Merge pull request #14056 from horizon-rust/layers/packs-polytone-1

🤖 Agent: a pack's own options move to the engine crate horizon-pack-options with no dependencies; Polytone's config reading reaches it only through pack format hooks. layer plan M6 step 8.
Merge pull request #14040 from horizon-rust/layers/packs-cem-mobs
2026-11-09 10:39:46 -10:00 · 2026-11-09 20:59:07 +01:00 · 2026-11-09 20:55:04 +01:00 · 2026-11-09 18:57:34 +01:00 · 2026-11-09 18:57:06 +01:00 · 2026-11-09 18:57:05 +01:00
673 changed files with 27343 additions and 13435 deletions
@@ -80,21 +80,24 @@ jobs:
          rustup toolchain install stable --profile minimal --component rustfmt --component clippy
          rustup default stable
          echo "WGPU_BACKEND=dx12" >> "$GITHUB_ENV"
+      # On a pull request, the next three checks compare with HEAD^1: the main that GitHub's merge commit puts the pull
+      # request on. pull_request.base.sha is main at the pull request's last push and falls behind, so main's own
+      # changes since then would count as the pull request's (#13874).
      # docs/layers.md: a crate depends only on its own layer or a lower one; today's exceptions only shrink.
      - name: Crates follow the layers
        env:
-          BASE_SHA: ${{ github.event.pull_request.base.sha }}
-        run: python3 tools/check_layers.py ${BASE_SHA:+--base "$BASE_SHA"}
+          BASE: ${{ github.event_name == 'pull_request' && 'HEAD^1' || '' }}
+        run: python3 tools/check_layers.py ${BASE:+--base "$BASE"}
      # docs/layers.md#built-in-addresses: every built-in outside address in the Horizon layer's home; the rest only shrinks.
      - name: Built-in addresses stay in their home
        env:
-          BASE_SHA: ${{ github.event.pull_request.base.sha }}
-        run: python3 tools/check_addresses.py ${BASE_SHA:+--base "$BASE_SHA"}
+          BASE: ${{ github.event_name == 'pull_request' && 'HEAD^1' || '' }}
+        run: python3 tools/check_addresses.py ${BASE:+--base "$BASE"}
      # docs/layers.md#file-size: a Rust file over 3000 lines may not grow (pull requests; main has no base to compare).
      - name: Big files don't grow
        env:
-          BASE_SHA: ${{ github.event.pull_request.base.sha }}
-        run: python3 tools/check_file_size.py ${BASE_SHA:+--base "$BASE_SHA"}
+          BASE: ${{ github.event_name == 'pull_request' && 'HEAD^1' || '' }}
+        run: python3 tools/check_file_size.py ${BASE:+--base "$BASE"}
      - name: Test offline research tooling
        run: python -m unittest discover -s tests -v
      - name: Install Rust toolchain and the ALSA and udev headers the client links against
@@ -217,17 +220,17 @@ jobs:
          $clang = Get-Command clang -ErrorAction Stop
          Write-Output "Using $($clang.Source)"
          & $clang.Source --version
-      - name: Build the game for native Windows ARM64
-        run: cargo build --release --locked --target aarch64-pc-windows-msvc -p horizon-client -p horizon-client-lib --bin horizon-client --bin horizon-ctl -p horizon-prepare --bin horizon-prepare -p horizon-server --bin horizon-server
+      - name: Build the game for native Windows ARM64 (the official game, as game-build.yml ships it)
+        run: cargo build --release --locked --target aarch64-pc-windows-msvc -p horizon-official --bin horizon-official -p horizon-client-lib --bin horizon-ctl -p horizon-prepare --bin horizon-prepare -p horizon-server --bin horizon-server
      - name: Check the game's PE machine
-        run: python tools/check_pe_arch.py arm64 target/aarch64-pc-windows-msvc/release/horizon-client.exe target/aarch64-pc-windows-msvc/release/horizon-ctl.exe target/aarch64-pc-windows-msvc/release/horizon-prepare.exe target/aarch64-pc-windows-msvc/release/horizon-server.exe
+        run: python tools/check_pe_arch.py arm64 target/aarch64-pc-windows-msvc/release/horizon-official.exe target/aarch64-pc-windows-msvc/release/horizon-ctl.exe target/aarch64-pc-windows-msvc/release/horizon-prepare.exe target/aarch64-pc-windows-msvc/release/horizon-server.exe
      - name: Check game DLL imports
-        run: python tools/check_imports.py target/aarch64-pc-windows-msvc/release/horizon-client.exe target/aarch64-pc-windows-msvc/release/horizon-ctl.exe target/aarch64-pc-windows-msvc/release/horizon-prepare.exe target/aarch64-pc-windows-msvc/release/horizon-server.exe
+        run: python tools/check_imports.py target/aarch64-pc-windows-msvc/release/horizon-official.exe target/aarch64-pc-windows-msvc/release/horizon-ctl.exe target/aarch64-pc-windows-msvc/release/horizon-prepare.exe target/aarch64-pc-windows-msvc/release/horizon-server.exe
      - name: Start every game executable
        shell: pwsh
        run: |
          $ErrorActionPreference = 'Stop'
-          $client = 'target/aarch64-pc-windows-msvc/release/horizon-client.exe'
+          $client = 'target/aarch64-pc-windows-msvc/release/horizon-official.exe'
          $output = & $client --help 2>&1
          if ($LASTEXITCODE -ne 0 -or ($output -join "`n") -notmatch '--resources') { throw 'horizon-client --help failed' }
          foreach ($binary in @('horizon-ctl.exe', 'horizon-prepare.exe', 'horizon-server.exe')) {
@@ -168,9 +168,14 @@ jobs:
      - name: ALSA and udev headers
        if: runner.os == 'Linux' && !matrix.musl
        run: sudo apt-get update && sudo apt-get install -y --no-install-recommends libasound2-dev libudev-dev
-      - name: Build the client, horizon-ctl, horizon-prepare and horizon-server
+      - name: Build the official game, horizon-ctl, horizon-prepare and horizon-server
        if: ${{ !matrix.musl }}
-        run: cargo build --release --locked ${{ matrix.target && format('--target {0}', matrix.target) || '' }} -p horizon-client -p horizon-client-lib --bin horizon-client --bin horizon-ctl -p horizon-prepare --bin horizon-prepare -p horizon-server --bin horizon-server
+        run: cargo build --release --locked ${{ matrix.target && format('--target {0}', matrix.target) || '' }} -p horizon-official --bin horizon-official -p horizon-client-lib --bin horizon-ctl -p horizon-prepare --bin horizon-prepare -p horizon-server --bin horizon-server
+      - name: The official game is the game players get, under its name
+        # horizon-official: horizon-client's game with Horizon's own parts plugged in (docs/layers.md, "How a
+        # Horizon crate plugs in"). Everything below, the launcher and players know it as horizon-client.
+        if: ${{ !matrix.musl }}
+        run: cp -f "$BIN/horizon-official${{ matrix.exe }}" "$BIN/horizon-client${{ matrix.exe }}"
      - name: Every program the release folder takes was built
        if: ${{ !matrix.musl }}
        run: |
@@ -201,6 +201,9 @@ jobs:
      - name: Verify Windows executable architecture
        if: runner.os == 'Windows'
        run: python ../tools/check_pe_arch.py "${{ matrix.pe_arch }}" "$BIN/${{ matrix.binary }}"
+      - name: Unrelated DLLs cannot intercept launcher or setup startup
+        if: runner.os == 'Windows'
+        run: python ../tools/test_launcher_dll_search.py "$BIN/${{ matrix.binary }}"
      - name: The version is the release's
        run: |
          out=$("$BIN/${{ matrix.binary }}" --version)
@@ -181,7 +181,7 @@ jobs:
          musl=(); if [[ -f dist/horizon-linux-musl-x86_64.tar.gz ]]; then musl=(dist/horizon-linux-musl-x86_64.tar.gz)
          else echo "::warning::horizon-linux-musl-x86_64.tar.gz is missing: SHA256SUMS goes out without it"; fi
          bash tools/ci/sign_release.sh nightly dist/horizon-linux-x86_64.tar.gz dist/horizon-windows-x64.zip \
-            "${arm64[@]}" "${musl[@]}" \
+            ${arm64[@]+"${arm64[@]}"} ${musl[@]+"${musl[@]}"} \
            dist/horizon-macos-arm64.zip dist/horizon-macos-x64.zip dist/horizon-server-linux-x86_64.tar.gz \
            dist/horizon-source.tar.gz
      - uses: actions/upload-artifact@v7
@@ -267,9 +267,9 @@ jobs:
          gh release create nightly --prerelease --latest=false --target "$SHA" \
            --title "Nightly $DATE · ${SHA:0:7}" --notes-file dist/nightly-notes.md \
            "dist/horizon-linux-x86_64.tar.gz#Game files the launcher installs (Nightly): Linux (horizon-linux-x86_64.tar.gz)" \
-            "${musl[@]}" \
+            ${musl[@]+"${musl[@]}"} \
            "dist/horizon-windows-x64.zip#Game files the launcher installs (Nightly): Windows (horizon-windows-x64.zip)" \
-            "${arm64[@]}" \
+            ${arm64[@]+"${arm64[@]}"} \
            "dist/horizon-macos-arm64.zip#Game files the launcher installs (Nightly): macOS on Apple Silicon (horizon-macos-arm64.zip)" \
            "dist/horizon-macos-x64.zip#Game files the launcher installs (Nightly): macOS on Intel (horizon-macos-x64.zip)" \
            "dist/horizon-server-linux-x86_64.tar.gz#Nightly dedicated server for Linux (horizon-server-linux-x86_64.tar.gz)" \
@@ -44,6 +44,8 @@ Feature → files → harness for the most-changed areas: [docs/architecture.md]
 - **Machine translations stay unreviewed.** `tools/lang_review/` records only text a person who speaks the language
  wrote or checked; never `lang_coverage.py --mark-reviewed` machine text ([docs/translations.md](docs/translations.md)).
 - **Controllers reach what registers.** Draw controls with a registering helper (`ui::button`, `settings_shell::foot_button`); `graphics_style::button` and `screen_draw::button` only paint, and registering one part of a screen ends its crosshair, so register all of it.
+- **Render passes keep HDR's light.** A pass that reads, filters or redraws the world's picture (upscaling,
+  anti-aliasing, sharpening, frame generation, post effects, captures) follows [docs/hdr-passes.md](docs/hdr-passes.md).

 ## Crates

@@ -73,12 +75,14 @@ Game workspace (root `Cargo.toml`); `launcher/` and `crates/horizon-telemetry-se
 | `horizon-port-pack` | Porting Java modpacks ([docs/modpacks.md](docs/modpacks.md)) |
 | `horizon-optifine` | OptiFine-format pack files below every feature that reads them: `.properties`, the name/range/block matchers, paths and `optifine/` folders, and custom entity models (`cem/`: `.jem`/`.jpm` parsing and baking) |
 | `horizon-polytone` | Polytone-format pack files (`assets/*/polytone/`), read clean-room from the public wiki: targets, biome and dimension modifiers and their environment attribute layers (#11486) |
+| `horizon-pack-options` | A resource pack's own options as the game lists and keeps them (entries, controls, values, presets), whatever pack format declares them; engine, no dependencies |
 | `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 |
 | `horizon-system` | The machine the game runs on (OS, CPU, memory, drive, power, GPU maker and memory), for the crash report, the renderer's GPU info and telemetry |
 | `horizon-platform` | The platform's public API: what the Horizon layer may use of the engine ([docs/layers.md](docs/layers.md)); re-exports `horizon-system` today |
+| `horizon-hooks`, `horizon-game`, `horizon-official`, `horizon-heartbeat` | The layer seam: the engine's hooks for crates above it, the game an executable starts, the official executable (shipped as `horizon-client`) that registers Horizon's in-game parts, the first of them ([docs/layers.md](docs/layers.md#how-a-horizon-crate-plugs-in)) |
 | `horizon-dualsense`, `horizon-threads`, `horizon-release-sign`, `horizon-bots`, `xtask` | DualSense output, thread priorities, signed release checksums, load-test bots, repo tasks |
 | `launcher/` | GPUI launcher: `main.rs` (UI), `backend.rs` (installs, updates), `cli.rs`, `mcp.rs`, `*_page.rs` |

