksPath .githooks` runs it before every commit).
+The pre-push hook checks the full history reachable from the branches and tags being pushed. Run
+`python3 tools/check_public_tree.py --history` to audit the history of all local refs.
 
 ## Only original code
 

Cargo.lock

@@ -428,6 +428,8 @@ version = "0.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "af491d569909a7e4dee0ad7db7f5341fef5c614d5b8ec8cf765732aba3cff681"
 dependencies = [
+ "serde",
+ "termcolor",
  "unicode-width",
 ]
 
@@ -1266,6 +1268,7 @@ dependencies = [
  "horizon-mods",
  "horizon-protocol",
  "horizon-server-files",
+ "horizon-shaders",
  "horizon-telemetry",
  "horizon-theme",
  "horizon-threads",
@@ -1434,10 +1437,25 @@ dependencies = [
  "ureq",
 ]
 
+[[package]]
+name = "horizon-shader-api"
+version = "0.1.0"
+dependencies = [
+ "bytemuck",
+ "naga",
+ "serde",
+ "serde_json",
+ "sha2",
+ "toml",
+ "zip",
+]
+
 [[package]]
 name = "horizon-shaders"
 version = "0.1.0"
 dependencies = [
+ "horizon-core",
+ "naga",
  "zip",
 ]
 
@@ -1973,6 +1991,7 @@ dependencies = [
  "naga-types",
  "num-traits",
  "once_cell",
+ "pp-rs",
  "rustc-hash 1.1.0",
  "spirv",
  "thiserror 2.0.21",
@@ -2649,6 +2668,15 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "pp-rs"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb458bb7f6e250e6eb79d5026badc10a3ebb8f9a15d1fff0f13d17c71f4d6dee"
+dependencies = [
+ "unicode-xid",
+]
+
 [[package]]
 name = "presser"
 version = "0.3.1"
@@ -4197,6 +4225,7 @@ dependencies = [
  "hashbrown 0.17.1",
  "js-sys",
  "log",
+ "naga",
  "parking_lot",
  "portable-atomic",
  "profiling",

Cargo.toml

@@ -1,6 +1,6 @@
 [workspace]
-exclude = ["launcher", "crates/horizon-telemetry-server", "third_party/wgpu-hal"]
-members = ["crates/horizon-core", "crates/horizon-dualsense", "crates/horizon-threads", "crates/horizon-world", "crates/horizon-client", "crates/horizon-server-files", "crates/horizon-server", "crates/horizon-bots", "crates/horizon-assets", "crates/horizon-protocol", "crates/horizon-theme", "crates/horizon-prepare", "crates/horizon-telemetry", "crates/horizon-bench", "crates/horizon-friends", "crates/horizon-relay", "crates/horizon-mod-sdk", "crates/horizon-mods", "crates/horizon-mods/tests/guest", "crates/cargo-horizon-mod", "crates/horizon-port-pack", "crates/horizon-shaders", "crates/horizon-release-sign", "crates/horizon-mod-sdk/examples/coords-hud", "xtask"]
+exclude = ["launcher", "crates/horizon-telemetry-server", "crates/horizon-mod-registry", "third_party/wgpu-hal"]
+members = ["crates/horizon-core", "crates/horizon-dualsense", "crates/horizon-threads", "crates/horizon-world", "crates/horizon-client", "crates/horizon-server-files", "crates/horizon-server", "crates/horizon-bots", "crates/horizon-assets", "crates/horizon-protocol", "crates/horizon-theme", "crates/horizon-prepare", "crates/horizon-telemetry", "crates/horizon-bench", "crates/horizon-friends", "crates/horizon-relay", "crates/horizon-mod-sdk", "crates/horizon-mods", "crates/horizon-mods/tests/guest", "crates/cargo-horizon-mod", "crates/horizon-port-pack", "crates/horizon-shaders", "crates/horizon-shader-api", "crates/horizon-release-sign", "crates/horizon-mod-sdk/examples/coords-hud", "xtask"]
 resolver = "2"
 
 [workspace.package]

README.md

@@ -16,6 +16,7 @@
   <a href="#download"><b>Download</b></a> ·
   <a href="https://playhorizon.dev/docs/"><b>Documentation</b></a> ·
   <a href="https://github.com/ludovic111/horizon/releases"><b>Release notes</b></a> ·
+  <a href="ROADMAP.md"><b>Roadmap</b></a> ·
   <a href="#project-status"><b>Project status</b></a> ·
   <a href="#contributing"><b>Contributing</b></a>
 </p>
@@ -109,6 +110,10 @@ Everything prepared lands in the gitignored `.local/`. It is derived from the ga
 
 The client starts on the title screen. Command-line options (`--world`, `--seed`, `--creative`, `--render-distance`, `--dedicated`), controls, scripting through `horizon-ctl` and the architecture are described in [the native client guide](docs/native-client.md). The rest of the developer documentation is indexed in [docs/README.md](docs/README.md), including [the parity workflow](docs/parity-workflow.md).
 
+## Roadmap
+
+What is being done now, what comes next and where you can help, in plain words and in technical detail: [ROADMAP.md](ROADMAP.md). [playhorizon.dev/hub](https://playhorizon.dev/hub) shows it with the work board, the journal of what shipped and how to help.
+
 ## Contributing
 
 Issues and pull requests are welcome: see [CONTRIBUTING.md](CONTRIBUTING.md) for how we work (vanilla first, small pull requests, labels), or [the contributing guide](https://playhorizon.dev/docs/contributing) on the site. Questions and ideas: [Discord](https://discord.gg/HcTeMZxe5E). Before opening a pull request, run the self-check and paste the block it prints:

ROADMAP.md

@@ -0,0 +1,947 @@
+# Horizon roadmap
+
+<!-- Generated by tools/roadmap.py from roadmap/roadmap.toml: edit that file, then run `python3 tools/roadmap.py build`. -->
+
+What is being done on Horizon, what comes next and where you can help. There are no dates: things are Now, Next or Later. Each item is said in plain words, with the technical picture folded under it. The same roadmap, with a Simple / Technical switch, the board, the journal and how to help, is on [playhorizon.dev/hub](https://playhorizon.dev/hub). Pull requests carry the `roadmap:<id>` label of their item.
+
+## At a glance
+
+Horizon is Minecraft: Java Edition 26.3 rewritten from scratch in Rust, so it runs faster on the same computer. Single player, LAN, servers, resource packs and Horizon's own mods work today, on your own copy of the game.
+
+**Being done now**
+
+- **Steady frames at long render distances**: Making Horizon faster than vanilla on every computer, with smooth camera movement even at 32 chunks, by spreading the work better over the processor's cores.
+- **Modpacks' world generation, natively**: Making the world-generation mods of popular modpacks (new structures, YUNG's dungeons and mineshafts, packs built on Lithostitched) generate their worlds in Horizon, natively and fast.
+- **Playing on servers: everything shows as it should**: When you play on a server, other players, mobs, items and menus look and behave as in vanilla: skins, poses, item names, inventories and server networks.
+- **Single player as a server: the last differences**: Single player now runs a small server in the background, as vanilla does. We are fixing what still behaves differently there; every fix also works for LAN and server players.
+- **Horizon's mod registry**: One place for mods, modpacks and resource packs made for Horizon: browse them on the website and install them from the launcher in one click.
+
+**Next**: Microsoft sign-in (coming soon); CurseForge in the mod browser (coming soon); Fresh benchmarks against vanilla; Pistons push players and mobs; Horizon on Intel Macs; Faster world creation and entry on small CPUs; Servers that hold 20 TPS with 50 to 100 players; Low-end computers: Steam Deck, old Macs, 8 GB; Native upscaling; A batch of targeted optimisations; A Convert to Rust button for what isn't rewritten yet; Mods with code: machines, magic, mobs; Data packs in the mod browser; Prepare a version without Java; Server console, bans and a full admin API; Hosting polish: Windows service, safe updates; Guided hosting with Tailscale and an invite button; An official Docker image for servers; One single-player path: remove the in-frame world; Villages and combat, exactly as in vanilla; Choose the audio output device; Mods that read and change the world; Machines and blocks with inventories (API 0.4); Lua and other languages for mods; Well-known shader looks, rewritten for Horizon; A visible beta label; Wayland and Hyprland polish; A versioned agent-control protocol; Port mods with your own AI agent; Horizon on X (coming soon); Pipeline protection and a GitHub App for agents; Signed updates everywhere, installers included.
+
+**How to help**: Play it and tell us what differs from vanilla (Discord or GitHub), run the benchmark on your computer, vote for what you want next, or pick one of the Help wanted items.
+
+**Developers**: Read CONTRIBUTING.md, pick a Help wanted item or a To do card, check vanilla's code for the behaviour, and paste the block `python3 tools/pr_ready.py` prints in your pull request.
+
+## Now
+
+### Performance
+
+#### Steady frames at long render distances
+
+Making Horizon faster than vanilla on every computer, with smooth camera movement even at 32 chunks, by spreading the work better over the processor's cores.
+
+<details><summary>Technical</summary>
+
+Frame pacing at render distance 32 ([#678](https://github.com/ludovic111/horizon/issues/678)): long frames come from work competing with the render thread. In review: world generation workers build free structure starts instead of queueing them ([#1760](https://github.com/ludovic111/horizon/issues/1760)), the worker pool leaves one core as vanilla does ([#1778](https://github.com/ludovic111/horizon/issues/1778)), and the terrain vertex arena is read as storage where flat draws run ([#1742](https://github.com/ludovic111/horizon/issues/1742)). Still open: far terrain at 48 to 64 chunks ([#718](https://github.com/ludovic111/horizon/issues/718)) and CPU-bound fields of block entities ([#717](https://github.com/ludovic111/horizon/issues/717)). Every change shows before and after numbers from `tools/perf_bench.py` against vanilla 26.3 ([docs/benchmark.md](docs/benchmark.md)).
+
+</details>
+
+#### Faster block lookups
+
+Speeding up the code that reads and writes the blocks of the world, which almost everything in the game goes through: generation, lighting, meshing and ticking.
+
+<details><summary>Technical</summary>
+
+`PalettedContainer` and `PackedStorage` find an entry's word by multiply and shift instead of an integer division ([#1790](https://github.com/ludovic111/horizon/issues/1790), [#1794](https://github.com/ludovic111/horizon/issues/1794)); meshing looks up baked models by index, not by name ([#1747](https://github.com/ludovic111/horizon/issues/1747)). Each change keeps the paletted storage harnesses identical and shows its microbenchmark ([docs/performance/paletted-container-access-results.md](docs/performance/paletted-container-access-results.md)).
+
+</details>
+
+### Modpacks
+
+#### Modpacks' world generation, natively
+
+Making the world-generation mods of popular modpacks (new structures, YUNG's dungeons and mineshafts, packs built on Lithostitched) generate their worlds in Horizon, natively and fast.
+
+<details><summary>Technical</summary>
+
+`horizon-port-pack` carries a pack's data-driven content over; structure mods that need code get a native port: YUNG's worldgen as written ([#1746](https://github.com/ludovic111/horizon/issues/1746)), Lithostitched's limited and guaranteed elements with pool and processor modifiers ([#1777](https://github.com/ludovic111/horizon/issues/1777)), its processors as the game's own types ([#1765](https://github.com/ludovic111/horizon/issues/1765)). Proved by the structure blocks and layout harnesses ([#1753](https://github.com/ludovic111/horizon/issues/1753), [#1757](https://github.com/ludovic111/horizon/issues/1757)). Mods whose Java code does more than world generation don't run ([docs/modpacks.md](docs/modpacks.md)).
+
+</details>
+
+### Servers and multiplayer
+
+#### Playing on servers: everything shows as it should
+
+When you play on a server, other players, mobs, items and menus look and behave as in vanilla: skins, poses, item names, inventories and server networks.
+
+<details><summary>Technical</summary>
+
+Client-of-a-server fixes in `game/remote*.rs` and `horizon-protocol`: mobs' aggressive and item-use flags ([#1802](https://github.com/ludovic111/horizon/issues/1802), [#1798](https://github.com/ludovic111/horizon/issues/1798)), ghost items after a remote menu ([#1795](https://github.com/ludovic111/horizon/issues/1795)), skins ([#1652](https://github.com/ludovic111/horizon/issues/1652)), cookies and transfer packets for proxy networks ([#1650](https://github.com/ludovic111/horizon/issues/1650)), firework boosts ([#1671](https://github.com/ludovic111/horizon/issues/1671)), living-entity attributes and simulation distance ([#1731](https://github.com/ludovic111/horizon/issues/1731)), styled item names ([#1702](https://github.com/ludovic111/horizon/issues/1702)), primed TNT between updates ([#1710](https://github.com/ludovic111/horizon/issues/1710)).
+
+</details>
+
+#### Server dialogs and login screens
+
+Servers that show dialogs, such as the register and login screens of AuthMe, will work in Horizon.
+
+<details><summary>Technical</summary>
+
+26.3's dialog packets and model ([#1720](https://github.com/ludovic111/horizon/issues/1720)), the dialog screen with its buttons and actions ([#1734](https://github.com/ludovic111/horizon/issues/1734)), then text and boolean inputs ([#1735](https://github.com/ludovic111/horizon/issues/1735)).
+
+</details>
+
+#### Pre-generate an area with /pregen
+
+A /pregen command that builds an area of the world ahead of time, so players don't wait for new terrain when they explore.
+
+<details><summary>Technical</summary>
+
+Generates, lights and saves an area before anyone walks there ([#1805](https://github.com/ludovic111/horizon/issues/1805), a contributor's pull request, in review). Useful on servers, and it moves the generation cost away from the first visit; the generation speed-ups are under 'Steady frames at long render distances'.
+
+</details>
+
+### Mods and API
+
+#### Horizon's mod registry
+
+One place for mods, modpacks and resource packs made for Horizon: browse them on the website and install them from the launcher in one click.
+
+<details><summary>Technical</summary>
+
+Merged: the registry index (schema 1, `.hpack`, checks before install, [#1634](https://github.com/ludovic111/horizon/issues/1634)), `cargo horizon-mod check` ([#1642](https://github.com/ludovic111/horizon/issues/1642)) and the submission service (`crates/horizon-mod-registry`, [#1659](https://github.com/ludovic111/horizon/issues/1659)). In review: the website's /mods ([#1596](https://github.com/ludovic111/horizon/issues/1596)) and /mods/submit ([#1635](https://github.com/ludovic111/horizon/issues/1635)), and in the launcher the registry as a source ([#1636](https://github.com/ludovic111/horizon/issues/1636)), install, enable and takedowns ([#1637](https://github.com/ludovic111/horizon/issues/1637)), the Mods page ([#1638](https://github.com/ludovic111/horizon/issues/1638)) and modpacks as their own profiles ([#1640](https://github.com/ludovic111/horizon/issues/1640)).
+
+More: [docs/mods.md](docs/mods.md)
+
+</details>
+
+#### Mods that run on the server
+
+Mods that run on the server side of a world, so a dedicated server or a LAN world can have mods that react to players joining, chat and blocks being broken or placed, and that add commands.
+
+<details><summary>Technical</summary>
+
+API 0.3, experimental first ([#1833](https://github.com/ludovic111/horizon/issues/1833), in review): the same sandboxed component runs on the server thread and the dedicated server, with world events (block broken or placed, entity spawned or killed, player joined or left), game rules and server commands with typed arguments. The world, item and entity interfaces come after (see 'Mods that read and change the world'). [docs/api/mods.md](docs/api/mods.md), [docs/mods.md](docs/mods.md).
+
+</details>
+
+#### Screens, input and drawing for mods
+
+Mods will be able to open their own screens and settings pages and react to keys and item use, so bigger mods, such as the Orbital Laser, can run on the normal game.
+
+<details><summary>Technical</summary>
+
+Capability `ui` is in review ([#1864](https://github.com/ludovic111/horizon/issues/1864)): mod-owned screens and a settings page under Options > Mods, built from vanilla's widgets. Still to design: `input` (an item's use, key binds, the crosshair target), `render` (a budgeted draw list on the native shader API) and `world` (changing blocks). Orbital Laser is the acceptance test: it needs all four today through its author's fork (see 'Orbital Laser on the normal game').
+
+More: [docs/mods.md](docs/mods.md)
+
+</details>
+
+#### Tools for people who make mods
+
+Better tools for mod makers: a test runner that needs no game window, templates for each kind of mod, and clear promises about what keeps working from one version to the next.
+
+<details><summary>Technical</summary>
+
+`cargo horizon-mod test` runs a mod's test scripts against a fake game snapshot ([#1816](https://github.com/ludovic111/horizon/issues/1816)) and, for server mods, scripted server events ([#1837](https://github.com/ludovic111/horizon/issues/1837)); the content template and the guides are merged ([#1859](https://github.com/ludovic111/horizon/issues/1859), [#1810](https://github.com/ludovic111/horizon/issues/1810), [docs/api/stability.md](docs/api/stability.md)). Left: templates for hud, server and machine mods, typed wrappers in the SDK, a frozen 0.1 compatibility mod that every runtime must load, a CI check that fails when a stable reference entry is removed without a new major version, and the SDK on crates.io once the API is stable.
+
+More: [website/docs/test-a-mod.md](website/docs/test-a-mod.md)
+
+</details>
+
+### Gameplay parity
+
+#### Single player as a server: the last differences
+
+Single player now runs a small server in the background, as vanilla does. We are fixing what still behaves differently there; every fix also works for LAN and server players.
+
+<details><summary>Technical</summary>
+
+Since [#1514](https://github.com/ludovic111/horizon/issues/1514) single player runs on the server thread (`game/integrated.rs`) and the window joins it as a client; `--in-frame` keeps the old path. The open `[server-thread]` issues list the gaps. In review: a tool that changes a block ends the click ([#1797](https://github.com/ludovic111/horizon/issues/1797)), potions keep their potion over the connection ([#1796](https://github.com/ludovic111/horizon/issues/1796)), mobs' aggression and arm swings ([#1802](https://github.com/ludovic111/horizon/issues/1802)). [docs/server-levels.md](docs/server-levels.md).
+
+</details>
+
+#### Play in your language
+
+Item names, container titles and server messages follow the language you pick, as in vanilla. Today parts of the game stay in English.
+
+<details><summary>Technical</summary>
+
+Translatable components resolved through the selected language for items, containers and server text ([#1806](https://github.com/ludovic111/horizon/issues/1806)), on top of the bundled languages the prepared resources carry ([#1594](https://github.com/ludovic111/horizon/issues/1594)). Left: the client's own screens ([#1672](https://github.com/ludovic111/horizon/issues/1672)) and the main menu with zh_cn ([#1774](https://github.com/ludovic111/horizon/issues/1774)).
+
+</details>
+
+### Rendering
+
+#### Shader packs, written again from scratch
+
+Shader packs were removed and are being rebuilt from scratch. They come back, off by default, once the best-known packs draw properly.
+
+<details><summary>Technical</summary>
+
+A clean-room rewrite in `horizon-shaderpack`, from the packs' public format documentation only: reading packs, the preprocessor and `.properties` files are merged ([#1584](https://github.com/ludovic111/horizon/issues/1584), [#1585](https://github.com/ludovic111/horizon/issues/1585), [#1586](https://github.com/ludovic111/horizon/issues/1586)); translating programs to WGSL through naga, buffers, uniforms and the terrain, entity, sky, weather and hand stages are in review ([#1698](https://github.com/ludovic111/horizon/issues/1698) to [#1801](https://github.com/ludovic111/horizon/issues/1801)).
+
+More: [#1561](https://github.com/ludovic111/horizon/issues/1561) · [#1771](https://github.com/ludovic111/horizon/issues/1771) · [#1786](https://github.com/ludovic111/horizon/issues/1786)
+
+</details>
+
+#### Horizon's own shader format and kit
+
+Horizon's own way to make shader packs, with tools to write and test them. Every pack is checked before it runs, and the registry will list them.
+
+<details><summary>Technical</summary>
+
+`horizon-shader-api` (API 0.1, experimental): WGSL stages with typed inputs inside the renderer's passes, options as WGSL override constants, and the `horizon-shader new|check|pack` tool with templates and the example pack Golden Hour. Merged: the check every pack passes ([#1820](https://github.com/ludovic111/horizon/issues/1820)) and the tool, templates and guide ([#1822](https://github.com/ludovic111/horizon/issues/1822)). In review: the post stage running in the game with hot reload ([#1861](https://github.com/ludovic111/horizon/issues/1861)), the sky stage ([#1863](https://github.com/ludovic111/horizon/issues/1863)) and registry checks that use the game's own check ([#1855](https://github.com/ludovic111/horizon/issues/1855)). Left: the material, lighting and shadow stages, a last-good fallback on reload, a GPU-time overlay per stage and budgets ([docs/shaders.md](docs/shaders.md), [docs/api/shaders.md](docs/api/shaders.md)). The Iris/OptiFine loader is a separate item, 'Shader packs, written again from scratch'.
+
+</details>
+
+### Horizon extras
+
+#### Discord Rich Presence
+
+Your Discord profile can show that you are playing Horizon, with a switch to turn it off.
+
+<details><summary>Technical</summary>
+
+A Discord IPC client on its own thread ([#1787](https://github.com/ludovic111/horizon/issues/1787)) and the presence with its setting ([#1788](https://github.com/ludovic111/horizon/issues/1788)). Merged: it ships with the next release.
+
+</details>
+
+### Code and tools
+
+#### A leaner codebase that builds faster
+
+Cleaning up Horizon's code: removing what nothing uses and making it quicker to build, so fixes and new features land faster.
+
+<details><summary>Technical</summary>
+
+A review of the whole tree: dead code and stubs removed ([#1432](https://github.com/ludovic111/horizon/issues/1432), [#1658](https://github.com/ludovic111/horizon/issues/1658)), one probe binary per crate ([#1453](https://github.com/ludovic111/horizon/issues/1453), [#1454](https://github.com/ludovic111/horizon/issues/1454)), shared harness helpers ([#1448](https://github.com/ludovic111/horizon/issues/1448)), clippy clean on the whole tree ([#1707](https://github.com/ludovic111/horizon/issues/1707)). [docs/architecture.md](docs/architecture.md) maps each feature to its files and harnesses.
+
+</details>
+
+## Next
+
+### Performance
+
+#### Fresh benchmarks against vanilla
+
+New public numbers comparing Horizon with vanilla on many kinds of computers, measured the same way every time, with a history that shows what each release changed.
+
+<details><summary>Technical</summary>
+
+Redo the comparison after the current performance work ([#1073](https://github.com/ludovic111/horizon/issues/1073)); reliability, coverage and presentation ([#1346](https://github.com/ludovic111/horizon/issues/1346)); a scene must count as loaded only once its first chunk arrives ([#1749](https://github.com/ludovic111/horizon/issues/1749)). Next: a performance history across releases (an automatic comparison of each release with the last, on a timeline), more report fields (server TPS and MSPT, power, battery drain, temperature, throttling) and more hardware (a MacBook on battery, low-end laptops, community reports). Players' reports come in through `--benchmark` and `horizon-launcher data benchmark` ([docs/benchmark.md](docs/benchmark.md)).
+
+</details>
+
+#### Faster world creation and entry on small CPUs
+
+Creating a world and joining it should be quick even on a four-thread laptop, where a fresh world at 32 chunks can make you wait minutes for the first terrain.
+
+<details><summary>Technical</summary>
+
+Cut the per-column generation cost (noise sampling, surface rules, aquifers) and the lock convoy on structure starts, and leave one core free for the rest of the game as vanilla does ([#1760](https://github.com/ludovic111/horizon/issues/1760) and [#1778](https://github.com/ludovic111/horizon/issues/1778), in review, are listed under 'Steady frames at long render distances'). Still to profile on small CPUs: the first seconds of a fresh world deliver no chunk, and fluids remesh for about a minute after loading. Measured with `tools/perf_bench.py` ([docs/benchmark.md](docs/benchmark.md), [docs/profiling.md](docs/profiling.md)).
+
+</details>
+
+#### Servers that hold 20 TPS with 50 to 100 players
+
+Servers that keep 20 ticks per second with 50 to 100 players. Today Horizon holds it up to 50 bots and drops to about 10 at 100.
+
+<details><summary>Technical</summary>
+
+Measured against vanilla on equal work ([docs/server.md](docs/server.md), Scale): Horizon is ahead with few players and when exploring, but vanilla's tick is shorter with 25 to 50 players near spawn. Ideas on the list: send entity changes instead of rebuilding every entity each tick (about 15 percent), fewer memory reads in random ticks and collision scans, cheaper item collision checks, mob AI and natural spawning. The bot benchmark (`horizon-bots`) is the proof.
+
+</details>
+
+#### Low-end computers: Steam Deck, old Macs, 8 GB
+
+Horizon should run well on small machines: integrated graphics, the Steam Deck, older Macs and 8 GB of memory, with a battery mode that saves power on laptops.
+
+<details><summary>Technical</summary>
+
+Partly done: an opt-in 60 FPS cap with fewer workers on battery, Far Detail Reduced for integrated GPUs and animated textures on the GPU (both shipped). Left: measured targets and fixes per class of machine (memory use, worker counts, startup) on a Steam Deck, old Intel and Apple Silicon Macs and 8 GB computers, reported on the Benchmarks page.
+
+More: [docs/benchmark.md](docs/benchmark.md) · [website/docs/performance.md](website/docs/performance.md)
+
+</details>
+
+#### Native upscaling
+
+Draw the game at a lower resolution and sharpen it to your screen's size, in the way of FSR or DLSS, to gain frames on weaker graphics cards. An optional graphics setting.
+
+<details><summary>Technical</summary>
+
+A render-scale setting below the window size with an upscaler of our own that runs on every wgpu backend. Proof: frame time against native resolution on integrated GPUs, and screenshots for image quality. Issue [#1403](https://github.com/ludovic111/horizon/issues/1403).
+
+</details>
+
+#### A batch of targeted optimisations
+
+Several smaller speed-ups, each measured: idle block entities that sleep, cheaper particles, faster structure placement, high-rate mice and very large texture packs.
+
+<details><summary>Technical</summary>
+
+Block entities and hoppers that skip work when idle (the hopper item scan is already skipped when no item is near); a particle frustum test first (also a parity gap), then particle quads built on the GPU; jigsaw shortcuts that skip blocked connectors and pool elements known not to fit, with layouts unchanged (trial chambers and ancient cities first); batched raw mouse input on Windows for 8000 Hz mice; a better atlas packer for huge resource packs (a 64x pack builds a 704 MiB atlas for 452 MiB of textures); sign-heavy scenes ([#1461](https://github.com/ludovic111/horizon/issues/1461)). Profile first, keep what pays, show before and after numbers.
+
+More: [docs/profiling.md](docs/profiling.md)
+
+</details>
+
+### Modpacks
+
+#### CurseForge in the mod browser (coming soon)
+
+Coming soon: search and download CurseForge mods and modpacks from the launcher, as you can with Modrinth today.
+
+<details><summary>Technical</summary>
+
+The mod browser lists CurseForge as coming soon ([docs/mod-browser.md](docs/mod-browser.md)): it needs CurseForge API access. Meanwhile packs import from a CurseForge zip or instance folder, and jars only CurseForge hosts come from the player's own instance ([docs/modpacks.md](docs/modpacks.md)).
+
+</details>
+
+#### A Convert to Rust button for what isn't rewritten yet
+
+When a mod, shader pack or modpack hasn't been rewritten for Horizon, one button converts what can be converted, so you don't have to wait for the rewrite.
+
+<details><summary>Technical</summary>
+
+Generalise the mod browser's Port step (`horizon-port-pack`: the data, assets, worldgen and block and item definitions of Java mods, .mrpack and CurseForge zips) to every kind of content: code mods where the API allows it (see 'Mods with code') and shader packs, converting an Iris/OptiFine pack into Horizon's format. The browser says what works before the install. Java code itself does not run ([docs/modpacks.md](docs/modpacks.md), [docs/mod-browser.md](docs/mod-browser.md)).
+
+</details>
+
+#### Mods with code: machines, magic, mobs
+
+Making mods that add machines, magic and mobs work in Horizon, in steps, starting with machines. They are most of what a big modpack is made of.
+
+<details><summary>Technical</summary>
+
+333 of the 496 mods in a big pack (ATM10) contain code. Issue [#1854](https://github.com/ludovic111/horizon/issues/1854) ranks the API gaps (ticking block entities, networking, rendering, menus, inventories) that unlock them in tiers, with machines first as the recommended path and a furnace ported tick for tick as proof. The first API step is a draft ([#1189](https://github.com/ludovic111/horizon/issues/1189), see 'Machines and blocks with inventories'). The path isn't started yet ([docs/modpacks.md](docs/modpacks.md)).
+
+</details>
+
+#### Data packs in the mod browser
+
+Search and install data packs from the launcher's mod browser, for the world you choose, as you do mods and resource packs.
+
+<details><summary>Technical</summary>
+
+A Datapacks tab beside Mods and Resource packs: install into a chosen world's datapacks folder, with the same checks and 'works in Horizon' notes as the other kinds ([docs/mod-browser.md](docs/mod-browser.md)).
+
+</details>
+
+### Servers and multiplayer
+
+#### Prepare a version without Java
+
+Set up Horizon, a server first, without Java on your computer: published tables are combined with your own copy of the game.
+
+<details><summary>Technical</summary>
+
+Today `horizon-prepare` runs Mojang's exporters with Java. Issue [#1750](https://github.com/ludovic111/horizon/issues/1750) proposes publishing the computed version tables once from CI and assembling the rest locally from the player's own jar and assets, provided the tables hold no Mojang content; a contributor offered a pull request, and it would help phones too. A server-only prepare from `server.jar` alone is the first step ([docs/server.md](docs/server.md)).
+
+</details>
+
+#### Server console, bans and a full admin API
+
+Manage a server from a console, ban and pardon players, and drive it from other tools through a full admin API and an MCP server for AI agents.
+
+<details><summary>Technical</summary>
+
+`horizon-server console` (a text interface), `ban`, `pardon`, `ban-ip` and `mcp` over stdio. Admin API additions: the player list, kick, ban, op and whitelist, an SSE stream of logs and events, a text metrics endpoint, config GET and PATCH, backup delete and download. The panel's later features (bans, worlds, server.properties import, logs and crash reports, modpacks) and vanilla's management protocol (the JSON-RPC over WebSocket that the `management-server-*` keys configure), so vanilla's tools can manage a Horizon server. [docs/server.md](docs/server.md), [docs/api/server.md](docs/api/server.md).
+
+</details>
+
+#### Hosting polish: Windows service, safe updates
+
+Smoother hosting: a real Windows service, a backup before every update, backups that keep the world and each player's state, and a changed view distance or message without a restart.
+
+<details><summary>Technical</summary>
+
+A Windows service wrapper instead of the logon scheduled task; `backups.before_update`; hot reload of config for view distance and the message of the day (needs engine support); backups that keep world and player state ([#1808](https://github.com/ludovic111/horizon/issues/1808), a contributor's draft, in review). [docs/hosting.md](docs/hosting.md), docs/server.md.
+
+</details>
+
+#### Guided hosting with Tailscale and an invite button
+
+In the launcher, a guide and a button to host a server and invite friends over Tailscale, so nobody has to open ports on a router.
+
+<details><summary>Technical</summary>
+
+On the Servers page (create, start, back up, update and invite are shipped) add a Tailscale setup that explains and checks each step, and an invite button that hands friends what they need to join over the tailnet. Buttons first, no docs needed, with the details in an Advanced section. Remote access over Tailscale is already described in [docs/server.md](docs/server.md).
+
+More: [docs/hosting.md](docs/hosting.md)
+
+</details>
+
+#### An official Docker image for servers
+
+An official image to run a Horizon dedicated server in Docker with one command, your own copy of the game files mounted in.
+
+<details><summary>Technical</summary>
+
+The repository has the Dockerfile (`packaging/server/Dockerfile`: a multi-stage build on Debian bookworm-slim, user `horizon`, volume `/data`, port 25565, game files mounted read-only, `HORIZON_EULA` and friends answering the first-start questions), and anyone can build it ([docs/hosting.md](docs/hosting.md), section 9). Left: publish the image to a public registry from the release workflow, tagged per release, so it follows the same checks, and update the docs and the launcher. The image never holds Mojang's files.
+
+More: [docs/server.md](docs/server.md)
+
+</details>
+
+### Mods and API
+
+#### Mods that read and change the world
+
+Mods that can see and change blocks, read inventories and items, and find and affect entities, all through the server so every player sees the same thing.
+
+<details><summary>Technical</summary>
+
+After server mods: read blocks, states and biomes in loaded chunks and change them through the server's block log, so clients and the parity harnesses see vanilla's updates; the player's inventory, held item, open container and item stacks with components; entity queries near a position, a safe subset of entity data and data-driven mod entity types. Snapshots and batched calls per tick, never per-block host calls in hot paths. [docs/api/mods.md](docs/api/mods.md) ('Not there yet').
+
+More: [docs/modpacks.md](docs/modpacks.md)
+
+</details>
+
+#### Machines and blocks with inventories (API 0.4)
+
+Mods that add machines: blocks that tick, hold items and have their own menus. This unlocks the technology mods of big modpacks.
+
+<details><summary>Technical</summary>
+
+Block entities and menus: ticking machines with slots, server menu logic and the menu protocol to clients, energy, item and fluid transfer, data attachments, accessory slots and custom recipe types, with a typed client and server channel and typed config beside them. A draft ([#1189](https://github.com/ludovic111/horizon/issues/1189)) proves a furnace ported tick for tick and holds the ATM10 code-mods plan; the design is redone through the API policy before it merges ([docs/modpacks.md](docs/modpacks.md), docs/api/stability.md).
+
+</details>
+
+#### Lua and other languages for mods
+
+Write mods as Lua scripts, in the style of KubeJS, with no compiler, and later in other languages that pass the tests. Every language runs in the same sandbox.
+
+<details><summary>Technical</summary>
+
+Lua first: Horizon ships a Lua interpreter that is itself a WebAssembly mod, and a script mod's manifest names it and the capabilities it uses, so a script can do exactly what a compiled mod with the same manifest can, with hot reload of `main.lua`. Then C, C++, Zig, Go (TinyGo), AssemblyScript and JavaScript or TypeScript are measured against Rust on the same tick-heavy example, and each is supported only with a template, an example and a CI test. [docs/api/mods.md](docs/api/mods.md) ('Ways in').
+
+</details>
+
+### Gameplay parity
+
+#### Pistons push players and mobs
+
+Pistons and slime blocks will push players, mobs and items as in vanilla. Today moving blocks pass through them.
+
+<details><summary>Technical</summary>
+
+Port `PistonMovingBlockEntity.moveCollidedEntities` and `moveStuckEntities` (honey), the slime bounce and `Entity.limitPistonMovement` for `MoverType.PISTON`, in single player and for a server's players. Issues [#1496](https://github.com/ludovic111/horizon/issues/1496), [#1609](https://github.com/ludovic111/horizon/issues/1609), [#1608](https://github.com/ludovic111/horizon/issues/1608), [#1704](https://github.com/ludovic111/horizon/issues/1704), [#1758](https://github.com/ludovic111/horizon/issues/1758).
+
+</details>
+
+#### One single-player path: remove the in-frame world
+
+Single player will have one way to run, the server thread, so every fix works everywhere and there are fewer bugs. The older in-frame mode goes once everything passes without it.
+
+<details><summary>Technical</summary>
+
+`--in-frame` (also `--no-server-thread` and `HORIZON_SERVER_THREAD=0`) still ticks the world inside the window's `Game`, and most harnesses test that path. Delete it once `lan_e2e --server-thread` and the parity harnesses pass on the server thread, which also halves the bug surface. See also 'Single player as a server' and [docs/server-levels.md](docs/server-levels.md).
+
+</details>
+
+#### Villages and combat, exactly as in vanilla
+
+Villages and fights behaving as in vanilla: iron golems defending villages, villagers remembering their homes, mace smashes and knockback.
+
+<details><summary>Technical</summary>
+
+Villages: iron golem village goals, villager memories across saves, villager age, job-site claiming on dedicated servers, flower offers ([#1639](https://github.com/ludovic111/horizon/issues/1639) is one report). Combat: the mobs' `attack_knockback` attribute, mace smash logic, the hit knockback source on the host, the fire burnout biome tag. Each is checked against vanilla by a harness ([docs/rust-parity.md](docs/rust-parity.md)).
+
+</details>
+
+#### Choose the audio output device
+
+Pick the speakers or headphones Horizon plays through, in Music & Sounds.
+
+<details><summary>Technical</summary>
+
+An output device list in Music & Sounds, falling back to the system default. [#1035](https://github.com/ludovic111/horizon/issues/1035) started it: a player on an older Windows computer had no sound at all, and a device choice is how such cases are found and fixed.
+
+</details>
+
+### Rendering
+
+#### Well-known shader looks, rewritten for Horizon
+
+Popular shader packs rewritten in Horizon's format, so good packs exist from the start. Only packs whose licence is open source and compatible with ours are rewritten, never anything else.
+
+<details><summary>Technical</summary>
+
+The first candidates are Photon, Chocapic13 and MakeUp Ultra Fast, each only after its licence is read and recorded: a pack is rewritten only if it is open source and compatible with Horizon's licence, and the rewrite is written from the shader format's documentation and the look on screen, not from anyone's code. Today only the Golden Hour example exists (`[crates/horizon-shader-api/packs/golden_hour](crates/horizon-shader-api/packs/golden_hour)`).
+
+More: [docs/shaders.md](docs/shaders.md)
+
+</details>
+
+### Launcher
+
+#### Microsoft sign-in (coming soon)
+
+Coming soon: sign in with your Microsoft account to play on online-mode servers. The code is ready; it waits for Microsoft's approval.
+
+<details><summary>Technical</summary>
+
+Device-code sign-in in the launcher and online-mode login in the client ([docs/microsoft-account.md](docs/microsoft-account.md)). It is turned on by setting the app's client id once Minecraft API access is approved; until then the launcher shows "Coming soon".
+
+More: [#1270](https://github.com/ludovic111/horizon/issues/1270)
+
+</details>
+
+#### A visible beta label
+
+A clear 'beta' label in the launcher and the game, so nobody is surprised that Horizon is still being built.
+
+<details><summary>Technical</summary>
+
+Show Beta in the launcher's header and about page, on the game's title screen and on the website, beside the version number ([docs/versioning.md](docs/versioning.md)).
+
+</details>
+
+### Platforms
+
+#### Horizon on Intel Macs
+
+Builds of the game and the launcher for Macs with an Intel processor.
+
+<details><summary>Technical</summary>
+
+x86_64 game and launcher builds, picked per processor ([#1171](https://github.com/ludovic111/horizon/issues/1171)). Before it ships it needs a run on a real Intel Mac: Rosetta on Apple Silicon only proves the CPU code. Requests: [#1161](https://github.com/ludovic111/horizon/issues/1161), [#1792](https://github.com/ludovic111/horizon/issues/1792).
+
+</details>
+
+#### Wayland and Hyprland polish
+
+Fixes for Linux desktops that use Wayland and Hyprland: fullscreen, the clipboard, the GUI scale after a restart and the like.
+
+<details><summary>Technical</summary>
+
+Open: the GUI Scale is clamped to 2 after a restart under Hyprland, while XWayland keeps it ([#1866](https://github.com/ludovic111/horizon/issues/1866)). Earlier reports covered fullscreen dropping on menu clicks, the clipboard and a white overlay ([#1007](https://github.com/ludovic111/horizon/issues/1007), closed). Checked on a real Wayland session.
+
+</details>
+
+### AI and agents
+
+#### A versioned agent-control protocol
+
+A stable, documented way for AI agents and scripts to drive the game and the launcher, with versions and an event stream so tools keep working as Horizon changes.
+
+<details><summary>Technical</summary>
+
+`hello` answers with the API version, the release and the features; `horizon-ctl --api`; MCP serverInfo; reply schemas generated into the reference; a `test.` namespace for hooks; transcript compatibility tests; `subscribe` as a stream of events on one connection; Horizon option files by key and saved-server commands. Agent control itself (`horizon-ctl`, both MCP servers, the No AI switch) is done: [docs/agent-control.md](docs/agent-control.md), [docs/api/agent-control.md](docs/api/agent-control.md).
+
+More: [docs/api/stability.md](docs/api/stability.md)
+
+</details>
+
+#### Port mods with your own AI agent
+
+You can port a mod to Horizon with your own AI agent on your own computer. Horizon documents how and gives you the tools, but provides no hosted agents.
+
+<details><summary>Technical</summary>
+
+A player runs their own agent locally with `horizon-ctl` and the MCP servers ([docs/agent-control.md](docs/agent-control.md)), `cargo horizon-mod`, `horizon-port-pack` and the parity harnesses as the check. Horizon writes the guide ([website/docs/agents.md](website/docs/agents.md), [docs/modpacks.md](docs/modpacks.md)) and runs no agents, accounts or keys for players. The No AI switch turns all of it off.
+
+</details>
+
+### Community
+
+#### Horizon on X (coming soon)
+
+Coming soon: an official Horizon account on X, used to announce releases and the weekly summary.
+
+<details><summary>Technical</summary>
+
+Kira already posts the roadmap items marked `announce = true` when they ship, and the weekly summary, as soon as the account's credentials exist ([roadmap/README.md](roadmap/README.md), 'The journal'). Waiting for the account itself.
+
+</details>
+
+### Code and tools
+
+#### Pipeline protection and a GitHub App for agents
+
+Safer releases: changes to the release machinery need the owner's review, and AI agents use a smaller identity of their own instead of a personal account.
+
+<details><summary>Technical</summary>
+
+`.github/CODEOWNERS` lists the workflows, the release and signing tools, the update-checking code and the installers ([#1015](https://github.com/ludovic111/horizon/issues/1015)); the branch protection that makes it count waits for the `horizon-agent` GitHub App, which reads and writes code, pull requests and issues but can't change settings, workflows, secrets or members, and whose tokens last an hour. It needs the owner to create the App and switch the protection on ([docs/security.md](docs/security.md)).
+
+</details>
+
+#### Signed updates everywhere, installers included
+
+Every download Horizon makes is checked against the project's signature, including the first install with install.sh and install.ps1.
+
+<details><summary>Technical</summary>
+
+Releases carry signed checksums, and the launcher and `horizon-server update` refuse anything unsigned ([#1011](https://github.com/ludovic111/horizon/issues/1011), [#1014](https://github.com/ludovic111/horizon/issues/1014)). Left: the first install through `install.sh` and `install.ps1` still trusts only the checksum GitHub publishes, because verifying Ed25519 signatures needs OpenSSL 3, which macOS doesn't ship ([docs/security.md](docs/security.md)).
+
+</details>
+
+## Later
+
+### Performance
+
+#### Exact far terrain from real chunks
+
+Far terrain drawn from the world you really built and explored, caves and builds included, not only a preview from the seed.
+
+<details><summary>Technical</summary>
+
+Keep a 3D mip store on disk built from real chunks, drawn by the GPU beside the seed preview for areas nobody has visited. Written from scratch and measured before it is kept. Builds on Far Detail and the far-terrain levels of detail already shipped; the open work on them is [#718](https://github.com/ludovic111/horizon/issues/718).
+
+</details>
+
+### Modpacks
+
+#### Older Fabric and Forge mods
+
+Recognise mods built for versions before 26.1 in the mod browser, so they can be checked and carried over like newer ones.
+
+<details><summary>Technical</summary>
+
+A mapping table from intermediary and SRG names so pre-26.1 jars can be classified, and a rename for mod ids with dashes (`fabric-api`); the port step then treats them like newer jars ([docs/mod-browser.md](docs/mod-browser.md)).
+
+</details>
+
+#### A modpack's own resource and shader packs
+
+Importing a modpack also brings the resource packs and shader packs it ships with, where Horizon can use them.
+
+<details><summary>Technical</summary>
+
+Porting a pack carries data, assets and worldgen today; the resource packs and shader packs bundled with it are left out. Resource packs can be carried as they are; shader packs go through the converter ([docs/modpacks.md](docs/modpacks.md)).
+
+</details>
+
+#### Whole modpacks, such as ATM10, rewritten
+
+Rewriting a complete big modpack for Horizon so it runs far better than the original. Not a priority now: the work above comes first.
+
+<details><summary>Technical</summary>
+
+The project's first goal for modpacks: support them ten times better than vanilla and port any of them. It was set aside in favour of compatibility through the browser. What exists: ATM10's world generates and 42 of its 496 mods are carried at least in part ([docs/modpacks.md](docs/modpacks.md)). It depends on 'Mods with code' and the native mod API.
+
+</details>
+
+#### Running Java mods that aren't rewritten
+
+Run Java mods that nobody has rewritten for Horizon yet, through a bridge or a converter. Hard and not started: the Convert button and native rewrites come first.
+
+<details><summary>Technical</summary>
+
+Earlier research ([#527](https://github.com/ludovic111/horizon/issues/527), closed) found that Java mods can't simply run, because they call Minecraft's own classes. Options to look at again: a jar-to-WebAssembly backend, or a bridge for simple Fabric mods. Whatever is chosen has to run inside the same sandbox and capability checks as native mods.
+
+</details>
+
+### Servers and multiplayer
+
+#### Ely.by and other sign-in providers
+
+Sign in with other account providers, such as Ely.by or any Yggdrasil-compatible one, beside Microsoft.
+
+<details><summary>Technical</summary>
+
+Issue [#1270](https://github.com/ludovic111/horizon/issues/1270) asks for Ely.by and Yggdrasil-compatible servers with an account selector in the launcher. It builds on the Microsoft sign-in ([docs/microsoft-account.md](docs/microsoft-account.md)).
+
+</details>
+
+#### Online-mode checks for Play with Friends
+
+Friends who join through an invite code could prove who they are with their Microsoft account, as on online-mode servers.
+
+<details><summary>Technical</summary>
+
+Play with Friends joins over an encrypted tunnel with an invite code ([docs/play-with-friends.md](docs/play-with-friends.md), 'Identity'). Online-mode checks against Mojang's session servers can be added on top of the same tunnel; they need Microsoft sign-in first, which is coming soon. Play with Friends stays self-hosted between players, with no relay run by the project.
+
+</details>
+
+### Mods and API
+
+#### Orbital Laser on the normal game
+
+The community mod Orbital Laser, made for a fork of Horizon, running on the normal game and listed in the registry as the showcase of the mod API.
+
+<details><summary>Technical</summary>
+
+A pull request on [https://github.com/Stink-O/orbital-laser](https://github.com/Stink-O/orbital-laser) (MIT) once the input, ui, render and world capabilities exist (see 'Screens, input and drawing for mods'): today the mod needs them through its author's fork. Tested in the game, and listed in the registry.
+
+</details>
+
+#### Native versions of popular client mods
+
+Built-in versions of the client mods players ask for: block info on hover, a recipe viewer like JEI, a world map and schematic overlays.
+
+<details><summary>Technical</summary>
+
+Done as extras: a mod list and menu, a minimap and a zoom ([docs/extras.md](docs/extras.md)). Left: block info tooltips, a recipe viewer (a contributor offered to port JEI if it becomes a native feature), a world map and a schematic overlay. They need the read-only interfaces `inventory-read`, `recipes`, `world-read` and `render` in the mod API, or they go into the game directly.
+
+More: [docs/mods.md](docs/mods.md)
+
+</details>
+
+#### Create-style physics as a native mod
+
+Contraptions and physics like the Create and Aeronautics mods, as a mod for Horizon rather than part of the base game.
+
+<details><summary>Technical</summary>
+
+Issue [#805](https://github.com/ludovic111/horizon/issues/805) (porting QOL mods) closed with this answer: it would come as a native Horizon mod on the mod API. It needs server mods, entities and rendering first.
+
+</details>
+
+#### Proximity voice chat as a native mod
+
+Hear nearby players talk, as with the voice chat mods of other Minecraft versions, as a Horizon mod.
+
+<details><summary>Technical</summary>
+
+Needs server mods, mod networking and an audio interface in the mod API before anything can be built ([docs/api/mods.md](docs/api/mods.md)).
+
+</details>
+
+### Gameplay parity
+
+#### Every Minecraft version, prepared automatically
+
+Every past and future Minecraft version prepared for Horizon automatically. When Mojang releases one, Horizon follows it, and every system is checked against it again.
+
+<details><summary>Technical</summary>
+
+The port pipeline ([docs/version-ports.md](docs/version-ports.md), `tools/version_port.py`) detects a release, prepares it, diffs its classes against the pinned 26.3, regenerates the data-driven tables, runs every parity harness on it and writes a port report that becomes issues. The goal is as little human work as possible for any version, past or future. Detection and the first slices are merged; the scheduled agent that runs it every day isn't installed yet. Two versions in one build are out of scope.
+
+</details>
+
+#### Controllers: tested on real pads, and in the launcher
+
+Make controller support solid: tested with real PlayStation and Xbox pads and a Steam Deck, and usable in the launcher too.
+
+<details><summary>Technical</summary>
+
+The game side is merged ([docs/controllers.md](docs/controllers.md)): pads read with gilrs, menus, rumble, glyphs, remapping and DualSense adaptive triggers, lightbar and haptics, but not yet confirmed on real pads or a Steam Deck (DualSense haptics stay behind a switch until then). Left: a test pass on real hardware, and the same focus navigation in the GPUI launcher.
+
+</details>
+
+#### The full debug screen
+
+Vanilla's complete F3 screen: debug options, a profiler chart, ten-second captures and an atlas dump.
+
+<details><summary>Technical</summary>
+
+Today F3 shows position, chunk, light, biome and FPS ([docs/native-client.md](docs/native-client.md)). Vanilla also has F3+F6 debug options with profiles, F3+1 the profiler pie, F3+L a ten-second capture and F3+S the atlas dump ([#562](https://github.com/ludovic111/horizon/issues/562) asked for the F3 editor).
+
+</details>
+
+### Rendering
+
+#### A light default shader pack
+
+A small built-in look (tone mapping, colour grade, a cheap vignette) that costs almost nothing, for players who want a nicer picture without a heavy pack.
+
+<details><summary>Technical</summary>
+
+An opt-in, composite-only pack on the native shader API, under about 0.3 ms at 1080p, shown on the Shader Packs page. Pack option sliders and profiles, and a Failed row with the full error, belong with it.
+
+More: [docs/shaders.md](docs/shaders.md)
+
+</details>
+
+#### Optional ray tracing
+
+An optional ray-tracing mode for graphics cards that support it (RTX and recent AMD): shadows, water reflections and global lighting on top of the vanilla look.
+
+<details><summary>Technical</summary>
+
+A spike with ray-traced sun shadows, off by default, is a draft ([#1180](https://github.com/ludovic111/horizon/issues/1180)). Reflections, global illumination, Apple M3 and newer if it is cheap, and a performance report per card come after.
+
+</details>
+
+#### HDR monitors
+
+Output for HDR monitors: brighter highlights and richer colour where your screen supports it.
+
+<details><summary>Technical</summary>
+
+Issue [#1441](https://github.com/ludovic111/horizon/issues/1441). Needs a surface format and a tone-mapping path per backend, and tests on real HDR screens on Windows, macOS and Linux.
+
+</details>
+
+#### MSAA, anisotropic filtering, exclusive fullscreen
+
+More graphics options: multisample anti-aliasing, anisotropic filtering and an exclusive fullscreen mode. Today Horizon has FXAA and borderless fullscreen.
+
+<details><summary>Technical</summary>
+
+Not implemented ([docs/graphics.md](docs/graphics.md)). Anisotropic filtering needs linear magnification in wgpu, which blurs close blocks, so close-up sharpness has to be kept first; MSAA would sit beside FXAA; exclusive fullscreen where the backend supports it.
+
+</details>
+
+### Launcher
+
+#### Lean installs that use less disk
+
+Smaller installs: Horizon keeps one shared copy of the prepared game files and removes what only the preparation needed.
+
+<details><summary>Technical</summary>
+
+A shared resource store keyed by the preparer's digest, no prepare intermediates left behind, the current and the previous version kept, and an automatic clean-up. Not started.
+
+</details>
+
+### Platforms
+
+#### Horizon on Linux ARM64
+
+Game and launcher builds for 64-bit ARM Linux computers.
+
+<details><summary>Technical</summary>
+
+Issue [#1709](https://github.com/ludovic111/horizon/issues/1709): aarch64 builds of the game and the launcher in the release workflow, tested on a real ARM machine with its Vulkan driver. The server build already drops audio and controllers (`--no-default-features`).
+
+</details>
+
+#### OpenGL for old computers
+
+A way to play on old PCs and Linux machines that have no Vulkan or DirectX 12, through OpenGL.
+
+<details><summary>Technical</summary>
+
+Players on older hardware ask whether Vulkan is the only way. Horizon draws with wgpu, which has an OpenGL backend; what is needed is to see which features hold up on it, how fast it runs, and a launcher switch like the DirectX 12 fallback that already ships.
+
+More: [docs/graphics.md](docs/graphics.md)
+
+</details>
+
+#### Android, iOS and the browser
+
+Versions of Horizon for Android, iOS and web browsers. Nothing official yet; contributors have started the first pieces.
+
+<details><summary>Technical</summary>
+
+No official build. Android was first closed as not planned, with touch controls, a mobile interface, packaging and loading the player's own assets all missing; the roadmap now includes it, iOS and a WebAssembly build for the browser as long-term goals. First pieces from contributors: `horizon-dualsense` compiling on iOS ([#1813](https://github.com/ludovic111/horizon/issues/1813)) and helper-thread limits on Android ([#1751](https://github.com/ludovic111/horizon/issues/1751)). Preparing without Java ([#1750](https://github.com/ludovic111/horizon/issues/1750)) matters here too. Horizon ships none of Mojang's files on any platform.
+
+</details>
+
+### Horizon extras
+
+#### A complete video studio inside the game
+
+Record, replay and edit videos without leaving the game: record in a keypress, replay a session, cut and finish the video. One of Horizon's original goals.
+
+<details><summary>Technical</summary>
+
+Three stages. Recording: capture gameplay in a keypress with an encoder thread and little frame-time cost. Replay: a replay mode for recorded sessions. Editing: cuts, camera paths, titles and export. None of it exists yet; the agent-control socket ([docs/agent-control.md](docs/agent-control.md)) already lets tools drive the game for scripted shots.
+
+</details>
+
+### AI and agents
+
+#### An optional AI teammate
+
+An optional AI teammate you can talk to by voice. It plays beside you, helps or finishes the game with you, runs on your computer first, and exists only if you turn it on. The No AI switch hides it.
+
+<details><summary>Technical</summary>
+
+Draft pull requests: the companion ([#1068](https://github.com/ludovic111/horizon/issues/1068)), its safety modes and their evaluation ([#1069](https://github.com/ludovic111/horizon/issues/1069)) and a route that finishes the game ([#1070](https://github.com/ludovic111/horizon/issues/1070)). In the drafts: a companion that follows, fights, mines, crafts, sleeps and respawns; chat and push-to-talk voice, with speech recognition and a choice of voices; presets (very strong, helper, beat the game); a guard model with Clean, Kid and Salty modes; perception levels from Fair to All-knowing; hardware detection with a simple mode and an Advanced tab; local models first, cloud keys optional. The No AI switch is already in the game. Left: the speedrun route doesn't finish the game reliably yet, voices for more languages, and the safety evaluation, which must pass before it ships.
+
+</details>
+
+### Community
+
+#### A video series about Horizon
+
+A series of videos about how Horizon is made and what is new, with each upload announced on Discord.
+
+<details><summary>Technical</summary>
+
+Kira already shows new uploads in a read-only Discord channel (done). The series follows each stage of the project: a script, edits, titles and a thumbnail per video.
+
+</details>
+
+## Help wanted
+
+### Performance
+
+#### Benchmark your computer
+
+Run Horizon's built-in benchmark and share the report: every new computer makes the performance work more accurate. No coding needed.
+
+<details><summary>Technical</summary>
+
+`horizon-launcher play --arg=--benchmark --arg=standard` writes a JSON report; `horizon-launcher data benchmark <report>` shows what would be sent and uploads it ([website/docs/performance.md](website/docs/performance.md)). Results from three installs with the same hardware appear on the Benchmarks page. Example: [#1711](https://github.com/ludovic111/horizon/issues/1711).
+
+</details>
+
+### Gameplay parity
+
+#### End city banners keep their pattern
+
+Banners in End cities show as plain magenta instead of with their pattern.
+
+<details><summary>Technical</summary>
+
+Compare the banner block entities the End city templates place with vanilla's (`EndCityPieces`, the templates' block entity NBT, `BannerBlockEntity`'s patterns), in `crates/horizon-world/src/worldgen/structure/`. Issue [#1438](https://github.com/ludovic111/horizon/issues/1438); possibly related: [#526](https://github.com/ludovic111/horizon/issues/526).
+
+</details>
+
+#### Enchanted loot in End cities
+
+Armour and tools in End city chests should come enchanted, as in vanilla.
+
+<details><summary>Technical</summary>
+
+`loot.rs` implements `enchant_with_levels`: find why the End city chest table's rolls come out bare, and compare them with vanilla's for a few seeds. Issues [#1437](https://github.com/ludovic111/horizon/issues/1437), [#1660](https://github.com/ludovic111/horizon/issues/1660).
+
+</details>
+
+#### Cooldowns drawn on items
+
+After you throw an ender pearl, its slot should show the cooldown sweeping away, as in vanilla.
+
+<details><summary>Technical</summary>
+
+Vanilla draws `ItemCooldowns`' percent as a white overlay over the slot (`GuiGraphicsExtractor.itemDecorations` and `itemCooldown`) in the hotbar and in inventories. Issue [#1763](https://github.com/ludovic111/horizon/issues/1763).
+
+</details>
+
+#### Chat settings and team prefixes
+
+The Hidden and Commands Only chat settings should hide chat, and team prefixes should appear before names in chat.
+
+<details><summary>Technical</summary>
+
+Vanilla checks `ChatVisiblity` before it delivers chat and system messages ([#1376](https://github.com/ludovic111/horizon/issues/1376)), and chat uses the team-formatted display name ([#1378](https://github.com/ludovic111/horizon/issues/1378)). Both issues have exact steps to reproduce.
+
+</details>
+
+#### A pointing hand over buttons
+
+The mouse pointer should turn into a pointing hand over menu buttons, as in vanilla 26.3.
+
+<details><summary>Technical</summary>
+
+26.3's `AbstractWidget` asks for a cursor from `CursorTypes` when it is hovered; winit's `CursorIcon::Pointer` gives the same shape. Issue [#1347](https://github.com/ludovic111/horizon/issues/1347).
+
+</details>
+
+#### Ctrl+Backspace and scroll bars in menus
+
+Ctrl+Backspace should delete a whole word in the creative search, and every list's scroll bar should be draggable.
+
+<details><summary>Technical</summary>
+
+`EditBox` deletes by word with Ctrl ([#1764](https://github.com/ludovic111/horizon/issues/1764)); the Game Rules and Statistics lists' scroll bars can't be dragged ([#1782](https://github.com/ludovic111/horizon/issues/1782), after [#978](https://github.com/ludovic111/horizon/issues/978)).
+
+</details>
+
+#### Chickens flap while they fall
+
+Chickens should flap their wings while they fall, not stand still in the air.
+
+<details><summary>Technical</summary>
+
+Vanilla's `Chicken.aiStep` updates `flap` and `flapSpeed` when the chicken isn't on the ground, and the model's wings follow them. Issue [#1706](https://github.com/ludovic111/horizon/issues/1706).
+
+</details>
+
+## Recently shipped
+
+- **Server resource packs** (v0.2.48): Servers can send you their resource pack: Horizon asks, downloads it and applies it, like vanilla. [#1562](https://github.com/ludovic111/horizon/issues/1562) · [#1569](https://github.com/ludovic111/horizon/issues/1569) · [#1570](https://github.com/ludovic111/horizon/issues/1570)
+- **Single player on its own server thread** (v0.2.39): Single player runs on a server thread, as vanilla does, so the world keeps ticking smoothly while the window draws. [#1514](https://github.com/ludovic111/horizon/issues/1514) · [docs/server-levels.md](docs/server-levels.md)
+- **GPU occlusion culling on Macs** (v0.2.17): On Macs the GPU now skips terrain hidden behind hills and caves: 8 to 48% more frames per second at 32 chunks on an M4 Pro. [#1434](https://github.com/ludovic111/horizon/issues/1434)
+- **Animated textures on the GPU** (v0.2.5): Water, lava and other animated blocks are now animated by the graphics card: 1.7 to 2.4 times better 1% lows on Intel graphics. [#1239](https://github.com/ludovic111/horizon/issues/1239)
+- **Far Detail for integrated graphics** (v0.2.5): An optional Reduced setting for far terrain, suggested on integrated graphics, that saves 2 to 4 ms of GPU time per frame. [#1199](https://github.com/ludovic111/horizon/issues/1199) · [#1029](https://github.com/ludovic111/horizon/issues/1029)
+- **The launcher's mod browser** (launcher@0.2.0): Search Modrinth for mods, modpacks and resource packs from the launcher; it says before installing what works in Horizon. [#1154](https://github.com/ludovic111/horizon/issues/1154) · [#1242](https://github.com/ludovic111/horizon/issues/1242) · [#1243](https://github.com/ludovic111/horizon/issues/1243) · [#1246](https://github.com/ludovic111/horizon/issues/1246) · [docs/mod-browser.md](docs/mod-browser.md)
+- **A blocky, Minecraft-like launcher** (launcher@0.2.0): The launcher got a new blocky look in Horizon's purple, in dark and light. [#1269](https://github.com/ludovic111/horizon/issues/1269) · [docs/design-system.md](docs/design-system.md)
+- **Dynamic lights** (v2026.10.22): An optional extra: torches you hold, drop or set on fire light up what is around them. [#1162](https://github.com/ludovic111/horizon/issues/1162)
+- **Host a server from the launcher** (launcher-v0.15.0): The launcher's Servers page creates, starts, backs up and updates a Horizon server with buttons, and invites friends. [#1026](https://github.com/ludovic111/horizon/issues/1026) · [docs/hosting.md](docs/hosting.md)

crates/cargo-horizon-mod/Cargo.toml

@@ -4,10 +4,10 @@ version = "0.1.0"
 edition.workspace = true
 license.workspace = true
 rust-version = "1.86"
-description = "cargo horizon-mod new/build/run: make Horizon mods in Rust (docs/mods.md)"
+description = "cargo horizon-mod new/build/run/check: make Horizon mods in Rust (docs/mods.md)"
 