@@ -1450,6 +1450,7 @@ dependencies = [
 "horizon-dualsense",
 "horizon-friends",
 "horizon-hdr",
+ "horizon-hooks",
 "horizon-items",
 "horizon-mod-api-gen",
 "horizon-mods",
@@ -1500,7 +1501,6 @@ version = "0.1.0"
 dependencies = [
 "arboard",
 "horizon-client-core",
- "horizon-dualsense",
 "horizon-theme",
 "png",
 "winit",
@@ -1528,10 +1528,9 @@ dependencies = [
 "horizon-client-render",
 "horizon-command",
 "horizon-core",
- "horizon-cosmetics",
- "horizon-dualsense",
 "horizon-friends",
 "horizon-hdr",
+ "horizon-hooks",
 "horizon-items",
 "horizon-mcp",
 "horizon-mods",
@@ -1587,10 +1586,11 @@ dependencies = [
 "horizon-core",
 "horizon-cosmetics",
 "horizon-hdr",
+ "horizon-hooks",
 "horizon-items",
- "horizon-mod-api-gen",
 "horizon-narrator",
 "horizon-optifine",
+ "horizon-pack-options",
 "horizon-polytone",
 "horizon-protocol",
 "horizon-render-pipeline",
@@ -1677,6 +1677,15 @@ dependencies = [
 "spake2",
 ]

+[[package]]
+name = "horizon-game"
+version = "0.1.0"
+dependencies = [
+ "horizon-client",
+ "horizon-mods",
+ "horizon-threads",
+]
+
 [[package]]
 name = "horizon-hdr"
 version = "0.1.0"
@@ -1688,6 +1697,19 @@ dependencies = [
 "wgpu",
 ]

+[[package]]
+name = "horizon-heartbeat"
+version = "0.1.0"
+dependencies = [
+ "horizon-platform",
+ "horizon-telemetry",
+ "log",
+]
+
+[[package]]
+name = "horizon-hooks"
+version = "0.1.0"
+
 [[package]]
 name = "horizon-items"
 version = "0.1.0"
@@ -1768,6 +1790,17 @@ dependencies = [
 "windows 0.62.2",
 ]

+[[package]]
+name = "horizon-official"
+version = "0.1.0"
+dependencies = [
+ "horizon-game",
+ "horizon-heartbeat",
+ "horizon-platform",
+ "log",
+ "winresource",
+]
+
 [[package]]
 name = "horizon-optifine"
 version = "0.1.0"
@@ -1778,17 +1811,28 @@ dependencies = [
 "regex",
 ]

+[[package]]
+name = "horizon-pack-options"
+version = "0.1.0"
+
 [[package]]
 name = "horizon-platform"
 version = "0.1.0"
 dependencies = [
+ "horizon-core",
+ "horizon-hooks",
+ "horizon-prepare",
+ "horizon-protocol",
+ "horizon-server-files",
 "horizon-system",
+ "horizon-world",
 ]

 [[package]]
 name = "horizon-polytone"
 version = "0.1.0"
 dependencies = [
+ "horizon-pack-options",
 "log",
 "regex",
 "serde_json",
@@ -1856,10 +1900,6 @@ dependencies = [
 [[package]]
 name = "horizon-render-pipeline"
 version = "0.1.0"
-dependencies = [
- "bytemuck",
- "naga",
-]

 [[package]]
 name = "horizon-server"
@@ -1872,11 +1912,9 @@ dependencies = [
 "horizon-anticheat",
 "horizon-bench",
 "horizon-chat-filter",
- "horizon-core",
 "horizon-mcp",
+ "horizon-platform",
 "horizon-release-sign",
- "horizon-server-files",
- "horizon-world",
 "libc",
 "p12-keystore",
 "png",
@@ -1909,7 +1947,7 @@ dependencies = [
 name = "horizon-shader-api"
 version = "0.1.0"
 dependencies = [
- "horizon-render-pipeline",
+ "bytemuck",
 "naga",
 "png",
 "serde",
@@ -30,6 +30,10 @@ members = [
    "crates/horizon-telemetry",
    "crates/horizon-system",
    "crates/horizon-platform",
+    "crates/horizon-hooks",
+    "crates/horizon-game",
+    "crates/horizon-official",
+    "crates/horizon-heartbeat",
    "crates/horizon-bench",
    "crates/horizon-friends",
    "crates/horizon-relay",
@@ -42,6 +46,7 @@ members = [
    "crates/horizon-render-pipeline",
    "crates/horizon-optifine",
    "crates/horizon-polytone",
+    "crates/horizon-pack-options",
    "crates/horizon-shader-api",
    "crates/horizon-release-sign",
    "crates/horizon-mod-deps",
@@ -129,8 +129,9 @@ ports to WGSL of the optical flow and frame interpolation shaders of the
 [AMD FidelityFX SDK](https://github.com/GPUOpen-LibrariesAndSDKs/FidelityFX-SDK) 1.1.4
 (`sdk/include/FidelityFX/gpu/{opticalflow,frameinterpolation}`, at commit
 [c6efa6bf7f20](https://github.com/GPUOpen-LibrariesAndSDKs/FidelityFX-SDK/tree/c6efa6bf7f2027b3ec94f28578bb5965eabb9e55)),
-and `optical_flow.rs` follows the SDK's `sdk/src/components/opticalflow/ffx_opticalflow.cpp`
-(its passes, their order and their dispatch sizes). Copyright (C) 2024 Advanced Micro Devices,
+and `optical_flow.rs` and `interpolation.rs` follow the SDK's
+`sdk/src/components/{opticalflow/ffx_opticalflow.cpp,frameinterpolation/ffx_frameinterpolation.cpp}`
+(their passes, their order and their dispatch sizes). Copyright (C) 2024 Advanced Micro Devices,
 Inc., under the MIT license, whose text heads each file. AMD and FidelityFX are AMD's
 trademarks; Horizon is not affiliated with AMD.

@@ -90,6 +90,7 @@ impl Report {
 /// The kind a file's extension says.
 pub fn kind_of(path: &Path) -> Option<Kind> {
    match path.extension()?.to_str()? {
+        "hmod" if horizon_mods::index::native::holds(path) => Some(Kind::NativeMod),
        "hmod" => Some(Kind::Mod),
        "hnmod" => Some(Kind::NativeMod),
        "hpack" => Some(Kind::Modpack),
@@ -377,6 +377,13 @@ mod tests {
        zip.finish().unwrap();
        let report = check::check(&hnmod, check::kind_of(&hnmod).unwrap(), None, None).unwrap();
        assert!(report.text().contains("machine_mod"), "{}", report.text());
+        let combined = dir.join("machine_mod.hmod");
+        std::fs::copy(&hnmod, &combined).unwrap();
+        assert_eq!(
+            check::kind_of(&combined),
+            Some(horizon_mods::index::Kind::NativeMod)
+        );
+        assert!(check::check(&combined, check::kind_of(&combined).unwrap(), None, None).is_ok());
        // A pin that is not a commit is refused; with none, the folder builds on the
        // instance's Horizon.
        let bad = [
@@ -80,8 +80,8 @@ pub fn main(args: &[String]) -> Result<(), String> {
            };
            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);
+            let (head, revoked) = registry::load(Path::new(head)).map_err(lines)?;
+            let review = registry::review_with_revoked(&base, &head, &revoked, author);
            if rest.iter().any(|a| a == "--json") {
                let json = serde_json::json!({"errors": review.errors, "notes": review.notes});
                println!("{json}");
@@ -26,18 +26,23 @@ pub struct AnimationMetadata {
 pub enum ClipMode {
    /// `day_time`: frame 0 at time 0, the last at the cycle's end, then again.
    DayTime { cycle: i64 },
+    /// `screen_time`: the ticks the open screen has been open, over the cycle, held on the last
+    /// frame once it has run (it doesn't loop, measured on the real mod).
+    ScreenTime { cycle: i64 },
    /// `weather`: frame 0 in clear weather, 1 in rain, 2 in a storm (the rain and thunder levels
    /// added up), at most the last.
    Weather,
    /// A Polytone expression: its value's fraction is how far through the animation it is.
    Expression(String),
-    /// `game_time`, `screen_time`, `season`: not driven yet; the animation runs on ticks.
+    /// `game_time`, `season`: not driven; the animation runs on ticks.
    Unsupported(String),
 }

 /// The values [`ClipMode`]s read this frame.
 pub struct ModeInputs<'a> {
    pub day_time: i64,
+    /// The ticks the open screen has been open (0 without one).
+    pub screen_time: i64,
    /// The rain level plus the thunder level, 0 to 2.
    pub weather: f32,
    /// An expression's value this frame, by its source.
@@ -116,7 +121,8 @@ impl AnimationMetadata {
                    match mode.as_str() {
                        "day_time" => ClipMode::DayTime { cycle },
                        "weather" => ClipMode::Weather,
-                        "game_time" | "screen_time" | "season" => ClipMode::Unsupported(mode),
+                        "screen_time" => ClipMode::ScreenTime { cycle },
+                        "game_time" | "season" => ClipMode::Unsupported(mode),
                        _ => ClipMode::Expression(mode),
                    }
                }),
@@ -239,6 +245,9 @@ impl AnimationClip {
    pub fn sample_mode(&self, inputs: &ModeInputs) -> Option<AnimationSample> {
        let fraction = match self.mode.as_ref()? {
            ClipMode::DayTime { cycle } => day_fraction(inputs.day_time, *cycle),
+            ClipMode::ScreenTime { cycle } => {
+                (inputs.screen_time.max(0) as f64 / *cycle as f64).min(1.0 - f64::EPSILON)
+            }
            ClipMode::Weather => {
                let last = self.sequence.len() - 1;
                let index = (inputs.weather.max(0.0) as usize).min(last);
@@ -288,6 +297,7 @@ mod mode_tests {
        let expression = move |_: &str| Some(value);
        clip.sample_mode(&ModeInputs {
            day_time,
+            screen_time: day_time,
            weather,
            expression: &expression,
        })
@@ -302,6 +312,13 @@ mod mode_tests {
            .map(|t| frame(&day, t, 0.0, 0.0))
            .into();
        assert_eq!(frames, [0, 1, 2, 3, 1]);
+        // 26.3-6.8.6, four frames over 200 ticks: 40 ticks open show the first, and from ten
+        // seconds on the last, even after 27 (it doesn't loop).
+        let screen = clip(r#"{"frametime": 1, "mode": "screen_time", "time_cycle_duration": 200}"#);
+        let frames: Vec<u32> = [0, 40, 200, 360, 540]
+            .map(|t| frame(&screen, t, 0.0, 0.0))
+            .into();
+        assert_eq!(frames, [0, 0, 3, 3, 3]);
        let value = clip(r#"{"frametime": 1, "mode": "0.6"}"#);
        assert_eq!(frame(&value, 0, 0.0, 0.6), 2);
        assert_eq!(frame(&value, 0, 0.0, 2.0), 0);
@@ -321,6 +338,7 @@ mod mode_tests {
            clip(r#"{"frametime": 1}"#)
                .sample_mode(&ModeInputs {
                    day_time: 0,
+                    screen_time: 0,
                    weather: 0.0,
                    expression: &|_| None
                })
@@ -330,6 +348,7 @@ mod mode_tests {
            clip(r#"{"frametime": 1, "mode": "season"}"#)
                .sample_mode(&ModeInputs {
                    day_time: 0,
+                    screen_time: 0,
                    weather: 0.0,
                    expression: &|_| None
                })
@@ -13,11 +13,9 @@ winit = "0.30.13"
 horizon-theme = { path = "../horizon-theme" }
 png = "0.18"
 arboard = { version = "3.6.1", default-features = false, features = ["wayland-data-control"] }
-# The DualSense's trigger effects (the `controllers` feature).
-horizon-dualsense = { path = "../horizon-dualsense", optional = true }

 [features]
-controllers = ["dep:horizon-dualsense"]
+controllers = []

 [lints]
 workspace = true
@@ -1523,9 +1523,8 @@ impl Rumble {
    }
 }

-/// What a trigger feels like on a DualSense, from what its action is doing (docs/controllers.md
-/// "Adaptive triggers" for the choices). Only the pad's official modes: Nielk1's notes warn the
-/// others may leave the firmware.
+/// What a trigger feels like, from what its action is doing (docs/controllers.md "Adaptive
+/// triggers"); the controller code turns it into a DualSense trigger effect.
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum TriggerFeel {
    Free,
@@ -1544,66 +1543,6 @@ pub enum TriggerFeel {
    /// Mining a block of this hardness: a buzz, stronger and slower on harder blocks.
    Texture(f32),
 }
-#[cfg(feature = "controllers")]
-impl TriggerFeel {
-    /// The effect, for a trigger that presses its action at `threshold` (0..1) of its travel.
-    pub fn effect(self, threshold: f32) -> horizon_dualsense::TriggerEffect {
-        use horizon_dualsense::trigger;
-        // The zone (of ten along the travel) where the action presses: a catch gives way there,
-        // so the click and the shot coincide.
-        let press = ((threshold.clamp(0.0, 1.0) * 10.0) as u8).clamp(3, 8);
-        match self {
-            TriggerFeel::Free => horizon_dualsense::TRIGGER_OFF,
-            // From the third zone, so the press itself stays light; at most 6 of 8, as the
-            // draw is held.
-            TriggerFeel::Draw(charge) => {
-                trigger::feedback(2, 1 + (5.0 * charge.clamp(0.0, 1.0)).round() as u8)
-            }
-            TriggerFeel::Click => trigger::weapon((press - 2).max(2), press, 8),
-            TriggerFeel::Boost => trigger::weapon((press - 2).max(2), press, 5),
-            TriggerFeel::Brace => trigger::feedback(2, 3),
-            TriggerFeel::Locked => trigger::feedback(1, 8),
-            TriggerFeel::Texture(hardness) if hardness > 0.0 => {
-                // Dirt 2, stone 3, deepslate 4, obsidian 5 of 8.
-                let amplitude = (1.0 + 1.6 * hardness.sqrt()).round().clamp(1.0, 5.0);
-                // Sand and dirt a fine 40 Hz grit; stone 30; wood, deepslate and ores 20;
-                // obsidian a 10 Hz chisel.
-                let hertz = match hardness {
-                    h if h < 1.0 => 40,
-                    h if h < 2.0 => 30,
-                    h if h < 5.0 => 20,
-                    _ => 10,
-                };
-                trigger::vibration(1, amplitude as u8, hertz)
-            }
-            TriggerFeel::Texture(_) => horizon_dualsense::TRIGGER_OFF,
-        }
-    }
-}
-#[cfg(feature = "controllers")]
-impl PadSettings {
-    /// The left and right triggers' effects: each feels the action bound to it, `key.use` or
-    /// `key.attack`.
-    pub fn trigger_effects(
-        &self,
-        using: TriggerFeel,
-        attacking: TriggerFeel,
-    ) -> [horizon_dualsense::TriggerEffect; 2] {
-        [Button::LeftTrigger, Button::RightTrigger].map(|trigger| {
-            let actions = self.actions_of(trigger);
-            let feel = if !self.adaptive_triggers {
-                TriggerFeel::Free
-            } else if actions.contains(&"key.use") {
-                using
-            } else if actions.contains(&"key.attack") {
-                attacking
-            } else {
-                TriggerFeel::Free
-            };
-            feel.effect(self.trigger_threshold)
-        })
-    }
-}
 /// What a DualSense's lightbar shows (`lightbar:`).
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Lightbar {
@@ -2438,52 +2377,6 @@ bind_key.hotbar.2:north
        assert_eq!(w.observe(Some(1.0)), Some(1.0));
    }

-    #[cfg(feature = "controllers")]
-    #[test]
-    fn triggers_feel_their_action() {
-        use horizon_dualsense::{TRIGGER_OFF, trigger};
-        let mut s = PadSettings::default();
-        // Use is LT, attack RT by default.
-        let [left, right] = s.trigger_effects(TriggerFeel::Draw(1.0), TriggerFeel::Texture(1.5));
-        assert_eq!(left, trigger::feedback(2, 6));
-        assert_eq!(right, trigger::vibration(1, 3, 30));
-        assert_eq!(
-            s.trigger_effects(TriggerFeel::Draw(0.0), TriggerFeel::Free),
-            [trigger::feedback(2, 1), TRIGGER_OFF]
-        );
-        // The catch gives way in the zone where the default threshold (0.4) presses: weapon
-        // 0x25, zones 2 and 4, strength 8 (stored 7) or 5 (stored 4).
-        let catch = |strength| [0x25, 0x14, 0x00, strength, 0, 0, 0, 0, 0, 0, 0];
-        assert_eq!(TriggerFeel::Click.effect(0.4), catch(7));
-        assert_eq!(TriggerFeel::Boost.effect(0.4), catch(4));
-        // A deeper threshold moves it: zones 5 and 7.
-        assert_eq!(TriggerFeel::Click.effect(0.7)[1..3], [0xa0, 0x00]);
-        assert_eq!(TriggerFeel::Click.effect(0.1), trigger::weapon(2, 3, 8));
-        assert_eq!(TriggerFeel::Brace.effect(0.4), trigger::feedback(2, 3));
-        assert_eq!(TriggerFeel::Locked.effect(0.4), trigger::feedback(1, 8));
-        // Harder blocks buzz harder and slower; instant-break blocks don't.
-        assert_eq!(
-            TriggerFeel::Texture(0.5).effect(0.4),
-            trigger::vibration(1, 2, 40)
-        );
-        assert_eq!(
-            TriggerFeel::Texture(3.0).effect(0.4),
-            trigger::vibration(1, 4, 20)
-        );
-        assert_eq!(
-            TriggerFeel::Texture(50.0).effect(0.4),
-            trigger::vibration(1, 5, 10)
-        );
-        assert_eq!(TriggerFeel::Texture(0.0).effect(0.4), TRIGGER_OFF);
-        assert_eq!(TriggerFeel::Texture(-1.0).effect(0.4), TRIGGER_OFF);
-        s.adaptive_triggers = false;
-        assert_eq!(
-            s.trigger_effects(TriggerFeel::Click, TriggerFeel::Boost),
-            [TRIGGER_OFF; 2]
-        );
-        assert!(!PadSettings::parse(&s.serialize()).adaptive_triggers);
-    }
-
    #[test]
    fn lightbar_colours() {
        let full = Lightbar::Health.colour(1.0, "minecraft:overworld").unwrap();
@@ -18,10 +18,10 @@ horizon-client-core = { path = "../horizon-client-core" }
 horizon-client-input = { path = "../horizon-client-input" }
 horizon-client-render = { path = "../horizon-client-render" }
 horizon-command = { path = "../horizon-command" }
-# Emotes pose the player model (`Mob::emote`, `mobs::anim::setup`).
-horizon-cosmetics = { path = "../horizon-cosmetics" }
 horizon-items = { path = "../horizon-items" }
 horizon-core = { path = "../horizon-core" }
+# Extension points for the crates above the engine (docs/layers.md, "How a Horizon crate plugs in").
+horizon-hooks = { path = "../horizon-hooks" }
 # `horizon-ctl mcp`: the Model Context Protocol, shared with the launcher and the server.
 horizon-mcp = { path = "../horizon-mcp" }
 # The server thread ahead of the workers (MinecraftServer.spin's Thread.setPriority).
@@ -73,16 +73,13 @@ mio = { version = "1.2.4", features = ["os-poll", "net"] }
 # Shared chunk frames are found by one keyed 128-bit hash of their body (lan/conn.rs SharedFrames).
 xxhash-rust = { version = "0.8.19", features = ["xxh3"] }
 horizon-theme = { path = "../horizon-theme" }
-# Opt-in data collection: the game keeps, the launcher sends (docs/telemetry.md); `live` is
-# the anonymous "I'm playing" ping the game sends itself (`heartbeat.rs`), the `heartbeat` feature.
+# Opt-in data collection: the game keeps, the launcher sends (docs/telemetry.md).
 horizon-telemetry = { path = "../horizon-telemetry", default-features = false }
 horizon-bench = { path = "../horizon-bench" }
 crc32fast = "1"
 zip = { version = "9.1.3", default-features = false, features = ["deflate"] }
 # Controllers (evdev + libudev on Linux, IOKit on macOS, Windows.Gaming.Input); the `controllers` feature.
 gilrs = { version = "0.11", optional = true }
-# The DualSense's rumble, adaptive triggers and lights over HID (gilrs only reads it).
-horizon-dualsense = { path = "../horizon-dualsense", optional = true }
 # HTTPS to the Minecraft services (online-mode session join).
 ureq = { version = "2", default-features = false, features = ["tls"] }
 unicode-bidi = "0.3.18"
@@ -114,18 +111,16 @@ objc2-foundation = { version = "0.3", default-features = false, features = ["std
 wgpu = { version = "30.0.1", default-features = false, features = ["gles"] }

 [features]
-default = ["audio", "controllers", "discord", "friends", "heartbeat"]
+default = ["audio", "controllers", "discord", "friends"]
 # Sound output. Without it (and `controllers`) the program links neither libasound nor libudev on
 # Linux: the server build (`--no-default-features`, released as horizon-engine; docs/server.md).
 audio = ["horizon-client-render/audio"]
 # Controllers: gilrs, and the DualSense's own output. Without it only `horizon-ctl pad`'s virtual pad.
-controllers = ["dep:gilrs", "dep:horizon-dualsense", "horizon-client-input/controllers"]
+controllers = ["dep:gilrs", "horizon-client-input/controllers"]
 # "Playing Horizon" on the player's Discord profile (`discord_presence`).
 discord = []
 # Play with Friends, joining side (`net.rs`): without it no invite code joins.
 friends = ["dep:horizon-friends"]
-# The anonymous "I'm playing" ping (`heartbeat.rs`, docs/telemetry.md).
-heartbeat = ["horizon-telemetry/live"]
 # Records the call sites of mob random draws (`mob_ai_probe` traces).
 rng-trace = ["horizon-core/rng-trace"]
 # Compatibility with earlier experiment commands: main already uses mimalloc.
@@ -7,6 +7,8 @@ rust-version.workspace = true
 description = "The client's world data, rendering and screens: chunks, meshing, light, streaming, the renderer, the HUD, menus and settings; no gameplay"

 [dependencies]
+# The settings stores of the crates above the engine (docs/layers.md, "Platform registries").
+horizon-hooks = { path = "../horizon-hooks" }
 horizon-cosmetics = { path = "../horizon-cosmetics" }
 # The GUI atlas's pixels, kept compressed once uploaded (hud.rs `pack_pixels`).
 lz4_flex = { version = "0.14", default-features = false, features = ["std", "safe-encode", "safe-decode", "checked-decode"] }
@@ -22,6 +24,7 @@ horizon-narrator = { path = "../horizon-narrator" }
 # OptiFine-format pack files: random entity textures (hud.rs), connected textures
 # (connected.rs) and custom item texture rules (cit.rs).
 horizon-optifine = { path = "../horizon-optifine" }
+horizon-pack-options = { path = "../horizon-pack-options" }
 horizon-polytone = { path = "../horizon-polytone" }
 horizon-protocol = { path = "../horizon-protocol" }
 horizon-render-pipeline = { path = "../horizon-render-pipeline" }
@@ -76,9 +79,6 @@ audio = ["dep:cpal"]
 # Helpers horizon-client's tests build their fixtures with.
 test-support = []

-[build-dependencies]
-horizon-mod-api-gen = { path = "../horizon-mod-api-gen" }
-
 [lints]
 workspace = true