 [dependencies]
-horizon-mods = { path = "../horizon-mods", default-features = false, features = ["pack"] }
+horizon-mods = { path = "../horizon-mods", default-features = false, features = ["pack", "runtime", "index"] }
 serde_json = "1.0.151"
 
 [lints]

crates/cargo-horizon-mod/src/check.rs

@@ -0,0 +1,278 @@
+//! `cargo horizon-mod check <file>`: what the registry checks of a submission,
+//! run anywhere: its kind's own checks (docs/api/mod-index.md), its signature
+//! when given a key, and for a mod a trial run in the sandbox: it must start,
+//! survive ticks, frames, a chat line and each of its commands, and import
+//! no more than its capabilities.
+use horizon_mods::{
+    Clock, Mods, Output, Package, Player, Snapshot, Status,
+    index::{self, Facts, Kind},
+    manifest::component_imports,
+};
+use serde_json::{Value, json};
+use std::path::Path;
+
+/// How long the trial run plays: two seconds of game.
+const TICKS: u64 = 40;
+const FRAMES_PER_TICK: u64 = 3;
+
+pub struct Report {
+    pub kind: Kind,
+    pub facts: Facts,
+    pub sha256: String,
+    pub size: u64,
+    pub signed: bool,
+    /// A mod has code to run (a content mod may have none).
+    pub code: bool,
+    /// A mod's component imports.
+    pub imports: Vec<String>,
+    /// A mod's commands, each run once.
+    pub commands: Vec<String>,
+    /// What the mod showed during the trial run.
+    pub output: Vec<String>,
+}
+
+impl Report {
+    pub fn json(&self) -> Value {
+        let requires: Vec<Value> = self
+            .facts
+            .requires
+            .iter()
+            .map(|r| json!({"id": r.id, "version": r.version, "sha256": r.sha256}))
+            .collect();
+        json!({
+            "kind": self.kind.name(),
+            "id": self.facts.id,
+            "version": self.facts.version,
+            "api": self.facts.api,
+            "side": self.facts.side,
+            "capabilities": self.facts.capabilities,
+            "game": self.facts.game,
+            "requires": requires,
+            "sha256": self.sha256,
+            "size": self.size,
+            "signed": self.signed,
+            "code": self.code,
+            "imports": self.imports,
+            "commands": self.commands,
+            "output": self.output,
+        })
+    }
+
+    pub fn text(&self) -> String {
+        let f = &self.facts;
+        let mut out = format!(
+            "{} {} ({}",
+            f.id.as_deref().unwrap_or("resource pack"),
+            f.version.as_deref().unwrap_or(""),
+            self.kind.name()
+        );
+        if let Some(side) = f.side {
+            let side = serde_json::to_value(side).unwrap_or_default();
+            out += &format!(", API {}, {}", f.api, side.as_str().unwrap_or("?"));
+        } else if !f.api.is_empty() {
+            out += &format!(", format {}", f.api);
+        }
+        if let Some(game) = &f.game {
+            out += &format!(", for {game}");
+        }
+        let signed = if self.signed {
+            "signature verified"
+        } else {
+            "unsigned"
+        };
+        out += &format!(
+            ")\n  {} bytes, SHA-256 {}, {signed}\n",
+            self.size, self.sha256
+        );
+        for c in &f.capabilities {
+            out += &format!("  may {}\n", c.describe());
+        }
+        for r in &f.requires {
+            out += &format!("  needs {} {} ({})\n", r.id, r.version, &r.sha256[..12]);
+        }
+        if self.kind == Kind::Mod && !self.code {
+            out += "  no code: content only, nothing to run\n";
+        } else if self.kind == Kind::Mod {
+            let commands = if self.commands.is_empty() {
+                String::new()
+            } else {
+                format!(", /{}", self.commands.join(", /"))
+            };
+            out += &format!(
+                "  trial run: started, {TICKS} ticks, {} frames, a chat line{commands}: ok\n",
+                TICKS * FRAMES_PER_TICK
+            );
+        }
+        out
+    }
+}
+
+/// The kind a file's extension says.
+pub fn kind_of(path: &Path) -> Option<Kind> {
+    match path.extension()?.to_str()? {
+        "hmod" => Some(Kind::Mod),
+        "hpack" => Some(Kind::Modpack),
+        "zip" => Some(Kind::ResourcePack),
+        _ => None,
+    }
+}
+
+/// Checks the file at `path` as `kind`; `key` and `signature` (the
+/// `.minisig` text) check its signature.
+pub fn check(
+    path: &Path,
+    kind: Kind,
+    key: Option<&str>,
+    signature: Option<&str>,
+) -> Result<Report, String> {
+    let size = std::fs::metadata(path)
+        .map_err(|e| format!("{}: {e}", path.display()))?
+        .len();
+    if size > index::MAX_FILE {
+        return Err(format!("over {} MiB", index::MAX_FILE >> 20));
+    }
+    index::open(&kind)?;
+    let facts = index::inspect(&kind, path)?;
+    let signed = match (key, signature) {
+        (Some(key), Some(sig)) => {
+            index::verify_signature(key, sig, path)?;
+            true
+        }
+        (None, None) => false,
+        _ => return Err("--key and --signature go together".into()),
+    };
+    let mut report = Report {
+        kind,
+        facts,
+        sha256: index::sha256_file(path)?,
+        size,
+        signed,
+        code: false,
+        imports: Vec::new(),
+        commands: Vec::new(),
+        output: Vec::new(),
+    };
+    if report.kind == Kind::Mod {
+        trial_run(path, &mut report)?;
+    }
+    Ok(report)
+}
+
+/// Runs a mod in the sandbox, as the game does, from a scratch copy so its
+/// storage lands in a folder removed afterwards. A content mod has no code to
+/// run: `inspect` already read its content as the game does.
+fn trial_run(path: &Path, report: &mut Report) -> Result<(), String> {
+    let package = Package::read(path)?;
+    let Some(wasm) = package.wasm.as_deref() else {
+        return Ok(());
+    };
+    report.code = true;
+    report.imports = component_imports(wasm)?;
+    package
+        .manifest
+        .check_imports(report.imports.iter().map(String::as_str))?;
+    let dir = std::env::temp_dir().join(format!("horizon-mod-check-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).map_err(|e| e.to_string())?;
+    let copy = dir.join("mod.hmod");
+    let result = std::fs::copy(path, &copy)
+        .map_err(|e| e.to_string())
+        .and_then(|_| play(&copy, report));
+    let _ = std::fs::remove_dir_all(&dir);
+    result
+}
+
+fn play(path: &Path, report: &mut Report) -> Result<(), String> {
+    let mut mods = Mods::load(&[path.to_path_buf()], |_| true, |_| false);
+    let failed = |mods: &Mods| match &mods.entries()[0].status {
+        Status::Failed(reason) => Some(reason.clone()),
+        _ => None,
+    };
+    if let Some(reason) = failed(&mods) {
+        return Err(format!("it didn't start: {reason}"));
+    }
+    report.commands = mods.commands().map(str::to_owned).collect();
+    for t in 0..TICKS {
+        mods.set_snapshot(Snapshot {
+            player: Some(Player {
+                x: 0.5 + t as f64 * 0.1,
+                y: 64.0,
+                z: 0.5,
+                yaw: 90.0,
+                pitch: 0.0,
+                health: 20.0,
+                food: 20,
+                dimension: "minecraft:overworld".into(),
+            }),
+            clock: Some(Clock {
+                game_time: t,
+                day_time: 1000 + t,
+            }),
+        });
+        mods.tick(t);
+        for _ in 0..FRAMES_PER_TICK {
+            mods.frame(1.0 / 60.0);
+        }
+    }
+    mods.chat("<Steve> hello");
+    for name in report.commands.clone() {
+        mods.command(&name);
+    }
+    for out in mods.drain() {
+        report.output.push(match out {
+            Output::Chat { text, .. } => format!("chat: {text}"),
+            Output::Feedback { text, error } => {
+                format!("{}: {text}", if error { "error" } else { "feedback" })
+            }
+            Output::Stopped { reason, .. } => return Err(format!("it stopped: {reason}")),
+        });
+    }
+    match failed(&mods) {
+        Some(reason) => Err(format!("it stopped: {reason}")),
+        None => Ok(()),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn fixture(name: &str) -> std::path::PathBuf {
+        Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("../horizon-mods/tests/index")
+            .join(name)
+    }
+
+    #[test]
+    fn checks_each_kind_its_own_way() {
+        let pack = fixture("cozy-1.0.0.hpack");
+        let report = check(&pack, kind_of(&pack).unwrap(), None, None).unwrap();
+        assert_eq!(report.facts.requires[0].id, "coords_hud");
+        assert!(
+            report
+                .text()
+                .contains("cozy 1.0.0 (modpack, format 1, for 26.3)")
+        );
+        // The fixture mod's code is a stand-in: its manifest reads, its run fails.
+        let hmod = fixture("coords_hud-0.1.0.hmod");
+        let key = std::fs::read_to_string(fixture("test.pub")).unwrap();
+        let sig = std::fs::read_to_string(fixture("coords_hud-0.1.0.hmod.minisig")).unwrap();
+        let key = key.lines().last().unwrap();
+        let e = check(&hmod, Kind::Mod, Some(key), Some(&sig))
+            .err()
+            .unwrap();
+        assert!(e.contains("didn't start"), "{e}");
+        let e = check(
+            &hmod,
+            Kind::Mod,
+            Some(key),
+            Some("untrusted comment: x\nRUQ=\n"),
+        )
+        .err()
+        .unwrap();
+        assert!(e.contains("signature"), "{e}");
+        let e = check(&pack, Kind::Shader, None, None).err().unwrap();
+        assert!(e.contains("shader packs open"), "{e}");
+        assert!(check(&pack, Kind::Mod, None, None).is_err());
+    }
+}

crates/cargo-horizon-mod/src/main.rs

@@ -1,13 +1,21 @@
 //! `cargo horizon-mod`: make Horizon mods in Rust (`docs/mods.md`).
 //!
-//! - `new <path> [--name "Name"] [--sdk-path <dir>]`: a mod crate from the template.
-//! - `build [--debug]`: the `.hmod` in `target/horizon-mod/`.
+//! - `new <path> [--template code|content] [--name "Name"] [--sdk-path <dir>]`:
+//!   a mod from a template: a Rust crate, or a content mod (no code).
+//! - `build [--debug]`: the `.hmod` in `target/horizon-mod/`, with the mod's
+//!   `assets/` and `data/`; a folder without `Cargo.toml` is content only.
 //! - `run [--game <horizon-client>] [-- <game args>]`: build, then play with
 //!   the mod; run `build` again and the game reloads it.
+//! - `check <file> [--json]`: what the registry checks of a submission
+//!   (`.hmod`, `.hpack`, resource pack `.zip`), with a trial run for a mod.
+//! - `registry build|review|check|list`: the registry repository's CI.
 use horizon_mods::{
-    Manifest, Package,
+    Capability, Content, Manifest, Package,
     manifest::{MANIFEST, component_imports, componentize},
 };
+mod check;
+mod registry;
+
 use std::{
     path::{Path, PathBuf},
     process::{Command, ExitCode, Stdio},
@@ -28,7 +36,9 @@ fn main() -> ExitCode {
             println!("Built {}", p.display());
         }),
         Some("run") => run(&args[1..]),
-        _ => Err("usage: cargo horizon-mod new <path> | build [--debug] | run [--game <horizon-client>] [-- <game args>]".into()),
+        Some("check") => check(&args[1..]),
+        Some("registry") => registry::main(&args[1..]),
+        _ => Err("usage: cargo horizon-mod new <path> [--template code|content] | build [--debug] | run [--game <horizon-client>] [-- <game args>] | check <file> [--kind <kind>] [--key <public key> --signature <file.minisig>] [--json] | registry build|review|check|list".into()),
     };
     match result {
         Ok(()) => ExitCode::SUCCESS,
@@ -82,19 +92,68 @@ fn new(args: &[String]) -> Result<(), String> {
             .replace("{name}", &name)
             .replace("{sdk}", &sdk)
     };
-    let files = [
+    let code = [
         ("Cargo.toml", include_str!("../template/Cargo.toml.in")),
         (MANIFEST, include_str!("../template/horizon-mod.toml")),
         ("src/lib.rs", include_str!("../template/src/lib.rs")),
         (".gitignore", include_str!("../template/gitignore")),
     ];
-    for (file, text) in files {
+    // A block copying a vanilla one, with its model, name, loot, recipe and tag.
+    let content = [
+        (
+            MANIFEST,
+            include_str!("../template/content/horizon-mod.toml"),
+        ),
+        (
+            "data/{id}/horizon/block/glowing_amethyst.json",
+            include_str!("../template/content/block.json"),
+        ),
+        (
+            "assets/{id}/blockstates/glowing_amethyst.json",
+            include_str!("../template/content/blockstate.json"),
+        ),
+        (
+            "assets/{id}/models/block/glowing_amethyst.json",
+            include_str!("../template/content/model.json"),
+        ),
+        (
+            "assets/{id}/items/glowing_amethyst.json",
+            include_str!("../template/content/item.json"),
+        ),
+        (
+            "assets/{id}/lang/en_us.json",
+            include_str!("../template/content/lang.json"),
+        ),
+        (
+            "data/{id}/loot_table/blocks/glowing_amethyst.json",
+            include_str!("../template/content/loot.json"),
+        ),
+        (
+            "data/{id}/recipe/glowing_amethyst.json",
+            include_str!("../template/content/recipe.json"),
+        ),
+        (
+            "data/minecraft/tags/block/mineable/pickaxe.json",
+            include_str!("../template/content/pickaxe.json"),
+        ),
+        (".gitignore", include_str!("../template/gitignore")),
+    ];
+    let files: &[(&str, &str)] = match flag(args, "--template").unwrap_or("code") {
+        "code" => &code,
+        "content" => &content,
+        other => return Err(format!("no template {other}: code or content")),
+    };
+    for &(file, text) in files {
+        let file = fill(file);
+        let file = file.as_str();
         let to = dir.join(file);
         std::fs::create_dir_all(to.parent().expect("a file in the mod"))
             .map_err(|e| e.to_string())?;
         std::fs::write(&to, fill(text)).map_err(|e| format!("{}: {e}", to.display()))?;
     }
-    Manifest::parse(&std::fs::read_to_string(dir.join(MANIFEST)).map_err(|e| e.to_string())?)?;
+    let manifest =
+        Manifest::parse(&std::fs::read_to_string(dir.join(MANIFEST)).map_err(|e| e.to_string())?)?;
+    Content::read(dir, &manifest)?;
     println!(
         "Created {} (mod id {id}). Next: cd {path} && cargo horizon-mod run",
         dir.display()
@@ -102,14 +161,53 @@ fn new(args: &[String]) -> Result<(), String> {
     Ok(())
 }
 
-/// Builds the crate in the current folder and packs `target/horizon-mod/<id>.hmod`.
+/// Builds the mod in the current folder and packs `target/horizon-mod/<id>.hmod`:
+/// the manifest, the crate's component (none without a `Cargo.toml`: a
+/// content mod) and the files in `assets/` and `data/`.
 fn build(release: bool) -> Result<PathBuf, String> {
-    let manifest_text = std::fs::read_to_string(MANIFEST)
+    build_in(Path::new("."), release)
+}
+
+fn build_in(root: &Path, release: bool) -> Result<PathBuf, String> {
+    let manifest_text = std::fs::read_to_string(root.join(MANIFEST))
         .map_err(|e| format!("{MANIFEST}: {e} (run this in a mod's folder)"))?;
     let manifest = Manifest::parse(&manifest_text)?;
+    let (wasm, target_dir) = if root.join("Cargo.toml").exists() {
+        let (wasm, target) = compile(root, release)?;
+        // The game refuses a component importing capabilities the manifest lacks.
+        manifest.check_imports(component_imports(&wasm)?.iter().map(String::as_str))?;
+        (Some(wasm), target)
+    } else if manifest.capabilities.contains(&Capability::Registries) {
+        (None, root.join("target"))
+    } else {
+        return Err(format!(
+            "no Cargo.toml: only a content mod (capability registries in {MANIFEST}) has no code"
+        ));
+    };
+    // The same checks as the game's, and the files in the order it lists them.
+    let content = Content::read(root, &manifest)?;
+    let mut reader = content.reader()?;
+    let mut files = Vec::with_capacity(content.files.len());
+    for name in &content.files {
+        files.push((name.as_str(), reader.read(name)?));
+    }
+    let files: Vec<(&str, &[u8])> = files.iter().map(|(n, b)| (*n, b.as_slice())).collect();
+    let dir = target_dir.join("horizon-mod");
+    std::fs::create_dir_all(&dir).map_err(|e| e.to_string())?;
+    let path = dir.join(format!("{}.hmod", manifest.id));
+    // Write then rename, so a running game never reads half a file.
+    let partial = path.with_extension("hmod.partial");
+    let bytes = Package::write_files(&manifest_text, wasm.as_deref(), &files)?;
+    std::fs::write(&partial, bytes).map_err(|e| e.to_string())?;
+    std::fs::rename(&partial, &path).map_err(|e| e.to_string())?;
+    Ok(path)
+}
+
+/// Builds the crate for WebAssembly: its component, and Cargo's target folder.
+fn compile(root: &Path, release: bool) -> Result<(Vec<u8>, PathBuf), String> {
     let cargo = std::env::var("CARGO").unwrap_or_else(|_| "cargo".into());
     let mut cmd = Command::new(cargo);
-    cmd.args([
+    cmd.current_dir(root).args([
         "build",
         "--lib",
         "--target",
@@ -137,17 +235,39 @@ fn build(release: bool) -> Result<PathBuf, String> {
         .rfind(|f| f.extension().is_some_and(|e| e == "wasm"))
         .ok_or("the build made no .wasm: is the crate a cdylib?")?;
     let wasm = componentize(&std::fs::read(&core).map_err(|e| e.to_string())?)?;
-    // The game refuses a component importing capabilities the manifest lacks.
-    manifest.check_imports(component_imports(&wasm)?.iter().map(String::as_str))?;
-    let target_dir = core.ancestors().nth(3).ok_or("unexpected target folder")?;
-    let dir = target_dir.join("horizon-mod");
-    std::fs::create_dir_all(&dir).map_err(|e| e.to_string())?;
-    let path = dir.join(format!("{}.hmod", manifest.id));
-    // Write then rename, so a running game never reads half a file.
-    let partial = path.with_extension("hmod.partial");
-    std::fs::write(&partial, Package::write(&manifest_text, &wasm)?).map_err(|e| e.to_string())?;
-    std::fs::rename(&partial, &path).map_err(|e| e.to_string())?;
-    Ok(path)
+    let target = core.ancestors().nth(3).ok_or("unexpected target folder")?;
+    Ok((wasm, target.to_path_buf()))
+}
+
+/// `check <file>`: the registry's checks of a submission, printed; fails
+/// when one does.
+fn check(args: &[String]) -> Result<(), String> {
+    let file = args
+        .first()
+        .filter(|a| !a.starts_with("--"))
+        .ok_or("cargo horizon-mod check <file>")?;
+    let path = Path::new(file);
+    let kind = match flag(args, "--kind") {
+        Some(k) => horizon_mods::index::Kind::from(k.to_string()),
+        None => check::kind_of(path)
+            .ok_or("pass --kind mod|modpack|resourcepack: the extension doesn't say")?,
+    };
+    let signature = flag(args, "--signature")
+        .map(|p| std::fs::read_to_string(p).map_err(|e| format!("{p}: {e}")))
+        .transpose()?;
+    let report = check::check(path, kind, flag(args, "--key"), signature.as_deref());
+    if args.iter().any(|a| a == "--json") {
+        let json = match &report {
+            Ok(r) => serde_json::json!({"ok": true, "report": r.json()}),
+            Err(e) => serde_json::json!({"ok": false, "error": e}),
+        };
+        println!("{json}");
+    }
+    let report = report?;
+    if !args.iter().any(|a| a == "--json") {
+        print!("{}", report.text());
+    }
+    Ok(())
 }
 
 fn run(args: &[String]) -> Result<(), String> {
@@ -198,4 +318,49 @@ mod tests {
         );
         std::fs::remove_dir_all(&dir).unwrap();
     }
+
+    #[test]
+    fn the_content_template_builds_and_checks_with_no_code() {
+        let dir = std::env::temp_dir().join(format!("horizon-mod-content-{}", std::process::id()));
+        let path = dir.join("gems");
+        let new_args = [
+            path.display().to_string(),
+            "--template".into(),
+            "content".into(),
+        ];
+        new(&new_args).unwrap();
+        assert!(!path.join("Cargo.toml").exists());
+        let hmod = build_in(&path, true).unwrap();
+        assert_eq!(hmod, path.join("target/horizon-mod/gems.hmod"));
+        let package = Package::read(&hmod).unwrap();
+        assert!(package.wasm.is_none());
+        let content = Content::read(&hmod, &package.manifest).unwrap();
+        assert!(
+            content
+                .files
+                .contains(&"data/gems/horizon/block/glowing_amethyst.json".into())
+        );
+        assert_eq!(content.files.len(), 8, "{:?}", content.files);
+        let report = check::check(&hmod, check::kind_of(&hmod).unwrap(), None, None).unwrap();
+        assert!(!report.code);
+        assert!(
+            report.text().contains("no code: content only"),
+            "{}",
+            report.text()
+        );
+        // Without registries, a mod needs code.
+        let manifest = std::fs::read_to_string(path.join(MANIFEST)).unwrap();
+        let manifest = manifest.replace("[\"registries\"]", "[]");
+        std::fs::write(path.join(MANIFEST), manifest).unwrap();
+        assert!(build_in(&path, true).unwrap_err().contains("no Cargo.toml"));
+        assert!(
+            new(&[
+                dir.join("x").display().to_string(),
+                "--template".into(),
+                "lua".into()
+            ])
+            .is_err()
+        );
+        std::fs::remove_dir_all(&dir).unwrap();
+    }
 }

crates/cargo-horizon-mod/src/registry.rs

@@ -0,0 +1,159 @@
+//! `cargo horizon-mod registry build|review|check|list`: the registry repository's CI
+//! (`ludovic111/horizon-mods`, docs/api/mod-index.md). Network-free: the
+//! workflow downloads the files and publishes what this writes.
+use horizon_mods::index::{
+    FILE_HOST,
+    registry::{self, Sources},
+};
+use std::path::Path;
+
+/// Where the registry's site is published (its icons).
+const SITE: &str = "https://ludovic111.github.io/horizon-mods/";
+
+const USAGE: &str = "usage: cargo horizon-mod registry build <checkout> --files <dir> --out <index.json> [--release <url>] [--site <url>] [--generated <time>]
+       cargo horizon-mod registry review <base checkout> <head checkout> --author <login> [--json]
+       cargo horizon-mod registry check <base checkout> <head checkout> --files <dir>
+       cargo horizon-mod registry list <checkout>";
+
+fn flag<'a>(args: &'a [String], name: &str) -> Option<&'a str> {
+    super::flag(args, name)
+}
+
+fn positional(args: &[String]) -> Vec<&str> {
+    let mut out = Vec::new();
+    let mut skip = false;
+    for a in args {
+        if skip {
+            skip = false;
+        } else if a == "--json" {
+        } else if a.starts_with("--") {
+            skip = true;
+        } else {
+            out.push(a.as_str());
+        }
+    }
+    out
+}
+
+fn lines(errors: Vec<String>) -> String {
+    format!("{} problem(s):\n  {}", errors.len(), errors.join("\n  "))
+}
+
+pub fn main(args: &[String]) -> Result<(), String> {
+    let rest = args.get(1..).unwrap_or_default();
+    let pos = positional(rest);
+    match args.first().map(String::as_str) {
+        Some("build") => {
+            let [checkout] = pos[..] else {
+                return Err(USAGE.into());
+            };
+            let (files, out) = (flag(rest, "--files"), flag(rest, "--out"));
+            let (Some(files), Some(out)) = (files, out) else {
+                return Err(USAGE.into());
+            };
+            let generated = flag(rest, "--generated")
+                .map(str::to_owned)
+                .or_else(|| std::env::var("REGISTRY_GENERATED").ok())
+                .unwrap_or_default();
+            let index = registry::build(&Sources {
+                registry: Path::new(checkout),
+                files: Path::new(files),
+                release: flag(rest, "--release").unwrap_or(FILE_HOST),
+                site: flag(rest, "--site").unwrap_or(SITE),
+                generated,
+            })
+            .map_err(lines)?;
+            let text = serde_json::to_string_pretty(&index).map_err(|e| e.to_string())?;
+            std::fs::write(out, text + "\n").map_err(|e| format!("{out}: {e}"))?;
+            println!(
+                "Wrote {out}: {} project(s), {} taken down",
+                index.projects.len(),
+                index.revoked.len()
+            );
+            Ok(())
+        }
+        Some("review") => {
+            let [base, head] = pos[..] else {
+                return Err(USAGE.into());
+            };
+            let author = flag(rest, "--author").ok_or(USAGE)?;
+            let (base, _) = registry::load(Path::new(base)).map_err(lines)?;
+            let (head, _) = registry::load(Path::new(head)).map_err(lines)?;
+            let review = registry::review(&base, &head, author);
+            if rest.iter().any(|a| a == "--json") {
+                let json = serde_json::json!({"errors": review.errors, "notes": review.notes});
+                println!("{json}");
+            } else {
+                for n in &review.notes {
+                    println!("note: {n}");
+                }
+                for e in &review.errors {
+                    println!("error: {e}");
+                }
+            }
+            if review.errors.is_empty() {
+                Ok(())
+            } else {
+                Err(format!(
+                    "{} change(s) the registry refuses",
+                    review.errors.len()
+                ))
+            }
+        }
+        // `check` (and its trial run) on each file `head` lists and `base`
+        // doesn't: a pull request's new files.
+        Some("check") => {
+            let [base, head] = pos[..] else {
+                return Err(USAGE.into());
+            };
+            let files = Path::new(flag(rest, "--files").ok_or(USAGE)?);
+            let old: Vec<String> = match registry::load(Path::new(base)) {
+                Ok((entries, _)) => entries
+                    .iter()
+                    .flat_map(|e| e.versions.iter().map(|v| v.sha256.clone()))
+                    .collect(),
+                // The first pull request has no entries to compare with.
+                Err(_) => Vec::new(),
+            };
+            let (entries, _) = registry::load(Path::new(head)).map_err(lines)?;
+            let mut failed = 0;
+            for e in &entries {
+                for v in e.versions.iter().filter(|v| !old.contains(&v.sha256)) {
+                    println!("{} {} ({}):", e.id, v.version, v.file);
+                    let report = crate::check::check(
+                        &files.join(&v.sha256),
+                        e.kind.clone(),
+                        e.key.as_deref(),
+                        v.signature.as_deref(),
+                    );
+                    match report {
+                        Ok(r) => print!("{}", r.text()),
+                        Err(err) => {
+                            failed += 1;
+                            println!("  error: {err}");
+                        }
+                    }
+                }
+            }
+            if failed == 0 {
+                Ok(())
+            } else {
+                Err(format!("{failed} file(s) failed their check"))
+            }
+        }
+        // The files CI must download for `build`: `<sha256> <id> <version> <file>`.
+        Some("list") => {
+            let [checkout] = pos[..] else {
+                return Err(USAGE.into());
+            };
+            let (entries, _) = registry::load(Path::new(checkout)).map_err(lines)?;
+            for e in &entries {
+                for v in &e.versions {
+                    println!("{} {} {} {}", v.sha256, e.id, v.version, v.file);
+                }
+            }
+            Ok(())
+        }
+        _ => Err(USAGE.into()),
+    }
+}

crates/cargo-horizon-mod/template/content/block.json

@@ -0,0 +1,4 @@
+{
+  "template": "minecraft:amethyst_block",
+  "properties": { "hardness": 2.0, "light": 7 }
+}

crates/cargo-horizon-mod/template/content/blockstate.json

@@ -0,0 +1,5 @@
+{
+  "variants": {
+    "": { "model": "{id}:block/glowing_amethyst" }
+  }
+}

crates/cargo-horizon-mod/template/content/horizon-mod.toml

@@ -0,0 +1,10 @@
+id = "{id}"
+name = "{name}"
+version = "0.1.0"
+description = ""
+authors = []
+# A content mod: blocks and items from data/ and assets/, no code (API 0.2).
+api = "0.2"
+side = "both"
+# registries: "May add blocks and items to your worlds".
+capabilities = ["registries"]

crates/cargo-horizon-mod/template/content/item.json

@@ -0,0 +1,3 @@
+{
+  "model": { "type": "minecraft:model", "model": "{id}:block/glowing_amethyst" }
+}

crates/cargo-horizon-mod/template/content/lang.json

@@ -0,0 +1,3 @@
+{
+  "block.{id}.glowing_amethyst": "Glowing Amethyst"
+}

crates/cargo-horizon-mod/template/content/loot.json

@@ -0,0 +1,11 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "condition": { "type": "minecraft:survives_explosion" },
+      "entries": [{ "type": "minecraft:item", "name": "{id}:glowing_amethyst" }],
+      "rolls": 1
+    }
+  ],
+  "random_sequence": "{id}:blocks/glowing_amethyst"
+}

crates/cargo-horizon-mod/template/content/model.json

@@ -0,0 +1,4 @@
+{
+  "parent": "minecraft:block/cube_all",
+  "textures": { "all": "minecraft:block/amethyst_block" }
+}

crates/cargo-horizon-mod/template/content/pickaxe.json

@@ -0,0 +1,3 @@
+{
+  "values": ["{id}:glowing_amethyst"]
+}

crates/cargo-horizon-mod/template/content/recipe.json

@@ -0,0 +1,6 @@
+{
+  "type": "minecraft:crafting_shapeless",
+  "category": "building",
+  "ingredients": ["minecraft:amethyst_block", "minecraft:glowstone_dust"],
+  "result": { "id": "{id}:glowing_amethyst" }
+}

crates/horizon-assets/src/blockstate/choice.rs

@@ -4,15 +4,15 @@ use crate::json::{Result, error};
 use horizon_core::random::RandomSource;
 
 #[derive(Clone, Debug)]
-enum Choice {
-    Single(Variant),
+enum Choice<T> {
+    Single(T),
     Weighted {
-        variants: Vec<Variant>,
+        variants: Vec<T>,
         ends: Vec<i32>,
         total: i32,
     },
 }
-impl Choice {
+impl Choice<Variant> {
     fn new(value: &VariantSet) -> Result<Self> {
         match value {
             VariantSet::Single(value) => Ok(Self::Single(value.clone())),
@@ -41,7 +41,23 @@ impl Choice {
             }
         }
     }
-    fn select(&self, random: &mut impl RandomSource) -> &Variant {
+}
+impl<T> Choice<T> {
+    fn map<U>(&self, f: &mut impl FnMut(&T) -> U) -> Choice<U> {
+        match self {
+            Self::Single(value) => Choice::Single(f(value)),
+            Self::Weighted {
+                variants,
+                ends,
+                total,
+            } => Choice::Weighted {
+                variants: variants.iter().map(&mut *f).collect(),
+                ends: ends.clone(),
+                total: *total,
+            },
+        }
+    }
+    fn select(&self, random: &mut impl RandomSource) -> &T {
         match self {
             Self::Single(value) => value,
             Self::Weighted {
@@ -60,10 +76,11 @@ impl Choice {
 }
 /// Compile once per definition and share across its bound block states. Prefix
 /// sums avoid rebuilding weight totals or scanning all entries during selection.
+/// `map` swaps each variant for what it stands for (its baked model).
 #[derive(Clone, Debug)]
-pub struct CompiledChoices {
-    variants: Vec<Choice>,
-    multipart: Vec<Choice>,
+pub struct CompiledChoices<T = Variant> {
+    variants: Vec<Choice<T>>,
+    multipart: Vec<Choice<T>>,
 }
 impl CompiledChoices {
     pub fn new(definition: &BlockStateDefinition) -> Result<Self> {
@@ -82,10 +99,19 @@ impl CompiledChoices {
                 .collect::<Result<_>>()?,
         })
     }
+}
+impl<T> CompiledChoices<T> {
+    /// The same choices, with `f` of each variant in its place.
+    pub fn map<U>(&self, mut f: impl FnMut(&T) -> U) -> CompiledChoices<U> {
+        CompiledChoices {
+            variants: self.variants.iter().map(|c| c.map(&mut f)).collect(),
+            multipart: self.multipart.iter().map(|c| c.map(&mut f)).collect(),
+        }
+    }
     /// The variant `particleMaterial` comes from: the first entry of a weighted
     /// list (`WeightedVariants`) and, for a multipart root, of its first
     /// selector whether or not that selector applies (`MultiPartModel`).
-    pub fn particle_variant(&self, selected: &SelectedModels) -> Option<&Variant> {
+    pub fn particle_variant(&self, selected: &SelectedModels) -> Option<&T> {
         let choice = match selected {
             SelectedModels::Variant(index) => self.variants.get(*index)?,
             SelectedModels::Multipart(_) => self.multipart.first()?,
@@ -95,14 +121,23 @@ impl CompiledChoices {
             Choice::Weighted { variants, .. } => variants.first()?,
         })
     }
-    /// Append selected variants without allocating intermediate part lists. A
-    /// multipart root consumes nextLong even for an empty selected subset, then
-    /// resets the same random source to that seed before each selected part.
+    /// Append selected variants without allocating intermediate part lists.
     pub fn collect<'a>(
         &'a self,
         selected: &SelectedModels,
         random: &mut impl RandomSource,
-        output: &mut Vec<&'a Variant>,
+        output: &mut Vec<&'a T>,
+    ) -> Result<()> {
+        self.for_each(selected, random, |v| output.push(v))
+    }
+    /// Each selected variant, in order. A multipart root consumes nextLong
+    /// even for an empty selected subset, then resets the same random source
+    /// to that seed before each selected part.
+    pub fn for_each<'a>(
+        &'a self,
+        selected: &SelectedModels,
+        random: &mut impl RandomSource,
+        mut f: impl FnMut(&'a T),
     ) -> Result<()> {
         match selected {
             SelectedModels::Variant(index) => {
@@ -110,7 +145,7 @@ impl CompiledChoices {
                     .variants
                     .get(*index)
                     .ok_or_else(|| error("invalid variant selection"))?;
-                output.push(choice.select(random));
+                f(choice.select(random));
             }
             SelectedModels::Multipart(indices) => {
                 if indices.iter().any(|index| *index >= self.multipart.len()) {
@@ -119,7 +154,7 @@ impl CompiledChoices {
                 let seed = random.next_long();
                 for index in indices {
                     random.set_seed(seed);
-                    output.push(self.multipart[*index].select(random));
+                    f(self.multipart[*index].select(random));
                 }
             }
         }

crates/horizon-bots/src/main.rs

@@ -173,6 +173,11 @@ impl Random {
     }
 }
 
+/// One bot thread that panics poisons the locks it held; the others and the report go on.
+fn lock<T>(m: &Mutex<T>) -> std::sync::MutexGuard<'_, T> {
+    m.lock().unwrap_or_else(std::sync::PoisonError::into_inner)
+}
+
 fn raw(id: i32, write: impl FnOnce(&mut Writer)) -> Vec<u8> {
     let mut w = Writer::new();
     w.varint(id);
@@ -329,7 +334,7 @@ fn read(
 ) {
     use ids::play::clientbound as cb;
     use ids::play::serverbound as sb;
-    let send = |body: Vec<u8>| writer.lock().unwrap().send(&body);
+    let send = |body: Vec<u8>| lock(&writer).send(&body);
     let mut seen = HashSet::new();
     let mut batch = BatchSize::new();
     let mut teleports = 0u64;
@@ -338,7 +343,7 @@ fn read(
             Ok(packet) => packet,
             Err(e) => {
                 if bot.online.swap(false, Ordering::SeqCst) {
-                    *bot.error.lock().unwrap() = Some(e.to_string());
+                    *lock(&bot.error) = Some(e.to_string());
                 }
                 return;
             }
@@ -356,7 +361,7 @@ fn read(
             cb::LEVEL_CHUNK_WITH_LIGHT => {
                 bot.chunks.fetch_add(1, Ordering::Relaxed);
                 if let (Ok(x), Ok(z)) = (r.i32(), r.i32()) {
-                    if !bot.held.lock().unwrap().insert((x, z)) {
+                    if !lock(&bot.held).insert((x, z)) {
                         bot.resent.fetch_add(1, Ordering::Relaxed);
                     }
                     if seen.insert((x, z)) {
@@ -368,7 +373,7 @@ fn read(
             cb::FORGET_LEVEL_CHUNK => {
                 if let Ok(play::Clientbound::ForgetLevelChunk(p)) =
                     play::Clientbound::decode(id, &body)
-                    && bot.held.lock().unwrap().remove(&(p.pos[0], p.pos[1]))
+                    && lock(&bot.held).remove(&(p.pos[0], p.pos[1]))
                 {
                     bot.forgotten.fetch_add(1, Ordering::Relaxed);
                 }
@@ -389,7 +394,7 @@ fn read(
             }
             cb::PLAYER_POSITION => match play::Clientbound::decode(id, &body) {
                 Ok(play::Clientbound::PlayerPosition(p)) => {
-                    let mut at = bot.teleport.lock().unwrap();
+                    let mut at = lock(&bot.teleport);
                     let previous = at.unwrap_or([0.0; 3]);
                     // Relative flags: X 1, Y 2, Z 4.
                     let pos: [f64; 3] = std::array::from_fn(|i| {
@@ -420,7 +425,7 @@ fn read(
             },
             cb::DISCONNECT | cb::START_CONFIGURATION => {
                 bot.online.store(false, Ordering::SeqCst);
-                *bot.error.lock().unwrap() = Some(if id == cb::DISCONNECT {
+                *lock(&bot.error) = Some(if id == cb::DISCONNECT {
                     format!(
                         "disconnected: {}",
                         String::from_utf8_lossy(&body)
@@ -455,7 +460,7 @@ fn run_bot(
     let connection = match join(&o, &name) {
         Ok(c) => c,
         Err(e) => {
-            *bot.error.lock().unwrap() = Some(e);
+            *lock(&bot.error) = Some(e);
             return;
         }
     };
@@ -469,12 +474,12 @@ fn run_bot(
     use ids::play::serverbound as sb;
     // Wait for the spawn position.
     let spawn = loop {
-        if let Some(at) = *bot.teleport.lock().unwrap() {
+        if let Some(at) = *lock(&bot.teleport) {
             break at;
         }
         if !bot.online.load(Ordering::SeqCst) || asked.elapsed() > Duration::from_secs(60) {
-            if bot.error.lock().unwrap().is_none() {
-                *bot.error.lock().unwrap() = Some("no spawn position within 60 s".into());
+            if lock(&bot.error).is_none() {
+                *lock(&bot.error) = Some("no spawn position within 60 s".into());
             }
             return;
         }
@@ -482,7 +487,7 @@ fn run_bot(
     };
     bot.joined_after_ms
         .store(asked.elapsed().as_millis() as u64, Ordering::SeqCst);
-    let send = |body: Vec<u8>| writer.lock().unwrap().send(&body).is_ok();
+    let send = |body: Vec<u8>| lock(&writer).send(&body).is_ok();
     send(raw(sb::PLAYER_LOADED, |_| {}));
     let mut random = Random(o.seed ^ (index as u64).wrapping_mul(0x2545_F491_4F6C_DD1D));
     let mut pos = spawn;
@@ -491,17 +496,15 @@ fn run_bot(
     let mut target = pos;
     let mut next = Instant::now();
     loop {
-        if until.lock().unwrap().is_some_and(|u| Instant::now() >= u)
-            || !bot.online.load(Ordering::SeqCst)
-        {
+        if lock(&until).is_some_and(|u| Instant::now() >= u) || !bot.online.load(Ordering::SeqCst) {
             break;
         }
         // A teleport from the server wins over where the bot thought it was.
-        if let Some(at) = bot.teleport.lock().unwrap().take() {
+        if let Some(at) = lock(&bot.teleport).take() {
             pos = at;
         }
         let here = ((pos[0].floor() as i32) >> 4, (pos[2].floor() as i32) >> 4);
-        if !bot.held.lock().unwrap().contains(&here) {
+        if !lock(&bot.held).contains(&here) {
             bot.waited.fetch_add(1, Ordering::Relaxed);
         } else if pos[1] < cruise {
             pos[1] = (pos[1] + 0.5).min(cruise);
@@ -558,7 +561,7 @@ fn run_bot(
     }
     // Offline first, so the reader doesn't count the closed connection as a failure.
     bot.online.store(false, Ordering::SeqCst);
-    writer.lock().unwrap().shutdown();
+    lock(&writer).shutdown();
 }
 
 fn behaviour_of(mode: &str, index: usize) -> Behaviour {
@@ -612,13 +615,10 @@ fn main() {
         let total = |f: fn(&Bot) -> &AtomicU64| -> u64 {
             bots.iter().map(|b| f(b).load(Ordering::Relaxed)).sum()
         };
-        let failed = bots
-            .iter()
-            .filter(|b| b.error.lock().unwrap().is_some())
-            .count();
+        let failed = bots.iter().filter(|b| lock(&b.error).is_some()).count();
         if first.is_none() && online > 0 {
             first = Some(Instant::now());
-            *until.lock().unwrap() = Some(Instant::now() + Duration::from_secs(o.seconds));
+            *lock(&until) = Some(Instant::now() + Duration::from_secs(o.seconds));
         }
         println!(
             "{}",
@@ -636,10 +636,10 @@ fn main() {
             })
         );
         previous_chunks = chunks;
-        let over = until.lock().unwrap().is_some_and(|u| Instant::now() >= u);
+        let over = lock(&until).is_some_and(|u| Instant::now() >= u);
         let all_failed = failed == o.bots;
         if over || all_failed || (first.is_none() && start.elapsed() > Duration::from_secs(120)) {
-            *until.lock().unwrap() = Some(Instant::now());
+            *lock(&until) = Some(Instant::now());
             break;
         }
     }
@@ -669,7 +669,7 @@ fn main() {
             "forgotten": b.forgotten.load(Ordering::Relaxed),
             "pulled_back": b.pulled_back.load(Ordering::Relaxed),
             "waited_ticks": b.waited.load(Ordering::Relaxed),
-            "error": *b.error.lock().unwrap(),
+            "error": *lock(&b.error),
         })).collect::<Vec<_>>(),
     });
     if o.report.as_deref() == Some("-") {

crates/horizon-client/Cargo.toml

@@ -16,11 +16,13 @@ horizon-world = { path = "../horizon-world" }
 horizon-protocol = { path = "../horizon-protocol" }
 # server.properties, eula.txt and the user lists, shared with horizon-server.
 horizon-server-files = { path = "../horizon-server-files" }
+# Shader packs: reading them and turning their GLSL into naga modules.
+horizon-shaders = { path = "../horizon-shaders" }
 horizon-friends = { path = "../horizon-friends" }
 # Horizon mods: sandboxed WebAssembly components, off unless installed and turned on (docs/mods.md).
 # Their runtime is the `mods` feature.
 horizon-mods = { path = "../horizon-mods", default-features = false }
-wgpu = { version = "30.0.1", default-features = false, features = ["std", "parking_lot", "vulkan", "metal", "wgsl"] }
+wgpu = { version = "30.0.1", default-features = false, features = ["std", "parking_lot", "vulkan", "metal", "wgsl", "naga-ir"] }
 winit = "0.30.13"
 pollster = "0.4"
 bytemuck = { version = "1.24", features = ["derive"] }

crates/horizon-client/assets/horizon/lang/en_us.json

@@ -0,0 +1,15 @@
+{
+  "horizon.options.controller": "Controller",
+  "horizon.options.vibration": "Vibration",
+  "horizon.options.adaptive_triggers": "Adaptive Triggers",
+  "horizon.options.lightbar": "Lightbar",
+  "horizon.options.look_sensitivity": "Look Sensitivity",
+  "horizon.options.invert_x": "Invert Look X",
+  "horizon.options.invert_y": "Invert Look Y",
+  "horizon.options.sneak_button": "Sneak Button",
+  "horizon.options.move_deadzone": "Move Deadzone",
+  "horizon.options.look_deadzone": "Look Deadzone",
+  "horizon.options.button_glyphs": "Button Glyphs",
+  "horizon.options.menu_navigation": "Menu Navigation",
+  "horizon.options.on_screen_keyboard": "On-Screen Keyboard"
+}

crates/horizon-client/assets/horizon/lang/ru_ru.json

@@ -0,0 +1,15 @@
+{
+  "horizon.options.controller": "Геймпад",
+  "horizon.options.vibration": "Вибрация",
+  "horizon.options.adaptive_triggers": "Адаптивные триггеры",
+  "horizon.options.lightbar": "Подсветка",
+  "horizon.options.look_sensitivity": "Чувствительность обзора",
+  "horizon.options.invert_x": "Инверсия обзора по X",
+  "horizon.options.invert_y": "Инверсия обзора по Y",
+  "horizon.options.sneak_button": "Кнопка приседания",
+  "horizon.options.move_deadzone": "Мёртвая зона движения",
+  "horizon.options.look_deadzone": "Мёртвая зона обзора",
+  "horizon.options.button_glyphs": "Символы кнопок",
+  "horizon.options.menu_navigation": "Навигация по меню",
+  "horizon.options.on_screen_keyboard": "Экранная клавиатура"
+}

crates/horizon-client/examples/chunk_load_bench.rs

@@ -0,0 +1,168 @@
+//! What a column costs to load, on real terrain: generates and lights the
+//! columns around a point with the vanilla generator, as a world being explored
+//! does, then meshes every section of the inner columns on this one thread, so a
+//! change to generation or meshing shows as time per column and per section.
+//!
+//!     cargo run --release -p horizon-client --example chunk_load_bench -- \
+//!         .local/horizon-client/26.3 [--seed 1234] [--center CX CZ] [--radius 8]
+//!         [--threads N] [--rounds 3]
+//!
+//! The default centre is the village of `tools/perf_bench.py`. The generation
+//! figure is wall time with N workers (the game's own pool); the mesh figure is
+//! this thread's CPU time in `Mesher::mesh`, the best of `--rounds`, so other
+//! work on the machine changes it less. The checksum of the meshes shows that an
+//! A/B pair of builds made the same ones.
+use horizon_client::{
+    assets::Assets,
+    biome::Biomes,
+    blocks::BlockFacts,
+    chunk::HEIGHT,
+    light::LightTables,
+    mesher::{MeshTables, Mesher, Region, borrow},
+    models,
+    spans::thread_cpu,
+    streaming::{Streaming, WorkerContext},
+    vanillagen::VanillaTerrain,
+    world::World,
+};
+use horizon_core::biome::{BiomeZoom, obfuscate_seed};
+use horizon_world::registry::BlockStateId;
+use std::{
+    hash::{DefaultHasher, Hash, Hasher},
+    path::PathBuf,
+    sync::Arc,
+    thread,
+    time::{Duration, Instant},
+};
+
+type Error = Box<dyn std::error::Error>;
+
+fn flag<T: std::str::FromStr>(args: &[String], name: &str, default: T) -> T {
+    args.iter()
+        .position(|a| a == name)
+        .and_then(|i| args.get(i + 1)?.parse().ok())
+        .unwrap_or(default)
+}
+
+fn main() -> Result<(), Error> {
+    let args: Vec<String> = std::env::args().collect();
+    let root = PathBuf::from(args.get(1).ok_or("usage: chunk_load_bench <resources>")?);
+    let seed: i64 = flag(&args, "--seed", 1234);
+    let radius: i32 = flag(&args, "--radius", 8);
+    let rounds: usize = flag(&args, "--rounds", 3);
+    let threads: usize = flag(
+        &args,
+        "--threads",
+        thread::available_parallelism().map_or(2, |n| n.get()),
+    );
+    let center = args
+        .iter()
+        .position(|a| a == "--center")
+        .map(|i| -> Result<(i32, i32), Error> {
+            Ok((
+                args.get(i + 1).ok_or("--center CX CZ")?.parse()?,
+                args.get(i + 2).ok_or("--center CX CZ")?.parse()?,
+            ))
+        })
+        .transpose()?
+        .unwrap_or((-60, 10));
+
+    let assets = Arc::new(Assets::load(&root)?);
+    let render = Arc::new(assets.reload(&root)?);
+    let facts = BlockFacts::load(&root, assets.registry)?;
+    let visibility = models::load_visibility(&root, assets.registry)?;
+    let biomes = Arc::new(Biomes::load(&root)?);
+    let context = Arc::new(WorkerContext {
+        tables: Arc::new(MeshTables::new(&assets, &render, &facts, visibility)?),
+        light: Arc::new(LightTables::load(&root, assets.registry, &facts)?),
+        biomes: biomes.clone(),
+        assets: assets.clone(),
+        render,
+    });
+    let terrain = VanillaTerrain::new(&root.join("worldgen"), assets.registry, &biomes, seed)?;
+
+    // Generation and light, on the game's worker pool. Meshing is left out
+    // here and measured on its own below.
+    let mut streaming = Streaming::new(Arc::new(terrain), context.clone(), threads);
+    streaming.mesh = false;
+    streaming.center = center;
+    streaming.radius = radius;
+    let mut world = World::new(BlockStateId(0), 0);
+    let started = Instant::now();
+    let mut quiet = 0;
+    while quiet < 100 {
+        let before = world.chunks.len();
+        let _ = streaming.update(&mut world);
+        thread::sleep(Duration::from_millis(2));
+        quiet = if streaming.pending() == 0 && before == world.chunks.len() {
+            quiet + 1
+        } else {
+            0
+        };
+    }
+    let generated = started.elapsed() - Duration::from_millis(2 * 100);
+    let columns = world.chunks.len();
+    println!(
+        "generated and lit {columns} columns in {:.0} ms with {threads} workers ({:.2} ms per column)",
+        generated.as_secs_f64() * 1e3,
+        generated.as_secs_f64() * 1e3 / columns.max(1) as f64
+    );
+
+    // Meshing every section of the columns whose neighbours are all loaded.
+    let inner = radius - 1;
+    let regions: Vec<(Region, i32)> = (center.0 - inner..=center.0 + inner)
+        .flat_map(|x| (center.1 - inner..=center.1 + inner).map(move |z| (x, z)))
+        .filter_map(|(x, z)| {
+            let region: Region = std::array::from_fn(|dz| {
+                std::array::from_fn(|dx| {
+                    world
+                        .chunks
+                        .get(&(x + dx as i32 - 1, z + dz as i32 - 1))
+                        .cloned()
+                })
+            });
+            region
+                .iter()
+                .flatten()
+                .all(Option::is_some)
+                .then_some(region)
+        })
+        .flat_map(|region| (0..HEIGHT / 16).map(move |sy| (region.clone(), sy)))
+        .collect();
+    let mut best = Duration::MAX;
+    let (mut vertices, mut checksum) = (0, 0);
+    for _ in 0..rounds.max(1) {
+        let mut mesher = Mesher {
+            nether_shading: false,
+            zoom: BiomeZoom::new(obfuscate_seed(seed)),
+            blend_radius: 2,
+            smooth_lighting: true,
+            cutout_leaves: true,
+            assets: &context.assets,
+            render: &context.render,
+            tables: &context.tables,
+            biomes: &context.biomes,
+            visibility: context.tables.visibility.clone(),
+        };
+        vertices = 0;
+        let mut hash = DefaultHasher::new();
+        let mut spent = Duration::ZERO;
+        for (region, sy) in &regions {
+            let started = thread_cpu().ok_or("no thread CPU clock here")?;
+            let mesh = mesher.mesh(&borrow(region), *sy);
+            spent += thread_cpu().ok_or("no thread CPU clock here")? - started;
+            vertices += mesh.solid.len() + mesh.translucent.len();
+            bytemuck::cast_slice::<_, u8>(&mesh.solid).hash(&mut hash);
+            bytemuck::cast_slice::<_, u8>(&mesh.translucent).hash(&mut hash);
+        }
+        checksum = hash.finish();
+        best = best.min(spent);
+    }
+    println!(
+        "meshed {} sections ({vertices} vertices, checksum {checksum:016x}) in {:.1} ms of CPU ({:.1} us per section)",
+        regions.len(),
+        best.as_secs_f64() * 1e3,
+        best.as_secs_f64() * 1e6 / regions.len().max(1) as f64
+    );
+    Ok(())
+}