@@ -1,7 +0,0 @@
-fn main() {
-    let root =
-        std::path::PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap()).join("../..");
-    let out_dir = std::path::PathBuf::from(std::env::var_os("OUT_DIR").unwrap());
-    horizon_mod_api_gen::generate(&root, &out_dir, horizon_mod_api_gen::Target::Render)
-        .expect("generating native render mod API");
-}
@@ -288,6 +288,8 @@ fn zip_pack(id: &str, path: PathBuf) -> Pack {
 }

 fn main() {
+    // The pack formats the game installs at startup, so their loading is measured too.
+    horizon_client_render::pack_formats::install();
    let args: Vec<String> = std::env::args().collect();
    let scale = args
        .iter()
@@ -99,10 +99,8 @@ pub struct RenderAssets {
    pub pbr_normals: Vec<u8>,
    pub pbr_specular: Vec<u8>,
    pub pbr_size: u32,
-    /// OptiFine connected textures (empty without `optifine/ctm` files).
-    pub connected: crate::connected::ConnectedTextures,
-    /// Fusion connected textures (empty without Fusion's connecting textures and models).
-    pub fusion: crate::fusion::FusionTextures,
+    /// The packs' connected textures (OptiFine's, Fusion's), when they have some.
+    pub connected: Option<crate::connected::Connected>,
    /// Counts up each time resources load, from 1: a native mod asks again where blocks'
    /// sprites are when it changes (`native_block_sprites_version`).
    pub generation: u64,
@@ -345,45 +343,32 @@ impl RenderAssets {
            sprites.insert(root, &format!("minecraft:block/destroy_stage_{stage}"))?;
            sprites.insert(root, &format!("minecraft:block/destroy_oit_stage_{stage}"))?;
        }
-        let fusion = if draws {
-            let _step = crate::spans::startup::step("core.fusion");
-            crate::fusion::FusionTextures::load(root, registry, &mut sprites, &mut models.catalog)
-        } else {
-            Default::default()
-        };
        let mut emissive = Vec::new();
        let connected = if draws {
-            crate::native_emissive::load(root, &mut sprites);
-            // A side's sprite, for rules that connect by tile: the first quad facing it.
-            let catalog = &models.catalog;
-            let mut found = Vec::new();
-            crate::connected::ConnectedTextures::load(
+            // Native mods' emissive textures go where the pack format puts them (after its
+            // models' tiles, before its rules' tiles), else after both.
+            let mut native_loaded = false;
+            let mut native = |sprites: &mut crate::sprites::Sprites| {
+                if !std::mem::replace(&mut native_loaded, true) {
+                    crate::native_emissive::load(root, sprites);
+                }
+            };
+            let connected = crate::pack_hooks::formats().connected_textures(
                root,
                registry,
                &mut sprites,
-                |state, face| {
-                    let side = horizon_assets::model::Direction::ALL[face as usize];
-                    catalog
-                        .models_at(
-                            state,
-                            horizon_core::position::BlockPos::new(0, 0, 0),
-                            &mut found,
-                        )
-                        .ok()?;
-                    found
-                        .iter()
-                        .flat_map(|m| &m.faces)
-                        .find(|f| f.quad.facing == side)
-                        .map(|f| f.layer)
-                },
-            )
+                &mut models.catalog,
+                &mut native,
+            );
+            native(&mut sprites);
+            connected
        } else {
-            Default::default()
+            None
        };
        // After the connected tiles: a tile identical to a block shares its layer, and the
        // overlays skip shared layers.
-        if draws {
-            emissive = crate::native_emissive::load_optifine(root, &mut sprites);
+        if draws && let Some(suffix) = crate::pack_hooks::formats().emissive_suffix(root) {
+            emissive = crate::native_emissive::load_overlays(root, &suffix, &mut sprites);
        }
        sprites.save_disk_cache();
        if draws {
@@ -411,7 +396,6 @@ impl RenderAssets {
            pbr_specular: sprites.specular,
            pbr_size: sprites.pbr_size,
            connected,
-            fusion,
            generation: GENERATION.fetch_add(1, std::sync::atomic::Ordering::Relaxed) + 1,
        })
    }
@@ -233,11 +233,11 @@ pub fn texture_path(root: &Path, texture: &str, directory: &str) -> PathBuf {
    }
    let (namespace, path) = texture.split_once(':').unwrap_or(("minecraft", texture));
    let rel = format!("assets/{namespace}/{directory}/{path}.png");
-    root.join(if horizon_optifine::paths::valid(&rel) {
-        &rel
-    } else {
-        NOWHERE
-    })
+    // No `.`, `..` or empty segment, and no `\` (a separator on Windows, where `..\..` climbs).
+    let stays = rel
+        .split('/')
+        .all(|segment| !matches!(segment, "" | "." | "..") && !segment.contains('\\'));
+    root.join(if stays { &rel } else { NOWHERE })
 }

 /// `SpriteSourceList.list`: every sprite id of the atlas and its origin.
@@ -960,7 +960,7 @@ pub struct Scene<'a> {
    pub world: &'a World,
    pub sprites: &'a HashMap<String, Rect>,
    /// The packs' OptiFine emissive overlays of the sprites.
-    pub emissive: &'a horizon_optifine::emissive::Emissive,
+    pub emissive: &'a crate::entity_textures::Emissive,
    /// Atlas sprites that contain a texel with fractional alpha. Static
    /// geometry stays on the cutout pipeline; these models keep the blended
    /// entity path so resource packs retain their alpha behavior.
@@ -1039,7 +1039,7 @@ impl CacheOptions {
    }
 }
 /// The block-entity models and what is baked from them: vanilla's, or the packs' custom entity
-/// models over them ([`crate::block_entity_cem`]).
+/// models over them ([`crate::pack_hooks::PackFormats::block_entity_models`]).
 #[derive(Default)]
 pub struct BlockEntityShapes {
    models: HashMap<&'static str, ModelPart>,
@@ -1555,7 +1555,7 @@ impl BlockEntityRenderer {
    /// The models the packs under `root` give, their `.jem` files over vanilla's, for
    /// [`Self::set_shapes`] (a pack reload): vanilla's own, shared, without any.
    pub fn shapes_for(&self, root: &Path) -> Arc<BlockEntityShapes> {
-        match crate::block_entity_cem::reshape(root, &self.vanilla.models) {
+        match crate::pack_hooks::formats().block_entity_models(root, &self.vanilla.models) {
            Some((models, textures)) => Arc::new(BlockEntityShapes::new(models, textures)),
            None => self.vanilla.clone(),
        }
@@ -4768,7 +4768,8 @@ mod tests {

    #[test]
    fn a_chest_jem_reshapes_the_closed_chest_and_paints_its_texture() {
-        use crate::block_entity_cem::tests::{BOX, chest, pack};
+        use crate::pack_formats::block_entity_cem::tests::{BOX, chest, pack};
+        crate::pack_formats::install();
        let vanilla = Arc::new(BlockEntityShapes::new(
            HashMap::from([("chest", chest())]),
            HashMap::new(),
@@ -4864,8 +4865,8 @@ mod tests {
        };
        // The chest's three faces become the bottom's, the lock's and the custom lid's six, in
        // the `.jem`'s texture. Ender and copper chests have no file of their own: vanilla's
-        // three faces in their own textures. (Trapped chests: `block_entity_cem`'s tests; their
-        // texture turns festive in late December.)
+        // three faces in their own textures. (Trapped chests: `block_entity_cem`'s tests in
+        // `pack_formats`; their texture turns festive in late December.)
        for (block, texture, u0, faces) in [
            ("chest", "entity/chest/normal", 0.4, 8),
            ("ender_chest", "entity/chest/ender", 0.2, 3),
@@ -16,6 +16,45 @@ use crate::{
 #[path = "chat_tests.rs"]
 mod tests;

+/// `FilterMask.applyWithFormatting` over a player message's signed content, as
+/// the packet's mask `(type, bit set)`: as it is when passed through, none when
+/// fully filtered, and when partly filtered each masked UTF-16 unit becomes a
+/// `#` in `FILTERED_STYLE` (dark grey, hover "chat.filtered").
+pub fn filtered_message(
+    content: &str,
+    (kind, bits): &(i32, Vec<i64>),
+) -> Option<serde_json::Value> {
+    match kind {
+        1 => return None,
+        2 => {}
+        _ => return Some(serde_json::Value::from(content)),
+    }
+    let masked = |i: usize| {
+        bits.get(i / 64)
+            .is_some_and(|w| (*w as u64 >> (i % 64)) & 1 != 0)
+    };
+    let units: Vec<u16> = content.encode_utf16().collect();
+    let mut parts = Vec::new();
+    let mut start = 0;
+    while start < units.len() {
+        let filtered = masked(start);
+        let end = (start..units.len())
+            .find(|&i| masked(i) != filtered)
+            .unwrap_or(units.len());
+        parts.push(if filtered {
+            serde_json::json!({
+                "text": "#".repeat(end - start),
+                "color": "dark_gray",
+                "hover_event": {"action": "show_text", "value": {"translate": "chat.filtered"}},
+            })
+        } else {
+            serde_json::Value::from(String::from_utf16_lossy(&units[start..end]))
+        });
+        start = end;
+    }
+    Some(serde_json::json!({"text": "", "extra": parts}))
+}
+
 /// `CommandHistory.PERSISTED_COMMANDS_FILE_NAME` and its size cap.
 const COMMAND_HISTORY_FILE: &str = "command_history.txt";
 const MAX_PERSISTED_COMMAND_HISTORY: usize = 50;
@@ -1026,3 +1026,43 @@ fn a_compact_repeat_keeps_the_scrolled_view_still() {
    says(&mut chat, "new");
    assert_eq!(chat.scroll, 6);
 }
+
+/// `FilterMask.applyWithFormatting`: a pass-through mask keeps the message, a
+/// fully filtered one hides it, and a partial one turns each masked UTF-16 unit
+/// into a dark grey `#` whose hover reads `chat.filtered`.
+#[test]
+fn a_server_filter_mask_hides_or_masks_the_message() {
+    let text = |v: &serde_json::Value| crate::component::to_text(v, &mut |s| Text::literal(s));
+    let shown = |content: &str, mask: (i32, Vec<i64>)| {
+        filtered_message(content, &mask).map(|v| text(&v).plain())
+    };
+    assert_eq!(shown("hello", (0, vec![])), Some("hello".to_owned()));
+    assert_eq!(shown("hello", (1, vec![])), None);
+    assert_eq!(shown("hello", (2, vec![0b0110])), Some("h##lo".to_owned()));
+    assert_eq!(
+        shown("hello", (2, vec![0b1_0001])),
+        Some("#ell#".to_owned())
+    );
+    // An emoji is two UTF-16 units, so two bits and two `#`.
+    assert_eq!(
+        shown("a\u{1F600}b", (2, vec![0b0110])),
+        Some("a##b".to_owned())
+    );
+    // Bit 65 is in the second word.
+    let long = "x".repeat(70);
+    let mut expected = long.clone();
+    expected.replace_range(65..66, "#");
+    assert_eq!(shown(&long, (2, vec![0, 0b10])), Some(expected));
+    let masked = text(&filtered_message("hello", &(2, vec![0b0110])).unwrap());
+    let hash = masked.spans.iter().find(|s| s.text == "##").unwrap();
+    assert_eq!(hash.style.color, Some(text::DARK_GRAY));
+    let hover = hash.style.hover.as_ref().unwrap();
+    assert_eq!(hover.spans[0].text, "chat.filtered");
+    assert!(
+        masked
+            .spans
+            .iter()
+            .filter(|s| s.text != "##")
+            .all(|s| s.style.color.is_none())
+    );
+}
@@ -1,116 +1,157 @@
-//! OptiFine's Custom Item Textures (and CIT Resewn's): the rules of the enabled packs'
-//! `optifine/cit/**/*.properties`, read from the overlay resource root. The rules themselves are
-//! `horizon_optifine::cit`'s.
+//! Custom item textures: rules a pack format vanilla doesn't read (OptiFine's and CIT Resewn's
+//! `cit/` folders) gives, which change a stack's texture, model, worn armour layers or
+//! enchantment glint. The platform's pack formats read and match them ([`crate::pack_hooks`]);
+//! the engine draws what the matching rule says ([`Rule`]).