crates/horizon-client/examples/probe/main.rs

@@ -85,6 +85,7 @@ mod sprint_probe;
 mod subtitle_fixture;
 mod tab_list_fixture;
 mod team_rules_fixture;
+mod text_display_fixture;
 mod toggle_keys_probe;
 mod tooltip_display_fixture;
 mod trading_fixture;
@@ -170,6 +171,7 @@ probes! {
     team_rules_fixture,
     toggle_keys_probe,
     tooltip_display_fixture,
+    text_display_fixture,
     trading_fixture,
     translucency_fixture,
     weather_fixture,

crates/horizon-client/examples/probe/marker_particles_probe.rs

@@ -49,7 +49,7 @@ pub fn main() -> Result<()> {
             }
         }
     }
-    let mut engine = ParticleEngine::new(root, &HashMap::new());
+    let mut engine = ParticleEngine::new(root, &HashMap::new(), &Default::default());
     let mut out = BufWriter::new(File::create(&args[2])?);
     for line in BufReader::new(File::open(&args[1])?).lines() {
         let case: Value = serde_json::from_str(&line?)?;

crates/horizon-client/examples/probe/particle_providers_probe.rs

@@ -152,7 +152,7 @@ pub fn main() -> Result<()> {
         world(&assets, &facts, false, true)?,
         world(&assets, &facts, true, true)?,
     ];
-    let mut engine = ParticleEngine::new(root, &HashMap::new());
+    let mut engine = ParticleEngine::new(root, &HashMap::new(), &Default::default());
     for (ty, item) in [
         (ParticleType::ItemSlime, "item_slime_ball"),
         (ParticleType::ItemSnowball, "item_snowball"),

crates/horizon-client/examples/probe/recipe_book_fixture.rs

@@ -83,7 +83,7 @@ pub fn main() -> horizon_client::Result<()> {
             let mut extra = String::new();
             match kind {
                 "give" => count = book.add_recipes(&index, &list()).0,
-                "take" => count = book.remove_recipes(&index, &list()),
+                "take" => count = book.remove_recipes(&index, &list()).len(),
                 "seen" => book.remove_highlight(op["id"].as_str().unwrap_or_default()),
                 "set" => {
                     let i = match op["type"].as_str().unwrap_or_default() {

crates/horizon-client/examples/probe/text_display_fixture.rs

@@ -0,0 +1,37 @@
+use horizon_client::text_display::TextDisplayData;
+use horizon_protocol::{ids, packets::play::Clientbound};
+use std::{error::Error, io::Write};
+
+pub fn main() -> Result<(), Box<dyn Error>> {
+    let args: Vec<String> = crate::args().collect();
+    let mut out = std::fs::File::create(&args[2])?;
+    for line in std::fs::read_to_string(&args[1])?.lines() {
+        let input: serde_json::Value = serde_json::from_str(line)?;
+        let hex = input["wire"].as_str().unwrap();
+        let bytes: Vec<u8> = (0..hex.len())
+            .step_by(2)
+            .map(|i| u8::from_str_radix(&hex[i..i + 2], 16))
+            .collect::<Result<_, _>>()?;
+        let Clientbound::SetEntityData(packet) =
+            Clientbound::decode(ids::play::clientbound::SET_ENTITY_DATA, &bytes)?
+        else {
+            unreachable!()
+        };
+        let mut display = TextDisplayData::default();
+        display.apply(&packet.values);
+        if let Some(angles) = input["angles"].as_array() {
+            let a: Vec<_> = angles.iter().map(|v| v.as_f64().unwrap() as f32).collect();
+            writeln!(
+                out,
+                "{}",
+                serde_json::to_string(&display.matrix([a[0], a[1]], [a[2], a[3]]).to_cols_array())?
+            )?;
+            continue;
+        }
+        let mut state = serde_json::to_value(&display)?;
+        state["text"] = display.text.plain().into();
+        state["alignment"] = format!("{:?}", display.align()).to_uppercase().into();
+        writeln!(out, "{}", state)?;
+    }
+    Ok(())
+}

crates/horizon-client/src/audio.rs

@@ -161,6 +161,9 @@ pub struct Audio {
     /// How many times each positional sound played (the control socket's `status`),
     /// with or without an audio device.
     pub heard: std::collections::BTreeMap<String, u32>,
+    /// How many times each selection was stopped ("record *", "* minecraft:…", `*` for
+    /// any), with or without an audio device, as `heard`.
+    pub stopped: std::collections::BTreeMap<String, u32>,
 }
 fn decode(path: &Path) -> Option<(Vec<f32>, u32)> {
     use symphonia::core::{
@@ -595,6 +598,7 @@ impl Audio {
             source_override: None,
             capture: None,
             heard: Default::default(),
+            stopped: Default::default(),
         }
     }
     #[cfg(not(feature = "audio"))]
@@ -825,6 +829,14 @@ impl Audio {
     /// and/or a source.
     pub fn stop_sounds(&mut self, event: Option<&str>, source: Option<usize>) {
         let event = event.map(crate::sound_events::normalize);
+        let selection = format!(
+            "{} {}",
+            source
+                .and_then(|s| crate::settings::SOUND_SOURCES.get(s))
+                .map_or("*", |s| s),
+            event.as_deref().unwrap_or("*")
+        );
+        *self.stopped.entry(selection).or_default() += 1;
         self.engine
             .stop_matching(event.as_deref(), source, &mut self.backend);
     }

crates/horizon-client/src/boss_overlay.rs

@@ -0,0 +1,243 @@
+//! `BossHealthOverlay` and `LerpingBossEvent`: the boss bars a client is
+//! showing, in the order their add packets arrived.
+use crate::{
+    hud_overlays::BossBar,
+    scoreboard::{comp_text, tag_to_json},
+    text::Text,
+};
+use horizon_protocol::packets::play::{BossAction, BossEvent};
+
+/// `LerpingBossEvent.LERP_MILLISECONDS`.
+const LERP_MS: u128 = 100;
+
+/// `Util.getMillis`.
+pub fn now_millis() -> u128 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_millis())
+        .unwrap_or(0)
+}
+
+/// One `LerpingBossEvent`.
+#[derive(Clone, Debug)]
+struct Event {
+    id: u128,
+    name: Text,
+    /// The progress the lerp started from (`progress`).
+    progress: f32,
+    /// `targetPercent`.
+    target: f32,
+    /// `setTime`.
+    set_at: u128,
+    color: u8,
+    overlay: u8,
+    darken: bool,
+    music: bool,
+    fog: bool,
+}
+impl Event {
+    /// `LerpingBossEvent.getProgress`.
+    fn displayed(&self, now: u128) -> f32 {
+        let t = ((now.saturating_sub(self.set_at)) as f32 / LERP_MS as f32).clamp(0.0, 1.0);
+        self.progress + (self.target - self.progress) * t
+    }
+    /// `LerpingBossEvent.setProgress`: the bar starts the next lerp from
+    /// whatever it is showing now.
+    fn set_progress(&mut self, progress: f32, now: u128) {
+        self.progress = self.displayed(now);
+        self.target = progress;
+        self.set_at = now;
+    }
+}
+
+/// `BossHealthOverlay`: the events, plus `GameRenderer`'s world darkening.
+#[derive(Clone, Debug, Default)]
+pub struct BossOverlay {
+    events: Vec<Event>,
+    /// `bossOverlayWorldDarkening` and the previous tick's value.
+    darken: f32,
+    darken_o: f32,
+}
+impl BossOverlay {
+    pub fn reset(&mut self) {
+        *self = Self::default();
+    }
+    /// `ClientboundBossEventPacket.dispatch` into `BossHealthOverlay`'s
+    /// handler. An id already shown keeps its place when added again.
+    pub fn apply(&mut self, packet: &BossEvent, now: u128) {
+        // An ordinal past the enum shows as its last value.
+        let color = |c: i32| c.clamp(0, 6) as u8;
+        let overlay = |o: i32| o.clamp(0, 4) as u8;
+        let id = packet.id;
+        if let BossAction::Add {
+            name,
+            progress,
+            color: c,
+            overlay: o,
+            darken,
+            music,
+            fog,
+        } = &packet.action
+        {
+            let event = Event {
+                id,
+                name: comp_text(&tag_to_json(name)),
+                progress: *progress,
+                target: *progress,
+                set_at: now,
+                color: color(*c),
+                overlay: overlay(*o),
+                darken: *darken,
+                music: *music,
+                fog: *fog,
+            };
+            match self.events.iter_mut().find(|e| e.id == id) {
+                Some(slot) => *slot = event,
+                None => self.events.push(event),
+            }
+            return;
+        }
+        if let BossAction::Remove = packet.action {
+            self.events.retain(|e| e.id != id);
+            return;
+        }
+        let Some(e) = self.events.iter_mut().find(|e| e.id == id) else {
+            return;
+        };
+        match &packet.action {
+            BossAction::UpdateProgress { progress } => e.set_progress(*progress, now),
+            BossAction::UpdateName { name } => e.name = comp_text(&tag_to_json(name)),
+            BossAction::UpdateStyle {
+                color: c,
+                overlay: o,
+            } => {
+                e.color = color(*c);
+                e.overlay = overlay(*o);
+            }
+            BossAction::UpdateProperties { darken, music, fog } => {
+                (e.darken, e.music, e.fog) = (*darken, *music, *fog);
+            }
+            BossAction::Add { .. } | BossAction::Remove => {}
+        }
+    }
+    /// `GameRenderer.tick` while the level runs.
+    pub fn tick_darken(&mut self, running: bool) {
+        if !running {
+            return;
+        }
+        self.darken_o = self.darken;
+        if self.should_darken() {
+            self.darken = (self.darken + 0.05).min(1.0);
+        } else if self.darken > 0.0 {
+            self.darken = (self.darken - 0.0125).max(0.0);
+        }
+    }
+    /// `GameRenderer.bossOverlayWorldDarkening`.
+    pub fn darken_amount(&self, partial: f32) -> f32 {
+        let t = partial.clamp(0.0, 1.0);
+        self.darken_o + (self.darken - self.darken_o) * t
+    }
+    pub fn should_darken(&self) -> bool {
+        self.events.iter().any(|e| e.darken)
+    }
+    pub fn should_play_music(&self) -> bool {
+        self.events.iter().any(|e| e.music)
+    }
+    pub fn should_create_world_fog(&self) -> bool {
+        self.events.iter().any(|e| e.fog)
+    }
+    /// The bars `extractRenderState` walks, with the lerped progress.
+    pub fn bars(&self, now: u128) -> Vec<BossBar> {
+        self.events
+            .iter()
+            .map(|e| BossBar {
+                name: e.name.clone(),
+                progress: e.displayed(now),
+                color: e.color as usize,
+                overlay: e.overlay as usize,
+            })
+            .collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use horizon_world::nbt::Tag;
+
+    fn add(id: u128, name: &str, progress: f32, darken: bool, fog: bool) -> BossEvent {
+        BossEvent {
+            id,
+            action: BossAction::Add {
+                name: Tag::String(name.into()),
+                progress,
+                color: 5,
+                overlay: 0,
+                darken,
+                music: false,
+                fog,
+            },
+        }
+    }
+    fn progress(id: u128, progress: f32) -> BossEvent {
+        BossEvent {
+            id,
+            action: BossAction::UpdateProgress { progress },
+        }
+    }
+
+    #[test]
+    fn progress_lerps_over_a_tenth_of_a_second() {
+        let mut overlay = BossOverlay::default();
+        overlay.apply(&add(1, "W", 0.0, true, false), 0);
+        overlay.apply(&progress(1, 1.0), 0);
+        assert!((overlay.bars(50)[0].progress - 0.5).abs() < 1.0e-5);
+        assert!((overlay.bars(100)[0].progress - 1.0).abs() < 1.0e-5);
+        // A new target starts from the value on screen.
+        overlay.apply(&progress(1, 0.0), 50);
+        assert!((overlay.bars(150)[0].progress - 0.0).abs() < 1.0e-5);
+    }
+
+    #[test]
+    fn darken_ramps_and_fades() {
+        let mut overlay = BossOverlay::default();
+        overlay.apply(&add(1, "W", 1.0, true, false), 0);
+        overlay.tick_darken(true);
+        assert!((overlay.darken_amount(1.0) - 0.05).abs() < 1.0e-5);
+        overlay.apply(
+            &BossEvent {
+                id: 1,
+                action: BossAction::Remove,
+            },
+            0,
+        );
+        overlay.tick_darken(true);
+        assert!((overlay.darken - 0.0375).abs() < 1.0e-5);
+        assert!(!overlay.should_play_music());
+    }
+
+    #[test]
+    fn bars_keep_arrival_order() {
+        let mut overlay = BossOverlay::default();
+        overlay.apply(&add(2, "b", 1.0, false, true), 0);
+        overlay.apply(&add(1, "a", 1.0, false, false), 0);
+        overlay.apply(&add(2, "c", 0.5, false, true), 0);
+        // An update for a bar this client never got is ignored.
+        overlay.apply(&progress(9, 0.5), 0);
+        let names: Vec<_> = overlay
+            .bars(0)
+            .into_iter()
+            .map(|b| b.name.plain())
+            .collect();
+        assert_eq!(names, ["c", "a"]);
+        assert!(overlay.should_create_world_fog());
+        overlay.apply(
+            &BossEvent {
+                id: 2,
+                action: BossAction::Remove,
+            },
+            0,
+        );
+        assert!(!overlay.should_create_world_fog());
+    }
+}

crates/horizon-client/src/bossbar.rs

@@ -14,40 +14,64 @@ pub const STYLES: [&str; 5] = [
     "notched_12",
     "notched_20",
 ];
-/// `BossBarColor.getFormatting`.
+/// `BossBarColor.getFormatting`. Purple is dark blue in 26.3.
 pub fn color_rgb(color: &str) -> u32 {
     let name = match color {
         "pink" => "red",
         "red" => "dark_red",
-        "purple" => "dark_purple",
+        "purple" => "dark_blue",
         other => other,
     };
     text::named_color(name).unwrap_or(text::WHITE)
 }
 
+/// A version-4 shaped id from a resource id. Saved boss events do not keep
+/// their UUID (`CustomBossEvents` mints a new one on load).
+pub fn stable_uuid(id: &str) -> u128 {
+    let mut h = 0xcbf29ce484222325u64;
+    for b in id.as_bytes() {
+        h ^= u64::from(*b);
+        h = h.wrapping_mul(0x100000001b3);
+    }
+    let most = (h as i64) & -61441 | 16384;
+    let least = (h.rotate_left(17) as i64) & 4_611_686_018_427_387_903 | i64::MIN;
+    ((most as u64 as u128) << 64) | (least as u64 as u128)
+}
+
 #[derive(Clone, Debug, PartialEq)]
 pub struct BossBar {
     pub id: String,
+    /// The `ServerBossEvent` UUID. Not saved.
+    pub uuid: u128,
     pub name: Comp,
     pub color: String,
     pub style: String,
     pub value: i32,
     pub max: i32,
+    /// `ServerBossEvent.visible`. A new bar is visible; nobody sees it until
+    /// a player is added.
     pub visible: bool,
-    /// Whether the (single) local player is in the bar's player set.
-    pub player: bool,
+    pub darken: bool,
+    pub music: bool,
+    pub fog: bool,
+    /// `CustomBossEvent.players`, the UUIDs told about the bar.
+    pub players: Vec<[i32; 4]>,
 }
 impl BossBar {
     pub fn new(id: &str, name: Comp) -> Self {
         Self {
             id: id.to_owned(),
+            uuid: stable_uuid(id),
             name,
             color: "white".into(),
             style: "progress".into(),
             value: 0,
             max: 100,
             visible: true,
-            player: false,
+            darken: false,
+            music: false,
+            fog: false,
+            players: Vec::new(),
         }
     }
     /// `CustomBossEvent.getDisplayName`.
@@ -91,31 +115,34 @@ impl BossBars {
     pub fn ids(&self) -> Vec<String> {
         self.bars.iter().map(|b| b.id.clone()).collect()
     }
-    /// The saved compound; the player's UUID stands for "the local player".
-    pub fn pack(&self, player: Option<[i32; 4]>) -> Tag {
+    /// The saved compound (`CustomBossEvent.Packed`).
+    pub fn pack(&self) -> Tag {
         let mut c = Compound::new();
         for b in &self.bars {
-            let mut e = vec![
-                ("Name", json_to_tag(&b.name)),
-                ("Visible", Tag::Byte(i8::from(b.visible))),
-                ("Value", Tag::Int(b.value)),
-                ("Max", Tag::Int(b.max)),
-                ("Color", Tag::String(b.color.as_str().into())),
-                ("Overlay", Tag::String(b.style.as_str().into())),
-                ("DarkenScreen", Tag::Byte(0)),
-                ("PlayBossMusic", Tag::Byte(0)),
-                ("CreateWorldFog", Tag::Byte(0)),
-            ];
-            let players = match (b.player, player) {
-                (true, Some(u)) => vec![Tag::IntArray(u.to_vec())],
-                _ => Vec::new(),
-            };
-            e.push(("Players", Tag::List(players)));
-            c.insert(b.id.as_str().into(), Tag::compound(e));
+            let players = b
+                .players
+                .iter()
+                .map(|u| Tag::IntArray(u.to_vec()))
+                .collect();
+            c.insert(
+                b.id.as_str().into(),
+                Tag::compound([
+                    ("Name", json_to_tag(&b.name)),
+                    ("Visible", Tag::Byte(i8::from(b.visible))),
+                    ("Value", Tag::Int(b.value)),
+                    ("Max", Tag::Int(b.max)),
+                    ("Color", Tag::String(b.color.as_str().into())),
+                    ("Overlay", Tag::String(b.style.as_str().into())),
+                    ("DarkenScreen", Tag::Byte(i8::from(b.darken))),
+                    ("PlayBossMusic", Tag::Byte(i8::from(b.music))),
+                    ("CreateWorldFog", Tag::Byte(i8::from(b.fog))),
+                    ("Players", Tag::List(players)),
+                ]),
+            );
         }
         Tag::Compound(c)
     }
-    pub fn unpack(data: &Tag, player: Option<[i32; 4]>) -> Self {
+    pub fn unpack(data: &Tag) -> Self {
         let mut bars = Vec::new();
         if let Tag::Compound(c) = data {
             for (id, e) in c {
@@ -130,21 +157,30 @@ impl BossBars {
                     Some(Tag::Byte(v)) => i32::from(*v),
                     _ => d,
                 };
-                let in_players = match (get("Players"), player) {
-                    (Some(Tag::List(l)), Some(u)) => l
+                let players = match get("Players") {
+                    Some(Tag::List(l)) => l
                         .iter()
-                        .any(|t| matches!(t, Tag::IntArray(a) if a.as_slice() == u)),
-                    _ => false,
+                        .filter_map(|t| match t {
+                            Tag::IntArray(a) if a.len() == 4 => Some([a[0], a[1], a[2], a[3]]),
+                            _ => None,
+                        })
+                        .collect(),
+                    _ => Vec::new(),
                 };
+                let id = id.to_string_lossy();
                 bars.push(BossBar {
-                    id: id.to_string_lossy(),
+                    uuid: stable_uuid(&id),
+                    id,
                     name: get("Name").map_or_else(|| literal(""), tag_to_json),
                     color: text("Color", "white"),
                     style: text("Overlay", "progress"),
                     value: num("Value", 0),
                     max: num("Max", 100),
                     visible: num("Visible", 0) != 0,
-                    player: in_players,
+                    darken: num("DarkenScreen", 0) != 0,
+                    music: num("PlayBossMusic", 0) != 0,
+                    fog: num("CreateWorldFog", 0) != 0,
+                    players,
                 });
             }
         }
@@ -167,17 +203,15 @@ mod tests {
         bar.value = 25;
         bar.max = 50;
         bar.visible = true;
-        bar.player = true;
-        let uuid = Some([1, 2, 3, 4]);
-        let back = BossBars::unpack(&b.pack(uuid), uuid);
+        bar.darken = true;
+        bar.players = vec![[1, 2, 3, 4]];
+        let back = BossBars::unpack(&b.pack());
         assert_eq!(back, b);
-        // Another player's UUID does not include the local player.
-        assert!(!BossBars::unpack(&b.pack(uuid), Some([9, 9, 9, 9])).bars[0].player);
         let bar = b.get("test:x").unwrap();
         assert_eq!(bar.progress(), 0.5);
         assert_eq!(bar.display_name().plain(), "chat.square_brackets");
         assert_eq!(color_rgb("pink"), text::RED);
-        assert_eq!(color_rgb("purple"), 0xAA00AA);
+        assert_eq!(color_rgb("purple"), text::named_color("dark_blue").unwrap());
         b.remove("test:x");
         assert!(b.bars.is_empty());
     }

crates/horizon-client/src/command_storage.rs

@@ -55,7 +55,7 @@ impl CommandStorage {
                 .iter()
                 .map(|(k, v)| (k.as_str().into(), v.clone()))
                 .collect();
-            let _ = save::write_dat(
+            if let Err(e) = save::write_dat(
                 &file(root, namespace),
                 Tag::compound([
                     (
@@ -64,7 +64,9 @@ impl CommandStorage {
                     ),
                     ("DataVersion", Tag::Int(horizon_world::DATA_VERSION)),
                 ]),
-            );
+            ) {
+                log::warn!("command storage {namespace} was not written: {e}");
+            }
         }
     }
     /// `get`: an empty compound when unset.

crates/horizon-client/src/discord_presence.rs

@@ -0,0 +1,623 @@
+//! Discord Rich Presence: "Playing Horizon" on the player's Discord profile, with what they are
+//! doing (docs/native-client.md). A thread of its own talks to the Discord app on this computer
+//! through its local IPC socket (Discord's RPC docs: `discord-ipc-N`, frames of opcode u32 LE +
+//! length u32 LE + JSON). The game only calls [`set`] each frame: a change wakes the thread,
+//! which connects when Discord runs, retries every 15 s when it doesn't, keeps under Discord's
+//! update limit and clears the activity on quit. Nothing is sent with the setting off,
+//! or with `HORIZON_NO_DISCORD=1`.
+use std::collections::VecDeque;
+use std::io::{self, Read, Write};
+use std::path::PathBuf;
+use std::sync::{Condvar, Mutex, OnceLock};
+use std::thread::Thread;
+use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
+
+use serde_json::{Value, json};
+
+use crate::command::args::GameMode;
+
+/// The "Horizon" application on Discord's developer portal (public: it names the game). Its
+/// Rich Presence assets: `horizon`, the logo.
+pub const DISCORD_APP_ID: &str = "1563857609738690560";
+/// Whether the application has the game-mode images (`survival`, `creative`, `adventure`,
+/// `spectator`) beside the logo; it doesn't yet.
+const MODE_IMAGES: bool = false;
+/// Points the game at a test's fake Discord (a folder holding `discord-ipc-0`).
+const IPC_DIR_ENV: &str = "HORIZON_DISCORD_IPC_DIR";
+
+/// Discord drops activity updates beyond 5 in 20 seconds.
+const BURST: usize = 5;
+const WINDOW: Duration = Duration::from_secs(20);
+/// Between two tries to reach Discord while it isn't running.
+const RETRY: Duration = Duration::from_secs(15);
+/// The activity is sent again this often, so a Discord restarted meanwhile gets it back.
+const REFRESH: Duration = Duration::from_secs(60);
+
+const HANDSHAKE: u32 = 0;
+const FRAME: u32 = 1;
+const CLOSE: u32 = 2;
+const PING: u32 = 3;
+const PONG: u32 = 4;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Dimension {
+    Overworld,
+    Nether,
+    End,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Play {
+    Singleplayer,
+    /// A server or someone else's LAN world. Its address and name are never shown.
+    Multiplayer,
+    /// This world is open to LAN or friends; `players` counts the host.
+    Hosting {
+        players: usize,
+    },
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Status {
+    /// The player turned Rich Presence off: the activity is cleared.
+    Off,
+    Menus,
+    World {
+        play: Play,
+        dimension: Dimension,
+        mode: GameMode,
+    },
+}
+
+/// What the game wants shown, and since when it has been in a world.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+struct Wanted {
+    status: Status,
+    /// Unix seconds: when the player entered the world (dimension changes keep it).
+    since: Option<u64>,
+}
+impl Wanted {
+    /// A new status at `now`; false if it is the one already wanted.
+    fn update(&mut self, status: Status, now: u64) -> bool {
+        if self.status == status {
+            return false;
+        }
+        let in_world = |s: Status| matches!(s, Status::World { .. });
+        if !in_world(status) {
+            self.since = None;
+        } else if !in_world(self.status) {
+            self.since = Some(now);
+        }
+        self.status = status;
+        true
+    }
+}
+
+struct Shared {
+    wanted: Wanted,
+    stop: bool,
+    stopped: bool,
+}
+static SHARED: Mutex<Shared> = Mutex::new(Shared {
+    wanted: Wanted {
+        status: Status::Menus,
+        since: None,
+    },
+    stop: false,
+    stopped: false,
+});
+static STOPPED: Condvar = Condvar::new();
+static THREAD: OnceLock<Thread> = OnceLock::new();
+
+/// Starts the presence thread, once: when the game starts, never for a dedicated server.
+/// `automated` runs (offscreen, benchmarks) only talk to a test's fake Discord.
+pub fn start(enabled: bool, automated: bool) {
+    let fake_discord = std::env::var_os(IPC_DIR_ENV).is_some();
+    if THREAD.get().is_some()
+        || std::env::var_os("HORIZON_NO_DISCORD").is_some_and(|v| v != "0")
+        || (automated && !fake_discord)
+    {
+        return;
+    }
+    if !enabled {
+        lock().wanted.status = Status::Off;
+    }
+    match std::thread::Builder::new()
+        .name("Discord presence".into())
+        .spawn(run)
+    {
+        Ok(handle) => {
+            let _ = THREAD.set(handle.thread().clone());
+        }
+        Err(e) => log::warn!("Horizon: no Discord presence: {e}"),
+    }
+}
+
+/// What the player does now; only a change wakes the thread. Free without [`start`].
+pub fn set(status: Status) {
+    let Some(thread) = THREAD.get() else {
+        return;
+    };
+    if lock().wanted.update(status, unix_now()) {
+        thread.unpark();
+    }
+}
+
+/// On quit: clears the activity, waiting at most a moment for Discord.
+pub fn stop() {
+    let Some(thread) = THREAD.get() else {
+        return;
+    };
+    let mut shared = lock();
+    shared.stop = true;
+    thread.unpark();
+    let _ = STOPPED.wait_timeout_while(shared, Duration::from_millis(300), |s| !s.stopped);
+}
+
+fn lock() -> std::sync::MutexGuard<'static, Shared> {
+    SHARED.lock().unwrap_or_else(|e| e.into_inner())
+}
+
+fn unix_now() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map_or(0, |d| d.as_secs())
+}
+
+fn run() {
+    let mut client: Option<Client> = None;
+    let mut sent: Option<(Wanted, Instant)> = None;
+    let mut last_try: Option<Instant> = None;
+    let mut limit = RateLimit::default();
+    loop {
+        let (wanted, stop) = {
+            let s = lock();
+            (s.wanted, s.stop)
+        };
+        if stop || wanted.status == Status::Off {
+            if let Some(mut c) = client.take() {
+                let _ = c.set_activity(None);
+                c.close();
+            }
+            sent = None;
+            if stop {
+                lock().stopped = true;
+                STOPPED.notify_all();
+                return;
+            }
+            std::thread::park();
+            continue;
+        }
+        let now = Instant::now();
+        if client.is_none() {
+            if let Some(wait) = last_try.and_then(|t| RETRY.checked_sub(now - t)) {
+                std::thread::park_timeout(wait);
+                continue;
+            }
+            last_try = Some(now);
+            client = Client::connect();
+            if client.is_none() {
+                continue;
+            }
+        }
+        let due = sent.is_none_or(|(w, at)| w != wanted || now - at >= REFRESH);
+        if !due {
+            let (_, at) = sent.expect("sent");
+            std::thread::park_timeout(REFRESH - (now - at));
+            continue;
+        }
+        let wait = limit.wait(now);
+        if !wait.is_zero() {
+            std::thread::park_timeout(wait);
+            continue;
+        }
+        limit.record(now);
+        let c = client.as_mut().expect("connected");
+        match c.set_activity(activity(wanted.status, wanted.since)) {
+            Ok(()) => sent = Some((wanted, now)),
+            Err(e) => {
+                log::info!("Horizon: Discord presence disconnected ({e})");
+                client = None;
+                sent = None;
+            }
+        }
+    }
+}
+
+/// The activity Discord shows for `status`; `None` clears it.
+fn activity(status: Status, since: Option<u64>) -> Option<Value> {
+    let mut assets = json!({"large_image": "horizon", "large_text": "Horizon"});
+    let (details, state, party) = match status {
+        Status::Off => return None,
+        Status::Menus => ("In the menus", None, None),
+        Status::World {
+            play,
+            dimension,
+            mode,
+        } => {
+            if MODE_IMAGES {
+                let (key, text) = match mode {
+                    GameMode::Survival => ("survival", "Survival"),
+                    GameMode::Creative => ("creative", "Creative"),
+                    GameMode::Adventure => ("adventure", "Adventure"),
+                    GameMode::Spectator => ("spectator", "Spectator"),
+                };
+                assets["small_image"] = key.into();
+                assets["small_text"] = text.into();
+            }
+            let place = match dimension {
+                Dimension::Overworld => "In the Overworld",
+                Dimension::Nether => "In the Nether",
+                Dimension::End => "In the End",
+            };
+            let (details, party) = match play {
+                Play::Singleplayer => ("Singleplayer", None),
+                Play::Multiplayer => ("Multiplayer", None),
+                Play::Hosting { players } => ("Hosting a world", Some(players)),
+            };
+            (details, Some(place), party)
+        }
+    };
+    let mut a = json!({"details": details, "assets": assets});
+    if let Some(state) = state {
+        a["state"] = state.into();
+    }
+    if let Some(start) = since {
+        a["timestamps"] = json!({"start": start});
+    }
+    if let Some(players) = party {
+        let max = crate::lan::MAX_PLAYERS;
+        a["party"] = json!({
+            "id": format!("horizon-{}", std::process::id()),
+            "size": [players.clamp(1, max), max],
+        });
+    }
+    Some(a)
+}
+
+/// At most [`BURST`] updates in any [`WINDOW`].
+#[derive(Default)]
+struct RateLimit {
+    sent: VecDeque<Instant>,
+}
+impl RateLimit {
+    /// How long until the next update may go.
+    fn wait(&self, now: Instant) -> Duration {
+        if self.sent.len() < BURST {
+            return Duration::ZERO;
+        }
+        (self.sent[0] + WINDOW).saturating_duration_since(now)
+    }
+    fn record(&mut self, now: Instant) {
+        if self.sent.len() == BURST {
+            self.sent.pop_front();
+        }
+        self.sent.push_back(now);
+    }
+}
+
+fn encode(op: u32, payload: &Value) -> Vec<u8> {
+    let body = payload.to_string();
+    let mut frame = Vec::with_capacity(8 + body.len());
+    frame.extend_from_slice(&op.to_le_bytes());
+    frame.extend_from_slice(&(body.len() as u32).to_le_bytes());
+    frame.extend_from_slice(body.as_bytes());
+    frame
+}
+
+fn read_frame(r: &mut impl Read) -> io::Result<(u32, Value)> {
+    let mut header = [0; 8];
+    r.read_exact(&mut header)?;
+    let op = u32::from_le_bytes(header[..4].try_into().expect("4 bytes"));
+    let len = u32::from_le_bytes(header[4..].try_into().expect("4 bytes")) as usize;
+    if len > 1 << 20 {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            "frame too large",
+        ));
+    }
+    let mut body = vec![0; len];
+    r.read_exact(&mut body)?;
+    Ok((op, serde_json::from_slice(&body)?))
+}
+
+trait Pipe: Read + Write + Send {}
+impl<T: Read + Write + Send> Pipe for T {}
+
+struct Client {
+    pipe: Box<dyn Pipe>,
+    nonce: u64,
+}
+impl Client {
+    /// The first Discord socket that answers the handshake with READY.
+    fn connect() -> Option<Self> {
+        sockets().into_iter().find_map(|path| {
+            let mut client = Client {
+                pipe: open(&path).ok()?,
+                nonce: 0,
+            };
+            match client.handshake() {
+                Ok(()) => {
+                    log::info!("Horizon: connected to Discord for Rich Presence");
+                    Some(client)
+                }
+                Err(e) => {
+                    log::debug!("Horizon: Discord at {} refused: {e}", path.display());
+                    None
+                }
+            }
+        })
+    }
+    fn handshake(&mut self) -> io::Result<()> {
+        let hello = json!({"v": 1, "client_id": DISCORD_APP_ID});
+        self.pipe.write_all(&encode(HANDSHAKE, &hello))?;
+        self.reply(|frame| frame["evt"] == "READY")
+    }
+    fn set_activity(&mut self, activity: Option<Value>) -> io::Result<()> {
+        self.nonce += 1;
+        let nonce = self.nonce.to_string();
+        let command = json!({
+            "cmd": "SET_ACTIVITY",
+            "args": {"pid": std::process::id(), "activity": activity},
+            "nonce": nonce,
+        });
+        self.pipe.write_all(&encode(FRAME, &command))?;
+        self.reply(|frame| frame["nonce"] == nonce.as_str())
+    }
+    /// Reads until the frame `ours` picks, answering pings; an ERROR is logged, not fatal.
+    fn reply(&mut self, ours: impl Fn(&Value) -> bool) -> io::Result<()> {
+        loop {
+            match read_frame(&mut self.pipe)? {
+                (FRAME, frame) if ours(&frame) => {
+                    if frame["evt"] == "ERROR" {
+                        log::info!("Horizon: Discord presence: {}", frame["data"]["message"]);
+                    }
+                    return Ok(());
+                }
+                (PING, frame) => self.pipe.write_all(&encode(PONG, &frame))?,
+                (CLOSE, frame) => {
+                    return Err(io::Error::new(
+                        io::ErrorKind::ConnectionAborted,
+                        frame["message"].as_str().unwrap_or("closed").to_owned(),
+                    ));
+                }
+                _ => {}
+            }
+        }
+    }
+    fn close(mut self) {
+        let _ = self.pipe.write_all(&encode(CLOSE, &json!({})));
+    }
+}
+
+/// Where Discord listens: `discord-ipc-0..9` in the temporary folders (and Flatpak's and
+/// Snap's subfolders) on Linux and macOS, named pipes on Windows.
+fn sockets() -> Vec<PathBuf> {
+    sockets_with(|key| std::env::var_os(key), cfg!(windows))
+}
+
+fn sockets_with(var: impl Fn(&str) -> Option<std::ffi::OsString>, windows: bool) -> Vec<PathBuf> {
+    let names = (0..10).map(|n| format!("discord-ipc-{n}"));
+    if let Some(dir) = var(IPC_DIR_ENV) {
+        return names.map(|n| PathBuf::from(&dir).join(n)).collect();
+    }
+    if windows {
+        return names.map(|n| PathBuf::from(r"\\?\pipe\").join(n)).collect();
+    }
+    let mut dirs: Vec<PathBuf> = ["XDG_RUNTIME_DIR", "TMPDIR", "TMP", "TEMP"]
+        .into_iter()
+        .filter_map(&var)
+        .map(PathBuf::from)
+        .collect();
+    dirs.push("/tmp".into());
+    dirs.dedup();
+    let mut paths = Vec::new();
+    for dir in dirs {
+        for sub in ["", "app/com.discordapp.Discord", "snap.discord"] {
+            paths.extend(names.clone().map(|n| dir.join(sub).join(n)));
+        }
+    }
+    paths
+}
+
+#[cfg(unix)]
+fn open(path: &std::path::Path) -> io::Result<Box<dyn Pipe>> {
+    let stream = std::os::unix::net::UnixStream::connect(path)?;
+    // A Discord that stops answering costs this thread a few seconds, never the game.
+    stream.set_read_timeout(Some(Duration::from_secs(5)))?;
+    Ok(Box::new(stream))
+}
+
+#[cfg(windows)]
+fn open(path: &std::path::Path) -> io::Result<Box<dyn Pipe>> {
+    let pipe = std::fs::OpenOptions::new()
+        .read(true)
+        .write(true)
+        .open(path)?;
+    Ok(Box::new(pipe))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn world(play: Play, dimension: Dimension) -> Status {
+        Status::World {
+            play,
+            dimension,
+            mode: GameMode::Survival,
+        }
+    }
+
+    /// The folders a real Discord listens in: `$TMPDIR` on macOS, `$XDG_RUNTIME_DIR` on Linux (and its
+    /// Flatpak and Snap subfolders), named pipes on Windows.
+    #[test]
+    fn sockets_cover_where_discord_listens() {
+        let env = |pairs: &'static [(&'static str, &'static str)]| {
+            move |key: &str| {
+                pairs
+                    .iter()
+                    .find(|(k, _)| *k == key)
+                    .map(|(_, v)| std::ffi::OsString::from(v))
+            }
+        };
+        let macos = sockets_with(env(&[("TMPDIR", "/var/folders/xy/abc/T/")]), false);
+        assert_eq!(
+            macos[0],
+            PathBuf::from("/var/folders/xy/abc/T/discord-ipc-0")
+        );
+        assert!(macos.contains(&PathBuf::from("/var/folders/xy/abc/T/discord-ipc-9")));
+        assert!(macos.contains(&PathBuf::from("/tmp/discord-ipc-0")));
+
+        let linux = sockets_with(
+            env(&[("XDG_RUNTIME_DIR", "/run/user/1000"), ("TMPDIR", "/tmp")]),
+            false,
+        );
+        assert_eq!(linux[0], PathBuf::from("/run/user/1000/discord-ipc-0"));
+        for path in [
+            "/run/user/1000/app/com.discordapp.Discord/discord-ipc-0",
+            "/run/user/1000/snap.discord/discord-ipc-0",
+            "/tmp/discord-ipc-0",
+        ] {
+            assert!(linux.contains(&PathBuf::from(path)), "{path}");
+        }
+        assert_eq!(linux.len(), 2 * 3 * 10, "/tmp is listed once");
+
+        let bare = sockets_with(env(&[]), false);
+        assert_eq!(bare[0], PathBuf::from("/tmp/discord-ipc-0"));
+
+        let windows = sockets_with(env(&[("TEMP", r"C:\Temp")]), true);
+        assert_eq!(windows.len(), 10);
+        // `Path::join` only uses `\` as the separator on Windows itself.
+        #[cfg(windows)]
+        assert_eq!(windows[0], PathBuf::from(r"\\?\pipe\discord-ipc-0"));
+
+        let fake = sockets_with(
+            env(&[("HORIZON_DISCORD_IPC_DIR", "/tmp/hz"), ("TMPDIR", "/x")]),
+            false,
+        );
+        assert_eq!(fake.len(), 10);
+        assert_eq!(fake[0], PathBuf::from("/tmp/hz/discord-ipc-0"));
+    }
+
+    #[test]
+    fn frames_round_trip() {
+        let frame = encode(FRAME, &json!({"cmd": "SET_ACTIVITY"}));
+        assert_eq!(&frame[..4], &[1, 0, 0, 0]);
+        assert_eq!(frame[4..8], (frame.len() as u32 - 8).to_le_bytes());
+        let (op, value) = read_frame(&mut frame.as_slice()).unwrap();
+        assert_eq!((op, value), (FRAME, json!({"cmd": "SET_ACTIVITY"})));
+        assert!(read_frame(&mut &frame[..6]).is_err());
+        let huge = [1, 0, 0, 0, 0, 0, 0, 2];
+        assert!(read_frame(&mut huge.as_slice()).is_err());
+    }
+
+    #[test]
+    fn activities_say_what_the_player_does_and_nothing_private() {
+        assert_eq!(activity(Status::Off, None), None);
+        let menus = activity(Status::Menus, None).unwrap();
+        assert_eq!(menus["details"], "In the menus");
+        assert!(menus.get("state").is_none() && menus.get("timestamps").is_none());
+        assert_eq!(menus["assets"]["large_image"], "horizon");
+
+        let single = activity(world(Play::Singleplayer, Dimension::Nether), Some(1000)).unwrap();
+        assert_eq!(single["details"], "Singleplayer");
+        assert_eq!(single["state"], "In the Nether");
+        assert_eq!(single["timestamps"]["start"], 1000);
+        assert!(single.get("party").is_none());
+        assert!(single["assets"].get("small_image").is_none());
+
+        let multi = activity(world(Play::Multiplayer, Dimension::End), Some(5)).unwrap();
+        assert_eq!(multi["details"], "Multiplayer");
+        assert_eq!(multi["state"], "In the End");
+
+        let host = world(Play::Hosting { players: 3 }, Dimension::Overworld);
+        let host = activity(host, Some(5)).unwrap();
+        assert_eq!(host["details"], "Hosting a world");
+        assert_eq!(host["state"], "In the Overworld");
+        assert_eq!(host["party"]["size"], json!([3, 8]));
+    }
+
+    #[test]
+    fn time_counts_from_entering_the_world() {
+        let mut w = Wanted {
+            status: Status::Menus,
+            since: None,
+        };
+        assert!(!w.update(Status::Menus, 10));
+        assert!(w.update(world(Play::Singleplayer, Dimension::Overworld), 20));
+        assert_eq!(w.since, Some(20));
+        // Another dimension, opening to LAN: the same visit.
+        assert!(w.update(world(Play::Singleplayer, Dimension::Nether), 30));
+        assert!(w.update(world(Play::Hosting { players: 1 }, Dimension::Nether), 40));
+        assert_eq!(w.since, Some(20));
+        assert!(w.update(Status::Menus, 50));
+        assert_eq!(w.since, None);
+        assert!(w.update(world(Play::Multiplayer, Dimension::Overworld), 60));
+        assert_eq!(w.since, Some(60));
+        assert!(w.update(Status::Off, 70));
+        assert_eq!(w.since, None);
+    }
+
+    #[test]
+    fn at_most_five_updates_in_twenty_seconds() {
+        let t = Instant::now();
+        let mut limit = RateLimit::default();
+        for i in 0..5 {
+            let now = t + Duration::from_secs(i);
+            assert_eq!(limit.wait(now), Duration::ZERO);
+            limit.record(now);
+        }
+        assert_eq!(
+            limit.wait(t + Duration::from_secs(5)),
+            Duration::from_secs(15)
+        );
+        assert_eq!(limit.wait(t + WINDOW), Duration::ZERO);
+        limit.record(t + WINDOW);
+        assert_eq!(limit.wait(t + WINDOW), Duration::from_secs(1));
+    }
+
+    /// A fake Discord: answers the handshake with READY, each command with its nonce, after a ping.
+    #[cfg(unix)]
+    #[test]
+    fn talks_to_discord_over_its_socket() {
+        let dir = std::env::temp_dir().join(format!("horizon-discord-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let path = dir.join("discord-ipc-0");
+        let _ = std::fs::remove_file(&path);
+        let listener = std::os::unix::net::UnixListener::bind(&path).unwrap();
+        let server = std::thread::spawn(move || {
+            let (mut s, _) = listener.accept().unwrap();
+            let (op, hello) = read_frame(&mut s).unwrap();
+            assert_eq!((op, &hello["v"]), (HANDSHAKE, &json!(1)));
+            let ready = json!({"cmd": "DISPATCH", "evt": "READY", "data": {"v": 1}});
+            s.write_all(&encode(FRAME, &ready)).unwrap();
+            let mut got = Vec::new();
+            for _ in 0..2 {
+                let (op, cmd) = read_frame(&mut s).unwrap();
+                assert_eq!(op, FRAME);
+                s.write_all(&encode(PING, &json!({"n": 1}))).unwrap();
+                assert_eq!(read_frame(&mut s).unwrap(), (PONG, json!({"n": 1})));
+                let reply = json!({"cmd": "SET_ACTIVITY", "nonce": cmd["nonce"], "data": null});
+                s.write_all(&encode(FRAME, &reply)).unwrap();
+                got.push(cmd);
+            }
+            got
+        });
+        let mut client = Client {
+            pipe: open(&path).unwrap(),
+            nonce: 0,
+        };
+        client.handshake().unwrap();
+        let shown = activity(world(Play::Singleplayer, Dimension::End), Some(7));
+        client.set_activity(shown.clone()).unwrap();
+        client.set_activity(None).unwrap();
+        let got = server.join().unwrap();
+        assert_eq!(got[0]["cmd"], "SET_ACTIVITY");
+        assert_eq!(got[0]["args"]["pid"], std::process::id());
+        assert_eq!(got[0]["args"]["activity"], shown.unwrap());
+        assert_eq!(got[1]["args"]["activity"], Value::Null);
+        assert_ne!(got[0]["nonce"], got[1]["nonce"]);
+        let _ = std::fs::remove_dir_all(dir);
+    }
+}

crates/horizon-client/src/entity_nbt.rs

@@ -617,9 +617,23 @@ pub fn mob_from_nbt(tag: &Tag, types: &HashMap<String, Arc<MobType>>, id: u32) -
     m.head_pitch = pitch;
     m.on_ground = flag(tag, "OnGround");
     m.fall_distance = float(tag.get("fall_distance")).unwrap_or(0.0);
-    if let Some(h) = float(tag.get("Health")) {
-        m.health = h as f32;
+    // LivingEntity.readAdditionalSaveData: the saved attribute bases, then
+    // the health, the max health when there is none.
+    if let Some(Tag::List(attrs)) = tag.get("attributes") {
+        for a in attrs {
+            let (Some(id), Some(Tag::Double(bits))) = (text(a.get("id")), a.get("base")) else {
+                continue;
+            };
+            let v = f64::from_bits(*bits);
+            match id.as_str() {
+                "minecraft:max_health" => m.attrs.max_health = v as f32,
+                "minecraft:movement_speed" => m.attrs.speed = v,
+                "minecraft:attack_damage" => m.attrs.attack_damage = v as f32,
+                _ => {}
+            }
+        }
     }
+    m.health = float(tag.get("Health")).map_or(m.attrs.max_health, |h| h as f32);
     m.hurt_time = number(tag.get("HurtTime")).unwrap_or(0) as i32;
     // What it holds (equipment.mainhand / offhand), when saved.
     if let Some(eq) = tag.get("equipment") {
@@ -735,12 +749,8 @@ pub fn mob_from_nbt(tag: &Tag, types: &HashMap<String, Arc<MobType>>, id: u32) -
                 let (Some(id), Some(Tag::Double(bits))) = (text(a.get("id")), a.get("base")) else {
                     continue;
                 };
-                let v = f64::from_bits(*bits);
-                match id.as_str() {
-                    "minecraft:max_health" => m.attrs.max_health = v as f32,
-                    "minecraft:movement_speed" => m.attrs.speed = v,
-                    "minecraft:jump_strength" => m.extra.vector[0] = v,
-                    _ => {}
+                if id == "minecraft:jump_strength" {
+                    m.extra.vector[0] = f64::from_bits(*bits);
                 }
             }
         }
@@ -1155,6 +1165,72 @@ pub fn arrow_from_nbt(
     Some((p, tag.get("inBlockState").cloned()))
 }
 
+/// `LargeFireball` and `SmallFireball`: `AbstractHurtingProjectile`'s
+/// `acceleration_power`, `Projectile`'s owner and flags, `ExplosionPower`.
+pub fn fireball_to_nbt(
+    p: &Projectile,
+    uuid: [i32; 4],
+    owner: Option<[i32; 4]>,
+    raw: Option<&Tag>,
+) -> Option<Tag> {
+    let power = match p.kind {
+        ProjectileKind::LargeFireball { power } => Some(power),
+        ProjectileKind::SmallFireball => None,
+        _ => return None,
+    };
+    let base = Base {
+        id: p.kind.id(),
+        uuid,
+        position: p.position,
+        motion: p.velocity,
+        rotation: [p.yaw, p.pitch],
+        on_ground: false,
+        fall_distance: 0.0,
+    };
+    let mut tag = base.tag(raw);
+    put(
+        &mut tag,
+        "acceleration_power",
+        Tag::Double(p.acceleration.to_bits()),
+    );
+    // Projectile: LeftOwner only when set; HasBeenShot once it has ticked
+    // (a fireball saved before its first tick keeps what it was loaded with).
+    if let Tag::Compound(map) = &mut tag {
+        map.remove(&"LeftOwner".into());
+    }
+    if p.left_owner {
+        put(&mut tag, "LeftOwner", Tag::Byte(1));
+    }
+    if p.age > 0 || tag.get("HasBeenShot").is_none() {
+        put(&mut tag, "HasBeenShot", Tag::Byte(i8::from(p.age > 0)));
+    }
+    if let Some(power) = power {
+        put(&mut tag, "ExplosionPower", Tag::Byte(power as i8));
+    }
+    if let Some(owner) = owner {
+        put(&mut tag, "Owner", Tag::IntArray(owner.to_vec()));
+    }
+    Some(tag)
+}
+
+pub fn fireball_from_nbt(tag: &Tag, player: Option<[i32; 4]>) -> Option<Projectile> {
+    let kind = match kind(tag)?.as_str() {
+        "minecraft:fireball" => ProjectileKind::LargeFireball {
+            power: number(tag.get("ExplosionPower")).unwrap_or(1) as i32,
+        },
+        "minecraft:small_fireball" => ProjectileKind::SmallFireball,
+        _ => return None,
+    };
+    let owner = uuid_from_tag(tag.get("Owner"));
+    let from_player = player.is_some() && owner == player;
+    let mut p = Projectile::new(kind, position(tag)?, from_player.then_some(Who::Player));
+    p.velocity = motion(tag);
+    [p.yaw, p.pitch] = rotation(tag);
+    p.left_owner = flag(tag, "LeftOwner");
+    p.acceleration = float(tag.get("acceleration_power")).unwrap_or(0.1);
+    Some(p)
+}
+
 /// `FallingBlockEntity`: BlockState, Time, DropItem, HurtEntities.
 #[allow(clippy::too_many_arguments)]
 pub fn falling_block_to_nbt(
@@ -2139,3 +2215,41 @@ mod sheep_nbt_tests {
         assert_eq!((back.extra.color, back.extra.sheared), (14, true));
     }
 }
+
+#[cfg(test)]
+mod fireball_nbt_tests {
+    use super::*;
+    #[test]
+    fn a_fireball_round_trips_its_flight() {
+        let raw = Tag::compound([
+            ("id", Tag::String("minecraft:fireball".into())),
+            ("Pos", doubles(&[1.0, 70.0, -2.5])),
+            ("Motion", doubles(&[0.0, -0.5, 1.0])),
+            ("ExplosionPower", Tag::Byte(4)),
+            ("acceleration_power", Tag::Double(0.0f64.to_bits())),
+        ]);
+        let p = fireball_from_nbt(&raw, None).unwrap();
+        assert_eq!(p.kind, ProjectileKind::LargeFireball { power: 4 });
+        assert_eq!((p.velocity.z, p.acceleration), (1.0, 0.0));
+        let back = fireball_to_nbt(&p, [1, 2, 3, 4], None, None).unwrap();
+        assert_eq!(number(back.get("ExplosionPower")), Some(4));
+        assert_eq!(float(back.get("acceleration_power")), Some(0.0));
+        // Projectile.addAdditionalSaveData: no LeftOwner unless set, HasBeenShot always.
+        assert!(back.get("LeftOwner").is_none());
+        assert_eq!(number(back.get("HasBeenShot")), Some(0));
+        assert_eq!(
+            read_doubles::<3>(back.get("Motion")),
+            Some([0.0, -0.5, 1.0])
+        );
+        // A default fireball keeps vanilla's power and acceleration.
+        let plain = Tag::compound([
+            ("id", Tag::String("minecraft:fireball".into())),
+            ("Pos", doubles(&[0.0, 0.0, 0.0])),
+        ]);
+        let p = fireball_from_nbt(&plain, None).unwrap();
+        assert_eq!(
+            (p.kind, p.acceleration),
+            (ProjectileKind::LargeFireball { power: 1 }, 0.1)
+        );
+    }
+}

crates/horizon-client/src/extras.rs

@@ -1,7 +1,8 @@
 //! Horizon's optional extras (zoom, FPS counter, keystroke overlay): their
 //! settings, kept in `horizon-extras.txt` next to `options.txt` so that file
 //! stays exactly vanilla's, and the logic behind them. Every extra is off by
-//! default; see `docs/extras.md`.
+//! default; see `docs/extras.md`. Horizon's own switches outside the Extras page
+//! (No AI, Agent Control, Discord Rich Presence) are kept here too.
 use std::{collections::VecDeque, fs, path::Path};
 
 pub const FILE: &str = "horizon-extras.txt";
@@ -112,6 +113,8 @@ pub struct Extras {
     /// Agents may control the game the player starts: it opens its control socket for
     /// horizon-ctl and MCP clients (off by default; an agent's own launch always opens it).
     pub agent_control: bool,
+    /// "Playing Horizon" on the player's Discord profile (`discord_presence`; on by default).
+    pub discord_presence: bool,
 }
 impl Default for Extras {
     fn default() -> Self {
@@ -142,6 +145,7 @@ impl Default for Extras {
             sort_key: "key.keyboard.unknown".into(),
             no_ai: false,
             agent_control: false,
+            discord_presence: true,
         }
     }
 }
@@ -207,6 +211,7 @@ impl Extras {
                 "sortKey" if value.starts_with("key.") => e.sort_key = value.to_owned(),
                 horizon_core::no_ai::KEY => e.no_ai = flag(e.no_ai),
                 "agentControl" => e.agent_control = flag(e.agent_control),
+                "discordPresence" => e.discord_presence = flag(e.discord_presence),
                 _ => {}
             }
         }
@@ -214,7 +219,7 @@ impl Extras {
     }
     pub fn serialize(&self) -> String {
         format!(
-            "fullbright:{}\ndynamicLights:{}\nzoom:{}\nzoomKey:{}\nzoomLevel:{}\nzoomSmooth:{}\nzoomSensitivity:{}\nfps:{}\nfpsCorner:{}\nfpsLows:{}\nkeystrokes:{}\nkeystrokesCorner:{}\nkeystrokesCps:{}\nminimap:{}\nminimapCorner:{}\nminimapSize:{}\nminimapShape:{}\nminimapZoom:{}\nminimapRotate:{}\nautoReconnect:{}\nmouseTweaks:{}\nmouseTweaksWheel:{}\nsort:{}\nsortKey:{}\n{}:{}\nagentControl:{}\n",
+            "fullbright:{}\ndynamicLights:{}\nzoom:{}\nzoomKey:{}\nzoomLevel:{}\nzoomSmooth:{}\nzoomSensitivity:{}\nfps:{}\nfpsCorner:{}\nfpsLows:{}\nkeystrokes:{}\nkeystrokesCorner:{}\nkeystrokesCps:{}\nminimap:{}\nminimapCorner:{}\nminimapSize:{}\nminimapShape:{}\nminimapZoom:{}\nminimapRotate:{}\nautoReconnect:{}\nmouseTweaks:{}\nmouseTweaksWheel:{}\nsort:{}\nsortKey:{}\n{}:{}\nagentControl:{}\ndiscordPresence:{}\n",
             bool_text(self.fullbright),
             bool_text(self.dynamic_lights),
             bool_text(self.zoom),
@@ -246,6 +251,7 @@ impl Extras {
             horizon_core::no_ai::KEY,
             bool_text(self.no_ai),
             bool_text(self.agent_control),
+            bool_text(self.discord_presence),
         )
     }
     /// Binds the extra key `name` (`ZOOM_KEY`, `SORT_KEY`); false for
@@ -466,6 +472,8 @@ pub enum Item {
     /// Not on the Extras page: Horizon Settings shows No AI, its AI Agent page Agent Control.
     NoAi,
     AgentControl,
+    /// On the Horizon Settings page.
+    DiscordPresence,
 }
 /// The Extras page: headers and items.
 pub fn rows() -> Vec<Result<Item, &'static str>> {
@@ -546,6 +554,7 @@ impl Item {
             Item::KeystrokesCps => "Clicks per second",
             Item::NoAi => "No AI",
             Item::AgentControl => "Agent Control",
+            Item::DiscordPresence => "Discord Rich Presence",
         }
     }
     /// The switch this setting belongs to: it does nothing while that is off.
@@ -559,7 +568,7 @@ impl Item {
             MouseTweaksWheel => MouseTweaks,
             SortKey => Sort,
             Fullbright | DynamicLights | Zoom | Minimap | Fps | Keystrokes | MouseTweaks | Sort
-            | AutoReconnect | NoAi | AgentControl => {
+            | AutoReconnect | NoAi | AgentControl | DiscordPresence => {
                 return None;
             }
         })
@@ -606,6 +615,9 @@ impl Item {
             Item::NoAi => {
                 "Hides and turns off every AI feature: agent control, horizon-ctl and the MCP servers. The launcher's switch too."
             }
+            Item::DiscordPresence => {
+                "Shows Playing Horizon on your Discord profile while Discord runs: menus, single player or multiplayer, the dimension and the time played. Never a world's name or a server's address."
+            }
             Item::AgentControl => {
                 "Your own AI agent can play this game through horizon-ctl or an MCP client, on this computer only."
             }
@@ -641,6 +653,7 @@ impl Item {
             Item::Sort => e.sort,
             Item::NoAi => e.no_ai,
             Item::AgentControl => e.agent_control,
+            Item::DiscordPresence => e.discord_presence,
             _ => return None,
         })
     }
@@ -698,6 +711,7 @@ impl Item {
             Item::MinimapZoom => e.minimap_zoom = next(&MINIMAP_ZOOMS, e.minimap_zoom, back),
             Item::NoAi => e.no_ai = !e.no_ai,
             Item::AgentControl => e.agent_control = !e.agent_control,
+            Item::DiscordPresence => e.discord_presence = !e.discord_presence,
             Item::ZoomKey | Item::SortKey => {}
         }
     }
@@ -721,6 +735,7 @@ mod tests {
         assert!(!d.fullbright && !d.dynamic_lights);
         assert!(!d.zoom && !d.fps && !d.keystrokes && !d.minimap && !d.auto_reconnect);
         assert!(!d.mouse_tweaks && !d.sort);
+        assert!(d.discord_presence);
         assert_eq!(Extras::parse(""), d);
         assert_eq!(Extras::parse(&d.serialize()), d);
         let mut e = d.clone();
@@ -746,6 +761,7 @@ mod tests {
         e.mouse_tweaks_wheel = false;
         e.sort = true;
         e.sort_key = "key.keyboard.r".into();
+        e.discord_presence = false;
         assert_eq!(Extras::parse(&e.serialize()), e);
     }
 

crates/horizon-client/src/fog.rs

@@ -198,6 +198,8 @@ pub struct FogInputs<'a> {
     pub blindness: Option<(i32, bool)>,
     /// The darkness effect's blend factor, while the effect is on.
     pub darkness: Option<f32>,
+    /// `GameRenderer.bossOverlayWorldDarkening`: a wither's bar dims the fog.
+    pub darken_world: f32,
     /// `BossHealthOverlay.shouldCreateWorldFog`: a boss bar with
     /// `createWorldFog` is shown (the Ender Dragon's).
     pub boss_world_fog: bool,
@@ -263,6 +265,13 @@ pub fn setup_fog(tables: &FogTables, state: &FogState, input: &FogInputs) -> Fog
         let brightness = (1.0 - darkness) * (1.0 - darkness);
         color = color.map(|c| c * brightness);
     }
+    // FogRenderer.computeFogColor: a boss bar's world darkening.
+    if input.darken_world > 0.0 {
+        let t = input.darken_world;
+        color[0] += (color[0] * 0.7 - color[0]) * t;
+        color[1] += (color[1] * 0.6 - color[1]) * t;
+        color[2] += (color[2] * 0.6 - color[2]) * t;
+    }
     let brighten = if eye_in_water { water_vision } else { 0.0 };
     if color.iter().all(|&c| c != 0.0) {
         let scale = 1.0 / color[0].max(color[1]).max(color[2]);
@@ -394,6 +403,7 @@ mod tests {
             skybox: true,
             blindness: None,
             darkness: None,
+            darken_world: 0.0,
             boss_world_fog: false,
         }
     }
@@ -422,6 +432,25 @@ mod tests {
         assert_eq!(water.environmental_start, -8.0);
     }
     #[test]
+    fn boss_darkening_dims_fog_color() {
+        // FogRenderer.computeFogColor: lerp toward 70/60/60% of each channel.
+        let sky = Sky {
+            fog_color: [1.0, 1.0, 1.0],
+            sky_color: [1.0, 1.0, 1.0],
+            ..Sky::default()
+        };
+        let tables = FogTables {
+            water_fog_end: vec![1.0],
+        };
+        let mut input = inputs(&sky);
+        input.skybox = false;
+        input.darken_world = 1.0;
+        let fog = setup_fog(&tables, &FogState::default(), &input);
+        assert!((fog.color[0] - 0.7).abs() < 1.0e-5);
+        assert!((fog.color[1] - 0.6).abs() < 1.0e-5);
+        assert!((fog.color[2] - 0.6).abs() < 1.0e-5);
+    }
+    #[test]
     fn void_darkness_starts_32_above_the_floor() {
         let sky = Sky {
             fog_end: 1024.0,

crates/horizon-client/src/game.rs

@@ -36,6 +36,7 @@ mod debug_keys;
 mod decorated_pot;
 mod dedicated;
 mod deflect;
+mod discord;
 mod dispense_fixture;
 mod dispenser;
 mod dragon;
@@ -44,6 +45,7 @@ mod enchant_effects;
 mod end;
 mod entity_culling;
 mod events;
+mod execution_role;
 mod explosion;
 mod extras;
 mod falling_damage;
@@ -140,6 +142,7 @@ mod sculk;
 mod sculk_fixture;
 mod server_packs;
 mod server_travel;
+mod shader_packs;
 mod shield;
 mod sign_edit;
 mod sniffers;
@@ -154,6 +157,7 @@ mod storage;
 mod structures;
 mod subtitle_hud;
 mod sulfur_cubes;
+mod text_displays;
 mod titles;
 mod tnt;
 mod totem;
@@ -290,8 +294,8 @@ struct Options {
     /// as vanilla's does: the default. `--in-frame` (or `--no-server-thread`,
     /// or `HORIZON_SERVER_THREAD=0`) runs the world in the frame instead.
     server_thread: bool,
-    /// Set on the integrated server's own options: it draws nothing, so it skips meshing.
-    integrated: bool,
+    /// What this Game executes; independent of its current server connection.
+    execution_role: execution_role::ExecutionRole,
 }
 impl Options {
     /// The name to join servers with: the one given, else the offline name kept
@@ -348,7 +352,7 @@ impl Options {
             // itself, without the event loop: it stays in the frame.
             server_thread: std::env::var("HORIZON_SERVER_THREAD").map_or(true, |v| v != "0")
                 && std::env::var_os("HORIZON_COMMAND_SCRIPT").is_none(),
-            integrated: false,
+            execution_role: execution_role::ExecutionRole::Client,
         };
         let mut session_file = std::env::var("HORIZON_SESSION_FILE").ok();
         let mut args = std::env::args().skip(1);
@@ -362,6 +366,7 @@ impl Options {
                     return Ok(None);
                 }
                 "--dedicated" => {
+                    o.execution_role = execution_role::ExecutionRole::DedicatedServer;
                     o.dedicated = Some(args.by_ref().collect());
                     break;
                 }
@@ -1163,6 +1168,8 @@ struct Game<'a> {
     carried: Option<ItemStack>,
     craft_grid: Vec<Option<ItemStack>>,
     craft_size: usize,
+    /// The crafting table the 3x3 grid belongs to (`CraftingMenu.access`).
+    craft_table: Option<[i32; 3]>,
     /// A quick craft drag over inventory slots: (button, game slots so far).
     inv_drag: Option<(i32, Vec<usize>)>,
     /// `AbstractContainerScreen`'s quick craft and skip-release state.
@@ -1422,6 +1429,8 @@ struct Game<'a> {
     dragon_model: Option<horizon_client::mobs::Part>,
     /// Map textures waiting for the next HUD batch to upload them.
     map_patches: Vec<horizon_client::font::Patch>,
+    text_displays: std::collections::HashMap<i32, text_displays::RemoteTextDisplay>,
+    text_display_vertices: usize,
     /// Player skin downloads, and which skin each atlas skin slot holds
     /// (least recently shown first).
     skin_downloads: RefCell<horizon_client::skins::Downloader>,
@@ -1566,6 +1575,8 @@ struct Game<'a> {
     score: scoreboard::ScoreState,
     fns: functions::FnState,
     bosses: bossbars::BossState,
+    /// `Hud.bossOverlay`: the bars this window is showing.
+    boss_overlay: horizon_client::boss_overlay::BossOverlay,
     exec: commands::execute::ExecState,
     rand_sequences: horizon_client::random_sequences::RandomSequences,
     border: horizon_client::worldborder::WorldBorder,
@@ -2907,6 +2918,7 @@ impl Game<'_> {
         }
         if &*name == "minecraft:crafting_table" {
             self.craft_size = 3;
+            self.craft_table = Some(pos);
         } else if &*name == "minecraft:ender_chest" {
             self.open_ender_chest(key);
             self.container_opener_event(key, true);
@@ -4046,6 +4058,20 @@ impl Game<'_> {
         self.capture_loaded_world();
         Ok(())
     }
+    /// Landing rules (farmland trampling, turtle eggs) wrote or removed the block
+    /// raw: finish `Level.setBlock`'s neighbour updates, so a crop on trampled
+    /// farmland breaks. The local player's and every server player's landings.
+    fn landing_block_updates(&mut self, event: &horizon_client::landing::FallEvent) {
+        use horizon_client::landing::FallEvent;
+        let (position, flags) = match *event {
+            FallEvent::Write {
+                position, flags, ..
+            } => (position, flags as i32),
+            FallEvent::Destroy { position, .. } => (position, level_flags::UPDATE_ALL),
+            _ => return,
+        };
+        self.with_level(|b, level, ticks| b.notify_written(level, ticks, position, flags));
+    }
     fn tick(&mut self) -> Result<()> {
         self.tick_debug_keys()?;
         self.tick_debug_charts();
@@ -4064,6 +4090,8 @@ impl Game<'_> {
         self.track_experience_display();
         // `/tick freeze` stops the world but not the player.
         let running = self.clock.world_runs();
+        // GameRenderer.tick: a wither's bar darkens the world, then fades.
+        self.boss_overlay.tick_darken(running);
         if running {
             self.world.game_time += 1;
             if self.ui.rules.bool("advance_weather") {
@@ -4260,23 +4288,7 @@ impl Game<'_> {
                     };
                     self.audio.play(name, Some(feet), volume, pitch);
                 }
-                MotionEvent::Fall(horizon_client::landing::FallEvent::Write {
-                    position,
-                    flags,
-                    ..
-                }) => {
-                    // Landing rules (farmland trampling, turtle eggs) wrote the block raw.
-                    self.with_level(|b, level, ticks| {
-                        b.notify_written(level, ticks, position, flags as i32)
-                    });
-                }
-                MotionEvent::Fall(horizon_client::landing::FallEvent::Destroy {
-                    position, ..
-                }) => {
-                    self.with_level(|b, level, ticks| {
-                        b.notify_written(level, ticks, position, level_flags::UPDATE_ALL)
-                    });
-                }
+                MotionEvent::Fall(event) => self.landing_block_updates(&event),
                 MotionEvent::Snowflake { position, velocity } => self.snowflake(position, velocity),
                 MotionEvent::EnterBlock { state } => self.trigger_enter_block(state),
                 MotionEvent::InsidePortal { pos } => self.player_inside_nether_portal(pos),
@@ -4439,6 +4451,8 @@ impl Game<'_> {
             });
             horizon_client::spans::time("tick_particles", || self.tick_particles());
         }
+        // ServerBossEvent broadcasts, after this level's entities have ticked.
+        self.publish_boss_bars();
         // Minecraft.handleKeybinds: held use repeats only while no item is in
         // use (a raised shield or a drawn bow places and uses nothing).
         if self.right
@@ -4819,11 +4833,15 @@ impl Game<'_> {
         }
         let atlas_ptr: *const HudAtlas = &self.gui.atlas;
         let _ = atlas_ptr;
+        // The ToastManager draws over every screen: a server's packs
+        // download while the connection screen shows.
         if self.remote_overlay(&mut batch) {
+            self.draw_pack_toasts(&mut batch);
             return batch;
         }
         if let Some(reason) = self.loading_reason() {
             self.draw_level_loading(&mut batch, reason);
+            self.draw_pack_toasts(&mut batch);
             return batch;
         }
         // Hud.extractRenderState: F1 (keyToggleGui) hides camera overlays, the
@@ -5035,6 +5053,7 @@ impl Game<'_> {
             Screen::Playing | Screen::Options | Screen::Win => {}
         }
         self.draw_toasts(&mut batch);
+        self.draw_pack_toasts(&mut batch);
         self.remote_hud(&mut batch);
         self.draw_sign_editor(&mut batch);
         self.draw_book(&mut batch);
@@ -5409,6 +5428,7 @@ impl Game<'_> {
             }
         }
         self.craft_size = 2;
+        self.craft_table = None;
         if let Some(key) = self.container.take() {
             self.container_opener_event(key, false);
             self.post_block_game_event(
@@ -6772,6 +6792,7 @@ impl Game<'_> {
         let mut see_through = std::mem::take(&mut self.see_through_vertices);
         see_through.clear();
         self.name_tag_geometry(camera, alpha, &mut out, &mut see_through);
+        self.text_display_geometry(camera, alpha, &mut out, &mut see_through);
         self.see_through_vertices = see_through;
         // Entity shadows (EntityRenderer.extractShadow).
         if let Some(sprite) = self.gui.atlas.sprites.get("misc/shadow").copied() {
@@ -7502,7 +7523,7 @@ impl Game<'_> {
             (sky.star_brightness > 0.0).then(|| (frame(sky.star_angle), sky.star_brightness));
         (out, stars)
     }
-    /// Load (or create) a world folder under saves/ and start streaming it.
+    /// Enter a local world from the client, selecting its simulation mode.
     fn open_world(
         &mut self,
         folder: &str,
@@ -7521,20 +7542,16 @@ impl Game<'_> {
             return Ok(());
         }
         self.join_world_rest()?;
-        let save_root = std::env::current_dir()?.join("saves").join(folder);
-        if integrated::wanted(&self.options, &save_root) {
+        if self
+            .options
+            .execution_role
+            .starts_integrated_server(self.options.server_thread)
+        {
             return self.open_integrated(folder, name, seed, creative, create);
         }
-        self.perf.world_opening();
-        let request = world_loading::WorldRequest {
-            save_root,
-            folder: folder.to_owned(),
-            name: name.map(str::to_owned),
-            seed,
-            creative,
-            create: create.cloned(),
-        };
+        let request = world_loading::WorldRequest::new(folder, name, seed, creative, create)?;
         if self.window.is_some() {
+            self.perf.world_opening();
             if self.title.is_none() {
                 self.title = Some(Title::new(
                     std::env::current_dir()?.join("saves"),
@@ -7550,6 +7567,14 @@ impl Game<'_> {
             )?);
             return Ok(());
         }
+        self.load_world(request)
+    }
+
+    /// Load authoritative world state synchronously, without client entry or
+    /// integrated-server selection. Server startup must use this entry point.
+    fn load_world(&mut self, request: world_loading::WorldRequest) -> Result<()> {
+        self.join_world_rest()?;
+        self.perf.world_opening();
         let prepared = request.prepare(&self.res, &self.pack, &self.options, &self.settings)?;
         self.finish_open_world(prepared)
     }
@@ -7858,8 +7883,12 @@ impl Game<'_> {
             (0..width).all(|i| frame([left[0] + d[0] * i, left[1] + height, left[2] + d[2] * i]));
         ((3..=21).contains(&height) && top_ok).then_some((left, width, height))
     }
-    /// BaseFireBlock.onPlace: lighting fire inside a frame creates a portal.
+    /// BaseFireBlock.onPlace: lighting fire inside a frame creates a portal,
+    /// only in the Overworld and the Nether (`inPortalDimension`).
     fn try_light_portal(&mut self, at: [i32; 3]) -> Result<bool> {
+        if !matches!(self.dim, Dim::Overworld | Dim::Nether) {
+            return Ok(false);
+        }
         for x_axis in [true, false] {
             if let Some((origin, width, height)) = self.portal_shape(at, x_axis) {
                 let d = if x_axis { [1, 0, 0] } else { [0, 0, 1] };
@@ -7963,6 +7992,8 @@ impl Game<'_> {
         self.session_lock = None;
         horizon_client::crash::clear_detail("World");
         self.debug_charts.reset();
+        self.boss_overlay.reset();
+        self.bosses = Default::default();
         self.streaming.paused = true;
         self.world = World::new(self.res.facts().air, 0);
         self.player = None;
@@ -9541,13 +9572,13 @@ impl Game<'_> {
                 let (x, y) = (ox + 9.0 + c as f32 * 18.0, oy + 112.0);
                 let stack = self.inventory[c].clone();
                 self.draw_slot_item(batch, drag.as_ref(), c, stack.clone(), x, y);
-                if let Some(stack) = stack
-                    && self.cursor.0 >= x
+                if self.cursor.0 >= x
                     && self.cursor.0 < x + 16.0
                     && self.cursor.1 >= y
                     && self.cursor.1 < y + 16.0
                 {
-                    hovered = Some(stack);
+                    batch.fill(&self.gui.atlas, x, y, 16.0, 16.0, rgba(255, 255, 255, 128));
+                    hovered = stack;
                 }
             }
             let scrollable = self.creative_screen.rows(&self.pack.names) > 5;
@@ -10064,6 +10095,11 @@ impl Game<'_> {
         } else {
             self.gather_dynamic_lights(camera, alpha);
         }
+        let pack_inputs = if title {
+            Default::default()
+        } else {
+            self.shader_pack_inputs(camera, alpha as f32)
+        };
         let frame = Frame {
             weather: &weather,
             weather_time: horizon_client::weather::Time::new(self.world.game_time, alpha as f32),
@@ -10096,7 +10132,7 @@ impl Game<'_> {
                 if !self.settings.horizon.fog
                     && !underwater
                     && self.darkness_fog().is_none()
-                    && !self.dragon_bar_shown()
+                    && !self.boss_overlay.should_create_world_fog()
                     && self.potions.effects.get("blindness").is_none()
                     && fog.environmental_end >= (self.streaming.radius * 16) as f32
                 {
@@ -10147,6 +10183,7 @@ impl Game<'_> {
             hand: &hand,
             hand_fov_degrees: self.hud_fov_degrees(camera_alpha as f32, camera.to_array()),
             screen: &screen,
+            pack: pack_inputs,
             border,
             game_time: self.world.game_time as f32,
             shader_game_time: ((self.world.game_time % 24000) as f32 + alpha as f32) / 24000.0,
@@ -10167,6 +10204,9 @@ impl Game<'_> {
             darkness: self.darkness_lighting(alpha as f32),
             night_vision: self.night_vision_intensity(),
             block_flicker: self.fog.block_light_flicker,
+            boss_darken: self
+                .boss_overlay
+                .darken_amount(self.clock.fraction() as f32),
             menu_blur: self.menu_blur(),
         };
         let result = match self.renderer.as_mut() {
@@ -10557,7 +10597,7 @@ impl Game<'_> {
         }
         // The loading screen's chunk map fills ring by ring, as vanilla's.
         self.streaming.loading =
-            self.options.dedicated.is_none() && self.loading_reason().is_some();
+            self.options.execution_role.is_client() && self.loading_reason().is_some();
         let (uploads, unloaded) =
             horizon_client::spans::time("streaming", || self.streaming.update(&mut self.world));
         if let Some(lod) = &mut self.lod {
@@ -11394,6 +11434,7 @@ impl ApplicationHandler for Game<'_> {
                     self.track_toggle_screens();
                     // For the "I'm playing" ping: an atomic, sent on when it changes.
                     horizon_client::heartbeat::set_lan(self.is_published());
+                    self.update_discord_presence();
                     let steps = self.clock.advance(elapsed);
                     // The world ticking in the frame: once its ticks took a
                     // tick's length, the rest are dropped (`FixedStep::tick_fits`).
@@ -11676,7 +11717,11 @@ impl<'a> Game<'a> {
         let inventory = vec![None; 36];
         let now = Instant::now();
         let look = options.look;
-        let particles = horizon_client::particles::ParticleEngine::new(&root, &gui.atlas.sprites);
+        let particles = horizon_client::particles::ParticleEngine::new(
+            &root,
+            &gui.atlas.sprites,
+            &gui.atlas.translucent,
+        );
         Ok(Game {
             res: res.clone(),
             rest_loader: None,
@@ -11713,6 +11758,7 @@ impl<'a> Game<'a> {
             carried: None,
             craft_grid: vec![None; 9],
             craft_size: 2,
+            craft_table: None,
             inv_drag: None,
             tweaks: Default::default(),
             inv_clicks: Default::default(),
@@ -11884,6 +11930,8 @@ impl<'a> Game<'a> {
             breath_clouds: Vec::new(),
             dragon_model: prepared.dragon_model,
             map_patches: Vec::new(),
+            text_displays: Default::default(),
+            text_display_vertices: 0,
             skin_downloads: RefCell::new(horizon_client::skins::Downloader::new(
                 std::env::current_dir()
                     .unwrap_or_default()
@@ -11971,6 +12019,7 @@ impl<'a> Game<'a> {
             score: Default::default(),
             fns: Default::default(),
             bosses: Default::default(),
+            boss_overlay: Default::default(),
             exec: Default::default(),
             rand_sequences: Default::default(),
             border: Default::default(),
@@ -12062,6 +12111,8 @@ enum PendingWorldEntry {
     Server {
         address: String,
         name: String,
+        /// A transfer's carried-over server cookies (`TransferState`).
+        cookies: Option<horizon_client::net::Cookies>,
     },
 }
 
@@ -12136,8 +12187,12 @@ impl Game<'_> {
             }) => {
                 self.open_world(&folder, name.as_deref(), seed, creative, create.as_deref())?;
             }
-            Some(PendingWorldEntry::Server { address, name }) => {
-                self.connect_server(&address, &name)?;
+            Some(PendingWorldEntry::Server {
+                address,
+                name,
+                cookies,
+            }) => {
+                self.connect_server_with_cookies(&address, &name, cookies)?;
             }
             None => {}
         }
@@ -12244,7 +12299,7 @@ fn synchronous_startup(options: &Options) -> bool {
         || options.world_frames.is_some()
         || options.benchmark.is_some()
         || options.control.is_some()
-        || options.dedicated.is_some()
+        || !options.execution_role.is_client()
         || std::env::var_os("HORIZON_DISPENSE_FIXTURE").is_some()
         || std::env::var_os("HORIZON_SCULK_FIXTURE").is_some()
         || std::env::var_os("HORIZON_COMMAND_SCRIPT").is_some()
@@ -12689,6 +12744,7 @@ fn loading_frame(hud: &HudBatch) -> Frame<'_> {
         hand: &[],
         hand_fov_degrees: 70.0,
         screen: &[],
+        pack: Default::default(),
         border: None,
         game_time: 0.0,
         shader_game_time: 0.0,
@@ -12698,6 +12754,7 @@ fn loading_frame(hud: &HudBatch) -> Frame<'_> {
         darkness: (0.0, 0.0),
         night_vision: 0.0,
         block_flicker: 0.0,
+        boss_darken: 0.0,
         menu_blur: None,
     }
 }
@@ -12785,7 +12842,7 @@ fn start_game<'a>(
         game.sculk_fixture(&spec)?;
         return Ok(None);
     }
-    if game.options.dedicated.is_some() {
+    if game.options.execution_role == execution_role::ExecutionRole::DedicatedServer {
         game.run_dedicated()?;
         return Ok(None);
     }
@@ -12860,6 +12917,7 @@ fn write_report(game: &Game<'_>) -> Result<()> {
 
 fn run_event_loop(mut game: Game<'_>) -> Result<()> {
     EventLoop::new()?.run_app(&mut game)?;
+    horizon_client::discord_presence::stop();
     write_report(&game)?;
     if let Some(e) = game.error.take() {
         return Err(e);
@@ -13062,7 +13120,7 @@ impl Loading {
         );
         let renderer_ms = renderer_at.elapsed().as_millis();
         // Audio is created on the main thread, after the core is ready.
-        let audio = if options.dedicated.is_some() {
+        let audio = if !options.execution_role.is_client() {
             Audio::silent(&options.resources)
         } else {
             Audio::new(&options.resources)
@@ -13217,6 +13275,7 @@ fn run_loading(
     };
     let mut app = App::Loading(Box::new(loading));
     EventLoop::new()?.run_app(&mut app)?;
+    horizon_client::discord_presence::stop();
     match app {
         App::Ready(mut game) => {
             write_report(&game)?;
@@ -13237,13 +13296,15 @@ pub fn run() -> Result<()> {
     let Some(mut options) = Options::read()? else {
         return Ok(());
     };
-    if options.dedicated.is_some() && !dedicated::preflight(&mut options)? {
+    if options.execution_role == execution_role::ExecutionRole::DedicatedServer
+        && !dedicated::preflight(&mut options)?
+    {
         return Ok(());
     }
     // Before any worker starts: on Linux they go behind the server thread
     // and the render thread.
     horizon_threads::put_helpers_behind();
-    if options.dedicated.is_none() {
+    if options.execution_role.is_client() {
         // The render thread, like the server thread, ahead of the workers on
         // macOS and Windows. While terrain loads, the worker pools (two with
         // single player's server thread) and other programs outnumber the
@@ -13253,7 +13314,7 @@ pub fn run() -> Result<()> {
     }
     // Someone is playing: the anonymous ping behind the launcher's "N playing now". Not for a
     // server, a benchmark or a run that quits by itself.
-    if options.dedicated.is_none()
+    if options.execution_role.is_client()
         && options.benchmark.is_none()
         && !options.offscreen
         && options.frames.is_none()
@@ -13265,6 +13326,14 @@ pub fn run() -> Result<()> {
     horizon_client::spans::enable(options.spikes.is_some());
     let vanilla_root = options.resources.clone();
     let early_settings = Settings::load(&std::env::current_dir()?.join("options.txt"));
+    // "Playing Horizon" on Discord: never for a server; an automated run only talks to a test's fake Discord.
+    if options.dedicated.is_none() {
+        let automated = options.benchmark.is_some()
+            || options.offscreen
+            || options.frames.is_some()
+            || options.world_frames.is_some();
+        horizon_client::discord_presence::start(early_settings.extras.discord_presence, automated);
+    }
     // Snapshots of derived tables live in the game folder, never beside the
     // shared resources.
     Behaviours::set_cache_dir(std::env::current_dir()?.join(".horizon-cache"));
@@ -13294,7 +13363,7 @@ pub fn run() -> Result<()> {
     )?;
     let gui = loaded.gui.ok_or("missing menu bundle")?;
     options.resources = loaded.root.clone();
-    let audio = if options.dedicated.is_some() {
+    let audio = if !options.execution_role.is_client() {
         Audio::silent(&options.resources)
     } else {
         Audio::new(&options.resources)

crates/horizon-client/src/game/advancements.rs

@@ -881,30 +881,40 @@ pub(super) fn adv_name(a: &adv::Advancement) -> Text {
     let Some(d) = &a.display else {
         return Text::literal(a.id.clone());
     };
-    let color = match d.frame {
-        Frame::Challenge => text::DARK_PURPLE,
-        _ => text::GREEN,
-    };
-    // Advancement.decorateName: the title in the frame's colour (styles
-    // merged into it), a new line and the description.
-    let coloured = text_of(&d.title).with_color(color);
-    let mut component = coloured.component();
-    if let Some(o) = component.as_object_mut() {
-        o.insert(
-            "extra".into(),
-            serde_json::json!(["\n", text_of(&d.description).component()]),
-        );
-    }
-    let tooltip = coloured
-        .append("\n")
-        .append(text_of(&d.description))
-        .with_component(component);
+    let color = frame_color(d.frame);
     let title = text_of(&d.title).with_style(&Style {
-        hover: Some(Box::new(tooltip)),
+        hover: Some(Box::new(decorate_name(d))),
         ..Style::default()
     });
     Text::translate("chat.square_brackets", &[title]).with_color(color)
 }
+fn frame_color(frame: Frame) -> u32 {
+    match frame {
+        Frame::Challenge => text::DARK_PURPLE,
+        _ => text::GREEN,
+    }
+}
+/// `Advancement.decorateName`: a copy of the title with the frame's colour
+/// under its own style (mergeStyles), then a new line and the description
+/// after the title's own siblings, so both inherit the title's root style.
+/// Built on the title's JSON (a list as its first element with the rest as
+/// siblings): a parsed Text moves a styled root's style down a level once it
+/// has siblings.
+fn decorate_name(d: &adv::Display) -> Text {
+    let mut component = match horizon_client::scoreboard::canonical_component(&d.title) {
+        Value::String(s) => serde_json::json!({ "text": s }),
+        c => c,
+    };
+    if let Some(o) = component.as_object_mut() {
+        let frame = Text::empty().with_color(frame_color(d.frame)).component();
+        o.entry("color").or_insert_with(|| frame["color"].clone());
+        let extra = o.entry("extra").or_insert_with(|| serde_json::json!([]));
+        if let Some(extra) = extra.as_array_mut() {
+            extra.extend(["\n".into(), d.description.clone()]);
+        }
+    }
+    text_of(&component).with_component(component)
+}
 impl Game<'_> {
     /// `AdvancementCommands.Action.GRANT` on one advancement (or one of
     /// its criteria): false when nothing changed.
@@ -1051,17 +1061,10 @@ impl Game<'_> {
         }
     }
 }
-/// A text component from advancement JSON (`translate` or `text`).
+/// An advancement's title or description: a whole component (ComponentSerialization.CODEC),
+/// with its siblings and styles, as a plugin's `{"text":"","extra":[...]}` needs.
 pub(super) fn text_of(v: &Value) -> Text {
-    if let Some(key) = v["translate"].as_str() {
-        Text::translate(key, &[])
-    } else if let Some(s) = v["text"].as_str() {
-        Text::literal(s)
-    } else if let Some(s) = v.as_str() {
-        Text::literal(s)
-    } else {
-        Text::empty()
-    }
+    horizon_client::scoreboard::comp_text(v)
 }
 
 #[cfg(test)]
@@ -1095,6 +1098,105 @@ mod tests {
         (seen, None)
     }
 
+    #[test]
+    fn titles_keep_their_siblings_and_styles() {
+        let title = text_of(&serde_json::json!({
+            "text": "",
+            "extra": [{"text": "Quest ", "color": "gold"}, "Board"],
+        }));
+        assert_eq!(title.plain(), "Quest Board");
+        assert_eq!(title.spans[0].style.color, Some(text::GOLD));
+        assert_eq!(title.spans[1].style.color, None);
+        let vanilla = text_of(&serde_json::json!({"translate": "advancements.story.root.title"}));
+        assert_eq!(
+            vanilla,
+            Text::translate("advancements.story.root.title", &[])
+        );
+        assert_eq!(
+            vanilla.translation_key(),
+            Some("advancements.story.root.title")
+        );
+    }
+
+    fn announced(title: Value, description: Value) -> adv::Advancement {
+        adv::Advancement {
+            id: "quests:board".into(),
+            parent: None,
+            display: Some(adv::Display {
+                icon: "minecraft:book".into(),
+                title,
+                description,
+                frame: Frame::Task,
+                background: None,
+                show_toast: true,
+                announce: true,
+                hidden: false,
+            }),
+            criteria: Vec::new(),
+            requirements: Vec::new(),
+            rewards: adv::Rewards::default(),
+        }
+    }
+    /// The chat hover: the JSON a client receives, and the spans drawn here.
+    fn hover(a: &adv::Advancement) -> (Value, Text) {
+        let local = decorate_name(a.display.as_ref().unwrap());
+        let sent = adv_name(a).component()["with"][0]["hover_event"]["value"].clone();
+        (sent, local)
+    }
+
+    #[test]
+    fn chat_hover_keeps_the_titles_siblings_before_the_description() {
+        let a = announced(
+            serde_json::json!({"text": "", "extra": [{"text": "Quest ", "color": "gold"}, "Board"]}),
+            serde_json::json!("Open the board"),
+        );
+        let (sent, local) = hover(&a);
+        let sent = horizon_client::scoreboard::comp_text(&sent);
+        assert_eq!(sent.plain(), "Quest Board\nOpen the board");
+        let colors = |t: &Text| t.spans.iter().map(|s| s.style.color).collect::<Vec<_>>();
+        let (gold, green) = (Some(text::GOLD), Some(text::GREEN));
+        assert_eq!(colors(&sent), [gold, green, green, green]);
+        // The spans drawn here come from the same JSON a client receives.
+        assert_eq!(colors(&local), colors(&sent));
+    }
+
+    #[test]
+    fn chat_hover_description_takes_a_styled_titles_own_style() {
+        // mergeStyles keeps the title's gold; the description inherits it.
+        let object = announced(
+            serde_json::json!({"text": "Quest", "color": "gold", "bold": true, "extra": [" Board"]}),
+            serde_json::json!("Open the board"),
+        );
+        let list = announced(
+            serde_json::json!([{"text": "Quest", "color": "gold", "bold": true}, " Board"]),
+            serde_json::json!("Open the board"),
+        );
+        for a in [object, list] {
+            let (sent, local) = hover(&a);
+            let sent = horizon_client::scoreboard::comp_text(&sent);
+            assert_eq!(sent.plain(), "Quest Board\nOpen the board");
+            let last = &sent.spans.last().unwrap().style;
+            assert_eq!((last.color, last.bold), (Some(text::GOLD), Some(true)));
+            assert_eq!(local.spans.last().unwrap().style, *last);
+        }
+    }
+
+    #[test]
+    fn chat_hover_of_a_vanilla_advancement() {
+        let a = announced(
+            serde_json::json!({"translate": "advancements.story.root.title"}),
+            serde_json::json!({"translate": "advancements.story.root.description"}),
+        );
+        assert_eq!(
+            hover(&a).0,
+            serde_json::json!({
+                "translate": "advancements.story.root.title",
+                "color": "green",
+                "extra": ["\n", {"translate": "advancements.story.root.description"}],
+            })
+        );
+    }
+
     #[test]
     fn toasts_slide_in_squared_and_out_after_five_seconds() {
         let mut toast = recipes(1);

crates/horizon-client/src/game/agent.rs

@@ -469,7 +469,8 @@ impl Game<'_> {
                 "flying": p.flying,
                 "fall_flying": p.fall_flying,
                 "sneaking": self.keys.contains(&KeyCode::ShiftLeft),
-                "sprinting": self.keys.contains(&KeyCode::ControlLeft),
+                "sprinting": p.sprinting,
+                "fov_modifier": self.view.fov_modifier,
                 "health": p.health.health(),
                 "absorption": p.health.absorption(),
                 // The hurt animation's ticks left (the camera's hurt tilt).
@@ -1598,8 +1599,12 @@ impl Game<'_> {
                 if self.screen != Screen::Dead {
                     return Err("respawn needs the death screen".into());
                 }
-                let label =
-                    horizon_client::text::Text::translate("deathScreen.respawn", &[]).plain();
+                let key = if self.level.hardcore {
+                    "deathScreen.spectate"
+                } else {
+                    "deathScreen.respawn"
+                };
+                let label = horizon_client::text::Text::translate(key, &[]).plain();
                 let w = widgets::find(&widgets::last(), &label)?;
                 if !w.enabled {
                     // DeathScreen enables its buttons after 20 ticks.

crates/horizon-client/src/game/block_entity_ticks.rs

@@ -15,6 +15,8 @@ use horizon_world::registry::BlockStateId;
 impl Game<'_> {
     pub(super) fn tick_block_entities(&mut self) -> Result<()> {
         self.tick_mount_menu();
+        self.tick_craft_table();
+        self.tick_container_reach();
         self.load_entity_types();
         if !self.world.block_entities.has_states() {
             let states = self.ticking_states();

crates/horizon-client/src/game/bossbars.rs

@@ -1,22 +1,29 @@
 //! `/bossbar` (BossBarCommands) and drawing the custom boss bars.
 use super::{
-    Game,
-    commands::{R, err},
+    Dim, Game,
+    commands::{R, Target, err},
 };
 use horizon_client::{
+    boss_overlay,
     bossbar::{self, BossBars},
     command::{Arg, Context},
-    hud_overlays, save,
-    scoreboard::{self as sb, Comp, comp_text},
+    mobs::Species,
+    save,
+    scoreboard::{self as sb, Comp, json_to_tag},
     scoreboard_cmd::format_list,
     text::Text,
 };
+use horizon_core::random::RandomSource;
+use horizon_protocol::packets::play::{self, BossAction, Clientbound as C};
 use horizon_world::nbt::Tag;
+use std::collections::{HashMap, HashSet};
 
 #[derive(Default)]
 pub(super) struct BossState {
     pub bars: BossBars,
     loaded: bool,
+    /// What each viewer was last sent, so a change becomes one packet.
+    sent: HashMap<u128, HashMap<u128, Offer>>,
 }
 
 fn num(n: impl std::fmt::Display) -> Text {
@@ -36,7 +43,7 @@ impl Game<'_> {
         if let Some(root) = save::read_dat(&self.bossbar_path())
             && let Some(data) = root.get("data")
         {
-            self.bosses.bars = BossBars::unpack(data, self.level.player_uuid);
+            self.bosses.bars = BossBars::unpack(data);
         }
         self.ui.registries.bossbars = self.bosses.bars.ids();
     }
@@ -47,13 +54,15 @@ impl Game<'_> {
         if self.bosses.bars.bars.is_empty() && !self.bossbar_path().exists() {
             return;
         }
-        let _ = save::write_dat(
+        if let Err(e) = save::write_dat(
             &self.bossbar_path(),
             Tag::compound([
-                ("data", self.bosses.bars.pack(self.level.player_uuid)),
+                ("data", self.bosses.bars.pack()),
                 ("DataVersion", Tag::Int(horizon_world::DATA_VERSION)),
             ]),
-        );
+        ) {
+            log::warn!("boss bars were not written: {e}");
+        }
     }
     pub(in crate::game) fn bossbar_exists(&self, id: &str) -> bool {
         self.bosses.bars.get(id).is_some()
@@ -68,6 +77,7 @@ impl Game<'_> {
                 b.value = b.value.min(b.max);
             }
         }
+        self.publish_boss_bars();
     }
     fn bar_id(ctx: &Context) -> String {
         match ctx.get("id") {
@@ -86,6 +96,7 @@ impl Game<'_> {
         self.load_bossbars();
         let result = self.bossbar_command(id, ctx);
         self.ui.registries.bossbars = self.bosses.bars.ids();
+        self.publish_boss_bars();
         result
     }
     fn bossbar_command(&mut self, id: &str, ctx: &Context) -> R<i32> {
@@ -97,6 +108,10 @@ impl Game<'_> {
                 }
                 let name = self.component_json(ctx, "name")?;
                 self.bosses.bars.add(&bar, name);
+                if let Some(b) = self.bosses.bars.get_mut(&bar) {
+                    // CustomBossEvents.create: Mth.createInsecureUUID(level.random).
+                    b.uuid = insecure_uuid(&mut self.world.random);
+                }
                 let shown = self
                     .bosses
                     .bars
@@ -173,19 +188,20 @@ impl Game<'_> {
                         i32::from(b.visible)
                     }
                     _ => {
-                        if b.player {
-                            let name = self.target_name(super::commands::Target::Player);
-                            self.feedback(Text::translate(
-                                "commands.bossbar.get.players.some",
-                                &[s, num(1), format_list(vec![name])],
-                            ));
-                        } else {
+                        let names = self.bossbar_player_names(&b.players);
+                        let n = names.len();
+                        if n == 0 {
                             self.feedback(Text::translate(
                                 "commands.bossbar.get.players.none",
                                 &[s],
                             ));
+                        } else {
+                            self.feedback(Text::translate(
+                                "commands.bossbar.get.players.some",
+                                &[s, num(n), format_list(names)],
+                            ));
                         }
-                        i32::from(b.player)
+                        n as i32
                     }
                 })
             }
@@ -295,31 +311,46 @@ impl Game<'_> {
                 Ok(0)
             }
             _ => {
-                // players [<targets>]
-                let include = if ctx.get("targets").is_some() {
-                    !self.entities(ctx, "targets", true)?.is_empty()
+                // players [<targets>]: replace the set. No argument clears it.
+                let targets = if ctx.get("targets").is_some() {
+                    self.entities(ctx, "targets", true)?
                 } else {
-                    false
+                    Vec::new()
                 };
+                let mut uuids = Vec::new();
+                let mut names = Vec::new();
+                for t in &targets {
+                    let Some(uuid) = self.player_target_uuid(*t) else {
+                        continue;
+                    };
+                    if !uuids.contains(&uuid) {
+                        uuids.push(uuid);
+                        names.push(self.target_name(*t));
+                    }
+                }
                 let b = self.bosses.bars.get_mut(bar).expect("checked");
-                if b.player == include {
+                let mut had = b.players.clone();
+                had.sort();
+                let mut next = uuids.clone();
+                next.sort();
+                if had == next {
                     return Err(err("commands.bossbar.set.players.unchanged", &[]));
                 }
-                b.player = include;
+                b.players = uuids;
+                let n = b.players.len();
                 let s = shown(self);
-                if include {
-                    let name = self.target_name(super::commands::Target::Player);
-                    self.feedback(Text::translate(
-                        "commands.bossbar.set.players.success.some",
-                        &[s, num(1), format_list(vec![name])],
-                    ));
-                } else {
+                if n == 0 {
                     self.feedback(Text::translate(
                         "commands.bossbar.set.players.success.none",
                         &[s],
                     ));
+                } else {
+                    self.feedback(Text::translate(
+                        "commands.bossbar.set.players.success.some",
+                        &[s, num(targets.len()), format_list(names)],
+                    ));
                 }
-                Ok(i32::from(include))
+                Ok(n as i32)
             }
         }
     }
@@ -333,29 +364,316 @@ impl Game<'_> {
         Ok(self.resolve_component(value))
     }
 
-    // ---- drawing ------------------------------------------------------------------
-
-    /// The visible custom bars (`/bossbar`), after the built-in ones.
-    pub(super) fn custom_bossbars(&self, bars: &mut Vec<hud_overlays::BossBar>) {
-        for b in self
-            .bosses
-            .bars
-            .bars
-            .iter()
-            .filter(|b| b.visible && b.player)
-        {
-            bars.push(hud_overlays::BossBar {
-                name: comp_text(&b.name),
-                progress: b.progress(),
-                color: bossbar::COLORS
+    /// Names of the online players in a boss bar's set, in join order.
+    fn bossbar_player_names(&self, players: &[[i32; 4]]) -> Vec<Text> {
+        self.known_boss_players()
+            .into_iter()
+            .filter(|(uuid, _)| players.contains(uuid))
+            .map(|(_, name)| name)
+            .collect()
+    }
+    /// The players who can be told about a bar: the one in place, then guests.
+    fn known_boss_players(&self) -> Vec<([i32; 4], Text)> {
+        let mut out = Vec::new();
+        if self.player.is_some() {
+            out.push((self.acting_uuid(), self.target_name(Target::Player)));
+        }
+        if let Some(host) = &self.lan {
+            for g in host.hub.guests.iter().filter(|g| g.placed) {
+                let ints = horizon_client::lan::playerdata::uuid_ints(g.uuid);
+                if out.iter().any(|(uuid, _)| *uuid == ints) {
+                    continue;
+                }
+                out.push((ints, Text::literal(g.name.clone())));
+            }
+        }
+        out
+    }
+    fn player_target_uuid(&self, target: Target) -> Option<[i32; 4]> {
+        match target {
+            Target::Player => Some(self.acting_uuid()),
+            Target::Guest(conn) => self.lan.as_ref().and_then(|h| {
+                h.hub
+                    .guests
                     .iter()
-                    .position(|c| *c == b.color)
-                    .unwrap_or(0),
-                overlay: bossbar::STYLES
-                    .iter()
-                    .position(|s| *s == b.style)
-                    .unwrap_or(0),
-            });
+                    .find(|g| g.conn == conn)
+                    .map(|g| horizon_client::lan::playerdata::uuid_ints(g.uuid))
+            }),
+            _ => None,
         }
     }
+
+    // ---- ServerBossEvent delivery ------------------------------------------------
+
+    /// Tell every viewer the boss events they should be seeing. The window
+    /// that simulates the world applies them to its own overlay; everyone
+    /// else gets `ClientboundBossEventPacket`s.
+    pub(super) fn publish_boss_bars(&mut self) {
+        if self.remote.is_some() {
+            return;
+        }
+        self.load_bossbars();
+        let now = boss_overlay::now_millis();
+        let viewers = self.boss_viewers();
+        let live: HashSet<u128> = viewers.iter().map(|v| v.uuid).collect();
+        self.bosses.sent.retain(|id, _| live.contains(id));
+        let mut packets = Vec::new();
+        for viewer in &viewers {
+            let desired = self.boss_events_for(viewer);
+            for event in self.diff_boss_events(viewer, desired) {
+                if viewer.local {
+                    self.boss_overlay.apply(&event, now);
+                } else if let Some(conn) = viewer.conn {
+                    packets.push((conn, C::BossEvent(event)));
+                }
+            }
+        }
+        if packets.is_empty() {
+            return;
+        }
+        let Some(host) = self.lan.as_ref() else {
+            return;
+        };
+        for (conn, packet) in &packets {
+            host.hub.send_to(*conn, packet);
+        }
+    }
+    fn boss_viewers(&self) -> Vec<Viewer> {
+        let mut out = Vec::new();
+        // While `as_guest` has swapped a guest in, the host's own position
+        // is not in place. Their overlay updates once the tick puts it back.
+        let local =
+            self.serving.is_none() && self.options.dedicated.is_none() && self.lan_acting.is_none();
+        if local && let Some(p) = &self.player {
+            let ints = self.level.player_uuid.unwrap_or_else(|| self.acting_uuid());
+            out.push(Viewer {
+                uuid: horizon_client::lan::playerdata::ints_uuid(ints),
+                ints,
+                at: [p.position.x, p.position.y, p.position.z],
+                alive: !p.health.dead_or_dying(),
+                here: true,
+                local: true,
+                conn: None,
+                view_chunks: self.settings.render_distance,
+            });
+        }
+        if let Some(host) = &self.lan {
+            for g in host.hub.guests.iter().filter(|g| g.placed) {
+                if out.iter().any(|v| v.uuid == g.uuid) {
+                    continue;
+                }
+                out.push(Viewer {
+                    uuid: g.uuid,
+                    ints: horizon_client::lan::playerdata::uuid_ints(g.uuid),
+                    at: g.position,
+                    alive: !g.dead,
+                    here: g.dimension == self.dim.id(),
+                    local: false,
+                    conn: Some(g.conn),
+                    view_chunks: g.view_distance,
+                });
+            }
+        }
+        out
+    }
+    /// Custom bars (`CustomBossEvents.onPlayerConnect` sends them as a player
+    /// joins), then the dragon, withers and the raid.
+    fn boss_events_for(&self, viewer: &Viewer) -> Vec<Offer> {
+        let mut out = Vec::new();
+        for b in &self.bosses.bars.bars {
+            if !b.visible || !b.players.contains(&viewer.ints) {
+                continue;
+            }
+            out.push(Offer {
+                id: b.uuid,
+                name: json_to_tag(&b.name),
+                progress: b.progress(),
+                color: color_index(&b.color),
+                overlay: style_index(&b.style),
+                darken: b.darken,
+                music: b.music,
+                fog: b.fog,
+                scope: Scope::Global,
+            });
+        }
+        if viewer.here
+            && let Some(progress) = self.dragon_boss_progress(viewer.at, viewer.alive)
+        {
+            out.push(Offer {
+                id: bossbar::stable_uuid("minecraft:ender_dragon"),
+                name: translate_tag("entity.minecraft.ender_dragon"),
+                progress,
+                color: 0,
+                overlay: 0,
+                darken: false,
+                music: true,
+                fog: true,
+                scope: Scope::Level(self.dim),
+            });
+        }
+        if viewer.here {
+            let range = f64::from(10.min(viewer.view_chunks.max(0)) * 16);
+            for m in self
+                .mobs
+                .iter()
+                .filter(|m| m.species() == Species::Wither && m.alive() && !m.removed)
+            {
+                let (dx, dz) = (m.position.x - viewer.at[0], m.position.z - viewer.at[2]);
+                if dx * dx + dz * dz > range * range {
+                    continue;
+                }
+                let progress = if m.extra.counter > 0 {
+                    1.0 - m.extra.counter as f32 / horizon_client::mobs::wither::INVULNERABLE as f32
+                } else {
+                    (m.health / m.attrs.max_health).clamp(0.0, 1.0)
+                };
+                let name = if let Some(text) = &m.custom_name_text {
+                    json_to_tag(&text.component())
+                } else if let Some(name) = &m.custom_name {
+                    Tag::String(name.as_str().into())
+                } else {
+                    translate_tag("entity.minecraft.wither")
+                };
+                out.push(Offer {
+                    id: super::lan::entity_uuid(m.id),
+                    name,
+                    progress,
+                    color: 5,
+                    overlay: 0,
+                    darken: true,
+                    music: false,
+                    fog: false,
+                    scope: Scope::Level(self.dim),
+                });
+            }
+        }
+        if viewer.here
+            && let Some((id, name, progress)) = self.raid_boss_at(viewer.at, viewer.alive)
+        {
+            out.push(Offer {
+                id: bossbar::stable_uuid(&format!("raid:{id}")),
+                name,
+                progress,
+                color: 2,
+                overlay: 2,
+                darken: false,
+                music: false,
+                fog: false,
+                scope: Scope::Level(self.dim),
+            });
+        }
+        out
+    }
+    /// The packets that take `viewer` from what it was last sent to `desired`
+    /// (`ServerBossEvent`'s broadcasts).
+    fn diff_boss_events(&mut self, viewer: &Viewer, desired: Vec<Offer>) -> Vec<play::BossEvent> {
+        let full = viewer.local;
+        let dim = self.dim;
+        let sent = self.bosses.sent.entry(viewer.uuid).or_default();
+        let mut out = Vec::new();
+        let event = |id, action| play::BossEvent { id, action };
+        sent.retain(|id, prev| {
+            let owned = full || prev.scope == Scope::Global || prev.scope == Scope::Level(dim);
+            let keep = !owned || desired.iter().any(|e| e.id == *id);
+            if !keep {
+                out.push(event(*id, BossAction::Remove));
+            }
+            keep
+        });
+        for offer in desired {
+            let Some(prev) = sent.get(&offer.id) else {
+                out.push(event(
+                    offer.id,
+                    BossAction::Add {
+                        name: offer.name.clone(),
+                        progress: offer.progress,
+                        color: offer.color,
+                        overlay: offer.overlay,
+                        darken: offer.darken,
+                        music: offer.music,
+                        fog: offer.fog,
+                    },
+                ));
+                sent.insert(offer.id, offer);
+                continue;
+            };
+            let id = offer.id;
+            if prev.progress != offer.progress {
+                let progress = offer.progress;
+                out.push(event(id, BossAction::UpdateProgress { progress }));
+            }
+            if prev.name != offer.name {
+                let name = offer.name.clone();
+                out.push(event(id, BossAction::UpdateName { name }));
+            }
+            if (prev.color, prev.overlay) != (offer.color, offer.overlay) {
+                let (color, overlay) = (offer.color, offer.overlay);
+                out.push(event(id, BossAction::UpdateStyle { color, overlay }));
+            }
+            if (prev.darken, prev.music, prev.fog) != (offer.darken, offer.music, offer.fog) {
+                let (darken, music, fog) = (offer.darken, offer.music, offer.fog);
+                out.push(event(
+                    id,
+                    BossAction::UpdateProperties { darken, music, fog },
+                ));
+            }
+            sent.insert(id, offer);
+        }
+        out
+    }
+    /// `ClientPacketListener.handleBossUpdate`.
+    pub(super) fn apply_boss_event(&mut self, packet: &play::BossEvent) {
+        self.boss_overlay.apply(packet, boss_overlay::now_millis());
+    }
+}
+
+/// `Mth.createInsecureUUID`.
+fn insecure_uuid(random: &mut impl RandomSource) -> u128 {
+    let most = random.next_long() & -61441 | 16384;
+    let least = random.next_long() & 4_611_686_018_427_387_903 | i64::MIN;
+    ((most as u64 as u128) << 64) | (least as u64 as u128)
+}
+fn translate_tag(key: &str) -> Tag {
+    Tag::compound([("translate", Tag::String(key.into()))])
+}
+fn color_index(color: &str) -> i32 {
+    bossbar::COLORS
+        .iter()
+        .position(|c| *c == color)
+        .unwrap_or(6) as i32
+}
+fn style_index(style: &str) -> i32 {
+    bossbar::STYLES
+        .iter()
+        .position(|s| *s == style)
+        .unwrap_or(0) as i32
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Scope {
+    Global,
+    Level(Dim),
+}
+struct Viewer {
+    uuid: u128,
+    ints: [i32; 4],
+    at: [f64; 3],
+    alive: bool,
+    here: bool,
+    local: bool,
+    conn: Option<u32>,
+    view_chunks: i32,
+}
+/// A boss event as one viewer should see it, and as it was last sent.
+struct Offer {
+    id: u128,
+    name: Tag,
+    progress: f32,
+    /// `BossBarColor` and `BossBarOverlay` ordinals.
+    color: i32,
+    overlay: i32,
+    darken: bool,
+    music: bool,
+    fog: bool,
+    scope: Scope,
 }

crates/horizon-client/src/game/chat.rs

@@ -570,8 +570,14 @@ impl Game<'_> {
     /// ChatScreen.handleChatInput: history, then a command or a chat line.
     pub(super) fn handle_chat_input(&mut self, message: &str) {
         self.ui.chat.add_recent(message);
-        // On a server (single player's own included) the server runs it.
+        // On a server (single player's own included) the server runs it,
+        // unless a client mod owns the command.
         if self.remote.is_some() {
+            if let Some(command) = message.strip_prefix('/')
+                && self.mod_command(command)
+            {
+                return;
+            }
             self.send_chat(message);
             return;
         }
@@ -580,7 +586,7 @@ impl Game<'_> {
         } else {
             let line = Text::translate(
                 "chat.type.text",
-                &[Text::literal(PLAYER_NAME), Text::literal(message)],
+                &[self.player_display_name(), Text::literal(message)],
             );
             let focused = self.screen == Screen::Chat;
             let heard = self.mods.running().then(|| line.plain());
@@ -816,8 +822,12 @@ impl Game<'_> {
             ("data", data),
             ("DataVersion", Tag::Int(horizon_world::DATA_VERSION)),
         ]);
-        let _ = horizon_client::save::write_dat(&path, root);
-        let _ = write_difficulty(&self.world_root, self.ui.difficulty);
+        if let Err(e) = horizon_client::save::write_dat(&path, root) {
+            log::warn!("the world clocks were not written: {e}");
+        }
+        if let Err(e) = write_difficulty(&self.world_root, self.ui.difficulty) {
+            log::warn!("the difficulty was not written: {e}");
+        }
     }
     /// Death message in chat (CombatTracker.getDeathMessage, as far as the
     /// cause is known to the client).