-pub use horizon_optifine::cit::{Hand, Kind, Rule};
-
-use crate::cit_glint::{Global, StackGlint};
-use horizon_client_core::component::name_text;
-use horizon_client_core::scoreboard::comp_text;
-use horizon_items::item_data::{canon_tag, encode_components};
-use horizon_items::items::ItemStack;
-use horizon_optifine::cit::{ComponentTest, Source, ValueTest};
-use horizon_optifine::{Properties, properties_files_in};
-use horizon_world::nbt::{JavaString, Tag, parse_snbt};
-use std::borrow::Cow;
-use std::collections::HashMap;
-use std::fs;
-use std::hash::{DefaultHasher, Hash, Hasher};
 use std::path::Path;
-use std::sync::{Arc, Mutex};
+use std::sync::Arc;

-/// Every rule under the root's `optifine/cit/`, `mcpatcher/cit/` and CIT Resewn's
-/// `citresewn/cit/` folders, the one chosen first when several match first (`Rule::priority`).
-/// The pack's global `cit.properties` is not a rule.
-pub fn load_rules(root: &Path) -> Vec<Rule> {
-    let tops = ["optifine", "mcpatcher", "citresewn"];
-    let mut rules: Vec<Rule> = properties_files_in(root, &tops, "cit")
-        .into_iter()
-        .filter(|path| !path.ends_with("/cit.properties"))
-        .filter_map(|path| {
-            let props = read_properties(&root.join(&path))?;
-            let rule = Rule::parse(&path, &props, |p| root.join(p).is_file());
-            if rule.is_none() {
-                log::warn!("custom item textures: {path} is not a rule Horizon can read");
-            }
-            rule
-        })
-        .collect();
-    rules.sort_by(Rule::priority);
-    rules
+use horizon_items::items::ItemStack;
+
+use crate::cit_glint::StackGlint;
+
+/// What a rule changes.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Kind {
+    Item,
+    Armor,
+    Elytra,
+    Enchantment,
 }

-/// A `.properties` file as CIT Resewn reads them (`Properties::parse_equals_first`): UTF-8,
-/// else Latin-1 as Java reads them, so a pack saved that way still loads. `None` when it can't
-/// be read.
-pub fn read_properties(path: &Path) -> Option<Properties> {
-    let bytes = fs::read(path).ok()?;
-    let text = String::from_utf8(bytes)
-        .unwrap_or_else(|e| e.into_bytes().iter().map(|&b| char::from(b)).collect());
-    Some(Properties::parse_equals_first(&text))
+/// The hand a stack is drawn in; GUI items count as the main hand. `Any` is a rule's "either".
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Hand {
+    Any,
+    Main,
+    Off,
 }

-/// The rules with an index by item and a cache of what each stack matched.
-#[derive(Debug, Default)]
+/// An OpenGL blend factor (`GL_ONE`, `GL_SRC_ALPHA`...), as `glBlendFuncSeparate` takes them.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Factor {
+    Zero,
+    One,
+    SrcColor,
+    OneMinusSrcColor,
+    SrcAlpha,
+    OneMinusSrcAlpha,
+    DstAlpha,
+    OneMinusDstAlpha,
+    DstColor,
+    OneMinusDstColor,
+    SrcAlphaSaturate,
+}
+
+/// A glint layer's blend factors for colour and alpha.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Blend {
+    pub src: Factor,
+    pub dst: Factor,
+    pub src_alpha: Factor,
+    pub dst_alpha: Factor,
+}
+
+/// An enchantment rule's glint layer.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Glint {
+    pub layer: i32,
+    /// `None` draws without blending (replace).
+    pub blend: Option<Blend>,
+    /// Scroll speed: the texture runs through vanilla's glint periods at `speed` times the
+    /// clock in milliseconds.
+    pub speed: f32,
+    /// Degrees the texture turns by.
+    pub rotation: f32,
+    /// Seconds on this layer when the layers take turns.
+    pub duration: f32,
+    /// Multipliers of the texture's colour, never negative.
+    pub rgba: [f32; 4],
+    /// Whether the default glint still draws under this layer.
+    pub use_glint: bool,
+    /// Linear filtering, else nearest.
+    pub blur: bool,
+}
+
+/// A rule as the engine draws it.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Rule {
+    /// The rule's file, as a resource path.
+    pub path: String,
+    pub kind: Kind,
+    /// Its texture, as a resource path to a `.png`.
+    pub texture: Option<String>,
+    /// Its named textures: (name, resource path).
+    pub textures: Vec<(String, String)>,
+    /// Its model, as a resource path to a `.json`.
+    pub model: Option<String>,
+    /// Its named models.
+    pub models: Vec<(String, String)>,
+    /// What an Enchantment rule draws.
+    pub glint: Glint,
+}
+
+/// Which rules a stack matches: the pack format's own conditions.
+pub trait Matcher: Send + Sync {
+    /// The winning rule of `kind` (Item, Armor or Elytra) for this stack, as an index into
+    /// [`CitRules::rules`].
+    fn select(&self, kind: Kind, stack: &ItemStack, hand: Hand, max_damage: u32) -> Option<usize>;
+    /// Every matching Enchantment rule for the stack drawn in `hand`, in priority order.
+    fn enchantments(&self, stack: &ItemStack, hand: Hand, max_damage: u32) -> Vec<usize>;
+    /// The glint layers this stack draws in `hand`; `None` when the pack changes no glint.
+    /// `foil` is whether the stack draws a glint at all.
+    fn glint(
+        &self,
+        stack: &ItemStack,
+        hand: Hand,
+        max_damage: u32,
+        foil: bool,
+    ) -> Option<Arc<StackGlint>>;
+    /// Leave out the Enchantment rules `keep` refuses: they match no stack.
+    fn keep_glints(&mut self, keep: &dyn Fn(usize) -> bool);
+}
+
+/// The packs' custom item texture rules, the winner first, and their matcher.
 pub struct CitRules {
    pub rules: Vec<Rule>,
-    /// The pack's `cit.properties`.
-    pub global: Global,
-    /// Per kind (`Kind as usize`), the rules naming each item, in priority order.
-    by_item: [HashMap<String, Vec<u32>>; 4],
-    /// Enchantment rules without `items`, in priority order.
-    any_item: Vec<u32>,
-    /// Per rule, per component test: its literal read as SNBT and as a JSON text component.
-    literals: Vec<Vec<Prepared>>,
-    selected: Mutex<HashMap<u64, Option<u32>>>,
-    enchanted: Mutex<HashMap<u64, Vec<u32>>>,
-    glints: Mutex<HashMap<u64, Arc<StackGlint>>>,
+    /// Whether the default glint draws on items no enchantment rule matches.
+    pub use_glint: bool,
+    matcher: Option<Box<dyn Matcher>>,
 }

-#[derive(Debug, Default)]
-struct Prepared {
-    snbt: Option<Tag>,
-    json: Option<String>,
-}
-
-/// Cache entries kept before the cache starts over.
-const CACHE_LIMIT: usize = 4096;
-
-impl CitRules {
-    /// The enabled packs' rules under the overlay resource root.
-    pub fn load(root: &Path) -> Self {
+impl Default for CitRules {
+    fn default() -> Self {
        Self {
-            global: crate::cit_glint::load_global(root),
-            ..Self::new(load_rules(root))
+            rules: Vec::new(),
+            use_glint: true,
+            matcher: None,
        }
    }
+}

-    /// `rules` in priority order, the winner first.
-    pub fn new(rules: Vec<Rule>) -> Self {
-        let mut by_item: [HashMap<String, Vec<u32>>; 4] = Default::default();
-        let mut any_item = Vec::new();
-        for (i, rule) in rules.iter().enumerate() {
-            let i = i as u32;
-            if rule.kind == Kind::Enchantment && rule.items.is_empty() {
-                any_item.push(i);
-            }
-            for item in &rule.items {
-                let list = by_item[rule.kind as usize].entry(item.clone()).or_default();
-                if list.last() != Some(&i) {
-                    list.push(i);
-                }
-            }
-        }
-        let literals = rules
-            .iter()
-            .map(|r| r.components.iter().map(prepare).collect())
-            .collect();
+impl std::fmt::Debug for CitRules {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CitRules")
+            .field("rules", &self.rules)
+            .field("use_glint", &self.use_glint)
+            .finish_non_exhaustive()
+    }
+}
+
+impl CitRules {
+    /// The rules of the overlay at `root`, from the installed pack formats.
+    pub fn load(root: &Path) -> Self {
+        crate::pack_hooks::formats()
+            .item_textures(root)
+            .unwrap_or_default()
+    }
+
+    /// `rules`, in priority order, matched by `matcher`.
+    pub fn new(rules: Vec<Rule>, use_glint: bool, matcher: Box<dyn Matcher>) -> Self {
        Self {
            rules,
-            by_item,
-            any_item,
-            literals,
-            ..Default::default()
+            use_glint,
+            matcher: Some(matcher),
        }
    }

@@ -121,17 +162,12 @@ impl CitRules {
    /// Leave out the Enchantment rules `keep` refuses (those without a drawable texture): they
    /// match no stack, so vanilla's glint and the other rules of their layer stay.
    pub fn keep_glints(&mut self, keep: impl Fn(usize) -> bool) {
-        self.any_item.retain(|&i| keep(i as usize));
-        let named = &mut self.by_item[Kind::Enchantment as usize];
-        for list in named.values_mut() {
-            list.retain(|&i| keep(i as usize));
+        if let Some(matcher) = &mut self.matcher {
+            matcher.keep_glints(&keep);
        }
-        named.retain(|_, list| !list.is_empty());
-        lock(&self.enchanted).clear();
-        lock(&self.glints).clear();
    }

-    /// The winning rule of `kind` (Item, Armor or Elytra) for this stack, as an index into `rules`.
+    /// [`Matcher::select`].
    pub fn select(
        &self,
        kind: Kind,
@@ -139,51 +175,17 @@ impl CitRules {
        hand: Hand,
        max_damage: u32,
    ) -> Option<usize> {
-        let candidates = self.by_item[kind as usize].get(&*stack.item)?;
-        let comps = encode_components(stack);
-        let key = cache_key((0, kind, hand), stack, max_damage, comps.as_ref());
-        if let Some(hit) = lock(&self.selected).get(&key) {
-            return hit.map(|i| i as usize);
-        }
-        let found = candidates
-            .iter()
-            .copied()
-            .find(|&i| self.matches(i, stack, hand, max_damage, comps.as_ref()));
-        remember(&self.selected, key, found);
-        found.map(|i| i as usize)
+        self.matcher.as_ref()?.select(kind, stack, hand, max_damage)
    }

-    /// Every matching Enchantment rule for the stack drawn in `hand` (`Hand::Main` for one in a
-    /// GUI), in priority order.
+    /// [`Matcher::enchantments`].
    pub fn enchantments(&self, stack: &ItemStack, hand: Hand, max_damage: u32) -> Vec<usize> {
-        let named = self.by_item[Kind::Enchantment as usize]
-            .get(&*stack.item)
-            .map_or(&[][..], Vec::as_slice);
-        if named.is_empty() && self.any_item.is_empty() {
-            return Vec::new();
-        }
-        let comps = encode_components(stack);
-        let key = cache_key(
-            (1, Kind::Enchantment, hand),
-            stack,
-            max_damage,
-            comps.as_ref(),
-        );
-        let hit = lock(&self.enchanted).get(&key).cloned();
-        let found = hit.unwrap_or_else(|| {
-            let mut all: Vec<u32> = named.iter().chain(&self.any_item).copied().collect();
-            all.sort_unstable();
-            all.retain(|&i| self.matches(i, stack, hand, max_damage, comps.as_ref()));
-            remember(&self.enchanted, key, all.clone());
-            all
-        });
-        found.into_iter().map(|i| i as usize).collect()
+        self.matcher
+            .as_ref()
+            .map_or_else(Vec::new, |m| m.enchantments(stack, hand, max_damage))
    }