crates/horizon-client/src/game/commands.rs

@@ -42,7 +42,8 @@ pub(super) enum Target {
     Mob(u32),
     Item(u32),
     Orb(usize),
-    Arrow(usize),
+    /// By index in `creatures.projectiles`.
+    Projectile(usize),
     Stand(u32),
     Frame(u32),
     Painting(u32),
@@ -213,7 +214,7 @@ impl Game<'_> {
     }
     /// Player.getDisplayName: the name (team-formatted), suggesting a
     /// `/tell`, showing the player on hover, inserting the name.
-    fn player_display_name(&self) -> Text {
+    pub(super) fn player_display_name(&self) -> Text {
         let name = self.acting_player_name().to_owned();
         let Some(uuid) = self.lan_acting_uuid else {
             return self.target_name(Target::Player);
@@ -327,7 +328,7 @@ impl Game<'_> {
                 .orbs
                 .get(i)
                 .map(|o| [o.position.x, o.position.y, o.position.z]),
-            Target::Arrow(i) => self
+            Target::Projectile(i) => self
                 .creatures
                 .projectiles
                 .get(i)
@@ -382,7 +383,11 @@ impl Game<'_> {
                 }),
             Target::Item(_) => "minecraft:item".into(),
             Target::Orb(_) => "minecraft:experience_orb".into(),
-            Target::Arrow(_) => "minecraft:arrow".into(),
+            Target::Projectile(i) => self
+                .creatures
+                .projectiles
+                .get(i)
+                .map_or_else(String::new, |p| p.kind.id().into()),
             Target::Stand(_) => "minecraft:armor_stand".into(),
             Target::Frame(id) => {
                 if self.item_frames.iter().any(|f| f.id == id && f.glow) {
@@ -503,6 +508,7 @@ impl Game<'_> {
             _ => {}
         }
         if s.kind != 's' {
+            use horizon_client::projectiles::ProjectileKind as K;
             candidates.extend(self.player_candidates(s));
             candidates.extend(
                 self.mobs
@@ -517,8 +523,12 @@ impl Game<'_> {
                     .projectiles
                     .iter()
                     .enumerate()
-                    .filter(|(_, p)| p.arrow.is_some())
-                    .map(|(i, _)| Target::Arrow(i)),
+                    // The kinds /data can write (entity_nbt).
+                    .filter(|(_, p)| {
+                        p.arrow.is_some()
+                            || matches!(p.kind, K::LargeFireball { .. } | K::SmallFireball)
+                    })
+                    .map(|(i, _)| Target::Projectile(i)),
             );
             candidates.extend(self.armor_stands.iter().map(|a| Target::Stand(a.id)));
             candidates.extend(self.item_frames.iter().map(|f| Target::Frame(f.id)));
@@ -1082,6 +1092,8 @@ impl Game<'_> {
                 self.for_player(t, |g| g.teleport_to(Target::Player, pos, rotation));
             }
             Target::Player => {
+                // ServerPlayer.teleport: removeVehicle before placing the player.
+                self.stop_riding();
                 if let Some(p) = self.player.as_mut() {
                     p.position = v;
                     p.velocity = Vec3::new(0.0, 0.0, 0.0);
@@ -1098,9 +1110,15 @@ impl Game<'_> {
                 if let Some(m) = self.mobs.iter_mut().find(|m| m.id == id) {
                     m.position = v;
                     m.previous = v;
-                    if let Some([yaw, _]) = rotation {
+                    // Entity.teleportSetPosition: setYRot, setYHeadRot, setXRot
+                    // (clamped to -90..90), then setOldRot.
+                    if let Some([yaw, pitch]) = rotation {
                         m.yaw = yaw;
                         m.body_yaw = yaw;
+                        m.head_yaw = yaw;
+                        m.head_pitch = pitch.clamp(-90.0, 90.0);
+                        m.previous_yaw = m.yaw;
+                        m.previous_head_pitch = m.head_pitch;
                     }
                 }
             }
@@ -1116,7 +1134,7 @@ impl Game<'_> {
                     o.previous = v;
                 }
             }
-            Target::Arrow(i) => {
+            Target::Projectile(i) => {
                 if let Some(a) = self.creatures.projectiles.get_mut(i) {
                     a.position = v;
                     a.previous = v;
@@ -1540,14 +1558,10 @@ impl Game<'_> {
                     self.orbs[i].age = u32::MAX / 2;
                 }
             }
-            Target::Arrow(i) => {
-                if let Some(a) = self
-                    .creatures
-                    .projectiles
-                    .get_mut(i)
-                    .and_then(|p| p.arrow.as_mut())
-                {
-                    a.removed = true;
+            // cmd_kill goes from the highest index down.
+            Target::Projectile(i) => {
+                if i < self.creatures.projectiles.len() {
+                    self.creatures.projectiles.remove(i);
                 }
             }
             Target::Stand(id) => self.armor_stands.retain(|a| a.id != id),
@@ -1569,7 +1583,7 @@ impl Game<'_> {
         let mut ordered = targets.clone();
         ordered.sort_by_key(|t| {
             std::cmp::Reverse(match t {
-                Target::Orb(i) | Target::Arrow(i) => *i,
+                Target::Orb(i) | Target::Projectile(i) => *i,
                 _ => 0,
             })
         });
@@ -1577,9 +1591,6 @@ impl Game<'_> {
             self.kill_target(t);
         }
         self.orbs.retain(|o| o.age < u32::MAX / 2);
-        self.creatures
-            .projectiles
-            .retain(|p| !p.arrow.as_ref().is_some_and(|a| a.removed));
         let message = if targets.len() == 1 {
             Text::translate("commands.kill.success.single", &[names[0].clone()])
         } else {
@@ -2798,7 +2809,7 @@ impl Game<'_> {
         let name = match self.command_source.map(|s| s.entity) {
             Some(Some(t)) => self.target_name(t),
             Some(None) => Text::literal("Server"),
-            None => Text::literal(self.acting_player_name()),
+            None => self.player_display_name(),
         };
         let line = match id {
             "say" => Text::translate("chat.type.announcement", &[name, message]),
@@ -2808,14 +2819,14 @@ impl Game<'_> {
                 // Whispering to yourself: the incoming and outgoing lines.
                 let out = Text::translate(
                     "commands.message.display.outgoing",
-                    &[Text::literal(self.acting_player_name()), message.clone()],
+                    &[self.player_display_name(), message.clone()],
                 )
                 .with_color(text::GRAY)
                 .italic();
                 self.system_message(out);
                 Text::translate(
                     "commands.message.display.incoming",
-                    &[Text::literal(self.acting_player_name()), message],
+                    &[self.player_display_name(), message],
                 )
                 .with_color(text::GRAY)
                 .italic()

crates/horizon-client/src/game/commands/data.rs

@@ -65,9 +65,10 @@ impl Game<'_> {
                 tag
             }
             Target::Mob(id) => {
-                let uuid = self.uuid_for(id);
-                let m = self.mobs.iter().find(|m| m.id == id)?;
-                entity_nbt::mob_to_nbt(m, uuid, self.persist.raw.get(&id))
+                // `saveWithoutId` writes the entity as saved, riders under
+                // `Passengers`: `/data get` reads the same tree persistence does (#1519).
+                let i = self.mobs.iter().position(|m| m.id == id)?;
+                self.mob_tree_nbt(i)
             }
             Target::Item(id) => {
                 let uuid = self.uuid_for(id);
@@ -113,7 +114,7 @@ impl Game<'_> {
                 self.other_to_nbt(&o, uuid)
             }
             Target::Orb(i) => entity_nbt::orb_to_nbt(self.orbs.get(i)?, random_uuid()),
-            Target::Arrow(i) => {
+            Target::Projectile(i) => {
                 let p = self.creatures.projectiles.get(i)?;
                 let owner = if p.owner == Some(horizon_client::mobs::Who::Player) {
                     player_uuid
@@ -125,7 +126,8 @@ impl Game<'_> {
                     .as_ref()
                     .and_then(|a| a.last_state)
                     .map(|s| self.state_to_nbt(s));
-                entity_nbt::arrow_to_nbt(p, random_uuid(), owner, in_block, None)?
+                entity_nbt::arrow_to_nbt(p, random_uuid(), owner, in_block, None)
+                    .or_else(|| entity_nbt::fireball_to_nbt(p, random_uuid(), owner, None))?
             }
         })
     }

crates/horizon-client/src/game/commands/world_cmds.rs

@@ -59,7 +59,15 @@ impl Game<'_> {
                 self.recipe_unlocked(&unlocked);
                 count as i32
             } else {
-                self.level.recipe_book.remove_recipes(index, &recipes) as i32
+                let removed = self.level.recipe_book.remove_recipes(index, &recipes);
+                let count = removed.len() as i32;
+                // A network player's client drops them from its book.
+                if self.lan_acting.is_some() && !removed.is_empty() {
+                    self.guest_packets.push(C::RecipeBookRemove(
+                        horizon_protocol::packets::recipes::RecipeBookRemove { ids: removed },
+                    ));
+                }
+                count
             };
             tracker.track(&h, n);
         }
@@ -345,7 +353,26 @@ impl Game<'_> {
             Some(Arg::Resource(s)) => Some(s.clone()),
             _ => None,
         };
-        self.audio.stop_sounds(sound.as_deref(), source);
+        // StopSoundCommand: each target's connection gets the packet; the
+        // window's own player stops its sounds.
+        let packet = C::StopSound(play::StopSound {
+            source: source.map(|s| s as i32),
+            sound: sound.clone(),
+        });
+        for &t in &targets {
+            match t {
+                Target::Player if self.lan_acting.is_some() => {
+                    self.guest_packets.push(packet.clone());
+                }
+                Target::Player => self.audio.stop_sounds(sound.as_deref(), source),
+                Target::Guest(conn) => {
+                    if let Some(host) = self.lan.as_ref() {
+                        host.hub.send_to(conn, &packet);
+                    }
+                }
+                _ => {}
+            }
+        }
         let key = match (source, &sound) {
             (Some(_), Some(_)) => "commands.stopsound.success.source.sound",
             (Some(_), None) => "commands.stopsound.success.source.any",

crates/horizon-client/src/game/control.rs

@@ -226,6 +226,16 @@ impl Game<'_> {
                 }
                 Ok(Some(json!({ "ok": true, "cull": r.section_cull() })))
             }
+            "section-sides" => {
+                let r = self.renderer.as_mut().ok_or("no renderer")?;
+                match words.get(1).copied() {
+                    None => {}
+                    Some("on") => r.set_section_sides(true),
+                    Some("off") => r.set_section_sides(false),
+                    Some(other) => return Err(format!("unknown section sides mode {other}").into()),
+                }
+                Ok(Some(json!({ "ok": true, "sides": r.section_sides() })))
+            }
             "sculk" => Ok(Some(self.sculk_command(&words)?)),
             "status" => Ok(Some(self.control_status())),
             "pad" => Ok(Some(self.pad_command(&words)?)),
@@ -503,7 +513,10 @@ impl Game<'_> {
                 if self.pending_screenshot.is_some() {
                     return Err("a screenshot is already pending".into());
                 }
-                renderer.screenshot = Some(arg(1)?.into());
+                arg(1)?;
+                // The rest of the line: a path may hold spaces.
+                let path = line.trim_start().strip_prefix("screenshot").unwrap_or("");
+                renderer.screenshot = Some(path.trim().into());
                 self.pending_screenshot = Some(reply.clone());
                 Ok(None)
             }
@@ -981,6 +994,7 @@ impl Game<'_> {
         status["destroying"] = json!(destroying);
         status["physical_keys"] = json!(physical_keys);
         status["heard"] = json!(self.audio.heard);
+        status["stopped_sounds"] = json!(self.audio.stopped);
         // Boats, minecarts, armor stands, item frames and paintings.
         status["objects"] = json!(self.objects_status());
         status["lightning"] = json!({"bolts": self.bolts.len(), "struck": self.lightning_seen[0],

crates/horizon-client/src/game/creatures.rs

@@ -321,7 +321,7 @@ impl Game<'_> {
             .iter()
             .filter(|m| m.distance_sqr(center) <= radius * radius)
             .map(|m| {
-                serde_json::json!({
+                let mut state = serde_json::json!({
                     "id": m.id,
                     "kind": m.kind.id,
                     "pos": [m.position.x, m.position.y, m.position.z],
@@ -370,7 +370,11 @@ impl Game<'_> {
                         "patrol_target": s.patrol_target,
                         "vehicle": m.extra.mount,
                     })),
-                })
+                });
+                // Drawn seated (Entity.isPassenger); set apart because the
+                // json! above is at the macro recursion limit.
+                state["passenger"] = m.extra.passenger.into();
+                state
             })
             .collect();
         serde_json::json!({ "count": self.mobs.len(), "near": list, "projectiles": self.creatures.projectiles.len() })
@@ -978,7 +982,9 @@ impl Game<'_> {
                         m.ai.target = Some(target);
                     }
                 }
-                MobEvent::Projectile(p) => {
+                MobEvent::Projectile(mut p) => {
+                    self.next_entity += 1;
+                    p.id = self.next_entity;
                     let (owner, at) = (p.owner, [p.position.x, p.position.y, p.position.z]);
                     self.creatures.projectiles.push(p);
                     self.projectile_event("minecraft:projectile_shoot", owner, at);

crates/horizon-client/src/game/debug_keys.rs

@@ -185,7 +185,9 @@ impl Game<'_> {
                 // Minecraft.emergencySaveAndCrash: the world is saved, then the
                 // game stops; main writes the crash report.
                 let crash = horizon_client::crash::DebugCrash::new();
-                let _ = self.save_game();
+                if let Err(e) = self.save_game() {
+                    log::error!("the emergency save before the crash failed: {e}");
+                }
                 return Err(crash.into());
             }
         }

crates/horizon-client/src/game/dedicated.rs

@@ -6,7 +6,7 @@
 //! its simulation and the play-state hub that LAN hosting uses, configured
 //! from server.properties, with the operator, whitelist and ban lists and a
 //! console on standard input.
-use super::{Game, Options, lan::LanSettings};
+use super::{Game, Options, lan::LanSettings, world_loading::WorldRequest};
 use horizon_client::{
     Result,
     lan::{LoginGate, NetConfig, NetLog, OnlineMode, hub::HubConfig},
@@ -218,21 +218,22 @@ impl Lists {
             use_whitelist: false,
             enforce_whitelist: false,
         };
+        // DedicatedPlayerList's constructor order and its LOGGER.warn lines.
         let warn = |what: &str, r: std::result::Result<(), String>| {
             if let Err(e) = r {
-                log("WARN", &format!("Failed to load {what}: {e}"));
+                log("WARN", &format!("Failed to {what}: {e}"));
             }
         };
-        // DedicatedPlayerList's constructor order.
-        warn("user banlist", l.bans.load());
-        let _ = l.bans.save();
-        warn("ip banlist", l.ip_bans.load());
-        let _ = l.ip_bans.save();
-        warn("operators list", l.ops.load());
-        warn("white-list", l.white.load());
-        let _ = l.ops.save();
+        let saved = |r: std::io::Result<()>| r.map_err(|e| e.to_string());
+        warn("load user banlist", l.bans.load());
+        warn("save user banlist", saved(l.bans.save()));
+        warn("load ip banlist", l.ip_bans.load());
+        warn("save ip banlist", saved(l.ip_bans.save()));
+        warn("load operators list", l.ops.load());
+        warn("load white-list", l.white.load());
+        warn("save operators list", saved(l.ops.save()));
         if !l.white.file.exists() {
-            let _ = l.white.save();
+            warn("save white-list", saved(l.white.save()));
         }
         l
     }
@@ -546,13 +547,13 @@ impl Game<'_> {
         let lists = Arc::new(Mutex::new(lists));
         log("INFO", &format!("Preparing level \"{level_name}\""));
         let folder = world_dir.to_string_lossy().into_owned();
-        self.open_world(
+        self.load_world(WorldRequest::new(
             &folder,
             Some(&level_name),
             Some(props.seed),
             game_mode == 1,
             None,
-        )?;
+        )?)?;
         if new_world {
             self.level.hardcore = props.hardcore;
         }

crates/horizon-client/src/game/discord.rs

@@ -0,0 +1,43 @@
+//! What the player is doing, for Discord Rich Presence (`horizon_client::discord_presence`).
+use super::*;
+use horizon_client::discord_presence::{self as presence, Dimension, Play, Status};
+
+impl Game<'_> {
+    /// Each frame: only a change reaches the presence thread.
+    pub(super) fn update_discord_presence(&self) {
+        presence::set(self.discord_status());
+    }
+    fn discord_status(&self) -> Status {
+        if !self.settings.extras.discord_presence {
+            return Status::Off;
+        }
+        if self.title.is_some() {
+            return Status::Menus;
+        }
+        let play = if let Some(host) = &self.lan {
+            Play::Hosting {
+                players: 1 + host.hub.guests.len(),
+            }
+        } else if let Some(server) = &self.integrated {
+            match (server.published(), &self.remote) {
+                (Some(_), Some(remote)) => Play::Hosting {
+                    players: remote.player_count(),
+                },
+                _ => Play::Singleplayer,
+            }
+        } else if self.remote.is_some() {
+            Play::Multiplayer
+        } else {
+            Play::Singleplayer
+        };
+        Status::World {
+            play,
+            dimension: match self.dim {
+                Dim::Overworld => Dimension::Overworld,
+                Dim::Nether => Dimension::Nether,
+                Dim::End => Dimension::End,
+            },
+            mode: self.mode,
+        }
+    }
+}

crates/horizon-client/src/game/dragon.rs

@@ -12,7 +12,6 @@ use horizon_client::{
     hud_layout, hud_overlays,
     mesher::Vertex,
     particles::{ParticleOptions, ParticleType},
-    text::Text,
 };
 use horizon_core::{
     geometry::{Aabb, Vec3},
@@ -2157,23 +2156,12 @@ impl Game<'_> {
             });
         }
     }
-    /// `BossHealthOverlay`: the dragon's pink bar, then the withers', the
-    /// raids' and the custom bars, in that order.
+    /// `BossHealthOverlay.extractRenderState`: whatever `publish_boss_bars`
+    /// (or a server's packets) put on this client's overlay.
     pub(super) fn draw_boss_bars(&self, batch: &mut HudBatch) {
-        let mut bars = Vec::new();
-        if let Some(d) = self.dragon.as_ref().filter(|_| self.dragon_bar_shown()) {
-            bars.push(hud_overlays::BossBar {
-                name: Text::literal(
-                    self.translate("entity.minecraft.ender_dragon", "Ender Dragon"),
-                ),
-                progress: (d.health / MAX_HEALTH).clamp(0.0, 1.0),
-                color: 0,
-                overlay: 0,
-            });
-        }
-        self.wither_bars(&mut bars);
-        self.raid_bars(&mut bars);
-        self.custom_bossbars(&mut bars);
+        let bars = self
+            .boss_overlay
+            .bars(horizon_client::boss_overlay::now_millis());
         let draws = hud_overlays::boss_overlay(
             batch.width as i32,
             batch.height as i32,
@@ -2182,14 +2170,26 @@ impl Game<'_> {
         );
         hud_layout::paint(batch, &self.gui.atlas, &draws);
     }
-    /// The dragon fight's boss bar shows (`EnderDragonFight.dragonEvent`,
-    /// with `setCreateWorldFog`).
-    pub(super) fn dragon_bar_shown(&self) -> bool {
-        self.dim == Dim::End && self.dragon.is_some()
+    /// The dragon fight's bar for a player at `at`
+    /// (`EnderDragonFight.dragonEvent`, visible while the fight is not won
+    /// and the player is alive within 192 blocks of (0, 128, 0)).
+    pub(super) fn dragon_boss_progress(&self, at: [f64; 3], alive: bool) -> Option<f32> {
+        if self.dim != Dim::End || !alive || !self.fight.loaded || self.fight.killed {
+            return None;
+        }
+        let near = at[0].powi(2) + (at[1] - 128.0).powi(2) + at[2].powi(2) <= 192.0 * 192.0;
+        if !near {
+            return None;
+        }
+        Some(
+            self.dragon
+                .as_ref()
+                .map_or(1.0, |d| (d.health / MAX_HEALTH).clamp(0.0, 1.0)),
+        )
     }
-    /// `music.dragon` while the boss bar plays music.
+    /// `BossHealthOverlay.shouldPlayMusic`.
     pub(super) fn boss_music(&self) -> bool {
-        self.dim == Dim::End && self.dragon.is_some() || self.wither_near()
+        self.boss_overlay.should_play_music()
     }
 }
 pub(super) struct DragonFireball {

crates/horizon-client/src/game/execution_role.rs

@@ -0,0 +1,39 @@
+//! A Game's execution role is fixed at construction. Connecting or disconnecting
+//! changes `remote`, not this role. A client may simulate a world in-frame.
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(super) enum ExecutionRole {
+    Client,
+    IntegratedServer,
+    DedicatedServer,
+}
+
+impl ExecutionRole {
+    /// Only a client owns presentation work (audio, loading UI, chunk meshes).
+    pub fn is_client(self) -> bool {
+        self == Self::Client
+    }
+
+    /// The optional in-frame simulation remains a client execution mode.
+    pub fn starts_integrated_server(self, server_thread: bool) -> bool {
+        self.is_client() && server_thread
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::ExecutionRole::*;
+
+    #[test]
+    fn world_loading_keeps_in_frame_clients_and_server_roles_separate() {
+        for (role, client, threaded) in [
+            (Client, true, true),
+            (IntegratedServer, false, false),
+            (DedicatedServer, false, false),
+        ] {
+            assert_eq!(role.is_client(), client);
+            assert_eq!(role.starts_integrated_server(true), threaded);
+            assert!(!role.starts_integrated_server(false));
+        }
+    }
+}

crates/horizon-client/src/game/fov.rs

@@ -74,7 +74,7 @@ impl Game<'_> {
         })
     }
     /// The fluid at the camera, as `Camera.getFluidInCamera` reports it.
-    fn camera_fluid(&self, camera: [f64; 3]) -> CameraFluid {
+    pub(super) fn camera_fluid(&self, camera: [f64; 3]) -> CameraFluid {
         match fog_type(&self.world, self.res.facts(), camera, self.forward()) {
             FogType::Water => CameraFluid::Water,
             FogType::Lava => CameraFluid::Lava,

crates/horizon-client/src/game/integrated.rs

@@ -12,7 +12,9 @@
 //! way.
 use super::{
     Game, Options, PackResources, Resources, UiResources,
+    execution_role::ExecutionRole,
     lan::{LanSettings, Owner},
+    world_loading::WorldRequest,
 };
 use horizon_client::{
     Result,
@@ -26,7 +28,6 @@ use horizon_protocol::connection::Pipe;
 use horizon_protocol::{crypto::offline_uuid, text::translatable};
 use std::{
     net::TcpListener,
-    path::Path,
     sync::{
         Arc, Mutex,
         atomic::{AtomicBool, AtomicI32, AtomicU16, AtomicU32, Ordering},
@@ -170,11 +171,6 @@ struct Launch {
     player: String,
 }
 
-/// Whether this world opens on a server thread: asked for.
-pub(super) fn wanted(options: &Options, _world: &Path) -> bool {
-    options.server_thread && options.dedicated.is_none()
-}
-
 impl Game<'_> {
     /// `Minecraft.hasSingleplayerServer`: a world of this window's own, run
     /// in the frame or on its server thread.
@@ -215,9 +211,10 @@ impl Game<'_> {
         };
         let mut options = self.options.clone();
         // A server without a console: no local player, no window, no control socket.
+        // Compatibility for gameplay checks outside startup/world loading.
         options.dedicated = Some(Vec::new());
         options.server_thread = false;
-        options.integrated = true;
+        options.execution_role = ExecutionRole::IntegratedServer;
         options.control = None;
         options.benchmark = None;
         options.frames = None;
@@ -287,13 +284,13 @@ impl Game<'_> {
         tasks: Receiver<Task>,
         ready: &Sender<Ready>,
     ) -> Result<()> {
-        self.open_world(
+        self.load_world(WorldRequest::new(
             &launch.folder,
             launch.name.as_deref(),
             launch.seed,
             launch.creative,
             launch.create.as_ref(),
-        )?;
+        )?)?;
         let saved = Box::new(self.level.clone());
         // Math.max(2, options.renderDistance): past vanilla's 32 when the
         // window's render distance is (Horizon's options go to 64).

crates/horizon-client/src/game/lan.rs

@@ -55,8 +55,8 @@ pub(super) struct LanHost {
     pub play: HashMap<u32, super::lan_actions::GuestPlay>,
     /// Blocks broken this tick (their sound is a level event for the guests).
     pub broken: Vec<[f64; 3]>,
-    /// Hurt and death state of the mobs guests see.
-    mob_state: HashMap<super::Dim, HashMap<u32, (i32, bool)>>,
+    /// Hurt time, death and swing time (while swinging) of the mobs guests see.
+    mob_state: HashMap<super::Dim, HashMap<u32, (i32, bool, Option<i32>)>>,
     /// The guest each mob sees as its player, when not the host (game/lan_mobs.rs).
     pub mob_players: HashMap<u32, u32>,
     /// An integrated server's owner (game/integrated.rs).
@@ -168,11 +168,15 @@ fn mob_meta(
         meta.push((9, serializer::FLOAT, Value::Float(health)));
     }
     defaults.push((9, serializer::FLOAT, Value::Float(1.0)));
-    // Mob.DATA_MOB_FLAGS_ID: no AI 1, left-handed 2.
-    let flags = i8::from(m.no_ai) | i8::from(m.extra.left_handed) << 1;
+    // Mob.DATA_MOB_FLAGS_ID: no AI 1, left-handed 2, aggressive 4 (what
+    // draws a vindicator's axe, a skeleton's drawn bow, a piglin's raised
+    // weapon).
+    let flags =
+        i8::from(m.no_ai) | i8::from(m.extra.left_handed) << 1 | i8::from(m.ai.aggressive) << 2;
     if flags != 0 {
         meta.push((15, serializer::BYTE, Value::Byte(flags)));
     }
+    defaults.push((15, serializer::BYTE, Value::Byte(0)));
     // AgeableMob.DATA_BABY_ID (and Zombie's, Piglin's).
     if let Some(index) = baby_index(kind) {
         if m.is_baby() {
@@ -1193,7 +1197,17 @@ impl Game<'_> {
             if dead && !old.is_some_and(|o| o.1) {
                 host.hub.entity_event(m.id as i32, 3, at);
             }
-            seen.insert(m.id, (m.hurt_time, dead));
+            // LivingEntity.swing on a server (a melee hit, a thrown potion):
+            // ClientboundSwingAnimationPacket for the players around. A swing
+            // started since the last flush, or restarted (its time went back).
+            let swing = m.ai.swinging.then_some(m.ai.swing_time);
+            if let Some(time) = swing
+                && !dead
+                && old.and_then(|o| o.2).is_none_or(|before| time < before)
+            {
+                host.hub.swing(m.id as i32, 0, at, None);
+            }
+            seen.insert(m.id, (m.hurt_time, dead, swing));
         }
         host.mob_state.insert(self.dim, seen);
     }

crates/horizon-client/src/game/lan_actions.rs

@@ -117,6 +117,7 @@ pub(super) struct GuestSwap {
     host_command_block: Option<super::command_blocks::CommandBlockScreen>,
     host_mount_menu: super::mount_menu::MountMenu,
     craft_size: usize,
+    craft_table: Option<[i32; 3]>,
     craft_grid: Vec<Option<ItemStack>>,
     container: Option<(i32, i32, i32)>,
     mining: Option<Mining>,
@@ -307,6 +308,7 @@ impl Game<'_> {
         // The host's crafting grid stays theirs; a crafting table the guest
         // opens shows as the 3x3 size.
         let craft_size = std::mem::replace(&mut self.craft_size, 2);
+        let craft_table = self.craft_table.take();
         let craft_grid = std::mem::replace(&mut self.craft_grid, vec![None; 9]);
         let container = self.container.take();
         let mining = std::mem::replace(&mut self.mining, play.mining.take());
@@ -390,6 +392,7 @@ impl Game<'_> {
             host_command_block,
             host_mount_menu,
             craft_size,
+            craft_table,
             craft_grid,
             container,
             mining,
@@ -445,6 +448,7 @@ impl Game<'_> {
             host_command_block,
             host_mount_menu,
             craft_size,
+            craft_table,
             craft_grid,
             container,
             mining,
@@ -495,7 +499,10 @@ impl Game<'_> {
 
         // What the action opened: handed to the guest instead of the host.
         let opened = self.container.take();
-        let opened_table = std::mem::replace(&mut self.craft_size, craft_size) == 3;
+        let guest_table = std::mem::replace(&mut self.craft_table, craft_table);
+        let opened_table = (std::mem::replace(&mut self.craft_size, craft_size) == 3)
+            .then_some(guest_table)
+            .flatten();
         self.craft_grid = craft_grid;
         let opened_station = std::mem::replace(&mut self.station, host_station);
         let bed = std::mem::replace(&mut self.sleeping, sleeping);
@@ -671,8 +678,8 @@ impl Game<'_> {
         if let Some(key) = guest_lectern {
             self.lan_open_lectern(host, conn, key);
         }
-        if opened_table {
-            self.lan_open_crafting(host, conn);
+        if let Some(pos) = opened_table {
+            self.lan_open_crafting(host, conn, pos);
         }
         if let Some(mob) = guest_mount {
             self.lan_open_mount(host, conn, mob);
@@ -812,6 +819,31 @@ impl Game<'_> {
         }
     }
 
+    /// `ServerPlayer.tick`'s `stillValid`: a guest's block container closes
+    /// once the guest is out of reach of its block (a removed block closes it
+    /// in the hub's `sync_containers`).
+    fn lan_containers_tick(&mut self, host: &mut LanHost) {
+        let far: Vec<u32> = host
+            .hub
+            .guests
+            .iter()
+            .filter(|g| host.hub.here(g))
+            .filter(|g| {
+                g.menu.as_ref().is_some_and(|m| {
+                    m.slots.valid(&self.world) && !m.slots.still_valid(&self.world, g, m.pos)
+                })
+            })
+            .map(|g| g.conn)
+            .collect();
+        for conn in far {
+            self.guest_container_closed(host, conn);
+            host.hub.close_container(conn);
+            if let Some(gi) = host.hub.guests.iter().position(|g| g.conn == conn) {
+                self.guest_carried_back(host, gi);
+            }
+        }
+    }
+
     /// A packet from a guest that the hub does not handle itself.
     pub(super) fn lan_guest_packet(&mut self, host: &mut LanHost, conn: u32, packet: S) {
         let Some(gi) = host.hub.guests.iter().position(|g| g.conn == conn) else {
@@ -1075,7 +1107,20 @@ impl Game<'_> {
             }
             S::ContainerClick(p) => {
                 let rules = ItemRules(self.res.items());
+                let slots = host.hub.guests[gi]
+                    .menu
+                    .as_ref()
+                    .filter(|m| m.window == p.container)
+                    .map(|m| m.slots);
+                let before = slots.and_then(|s| s.read(&self.world, &host.hub.guests[gi]));
                 let drops = host.hub.container_click(conn, &p, &mut self.world, &rules);
+                // A click that changed the container's slots: BlockEntity.setChanged,
+                // so comparators read it again (a double chest's other half follows).
+                if let Some(Slots::Block(key) | Slots::Double(key, _)) = slots
+                    && slots.and_then(|s| s.read(&self.world, &host.hub.guests[gi])) != before
+                {
+                    self.container_changed(key);
+                }
                 self.drop_guest_items(host, gi, drops);
             }
             S::ContainerClose(p) => {
@@ -1231,6 +1276,13 @@ impl Game<'_> {
                 }
             }
         }
+        if let Some(Component::Potion {
+            potion: Some(id), ..
+        }) = s.component(component::POTION_CONTENTS)
+            && let Some(potion) = host.hub.registry_name("minecraft:potion", *id)
+        {
+            out = out.with_potion(potion);
+        }
         Some(out)
     }
 
@@ -1238,7 +1290,7 @@ impl Game<'_> {
     /// cursor goes back into their inventory (`placeItemBackInInventory`,
     /// dropped only if it doesn't fit), and their client's cursor empties
     /// with the inventory it is sent.
-    fn guest_carried_back(&mut self, host: &mut LanHost, gi: usize) {
+    pub(super) fn guest_carried_back(&mut self, host: &mut LanHost, gi: usize) {
         if let Some(c) = host.hub.guests[gi].carried.take() {
             self.lan_place_back(host, gi, vec![c]);
             host.hub.send_inventory(gi);
@@ -1649,6 +1701,11 @@ impl Game<'_> {
             border: &self.border,
         };
         host.hub.respawn(i, spawn, &ctx);
+        // ServerGamePacketListenerImpl.handleClientCommand: a hardcore world's
+        // respawned player only watches.
+        if self.level.hardcore {
+            host.hub.set_game_mode(conn, SPECTATOR);
+        }
         if let Some(config) = elsewhere {
             self.respawn_trip(conn, config);
         }
@@ -1680,6 +1737,8 @@ impl Game<'_> {
     pub(super) fn tick_guests(&mut self, host: &mut LanHost) {
         self.lan_merchant_tick(host);
         self.lan_stations_tick(host);
+        self.lan_tables_tick(host);
+        self.lan_containers_tick(host);
         self.tick_lan_mount_menus(host);
         self.announce_guest_advancements(host);
         let conns: Vec<u32> = host
@@ -1939,7 +1998,7 @@ impl Game<'_> {
         let in_wall = !g.sleeping && self.in_wall(g.position, g.eye_height());
         let at = g.position;
         let sneaking = g.sneaking;
-        let sounds = self.as_guest(host, conn, |game| {
+        let events = self.as_guest(host, conn, |game| {
             let (rules, motion) = (game.world.health_rules, game.motion);
             let health = &motion.health;
             let Some(player) = game.player.as_mut() else {
@@ -2036,20 +2095,17 @@ impl Game<'_> {
             // A hurt since the last tick marked the velocity (Entity.markHurt):
             // ServerEntity.sendChanges sends it as it is after this travel.
             let marked = std::mem::take(&mut player.health.sync_velocity);
-            let sounds = events
-                .into_iter()
-                .filter_map(|e| match e {
-                    MotionEvent::HurtSound(sound) => Some(sound),
-                    _ => None,
-                })
-                .collect::<Vec<_>>();
-            (sounds, marked.then_some(player.velocity))
+            (events, marked.then_some(player.velocity))
         });
-        let Some((sounds, marked)) = sounds else {
+        let Some((events, marked)) = events else {
             return;
         };
-        for sound in sounds {
-            self.player_hurt_sound(sound, at);
+        for event in events {
+            match event {
+                MotionEvent::HurtSound(sound) => self.player_hurt_sound(sound, at),
+                MotionEvent::Fall(event) => self.landing_block_updates(&event),
+                _ => {}
+            }
         }
         if let (Some(v), Some(g)) = (marked, host.hub.guest(conn)) {
             g.send(&C::SetEntityMotion(play::SetEntityMotion {
@@ -2452,6 +2508,32 @@ impl Game<'_> {
             .map_or(&[][..], |log| log.get(logged..).unwrap_or(&[]))
             .to_vec();
         let facts = self.res.facts();
+        // BlockItem.place: `playSound(player, ...)`, for the others only. The
+        // placer's client plays it as its block appears.
+        let placed: Vec<([f64; 3], String)> = changed
+            .iter()
+            .map(|&(x, y, z)| {
+                let at = [f64::from(x) + 0.5, f64::from(y) + 0.5, f64::from(z) + 0.5];
+                let name = &facts.get(self.world.block(x, y, z)).sounds.place;
+                (at, name.trim_start_matches("minecraft:").to_owned())
+            })
+            .collect();
+        if let Some(capture) = self.audio.capture.as_mut() {
+            let mut i = heard.min(capture.len());
+            while i < capture.len() {
+                let (name, at, ..) = &capture[i];
+                let place = placed
+                    .iter()
+                    .any(|(p, n)| p == at && name.trim_start_matches("minecraft:") == n.as_str());
+                if place {
+                    let (name, at, volume, pitch) = capture.remove(i);
+                    let source = horizon_client::settings::sound_source(&name) as i32;
+                    host.hub.sound(&name, at, volume, pitch, source, Some(conn));
+                } else {
+                    i += 1;
+                }
+            }
+        }
         if changed.is_empty()
             || !changed.iter().all(|&(x, y, z)| {
                 super::remote::hand_operated(&facts.get(self.world.block(x, y, z)).name)

crates/horizon-client/src/game/lan_crafting.rs

@@ -19,8 +19,8 @@ use horizon_protocol::packets::play::{self, Clientbound as C};
 pub(super) struct GuestCrafting {
     /// The inventory menu; its grid lives in the hub's guest.
     inventory: Option<Box<Menu>>,
-    /// The open crafting table: its window, state id and menu.
-    table: Option<(i32, i32, Box<Menu>)>,
+    /// The open crafting table: its window, state id, menu and block.
+    table: Option<(i32, i32, Box<Menu>, [i32; 3])>,
     /// The open furnace's or brewing stand's window and menu (`AbstractFurnaceMenu`,
     /// `BrewingStandMenu`); its slots live in the block entity and the hub's
     /// container menu keeps the client in sync.
@@ -383,17 +383,17 @@ impl Game<'_> {
             host.hub.send_inventory(gi);
             placed
         } else {
-            let Some((window, state, mut menu)) = host
+            let Some((window, state, mut menu, pos)) = host
                 .play
                 .get_mut(&conn)
-                .and_then(|play| play.crafting.table.take_if(|(w, _, _)| *w == p.container))
+                .and_then(|play| play.crafting.table.take_if(|(w, ..)| *w == p.container))
             else {
                 return;
             };
             let placed = self.guest_menu_op(host, gi, &mut menu, |menu, env| {
                 menu.place_recipe(env, &id, p.use_max, creative, None)
             });
-            host.play.entry(conn).or_default().crafting.table = Some((window, state, menu));
+            host.play.entry(conn).or_default().crafting.table = Some((window, state, menu, pos));
             self.lan_send_table_content(host, conn);
             placed
         };
@@ -403,7 +403,7 @@ impl Game<'_> {
     }
 
     /// The guest opened a crafting table (`CraftingTableBlock.getMenuProvider`).
-    pub(super) fn lan_open_crafting(&mut self, host: &mut LanHost, conn: u32) {
+    pub(super) fn lan_open_crafting(&mut self, host: &mut LanHost, conn: u32, pos: [i32; 3]) {
         self.lan_crafting_closed(host, conn, None);
         self.lan_station_closed(host, conn, None);
         // The container it replaces loses its opener.
@@ -413,7 +413,7 @@ impl Game<'_> {
             return;
         };
         let menu = Box::new(Menu::new(Kind::Crafting));
-        host.play.entry(conn).or_default().crafting.table = Some((window, 0, menu));
+        host.play.entry(conn).or_default().crafting.table = Some((window, 0, menu, pos));
         self.lan_send_table_content(host, conn);
     }
 
@@ -427,31 +427,72 @@ impl Game<'_> {
         let Some(play) = host.play.get_mut(&conn) else {
             return false;
         };
-        let Some((window, state, mut menu)) = play
+        let Some((window, state, mut menu, pos)) = play
             .crafting
             .table
-            .take_if(|(window, _, _)| *window == p.container)
+            .take_if(|(window, ..)| *window == p.container)
         else {
             return false;
         };
+        // A table that is no longer valid takes no clicks (handleContainerClick).
         if let Some(gi) = host.hub.guests.iter().position(|g| g.conn == conn)
             && !host.hub.guests[gi].spectator()
+            && self.lan_table_valid(&host.hub.guests[gi], pos)
         {
             self.guest_menu_op(host, gi, &mut menu, |menu, env| {
                 let _ = menu.click(env, i32::from(p.slot), i32::from(p.button), input(p.input));
             });
         }
-        host.play.entry(conn).or_default().crafting.table = Some((window, state, menu));
+        host.play.entry(conn).or_default().crafting.table = Some((window, state, menu, pos));
         self.lan_send_table_content(host, conn);
         true
     }
 
+    /// `CraftingMenu.stillValid`: the block is still a crafting table and the
+    /// guest is within reach of it.
+    fn lan_table_valid(&self, g: &Guest, pos: [i32; 3]) -> bool {
+        let name = &self
+            .res
+            .facts()
+            .get(self.world.block(pos[0], pos[1], pos[2]))
+            .name;
+        &**name == "minecraft:crafting_table" && g.within_block_range(pos, 4.0)
+    }
+
+    /// `ServerPlayer.tick`'s `stillValid`: a guest's crafting table closes
+    /// once it is gone or out of reach, giving its grid back.
+    pub(super) fn lan_tables_tick(&mut self, host: &mut LanHost) {
+        let invalid: Vec<(u32, i32)> = host
+            .play
+            .iter()
+            .filter_map(|(c, p)| p.crafting.table.as_ref().map(|t| (*c, t.0, t.3)))
+            .filter(|&(c, _, pos)| {
+                host.hub
+                    .guests
+                    .iter()
+                    .find(|g| g.conn == c)
+                    .is_some_and(|g| host.hub.here(g) && !self.lan_table_valid(g, pos))
+            })
+            .map(|(c, window, _)| (c, window))
+            .collect();
+        for (conn, window) in invalid {
+            self.lan_crafting_closed(host, conn, Some(window));
+            host.hub.send_to(
+                conn,
+                &C::ContainerClose(play::ContainerClose { container: window }),
+            );
+            if let Some(gi) = host.hub.guests.iter().position(|g| g.conn == conn) {
+                self.guest_carried_back(host, gi);
+            }
+        }
+    }
+
     /// The whole crafting table menu for the client (`sendAllDataToRemote`).
     fn lan_send_table_content(&mut self, host: &mut LanHost, conn: u32) {
         let Some(gi) = host.hub.guests.iter().position(|g| g.conn == conn) else {
             return;
         };
-        let Some((window, state, menu)) = host
+        let Some((window, state, menu, _)) = host
             .play
             .get_mut(&conn)
             .and_then(|p| p.crafting.table.as_mut())
@@ -499,9 +540,9 @@ impl Game<'_> {
         } else {
             match crafting
                 .table
-                .take_if(|(w, _, _)| window.is_none_or(|window| *w == window))
+                .take_if(|(w, ..)| window.is_none_or(|window| *w == window))
             {
-                Some((_, _, menu)) => (1..10).filter_map(|s| menu.slot(s).cloned()).collect(),
+                Some((_, _, menu, _)) => (1..10).filter_map(|s| menu.slot(s).cloned()).collect(),
                 None => return false,
             }
         };
@@ -527,7 +568,7 @@ impl Game<'_> {
         let mut grid: Vec<ItemStack> = g.craft_grid.iter_mut().filter_map(Option::take).collect();
         g.craft_result = None;
         if let Some(play) = play {
-            if let Some((_, _, menu)) = play.crafting.table {
+            if let Some((_, _, menu, _)) = play.crafting.table {
                 grid.extend((1..10).filter_map(|s| menu.slot(s).cloned()));
             }
             // A workstation's inputs too.

crates/horizon-client/src/game/lan_entities.rs

@@ -321,20 +321,7 @@ impl Game<'_> {
         }
         for p in self.creatures.projectiles.iter().filter(|p| p.id != 0) {
             use horizon_client::projectiles::ProjectileKind as K;
-            let kind = match &p.kind {
-                K::Arrow { .. } => "minecraft:arrow",
-                K::Snowball => "minecraft:snowball",
-                K::Egg => "minecraft:egg",
-                K::EnderPearl => "minecraft:ender_pearl",
-                K::SmallFireball => "minecraft:small_fireball",
-                K::LargeFireball { .. } => "minecraft:fireball",
-                K::LlamaSpit => "minecraft:llama_spit",
-                K::WindCharge => "minecraft:wind_charge",
-                K::BreezeWindCharge => "minecraft:breeze_wind_charge",
-                K::ShulkerBullet { .. } => "minecraft:shulker_bullet",
-                K::WitherSkull { .. } => "minecraft:wither_skull",
-                K::Potion { .. } => "minecraft:splash_potion",
-            };
+            let kind = p.kind.id();
             let mut e = state(p.id, kind, at(p.position), p.yaw, false);
             e.pitch = p.pitch;
             e.velocity = at(p.velocity);

crates/horizon-client/src/game/lan_stations.rs

@@ -588,7 +588,7 @@ impl Game<'_> {
             let [x, y, z] = gs.pos;
             let name = &self.res.facts().get(self.world.block(x, y, z)).name;
             let block = StationKind::from_block(name) == Some(gs.kind);
-            if !(block && within_reach(g, gs.pos)) {
+            if !(block && g.within_block_range(gs.pos, 4.0)) {
                 let window = gs.window;
                 self.lan_station_closed(host, conn, Some(window));
                 host.hub.send_to(
@@ -631,16 +631,7 @@ impl Game<'_> {
                 Some(BlockEntity::Lectern(l)) if l.book.is_some()
             );
             // Container.stillValidBlockEntity: the interaction range and its buffer.
-            let eye = [g.position[0], g.position[1] + g.eye_height(), g.position[2]];
-            let reach = if g.creative() { 5.0 } else { 4.5 } + 4.0;
-            let pos = [key.0, key.1, key.2];
-            let near = (0..3)
-                .map(|k| {
-                    let lo = f64::from(pos[k]);
-                    (lo - eye[k]).max(eye[k] - lo - 1.0).max(0.0).powi(2)
-                })
-                .sum::<f64>()
-                < reach * reach;
+            let near = g.within_block_range([key.0, key.1, key.2], 4.0);
             if has_book && near {
                 self.lan_send_lectern(host, conn, false);
             } else {
@@ -660,18 +651,3 @@ pub(super) fn station_inputs(gs: &GuestStation) -> Vec<ItemStack> {
         .map(|(_, _, inputs)| inputs.filter_map(|s| gs.menu.slot(s).cloned()).collect())
         .unwrap_or_default()
 }
-
-/// `Player.isWithinBlockInteractionRange(pos, 4)`: the guest's eyes within
-/// its block interaction range (4.5, creative 5) and a 4-block buffer of the
-/// block's box.
-pub(super) fn within_reach(g: &horizon_client::lan::guest::Guest, pos: [i32; 3]) -> bool {
-    let eye = [g.position[0], g.position[1] + g.eye_height(), g.position[2]];
-    let reach = if g.creative() { 5.0 } else { 4.5 } + 4.0;
-    (0..3)
-        .map(|k| {
-            let lo = f64::from(pos[k]);
-            (lo - eye[k]).max(eye[k] - lo - 1.0).max(0.0).powi(2)
-        })
-        .sum::<f64>()
-        < reach * reach
-}

crates/horizon-client/src/game/lan_trading.rs

@@ -48,10 +48,9 @@ impl Game<'_> {
         if let Some(id) = state.mob
             && state.session.villager
         {
-            // startTrading with the guest's reputation (their effects are
-            // not modelled on the host: no Hero of the Village).
+            // startTrading with the guest's reputation. The session already
+            // captured their Hero effect while they acted as the player.
             state.session.reputation = self.villager_reputation_of(id, uuid);
-            state.session.hero = None;
             state.session.update_special_prices();
         }
         let title = self.merchant_display_name(&state);

crates/horizon-client/src/game/levels.rs

@@ -221,7 +221,7 @@ impl Game<'_> {
     /// holds it (`self.lan` is taken during the network tick).
     pub(super) fn enter_level(&mut self, host: Option<&mut LanHost>, target: Dim) -> Result<()> {
         // The in-frame game keeps its one level (`enter_dimension`).
-        if self.options.dedicated.is_none() {
+        if self.options.execution_role.is_client() {
             return Ok(());
         }
         if target != self.dim {
@@ -261,7 +261,7 @@ impl Game<'_> {
     /// nobody is in it; returns the level to put back afterwards. Only a
     /// server holds other levels.
     pub(super) fn enter_command_level(&mut self, dim: Dim) -> Option<Dim> {
-        if self.options.dedicated.is_none() || dim == self.dim {
+        if self.options.execution_role.is_client() || dim == self.dim {
             return None;
         }
         let back = self.dim;

crates/horizon-client/src/game/persist.rs

@@ -76,15 +76,14 @@ impl Game<'_> {
         let pos = ChunkPos::new(chunk.x, chunk.z);
         let time = self.world.game_time;
         let mut extras: ChunkExtras = chunk.saved.as_deref().cloned().unwrap_or_default();
+        // A chunk the scheduler hasn't registered yet (one loaded and
+        // unloaded again before the next tick) still holds its saved ticks:
+        // `register_chunk_ticks` empties that list once it takes them.
         if let Some(t) = self.block_ticks.blocks.chunk(pos) {
             extras.block_ticks = t.pack(time);
-        } else {
-            extras.block_ticks.clear();
         }
         if let Some(t) = self.block_ticks.fluids.chunk(pos) {
             extras.fluid_ticks = t.pack(time);
-        } else {
-            extras.fluid_ticks.clear();
         }
         extras.last_update = time;
         // TheEndGatewayBlockEntity saves its Age (the server copy's).
@@ -156,6 +155,8 @@ impl Game<'_> {
                     kind.as_str(),
                     "minecraft:experience_orb"
                         | "minecraft:arrow"
+                        | "minecraft:fireball"
+                        | "minecraft:small_fireball"
                         | "minecraft:falling_block"
                         | "minecraft:end_crystal"
                         | "minecraft:ender_dragon"
@@ -195,6 +196,11 @@ impl Game<'_> {
                             self.creatures.projectiles.push(p);
                         }
                     }
+                    "minecraft:fireball" | "minecraft:small_fireball" => {
+                        if let Some(p) = entity_nbt::fireball_from_nbt(&tag, player_uuid) {
+                            self.creatures.projectiles.push(p);
+                        }
+                    }
                     "minecraft:falling_block" => {
                         if let Some((state, position, velocity, age, fall_distance)) =
                             entity_nbt::falling_block_from_nbt(&tag)
@@ -642,13 +648,15 @@ impl Game<'_> {
             } else {
                 None
             };
-            let (uuid, raw) = anon(&self.persist, "minecraft:arrow", p.position);
+            let (uuid, raw) = anon(&self.persist, p.kind.id(), p.position);
             let in_block = p
                 .arrow
                 .as_ref()
                 .and_then(|a| a.last_state)
                 .map(|s| self.state_to_nbt(s));
-            if let Some(tag) = entity_nbt::arrow_to_nbt(p, uuid, owner, in_block, raw.as_ref()) {
+            let tag = entity_nbt::arrow_to_nbt(p, uuid, owner, in_block, raw.as_ref())
+                .or_else(|| entity_nbt::fireball_to_nbt(p, uuid, owner, raw.as_ref()));
+            if let Some(tag) = tag {
                 out.entry(chunk_of(p.position)).or_default().push(tag);
             }
         }

crates/horizon-client/src/game/postprocess.rs

@@ -27,6 +27,11 @@ impl Game<'_> {
         if ready.is_empty() {
             return Ok(());
         }
+        // The ticks the marks schedule go to the chunks' containers, which a
+        // chunk that arrived since the last tick doesn't have yet
+        // (`LevelChunk.registerTickContainerInLevel` comes before
+        // `postProcessGeneration`).
+        self.sync_tick_chunks();
         for key in ready {
             let Some(chunk) = self.world.chunks.get_mut(&key) else {
                 continue;

crates/horizon-client/src/game/raids.rs

@@ -6,7 +6,6 @@ use super::{Dim, Game};
 use horizon_client::mobs::villager as mobs_villager;
 use horizon_client::{
     effects::{EffectInstance, OmenTick},
-    hud_overlays,
     mobs::{
         Mob, Species, raider,
         spawn_rules::{self, SpawnLevel},
@@ -15,9 +14,9 @@ use horizon_client::{
     },
     patrol::{GameplayAttributes, Member, PatrolLevel, PatrolSpawner},
     raid::{self, Action, BarName, RaidLevel, RaidPlayer, RaiderInfo, RaiderType, Raids, Spawn},
-    text::Text,
 };
 use horizon_core::{geometry::Vec3, random::RandomSource};
+use horizon_world::nbt::Tag;
 use std::collections::{HashMap, HashSet};
 
 /// Patrol and raid state owned by the game.
@@ -1063,37 +1062,18 @@ impl Game<'_> {
         }
     }
 
-    /// The raid boss bars: red and notched in tens, with the raid's title.
-    pub(super) fn raid_bars(&self, bars: &mut Vec<hud_overlays::BossBar>) {
-        for raid in self.raiding.raids.map.values() {
-            if !raid.bar.visible || !raid.bar.player || raid.is_stopped() {
-                continue;
-            }
-            let title = self.translate("event.minecraft.raid", "Raid");
-            let name = match raid.bar.name {
-                BarName::Raid => title,
-                BarName::Remaining(n) => format!(
-                    "{title} - {}",
-                    self.translate(
-                        "event.minecraft.raid.raiders_remaining",
-                        "Raiders Remaining: %s"
-                    )
-                    .replace("%s", &n.to_string())
-                ),
-                BarName::Victory => {
-                    self.translate("event.minecraft.raid.victory.full", "Raid - Victory")
-                }
-                BarName::Defeat => {
-                    self.translate("event.minecraft.raid.defeat.full", "Raid - Defeat")
-                }
-            };
-            bars.push(hud_overlays::BossBar {
-                name: Text::literal(name),
-                progress: raid.bar.progress,
-                color: 2,
-                overlay: 2,
-            });
+    /// The raid bar a living player at `at` is in (`Raid.getPlayers`): red,
+    /// notched in tens. The name is the translate component the client draws.
+    pub(super) fn raid_boss_at(&self, at: [f64; 3], alive: bool) -> Option<(i32, Tag, f32)> {
+        if !alive || self.dim != Dim::Overworld {
+            return None;
         }
+        let block = block_of(Vec3::new(at[0], at[1], at[2]));
+        let (id, raid) = self.raiding.raids.nearby(block)?;
+        if !raid.bar.visible || raid.is_stopped() {
+            return None;
+        }
+        Some((id, raid_name_tag(raid.bar.name), raid.bar.progress))
     }
     /// A firework a villager launches to celebrate (`CelebrateVillagersSurvivedRaid`).
     pub(super) fn villager_firework(&mut self, at: [f64; 3], color: usize, flight: u8) {
@@ -1239,6 +1219,36 @@ impl Game<'_> {
     }
 }
 
+/// `Raid.raidEvent`'s name: the raid title, the remaining-raiders line, or
+/// the victory and defeat lines.
+fn raid_name_tag(name: BarName) -> Tag {
+    let key = |k: &str| Tag::compound([("translate", Tag::String(k.into()))]);
+    match name {
+        BarName::Raid => key("event.minecraft.raid"),
+        BarName::Victory => key("event.minecraft.raid.victory.full"),
+        BarName::Defeat => key("event.minecraft.raid.defeat.full"),
+        BarName::Remaining(n) => Tag::compound([
+            ("translate", Tag::String("event.minecraft.raid".into())),
+            (
+                "extra",
+                Tag::List(vec![
+                    Tag::String(" - ".into()),
+                    Tag::compound([
+                        (
+                            "translate",
+                            Tag::String("event.minecraft.raid.raiders_remaining".into()),
+                        ),
+                        (
+                            "with",
+                            Tag::List(vec![Tag::String(n.to_string().as_str().into())]),
+                        ),
+                    ]),
+                ]),
+            ),
+        ]),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/horizon-client/src/game/remote.rs

@@ -193,6 +193,9 @@ pub(super) struct Remote {
     /// the oldest of them first waited (`poll_remote`).
     backlog: VecDeque<Event>,
     backlog_since: Option<Instant>,
+    /// `ClientboundTransferPacket`'s target: when the connection ends the
+    /// game connects here, the stored cookies carried over (`TransferState`).
+    transfer: Option<String>,
 }
 
 /// The time a frame spends on chunk packets before it leaves the rest of
@@ -257,14 +260,25 @@ fn number_format(f: &play::NumberFormat) -> horizon_client::scoreboard::NumberFo
 impl Game<'_> {
     /// Leave the title for a server (ConnectScreen): an empty world fed by the connection.
     pub(super) fn connect_server(&mut self, address: &str, name: &str) -> Result<()> {
+        self.connect_server_with_cookies(address, name, None)
+    }
+    /// `connect_server` carrying a transfer's stored server cookies
+    /// (`TransferState`); None on an ordinary join.
+    pub(super) fn connect_server_with_cookies(
+        &mut self,
+        address: &str,
+        name: &str,
+        cookies: Option<horizon_client::net::Cookies>,
+    ) -> Result<()> {
         if self.defer_world_entry(super::PendingWorldEntry::Server {
             address: address.to_owned(),
             name: name.to_owned(),
+            cookies: cookies.clone(),
         })? {
             return Ok(());
         }
         self.join_world_rest()?;
-        if let Err(error) = self.join_server(address, name, None) {
+        if let Err(error) = self.join_server(address, name, None, cookies) {
             log::warn!("Horizon: could not join server: {error}");
             if self.title.is_none() {
                 self.title = Some(horizon_client::title::Title::new(
@@ -285,13 +299,14 @@ impl Game<'_> {
         pipe: horizon_protocol::connection::Pipe,
         name: &str,
     ) -> Result<()> {
-        self.join_server("local", name, Some(pipe))
+        self.join_server("local", name, Some(pipe), None)
     }
     fn join_server(
         &mut self,
         address: &str,
         name: &str,
         local: Option<horizon_protocol::connection::Pipe>,
+        cookies: Option<horizon_client::net::Cookies>,
     ) -> Result<()> {
         self.perf.world_opening();
         let root = self.options.resources.clone();
@@ -323,7 +338,17 @@ impl Game<'_> {
             Some(pipe) => Session::connect_local(pipe, name, view, lang.clone()),
             None => {
                 self.extras_connecting(address, name);
-                Session::connect(address, name, auth.clone(), view, lang.clone())
+                match cookies {
+                    Some(cookies) => Session::connect_transferred(
+                        address,
+                        name,
+                        auth.clone(),
+                        view,
+                        lang.clone(),
+                        cookies,
+                    ),
+                    None => Session::connect(address, name, auth.clone(), view, lang.clone()),
+                }
             }
         };
         let player_type = super::perspective::player_type(&root);
@@ -383,6 +408,7 @@ impl Game<'_> {
         }
         self.apply_settings();
         self.clear_waypoints();
+        self.boss_overlay.reset();
         self.remote = Some(Remote {
             session,
             brand: "unknown".into(),
@@ -445,6 +471,7 @@ impl Game<'_> {
             chunk_center: (0, 0),
             backlog: VecDeque::new(),
             backlog_since: None,
+            transfer: None,
         });
         // The level's TickRateManager follows the server's ticking packets.
         self.clock = horizon_client::clock::FixedStep::client();
@@ -465,6 +492,7 @@ impl Game<'_> {
             self.extras_left();
         }
         self.clear_waypoints();
+        self.boss_overlay.reset();
         if let Some(mut r) = self.remote.take() {
             r.session.disconnect();
         }
@@ -612,6 +640,21 @@ impl Game<'_> {
                 continue;
             };
             let value = match c {
+                // Read past, not decoded: the item keeps its prototype's value.
+                Component::Raw(_) => continue,
+                // Trim materials and patterns are synced registries, as enchantments are.
+                Component::Trim { material, pattern } => {
+                    let (Some(material), Some(pattern)) = (
+                        r.registries.name("minecraft:trim_material", *material),
+                        r.registries.name("minecraft:trim_pattern", *pattern),
+                    ) else {
+                        continue;
+                    };
+                    Tag::compound([
+                        ("material", Tag::String(material.into())),
+                        ("pattern", Tag::String(pattern.into())),
+                    ])
+                }
                 Component::Int(v) if *kind == component::RARITY => {
                     let rarity = ["common", "uncommon", "rare", "epic"];
                     Tag::String(rarity.get(*v as usize).copied().unwrap_or("common").into())
@@ -657,6 +700,16 @@ impl Game<'_> {
                     ("mob_factor", Tag::Float(v[5].to_bits())),
                 ]),
                 Component::Profile(p) => profile_tag(p),
+                // PotionContents' NBT: the potion by name and the custom colour.
+                Component::Potion { potion, color, .. } => {
+                    let potion = potion.and_then(|id| r.builtin.get("minecraft:potion")?.name(id));
+                    Tag::compound(
+                        potion
+                            .map(|name| ("potion", Tag::String(name.into())))
+                            .into_iter()
+                            .chain(color.map(|c| ("custom_color", Tag::Int(c)))),
+                    )
+                }
                 // ItemStackTemplate.CODEC: id, count and components.
                 Component::Stacks(stacks) => Tag::List(
                     stacks
@@ -718,6 +771,20 @@ impl Game<'_> {
     fn to_network(&self, s: &Option<ItemStack>) -> Option<Stack> {
         let s = s.as_ref()?;
         let mut stack = Stack::new(self.item_id(&s.item), s.count as i32);
+        // A creative pick keeps its potion (PotionContents by its builtin id).
+        if let Some(id) = s.potion().and_then(|p| {
+            let potions = self.remote.as_ref()?.builtin.get("minecraft:potion")?;
+            potions.id(&horizon_world::datafix::dynamic::namespaced(p))
+        }) {
+            stack.added.push((
+                horizon_protocol::item::component::POTION_CONTENTS,
+                horizon_protocol::item::Component::Potion {
+                    potion: Some(id),
+                    color: None,
+                    rest: Vec::new(),
+                },
+            ));
+        }
         if s.damage > 0 {
             stack.added.push((
                 horizon_protocol::item::component::DAMAGE,
@@ -738,6 +805,9 @@ impl Game<'_> {
             self.ticks,
             self.screen == Screen::Chat,
         );
+        if self.mods.running() {
+            self.mods_chat(&text);
+        }
         if let Some(r) = self.remote.as_mut() {
             r.chat.push((text, Instant::now()));
             r.chat_received += 1;
@@ -834,7 +904,11 @@ impl Game<'_> {
                         r.joined = true;
                         r.profile = uuid;
                         r.profile_name = name.clone();
-                        r.status = format!("Joined as {name}; loading terrain...");
+                        // LevelLoadingScreen's line: no player name.
+                        r.status = horizon_client::lang::get_or(
+                            "multiplayer.downloadingTerrain",
+                            "Loading terrain...",
+                        );
                     }
                 }
                 Event::Brand(brand) => {
@@ -843,6 +917,15 @@ impl Game<'_> {
                     }
                 }
                 Event::Reconfigured(registries) => self.set_registries(registries),
+                // handleTransfer: "Cannot transfer to server from
+                // singleplayer" (no ServerData), so the world just closes.
+                Event::Transfer { host, port } => {
+                    if let Some(r) = self.remote.as_mut()
+                        && r.session.address != "local"
+                    {
+                        r.transfer = Some(format!("{host}:{port}"));
+                    }
+                }
                 Event::PackPush(p) => self.handle_pack_push(p),
                 Event::PackPop(id) => self.handle_pack_pop(id),
                 Event::DecodeError(e) => {
@@ -858,6 +941,20 @@ impl Game<'_> {
                     from_server,
                 } => {
                     log::info!("Horizon: disconnected: {reason}");
+                    // ClientboundTransferPacket left a target: connect there
+                    // instead of showing the disconnect, the stored cookies
+                    // carried over (ClientCommonPacketListenerImpl.
+                    // handleTransfer → ConnectScreen.startConnecting).
+                    let transfer = self.remote.as_mut().and_then(|r| {
+                        r.transfer.take().map(|address| {
+                            (address, r.session.name.clone(), r.session.cookies.clone())
+                        })
+                    });
+                    if let Some((address, name, cookies)) = transfer {
+                        self.leave_server(None)?;
+                        self.connect_server_with_cookies(&address, &name, Some(cookies))?;
+                        return Ok(());
+                    }
                     let retry = self.reconnect_after(&reason, from_server);
                     self.leave_server(Some(reason))?;
                     self.offer_reconnect(retry);
@@ -991,6 +1088,9 @@ impl Game<'_> {
                 r.stepped.clear();
                 r.head_lerps.clear();
                 r.pending_items.clear();
+                // The entity ids are the old world's; the new dimension's
+                // player entities re-map to their profiles on AddEntity.
+                r.level_players.clear();
                 // A new ClientLevel: a new chunk storage, centred on 0, 0.
                 r.chunk_center = (0, 0);
             }
@@ -1496,13 +1596,14 @@ impl Game<'_> {
             );
         }
         self.turn_remote_object(id, rotation.map(|(yaw, _)| yaw), on_ground);
+        self.move_remote_text_display(id, position, rotation);
         self.turn_remote_projectile(id, rotation);
     }
     fn remove_entity(&mut self, id: i32) {
-        // The vehicle the player rode is gone (Entity.removeVehicle).
-        if self.riding == Some(id as u32) {
-            self.riding = None;
-        }
+        // Entity.setRemoved detaches every passenger, even when no empty
+        // SetPassengers packet preceded the vehicle's removal. Otherwise
+        // mobs and other players keep their passenger pose after it is gone.
+        self.remote_set_passengers(id, &[]);
         self.mobs.retain(|m| m.id != id as u32);
         self.orbs.retain(|o| o.id != id as u32);
         self.dropped.retain(|d| d.id != id as u32);
@@ -1601,6 +1702,12 @@ impl Game<'_> {
             }
         }
     }
+    /// Find a game slot in the menu's complete, contiguous slot mapping.
+    fn menu_slot_index(menu: &str, internal: usize) -> Option<usize> {
+        (0..)
+            .map_while(|slot| Self::menu_slot(menu, slot))
+            .position(|slot| slot == internal)
+    }
     /// The workstation screen of a menu type a server opens.
     pub(super) fn remote_station_kind(menu: &str) -> Option<super::stations::Kind> {
         use super::stations::Kind;
@@ -1805,6 +1912,9 @@ impl Game<'_> {
                     self.audio.play(&name, Some(at), p.volume, p.pitch);
                 }
             }
+            C::StopSound(p) => self
+                .audio
+                .stop_sounds(p.sound.as_deref(), p.source.map(|s| s as usize)),
             C::AddEntity(p) => {
                 let kind = self
                     .remote
@@ -1838,6 +1948,7 @@ impl Game<'_> {
                         p.data,
                     );
                 }
+                self.move_remote_text_display(p.id, p.position, Some((rotation[0], rotation[1])));
             }
             C::RemoveEntities(p) => {
                 for id in p.ids {
@@ -1959,15 +2070,6 @@ impl Game<'_> {
                         }
                     }
                 }
-                if let Some(m) = self.mobs.iter_mut().find(|m| m.id == p.id as u32)
-                    && m.species() == horizon_client::mobs::Species::Rabbit
-                {
-                    for (index, _, value) in &p.values {
-                        if let (15, Value::Byte(flags)) = (index, value) {
-                            m.no_ai = flags & 1 != 0;
-                        }
-                    }
-                }
                 self.remote_mob_data(p.id, &p.values);
                 if let Some(m) = self.mobs.iter_mut().find(|m| m.id == p.id as u32)
                     && m.species() == horizon_client::mobs::Species::Creeper
@@ -2691,6 +2793,7 @@ impl Game<'_> {
             }
             // ClientPacketListener.setActionBarText, setTitleText,
             // setSubtitleText, setTitlesAnimation and handleTitlesClear.
+            C::BossEvent(p) => self.apply_boss_event(&p),
             C::SetActionBarText(p) => self.titles.set_overlay(remote_text(&p.text), false),
             C::SetTitleText(p) => self.titles.set_title(remote_text(&p.text)),
             C::SetSubtitleText(p) => self.titles.set_subtitle(remote_text(&p.text)),
@@ -3064,6 +3167,8 @@ impl Game<'_> {
             }
             None => {
                 let mut player = PlayerMotion::new(self.motion, position)?;
+                // Player.tick derives noPhysics from the current game mode.
+                player.spectator = self.spectator();
                 player.velocity = delta;
                 self.player = Some(player);
                 self.pad.player_replaced();
@@ -3098,6 +3203,8 @@ impl Game<'_> {
     /// One client tick while connected (Minecraft.tick with a ClientLevel).
     pub(super) fn tick_remote(&mut self) -> Result<()> {
         self.tick_remote_level()?;
+        // Client mods tick on any server, single player's own included.
+        self.tick_mods();
         // Minecraft.tick sends this even when the player cannot tick yet,
         // including while waiting for chunks. Keep it outside early returns.
         if self.remote.as_ref().is_some_and(|r| r.joined) {
@@ -3123,6 +3230,7 @@ impl Game<'_> {
         // Minecraft.tick: TickRateManager.tick; ClientLevel.tickTime advances
         // the time only while the level runs normally.
         let running = self.clock.world_runs();
+        self.boss_overlay.tick_darken(running);
         if running {
             self.world.game_time += 1;
             self.remote_clock_tick();
@@ -3407,6 +3515,9 @@ impl Game<'_> {
     /// ClientLevel.tickEntities; a frozen level only ticks the players
     /// (`TickRateManager.isEntityFrozen`).
     fn tick_remote_entities(&mut self, running: bool) {
+        if running {
+            self.tick_text_displays();
+        }
         // EntityFluidInteraction.update for the entities this window only displays: the
         // server never sends the fluid contact, and the renderers read it (cod, salmon and
         // tropical fish lie on their side without `in_water`, #1591).
@@ -3883,7 +3994,7 @@ impl Game<'_> {
         let sneaking = self.keys.contains(&KeyCode::ShiftLeft);
         // A boat, minecart, item frame, armor stand or painting nearer than
         // any mob: the server uses it (AbstractBoat.interact boards it).
-        if let Some(hit) = self.remote_object_hit()
+        if let Some(hit) = self.remote_object_hit(false)
             && self.mob_hit().is_none_or(|(_, d)| hit.distance < d)
             && self.before_block(hit.distance)
         {
@@ -3965,15 +4076,27 @@ impl Game<'_> {
             }
             if reacts {
                 self.predict_use(&changes, seq);
-            } else if let Some(stack) = held.as_ref() {
-                self.predict_item_on_block(stack, &hit);
+            } else if let Some(stack) = held.as_ref()
+                && self.predict_item_on_block(stack, &hit)
+            {
+                // Item.useOn succeeded here (InteractionResult.SUCCESS):
+                // this hand swings and the click ends, so the other hand
+                // (a shield, a torch) is never tried.
+                self.with_hand(hand, Game::swing_arm);
+                return true;
             }
             if held_block {
-                if reacts
-                    || held
-                        .as_ref()
-                        .is_some_and(|stack| self.remote_can_place(&hit, stack))
-                {
+                let placed = if reacts {
+                    None
+                } else {
+                    held.as_ref()
+                        .and_then(|stack| self.remote_can_place(&hit, stack))
+                };
+                if let Some(placed) = &placed {
+                    self.predict_place(placed, seq);
+                    self.with_hand(hand, Game::consume_held);
+                }
+                if reacts || placed.is_some() {
                     self.with_hand(hand, Game::swing_arm);
                 }
                 // BlockItem.place returns FAIL when placement is rejected:
@@ -3990,7 +4113,8 @@ impl Game<'_> {
     /// `playSound(player, ...)`: the server sends them to the others only):
     /// honeycomb waxing copper, and an axe, hoe or shovel transforming a
     /// block (stripping, scraping, removing wax, tilling, making a path).
-    fn predict_item_on_block(&mut self, stack: &ItemStack, hit: &super::Hit) {
+    /// Whether the item's use succeeded, which ends the click.
+    fn predict_item_on_block(&mut self, stack: &ItemStack, hit: &super::Hit) -> bool {
         let at = [
             f64::from(hit.pos[0]) + 0.5,
             f64::from(hit.pos[1]) + 0.5,
@@ -4009,11 +4133,15 @@ impl Game<'_> {
                 self.audio
                     .play("minecraft:item.honeycomb.wax_on", Some(at), 1.0, 1.0);
             }
+            waxes
         } else if let Some((_, sound, _, _, particle)) =
             self.block_transform(stack, hit.pos, hit.face)
         {
             self.transform_particle(&particle, hit.pos);
             self.audio.play(&sound, Some(at), 1.0, 1.0);
+            true
+        } else {
+            false
         }
     }
 
@@ -4033,18 +4161,7 @@ impl Game<'_> {
         {
             return;
         }
-        for &(p, state) in changes {
-            let pos = [p.x, p.y, p.z];
-            let before = self.world.block(p.x, p.y, p.z);
-            // BlockStatePredictionHandler.retainKnownServerState.
-            if let Some(r) = self.remote.as_mut() {
-                r.predictions
-                    .entry(pos)
-                    .and_modify(|e| e.0 = seq)
-                    .or_insert((seq, before.0 as i32));
-            }
-            self.set_block(pos, state.0 as i32);
-        }
+        self.predict_blocks(changes, seq);
         // `level.playSound(player, ...)`: the clicker hears it from its own use; the
         // server sends it to the others only.
         for (pos, sound, volume, pitch) in sounds {
@@ -4104,12 +4221,45 @@ impl Game<'_> {
         })
     }
 
-    /// Run BlockItem.place on a disposable level before predicting its swing.
-    /// The real level supplies collision shapes and building-blocking entities;
-    /// block writes, random draws, scheduled ticks and events stay in the preview.
-    fn remote_can_place(&mut self, hit: &super::Hit, stack: &ItemStack) -> bool {
+    /// MultiPlayerGameMode.useItemOn inside startPrediction, for a block item:
+    /// the blocks `BlockItem.place` set at `pos` are placed on this client's
+    /// level at once, so the next click of a fast bridge aims at them rather
+    /// than past them (the server would refuse it). Its place sound is the
+    /// placer's own (`playSound(player, ...)`: the server sends it to the
+    /// others only).
+    fn predict_place(&mut self, (pos, changes): &DryPlace, seq: i32) {
+        let ticks = self.ticks;
+        if let Some(r) = self.remote.as_mut() {
+            // set_block plays the place sound of the block at `placing`.
+            r.placing = Some(([pos.x, pos.y, pos.z], ticks));
+        }
+        self.predict_blocks(changes, seq);
+    }
+    /// The blocks a use changed, set on this client's level and kept as
+    /// predicted under the use's sequence until the server acknowledges it
+    /// (`BlockStatePredictionHandler.retainKnownServerState`): a use the
+    /// server refused goes back.
+    fn predict_blocks(&mut self, changes: &DryChanges, seq: i32) {
+        for &(p, state) in changes {
+            let pos = [p.x, p.y, p.z];
+            let before = self.world.block(p.x, p.y, p.z);
+            if let Some(r) = self.remote.as_mut() {
+                r.predictions
+                    .entry(pos)
+                    .and_modify(|e| e.0 = seq)
+                    .or_insert((seq, before.0 as i32));
+            }
+            self.set_block(pos, state.0 as i32);
+        }
+    }
+
+    /// Run BlockItem.place on a disposable level: where it placed and the
+    /// blocks it set. The real level supplies collision shapes and
+    /// building-blocking entities; random draws, scheduled ticks and events
+    /// stay in the preview.
+    fn remote_can_place(&mut self, hit: &super::Hit, stack: &ItemStack) -> Option<DryPlace> {
         if !self.may_build() {
-            return false;
+            return None;
         }
         let ctx = horizon_world::level::PlaceContext {
             clicked_pos: horizon_core::position::BlockPos::new(hit.pos[0], hit.pos[1], hit.pos[2]),
@@ -4124,14 +4274,16 @@ impl Game<'_> {
         };
         self.with_level(|b, level, _| {
             let mut level = DryLevel::new(level);
-            matches!(
-                b.place_block(
-                    &mut level,
-                    &mut horizon_world::level::Ticks::default(),
-                    &ctx
-                ),
-                horizon_world::level::PlaceOutcome::Placed { .. }
-            )
+            match b.place_block(
+                &mut level,
+                &mut horizon_world::level::Ticks::default(),
+                &ctx,
+            ) {
+                horizon_world::level::PlaceOutcome::Placed { pos, .. } => {
+                    Some((pos, level.changed.into_iter().collect()))
+                }
+                horizon_world::level::PlaceOutcome::Failed => None,
+            }
         })
     }
 
@@ -4233,11 +4385,13 @@ impl Game<'_> {
             return;
         };
         let stack = self.stack_in(slot).cloned();
+        // Another hotbar slot picked: LivingEntity.updatingUsingItem sees a
+        // different stack in the hand. The off hand keeps its item.
+        let in_hand = slot == self.selected || slot == super::shield::OFFHAND_SLOT;
         // A drawn bow, a charging crossbow, a raised shield...: held until
-        // the button lets go (or another slot is picked).
+        // the button lets go.
         if stack.as_ref().is_some_and(|s| self.held_until_released(s)) {
-            self.using = (slot == self.selected || slot == super::shield::OFFHAND_SLOT)
-                .then_some((slot, ticks + 1));
+            self.using = in_hand.then_some((slot, ticks + 1));
             return;
         }
         let consumable = stack
@@ -4251,7 +4405,7 @@ impl Game<'_> {
         // Button release belongs to the next handleKeybinds phase, which
         // sends RELEASE_USE_ITEM. Do not silently clear a use begun by a
         // quick press/release between ticks.
-        if slot != self.selected {
+        if !in_hand {
             self.using = None;
             return;
         }
@@ -4360,12 +4514,12 @@ impl Game<'_> {
                 id: self.creatures.projectiles[i].id as i32,
             }));
             self.reset_attack_strength();
-        } else if let Some(hit) = self.remote_object_hit()
+        } else if let Some(hit) = self.remote_object_hit(true)
             && self.mob_hit().is_none_or(|(_, d)| hit.distance < d)
             && self.before_block(hit.distance)
         {
             // VehicleEntity.hurtServer, ItemFrame and ArmorStand hurtServer,
-            // a painting broken: the server decides.
+            // a painting broken or an EndCrystal hurtServer: the server decides.
             self.send(S::Attack(play::Attack { id: hit.id }));
             self.reset_attack_strength();
         } else if let Some((i, distance)) = self.mob_hit()
@@ -4572,12 +4726,10 @@ impl Game<'_> {
         for &(slot, button, input) in ops {
             let slot = match slot {
                 None => -999,
-                Some(internal) => {
-                    match (0..64).find(|&s| Self::menu_slot(&menu, s) == Some(internal)) {
-                        Some(s) => s as i16,
-                        None => return false,
-                    }
-                }
+                Some(internal) => match Self::menu_slot_index(&menu, internal) {
+                    Some(s) => s as i16,
+                    None => return false,
+                },
             };
             clicks.push((slot, button, input));
         }
@@ -4646,7 +4798,7 @@ impl Game<'_> {
     /// such slot.
     pub(super) fn remote_slot_click(&mut self, internal: usize, button: i8, input: i32) -> bool {
         let (container, menu) = self.remote_menu();
-        let slot = (0..64).find(|&s| Self::menu_slot(&menu, s) == Some(internal));
+        let slot = Self::menu_slot_index(&menu, internal);
         let Some(slot) = slot else { return false };
         let carried = self.to_network(&self.carried).map(|s| Hashed::of(&s));
         let state = self.remote.as_ref().map_or(0, |r| r.state_id);
@@ -4722,6 +4874,11 @@ impl Game<'_> {
         self.mount_menu_reset();
         // The client's menu has no level access: what it holds is the server's.
         self.station = None;
+        // AbstractContainerMenu.removed: the server gives the grid and the
+        // carried stack back to the inventory and syncs it; the copies here
+        // are stale the moment the window closes.
+        self.craft_grid.fill(None);
+        self.carried = None;
         self.craft_size = 2;
         if let Some(key) = self.container.take() {
             // Server containers stay renderable but lose their copied slots.
@@ -5081,6 +5238,8 @@ impl Game<'_> {
                 .collect::<Vec<_>>(),
             // The player's own model exists (third person and the inventory draw it).
             "player_model": self.player_model.is_some(),
+            "text_display_vertices": self.text_display_vertices,
+            "text_displays": self.text_displays.len(),
             "health": r.health.0,
             "food": r.health.1,
             "decode_errors": r.decode_errors,
@@ -5180,11 +5339,12 @@ type DrySound = (
     f32,
     f32,
 );
+/// The blocks a use on the dry level set.
+type DryChanges = Vec<(horizon_core::position::BlockPos, BlockStateId)>;
 /// What a use on the dry level changed, and the sounds it played.
-type DryUse = (
-    Vec<(horizon_core::position::BlockPos, BlockStateId)>,
-    Vec<DrySound>,
-);
+type DryUse = (DryChanges, Vec<DrySound>);
+/// Where `BlockItem.place` on the dry level placed, and the blocks it set.
+type DryPlace = (horizon_core::position::BlockPos, DryChanges);
 
 /// The blocks a guest's hand flips that its use predicts (and hears at once): a wooden or
 /// copper door, trapdoor or fence gate, a lever or a button. An iron door or trapdoor has
@@ -5373,6 +5533,10 @@ impl horizon_client::interaction_input::InteractionWorld for RemoteInputWorld<'_
 }
 
 impl Remote {
+    /// Players in the server's player list, this one included.
+    pub(super) fn player_count(&self) -> usize {
+        self.players.len()
+    }
     /// The local player's profile UUID.
     pub(super) fn profile(&self) -> u128 {
         self.profile
@@ -5505,4 +5669,28 @@ mod tests {
         }
         assert_eq!(Game::menu_slot("inventory", 46), None);
     }
+
+    #[test]
+    fn remote_clicks_find_slots_past_the_old_large_chest_cutoff() {
+        for (menu, internal, index) in [
+            ("minecraft:generic_9x6", 18, 63),
+            ("minecraft:generic_9x6", 19, 64),
+            ("minecraft:generic_9x6", 0, 81),
+            ("minecraft:generic_9x6", 8, 89),
+            ("minecraft:generic_9x6", 353, 53),
+            ("minecraft:generic_9x5", 8, 80),
+            ("minecraft:generic_9x4", 8, 71),
+            ("minecraft:generic_9x3", 8, 62),
+            ("inventory", 504, 45),
+        ] {
+            assert_eq!(
+                Game::menu_slot_index(menu, internal),
+                Some(index),
+                "{menu}, game slot {internal}"
+            );
+        }
+        assert_eq!(Game::menu_slot_index("minecraft:generic_9x6", 354), None);
+        assert_eq!(Game::menu_slot_index("minecraft:generic_9x6", 504), None);
+        assert_eq!(Game::menu_slot_index("unknown", 0), None);
+    }
 }

crates/horizon-client/src/game/remote_mob_data.rs

@@ -23,6 +23,14 @@ fn apply(m: &mut Mob, values: &[(u8, i32, Value)], builtin: &Builtin) {
             // LivingEntity.DATA_HEALTH_ID: the boss bars and the death
             // animation follow it.
             (9, Value::Float(health)) => m.health = *health,
+            // Mob.DATA_MOB_FLAGS_ID: no AI 1, left-handed 2, aggressive 4.
+            // Mob.isAggressive draws the illagers' and skeletons' attack
+            // poses and the vindicator's axe.
+            (15, Value::Byte(flags)) => {
+                m.no_ai = flags & 1 != 0;
+                m.extra.left_handed = flags & 2 != 0;
+                m.ai.aggressive = flags & 4 != 0;
+            }
             (i, Value::Bool(b)) if Some(i) == baby => m.extra.age = if *b { -1 } else { 0 },
             _ => {}
         }
@@ -178,6 +186,19 @@ mod tests {
         assert_eq!(m.fire_ticks, 0);
     }
 
+    #[test]
+    fn mob_flags_turn_aggression_on_and_off() {
+        let Some(mut m) = mob("minecraft:vindicator") else {
+            return;
+        };
+        apply(&mut m, &[(15, s::BYTE, Value::Byte(4 | 2))]);
+        assert!(m.ai.aggressive && m.extra.left_handed && !m.no_ai);
+        assert!(horizon_client::mobs::illager::shows_item(&m));
+        apply(&mut m, &[(15, s::BYTE, Value::Byte(0))]);
+        assert!(!m.ai.aggressive && !m.extra.left_handed);
+        assert!(!horizon_client::mobs::illager::shows_item(&m));
+    }
+
     #[test]
     fn a_villager_takes_its_type_profession_and_level() {
         let Some(mut m) = mob("minecraft:villager") else {

crates/horizon-client/src/game/remote_objects.rs

@@ -24,7 +24,12 @@ impl Game<'_> {
         let at = Vec3::new(position[0], position[1], position[2]);
         let block = position.map(|v| v.floor() as i32);
         self.remove_remote_object(id);
-        if let Some(cart) = super::minecarts::CartKind::from_id(kind) {
+        if kind == "minecraft:text_display" {
+            self.text_displays.insert(
+                id as i32,
+                super::text_displays::RemoteTextDisplay::new(position, yaw),
+            );
+        } else if let Some(cart) = super::minecarts::CartKind::from_id(kind) {
             let mut c = super::minecarts::Minecart::new(id, cart, at);
             c.yaw = yaw;
             c.previous_yaw = yaw;
@@ -93,6 +98,10 @@ impl Game<'_> {
 
     /// `handleSetEntityData` for an object: what changes how it looks.
     pub(super) fn remote_object_data(&mut self, id: i32, values: &[(u8, i32, Value)]) {
+        if let Some(display) = self.text_displays.get_mut(&id) {
+            display.metadata(values);
+            return;
+        }
         let id = id as u32;
         for (index, _, value) in values {
             if self.item_frames.iter().any(|f| f.id == id) {
@@ -273,6 +282,7 @@ impl Game<'_> {
 
     /// Every object a server sent (a new connection, level or dimension).
     pub(super) fn clear_remote_objects(&mut self) {
+        self.text_displays.clear();
         self.carts.clear();
         self.boats.clear();
         self.armor_stands.clear();
@@ -281,6 +291,7 @@ impl Game<'_> {
     }
 
     pub(super) fn remove_remote_object(&mut self, id: u32) {
+        self.text_displays.remove(&(id as i32));
         self.carts.retain(|c| c.id != id);
         self.boats.retain(|b| b.id != id);
         self.armor_stands.retain(|a| a.id != id);

crates/horizon-client/src/game/remote_projectiles.rs

@@ -24,6 +24,14 @@ fn projectile_kind(kind: &str) -> Option<ProjectileKind> {
         "minecraft:llama_spit" => ProjectileKind::LlamaSpit,
         "minecraft:wind_charge" => ProjectileKind::WindCharge,
         "minecraft:breeze_wind_charge" => ProjectileKind::BreezeWindCharge,
+        // Homing state stays on the server; the client interpolates its positions.
+        "minecraft:shulker_bullet" => ProjectileKind::ShulkerBullet {
+            target: horizon_client::mobs::Who::Player,
+            dir: None,
+            steps: 0,
+            delta: [0.0; 3],
+            seed: 0,
+        },
         "minecraft:wither_skull" => ProjectileKind::WitherSkull { dangerous: false },
         _ => return None,
     })

crates/horizon-client/src/game/remote_vehicles.rs

@@ -9,8 +9,8 @@
 //! server (`LocalPlayer.tick`: `ServerboundMoveVehiclePacket`,
 //! `AbstractBoat.tick`: `ServerboundPaddleBoatPacket`). A minecart moves on
 //! the server with the rider's input, and the rider sits in it.
-use super::{Game, Keys, view_vector};
-use horizon_core::geometry::Vec3;
+use super::{Game, Keys, ray_box, view_vector};
+use horizon_core::geometry::{Aabb, Vec3};
 use horizon_protocol::packets::play::{self, Serverbound as S};
 
 /// An object under the crosshair: its entity id, how far along the view it
@@ -24,8 +24,8 @@ pub(super) struct ObjectHit {
 
 impl Game<'_> {
     /// The nearest boat, minecart, item frame, armor stand or painting the
-    /// view hits within reach.
-    pub(super) fn remote_object_hit(&self) -> Option<ObjectHit> {
+    /// view hits within reach; also End crystals when attacking.
+    pub(super) fn remote_object_hit(&self, attacking: bool) -> Option<ObjectHit> {
         let eye = self.eye_position()?;
         let dir = view_vector(self.yaw, self.pitch);
         let at = |d: f64| {
@@ -64,6 +64,22 @@ impl Game<'_> {
             let p = self.carts[i].position;
             hits.push((self.carts[i].id as i32, d, [p.x, p.y, p.z]));
         }
+        if attacking {
+            // EndCrystal.isPickable: its 2 x 2 box, with the server's entity
+            // id, not special_targets' local projectile target id.
+            // Entity.interact passes on a crystal, so right clicks use the item.
+            let reach = if self.creative { 5.0 } else { 3.0 };
+            for c in self.crystals.iter().filter(|c| c.id != 0) {
+                let p = c.position;
+                let bounds = Aabb::new(
+                    Vec3::new(p.x - 1.0, p.y, p.z - 1.0),
+                    Vec3::new(p.x + 1.0, p.y + 2.0, p.z + 1.0),
+                );
+                if let Some(d) = ray_box(eye, dir, reach, bounds) {
+                    hits.push((c.id as i32, d, [p.x, p.y, p.z]));
+                }
+            }
+        }
         let (id, distance, origin) = hits.into_iter().min_by(|a, b| a.1.total_cmp(&b.1))?;
         let point = at(distance);
         Some(ObjectHit {

crates/horizon-client/src/game/render_control.rs

@@ -13,6 +13,7 @@ pub const HELP: &[&str] = &[
     "signedit X Y Z [front|back]    open the sign editor for the sign at X Y Z",
     "section-draws [flat|indirect]  how terrain sections are drawn (A/B checks); replies the mode",
     "section-cull [on|off]          occlusion culling of solid sections (A/B checks); replies the mode",
+    "section-sides [on|off]         leave out solid quads facing away from the eye (A/B checks); replies the mode",
 ];
 
 impl Game<'_> {

crates/horizon-client/src/game/render_tick.rs

@@ -100,7 +100,10 @@ impl Game<'_> {
                 skybox: self.dim == Dim::Overworld,
                 blindness: None,
                 darkness: self.darkness_fog(),
-                boss_world_fog: self.dragon_bar_shown(),
+                darken_world: self
+                    .boss_overlay
+                    .darken_amount(self.clock.fraction() as f32),
+                boss_world_fog: self.boss_overlay.should_create_world_fog(),
             },
         )
     }

crates/horizon-client/src/game/scoreboard.rs

@@ -180,7 +180,7 @@ impl Game<'_> {
             | Target::Cart(id)
             | Target::Other(id) => self.persist.raw.get(&id),
             Target::Player => self.level.player_extra.as_ref(),
-            Target::Guest(_) | Target::Orb(_) | Target::Arrow(_) => None,
+            Target::Guest(_) | Target::Orb(_) | Target::Projectile(_) => None,
         };
         match raw.and_then(|r| r.get("Tags")) {
             Some(Tag::List(l)) => l
@@ -332,6 +332,7 @@ impl Game<'_> {
             return;
         }
         self.load_scoreboard();
+        host.hub.teams.clone_from(&self.score.board.teams);
         let view = horizon_client::lan::scoreboard::View::of(&self.score.board);
         for g in host.hub.guests.iter_mut().filter(|g| g.placed) {
             if g.scoreboard != view {

crates/horizon-client/src/game/screens.rs

@@ -2,6 +2,7 @@
 use super::{Game, Screen};
 use horizon_client::{
     Result,
+    command::args::GameMode,
     hud::{HudBatch, rgba},
     text::{self, Text},
     ui,
@@ -81,9 +82,15 @@ fn pause_icons(w: f32, h: f32) -> [(f32, f32, &'static str); 4] {
         (x0 + 72.0, y, "gui/sprites/pause_menu/player_reporting"),
     ]
 }
-fn death_buttons(w: f32, h: f32) -> [(f32, f32, &'static str, u8); 2] {
+/// DeathScreen.init: a hardcore player can only spectate.
+fn death_buttons(w: f32, h: f32, hardcore: bool) -> [(f32, f32, &'static str, u8); 2] {
+    let respawn = if hardcore {
+        "deathScreen.spectate"
+    } else {
+        "deathScreen.respawn"
+    };
     [
-        (w / 2.0 - 100.0, h / 4.0 + 72.0, "deathScreen.respawn", 0),
+        (w / 2.0 - 100.0, h / 4.0 + 72.0, respawn, 0),
         (
             w / 2.0 - 100.0,
             h / 4.0 + 96.0,
@@ -223,7 +230,12 @@ impl Game<'_> {
                 ),
             );
         }
-        let title = Text::translate("deathScreen.title", &[]);
+        let title = if self.level.hardcore {
+            "deathScreen.title.hardcore"
+        } else {
+            "deathScreen.title"
+        };
+        let title = Text::translate(title, &[]);
         let tw = atlas.font.width_text(&title);
         ui::text_scaled(
             batch,
@@ -258,7 +270,7 @@ impl Game<'_> {
             .ui
             .died_at
             .is_none_or(|t| t.elapsed().as_millis() >= 1000);
-        for (x, y, key, _) in death_buttons(w, h) {
+        for (x, y, key, _) in death_buttons(w, h, self.level.hardcore) {
             let hover = active && ui::hovered(self.cursor, x, y, 200.0, 20.0);
             ui::button(
                 batch,
@@ -286,7 +298,7 @@ impl Game<'_> {
             .as_ref()
             .map_or([1, 1], |r| [r.config.width, r.config.height]);
         let b = HudBatch::new(size);
-        let hit = death_buttons(b.width, b.height)
+        let hit = death_buttons(b.width, b.height, self.level.hardcore)
             .into_iter()
             .find(|d| ui::hovered(self.cursor, d.0, d.1, 200.0, 20.0))
             .map(|d| d.3);
@@ -330,6 +342,11 @@ impl Game<'_> {
             Some(1) => self.close_world()?,
             _ => {}
         }
+        // ServerGamePacketListenerImpl.handleClientCommand: a hardcore world's
+        // respawned player only watches.
+        if hit == Some(0) && self.remote.is_none() && self.level.hardcore {
+            self.set_mode(GameMode::Spectator);
+        }
         if hit.is_some() {
             self.audio.play_button_click();
         }

crates/horizon-client/src/game/server_packs.rs

@@ -8,14 +8,19 @@ use horizon_client::{
     Result,
     confirm_screen::Confirm,
     hud::{HudAtlas, HudBatch},
-    multiplayer, packs,
+    java_text, multiplayer, packs,
     scoreboard::{comp_text, tag_to_json},
     server_packs::{Prompt, ServerPacks, action, download, parse_sha1, valid_url},
     text::{Text, named_color},
+    toasts::SystemToast,
     ui,
 };
+use horizon_core::jmath;
 use horizon_protocol::{packets::configuration::ResourcePackPush, servers};
-use std::path::PathBuf;
+use std::{
+    path::PathBuf,
+    sync::mpsc::{Receiver, TryRecvError},
+};
 
 /// `ClientCommonPacketListenerImpl.PackConfirmScreen`: the packs it asks
 /// about, whether the last one is required, and the server's message.
@@ -75,6 +80,111 @@ pub(super) struct ServerPackState {
     user: (String, u128),
     /// The packs loaded on top of the player's own, bottom first.
     pub(super) active: Vec<packs::Pack>,
+    /// The download batches' notifiers, oldest first.
+    notifiers: Vec<PackNotifier>,
+}
+/// `DownloadedPackSource.createDownloadNotifier`: one batch's progress in its
+/// own `SystemToast`.
+struct PackNotifier {
+    progress: Receiver<download::Progress>,
+    total: usize,
+    /// `count`: the requests started.
+    count: usize,
+    /// `failCount`.
+    failed: usize,
+    /// `totalBytes`: the Content-Length of the request in flight.
+    size: Option<u64>,
+    /// The bytes it has written so far: none before the first response.
+    bytes: Option<u64>,
+    /// The last request has finished.
+    done: bool,
+    toast: Option<SystemToast>,
+}
+impl PackNotifier {
+    fn new(progress: Receiver<download::Progress>, total: usize) -> Self {
+        Self {
+            progress,
+            total,
+            count: 0,
+            failed: 0,
+            size: None,
+            bytes: None,
+            done: false,
+            toast: None,
+        }
+    }
+    /// The batch's events since the last call, with the toast updated once
+    /// for all of them. False once the batch has ended and its toast is gone.
+    fn poll(&mut self) -> bool {
+        let (mut changed, mut hide) = (false, false);
+        let ended = loop {
+            let event = match self.progress.try_recv() {
+                Ok(event) => event,
+                Err(e) => break e == TryRecvError::Disconnected,
+            };
+            changed |= match event {
+                download::Progress::RequestStart => {
+                    self.count += 1;
+                    true
+                }
+                download::Progress::DownloadStart(size) => {
+                    self.size = size;
+                    self.bytes = Some(0);
+                    true
+                }
+                download::Progress::Bytes(bytes) => {
+                    self.bytes = Some(bytes);
+                    true
+                }
+                download::Progress::RequestFinished(ok) => {
+                    self.failed += usize::from(!ok);
+                    self.done = self.count == self.total;
+                    // Every pack came: forceHide; else the failure title.
+                    hide |= self.done && self.failed == 0;
+                    self.done && self.failed > 0
+                }
+            };
+        };
+        if changed {
+            let (title, message) = self.text();
+            let (title, message) = (title.plain(), message.map(|m| m.plain()));
+            // SystemToast.addOrUpdate.
+            match &mut self.toast {
+                Some(toast) => toast.reset(title, message),
+                None => self.toast = Some(SystemToast::new(title, message)),
+            }
+        }
+        if hide && let Some(toast) = &mut self.toast {
+            toast.force_hide();
+        }
+        !ended || self.toast.is_some()
+    }
+    /// The toast's title and message.
+    fn text(&self) -> (Text, Option<Text>) {
+        if self.done && self.failed > 0 {
+            let failed = Text::tr("download.pack.failed", &[&self.failed, &self.total]);
+            return (failed, None);
+        }
+        let title = Text::tr("download.pack.title", &[&self.count, &self.total]);
+        let message = self.bytes.map(|bytes| match self.size {
+            Some(size) if size > 0 => {
+                Text::tr("download.pack.progress.percent", &[&(bytes * 100 / size)])
+            }
+            _ => Text::tr("download.pack.progress.bytes", &[&human_readable(bytes)]),
+        });
+        (title, message)
+    }
+}
+/// `com.mojang.realmsclient.Unit.humanReadable`, for
+/// `download.pack.progress.bytes`.
+fn human_readable(bytes: u64) -> String {
+    if bytes < 1024 {
+        return format!("{bytes} B");
+    }
+    let exp = (jmath::log(bytes as f64) / jmath::log(1024.0)) as i32;
+    let prefix = &"KMGTPE"[exp as usize - 1..exp as usize];
+    let value = bytes as f64 / 1024f64.powi(exp);
+    format!("{} {prefix}B", java_text::format_fixed(value, 1))
 }
 
 fn saves() -> PathBuf {
@@ -89,6 +199,7 @@ impl Game<'_> {
         let state = &mut self.server_packs;
         state.user = user;
         state.prompt = None;
+        state.notifiers.clear();
         let Some(address) = address else {
             state.address = None;
             state.packs.local_world();
@@ -103,6 +214,7 @@ impl Game<'_> {
     /// `Minecraft.clearDownloadedResourcePacks`: every server pack goes at once.
     pub(super) fn server_packs_disconnect(&mut self) {
         self.server_packs.prompt = None;
+        self.server_packs.notifiers.clear();
         self.server_packs.packs.disconnect();
         self.tick_server_packs();
     }
@@ -197,6 +309,7 @@ impl Game<'_> {
     /// that finished, the ones to start, a resource reload when the active
     /// packs change, and the statuses for the server.
     pub(super) fn tick_server_packs(&mut self) {
+        self.server_packs.notifiers.retain_mut(PackNotifier::poll);
         // A reload waits for the world's resources (`reload_packs`).
         if self.rest_loader.is_some() || self.world_loader.is_some() {
             return;
@@ -238,6 +351,15 @@ impl Game<'_> {
                 Ok(queue) => state.queue = Some(queue),
                 Err(e) => {
                     log::error!("Horizon: failed to open the download queue: {e}");
+                    // Every request failed, as the notifier would hear it.
+                    let (progress, events) = std::sync::mpsc::channel();
+                    for _ in &requests {
+                        let _ = progress.send(download::Progress::RequestStart);
+                        let _ = progress.send(download::Progress::RequestFinished(false));
+                    }
+                    state
+                        .notifiers
+                        .push(PackNotifier::new(events, requests.len()));
                     let failed = requests.iter().map(|r| r.id).collect();
                     state.packs.downloaded(horizon_client::server_packs::Batch {
                         downloaded: Vec::new(),
@@ -248,8 +370,12 @@ impl Game<'_> {
             }
         }
         let headers = download::headers(&state.user.0, state.user.1);
+        let (progress, events) = std::sync::mpsc::channel();
+        state
+            .notifiers
+            .push(PackNotifier::new(events, requests.len()));
         if let Some(queue) = &state.queue {
-            queue.download(requests, headers);
+            queue.download(requests, headers, progress);
         }
     }
     /// `DownloadedPackSource.startReload`: the packs on top of the player's
@@ -297,6 +423,29 @@ impl Game<'_> {
             .layout(atlas, (w, h))
             .draw(batch, atlas, self.cursor, [&yes, &no]);
     }
+    /// The download notifiers' toasts, each in the next 32-pixel slot
+    /// below an advancement or recipe toast (`ToastManager`).
+    pub(super) fn draw_pack_toasts(&mut self, batch: &mut HudBatch) {
+        let multiplier = f64::from(self.settings.notification_display_time);
+        let mut slot = usize::from(!self.adv.toasts.is_empty());
+        for notifier in &mut self.server_packs.notifiers {
+            let Some(toast) = &mut notifier.toast else {
+                continue;
+            };
+            let (sound, finished) = toast.update(multiplier);
+            if let Some(show) = sound {
+                let event = if show { "ui.toast.in" } else { "ui.toast.out" };
+                self.audio
+                    .play(&format!("minecraft:{event}"), None, 1.0, 1.0);
+            }
+            if finished {
+                notifier.toast = None;
+                continue;
+            }
+            toast.draw(&self.gui.atlas, batch, 32.0 * slot as f32);
+            slot += 1;
+        }
+    }
     /// A left click on the prompt: its answer when it hit a button.
     pub(super) fn pack_prompt_click(&mut self) -> Result<()> {
         let Some(prompt) = &self.server_packs.prompt else {
@@ -314,3 +463,97 @@ impl Game<'_> {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use download::Progress::*;
+
+    fn notifier(total: usize, events: &[download::Progress]) -> PackNotifier {
+        let (send, receive) = std::sync::mpsc::channel();
+        for event in events {
+            send.send(*event).unwrap();
+        }
+        let mut notifier = PackNotifier::new(receive, total);
+        assert!(notifier.poll());
+        notifier
+    }
+    fn texts(n: &PackNotifier) -> (serde_json::Value, Option<serde_json::Value>) {
+        let (title, message) = n.text();
+        (title.component(), message.map(|m| m.component()))
+    }
+
+    #[test]
+    fn the_toast_counts_requests_and_shows_progress() {
+        let n = notifier(2, &[RequestStart]);
+        let (title, message) = texts(&n);
+        assert_eq!(title["translate"], "download.pack.title");
+        assert_eq!(title["with"], serde_json::json!([1, 2]));
+        assert_eq!(message, None);
+        let n = notifier(2, &[RequestStart, DownloadStart(Some(400)), Bytes(100)]);
+        assert_eq!(
+            texts(&n).1.unwrap(),
+            serde_json::json!({"translate": "download.pack.progress.percent", "with": [25]})
+        );
+        let n = notifier(1, &[RequestStart, DownloadStart(None), Bytes(1280)]);
+        assert_eq!(
+            texts(&n).1.unwrap()["with"],
+            serde_json::json!([{"text": "1.3 KB"}])
+        );
+    }
+
+    #[test]
+    fn a_failed_pack_turns_the_toast_into_the_failure_count() {
+        let events = [
+            RequestStart,
+            RequestFinished(false),
+            RequestStart,
+            DownloadStart(Some(3)),
+            Bytes(3),
+        ];
+        let (send, receive) = std::sync::mpsc::channel();
+        for event in events {
+            send.send(event).unwrap();
+        }
+        let mut n = PackNotifier::new(receive, 2);
+        assert!(n.poll());
+        // Not the last request yet: still downloading.
+        assert_eq!(texts(&n).0["translate"], "download.pack.title");
+        send.send(RequestFinished(true)).unwrap();
+        drop(send);
+        assert!(n.poll(), "the failure toast stays until it slides out");
+        let (title, message) = texts(&n);
+        assert_eq!(
+            title,
+            serde_json::json!({"translate": "download.pack.failed", "with": [1, 2]})
+        );
+        assert_eq!(message, None);
+    }
+
+    #[test]
+    fn a_finished_batch_without_a_toast_is_dropped() {
+        let (send, receive) = std::sync::mpsc::channel::<download::Progress>();
+        drop(send);
+        assert!(!PackNotifier::new(receive, 1).poll());
+    }
+
+    #[test]
+    fn sizes_read_as_realms_unit_human_readable() {
+        // com.mojang.realmsclient.Unit.humanReadable, run on the 26.3 jar.
+        for (bytes, text) in [
+            (0, "0 B"),
+            (1023, "1023 B"),
+            (1024, "1.0 KB"),
+            (1280, "1.3 KB"),
+            (1535, "1.5 KB"),
+            (10_000, "9.8 KB"),
+            (1_048_575, "1024.0 KB"),
+            (1_048_576, "1.0 MB"),
+            (52_428_800, "50.0 MB"),
+            (262_144_000, "250.0 MB"),
+            (1_073_741_824, "1.0 GB"),
+        ] {
+            assert_eq!(human_readable(bytes), text, "{bytes}");
+        }
+    }
+}

crates/horizon-client/src/game/shader_packs.rs

@@ -0,0 +1,84 @@
+//! Shader packs, for development until the Shader Packs page exists: `HORIZON_SHADER_PACK=<name>`
+//! runs `shaderpacks/<name>` (a folder or a zip beside `options.txt`) over the world. The
+//! programs of the current dimension's folder are loaded when the dimension changes (spec 1.2).
+
+use horizon_client::camera::CameraFluid;
+use horizon_client::gfx::pack_uniforms::PackInputs;
+use horizon_shaders::{Macros, Pack, Properties, dimension_folder, load_post};
+
+use super::{Dim, Game};
+
+impl Game<'_> {
+    /// Loads the pack for the current dimension when it changed, and returns this frame's
+    /// inputs to the pack's uniforms.
+    pub(super) fn shader_pack_inputs(&mut self, camera: glam::DVec3, partial: f32) -> PackInputs {
+        let Some(name) = std::env::var_os("HORIZON_SHADER_PACK") else {
+            return PackInputs::default();
+        };
+        let dimension = match self.dim {
+            Dim::Overworld => 0,
+            Dim::Nether => -1,
+            Dim::End => 1,
+        };
+        if let Some(renderer) = &mut self.renderer
+            && renderer.shader_pack_dimension() != Some(dimension)
+        {
+            let name = name.to_string_lossy();
+            let started = std::time::Instant::now();
+            let path = std::env::current_dir()
+                .unwrap_or_default()
+                .join("shaderpacks")
+                .join(&*name);
+            match Pack::open(&path) {
+                Ok(pack) => {
+                    let macros = Macros::standard();
+                    let text = pack.read_text("shaders.properties").unwrap_or_default();
+                    let properties = Properties::parse(&text, &macros);
+                    for note in &properties.notes {
+                        log::warn!(
+                            "shader pack {name}: shaders.properties:{}: {}",
+                            note.line,
+                            note.message
+                        );
+                    }
+                    let folder = dimension_folder(&pack, dimension);
+                    let post = load_post(&pack, &folder, &properties, &macros, None);
+                    if let Some((programs, notes)) = renderer.set_shader_pack(dimension, Some(post))
+                    {
+                        for note in notes {
+                            log::warn!("shader pack {name}: {note}");
+                        }
+                        log::info!(
+                            "shader pack {name}: folder `{folder}`, {} programs ({}) in {} ms",
+                            programs.len(),
+                            programs.join(" "),
+                            started.elapsed().as_millis()
+                        );
+                    }
+                }
+                Err(e) => {
+                    log::warn!("shader pack {name}: {e}");
+                    renderer.set_shader_pack(dimension, None);
+                }
+            }
+        }
+        let lerp = |(old, new): (f32, f32)| old + (new - old) * partial;
+        let at = camera.floor().as_ivec3();
+        let light = self.world.light(at.x, at.y, at.z);
+        PackInputs {
+            day_time: self.world.day_time,
+            rain: lerp(self.world.weather.rain_level),
+            thunder: lerp(self.world.weather.thunder_level),
+            eye_in: match self.camera_fluid(camera.to_array()) {
+                CameraFluid::None => 0,
+                CameraFluid::Water => 1,
+                CameraFluid::Lava => 2,
+                CameraFluid::PowderSnow => 3,
+            },
+            blindness: f32::from(u8::from(self.potions.effects.get("blindness").is_some())),
+            eye_light: [i32::from(light & 15), i32::from(light >> 4)],
+            hide_gui: self.ui.hide_gui,
+            brightness: self.settings.gamma,
+        }
+    }
+}

crates/horizon-client/src/game/sign_edit.rs

@@ -78,7 +78,7 @@ impl Game<'_> {
         let Some(g) = host.hub.guest(conn) else {
             return;
         };
-        let near = super::lan_stations::within_reach(g, p.pos);
+        let near = g.within_block_range(p.pos, 4.0);
         let Some(play) = host.play.get_mut(&conn) else {
             return;
         };

crates/horizon-client/src/game/startup_menu.rs

@@ -33,6 +33,7 @@ impl StartupMenu {
             Some(PendingWorldEntry::Server {
                 address: address.clone(),
                 name: options.player_name(),
+                cookies: None,
             })
         } else {
             options
@@ -125,6 +126,7 @@ impl StartupMenu {
             Action::Connect { address } => PendingWorldEntry::Server {
                 address,
                 name: player_name,
+                cookies: None,
             },
             _ => return,
         };
@@ -762,7 +764,7 @@ mod tests {
             "Guest".into(),
         );
         assert!(
-            matches!(menu.pending.take(), Some(PendingWorldEntry::Server { address, name })
+            matches!(menu.pending.take(), Some(PendingWorldEntry::Server { address, name, .. })
             if address == "localhost:25565" && name == "Guest")
         );
         assert!(menu.pending.take().is_none(), "an entry is consumed once");

crates/horizon-client/src/game/storage.rs

@@ -127,6 +127,52 @@ impl Game<'_> {
             None => vec![own],
         }
     }
+    /// `Container.stillValidBlockEntity`: the open block container closes once
+    /// the player's eyes are out of reach of any of its blocks (a 4-block buffer).
+    pub(super) fn tick_container_reach(&mut self) {
+        // A server's menu ends when the server closes it.
+        if self.remote.is_some() {
+            return;
+        }
+        let Some(eye) = self.eye_position() else {
+            return;
+        };
+        if self
+            .container
+            .is_none_or(|k| k.1 == super::minecarts::CART_KEY_Y)
+        {
+            return;
+        }
+        let range = self.reach() + 4.0;
+        let near = self.container_parts().iter().all(|&((x, y, z), _)| {
+            horizon_client::lan::guest::within_block_range(eye, range, [x, y, z])
+        });
+        if !near {
+            self.close_container();
+            self.screen = super::Screen::Playing;
+            self.capture(true);
+        }
+    }
+    /// `CraftingMenu.stillValid`: the open crafting table closes once its
+    /// block is no longer a crafting table or the player's eyes are out of
+    /// reach (a 4-block buffer).
+    pub(super) fn tick_craft_table(&mut self) {
+        // A server's menu ends when the server closes it.
+        if self.remote.is_some() || self.craft_size != 3 {
+            return;
+        }
+        let (Some(pos), Some(eye)) = (self.craft_table, self.eye_position()) else {
+            return;
+        };
+        let state = self.world.block(pos[0], pos[1], pos[2]);
+        let table = &*self.res.facts().get(state).name == "minecraft:crafting_table";
+        let range = self.reach() + 4.0;
+        if !(table && horizon_client::lan::guest::within_block_range(eye, range, pos)) {
+            self.close_container();
+            self.screen = super::Screen::Playing;
+            self.capture(true);
+        }
+    }
     /// The number of slots of the open container.
     pub(super) fn container_size(&self) -> usize {
         self.container_parts().iter().map(|p| p.1).sum()