-    /// The glint layers this stack draws in `hand` (`Hand::Main` in a GUI) and whether
-    /// vanilla's still does (`StackGlint`), worked out once per stack and hand; `None` when the
-    /// pack changes no glint. `foil` is whether the stack draws a glint at all
-    /// (`ItemStack::has_foil`): one that doesn't gets no layers.
+    /// [`Matcher::glint`].
    pub fn glint(
        &self,
        stack: &ItemStack,
@@ -191,659 +193,6 @@ impl CitRules {
        max_damage: u32,
        foil: bool,
    ) -> Option<Arc<StackGlint>> {
-        let no_rules =
-            self.any_item.is_empty() && self.by_item[Kind::Enchantment as usize].is_empty();
-        // Before the cache, which `foil` is not part of.
-        if !foil || (no_rules && self.global.use_glint) {
-            return None;
-        }
-        let comps = encode_components(stack);
-        let key = cache_key(
-            (2, Kind::Enchantment, hand),
-            stack,
-            max_damage,
-            comps.as_ref(),
-        );
-        if let Some(hit) = lock(&self.glints).get(&key) {
-            return Some(hit.clone());
-        }
-        let matched = self.enchantments(stack, hand, max_damage);
-        let glint = Arc::new(StackGlint::new(
-            &self.rules,
-            &matched,
-            stack.crafting_enchantments(),
-            &self.global,
-        ));
-        remember(&self.glints, key, glint.clone());
-        Some(glint)
-    }
-
-    /// Whether rule `i` matches the stack drawn in `hand`.
-    fn matches(
-        &self,
-        i: u32,
-        stack: &ItemStack,
-        hand: Hand,
-        max_damage: u32,
-        comps: Option<&Tag>,
-    ) -> bool {
-        let rule = &self.rules[i as usize];
-        if rule.hand != Hand::Any && rule.hand != hand {
-            return false;
-        }
-        let count = i32::try_from(stack.count).unwrap_or(i32::MAX);
-        if rule.stack_size.as_ref().is_some_and(|r| !r.contains(count)) {
-            return false;
-        }
-        // CIT Resewn: only damageable items have damage.
-        let damage = if max_damage > 0 { stack.damage } else { 0 };
-        if rule
-            .damage
-            .as_ref()
-            .is_some_and(|d| !d.matches(damage, max_damage))
-        {
-            return false;
-        }
-        let enchantments = stack.crafting_enchantments();
-        let listed = |id: &str| rule.enchantments.iter().any(|e| e == id);
-        if !rule.enchantments.is_empty() && !enchantments.iter().any(|(id, _)| listed(id)) {
-            return false;
-        }
-        if let Some(levels) = &rule.enchantment_levels {
-            let level_in_range = enchantments.iter().any(|(id, level)| {
-                (rule.enchantments.is_empty() || listed(id))
-                    && levels.contains(i32::try_from(*level).unwrap_or(i32::MAX))
-            });
-            if !level_in_range {
-                return false;
-            }
-        }
-        let literals = &self.literals[i as usize];
-        rule.components
-            .iter()
-            .zip(literals)
-            .all(|(test, lit)| component_test(test, lit, stack, comps) != test.negate)
-    }
-}
-
-fn lock<T>(m: &Mutex<T>) -> std::sync::MutexGuard<'_, T> {
-    m.lock().unwrap_or_else(|e| e.into_inner())
-}
-
-fn remember<V>(cache: &Mutex<HashMap<u64, V>>, key: u64, value: V) {
-    let mut cache = lock(cache);
-    if cache.len() >= CACHE_LIMIT {
-        cache.clear();
-    }
-    cache.insert(key, value);
-}
-
-/// What a cached answer depends on; `query` tells `select`, `enchantments` and `glint` apart.
-fn cache_key(query: (u8, Kind, Hand), stack: &ItemStack, max: u32, comps: Option<&Tag>) -> u64 {
-    let mut h = DefaultHasher::new();
-    (query.0, query.1 as u8, query.2 as u8, &*stack.item).hash(&mut h);
-    (stack.count, stack.damage, max, comps).hash(&mut h);
-    h.finish()
-}
-
-fn prepare(test: &ComponentTest) -> Prepared {
-    let ValueTest::Literal(lit) = &test.value else {
-        return Prepared::default();
-    };
-    let text = lit.text.trim();
-    let snbt = match parse_snbt(text) {
-        Ok((tag, read)) if read == text.len() && text.starts_with(['{', '[']) => Some(tag),
-        _ => None,
-    };
-    let json = json_plain(text);
-    Prepared { snbt, json }
-}
-
-/// The plain text of `s` read as a JSON text component.
-fn json_plain(s: &str) -> Option<String> {
-    if !s.starts_with(['{', '[', '"']) {
-        return None;
-    }
-    let value: serde_json::Value = serde_json::from_str(s).ok()?;
-    Some(comp_text(&value).plain())
-}
-
-/// Whether one test passes, before its `negate`.
-fn component_test(
-    test: &ComponentTest,
-    lit: &Prepared,
-    stack: &ItemStack,
-    comps: Option<&Tag>,
-) -> bool {
-    let legacy;
-    let (root, text_depth) = match &test.source {
-        Source::Component(id) => {
-            let depth = match id.as_str() {
-                "minecraft:custom_name" | "minecraft:item_name" => Some(0),
-                "minecraft:lore" => Some(1),
-                _ => None,
-            };
-            (comps.and_then(|c| c.get(id)), depth)
-        }
-        Source::LegacyEnchantments { stored } => {
-            let levels = if *stored {
-                stack.stored_enchantments()
-            } else {
-                stack.enchantments()
-            };
-            legacy = Tag::List(
-                levels
-                    .iter()
-                    .map(|(id, lvl)| {
-                        let lvl = i16::try_from(*lvl).unwrap_or(i16::MAX);
-                        Tag::compound([
-                            ("id", Tag::String((&**id).into())),
-                            ("lvl", Tag::Short(lvl)),
-                        ])
-                    })
-                    .collect(),
-            );
-            (Some(&legacy), None)
-        }
-    };
-    // Fields the component leaves out when 0, which pre-1.20.5 items always wrote.
-    let defaulted;
-    let root = match (&test.source, root, test.path.first()) {
-        (Source::Component(id), Some(Tag::Compound(map)), Some(field))
-            if matches!(
-                (id.as_str(), field.as_str()),
-                ("minecraft:written_book_content", "generation")
-                    | ("minecraft:fireworks", "flight_duration")
-            ) && !map.contains_key(&JavaString::from(field.as_str())) =>
-        {
-            let mut map = map.clone();
-            map.insert(JavaString::from(field.as_str()), Tag::Int(0));
-            defaulted = Tag::Compound(map);
-            Some(&defaulted)
-        }
-        (_, root, _) => root,
-    };
-    let Some(root) = root else {
-        return matches!(test.value, ValueTest::Exists(false));
-    };
-    if let ValueTest::Exists(want) = test.value {
-        return walk(root, &test.path, 0, &mut |_, _| true) == want;
-    }
-    walk(root, &test.path, 0, &mut |tag, depth| {
-        value_test(&test.value, lit, tag, text_depth == Some(depth))
-    })
-}
-
-/// Visits what `path` reaches from `tag`, true once `visit` is.
-fn walk(
-    tag: &Tag,
-    path: &[String],
-    depth: usize,
-    visit: &mut dyn FnMut(&Tag, usize) -> bool,
-) -> bool {
-    let Some((seg, rest)) = path.split_first() else {
-        return visit(tag, depth);
-    };
-    let mut next = |t: &Tag| walk(t, rest, depth + 1, visit);
-    let len = match tag {
-        Tag::Compound(map) if seg == "*" => return map.values().any(&mut next),
-        Tag::Compound(map) => return map.get(&JavaString::from(seg.as_str())).is_some_and(next),
-        Tag::List(v) => v.len(),
-        Tag::ByteArray(v) => v.len(),
-        Tag::IntArray(v) => v.len(),
-        Tag::LongArray(v) => v.len(),
-        _ => return false,
-    };
-    let element = |i: usize| match tag {
-        Tag::List(v) => Cow::Borrowed(&v[i]),
-        Tag::ByteArray(v) => Cow::Owned(Tag::Byte(v[i] as i8)),
-        Tag::IntArray(v) => Cow::Owned(Tag::Int(v[i])),
-        Tag::LongArray(v) => Cow::Owned(Tag::Long(v[i])),
-        _ => Cow::Owned(Tag::End),
-    };
-    if seg == "count" {
-        return next(&Tag::Int(i32::try_from(len).unwrap_or(i32::MAX)));
-    }
-    if seg == "*" {
-        return (0..len).any(|i| next(&element(i)));
-    }
-    seg.parse::<usize>()
-        .ok()
-        .filter(|&i| i < len)
-        .is_some_and(|i| next(&element(i)))
-}
-
-fn int_value(tag: &Tag) -> Option<i64> {
-    match *tag {
-        Tag::Byte(v) => Some(v.into()),
-        Tag::Short(v) => Some(v.into()),
-        Tag::Int(v) => Some(v.into()),
-        Tag::Long(v) => Some(v),
-        _ => None,
-    }
-}
-
-/// A number as Java's `String.valueOf` writes it (`3`, `3.0`).
-fn decimal(tag: &Tag) -> Option<String> {
-    let s = match *tag {
-        Tag::Float(b) => f32::from_bits(b).to_string(),
-        Tag::Double(b) => f64::from_bits(b).to_string(),
-        _ => return int_value(tag).map(|v| v.to_string()),
-    };
-    Some(if s.contains(['.', 'e', 'N', 'i']) {
-        s
-    } else {
-        s + ".0"
-    })
-}
-
-/// `text` against a string, its JSON text, or the plain text of a text component.
-fn text_matches(tag: &Tag, is_text: bool, text: impl Fn(&str) -> bool) -> bool {
-    match tag {
-        Tag::String(s) => {
-            let s = s.to_string_lossy();
-            text(&s)
-                || (is_text && text(&name_text(tag).plain()))
-                || json_plain(&s).is_some_and(|p| text(&p))
-        }
-        Tag::Compound(_) | Tag::List(_) => is_text && text(&name_text(tag).plain()),
-        _ => false,
-    }
-}
-
-fn value_test(test: &ValueTest, lit: &Prepared, tag: &Tag, is_text: bool) -> bool {
-    match test {
-        ValueTest::Exists(_) => true,
-        ValueTest::Range(r) => {
-            int_value(tag).is_some_and(|v| i32::try_from(v).is_ok_and(|v| r.contains(v)))
-        }
-        ValueTest::Raw(name) => name.matches(&canon_tag(tag)),
-        ValueTest::Text(name) => match decimal(tag) {
-            Some(n) => name.matches(&n),
-            None => text_matches(tag, is_text, |s| name.matches(s)),
-        },
-        ValueTest::Literal(l) => match tag {
-            Tag::Float(b) => l.text.trim().parse::<f32>().ok() == Some(f32::from_bits(*b)),
-            Tag::Double(b) => l.float == Some(f64::from_bits(*b)),
-            Tag::Compound(_) | Tag::List(_)
-                if lit.snbt.as_ref().is_some_and(|e| contains(e, tag)) =>
-            {
-                true
-            }
-            _ => match int_value(tag) {
-                Some(v) => l.int == Some(v),
-                None => text_matches(tag, is_text, |s| {
-                    s == l.text || lit.json.as_deref() == Some(s)
-                }),
-            },
-        },
-    }
-}
-
-/// `NbtUtils.compareNbt(expected, actual, true)`: every key and element of `expected` found in
-/// `actual`.
-fn contains(expected: &Tag, actual: &Tag) -> bool {
-    match (expected, actual) {
-        (Tag::Compound(e), Tag::Compound(a)) => e
-            .iter()
-            .all(|(k, v)| a.get(k).is_some_and(|a| contains(v, a))),
-        (Tag::List(e), Tag::List(a)) if e.is_empty() => a.is_empty(),
-        (Tag::List(e), Tag::List(a)) => e.iter().all(|e| a.iter().any(|a| contains(e, a))),
-        _ => expected == actual,
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use std::sync::Arc;
-
-    /// Rules from (file stem, properties), sorted as `load_rules` sorts them.
-    fn rules(files: &[(&str, &str)]) -> CitRules {
-        let mut rules: Vec<Rule> = files
-            .iter()
-            .map(|(stem, text)| {
-                let path = format!("assets/minecraft/optifine/cit/{stem}.properties");
-                let text = format!("texture=x\n{text}");
-                Rule::parse(&path, &Properties::parse_equals_first(&text), |_| true).unwrap()
-            })
-            .collect();
-        rules.sort_by(Rule::priority);
-        CitRules::new(rules)
-    }
-
-    fn stem(cit: &CitRules, i: Option<usize>) -> Option<&str> {
-        let path = &cit.rules[i?].path;
-        path.rsplit('/').next()?.strip_suffix(".properties")
-    }
-
-    fn item(cit: &CitRules, stack: ItemStack) -> Option<&str> {
-        stem(cit, cit.select(Kind::Item, &stack, Hand::Main, 0))
-    }
-
-    fn new(id: &str) -> ItemStack {
-        ItemStack::new(&format!("minecraft:{id}"), 1)
-    }
-
-    fn string(s: &str) -> Tag {
-        Tag::String(s.into())
-    }
-
-    fn with(id: &str, component: &str, tag: Tag) -> ItemStack {
-        let mut stack = new(id);
-        let component = format!("minecraft:{component}");
-        stack.data_mut().other.push((component, tag));
-        stack
-    }
-
-    fn enchanted(id: &str, levels: &[(&str, u32)]) -> ItemStack {
-        let mut stack = new(id);
-        let levels = levels
-            .iter()
-            .map(|(e, l)| (Arc::from(format!("minecraft:{e}")), *l));
-        stack.data_mut().enchantments = levels.collect();