crates/horizon-client/src/game/text_displays.rs

@@ -0,0 +1,302 @@
+//! Server text displays: metadata, interpolation, billboard transforms and world text.
+use super::Game;
+use horizon_client::{
+    hud::{HudBatch, rgba},
+    mesher::Vertex,
+    text::Text,
+    text_display::{Align, TextDisplayData},
+};
+use horizon_protocol::entity_data::Value;
+
+pub(super) struct RemoteTextDisplay {
+    pub data: TextDisplayData,
+    from: TextDisplayData,
+    shown: TextDisplayData,
+    position: glam::DVec3,
+    previous: glam::DVec3,
+    target: glam::DVec3,
+    rotation: [f32; 2],
+    old_rotation: [f32; 2],
+    target_rotation: [f32; 2],
+    steps: i32,
+    age: i64,
+    start: i64,
+    duration: i32,
+    dirty: bool,
+    start_dirty: bool,
+    duration_dirty: bool,
+    initialized: bool,
+    /// `Display.lastProgress`: the progress the last frame drew, where a new
+    /// interpolation starts from.
+    last_progress: f32,
+    /// `TextDisplay.clientDisplayCache`: the split lines, until the render
+    /// state changes.
+    lines: Option<Lines>,
+}
+
+/// `TextDisplay.CachedInfo`: each line and its width, and the widest.
+struct Lines {
+    lines: Vec<(Text, f32)>,
+    width: f32,
+}
+
+/// `Display.RENDER_STATE_IDS` and `TextDisplay.TEXT_RENDER_STATE_IDS`: the
+/// data a render state is built from (not the view range, size or glow).
+fn renders(id: u8) -> bool {
+    matches!(id, 11..=16 | 18 | 19 | 23..=27)
+}
+
+impl RemoteTextDisplay {
+    pub fn new(position: [f64; 3], yaw: f32) -> Self {
+        Self {
+            data: Default::default(),
+            from: Default::default(),
+            shown: Default::default(),
+            position: position.into(),
+            previous: position.into(),
+            target: position.into(),
+            rotation: [yaw, 0.0],
+            old_rotation: [yaw, 0.0],
+            target_rotation: [yaw, 0.0],
+            steps: 0,
+            age: 0,
+            start: 0,
+            duration: 0,
+            dirty: true,
+            start_dirty: false,
+            duration_dirty: false,
+            initialized: false,
+            last_progress: 0.0,
+            lines: None,
+        }
+    }
+    fn progress(&self, partial: f32) -> f32 {
+        if self.duration <= 0 {
+            1.0
+        } else {
+            (((self.age - self.start) as f32 + partial) / self.duration as f32).clamp(0.0, 1.0)
+        }
+    }
+    pub fn metadata(&mut self, values: &[(u8, i32, Value)]) {
+        self.start_dirty |= values.iter().any(|v| v.0 == 8);
+        self.duration_dirty |= values.iter().any(|v| v.0 == 9);
+        self.dirty |= values.iter().any(|v| renders(v.0));
+        self.data.apply(values);
+    }
+    fn tick(&mut self) {
+        self.age += 1;
+        self.previous = self.position;
+        self.old_rotation = self.rotation;
+        if self.steps > 0 {
+            self.position += (self.target - self.position) / f64::from(self.steps);
+            for i in 0..2 {
+                self.rotation[i] +=
+                    angle(self.target_rotation[i] - self.rotation[i]) / self.steps as f32;
+            }
+            self.steps -= 1;
+        }
+        if self.start_dirty {
+            self.start = self.age + i64::from(self.data.interpolation_delay);
+        }
+        if self.duration_dirty {
+            self.duration = self.data.interpolation_duration;
+        }
+        if self.dirty {
+            self.from = if self.initialized && self.duration > 0 {
+                self.shown.blend(&self.from, self.last_progress)
+            } else {
+                self.data.clone()
+            };
+            self.shown = self.data.clone();
+            self.initialized = true;
+            self.lines = None;
+        }
+        self.dirty = false;
+        self.start_dirty = false;
+        self.duration_dirty = false;
+    }
+    fn move_to(&mut self, position: [f64; 3], rotation: Option<(f32, f32)>) {
+        self.target = position.into();
+        if let Some((yaw, pitch)) = rotation {
+            self.target_rotation = [yaw, pitch];
+        }
+        self.steps = self.data.teleport_duration.clamp(0, 59);
+        if self.steps == 0 {
+            self.position = self.target;
+            self.previous = self.target;
+            self.rotation = self.target_rotation;
+            self.old_rotation = self.rotation;
+        }
+    }
+}
+fn angle(d: f32) -> f32 {
+    (d + 180.0).rem_euclid(360.0) - 180.0
+}
+
+impl Game<'_> {
+    pub(super) fn move_remote_text_display(
+        &mut self,
+        id: i32,
+        position: [f64; 3],
+        rotation: Option<(f32, f32)>,
+    ) {
+        if let Some(d) = self.text_displays.get_mut(&id) {
+            d.move_to(position, rotation);
+        }
+    }
+    pub(super) fn tick_text_displays(&mut self) {
+        for display in self.text_displays.values_mut() {
+            display.tick();
+        }
+    }
+    pub(super) fn text_display_geometry(
+        &mut self,
+        camera: glam::DVec3,
+        partial: f64,
+        normal: &mut Vec<Vertex>,
+        see_through: &mut Vec<Vertex>,
+    ) {
+        self.text_display_vertices = 0;
+        let atlas = &self.gui.atlas;
+        let front = self.camera_type == super::perspective::CameraType::ThirdPersonFront;
+        let angles = if front {
+            [self.yaw + 180.0, -self.pitch]
+        } else {
+            [self.yaw, self.pitch]
+        };
+        for display in self.text_displays.values_mut() {
+            display.last_progress = display.progress(partial as f32);
+            let d = display.shown.blend(&display.from, display.last_progress);
+            let position = display.previous.lerp(display.position, partial);
+            let range = f64::from(d.view_range) * 64.0 * f64::from(self.settings.entity_distance);
+            if position.distance_squared(camera) >= range * range || d.text.is_empty() {
+                continue;
+            }
+            let rotation = std::array::from_fn(|i| {
+                display.old_rotation[i]
+                    + angle(display.rotation[i] - display.old_rotation[i]) * partial as f32
+            });
+            let mut matrix = glam::Mat4::from_translation((position - camera).as_vec3())
+                * d.matrix(rotation, angles)
+                * glam::Mat4::from_rotation_y(std::f32::consts::PI)
+                * glam::Mat4::from_scale(glam::Vec3::splat(-0.025));
+            if !matrix.is_finite() {
+                continue;
+            }
+            // TextDisplayRenderer.splitLines: Font.split, no indent on wrapped lines.
+            let Lines { lines, width } = display.lines.get_or_insert_with(|| {
+                let lines: Vec<_> = atlas
+                    .font
+                    .split(&d.text, d.line_width as f32)
+                    .into_iter()
+                    .map(|line| {
+                        let width = atlas.font.width_text(&line).ceil();
+                        (line, width)
+                    })
+                    .collect();
+                let width = lines.iter().map(|l| l.1).fold(0.0, f32::max);
+                Lines { lines, width }
+            });
+            let width = *width;
+            let height = lines.len() as f32 * 10.0 - 1.0;
+            matrix *=
+                glam::Mat4::from_translation(glam::Vec3::new(1.0 - width / 2.0, -height, 0.0));
+            let mut batch = HudBatch::new([1, 1]);
+            let bg = if d.flags & 4 != 0 {
+                self.settings.text_background(0.25)
+            } else {
+                d.background as u32
+            };
+            if bg != 0 {
+                batch.fill(
+                    atlas,
+                    -1.0,
+                    -1.0,
+                    width + 1.0,
+                    height + 1.0,
+                    rgba(
+                        (bg >> 16) as u8,
+                        (bg >> 8) as u8,
+                        bg as u8,
+                        (bg >> 24) as u8,
+                    ),
+                );
+            }
+            let align = d.align();
+            for (i, (line, line_width)) in lines.iter().enumerate() {
+                let x = match align {
+                    Align::Left => 0.0,
+                    Align::Right => width - line_width,
+                    Align::Center => (width - line_width) / 2.0,
+                };
+                batch.text_styled(
+                    atlas,
+                    line,
+                    x,
+                    i as f32 * 10.0,
+                    rgba(255, 255, 255, d.opacity as u8),
+                    d.flags & 1 != 0,
+                );
+            }
+            let world_light = self.world.light(
+                position.x.floor() as i32,
+                position.y.floor() as i32,
+                position.z.floor() as i32,
+            );
+            let light = if d.brightness == -1 {
+                horizon_client::block_entity_render::vertex_light(world_light)
+            } else {
+                ((d.brightness as u32 >> 20 & 15) * 16)
+                    | (((d.brightness as u32 >> 4 & 15) * 16) << 8)
+            };
+            let through = d.flags & 2 != 0;
+            let out = if through {
+                &mut *see_through
+            } else {
+                &mut *normal
+            };
+            for quad in batch.vertices.as_chunks::<6>().0 {
+                for i in [0, 1, 2, 5] {
+                    let v = quad[i];
+                    let point =
+                        matrix.transform_point3(glam::Vec3::new(v.pos[0], v.pos[1], v.depth));
+                    out.push(Vertex {
+                        pos: point.to_array(),
+                        uv: v.uv,
+                        color: v.color,
+                        light,
+                        layer: if through { 2 } else { 0 },
+                        normal: [0; 4],
+                    });
+                }
+            }
+            self.text_display_vertices += batch.vertices.len() / 6 * 4;
+            self.map_patches.extend(batch.patches);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn metadata_and_position_interpolation_keep_their_separate_clocks() {
+        let mut d = RemoteTextDisplay::new([0.0; 3], 0.0);
+        d.tick();
+        d.metadata(&[
+            (8, 1, Value::Int(0)),
+            (9, 1, Value::Int(4)),
+            (10, 1, Value::Int(2)),
+            (11, 0, Value::Floats(vec![4.0, 0.0, 0.0])),
+        ]);
+        d.tick();
+        assert_eq!(d.shown.blend(&d.from, d.progress(0.5)).translation[0], 0.5);
+        d.move_to([2.0, 0.0, 0.0], Some((90.0, 0.0)));
+        d.tick();
+        assert_eq!(d.position.x, 1.0);
+        assert_eq!(d.rotation[0], 45.0);
+        d.tick();
+        assert_eq!(d.position.x, 2.0);
+        assert_eq!(d.shown.blend(&d.from, d.progress(0.0)).translation[0], 2.0);
+    }
+}

crates/horizon-client/src/game/wither.rs

@@ -2,10 +2,8 @@
 //! its boss bar, and its skulls hitting and exploding.
 use super::Game;
 use horizon_client::{
-    hud_overlays,
     mobs::{Damage, DamageKind, Species, Who},
     projectiles::{Projectile, ProjectileKind},
-    text::Text,
 };
 
 impl Game<'_> {
@@ -78,45 +76,6 @@ impl Game<'_> {
         }
         Ok(())
     }
-    /// The wither boss bars (purple), within range.
-    pub(super) fn wither_bars(&self, bars: &mut Vec<hud_overlays::BossBar>) {
-        let Some(p) = self.player.as_ref() else {
-            return;
-        };
-        for m in self
-            .mobs
-            .iter()
-            .filter(|m| m.species() == Species::Wither && m.alive())
-        {
-            if m.position.distance_squared(p.position) > 64.0 * 64.0 {
-                continue;
-            }
-            let progress = if m.extra.counter > 0 {
-                1.0 - m.extra.counter as f32 / horizon_client::mobs::wither::INVULNERABLE as f32
-            } else {
-                (m.health / m.attrs.max_health).clamp(0.0, 1.0)
-            };
-            let name = m
-                .custom_name
-                .clone()
-                .unwrap_or_else(|| self.translate("entity.minecraft.wither", "Wither"));
-            bars.push(hud_overlays::BossBar {
-                name: Text::literal(name),
-                progress,
-                color: 5,
-                overlay: 0,
-            });
-        }
-    }
-    pub(super) fn wither_near(&self) -> bool {
-        self.player.as_ref().is_some_and(|p| {
-            self.mobs.iter().any(|m| {
-                m.species() == Species::Wither
-                    && m.alive()
-                    && m.position.distance_squared(p.position) <= 64.0 * 64.0
-            })
-        })
-    }
     /// `WitherSkull.onHitEntity` / `onHit`: 8 damage (healing the wither 5
     /// when it kills), withering for 10 seconds, then a power 1 blast.
     pub(super) fn wither_skull_hit(

crates/horizon-client/src/game/world_loading.rs

@@ -22,6 +22,23 @@ pub(super) struct PreparedWorld {
 }
 
 impl WorldRequest {
+    pub fn new(
+        folder: &str,
+        name: Option<&str>,
+        seed: Option<i64>,
+        creative: bool,
+        create: Option<&horizon_client::title::WorldOptions>,
+    ) -> Result<Self> {
+        Ok(Self {
+            save_root: std::env::current_dir()?.join("saves").join(folder),
+            folder: folder.to_owned(),
+            name: name.map(str::to_owned),
+            seed,
+            creative,
+            create: create.cloned(),
+        })
+    }
+
     pub fn prepare(
         self,
         res: &Resources,
@@ -250,7 +267,7 @@ pub(super) fn make_streaming(
     streaming.nether_shading = dim == Dim::Nether;
     // A server draws nothing: neither the integrated server nor the
     // dedicated one meshes sections.
-    streaming.mesh = !options.integrated && options.dedicated.is_none();
+    streaming.mesh = options.execution_role.is_client();
     Ok((streaming, save, locator))
 }
 

crates/horizon-client/src/gfx.rs

@@ -6,7 +6,7 @@ use crate::{
     environment::Sky,
     graphics::GraphicsApi,
     hud::{HudBatch, HudRenderer},
-    mesher::{SectionMesh, TerrainVertex, Vertex},
+    mesher::{SectionMesh, Sides, TerrainVertex, Vertex},
     sprites::SpriteAnimation,
 };
 use glam::{DVec3, Mat4, Vec3, Vec4};
@@ -35,7 +35,7 @@ fn entity_shader() -> String {
 mod entity_batch;
 mod weather;
 use entity_batch::EntityBatch;
-pub use entity_batch::{SHADOW_OVERLAY, WATER_MASK_OVERLAY};
+pub use entity_batch::{SHADOW_OVERLAY, TRANSLUCENT_PARTICLE_OVERLAY, WATER_MASK_OVERLAY};
 
 /// Window.getAppropriateLineWidth, in framebuffer pixels.
 pub fn outline_width(width: u32) -> f32 {
@@ -68,6 +68,9 @@ mod flat;
 pub mod lightning;
 mod lod;
 mod occlusion;
+mod pack_atlas;
+mod pack_post;
+pub mod pack_uniforms;
 mod page_runs;
 pub mod panorama;
 mod resident;
@@ -87,6 +90,7 @@ fn world_pass_after_culling<'e>(
     encoder: &'e mut wgpu::CommandEncoder,
     view: &wgpu::TextureView,
     depth: &wgpu::TextureView,
+    keep_depth: bool,
 ) -> wgpu::RenderPass<'e> {
     encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
         label: Some("Horizon world, after culling"),
@@ -103,7 +107,12 @@ fn world_pass_after_culling<'e>(
             view: depth,
             depth_ops: Some(wgpu::Operations {
                 load: wgpu::LoadOp::Load,
-                store: wgpu::StoreOp::Discard,
+                // A shader pack reads it as depthtex0.
+                store: if keep_depth {
+                    wgpu::StoreOp::Store
+                } else {
+                    wgpu::StoreOp::Discard
+                },
             }),
             stencil_ops: None,
         }),
@@ -156,9 +165,9 @@ struct SectionGpu {
     page: u32,
     start: u64,
     solid: u32,
+    /// Where the solid quads' buckets by facing side end (`mesher::Sides`).
+    sides: Sides,
     translucent: u32,
-    /// The solid quads by facing: back-facing groups are skipped.
-    faces: crate::mesher::FaceGroups,
     sort: translucency::SortState,
     sorted_indices: Option<(u32, u64)>,
     /// Its id for flat draws (`flat::Flat::add`), when they are on.
@@ -249,6 +258,8 @@ pub struct Frame<'a> {
     pub hand_fov_degrees: f32,
     /// Full-screen camera effects drawn over the world and hand, under the HUD.
     pub screen: &'a [crate::screen_effects::ScreenQuad],
+    /// What a shader pack's uniforms need from the game.
+    pub pack: pack_uniforms::PackInputs,
     /// The world border wall, when near enough to be drawn.
     pub border: Option<BorderDraw>,
     pub game_time: f32,
@@ -268,6 +279,8 @@ pub struct Frame<'a> {
     pub night_vision: f32,
     /// Torch flicker added to the block light factor of 1.4.
     pub block_flicker: f32,
+    /// `lightmap.fsh` BossOverlayWorldDarkeningFactor (a wither's bar).
+    pub boss_darken: f32,
     /// `Screen.extractBlurredBackground`: blur the frame by this radius
     /// (`menuBackgroundBlurriness`) before the screen is drawn over it.
     pub menu_blur: Option<f32>,
@@ -325,6 +338,8 @@ pub struct Renderer {
     /// counts reach a multi-draw's entries (Vulkan, Metal).
     cull: Option<cull::Cull>,
     cull_on: bool,
+    /// Solid quads facing away from the eye are left out (`mesher::Sides`).
+    sides_on: bool,
     sky: wgpu::RenderPipeline,
     dark_disc: wgpu::RenderPipeline,
     lines: wgpu::RenderPipeline,
@@ -456,6 +471,10 @@ pub struct Renderer {
     occlusion: occlusion::Occlusion,
     /// Resolution scale and FXAA (Horizon settings).
     world_post: world_post::Post,
+    /// The shader pack's post-processing, and the dimension (legacy id) it was loaded for.
+    pack_post: Option<(i32, Option<pack_post::PackPost>)>,
+    /// The block sprites as one atlas, while a shader pack is loaded.
+    pack_atlas: Option<pack_atlas::PackAtlas>,
     pub hud: HudRenderer,
     /// Vanilla's menu background blur, made on first use.
     menu_blur: Option<crate::menu_blur::MenuBlur>,
@@ -1304,6 +1323,8 @@ impl Renderer {
                         format: wgpu::TextureFormat::Rgba8Unorm,
                         usage: wgpu::TextureUsages::TEXTURE_BINDING
                             | wgpu::TextureUsages::COPY_DST
+                            // Shader packs' atlas copies them (pack_atlas.rs).
+                            | wgpu::TextureUsages::COPY_SRC
                             | wgpu::TextureUsages::STORAGE_BINDING,
                         view_formats: &[],
                     },
@@ -2157,7 +2178,7 @@ impl Renderer {
                     cull::Cull::new(&device, config.format.remove_srgb_suffix(), depth_test);
                 cull.always = cull_env.as_deref() == Ok("all");
                 if !cull.always && adapter.get_info().backend == wgpu::Backend::Metal {
-                    cull.min_draws = cull::TILED_MIN_DRAWS;
+                    cull.min_sections = cull::TILED_MIN_SECTIONS;
                 }
                 cull
             });
@@ -2204,6 +2225,7 @@ impl Renderer {
             translucent,
             flat_on: flat.is_some(),
             cull_on: cull.is_some(),
+            sides_on: true,
             cull,
             flat,
             sky,
@@ -2300,6 +2322,8 @@ impl Renderer {
             block_entity_revision: next_block_entity_revision(),
             occlusion: occlusion::Occlusion::new(crate::chunk::MIN_Y, crate::chunk::HEIGHT / 16),
             world_post,
+            pack_post: None,
+            pack_atlas: None,
             hud,
             menu_blur: None,
             info,
@@ -2453,6 +2477,14 @@ impl Renderer {
         self.flat_on = on;
         Ok(())
     }
+    /// Whether solid quads facing away from the eye are left out.
+    pub fn section_sides(&self) -> bool {
+        self.sides_on
+    }
+    /// Switches leaving out solid quads facing away, for A/B checks.
+    pub fn set_section_sides(&mut self, on: bool) {
+        self.sides_on = on;
+    }
     /// Whether solid sections are occlusion culled (`cull`).
     pub fn section_cull(&self) -> bool {
         self.cull_on
@@ -2575,8 +2607,12 @@ impl Renderer {
             page,
             start,
             solid,
+            sides: if mesh.sides.quads() == solid {
+                mesh.sides
+            } else {
+                Sides::unsorted(solid)
+            },
             translucent,
-            faces: mesh.faces,
             sort: translucency::SortState::new(
                 mesh.translucent
                     .as_chunks::<4>()
@@ -2718,6 +2754,51 @@ impl Renderer {
         self.world_post.scale = scale.clamp(0.25, 2.0);
         self.world_post.antialias = antialias;
     }
+    /// Runs `post` over the world from now on (`None`: no pack), for the dimension `dimension`.
+    /// Returns the programs that run and the notes of loading them.
+    pub fn set_shader_pack(
+        &mut self,
+        dimension: i32,
+        pack: Option<horizon_shaders::Post>,
+    ) -> Option<(Vec<String>, Vec<String>)> {
+        let post = pack.map(|post| {
+            pack_post::PackPost::new(
+                &self.device,
+                &self.queue,
+                post,
+                self.config.format.remove_srgb_suffix(),
+            )
+        });
+        if post.is_none() {
+            self.pack_atlas = None;
+        } else if self.pack_atlas.is_none() {
+            let mut encoder = self.device.create_command_encoder(&Default::default());
+            let layers = self
+                .sprite_textures
+                .iter()
+                .map(|t| t.depth_or_array_layers())
+                .sum();
+            self.pack_atlas = pack_atlas::PackAtlas::new(
+                &self.device,
+                &mut encoder,
+                &self.sprite_textures,
+                sprite_split(),
+                layers,
+                self.sprite_textures[0].width(),
+            );
+            self.queue.submit([encoder.finish()]);
+        }
+        let report = post.as_ref().map(|p| {
+            let programs = p.programs().into_iter().map(str::to_owned).collect();
+            (programs, p.notes.clone())
+        });
+        self.pack_post = Some((dimension, post));
+        report
+    }
+    /// The dimension the shader pack was last set for.
+    pub fn shader_pack_dimension(&self) -> Option<i32> {
+        self.pack_post.as_ref().map(|p| p.0)
+    }
     /// The Mipmap Levels option: block textures sample at most `levels`
     /// reduced copies (0: none).
     pub fn set_mipmap_levels(&mut self, levels: u32) {
@@ -2778,6 +2859,7 @@ impl Renderer {
         gamma: f32,
         night_vision: f32,
         flicker: f32,
+        boss_darken: f32,
     ) {
         // lightmap.fsh: per (block, sky) level.
         let brightness = |level: f32| level / (4.0 - 3.0 * level);
@@ -2795,6 +2877,8 @@ impl Renderer {
                 let parabolic = (2.0 * block_level - 1.0).powi(2);
                 let block_color = Vec3::from(sky.block_light_tint).lerp(Vec3::ONE, 0.9 * parabolic);
                 color += block_color * block_brightness;
+                // lightmap.fsh: a boss bar mixes the light toward 70/60/60%.
+                color = color.lerp(color * Vec3::new(0.7, 0.6, 0.6), boss_darken);
                 color -= Vec3::splat(darkness);
                 color = color.clamp(Vec3::ZERO, Vec3::ONE);
                 let max = color.max_element().max(1e-6);
@@ -2834,6 +2918,13 @@ impl Renderer {
     }
     fn animate(&mut self, encoder: &mut wgpu::CommandEncoder, tick: u64) {
         self.animations.animate(encoder, &mut self.uploads, tick);
+        if let Some(atlas) = &self.pack_atlas {
+            atlas.copy(
+                encoder,
+                &self.sprite_textures,
+                self.animations.changed().iter().copied(),
+            );
+        }
     }
     pub fn render(&mut self, frame: &Frame) -> Result<bool> {
         let rendered = self.draw_frame(frame);
@@ -2909,6 +3000,7 @@ impl Renderer {
             (self.gamma - frame.darkness.0).max(0.0),
             frame.night_vision,
             frame.block_flicker,
+            frame.boss_darken,
         );
         let view_proj = self.view_projection(frame);
         if frame.title {
@@ -3042,6 +3134,9 @@ impl Renderer {
         };
         let camera = frame.camera;
         let camera_section = camera_section(camera);
+        // Solid quads facing away from the eye are left out: the bob moves
+        // the eye off `camera`, so it is found from the projection.
+        let eye = projection_center(view_proj).filter(|_| self.sides_on);
         let culling = !frame.title && frame.cave_culling;
         if culling {
             crate::spans::time("occlusion", || {
@@ -3106,10 +3201,6 @@ impl Renderer {
         // as one list of indirect draws over the section arena.
         self.draws.clear();
         self.draw_pages.clear();
-        // The eye, camera-relative: view bobbing moves it off the camera.
-        let eye = (frame.bob * crate::camera::view_matrix(frame.yaw, frame.pitch))
-            .inverse()
-            .transform_point3(Vec3::ZERO);
         // Occlusion culling leaves the sections its last result did not see
         // to phase 2, after the others, with instance counts of 0. Whether
         // the frame has draws enough goes by the last one's.
@@ -3117,7 +3208,7 @@ impl Renderer {
             .cull
             .as_mut()
             .filter(|c| {
-                self.cull_on && !frame.title && self.multi_draw && self.section_draws >= c.min_draws
+                self.cull_on && !frame.title && self.multi_draw && visible.len() >= c.min_sections
             })
             .and_then(|cull| cull.begin(&self.device).then_some(cull));
         self.phase2_draws.clear();
@@ -3135,12 +3226,11 @@ impl Renderer {
             let start = draws.len();
             let instances = u32::from(first_phase);
             let mut indices = 0;
-            // Only the solid groups that can face the eye.
-            s.faces.ranges(eye - Vec3::from(v.origin), |first, quads| {
-                let first = s.start + u64::from(first) * 4;
-                draws.push([quads * 6, instances, 0, first as u32, i as u32]);
-                pages.push((s.page, None));
+            facing_runs(&s.sides, eye, v.origin, |first, quads| {
                 indices += quads * 6;
+                let base = s.start as u32 + first * 4;
+                draws.push([quads * 6, instances, 0, base, i as u32]);
+                pages.push((s.page, None));
             });
             let runs = if first_phase {
                 &mut self.solid_runs
@@ -3178,10 +3268,10 @@ impl Renderer {
         for (i, v) in visible_lods.iter().enumerate() {
             let s = &self.lods[&v.key].mesh;
             let start = self.draws.len();
-            s.faces.ranges(eye - Vec3::from(v.origin), |first, quads| {
-                let first = s.start + u64::from(first) * 4;
-                self.draws
-                    .push([quads * 6, 1, 0, first as u32, (visible.len() + i) as u32]);
+            let instance = (visible.len() + i) as u32;
+            facing_runs(&s.sides, eye, v.origin, |first, quads| {
+                let base = s.start as u32 + first * 4;
+                self.draws.push([quads * 6, 1, 0, base, instance]);
                 self.draw_pages.push((s.page, None));
             });
             self.solid_runs
@@ -3349,6 +3439,7 @@ impl Renderer {
             translucent_crumbling_quads,
             water_mask_quads,
             shadow_quads,
+            translucent_particle_quads,
         ] = self.entity_batch.update(
             frame.entities,
             frame.additive,
@@ -3360,7 +3451,8 @@ impl Renderer {
             + crumbling_quads
             + translucent_crumbling_quads
             + water_mask_quads
-            + shadow_quads;
+            + shadow_quads
+            + translucent_particle_quads;
         let cloud_quads = if let Some(input) = &frame.clouds {
             let (rebuilt, uniform) =
                 crate::spans::time("clouds", || self.cloud_mesh.prepare(input));
@@ -3520,7 +3612,9 @@ impl Renderer {
         }
         let flat_frame = match &mut self.flat {
             Some(flat)
-                if self.flat_on && !self.draws.is_empty() && self.draws.len() >= flat.min_draws =>
+                if self.flat_on
+                    && !self.draws.is_empty()
+                    && self.drawn_sections >= flat.min_sections =>
             {
                 let sections = &self.sections;
                 let lods = &self.lods;
@@ -3579,9 +3673,12 @@ impl Renderer {
             timer.begin(&mut encoder);
         }
         // The world's targets: the screen, or the scaled target of `post`.
-        let scaled = self
-            .world_post
-            .prepare(&self.device, [self.config.width, self.config.height]);
+        let pack_post = !frame.title && self.pack_post.as_ref().is_some_and(|p| p.1.is_some());
+        let scaled = self.world_post.prepare(
+            &self.device,
+            [self.config.width, self.config.height],
+            pack_post,
+        );
         let (world_view, world_depth) = match &scaled {
             Some((color, depth)) => (color, depth),
             None => (&view_target, &self.depth),
@@ -3618,8 +3715,8 @@ impl Renderer {
                     view: world_depth,
                     depth_ops: Some(wgpu::Operations {
                         load: wgpu::LoadOp::Clear(0.0),
-                        // Phase 2 of occlusion culling draws over it.
-                        store: if cull.is_some() {
+                        // Phase 2 of occlusion culling draws over it; a shader pack reads it.
+                        store: if cull.is_some() || pack_post {
                             wgpu::StoreOp::Store
                         } else {
                             wgpu::StoreOp::Discard
@@ -3678,7 +3775,12 @@ impl Renderer {
                             drop(pass);
                             cull.test_pass(&mut encoder);
                             flat.flatten_phase2(&mut encoder);
-                            pass = world_pass_after_culling(&mut encoder, world_view, world_depth);
+                            pass = world_pass_after_culling(
+                                &mut encoder,
+                                world_view,
+                                world_depth,
+                                pack_post,
+                            );
                             pass.set_bind_group(0, &self.group, &[]);
                             pass.set_pipeline(&flat.solid);
                             flat.draw_phase2(&mut pass, vertices);
@@ -3702,7 +3804,12 @@ impl Renderer {
                             cull.test(&mut pass);
                             drop(pass);
                             cull.test_pass(&mut encoder);
-                            pass = world_pass_after_culling(&mut encoder, world_view, world_depth);
+                            pass = world_pass_after_culling(
+                                &mut encoder,
+                                world_view,
+                                world_depth,
+                                pack_post,
+                            );
                             pass.set_bind_group(0, &self.group, &[]);
                             pass.set_pipeline(&self.solid);
                             pass.set_index_buffer(
@@ -3744,7 +3851,7 @@ impl Renderer {
                 pass.set_vertex_buffer(0, self.entity_buffer.slice(..));
                 pass.draw_indexed(
                     0..shadow_quads * 6,
-                    ((world_quads - shadow_quads) * 4) as i32,
+                    ((world_quads - translucent_particle_quads - shadow_quads) * 4) as i32,
                     0..1,
                 );
                 pass.set_bind_group(0, &self.group, &[]);
@@ -3812,6 +3919,22 @@ impl Renderer {
                     );
                 }
             }
+            // LevelRenderer.executeTranslucentAfterTerrain: vanilla's
+            // translucent particle layer draws after translucent terrain —
+            // the quads write depth, so before it they would hide the glass
+            // or water behind them.
+            if translucent_particle_quads > 0 {
+                pass.set_pipeline(&self.entity_pipeline);
+                pass.set_bind_group(0, &self.entity_group, &[]);
+                pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
+                pass.set_vertex_buffer(0, self.entity_buffer.slice(..));
+                pass.draw_indexed(
+                    0..translucent_particle_quads * 6,
+                    ((world_quads - translucent_particle_quads) * 4) as i32,
+                    0..1,
+                );
+                pass.set_bind_group(0, &self.group, &[]);
+            }
             // LevelRenderer.executeClassicTransparency: translucent targets'
             // outlines follow terrain, so its blending cannot wash them out.
             if outline_edges > 0 && frame.outline_after_terrain {
@@ -3861,7 +3984,24 @@ impl Renderer {
                 );
             }
         }
-        if scaled.is_some() {
+        if let Some((color, depth)) = &scaled
+            && pack_post
+            && let Some((_, Some(post))) = &mut self.pack_post
+        {
+            let size = self.world_post.size().unwrap_or([1, 1]);
+            post.run(
+                &self.device,
+                &self.queue,
+                &mut encoder,
+                color,
+                depth,
+                &view_target,
+                frame,
+                &frame.pack,
+                size,
+                [self.config.width, self.config.height],
+            );
+        } else if scaled.is_some() {
             self.world_post.finish(&mut encoder, &view_target);
         }
         if hand_quads > 0 {
@@ -4202,6 +4342,34 @@ fn world_projection(fov_degrees: f32, aspect: f32, far: f32) -> Mat4 {
     Mat4::perspective_rh(fov_degrees.to_radians(), aspect, far, 0.05)
 }
 
+/// Where a perspective `view_proj` sees from, in its own (camera-relative)
+/// space: the point whose clip x, y and w are all 0. `None` for a
+/// projection without one (orthographic).
+fn projection_center(view_proj: Mat4) -> Option<Vec3> {
+    let m = view_proj.as_dmat4();
+    let rows = [m.row(0), m.row(1), m.row(3)];
+    let a = glam::DMat3::from_cols(
+        DVec3::new(rows[0].x, rows[1].x, rows[2].x),
+        DVec3::new(rows[0].y, rows[1].y, rows[2].y),
+        DVec3::new(rows[0].z, rows[1].z, rows[2].z),
+    );
+    let det = a.determinant();
+    if !det.is_normal() {
+        return None;
+    }
+    let b = DVec3::new(rows[0].w, rows[1].w, rows[2].w);
+    Some((a.inverse() * -b).as_vec3())
+}
+/// Calls `draw(first, quads)` for each run of a mesh's solid quads that can
+/// face `eye` (`projection_center`), the mesh at the camera-relative
+/// `origin`; all of them when there is no eye.
+fn facing_runs(sides: &Sides, eye: Option<Vec3>, origin: [f32; 3], mut draw: impl FnMut(u32, u32)) {
+    match eye {
+        Some(eye) => sides.visible((eye - Vec3::from(origin)).to_array(), draw),
+        None if sides.quads() > 0 => draw(0, sides.quads()),
+        None => {}
+    }
+}
 fn frustum(m: Mat4) -> [Vec4; 6] {
     let r = |i| m.row(i);
     let planes = [
@@ -4273,14 +4441,23 @@ mod tests {
                 normal: [0; 4],
             }; 4]
         };
-        let entities: Vec<_> = [(0, 0), (14, 9), (4, 1), (11, 2), (7, 3), (4, 4), (12, 7)]
-            .into_iter()
-            .flat_map(|(layer, id)| quad(layer, id))
-            .collect();
+        let entities: Vec<_> = [
+            (0, 0),
+            (14, 9),
+            (4, 1),
+            (11, 2),
+            (15, 10),
+            (7, 3),
+            (4, 4),
+            (12, 7),
+        ]
+        .into_iter()
+        .flat_map(|(layer, id)| quad(layer, id))
+        .collect();
         let mut batch = super::EntityBatch::default();
         let counts = batch.update(&entities, &quad(3, 5), &quad(0, 6), &quad(0, 8));
         let vertices = &batch.combined;
-        assert_eq!(counts, [4, 1, 1, 0, 1]);
+        assert_eq!(counts, [4, 1, 1, 0, 1, 1]);
         assert_eq!(
             vertices
                 .as_chunks::<4>()
@@ -4288,7 +4465,7 @@ mod tests {
                 .iter()
                 .map(|q| q[0].light)
                 .collect::<Vec<_>>(),
-            [0, 1, 3, 4, 2, 7, 9, 5, 6, 8]
+            [0, 1, 3, 4, 2, 7, 9, 10, 5, 6, 8]
         );
     }
     #[test]
@@ -4429,6 +4606,25 @@ mod tests {
         assert_eq!(super::outline_width(3840), 5.0);
     }
     #[test]
+    fn the_projection_center_follows_the_view_bob() {
+        use glam::{Mat4, Vec3};
+        let projection = super::world_projection(70.0, 16.0 / 9.0, 512.0);
+        let view = crate::camera::view_matrix(30.0, 20.0);
+        let eye = super::projection_center(projection * view).unwrap();
+        assert!(eye.length() < 1e-5, "{eye}");
+        // A pose translated by the bob: the eye is where the pose's inverse
+        // takes the view's origin.
+        let bob = Mat4::from_rotation_z(0.02) * Mat4::from_translation(Vec3::new(0.03, -0.08, 0.0));
+        let expected = (bob * view).inverse().transform_point3(Vec3::ZERO);
+        let eye = super::projection_center(projection * bob * view).unwrap();
+        assert!(eye.distance(expected) < 1e-5, "{eye} {expected}");
+        assert!(expected.length() > 0.05);
+        assert!(
+            super::projection_center(Mat4::orthographic_rh(-1.0, 1.0, -1.0, 1.0, 0.0, 1.0))
+                .is_none()
+        );
+    }
+    #[test]
     fn indirect_draws_are_validated_only_in_debug_builds_and_on_directx_12() {
         let validated = |backends| {
             super::instance_descriptor(backends)

crates/horizon-client/src/gfx/animate.rs

@@ -51,6 +51,8 @@ pub(super) struct SpriteAnimator {
     pipeline: wgpu::ComputePipeline,
     /// Edge of the arrays' layers.
     size: u32,
+    /// The layers the last `animate` rewrote, counted over all arrays.
+    changed: Vec<u32>,
 }
 
 impl SpriteAnimator {
@@ -205,9 +207,15 @@ impl SpriteAnimator {
             jobs,
             pipeline,
             size,
+            changed: Vec::new(),
         }
     }
 
+    /// The layers the last `animate` rewrote (for the shader pack atlas).
+    pub fn changed(&self) -> &[u32] {
+        &self.changed
+    }
+
     /// Show every sprite's frame at `tick`, rewriting only the sprites whose
     /// frame or mix changed (`SpriteContents.AnimationState.tick`).
     pub fn animate(
@@ -245,12 +253,14 @@ impl SpriteAnimator {
     /// its layer shows; the number of jobs.
     fn collect(&mut self, tick: u64) -> usize {
         let mut count = 0;
+        self.changed.clear();
         for sprite in &mut self.sprites {
             let blend = sprite.animation.blend(tick);
             if sprite.shown == Some(blend) {
                 continue;
             }
             sprite.shown = Some(blend);
+            self.changed.push(sprite.animation.layer);
             let job = [
                 sprite.layer,
                 sprite.frames[blend.frame],

crates/horizon-client/src/gfx/cull.rs

@@ -46,13 +46,15 @@ const RETEST: u32 = 8;
 /// more than they save. Else one frame in `PROBE` tests every section.
 const MIN_SHARE: f32 = 0.1;
 const PROBE: u32 = 64;
-/// On Metal, section draws from which a frame culls. Apple's GPUs store and
-/// reload the whole frame at each of the passes the test adds, a fixed cost
-/// that the sections it hides repay only at high render distances: on an M4
-/// Pro at 1080p and render distance 12 (1,000–1,600 draws) culling added
-/// about 0.05 ms of GPU time while hiding 15–30% of the solid indices; at
-/// 32 (drawn flat, over this many draws) it saved 0.25–1.6 ms.
-pub const TILED_MIN_DRAWS: usize = 4096;
+/// On Metal, sections in view from which a frame culls. Apple's GPUs store
+/// and reload the whole frame at each of the passes the test adds, a fixed
+/// cost that the sections it hides repay only at high render distances: on
+/// an M4 Pro at 1080p and render distance 12 (1,000–1,600 draws) culling
+/// added about 0.05 ms of GPU time while hiding 15–30% of the solid
+/// indices; at 32 (over 4,096 draws) it saved 0.25–1.6 ms. Those draws were
+/// 2.2 to 2.5 per section; a section's draw count now depends on the sides
+/// it shows the eye (`mesher::Sides`), so the bar counts sections.
+pub const TILED_MIN_SECTIONS: usize = 1600;
 /// Boxes over more than this share of the screen count as seen untested.
 const BIG: f32 = 0.25;
 /// Results read back at once, some frames late so the CPU never waits.
@@ -148,8 +150,8 @@ pub struct Cull {
     pub hidden: ([usize; 2], f32),
     /// Cull every frame, whatever the hidden share (A/B checks).
     pub always: bool,
-    /// Frames with fewer section draws than this do not cull.
-    pub min_draws: usize,
+    /// Frames with fewer sections in view than this do not cull.
+    pub min_sections: usize,
 }
 
 fn buffer(
@@ -348,7 +350,7 @@ impl Cull {
             stamp: 0,
             hidden: ([0; 2], 1.0),
             always: false,
-            min_draws: 0,
+            min_sections: 0,
         }
     }
 

crates/horizon-client/src/gfx/entity_batch.rs

@@ -3,13 +3,16 @@ use super::Vertex;
 
 /// Entity materials by a quad's overlay (`Vertex::layer`), in draw order:
 /// ordinary entities, breaking cracks (11), translucent breaking cracks (12),
-/// the boat water mask (13, `RenderPipelines.WATER_MASK`) and entity shadows
-/// (14, `RenderPipelines.ENTITY_SHADOW`).
-const MATERIALS: usize = 5;
+/// the boat water mask (13, `RenderPipelines.WATER_MASK`), entity shadows
+/// (14, `RenderPipelines.ENTITY_SHADOW`) and translucent-layer particles (15,
+/// drawn after translucent terrain: `SubmitNodeCollection.submitQuadParticleGroup`).
+const MATERIALS: usize = 6;
 /// The overlay of depth-only quads that hide water (`RenderTypes.waterMask`).
 pub const WATER_MASK_OVERLAY: u32 = 13;
 /// The overlay of entity shadow quads (`RenderTypes.entityShadow`).
 pub const SHADOW_OVERLAY: u32 = 14;
+/// The overlay of translucent-layer particles (`SingleQuadParticle.Layer.translucent`).
+pub const TRANSLUCENT_PARTICLE_OVERLAY: u32 = 15;
 
 #[derive(Default)]
 pub(super) struct EntityBatch {
@@ -41,6 +44,7 @@ impl EntityBatch {
                 12 => 2,
                 WATER_MASK_OVERLAY => 3,
                 SHADOW_OVERLAY => 4,
+                TRANSLUCENT_PARTICLE_OVERLAY => 5,
                 _ => 0,
             };
             self.buckets[material][counts[material]] = index;
@@ -92,13 +96,14 @@ mod tests {
     ) -> (Vec<Vertex>, [u32; MATERIALS]) {
         let mut combined = Vec::with_capacity(entities.len() + additive.len() + hand.len());
         let mut counts = [0; MATERIALS];
-        for (i, layer) in [0, 11, 12, 13, 14].into_iter().enumerate() {
+        for (i, layer) in [0, 11, 12, 13, 14, 15].into_iter().enumerate() {
             for quad in entities.as_chunks::<4>().0 {
                 let material = match quad[0].layer {
                     11 => 11,
                     12 => 12,
                     13 => 13,
                     14 => 14,
+                    15 => 15,
                     _ => 0,
                 };
                 if material == layer {
@@ -118,7 +123,7 @@ mod tests {
                 pos: [index as f32, 2.0, 3.0],
                 uv: [index as f32, 5.0],
                 layer: if mixed {
-                    [7, 11, 14, 12, 4, 13, 0][index / 4 % 7]
+                    [7, 11, 14, 12, 4, 13, 15, 0][index / 4 % 8]
                 } else {
                     0
                 },

crates/horizon-client/src/gfx/flat.rs

@@ -96,17 +96,19 @@ pub struct Flat {
     pub calls: Vec<Call>,
     pub phase1_calls: usize,
     pub solid_calls: usize,
-    /// Frames with fewer section draws keep the per-section draws.
-    pub min_draws: usize,
+    /// Frames with fewer sections in view keep the per-section draws.
+    pub min_sections: usize,
     range_align: u64,
 }
 
-/// Section draws from which a frame is drawn flat. Below it the index list
-/// costs the GPU more than the draw calls cost the CPU: on an M4 Pro at
-/// render distance 16 (2,900 draws) the copy and the list add about 0.4 ms
-/// of GPU time for 0.5–0.8 ms less CPU time; at 32 (9,300 draws) the CPU
-/// saves 1.3 ms.
-const MIN_DRAWS: usize = 4096;
+/// Sections in view (and distant tiles) from which a frame is drawn flat.
+/// Below it the index list costs the GPU more than the draw calls cost the
+/// CPU: on an M4 Pro at render distance 16 (2,900 draws) the copy and the
+/// list add about 0.4 ms of GPU time for 0.5–0.8 ms less CPU time; at 32
+/// (9,300 draws) the CPU saves 1.3 ms. The bar was 4,096 draws when they
+/// were 2.2 to 2.5 per section; a section's draw count now depends on the
+/// sides it shows the eye (`mesher::Sides`), so it counts sections.
+const MIN_SECTIONS: usize = 1600;
 
 /// Whether flat draws apply: the backend emulates multi-draw, and vertex
 /// shaders can read storage buffers large enough for an index page.
@@ -337,10 +339,10 @@ impl Flat {
             calls: Vec::new(),
             phase1_calls: 0,
             solid_calls: 0,
-            min_draws: if std::env::var("HORIZON_FLAT_DRAWS").as_deref() == Ok("1") {
+            min_sections: if std::env::var("HORIZON_FLAT_DRAWS").as_deref() == Ok("1") {
                 0
             } else {
-                MIN_DRAWS
+                MIN_SECTIONS
             },
             range_align: (u64::from(device.limits().min_storage_buffer_offset_alignment) / 16)
                 .max(1),

crates/horizon-client/src/gfx/pack_atlas.rs

@@ -0,0 +1,197 @@
+//! The block atlas of shader packs (spec 5.1, `atlasSize` in 5.2): packs sample one 2D atlas
+//! with atlas coordinates, Horizon keeps block sprites in texture arrays. With a pack, every
+//! layer is copied into a grid, row by row from the top left, and an animated layer again
+//! whenever its frame changes.
+
+#[expect(dead_code, reason = "the gbuffers pass binds it (next slice)")]
+pub(super) struct PackAtlas {
+    texture: wgpu::Texture,
+    pub view: wgpu::TextureView,
+    /// Sprites per row.
+    pub columns: u32,
+    /// A sprite's edge in pixels, at the first level.
+    pub sprite: u32,
+    /// Layers per sprite array.
+    split: u32,
+}
+
+impl PackAtlas {
+    /// Copies `layers` layers of `arrays` (`split` per array, `sprite` pixels wide, `levels`
+    /// mip levels); `None` when the grid is larger than the device allows.
+    pub fn new(
+        device: &wgpu::Device,
+        encoder: &mut wgpu::CommandEncoder,
+        arrays: &[wgpu::Texture],
+        split: u32,
+        layers: u32,
+        sprite: u32,
+    ) -> Option<Self> {
+        let layers = layers.max(1);
+        let columns = (f64::from(layers).sqrt().ceil() as u32).max(1);
+        let rows = layers.div_ceil(columns);
+        let max = device.limits().max_texture_dimension_2d;
+        if columns * sprite > max || rows * sprite > max {
+            return None;
+        }
+        // Levels past a sprite's single pixel would mix neighbours: stop there.
+        let levels = arrays[0].mip_level_count().min(sprite.ilog2() + 1);
+        let texture = device.create_texture(&wgpu::TextureDescriptor {
+            label: Some("Shader pack block atlas"),
+            size: wgpu::Extent3d {
+                width: columns * sprite,
+                height: rows * sprite,
+                depth_or_array_layers: 1,
+            },
+            mip_level_count: levels,
+            sample_count: 1,
+            dimension: wgpu::TextureDimension::D2,
+            format: wgpu::TextureFormat::Rgba8Unorm,
+            usage: wgpu::TextureUsages::TEXTURE_BINDING
+                | wgpu::TextureUsages::COPY_DST
+                | wgpu::TextureUsages::COPY_SRC,
+            view_formats: &[],
+        });
+        let view = texture.create_view(&Default::default());
+        let atlas = Self {
+            texture,
+            view,
+            columns,
+            sprite,
+            split,
+        };
+        atlas.copy(encoder, arrays, 0..layers);
+        Some(atlas)
+    }
+
+    /// The atlas's size in pixels (`atlasSize`).
+    #[cfg_attr(
+        not(test),
+        expect(dead_code, reason = "the gbuffers pass reads it (next slice)")
+    )]
+    pub fn size(&self) -> [u32; 2] {
+        [self.texture.width(), self.texture.height()]
+    }
+
+    /// Copies `layers` from the sprite arrays again, every level.
+    pub fn copy(
+        &self,
+        encoder: &mut wgpu::CommandEncoder,
+        arrays: &[wgpu::Texture],
+        layers: impl IntoIterator<Item = u32>,
+    ) {
+        for layer in layers {
+            let Some(array) = arrays.get((layer / self.split) as usize) else {
+                continue;
+            };
+            let (column, row) = (layer % self.columns, layer / self.columns);
+            for level in 0..self.texture.mip_level_count() {
+                let edge = self.sprite >> level;
+                encoder.copy_texture_to_texture(
+                    wgpu::TexelCopyTextureInfo {
+                        texture: array,
+                        mip_level: level,
+                        origin: wgpu::Origin3d {
+                            x: 0,
+                            y: 0,
+                            z: layer % self.split,
+                        },
+                        aspect: wgpu::TextureAspect::All,
+                    },
+                    wgpu::TexelCopyTextureInfo {
+                        texture: &self.texture,
+                        mip_level: level,
+                        origin: wgpu::Origin3d {
+                            x: column * edge,
+                            y: row * edge,
+                            z: 0,
+                        },
+                        aspect: wgpu::TextureAspect::All,
+                    },
+                    wgpu::Extent3d {
+                        width: edge,
+                        height: edge,
+                        depth_or_array_layers: 1,
+                    },
+                );
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Two arrays of 2x2 sprites, one layer split; each layer a colour of its own.
+    #[test]
+    fn layers_land_in_their_cells() {
+        let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
+        let Ok(adapter) = pollster::block_on(instance.request_adapter(&Default::default())) else {
+            return;
+        };
+        let (device, queue) =
+            pollster::block_on(adapter.request_device(&Default::default())).unwrap();
+        let (split, layers, sprite) = (3u32, 5u32, 2u32);
+        let arrays: Vec<wgpu::Texture> = (0..2)
+            .map(|a| {
+                let count = (layers - a * split).min(split);
+                let pixels: Vec<u8> = (0..count)
+                    .flat_map(|l| [(a * split + l) as u8 * 40, 0, 0, 255].repeat(4))
+                    .collect();
+                wgpu::util::DeviceExt::create_texture_with_data(
+                    &device,
+                    &queue,
+                    &wgpu::TextureDescriptor {
+                        label: None,
+                        size: wgpu::Extent3d {
+                            width: sprite,
+                            height: sprite,
+                            depth_or_array_layers: count,
+                        },
+                        mip_level_count: 1,
+                        sample_count: 1,
+                        dimension: wgpu::TextureDimension::D2,
+                        format: wgpu::TextureFormat::Rgba8Unorm,
+                        usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_SRC,
+                        view_formats: &[],
+                    },
+                    wgpu::util::TextureDataOrder::LayerMajor,
+                    &pixels,
+                )
+            })
+            .collect();
+        let mut encoder = device.create_command_encoder(&Default::default());
+        let atlas = PackAtlas::new(&device, &mut encoder, &arrays, split, layers, sprite).unwrap();
+        assert_eq!((atlas.columns, atlas.size()), (3, [6, 4]));
+        let read = device.create_buffer(&wgpu::BufferDescriptor {
+            label: None,
+            size: 256 * 4,
+            usage: wgpu::BufferUsages::COPY_DST | wgpu::BufferUsages::MAP_READ,
+            mapped_at_creation: false,
+        });
+        encoder.copy_texture_to_buffer(
+            atlas.texture.as_image_copy(),
+            wgpu::TexelCopyBufferInfo {
+                buffer: &read,
+                layout: wgpu::TexelCopyBufferLayout {
+                    offset: 0,
+                    bytes_per_row: Some(256),
+                    rows_per_image: None,
+                },
+            },
+            wgpu::Extent3d {
+                width: 6,
+                height: 4,
+                depth_or_array_layers: 1,
+            },
+        );
+        queue.submit([encoder.finish()]);
+        read.slice(..).map_async(wgpu::MapMode::Read, |_| {});
+        device.poll(wgpu::PollType::wait_indefinitely()).unwrap();
+        let data = read.slice(..).get_mapped_range().unwrap();
+        let red = |x: usize, y: usize| data[y * 256 + x * 4];
+        // Layer 4 (second array, its second layer) is in row 1, column 1.
+        assert_eq!([red(0, 0), red(2, 0), red(4, 0)], [0, 40, 80]);
+        assert_eq!([red(1, 3), red(3, 2), red(5, 2)], [120, 160, 0]);
+    }
+}

crates/horizon-client/src/gfx/pack_post.rs

@@ -0,0 +1,929 @@
+//! A shader pack's post-processing over Horizon's own world (spec 2.1 rows 4, 6, 8, 9; 6.1; 6.2;
+//! 6.4): the world renders into its own target as with a resolution scale, its colour becomes
+//! colortex0 and its depth `depthtex0`, then the pack's `prepare`, `deferred`, `composite` and
+//! `final` programs run in order, and `final` draws onto the screen under the hand and HUD.
+//! Gbuffers programs come later; until then the pack's composites read Horizon's picture.
+//!
+//! Every colortex buffer a program reads or writes has two textures, A and B. Programs read
+//! "main" and write "alt", and each buffer a program wrote flips afterwards (6.1.6). The
+//! mapping carries over to the next frame, so a buffer that is not cleared reads back what was
+//! written last (OQ-8). Buffers are cleared at the start of the frame, "main" only.
+//! Pack buffers store rows as GL does (row 0 at the bottom: the translator negates clip y), so
+//! the world is copied in upside down, and its reverse-Z depth becomes GL window depth.
+
+use std::collections::HashMap;
+
+use horizon_shaders::{Format, Group, Kind, Post};
+
+use super::pack_uniforms::{self, FrameUniforms, PackInputs};
+
+const BUFFERS: usize = horizon_shaders::BUFFERS;
+
+/// The texture behind a pack sampler name.
+#[derive(Clone, Copy, PartialEq)]
+enum Source {
+    Color(usize),
+    Depth,
+    Noise,
+    /// A 1×1 stand-in for names this slice does not provide yet (custom textures...).
+    Dummy,
+    /// A 1×1 depth of 1.0 behind a comparison sampler, until shadow maps exist: no shadow.
+    Shadow,
+}
+
+struct Binding {
+    source: Source,
+    binding: u32,
+    /// A filtering sampler (the texture is filterable).
+    filtering: bool,
+}
+
+struct Pass {
+    name: String,
+    group: Group,
+    pipeline: wgpu::RenderPipeline,
+    layout: wgpu::BindGroupLayout,
+    ubo: wgpu::Buffer,
+    block: Vec<u8>,
+    /// (index into `pack_uniforms::NAMES`, declared type, offset).
+    uniforms: Vec<(Option<usize>, String, u32)>,
+    samplers: Vec<Binding>,
+    /// (location, buffer) of each output that reaches a buffer.
+    writes: Vec<(u32, usize)>,
+    /// Buffers flipped after the pass.
+    flip: u16,
+    /// Buffers sampled, for the bind group cache key.
+    reads: u16,
+    /// Buffers written.
+    written: u16,
+    groups: HashMap<u16, wgpu::BindGroup>,
+}
+
+struct Targets {
+    size: [u32; 2],
+    /// A and B of each buffer used.
+    color: [Option<[wgpu::TextureView; 2]>; BUFFERS],
+    depth: wgpu::TextureView,
+}
+
+pub struct PackPost {
+    pub notes: Vec<String>,
+    passes: Vec<Pass>,
+    deferred_pre: u16,
+    composite_pre: u16,
+    formats: [wgpu::TextureFormat; BUFFERS],
+    clears: [Option<[f32; 4]>; BUFFERS],
+    used: u16,
+    /// Bit n set: B is buffer n's "main".
+    main: u16,
+    targets: Option<Targets>,
+    noise: wgpu::TextureView,
+    dummy: wgpu::TextureView,
+    /// The stand-in shadow map and its comparison sampler; cleared on the first frame.
+    shadow: (wgpu::TextureView, wgpu::Sampler),
+    shadow_cleared: bool,
+    linear: wgpu::Sampler,
+    nearest: wgpu::Sampler,
+    repeat: wgpu::Sampler,
+    blit: (wgpu::RenderPipeline, wgpu::BindGroupLayout),
+    /// The blit also writes depthtex0 (some program reads it) and clears these buffers.
+    blit_depth: bool,
+    blit_clears: Vec<usize>,
+    /// Buffers cleared in passes of their own (more than the blit's eight attachments).
+    other_clears: Vec<usize>,
+    /// The blit's bindings, for the world target of this size.
+    blit_group: Option<([u32; 2], wgpu::BindGroup)>,
+    /// Shows colortex0 when the pack has no `final` (OQ-5).
+    copy: (wgpu::RenderPipeline, wgpu::BindGroupLayout),
+    uniforms: FrameUniforms,
+}
+
+/// The wgpu format of a pack format (6.7), the nearest one wgpu can render to.
+fn texture_format(f: Format, features: wgpu::Features) -> wgpu::TextureFormat {
+    use wgpu::TextureFormat as T;
+    let pick = |r, rg, rgba| match f.channels {
+        1 => r,
+        2 => rg,
+        _ => rgba,
+    };
+    let half = pick(T::R16Float, T::Rg16Float, T::Rgba16Float);
+    match (f.kind, f.bits) {
+        (Kind::Unorm, 10) => T::Rgb10a2Unorm,
+        (Kind::Unorm, 16) if features.contains(wgpu::Features::TEXTURE_FORMAT_16BIT_NORM) => {
+            pick(T::R16Unorm, T::Rg16Unorm, T::Rgba16Unorm)
+        }
+        (Kind::Unorm, b) if b <= 8 => pick(T::R8Unorm, T::Rg8Unorm, T::Rgba8Unorm),
+        (Kind::Float, 32) => pick(T::R32Float, T::Rg32Float, T::Rgba32Float),
+        (Kind::Float, 11) if features.contains(wgpu::Features::RG11B10UFLOAT_RENDERABLE) => {
+            T::Rg11b10Ufloat
+        }
+        (Kind::Int, 8) => pick(T::R8Sint, T::Rg8Sint, T::Rgba8Sint),
+        (Kind::Int, 16) => pick(T::R16Sint, T::Rg16Sint, T::Rgba16Sint),
+        (Kind::Int, _) => pick(T::R32Sint, T::Rg32Sint, T::Rgba32Sint),
+        (Kind::Uint, 8) => pick(T::R8Uint, T::Rg8Uint, T::Rgba8Uint),
+        (Kind::Uint, 10) => T::Rgb10a2Uint,
+        (Kind::Uint, 16) => pick(T::R16Uint, T::Rg16Uint, T::Rgba16Uint),
+        (Kind::Uint, _) => pick(T::R32Uint, T::Rg32Uint, T::Rgba32Uint),
+        // Snorm, 16-bit norm without the feature, RGB9_E5: half floats hold them.
+        _ => half,
+    }
+}
+
+fn source(name: &str) -> Source {
+    match name {
+        "depthtex0" | "gdepthtex" | "depthtex1" | "depthtex2" => Source::Depth,
+        "noisetex" => Source::Noise,
+        n => horizon_shaders::buffer_index(n).map_or(Source::Dummy, Source::Color),
+    }
+}
+
+/// 256×256 RGB white noise (6.4), from a fixed seed so every run looks the same.
+fn noise(device: &wgpu::Device, queue: &wgpu::Queue) -> wgpu::TextureView {
+    let mut state = 0x2545_f491_4f6c_dd1du64;
+    let texels: Vec<u8> = (0..256 * 256 * 4)
+        .map(|i| {
+            state ^= state << 13;
+            state ^= state >> 7;
+            state ^= state << 17;
+            if i % 4 == 3 { 255 } else { (state >> 56) as u8 }
+        })
+        .collect();
+    texture(device, queue, "Shader pack noisetex", 256, &texels)
+}
+
+fn texture(
+    device: &wgpu::Device,
+    queue: &wgpu::Queue,
+    label: &str,
+    side: u32,
+    texels: &[u8],
+) -> wgpu::TextureView {
+    let size = wgpu::Extent3d {
+        width: side,
+        height: side,
+        depth_or_array_layers: 1,
+    };
+    let tex = device.create_texture(&wgpu::TextureDescriptor {
+        label: Some(label),
+        size,
+        mip_level_count: 1,
+        sample_count: 1,
+        dimension: wgpu::TextureDimension::D2,
+        format: wgpu::TextureFormat::Rgba8Unorm,
+        usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
+        view_formats: &[],
+    });
+    queue.write_texture(
+        tex.as_image_copy(),
+        texels,
+        wgpu::TexelCopyBufferLayout {
+            offset: 0,
+            bytes_per_row: Some(side * 4),
+            rows_per_image: None,
+        },
+        size,
+    );
+    tex.create_view(&Default::default())
+}
+
+fn sampler(
+    device: &wgpu::Device,
+    filter: wgpu::FilterMode,
+    address: wgpu::AddressMode,
+) -> wgpu::Sampler {
+    device.create_sampler(&wgpu::SamplerDescriptor {
+        label: Some("Shader pack"),
+        address_mode_u: address,
+        address_mode_v: address,
+        address_mode_w: address,
+        mag_filter: filter,
+        min_filter: filter,
+        ..Default::default()
+    })
+}
+
+/// Runs `create` and returns its validation error, if any.
+fn checked<T>(device: &wgpu::Device, create: impl FnOnce() -> T) -> Result<T, String> {
+    let scope = device.push_error_scope(wgpu::ErrorFilter::Validation);
+    let value = create();
+    match pollster::block_on(scope.pop()) {
+        Some(e) => {
+            // The details are in the error's sources.
+            let mut message = e.to_string();
+            let mut source = std::error::Error::source(&e);
+            while let Some(s) = source {
+                message = format!("{message}: {s}");
+                source = s.source();
+            }
+            Err(message)
+        }
+        None => Ok(value),
+    }
+}
+
+/// A full-screen helper pipeline of ours (`pack_post.wgsl`).
+fn helper(
+    device: &wgpu::Device,
+    vertex: &str,
+    entry: &str,
+    entries: &[wgpu::BindGroupLayoutEntry],
+    targets: &[Option<wgpu::ColorTargetState>],
+) -> (wgpu::RenderPipeline, wgpu::BindGroupLayout) {
+    let module = device.create_shader_module(wgpu::ShaderModuleDescriptor {
+        label: Some("Shader pack helpers"),
+        source: wgpu::ShaderSource::Wgsl(include_str!("pack_post.wgsl").into()),
+    });
+    let layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+        label: Some(entry),
+        entries,
+    });
+    let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
+        label: Some(entry),
+        bind_group_layouts: &[Some(&layout)],
+        ..Default::default()
+    });
+    let pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
+        label: Some(entry),
+        layout: Some(&pipeline_layout),
+        vertex: wgpu::VertexState {
+            module: &module,
+            entry_point: Some(vertex),
+            compilation_options: Default::default(),
+            buffers: &[],
+        },
+        primitive: Default::default(),
+        depth_stencil: None,
+        multisample: Default::default(),
+        fragment: Some(wgpu::FragmentState {
+            module: &module,
+            entry_point: Some(entry),
+            compilation_options: Default::default(),
+            targets,
+        }),
+        multiview_mask: None,
+        cache: None,
+    });
+    (pipeline, layout)
+}
+
+fn entry(binding: u32, ty: wgpu::BindingType) -> wgpu::BindGroupLayoutEntry {
+    wgpu::BindGroupLayoutEntry {
+        binding,
+        visibility: wgpu::ShaderStages::VERTEX_FRAGMENT,
+        ty,
+        count: None,
+    }
+}
+
+fn texture_entry(binding: u32, sample_type: wgpu::TextureSampleType) -> wgpu::BindGroupLayoutEntry {
+    entry(
+        binding,
+        wgpu::BindingType::Texture {
+            sample_type,
+            view_dimension: wgpu::TextureViewDimension::D2,
+            multisampled: false,
+        },
+    )
+}
+
+fn target(format: wgpu::TextureFormat) -> Option<wgpu::ColorTargetState> {
+    Some(wgpu::ColorTargetState {
+        format,
+        blend: None,
+        write_mask: wgpu::ColorWrites::ALL,
+    })
+}
+
+fn attach(
+    view: &wgpu::TextureView,
+    ops: wgpu::Operations<wgpu::Color>,
+) -> Option<wgpu::RenderPassColorAttachment<'_>> {
+    Some(wgpu::RenderPassColorAttachment {
+        view,
+        resolve_target: None,
+        depth_slice: None,
+        ops,
+    })
+}
+
+impl PackPost {
+    /// Builds the pipelines of `post` for a screen of `screen` format.
+    pub fn new(
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        post: Post,
+        screen: wgpu::TextureFormat,
+    ) -> Self {
+        let features = device.features();
+        let formats: [wgpu::TextureFormat; BUFFERS] =
+            std::array::from_fn(|i| texture_format(post.config.buffers[i].format, features));
+        let clears = std::array::from_fn(|i| {
+            let b = &post.config.buffers[i];
+            b.clear.then(|| {
+                b.clear_color
+                    .unwrap_or(if i == 1 { [1.0; 4] } else { [0.0; 4] })
+            })
+        });
+        let mut notes = post.notes;
+        notes.extend(post.config.notes);
+        let mask =
+            |flips: &[(u32, bool)]| flips.iter().filter(|f| f.1).fold(0u16, |m, f| m | 1 << f.0);
+        let mut used = 1u16;
+        let mut passes = Vec::new();
+        for p in post.programs {
+            let interface = &p.program.interface;
+            let mut entries = vec![entry(
+                0,
+                wgpu::BindingType::Buffer {
+                    ty: wgpu::BufferBindingType::Uniform,
+                    has_dynamic_offset: false,
+                    min_binding_size: None,
+                },
+            )];
+            let mut samplers = Vec::new();
+            let mut reads = 0u16;
+            for s in &interface.samplers {
+                let mut src = source(&s.name);
+                let float = wgpu::TextureSampleType::Float { filterable: true };
+                let mut sample_type = match src {
+                    Source::Color(n) => formats[n]
+                        .sample_type(None, Some(features))
+                        .unwrap_or(float),
+                    Source::Depth => wgpu::TextureSampleType::Float { filterable: false },
+                    _ => float,
+                };
+                let int = !matches!(sample_type, wgpu::TextureSampleType::Float { .. });
+                if s.ty == "sampler2DShadow" {
+                    (src, sample_type) = (Source::Shadow, wgpu::TextureSampleType::Depth);
+                }
+                let wanted = match s.ty.as_str() {
+                    "sampler2DShadow" => true,
+                    "sampler2D" => !int,
+                    "isampler2D" => sample_type == wgpu::TextureSampleType::Sint,
+                    "usampler2D" => sample_type == wgpu::TextureSampleType::Uint,
+                    _ => false,
+                };
+                if !wanted {
+                    notes.push(format!(
+                        "{}: `{} {}` is not provided yet",
+                        p.name, s.ty, s.name
+                    ));
+                    (src, sample_type) = (Source::Dummy, float);
+                }
+                let filtering = sample_type == float;
+                if let Source::Color(n) = src {
+                    reads |= 1 << n;
+                }
+                entries.push(texture_entry(s.binding, sample_type));
+                entries.push(entry(
+                    s.binding + 1,
+                    wgpu::BindingType::Sampler(if src == Source::Shadow {
+                        wgpu::SamplerBindingType::Comparison
+                    } else if filtering {
+                        wgpu::SamplerBindingType::Filtering
+                    } else {
+                        wgpu::SamplerBindingType::NonFiltering
+                    }),
+                ));
+                samplers.push(Binding {
+                    source: src,
+                    binding: s.binding,
+                    filtering,
+                });
+            }
+            let final_pass = p.group == Group::Final;
+            let mut targets = Vec::new();
+            let mut writes = Vec::new();
+            for &location in &interface.outputs {
+                let l = location as usize;
+                if targets.len() <= l {
+                    targets.resize(l + 1, None);
+                }
+                if final_pass {
+                    if location == 0 {
+                        targets[0] = target(screen);
+                    }
+                } else if let Some(&buffer) = p.buffers.get(l) {
+                    targets[l] = target(formats[buffer as usize]);
+                    writes.push((location, buffer as usize));
+                }
+            }
+            if !final_pass && writes.is_empty() {
+                notes.push(format!("{}: writes no buffer; skipped", p.name));
+                continue;
+            }
+            let written = writes.iter().fold(0u16, |m, w| m | 1 << w.1);
+            let kept = p
+                .flips
+                .iter()
+                .filter(|f| !f.1)
+                .fold(0u16, |m, f| m | 1 << f.0);
+            let flip = if final_pass {
+                0
+            } else {
+                (written & !kept) | mask(&p.flips)
+            };
+            used |= reads | written | flip;
+            let layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+                label: Some(&p.name),
+                entries: &entries,
+            });
+            let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
+                label: Some(&p.name),
+                bind_group_layouts: &[Some(&layout)],
+                ..Default::default()
+            });
+            let created = checked(device, || {
+                let module = |m: naga::Module| {
+                    device.create_shader_module(wgpu::ShaderModuleDescriptor {
+                        label: Some(&p.name),
+                        source: wgpu::ShaderSource::Naga(std::borrow::Cow::Owned(m)),
+                    })
+                };
+                let (vs, fs) = (module(p.program.vertex), module(p.program.fragment));
+                device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
+                    label: Some(&p.name),
+                    layout: Some(&pipeline_layout),
+                    vertex: wgpu::VertexState {
+                        module: &vs,
+                        entry_point: Some("main"),
+                        compilation_options: Default::default(),
+                        buffers: &[],
+                    },
+                    primitive: Default::default(),
+                    depth_stencil: None,
+                    multisample: Default::default(),
+                    fragment: Some(wgpu::FragmentState {
+                        module: &fs,
+                        entry_point: Some("main"),
+                        compilation_options: Default::default(),
+                        targets: &targets,
+                    }),
+                    multiview_mask: None,
+                    cache: None,
+                })
+            });
+            let pipeline = match created {
+                Ok(p) => p,
+                Err(e) => {
+                    notes.push(format!("{}: skipped: {e}", p.name));
+                    continue;
+                }
+            };
+            let interface = &p.program.interface;
+            passes.push(Pass {
+                ubo: device.create_buffer(&wgpu::BufferDescriptor {
+                    label: Some(&p.name),
+                    size: u64::from(interface.uniform_size.max(16)),
+                    usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
+                    mapped_at_creation: false,
+                }),
+                block: vec![0; interface.uniform_size as usize],
+                uniforms: interface
+                    .uniforms
+                    .iter()
+                    .map(|u| (pack_uniforms::index(&u.name), u.ty.clone(), u.offset))
+                    .collect(),
+                name: p.name,
+                group: p.group,
+                pipeline,
+                layout,
+                samplers,
+                writes,
+                flip,
+                reads,
+                written,
+                groups: HashMap::new(),
+            });
+        }
+        // A clear only matters when a program reads the buffer before one writes all of it
+        // (composite passes cover their whole target); the others are skipped.
+        let mut cleared = Vec::new();
+        for b in 1..BUFFERS {
+            let bit = 1u16 << b;
+            let first = passes
+                .iter()
+                .find(|p| (p.reads | p.flip | p.written) & bit != 0);
+            if clears[b].is_some()
+                && first.is_some_and(|p| p.reads & bit != 0 || p.written & bit == 0)
+            {
+                cleared.push(b);
+            }
+        }
+        let blit_depth = passes
+            .iter()
+            .any(|p| p.samplers.iter().any(|s| s.source == Source::Depth));
+        let room = 8 - 1 - usize::from(blit_depth);
+        let other_clears = cleared.split_off(room.min(cleared.len()));
+        let float = wgpu::TextureSampleType::Float { filterable: true };
+        let mut blit_targets = vec![target(formats[0])];
+        if blit_depth {
+            blit_targets.push(target(wgpu::TextureFormat::R32Float));
+        }
+        // Cleared by the pass's load operation; the shader writes nothing there.
+        blit_targets.extend(cleared.iter().map(|&b| {
+            Some(wgpu::ColorTargetState {
+                format: formats[b],
+                blend: None,
+                write_mask: wgpu::ColorWrites::empty(),
+            })
+        }));
+        let blit = helper(
+            device,
+            "vs_full",
+            if blit_depth {
+                "fs_blit"
+            } else {
+                "fs_blit_color"
+            },
+            &[
+                texture_entry(0, float),
+                texture_entry(1, wgpu::TextureSampleType::Depth),
+            ],
+            &blit_targets,
+        );
+        let copy = helper(
+            device,
+            "vs_uv",
+            "fs_copy",
+            &[
+                texture_entry(0, float),
+                entry(
+                    2,
+                    wgpu::BindingType::Sampler(wgpu::SamplerBindingType::Filtering),
+                ),
+            ],
+            &[target(screen)],
+        );
+        let white = [255u8; 4];
+        Self {
+            notes,
+            passes,
+            deferred_pre: mask(&post.deferred_pre),
+            composite_pre: mask(&post.composite_pre),
+            formats,
+            clears,
+            used,
+            blit_depth,
+            blit_clears: cleared,
+            other_clears,
+            blit_group: None,
+            main: 0,
+            targets: None,
+            noise: noise(device, queue),
+            dummy: texture(device, queue, "Shader pack stand-in", 1, &white),
+            shadow: (
+                device
+                    .create_texture(&wgpu::TextureDescriptor {
+                        label: Some("Shader pack shadow stand-in"),
+                        size: wgpu::Extent3d {
+                            width: 1,
+                            height: 1,
+                            depth_or_array_layers: 1,
+                        },
+                        mip_level_count: 1,
+                        sample_count: 1,
+                        dimension: wgpu::TextureDimension::D2,
+                        format: wgpu::TextureFormat::Depth32Float,
+                        usage: wgpu::TextureUsages::TEXTURE_BINDING
+                            | wgpu::TextureUsages::RENDER_ATTACHMENT,
+                        view_formats: &[],
+                    })
+                    .create_view(&Default::default()),
+                device.create_sampler(&wgpu::SamplerDescriptor {
+                    label: Some("Shader pack shadow"),
+                    compare: Some(wgpu::CompareFunction::LessEqual),
+                    ..Default::default()
+                }),
+            ),
+            shadow_cleared: false,
+            linear: sampler(
+                device,
+                wgpu::FilterMode::Linear,
+                wgpu::AddressMode::ClampToEdge,
+            ),
+            nearest: sampler(
+                device,
+                wgpu::FilterMode::Nearest,
+                wgpu::AddressMode::ClampToEdge,
+            ),
+            repeat: sampler(device, wgpu::FilterMode::Linear, wgpu::AddressMode::Repeat),
+            blit,
+            copy,
+            uniforms: FrameUniforms::default(),
+        }
+    }
+
+    /// The names of the programs that run, in order.
+    pub fn programs(&self) -> Vec<&str> {
+        self.passes.iter().map(|p| p.name.as_str()).collect()
+    }
+
+    fn resize(&mut self, device: &wgpu::Device, size: [u32; 2]) {
+        if self.targets.as_ref().is_some_and(|t| t.size == size) {
+            return;
+        }
+        let make = |label: &str, format| {
+            device
+                .create_texture(&wgpu::TextureDescriptor {
+                    label: Some(label),
+                    size: wgpu::Extent3d {
+                        width: size[0],
+                        height: size[1],
+                        depth_or_array_layers: 1,
+                    },
+                    mip_level_count: 1,
+                    sample_count: 1,
+                    dimension: wgpu::TextureDimension::D2,
+                    format,
+                    usage: wgpu::TextureUsages::RENDER_ATTACHMENT
+                        | wgpu::TextureUsages::TEXTURE_BINDING,
+                    view_formats: &[],
+                })
+                .create_view(&Default::default())
+        };
+        let color = std::array::from_fn(|i| {
+            (self.used & 1 << i != 0).then(|| {
+                let label = format!("colortex{i}");
+                [make(&label, self.formats[i]), make(&label, self.formats[i])]
+            })
+        });
+        self.targets = Some(Targets {
+            size,
+            color,
+            depth: make("depthtex0", wgpu::TextureFormat::R32Float),
+        });
+        for pass in &mut self.passes {
+            pass.groups.clear();
+        }
+    }
+
+    /// Runs the pack over the world drawn into `world` (colour) and `world_depth`, then draws
+    /// the result onto `screen`.
+    #[allow(clippy::too_many_arguments)]
+    pub fn run(
+        &mut self,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        encoder: &mut wgpu::CommandEncoder,
+        world: &wgpu::TextureView,
+        world_depth: &wgpu::TextureView,
+        screen: &wgpu::TextureView,
+        frame: &super::Frame,
+        inputs: &PackInputs,
+        size: [u32; 2],
+        window: [u32; 2],
+    ) {
+        self.resize(device, size);
+        self.uniforms.update(frame, inputs, size);
+        let Some(targets) = &self.targets else { return };
+        let main = |m: u16, i: usize| usize::from(m & 1 << i != 0);
+        let view = |m: u16, i: usize, alt: bool| {
+            targets.color[i]
+                .as_ref()
+                .map(|t| &t[main(m, i) ^ usize::from(alt)])
+        };
+
+        if !self.shadow_cleared {
+            self.shadow_cleared = true;
+            encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                label: Some("Shader pack shadow stand-in"),
+                depth_stencil_attachment: Some(wgpu::RenderPassDepthStencilAttachment {
+                    view: &self.shadow.0,
+                    depth_ops: Some(wgpu::Operations {
+                        load: wgpu::LoadOp::Clear(1.0),
+                        store: wgpu::StoreOp::Store,
+                    }),
+                    stencil_ops: None,
+                }),
+                ..Default::default()
+            });
+        }
+        let clear_op = |b: usize| {
+            let c = self.clears[b].unwrap_or_default();
+            wgpu::Operations {
+                load: wgpu::LoadOp::Clear(wgpu::Color {
+                    r: c[0].into(),
+                    g: c[1].into(),
+                    b: c[2].into(),
+                    a: c[3].into(),
+                }),
+                store: wgpu::StoreOp::Store,
+            }
+        };
+        // Overwritten whole: clearing lets a tiled GPU skip loading the old content.
+        let overwrite = wgpu::Operations {
+            load: wgpu::LoadOp::Clear(wgpu::Color::TRANSPARENT),
+            store: wgpu::StoreOp::Store,
+        };
+        for chunk in self.other_clears.chunks(8) {
+            let attachments: Vec<_> = chunk
+                .iter()
+                .map(|&b| attach(view(self.main, b, false).expect("used buffer"), clear_op(b)))
+                .collect();
+            encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                label: Some("Shader pack clear"),
+                color_attachments: &attachments,
+                ..Default::default()
+            });
+        }
+
+        // The world into colortex0 and depthtex0, flipped to GL's rows, and the clears.
+        if self.blit_group.as_ref().is_none_or(|g| g.0 != size) {
+            let group = device.create_bind_group(&wgpu::BindGroupDescriptor {
+                label: Some("Shader pack world"),
+                layout: &self.blit.1,
+                entries: &[
+                    wgpu::BindGroupEntry {
+                        binding: 0,
+                        resource: wgpu::BindingResource::TextureView(world),
+                    },
+                    wgpu::BindGroupEntry {
+                        binding: 1,
+                        resource: wgpu::BindingResource::TextureView(world_depth),
+                    },
+                ],
+            });
+            self.blit_group = Some((size, group));
+        }
+        {
+            let mut attachments = vec![attach(
+                view(self.main, 0, false).expect("colortex0"),
+                overwrite,
+            )];
+            if self.blit_depth {
+                attachments.push(attach(&targets.depth, overwrite));
+            }
+            for &b in &self.blit_clears {
+                attachments.push(attach(
+                    view(self.main, b, false).expect("used buffer"),
+                    clear_op(b),
+                ));
+            }
+            let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                label: Some("Shader pack world"),
+                color_attachments: &attachments,
+                ..Default::default()
+            });
+            pass.set_pipeline(&self.blit.0);
+            pass.set_bind_group(0, self.blit_group.as_ref().map(|g| &g.1), &[]);
+            pass.draw(0..3, 0..1);
+        }
+
+        let fog = self.uniforms.fog();
+        let mut seen = (false, false);
+        let mut shown = false;
+        for pass in &mut self.passes {
+            if pass.group == Group::Deferred && !seen.0 {
+                seen.0 = true;
+                self.main ^= self.deferred_pre;
+            }
+            if pass.group == Group::Composite && !seen.1 {
+                seen.1 = true;
+                self.main ^= self.composite_pre;
+            }
+            let final_pass = pass.group == Group::Final;
+            let out = if final_pass { window } else { size };
+            // Our block members first (`hz_target`, `hz_fog_color`, `hz_fog`), then the pack's.
+            let ours = [
+                [
+                    out[0] as f32,
+                    out[1] as f32,
+                    1.0 / out[0] as f32,
+                    1.0 / out[1] as f32,
+                ],
+                fog[0].to_array(),
+                fog[1].to_array(),
+            ];
+            let head: &[u8] = bytemuck::cast_slice(&ours);
+            let n = head.len().min(pass.block.len());
+            pass.block[..n].copy_from_slice(&head[..n]);
+            for (index, ty, offset) in &pass.uniforms {
+                if let Some(v) = index.and_then(|i| self.uniforms.values.get(i)) {
+                    v.write(ty, &mut pass.block, *offset as usize);
+                }
+            }
+            if !pass.block.is_empty() {
+                queue.write_buffer(&pass.ubo, 0, &pass.block);
+            }
+            let key = self.main & pass.reads;
+            let group = pass.groups.entry(key).or_insert_with(|| {
+                let mut entries = vec![wgpu::BindGroupEntry {
+                    binding: 0,
+                    resource: pass.ubo.as_entire_binding(),
+                }];
+                for s in &pass.samplers {
+                    let filter = if s.filtering {
+                        &self.linear
+                    } else {
+                        &self.nearest
+                    };
+                    let (texture, sampler) = match s.source {
+                        Source::Color(i) => (view(key, i, false).unwrap_or(&self.dummy), filter),
+                        Source::Depth => (&targets.depth, &self.nearest),
+                        Source::Noise => (&self.noise, &self.repeat),
+                        Source::Dummy => (&self.dummy, &self.linear),
+                        Source::Shadow => (&self.shadow.0, &self.shadow.1),
+                    };
+                    entries.push(wgpu::BindGroupEntry {
+                        binding: s.binding,
+                        resource: wgpu::BindingResource::TextureView(texture),
+                    });
+                    entries.push(wgpu::BindGroupEntry {
+                        binding: s.binding + 1,
+                        resource: wgpu::BindingResource::Sampler(sampler),
+                    });
+                }
+                device.create_bind_group(&wgpu::BindGroupDescriptor {
+                    label: Some(&pass.name),
+                    layout: &pass.layout,
+                    entries: &entries,
+                })
+            });
+            let mut attachments: Vec<Option<wgpu::RenderPassColorAttachment>> = Vec::new();
+            if final_pass {
+                attachments.push(attach(screen, overwrite));
+                shown = true;
+            } else {
+                for &(location, buffer) in &pass.writes {
+                    let l = location as usize;
+                    if attachments.len() <= l {
+                        attachments.resize(l + 1, None);
+                    }
+                    attachments[l] =
+                        view(self.main, buffer, true).and_then(|v| attach(v, overwrite));
+                }
+            }
+            {
+                let mut rp = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                    label: Some(&pass.name),
+                    color_attachments: &attachments,
+                    ..Default::default()
+                });
+                rp.set_pipeline(&pass.pipeline);
+                rp.set_bind_group(0, &*group, &[]);
+                rp.draw(0..6, 0..1);
+            }
+            self.main ^= pass.flip;
+        }
+        if !shown {
+            let group = device.create_bind_group(&wgpu::BindGroupDescriptor {
+                label: Some("Shader pack colortex0"),
+                layout: &self.copy.1,
+                entries: &[
+                    wgpu::BindGroupEntry {
+                        binding: 0,
+                        resource: wgpu::BindingResource::TextureView(
+                            view(self.main, 0, false).expect("colortex0"),
+                        ),
+                    },
+                    wgpu::BindGroupEntry {
+                        binding: 2,
+                        resource: wgpu::BindingResource::Sampler(&self.linear),
+                    },
+                ],
+            });
+            let mut rp = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                label: Some("Shader pack colortex0"),
+                color_attachments: &[attach(screen, overwrite)],
+                ..Default::default()
+            });
+            rp.set_pipeline(&self.copy.0);
+            rp.set_bind_group(0, &group, &[]);
+            rp.draw(0..3, 0..1);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use wgpu::TextureFormat as T;
+
+    #[test]
+    fn pack_formats_map_to_renderable_ones() {
+        let f = |name| texture_format(Format::parse(name).unwrap(), wgpu::Features::empty());
+        assert_eq!(f("RGBA"), T::Rgba8Unorm);
+        assert_eq!(f("RGB8"), T::Rgba8Unorm, "no three-channel formats in wgpu");
+        assert_eq!(f("RG16F"), T::Rg16Float);
+        assert_eq!(f("R32F"), T::R32Float);
+        assert_eq!(f("RGB10_A2"), T::Rgb10a2Unorm);
+        assert_eq!(f("R32UI"), T::R32Uint);
+        assert_eq!(f("RGBA16"), T::Rgba16Float, "16-bit norm needs a feature");
+        assert_eq!(f("RGBA8_SNORM"), T::Rgba16Float, "snorm is not renderable");
+        assert_eq!(f("R11F_G11F_B10F"), T::Rgba16Float);
+        let all =
+            wgpu::Features::TEXTURE_FORMAT_16BIT_NORM | wgpu::Features::RG11B10UFLOAT_RENDERABLE;
+        let g = |name| texture_format(Format::parse(name).unwrap(), all);
+        assert_eq!(g("RGBA16"), T::Rgba16Unorm);
+        assert_eq!(g("R11F_G11F_B10F"), T::Rg11b10Ufloat);
+    }
+
+    #[test]
+    fn sampler_names() {
+        assert!(source("gaux1") == Source::Color(4));
+        assert!(source("gdepthtex") == Source::Depth);
+        assert!(source("noisetex") == Source::Noise);
+        assert!(source("shadowcolor0") == Source::Dummy);
+    }
+}

crates/horizon-client/src/gfx/pack_post.wgsl

@@ -0,0 +1,54 @@
+// Helpers of a shader pack's post-processing (pack_post.rs): the world into colortex0 and
+// depthtex0, and colortex0 onto the screen for packs without `final`.
+
+@vertex
+fn vs_full(@builtin(vertex_index) i: u32) -> @builtin(position) vec4<f32> {
+    let uv = vec2<f32>(f32((i << 1u) & 2u), f32(i & 2u));
+    return vec4<f32>(uv * 2.0 - 1.0, 0.0, 1.0);
+}
+
+@group(0) @binding(0) var source: texture_2d<f32>;
+@group(0) @binding(1) var world_depth: texture_depth_2d;
+
+struct World {
+    @location(0) color: vec4<f32>,
+    @location(1) depth: vec4<f32>,
+}
+
+// Pack buffers keep GL's rows (row 0 at the bottom), and GL's window depth: Horizon's
+// reverse-Z depth is 1 - d for the same near and far planes.
+@fragment
+fn fs_blit(@builtin(position) p: vec4<f32>) -> World {
+    let size = vec2<i32>(textureDimensions(source));
+    let at = vec2<i32>(i32(p.x), size.y - 1 - i32(p.y));
+    var out: World;
+    out.color = textureLoad(source, at, 0);
+    out.depth = vec4<f32>(1.0 - textureLoad(world_depth, at, 0), 0.0, 0.0, 1.0);
+    return out;
+}
+
+// The same without depthtex0, for packs that never read it.
+@fragment
+fn fs_blit_color(@builtin(position) p: vec4<f32>) -> @location(0) vec4<f32> {
+    let size = vec2<i32>(textureDimensions(source));
+    return textureLoad(source, vec2<i32>(i32(p.x), size.y - 1 - i32(p.y)), 0);
+}
+
+@group(0) @binding(2) var linear: sampler;
+
+struct Full {
+    @builtin(position) position: vec4<f32>,
+    @location(0) uv: vec2<f32>,
+}
+
+@vertex
+fn vs_uv(@builtin(vertex_index) i: u32) -> Full {
+    let uv = vec2<f32>(f32((i << 1u) & 2u), f32(i & 2u));
+    // Screen top (uv.y = 0 in wgpu) shows the buffer's top row, GL's last.
+    return Full(vec4<f32>(uv.x * 2.0 - 1.0, 1.0 - uv.y * 2.0, 0.0, 1.0), vec2<f32>(uv.x, 1.0 - uv.y));
+}
+
+@fragment
+fn fs_copy(v: Full) -> @location(0) vec4<f32> {
+    return textureSample(source, linear, v.uv);
+}

crates/horizon-client/src/gfx/pack_uniforms.rs

@@ -0,0 +1,329 @@
+//! The uniforms a shader pack's post-processing programs read once per frame (spec 5.2, class
+//! F), from the renderer's `Frame` and the few values only the game knows (`PackInputs`).
+//! Matrices follow GL's conventions (5.5): `gbufferProjection` maps view depth to clip z in
+//! [-w, w], and the depth buffers packs read hold GL window depth.
+
+use glam::{Mat4, Vec3, Vec4};
+
+use super::Frame;
+
+/// What the game passes for the pack's uniforms, beyond what `Frame` carries.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct PackInputs {
+    /// `Level.getDayTime`.
+    pub day_time: i64,
+    /// The interpolated rain and thunder levels, 0..1.
+    pub rain: f32,
+    pub thunder: f32,
+    /// The fluid at the camera: 0 none, 1 water, 2 lava, 3 powder snow.
+    pub eye_in: i32,
+    pub blindness: f32,
+    /// Block and sky light at the camera, 0..15.
+    pub eye_light: [i32; 2],
+    pub hide_gui: bool,
+    /// The brightness option, 0..1.
+    pub brightness: f32,
+}
+
+/// One uniform's value: up to 16 floats or 3 integers.
+#[derive(Clone, Copy, Debug)]
+pub enum Value {
+    F([f32; 16]),
+    I([i32; 3]),
+}
+
+impl Value {
+    fn f(v: &[f32]) -> Self {
+        let mut a = [0.0; 16];
+        a[..v.len()].copy_from_slice(v);
+        Value::F(a)
+    }
+    fn i(v: &[i32]) -> Self {
+        let mut a = [0; 3];
+        a[..v.len()].copy_from_slice(v);
+        Value::I(a)
+    }
+
+    /// Writes the value as the type the pack declared, at `offset` of a std140 block.
+    pub fn write(&self, ty: &str, out: &mut [u8], offset: usize) {
+        let ints = matches!(ty, "int" | "bool" | "uint") || ty.starts_with(['i', 'u']);
+        let (floats, integers): ([f32; 16], [i32; 16]) = match *self {
+            Value::F(f) => (f, f.map(|v| v as i32)),
+            Value::I(i) => {
+                let mut f = [0.0; 16];
+                let mut v = [0; 16];
+                for k in 0..3 {
+                    f[k] = i[k] as f32;
+                    v[k] = i[k];
+                }
+                (f, v)
+            }
+        };
+        let count = match ty {
+            "mat4" => 16,
+            "mat3" => {
+                // std140: three columns, each padded to a vec4, from the mat4's upper left.
+                for c in 0..3 {
+                    let column: [f32; 3] = std::array::from_fn(|r| floats[c * 4 + r]);
+                    put(out, offset + c * 16, bytemuck::cast_slice(&column));
+                }
+                return;
+            }
+            t => match t.as_bytes().last() {
+                Some(n @ b'2'..=b'4') if t.contains("vec") => (n - b'0') as usize,
+                _ => 1,
+            },
+        };
+        if ints {
+            put(out, offset, bytemuck::cast_slice(&integers[..count]));
+        } else {
+            put(out, offset, bytemuck::cast_slice(&floats[..count]));
+        }
+    }
+}
+
+fn put(out: &mut [u8], offset: usize, bytes: &[u8]) {
+    if let Some(dst) = out.get_mut(offset..offset + bytes.len()) {
+        dst.copy_from_slice(bytes);
+    }
+}
+
+/// The uniforms provided, in the order of [`FrameUniforms::values`].
+pub const NAMES: &[&str] = &[
+    "cameraPosition",
+    "previousCameraPosition",
+    "eyeAltitude",
+    "upPosition",
+    "sunPosition",
+    "moonPosition",
+    "shadowLightPosition",
+    "sunAngle",
+    "shadowAngle",
+    "worldTime",
+    "worldDay",
+    "moonPhase",
+    "frameCounter",
+    "frameTime",
+    "frameTimeCounter",
+    "viewWidth",
+    "viewHeight",
+    "aspectRatio",
+    "near",
+    "far",
+    "rainStrength",
+    "wetness",
+    "thunderStrength",
+    "fogColor",
+    "skyColor",
+    "fogMode",
+    "fogStart",
+    "fogEnd",
+    "fogDensity",
+    "fogShape",
+    "isEyeInWater",
+    "blindness",
+    "nightVision",
+    "darknessFactor",
+    "darknessLightFactor",
+    "screenBrightness",
+    "hideGUI",
+    "eyeBrightness",
+    "eyeBrightnessSmooth",
+    "heldItemId",
+    "heldItemId2",
+    "heldBlockLightValue",
+    "heldBlockLightValue2",
+    "renderStage",
+    "gbufferModelView",
+    "gbufferModelViewInverse",
+    "gbufferProjection",
+    "gbufferProjectionInverse",
+    "gbufferPreviousModelView",
+    "gbufferPreviousProjection",
+];
+
+/// Values carried from frame to frame.
+pub struct FrameUniforms {
+    pub values: Vec<Value>,
+    start: std::time::Instant,
+    last: Option<std::time::Instant>,
+    frame: u32,
+    previous: Option<(Vec3, Mat4, Mat4)>,
+    wetness: f32,
+    eye_smooth: [f32; 2],
+}
+
+impl Default for FrameUniforms {
+    fn default() -> Self {
+        Self {
+            values: Vec::new(),
+            start: std::time::Instant::now(),
+            last: None,
+            frame: 0,
+            previous: None,
+            wetness: 0.0,
+            eye_smooth: [0.0; 2],
+        }
+    }
+}
+
+/// `(0, 100, 0)` on the frame the sky draws a body on: Y -90°, then X by its angle in degrees.
+fn body(angle: f32) -> Vec3 {
+    (Mat4::from_rotation_y((-90.0f32).to_radians()) * Mat4::from_rotation_x(angle.to_radians()))
+        .transform_vector3(Vec3::new(0.0, 100.0, 0.0))
+}
+
+/// `value` moved toward `target` with a half-life of `half_life` seconds over `dt` (5.6).
+fn smooth(value: f32, target: f32, half_life: f32, dt: f32) -> f32 {
+    target + (value - target) * 0.5f32.powf(dt / half_life)
+}
+
+impl FrameUniforms {
+    /// This frame's values for a render size of `size` pixels.
+    pub fn update(&mut self, frame: &Frame, inputs: &PackInputs, size: [u32; 2]) {
+        let now = std::time::Instant::now();
+        let dt = self.last.map_or(0.0, |l| (now - l).as_secs_f32());
+        self.last = Some(now);
+        let aspect = size[0] as f32 / size[1].max(1) as f32;
+        let view = crate::camera::view_matrix(frame.yaw, frame.pitch);
+        let projection = Mat4::perspective_rh_gl(
+            frame.fov_degrees.to_radians(),
+            aspect,
+            0.05,
+            frame.depth_far,
+        ) * frame.bob;
+        let camera = frame.camera.as_vec3();
+        let (previous_camera, previous_view, previous_projection) =
+            self.previous
+                .unwrap_or((Vec3::ZERO, Mat4::ZERO, Mat4::ZERO));
+        self.previous = Some((camera, view, projection));
+
+        let to_view = |v: Vec3| view.transform_vector3(v);
+        let sun_angle = (frame.sky.sun_angle / 360.0 + 0.25).rem_euclid(1.0);
+        let day = sun_angle < 0.5;
+        let sun = to_view(body(frame.sky.sun_angle));
+        let moon = to_view(body(frame.sky.moon_angle));
+        // Half-lives are given in ticks (7.2); smoothing runs per frame in seconds (OQ-26).
+        let half_life = if inputs.rain > self.wetness {
+            600.0
+        } else {
+            200.0
+        };
+        self.wetness = smooth(self.wetness, inputs.rain, half_life / 20.0, dt);
+        let eye = inputs.eye_light.map(|l| (l * 16) as f32);
+        for (smoothed, target) in self.eye_smooth.iter_mut().zip(eye) {
+            *smoothed = smooth(*smoothed, target, 10.0 / 20.0, dt);
+        }
+        let (fog_color, fog_start, fog_end) = match &frame.fog {
+            Some(f) => (
+                [f.color[0], f.color[1], f.color[2]],
+                f.environmental_start.min(f.render_distance_start),
+                f.environmental_end.min(f.render_distance_end),
+            ),
+            None => (frame.sky.fog_color, frame.distance * 0.9, frame.distance),
+        };
+        let day_time = inputs.day_time.rem_euclid(24000) as i32;
+        let world_day = inputs.day_time.div_euclid(24000);
+        let seconds = (now - self.start).as_secs_f32() % 3600.0;
+
+        let value = |name: &str| -> Value {
+            let v3 = |v: Vec3| Value::f(&v.to_array());
+            let m4 = |m: Mat4| Value::f(&m.to_cols_array());
+            match name {
+                "cameraPosition" => v3(camera),
+                "previousCameraPosition" => v3(previous_camera),
+                "eyeAltitude" => Value::f(&[frame.camera.y as f32]),
+                "upPosition" => v3(to_view(Vec3::new(0.0, 100.0, 0.0))),
+                "sunPosition" => v3(sun),
+                "moonPosition" => v3(moon),
+                "shadowLightPosition" => v3(if day { sun } else { moon }),
+                "sunAngle" => Value::f(&[sun_angle]),
+                "shadowAngle" => Value::f(&[if day { sun_angle } else { sun_angle - 0.5 }]),
+                "worldTime" => Value::i(&[day_time]),
+                "worldDay" => Value::i(&[world_day as i32]),
+                "moonPhase" => Value::i(&[world_day.rem_euclid(8) as i32]),
+                "frameCounter" => Value::i(&[self.frame as i32]),
+                "frameTime" => Value::f(&[dt]),
+                "frameTimeCounter" => Value::f(&[seconds]),
+                "viewWidth" => Value::f(&[size[0] as f32]),
+                "viewHeight" => Value::f(&[size[1] as f32]),
+                "aspectRatio" => Value::f(&[aspect]),
+                "near" => Value::f(&[0.05]),
+                "far" => Value::f(&[frame.distance]),
+                "rainStrength" => Value::f(&[inputs.rain]),
+                "wetness" => Value::f(&[self.wetness]),
+                "thunderStrength" => Value::f(&[inputs.thunder]),
+                "fogColor" => Value::f(&fog_color),
+                "skyColor" => Value::f(&frame.sky.sky_color),
+                // GL_LINEAR: vanilla's fog is linear.
+                "fogMode" => Value::i(&[9729]),
+                "fogStart" => Value::f(&[fog_start]),
+                "fogEnd" => Value::f(&[fog_end]),
+                "fogDensity" => Value::f(&[1.0]),
+                "fogShape" => Value::i(&[0]),
+                "isEyeInWater" => Value::i(&[inputs.eye_in]),
+                "blindness" => Value::f(&[inputs.blindness]),
+                "nightVision" => Value::f(&[frame.night_vision]),
+                "darknessFactor" => Value::f(&[frame.darkness.0]),
+                "darknessLightFactor" => Value::f(&[frame.darkness.1]),
+                "screenBrightness" => Value::f(&[inputs.brightness]),
+                "hideGUI" => Value::i(&[inputs.hide_gui as i32]),
+                "eyeBrightness" => Value::i(&eye.map(|v| v as i32)),
+                "eyeBrightnessSmooth" => Value::i(&self.eye_smooth.map(|v| v.round() as i32)),
+                "gbufferModelView" => m4(view),
+                "gbufferModelViewInverse" => m4(view.inverse()),
+                "gbufferProjection" => m4(projection),
+                "gbufferProjectionInverse" => m4(projection.inverse()),
+                "gbufferPreviousModelView" => m4(previous_view),
+                "gbufferPreviousProjection" => m4(previous_projection),
+                // Held items wait for `item.properties` (5.3: 0 without the file); renderStage
+                // is NONE outside gbuffers draws.
+                _ => Value::i(&[0]),
+            }
+        };
+        self.values = NAMES.iter().map(|n| value(n)).collect();
+        self.frame = (self.frame + 1) % 720_720;
+    }
+
+    /// `hz_fog_color` and `hz_fog` of the translator's block (the compatibility `gl_Fog`).
+    pub fn fog(&self) -> [Vec4; 2] {
+        let get = |name| match index(name).and_then(|i| self.values.get(i)) {
+            Some(Value::F(f)) => *f,
+            _ => [0.0; 16],
+        };
+        let (color, start, end) = (get("fogColor"), get("fogStart")[0], get("fogEnd")[0]);
+        [
+            Vec4::new(color[0], color[1], color[2], 1.0),
+            Vec4::new(1.0, start, end, 1.0 / (end - start).max(1e-3)),
+        ]
+    }
+}
+
+/// The position of `name` in [`NAMES`].
+pub fn index(name: &str) -> Option<usize> {
+    NAMES.iter().position(|n| *n == name)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn values_follow_the_declared_type() {
+        let mut out = vec![0u8; 64];
+        Value::i(&[7]).write("float", &mut out, 0);
+        assert_eq!(f32::from_ne_bytes(out[0..4].try_into().unwrap()), 7.0);
+        Value::f(&[1.5, 2.5]).write("ivec2", &mut out, 4);
+        assert_eq!(i32::from_ne_bytes(out[8..12].try_into().unwrap()), 2);
+        Value::i(&[1]).write("bool", &mut out, 16);
+        assert_eq!(i32::from_ne_bytes(out[16..20].try_into().unwrap()), 1);
+        Value::f(&[1.0; 16]).write("mat4", &mut out, 60);
+        assert_eq!(out[60..64], [0; 4], "a value past the block is dropped");
+    }
+
+    #[test]
+    fn noon_is_straight_up_and_the_sun_sets_in_the_west() {
+        assert!(body(0.0).abs_diff_eq(Vec3::new(0.0, 100.0, 0.0), 1e-3));
+        assert!(body(90.0).abs_diff_eq(Vec3::new(-100.0, 0.0, 0.0), 1e-3));
+    }
+}

crates/horizon-client/src/gfx/world_post.rs

@@ -101,12 +101,14 @@ impl Post {
 
     /// The world's colour and depth targets this frame, or `None` to draw
     /// it straight to the screen.
+    /// `always`: a target even at scale 1 without FXAA (a shader pack reads it).
     pub fn prepare(
         &mut self,
         device: &wgpu::Device,
         window: [u32; 2],
+        always: bool,
     ) -> Option<(wgpu::TextureView, wgpu::TextureView)> {
-        if self.scale == 1.0 && !self.antialias {
+        if self.scale == 1.0 && !self.antialias && !always {
             self.target = None;
             return None;
         }
@@ -155,6 +157,11 @@ impl Post {
             .map(|t| (t.color.clone(), t.depth.clone()))
     }
 
+    /// The size of the world's own target, when it has one.
+    pub fn size(&self) -> Option<[u32; 2]> {
+        self.target.as_ref().map(|t| t.size)
+    }
+
     /// Bindings that copy (or anti-alias) `view` onto the screen in `finish_with`.
     pub fn bind(&self, device: &wgpu::Device, view: &wgpu::TextureView) -> wgpu::BindGroup {
         device.create_bind_group(&wgpu::BindGroupDescriptor {

crates/horizon-client/src/hud.rs

@@ -3,7 +3,7 @@
 //! GUI scale is applied when drawing).
 use crate::Result;
 use std::{
-    collections::HashMap,
+    collections::{HashMap, HashSet},
     fs,
     path::{Path, PathBuf},
 };
@@ -58,6 +58,9 @@ pub struct HudAtlas {
     pub width: u32,
     pub height: u32,
     pub sprites: HashMap<String, Rect>,
+    /// Sprites with a 0 < alpha < 255 texel (`SpriteContents.transparency().hasTranslucent`),
+    /// which puts their particles on vanilla's translucent layer.
+    pub translucent: HashSet<String>,
     /// Sprites whose `.png.mcmeta` sets `blur` or `clamp`; the others
     /// sample as vanilla's defaults (nearest, repeat).
     pub flags: HashMap<String, TextureFlags>,
@@ -78,7 +81,10 @@ pub const MAP_SLOTS: usize = 256;
 /// The atlas slot the minimap extra draws into.
 pub const MINIMAP_SPRITE: &str = "horizon/minimap";
 /// Atlas slots for downloaded player skins (`skins/<sha1>`), 64x64 each.
-pub const SKIN_SLOTS: usize = 32;
+/// Vanilla registers a texture per skin. Here a skin evicted from its slot
+/// is not stored again, and its player falls back to the default skin, so
+/// the slots must cover a busy server's player list.
+pub const SKIN_SLOTS: usize = 128;
 /// Reused by the visible rows of the classic world selector.
 pub const WORLD_ICON_SLOTS: usize = 32;
 /// Atlas slots for the pack icons on the pack screen, one per icon drawn
@@ -459,7 +465,16 @@ impl HudAtlas {
         let height = (glyph_region + GLYPH_ROWS).next_multiple_of(1024);
         let mut pixels = vec![0u8; (width * height * 4) as usize];
         let mut sprites = HashMap::new();
+        let mut translucent = HashSet::new();
         for ((name, w, h, data), (px, py)) in images.iter().zip(placements) {
+            if data
+                .as_chunks::<4>()
+                .0
+                .iter()
+                .any(|p| p[3] != 0 && p[3] != 255)
+            {
+                translucent.insert(name.clone());
+            }
             for row in 0..*h {
                 let src = &data[(row * w * 4) as usize..((row + 1) * w * 4) as usize];
                 let dst = (((py + row) * width + px) * 4) as usize;
@@ -524,6 +539,7 @@ impl HudAtlas {
             width,
             height,
             sprites,
+            translucent,
             flags,
             fire_animations,
             font,

crates/horizon-client/src/lan/containers.rs

@@ -343,6 +343,12 @@ impl Hub {
         if !window_ok || self.guests[i].spectator() {
             return Vec::new();
         }
+        // A menu that is no longer valid takes no clicks.
+        if let Some(m) = self.guests[i].menu.as_ref().filter(|_| in_menu)
+            && !m.slots.still_valid(world, &self.guests[i], m.pos)
+        {
+            return Vec::new();
+        }
         let source = self.guests[i].menu.as_ref().map(|m| m.slots);
         let mut drag = if in_menu {
             self.guests[i].menu.as_mut().and_then(|m| m.drag.take())

crates/horizon-client/src/lan/guest.rs

@@ -404,6 +404,17 @@ impl Guest {
     pub fn eye_height(&self) -> f64 {
         if self.sneaking { 1.27 } else { 1.62 }
     }
+    /// `Player.isWithinBlockInteractionRange(pos, buffer)` for the guest:
+    /// its block interaction range is 4.5, 5 in creative.
+    pub fn within_block_range(&self, pos: [i32; 3], buffer: f64) -> bool {
+        let eye = [
+            self.position[0],
+            self.position[1] + self.eye_height(),
+            self.position[2],
+        ];
+        let range = if self.creative() { 5.0 } else { 4.5 };
+        within_block_range(eye, range + buffer, pos)
+    }
     /// The inventory menu's 46 slots (ServerPlayer.inventoryMenu): 0 crafting
     /// result, 1..=4 crafting grid, 5..=8 armor, 9..=35 main, 36..=44 hotbar,
     /// 45 off hand.
@@ -432,18 +443,21 @@ impl Guest {
 }
 
 /// The off hand slot is conventionally 40 in saves and 45 in the menu.
+/// `synced_id` names an entry of a synced registry (enchantments, trim
+/// materials and patterns) by its id on this connection.
 pub fn stack_to_network(
     item_id: impl Fn(&str) -> i32,
-    enchantment_id: impl Fn(&str) -> Option<i32>,
+    synced_id: impl Fn(&str, &str) -> Option<i32>,
     s: &Option<ItemStack>,
 ) -> Option<Stack> {
-    network_stack(&item_id, &enchantment_id, s)
+    network_stack(&item_id, &synced_id, s)
 }
 fn network_stack(
     item_id: &dyn Fn(&str) -> i32,
-    enchantment_id: &dyn Fn(&str) -> Option<i32>,
+    synced_id: &dyn Fn(&str, &str) -> Option<i32>,
     s: &Option<ItemStack>,
 ) -> Option<Stack> {
+    let enchantment_id = |name: &str| synced_id("minecraft:enchantment", name);
     let s = s.as_ref()?;
     let mut stack = Stack::new(item_id(&s.item), s.count as i32);
     if s.damage > 0 {
@@ -481,6 +495,25 @@ fn network_stack(
                 horizon_protocol::item::Component::Int(rgb),
             ));
         }
+        // ArmorTrim: both holders as references into the synced registries.
+        if let Some((material, pattern)) = &d.trim {
+            let id = |registry: &str, name: &str| {
+                if name.contains(':') {
+                    synced_id(registry, name)
+                } else {
+                    synced_id(registry, &format!("minecraft:{name}"))
+                }
+            };
+            if let (Some(material), Some(pattern)) = (
+                id("minecraft:trim_material", material),
+                id("minecraft:trim_pattern", pattern),
+            ) {
+                stack.added.push((
+                    horizon_protocol::item::component::TRIM,
+                    horizon_protocol::item::Component::Trim { material, pattern },
+                ));
+            }
+        }
         if let Some(id) = d.map_id {
             stack.added.push((
                 horizon_protocol::item::component::MAP_ID,
@@ -499,12 +532,28 @@ fn network_stack(
                 horizon_protocol::item::Component::Int(i32::from(mode)),
             ));
         }
+        // PotionContents: the potion by its `minecraft:potion` id.
+        if let Some(id) = (d.potion.as_deref()).and_then(|potion| {
+            synced_id(
+                "minecraft:potion",
+                &horizon_world::datafix::dynamic::namespaced(potion),
+            )
+        }) {
+            stack.added.push((
+                horizon_protocol::item::component::POTION_CONTENTS,
+                horizon_protocol::item::Component::Potion {
+                    potion: Some(id),
+                    color: None,
+                    rest: Vec::new(),
+                },
+            ));
+        }
         // A loaded crossbow's ammunition.
         if !d.charged.is_empty() {
             let charged = d
                 .charged
                 .iter()
-                .filter_map(|c| network_stack(item_id, enchantment_id, &Some(c.clone())))
+                .filter_map(|c| network_stack(item_id, synced_id, &Some(c.clone())))
                 .collect();
             stack.added.push((
                 horizon_protocol::item::component::CHARGED_PROJECTILES,
@@ -545,3 +594,62 @@ fn network_stack(
     }
     Some(stack)
 }
+
+/// `Player.isWithinBlockInteractionRange`: `eye` closer than `range` to the
+/// box of the block at `pos` (`AABB.distanceToSqr`).
+pub fn within_block_range(eye: [f64; 3], range: f64, pos: [i32; 3]) -> bool {
+    (0..3)
+        .map(|k| {
+            let lo = f64::from(pos[k]);
+            (lo - eye[k]).max(eye[k] - lo - 1.0).max(0.0).powi(2)
+        })
+        .sum::<f64>()
+        < range * range
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use horizon_protocol::item::{Component, component};
+
+    #[test]
+    fn potions_go_as_potion_registry_ids() {
+        let synced_id = |registry: &str, name: &str| match (registry, name) {
+            ("minecraft:potion", "minecraft:swiftness") => Some(14),
+            _ => None,
+        };
+        let potion = ItemStack::new("minecraft:splash_potion", 1).with_potion("swiftness");
+        let stack = stack_to_network(|_| 7, synced_id, &Some(potion)).unwrap();
+        assert_eq!(
+            stack.component(component::POTION_CONTENTS),
+            Some(&Component::Potion {
+                potion: Some(14),
+                color: None,
+                rest: Vec::new(),
+            })
+        );
+    }
+
+    #[test]
+    fn trims_go_as_synced_registry_references() {
+        let mut chestplate = ItemStack::new("minecraft:diamond_chestplate", 1);
+        chestplate.data_mut().trim = Some(("minecraft:gold".into(), "coast".into()));
+        let synced_id = |registry: &str, name: &str| match (registry, name) {
+            ("minecraft:trim_material", "minecraft:gold") => Some(4),
+            ("minecraft:trim_pattern", "minecraft:coast") => Some(1),
+            _ => None,
+        };
+        let stack = stack_to_network(|_| 7, synced_id, &Some(chestplate.clone())).unwrap();
+        assert_eq!(
+            stack.component(component::TRIM),
+            Some(&Component::Trim {
+                material: 4,
+                pattern: 1
+            })
+        );
+        // A name the connection's registry lacks sends no trim.
+        chestplate.data_mut().trim = Some(("minecraft:x".into(), "coast".into()));
+        let stack = stack_to_network(|_| 7, synced_id, &Some(chestplate)).unwrap();
+        assert_eq!(stack.component(component::TRIM), None);
+    }
+}

crates/horizon-client/src/lan/hub.rs

@@ -149,6 +149,9 @@ pub struct Hub {
     pub singleplayer_owner: Option<u128>,
     /// Who rides what, set by the game before each tick.
     pub riding: super::entity::Riding,
+    /// The scoreboard's teams, set by the game each tick, for players'
+    /// display names.
+    pub teams: Vec<crate::scoreboard::Team>,
     last_clock: i64,
     last_rate: f32,
     ticking: (f32, bool),
@@ -206,6 +209,24 @@ pub fn display_name(uuid: u128, name: &str) -> Tag {
     ])
 }
 
+impl Hub {
+    /// Player.getDisplayName: the name formatted for the player's team
+    /// (PlayerTeam.formatNameForTeam), suggesting `/tell NAME `, showing the
+    /// player on hover and inserting the name.
+    pub fn player_display_name(&self, uuid: u128, name: &str) -> Tag {
+        let Some(team) = self.teams.iter().find(|t| t.players.contains(name)) else {
+            return display_name(uuid, name);
+        };
+        let mut c = team.formatted_name_comp(&crate::scoreboard::literal(name));
+        c["click_event"] =
+            serde_json::json!({"action": "suggest_command", "command": format!("/tell {name} ")});
+        c["hover_event"] = serde_json::json!({"action": "show_entity", "id": "minecraft:player",
+            "uuid": horizon_protocol::crypto::uuid_string(uuid), "name": name});
+        c["insertion"] = name.into();
+        crate::scoreboard::component_tag(&c)
+    }
+}
+
 /// A yellow translation of player names (`multiplayer.player.joined`).
 fn yellow_names(key: &str, names: Vec<Tag>) -> Tag {
     Tag::compound([
@@ -315,6 +336,7 @@ impl Hub {
             entity_types: Default::default(),
             entities: Default::default(),
             entity_out: Vec::new(),
+            teams: Vec::new(),
         }
     }
 
@@ -351,7 +373,7 @@ impl Hub {
     pub fn stack(&mut self, s: &Option<ItemStack>) -> Option<horizon_protocol::item::Stack> {
         let id = s.as_ref().map(|s| self.item_id(&s.item))?;
         let sync = self.sync.clone();
-        stack_to_network(|_| id, |name| sync.id("minecraft:enchantment", name), s)
+        stack_to_network(|_| id, |registry, name| sync.id(registry, name), s)
     }
 
     pub fn broadcast(&self, packet: &C) {
@@ -1827,7 +1849,9 @@ impl Hub {
     fn flush_advancements(&mut self, i: usize, show: bool) {
         let sync = self.sync.clone();
         let g = &mut self.guests[i];
-        let unlocked = std::mem::take(&mut g.recipes_unlocked);
+        let mut unlocked = std::mem::take(&mut g.recipes_unlocked);
+        // A recipe given and taken before this flush must not reappear.
+        unlocked.retain(|id| g.recipe_book.knows(id));
         if let Some(add) = sync.advancements.recipes_added(&unlocked, &sync) {
             g.send(&raw(ids::RECIPE_BOOK_ADD, add));
         }
@@ -1982,7 +2006,9 @@ impl Hub {
                 S::PlayerInput(p) => {
                     self.guests[i].input = p.flags;
                     self.guests[i].sneaking = p.flags & 32 != 0;
-                    self.guests[i].sprinting = p.flags & 64 != 0 && p.flags & 1 != 0;
+                    // handlePlayerInput only records keys and updates crouching.
+                    // Sprinting persists after the sprint key is released (or
+                    // starts with a double tap); PlayerCommand changes it.
                 }
                 // OPEN_INVENTORY (the ridden mount's inventory) and
                 // START_FALL_FLYING (checked against the guest's chest slot

crates/horizon-client/src/lan/hub/chat.rs

@@ -2,7 +2,7 @@
 //! handle it: chat sessions validated against the services' keys, signed
 //! messages checked link by link, the acknowledged window, and messages
 //! relayed with each connection's numbering and signature cache.
-use super::{HostEvent, Hub, display_name};
+use super::{HostEvent, Hub};
 use horizon_protocol::{
     packets::play::{self, Clientbound as C},
     secure_chat::{self, Body, Chain, ChatSession, DecodeError, ProfileKey, Signature, Unpacked},
@@ -214,7 +214,7 @@ impl Hub {
         }
         let bound = play::ChatTypeBound {
             chat_type: self.chat_type,
-            name: display_name(uuid, &name),
+            name: self.player_display_name(uuid, &name),
             target: None,
         };
         let line = format!("<{name}> {}", message.content);
@@ -427,7 +427,7 @@ impl Hub {
         let (uuid, name) = (self.guests[i].uuid, self.guests[i].name.clone());
         let bound = play::ChatTypeBound {
             chat_type: self.chat_type_id(chat_type),
-            name: display_name(uuid, &name),
+            name: self.player_display_name(uuid, &name),
             target: None,
         };
         let line = match chat_type {
@@ -467,15 +467,15 @@ impl Hub {
             self.chat_type_id("msg_command_incoming"),
         );
         for &t in targets {
-            let target = display_name(self.guests[t].uuid, &self.guests[t].name);
+            let target = self.player_display_name(self.guests[t].uuid, &self.guests[t].name);
             let out = play::ChatTypeBound {
                 chat_type: outgoing,
-                name: display_name(uuid, &name),
+                name: self.player_display_name(uuid, &name),
                 target: Some(target),
             };
             let inc = play::ChatTypeBound {
                 chat_type: incoming,
-                name: display_name(uuid, &name),
+                name: self.player_display_name(uuid, &name),
                 target: None,
             };
             match &message {