-        stack
-    }
-
-    #[test]
-    fn heavier_rules_win_and_kinds_stay_apart() {
-        let cit = rules(&[
-            ("plain", "items=stick"),
-            ("heavy", "items=stick\nweight=2\nstackSize=2-"),
-            ("offhand", "items=stick\nweight=5\nhand=off"),
-            ("armor", "type=armor\nitems=stick"),
-            ("wings", "type=elytra"),
-        ]);
-        assert_eq!(item(&cit, new("stick")), Some("plain"));
-        assert_eq!(
-            item(&cit, ItemStack::new("minecraft:stick", 3)),
-            Some("heavy")
-        );
-        let pick = |kind, id, hand, max| stem(&cit, cit.select(kind, &new(id), hand, max));
-        assert_eq!(pick(Kind::Item, "stick", Hand::Off, 0), Some("offhand"));
-        assert_eq!(item(&cit, new("stone")), None);
-        assert_eq!(item(&cit, new("elytra")), None);
-        assert_eq!(pick(Kind::Elytra, "elytra", Hand::Main, 432), Some("wings"));
-        assert_eq!(pick(Kind::Armor, "stick", Hand::Main, 0), Some("armor"));
-    }
-
-    #[test]
-    fn names_match_by_their_plain_text() {
-        let cit = rules(&[
-            ("glob", "items=stick\nnbt.display.Name=ipattern:*sword"),
-            ("exact", "items=stone\ncomponents.custom_name=My Sword"),
-            ("json", "items=dirt\nnbt.display.Name=[\"My \",\"Sword\"]"),
-        ]);
-        let named = |id: &str, name: Tag| {
-            let mut stack = new(id);
-            stack.data_mut().custom_name = Some(name);
-            stack
-        };
-        let styled = Tag::compound([("text", string("My Sword")), ("color", string("red"))]);
-        assert_eq!(item(&cit, named("stick", styled.clone())), Some("glob"));
-        assert_eq!(item(&cit, named("stick", string("Blade"))), None);
-        assert_eq!(item(&cit, new("stick")), None);
-        assert_eq!(item(&cit, named("stone", styled.clone())), Some("exact"));
-        assert_eq!(item(&cit, named("dirt", styled)), Some("json"));
-    }
-
-    #[test]
-    fn lore_lines_and_list_counts() {
-        let cit = rules(&[
-            (
-                "any_line",
-                "items=stick\nnbt.display.Lore.*=ipattern:*legendary*",
-            ),
-            ("two_lines", "items=stone\ncomponents.lore.count=2"),
-        ]);
-        let bold = Tag::compound([("text", string("A LEGENDARY item")), ("bold", Tag::Byte(1))]);
-        let lore = Tag::List(vec![string("Common"), bold]);
-        assert_eq!(
-            item(&cit, with("stick", "lore", lore.clone())),
-            Some("any_line")
-        );
-        assert_eq!(item(&cit, with("stone", "lore", lore)), Some("two_lines"));
-        let one = Tag::List(vec![string("A legendary item")]);
-        assert_eq!(item(&cit, with("stone", "lore", one)), None);
-    }
-
-    #[test]
-    fn custom_data_existence_and_negation() {
-        let cit = rules(&[
-            (
-                "aote",
-                "items=stick\nweight=2\nnbt.ExtraAttributes.id=ASPECT_OF_THE_END",
-            ),
-            (
-                "not_hyp",
-                "items=stick\nweight=1\ncomponent.custom_data.ExtraAttributes.id=!HYP",
-            ),
-            ("unnamed", "items=stick\nnbt.display.Name=exists:false"),
-        ]);
-        let data = |id: &str| {
-            let attributes =
-                Tag::compound([("ExtraAttributes", Tag::compound([("id", string(id))]))]);
-            with("stick", "custom_data", attributes)
-        };
-        assert_eq!(item(&cit, data("ASPECT_OF_THE_END")), Some("aote"));
-        assert_eq!(item(&cit, data("MIDAS")), Some("not_hyp"));
-        assert_eq!(item(&cit, data("HYP")), Some("unnamed"));
-        let mut named = data("HYP");
-        named.data_mut().custom_name = Some(string("Hyperion"));
-        assert_eq!(item(&cit, named), None);
-    }
-
-    #[test]
-    fn legacy_enchantment_lists_and_model_data() {
-        let cit = rules(&[
-            (
-                "sharp",
-                "items=stick\nnbt.Enchantments.*.id=minecraft:sharpness\nnbt.Enchantments.0.lvl=5",
-            ),
-            ("cmd", "items=stone\nnbt.CustomModelData=3"),
-            (
-                "cmd_snbt",
-                "items=dirt\ncomponents.custom_model_data={floats:[3.0f]}",
-            ),
-        ]);
-        assert_eq!(
-            item(&cit, enchanted("stick", &[("sharpness", 5)])),
-            Some("sharp")
-        );
-        assert_eq!(item(&cit, enchanted("stick", &[("sharpness", 4)])), None);
-        let model = |id: &str, f: f32| {
-            let floats = Tag::List(vec![Tag::Float(f.to_bits()), Tag::Float(7f32.to_bits())]);
-            with(id, "custom_model_data", Tag::compound([("floats", floats)]))
-        };
-        assert_eq!(item(&cit, model("stone", 3.0)), Some("cmd"));
-        assert_eq!(item(&cit, model("stone", 3.5)), None);
-        assert_eq!(item(&cit, model("dirt", 3.0)), Some("cmd_snbt"));
-        assert_eq!(item(&cit, model("dirt", 2.0)), None);
-    }
-
-    #[test]
-    fn fields_left_out_at_zero_read_as_zero() {
-        let cit = rules(&[("zero", "items=firework_rocket\nnbt.Fireworks.Flight=0")]);
-        let mut rocket = new("firework_rocket");
-        rocket.data_mut().fireworks = Some((0, Vec::new()));
-        assert_eq!(item(&cit, rocket.clone()), Some("zero"));
-        rocket.data_mut().fireworks = Some((2, Vec::new()));
-        assert_eq!(item(&cit, rocket), None);
-    }
-
-    #[test]
-    fn damage_counts_only_for_damageable_items() {
-        let cit = rules(&[
-            ("worn", "items=diamond_sword\ndamage=50-100%"),
-            ("new", "items=stick\ndamage=0"),
-        ]);
-        let damaged = |id: &str, damage: u32, max: u32| {
-            let mut stack = new(id);
-            stack.damage = damage;
-            stem(&cit, cit.select(Kind::Item, &stack, Hand::Main, max))
-        };
-        // Half of 1561 is 780.5.
-        assert_eq!(damaged("diamond_sword", 780, 1561), None);
-        assert_eq!(damaged("diamond_sword", 781, 1561), Some("worn"));
-        assert_eq!(damaged("stick", 5, 0), Some("new"));
-    }
-
-    #[test]
-    fn enchantment_levels_and_rules_for_any_item() {
-        let cit = rules(&[
-            (
-                "sharp3",
-                "items=stick\nenchantments=sharpness\nenchantmentLevels=3-",
-            ),
-            ("any3", "items=stone\nenchantmentLevels=3-"),
-            ("glint", "type=enchantment\nenchantments=sharpness"),
-            (
-                "sword_glint",
-                "type=enchantment\nitems=diamond_sword\nweight=2",
-            ),
-        ]);
-        let mixed = [("sharpness", 2), ("unbreaking", 3)];
-        assert_eq!(item(&cit, enchanted("stick", &mixed)), None);
-        assert_eq!(
-            item(&cit, enchanted("stick", &[("sharpness", 4)])),
-            Some("sharp3")
-        );
-        assert_eq!(item(&cit, enchanted("stone", &mixed)), Some("any3"));
-        let glints = |stack: ItemStack| -> Vec<&str> {
-            let found = cit.enchantments(&stack, Hand::Main, 0).into_iter();
-            found.map(|i| stem(&cit, Some(i)).unwrap()).collect()
-        };
-        let sharp = [("sharpness", 1)];
-        assert_eq!(
-            glints(enchanted("diamond_sword", &sharp)),
-            ["sword_glint", "glint"]
-        );
-        assert_eq!(glints(enchanted("stick", &sharp)), ["glint"]);
-        assert!(glints(new("stick")).is_empty());
-        // Glints are never an item's texture.
-        assert_eq!(item(&cit, enchanted("diamond_sword", &sharp)), None);
-    }
-
-    /// `CitRules::glint` in the main hand, with the stack's own `has_foil` as callers pass it.
-    fn glint(cit: &CitRules, stack: &ItemStack, item_glint: bool) -> Option<Arc<StackGlint>> {
-        cit.glint(stack, Hand::Main, 0, stack.has_foil(item_glint))
-    }
-
-    /// `stack` with its `enchantment_glint_override` set to `on`.
-    fn overridden(mut stack: ItemStack, on: bool) -> ItemStack {
-        let flag = (
-            "minecraft:enchantment_glint_override".to_owned(),
-            Tag::Byte(on.into()),
-        );
-        stack.data_mut().other.push(flag);
-        stack
-    }
-
-    #[test]
-    fn a_stack_glint_reads_the_book_and_the_pack_file() {
-        let mut cit = rules(&[
-            ("sharp", "type=enchantment\nenchantments=sharpness"),
-            (
-                "keep",
-                "type=enchantment\nlayer=1\nuseGlint=true\nenchantments=mending",
-            ),
-        ]);
-        // An enchanted book's glint follows its stored enchantments.
-        let mut book = new("enchanted_book");
-        book.data_mut().stored_enchantments = vec![
-            (Arc::from("minecraft:sharpness"), 3),
-            (Arc::from("minecraft:mending"), 1),
-        ];
-        let book = glint(&cit, &book, true).unwrap();
-        let weights: Vec<_> = book.layers.iter().map(|l| l.weight).collect();
-        assert_eq!(weights, [0.75, 0.25]);
-        assert!(book.vanilla);
-        let plain = glint(&cit, &enchanted("stick", &[("sharpness", 1)]), false).unwrap();
-        assert_eq!(plain.layers.len(), 1);
-        assert!(!plain.vanilla);
-        // No enchantment rules: nothing changes, unless the pack turns vanilla's glint off.
-        let mut bare = rules(&[("stick", "items=stick")]);
-        assert!(glint(&bare, &overridden(new("stick"), true), false).is_none());
-        bare.global.use_glint = false;
-        assert!(
-            !glint(&bare, &overridden(new("stick"), true), false)
-                .unwrap()
-                .vanilla
-        );
-        cit.global.use_glint = false;
-        assert!(
-            glint(&cit, &overridden(new("stick"), true), false)
-                .unwrap()
-                .is_empty()
-        );
-    }
-
-    #[test]
-    fn only_a_stack_with_a_glint_gets_layers() {
-        let cit = rules(&[("any", "type=enchantment")]);
-        assert!(glint(&cit, &new("stick"), false).is_none());
-        // The override turns an enchanted stack's glint off, and an unenchanted one's on.
-        let off = overridden(enchanted("stick", &[("sharpness", 1)]), false);
-        assert!(glint(&cit, &off, false).is_none());
-        let on = glint(&cit, &overridden(new("stick"), true), false).unwrap();
-        let weights: Vec<_> = on.layers.iter().map(|l| l.weight).collect();
-        assert_eq!(
-            weights,
-            [1.0],
-            "nothing to share: the rule at full strength"
-        );
-        // The same stack, asked again without its glint, is not answered from the cache.
-        assert!(
-            cit.glint(&overridden(new("stick"), true), Hand::Main, 0, false)
-                .is_none()
-        );
-    }
-
-    #[test]
-    fn a_rule_left_out_of_the_glints_matches_nothing() {
-        let mut cit = rules(&[
-            ("broken", "type=enchantment\nitems=diamond_sword\nweight=1"),
-            ("shown", "type=enchantment"),
-        ]);
-        let sword = enchanted("diamond_sword", &[("sharpness", 1)]);
-        let layers = |cit: &CitRules| -> Vec<String> {
-            let glint = glint(cit, &sword, false).unwrap();
-            let stems = glint
-                .layers
-                .iter()
-                .map(|l| stem(cit, Some(l.rule)).unwrap());
-            stems.map(str::to_owned).collect()
-        };
-        // The heavier rule wins the layer, until its texture is missing.
-        assert_eq!(layers(&cit), ["broken"]);
-        let broken = (0..cit.rules.len())
-            .find(|&i| stem(&cit, Some(i)) == Some("broken"))
-            .unwrap();
-        cit.keep_glints(|i| i != broken);
-        assert_eq!(layers(&cit), ["shown"]);
-        assert_eq!(cit.enchantments(&sword, Hand::Main, 0).len(), 1);
-        // None left: vanilla's glint stays.
-        cit.keep_glints(|_| false);
-        assert!(glint(&cit, &sword, false).is_none());
-    }
-
-    #[test]
-    fn an_off_hand_layer_draws_only_in_the_off_hand() {
-        let cit = rules(&[
-            ("left", "type=enchantment\nlayer=1\nhand=off"),
-            ("both", "type=enchantment"),
-        ]);
-        let sword = enchanted("diamond_sword", &[("sharpness", 1)]);
-        let layers = |hand| -> Vec<&str> {
-            let glint = cit.glint(&sword, hand, 0, true).unwrap();
-            glint
-                .layers
-                .iter()
-                .map(|l| stem(&cit, Some(l.rule)).unwrap())
-                .collect()
-        };
-        assert_eq!(layers(Hand::Off), ["both", "left"]);
-        // Asked in this order, a cache keyed without the hand would answer as for the off hand.
-        assert_eq!(layers(Hand::Main), ["both"]);
+        self.matcher.as_ref()?.glint(stack, hand, max_damage, foil)
    }
 }
@@ -6,8 +6,8 @@
 //! chestplate, boots) and `entity/equipment/humanoid_leggings/diamond` (layer 2), so the layers
 //! are mapped back to the old names here. An elytra rule's `texture` replaces the wings'.

+use crate::cit::{Kind, Rule};
 use crate::cit_assets::{rule_sprites, sprite_id};
-use horizon_optifine::cit::{Kind, Rule};
 use std::collections::BTreeSet;

 /// The pre-1.21.2 armour texture name of an equipment asset's layer: `asset` (`minecraft:gold`
@@ -114,10 +114,9 @@ pub fn armor_sprites(rules: &[Rule]) -> BTreeSet<String> {
 #[cfg(test)]
 mod tests {
    use super::*;
-    use horizon_optifine::Properties;

    fn rule(path: &str, text: &str) -> Rule {
-        Rule::parse(path, &Properties::parse_equals_first(text), |_| true).unwrap()
+        crate::pack_formats::cit::parse_rule(path, text).unwrap()
    }

    #[test]
@@ -5,8 +5,8 @@
 //! `horizon_cit:minecraft/optifine/cit/swords/flame`). A file already under `textures/` (or
 //! `models/`) keeps its vanilla id, so it is not packed twice.

+use crate::cit::{Kind, Rule};
 use horizon_assets::model::{CuboidModel, TextureSlot};
-use horizon_optifine::cit::{Kind, Rule};
 use std::collections::{BTreeMap, BTreeSet};
 use std::fs;
 use std::path::Path;
@@ -55,7 +55,7 @@ pub fn model_id(resource: &str) -> Option<String> {
 /// and for one that would leave the resource root (a pack model may write any id).
 pub fn resource(id: &str, ext: &str) -> Option<String> {
    let rest = id.strip_prefix(NAMESPACE)?.strip_prefix(':')?;
-    horizon_optifine::paths::valid(rest).then(|| format!("assets/{rest}.{ext}"))
+    stays_in_root(rest).then(|| format!("assets/{rest}.{ext}"))
 }

 /// Sprite ids the rules whose kind passes `keep` draw: their `texture` and `texture.<name>`
@@ -102,7 +102,14 @@ fn relative(file: &str, value: &str, ext: &str) -> Option<String> {
        .and_then(|r| r.strip_suffix('.'))
        .unwrap_or(rest);
    let path = format!("{dir}/{rest}.{ext}");
-    horizon_optifine::paths::valid(&path).then_some(path)
+    stays_in_root(&path).then_some(path)
+}
+
+/// Whether a resource path stays in the root: no `.`, `..` or empty segment, and no `\` (a
+/// separator on Windows, where `..\..` would climb).
+fn stays_in_root(path: &str) -> bool {
+    path.split('/')
+        .all(|segment| !matches!(segment, "" | "." | "..") && !segment.contains('\\'))
 }

 /// The id a relative value of the model at `file` names, as `CuboidModel::from_json` read it
@@ -294,11 +301,11 @@ mod tests {
            "base.json",
            r#"{"parent":"item/handheld","textures":{"layer2":"./glow.png"}}"#,
        );
-        let props =
-            horizon_optifine::Properties::parse_equals_first("items=stick\nmodel=./swords/flame");
-        let rule = Rule::parse("assets/minecraft/optifine/cit/a.properties", &props, |p| {
-            root.join(p).is_file()
-        })
+        let rule = crate::pack_formats::cit::parse_rule_in(
+            &root,
+            "assets/minecraft/optifine/cit/a.properties",
+            "items=stick\nmodel=./swords/flame",
+        )
        .unwrap();
        let models = load_models(&root, &[rule]);
        let _ = fs::remove_dir_all(&root);
@@ -1,26 +1,6 @@
-//! Custom Item Textures' enchantment glints (`type=enchantment`): which of a stack's matching
-//! rules draw, in which order and how strongly, and whether vanilla's glint still draws under
-//! them. The pack's `cit.properties` (`Global`) says how layers share an item.
-//!
-//! Written from OptiFine's `cit.properties` doc and CIT Resewn's (MIT) `TypeEnchantment` of
-//! before its 1.21.11 port, which implemented `method`, `cap` and `fade`: the sums and the
-//! cycle's fading follow it, except where noted.
-
-pub use horizon_optifine::cit::{Global, Method};
-
-use crate::cit::read_properties;
-use horizon_optifine::cit::Rule;
-use std::path::Path;
-
-/// The pack's global `cit.properties` under the overlay resource root: the first of
-/// `Global::PATHS` that exists, else the defaults.
-pub fn load_global(root: &Path) -> Global {
-    Global::PATHS
-        .iter()
-        .find_map(|path| read_properties(&root.join(path)))
-        .map(|props| Global::parse(&props))
-        .unwrap_or_default()
-}
+//! Custom item textures' enchantment glints: the layers a stack draws over (or instead of)
+//! vanilla's glint, and how strongly each draws over time. Which layers a stack gets is the pack
+//! format's ([`crate::cit::Matcher::glint`]); a layer's look is its rule's [`crate::cit::Glint`].

 /// One glint layer a stack draws.
 #[derive(Clone, Copy, Debug, PartialEq)]
@@ -33,6 +13,17 @@ pub struct GlintLayer {
    duration: f32,
 }

+impl GlintLayer {
+    /// Rule `rule`'s layer at `weight`, on for `duration` seconds when the layers take turns.
+    pub fn new(rule: usize, weight: f32, duration: f32) -> Self {
+        Self {
+            rule,
+            weight,
+            duration,
+        }
+    }
+}
+
 /// What a stack's glint is made of, worked out when the stack changes.
 #[derive(Clone, Debug, Default, PartialEq)]
 pub struct StackGlint {
@@ -45,84 +36,14 @@ pub struct StackGlint {
 }

 impl StackGlint {
-    /// The layers among `matched` (the stack's matching enchantment rules, in priority order,
-    /// as `CitRules::enchantments` gives them) that draw, for a stack with `enchantments`
-    /// (`ItemStack::crafting_enchantments`).
-    pub fn new(
-        rules: &[Rule],
-        matched: &[usize],
-        enchantments: &[(impl AsRef<str>, u32)],
-        global: &Global,
-    ) -> Self {
-        // The highest priority rule of each layer.
-        let mut layers: Vec<usize> = Vec::new();
-        for &i in matched {
-            let layer = rules[i].glint.layer;
-            if !layers.iter().any(|&j| rules[j].glint.layer == layer) {
-                layers.push(i);
-            }
-        }
-        layers.sort_by_key(|&i| rules[i].glint.layer);
-        let cycle = global.method == Method::Cycle;
-        // OptiFine's doc: `cap` is for `average` and `layered`, and keeps the topmost layers.
-        // `none`, which OptiFine lacks, is capped too, as CIT Resewn caps every method (it keeps
-        // the bottom layers, though, and caps cycles as well).
-        if let Some(cap) = global.cap.filter(|_| !cycle) {
-            let cap = usize::try_from(cap).unwrap_or(usize::MAX);
-            layers = layers.split_off(layers.len().saturating_sub(cap));
-        }
-        // CIT Resewn: any layer left asking for vanilla's glint keeps it, and the global
-        // `useGlint=false` removes it everywhere, as OptiFine's doc says too. `cap=0` leaves no
-        // custom layer, and vanilla's glint only if the pack's `useGlint` allows it.
-        let vanilla = global.use_glint
-            && (layers.is_empty() || layers.iter().any(|&i| rules[i].glint.use_glint));
-        // CIT Resewn: shares are against every enchantment of the stack, not only those the
-        // layers name.
-        let levels = enchantments.iter().map(|(_, level)| *level as f32);
-        let total = match global.method {
-            Method::Average => levels.sum::<f32>(),
-            Method::Layered => levels.fold(0.0, f32::max),
-            Method::None | Method::Cycle => 0.0,
-        };
-        let shared = matches!(global.method, Method::Average | Method::Layered);
-        let layers = layers
-            .into_iter()
-            .map(|i| {
-                let rule = &rules[i];
-                let named = &rule.enchantments;
-                let weight = if !shared || named.is_empty() {
-                    1.0
-                } else {
-                    // The highest level among the enchantments the rule names whose level also
-                    // passes its `enchantmentLevels` (CIT Resewn takes the first named one the
-                    // stack has, whatever its level).
-                    let in_range = |level: u32| {
-                        let level = i32::try_from(level).unwrap_or(i32::MAX);
-                        rule.enchantment_levels
-                            .as_ref()
-                            .is_none_or(|r| r.contains(level))
-                    };
-                    let level = enchantments
-                        .iter()
-                        .filter(|(id, level)| {
-                            let id: &str = id.as_ref();
-                            named.iter().any(|n| n == id) && in_range(*level)
-                        })
-                        .map(|(_, level)| *level as f32)
-                        .fold(0.0, f32::max);
-                    if total > 0.0 { level / total } else { 0.0 }
-                };
-                GlintLayer {
-                    rule: i,
-                    weight,
-                    duration: rule.glint.duration,
-                }
-            })
-            .collect();
+    /// `layers`, bottom first; `vanilla` whether vanilla's glint draws under them; `cycle_fade`
+    /// the seconds each layer fades into the next when they take turns, else `None` (each
+    /// draws at its weight).
+    pub fn from_parts(layers: Vec<GlintLayer>, vanilla: bool, cycle_fade: Option<f32>) -> Self {
        Self {
            layers,
            vanilla,
-            cycle_fade: cycle.then_some(global.fade),
+            cycle_fade,
        }
    }

@@ -179,208 +100,3 @@ fn cycle_intensity(layers: &[GlintLayer], fade: f32, index: usize, seconds: f64)
    // Not reached, as the last layer returns above; no layer rather than a panic.
    0.0
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use horizon_optifine::Properties;
-
-    const DIR: &str = "assets/minecraft/optifine/cit";
-
-    /// An enchantment rule named `name` with `text` after `type` and `texture`.
-    fn rule(name: &str, text: &str) -> Rule {
-        let text = format!("type=enchantment\ntexture=glint\n{text}");
-        let path = format!("{DIR}/{name}.properties");
-        Rule::parse(&path, &Properties::parse_equals_first(&text), |_| true).unwrap()
-    }
-
-    fn global(text: &str) -> Global {
-        Global::parse(&Properties::parse_equals_first(text))
-    }
-
-    fn rules_of(layers: &StackGlint) -> Vec<usize> {
-        layers.layers.iter().map(|l| l.rule).collect()
-    }
-
-    const SWORD: [(&str, u32); 2] = [("minecraft:sharpness", 3), ("minecraft:unbreaking", 1)];
-
-    #[test]
-    fn one_rule_per_layer_bottom_first() {
-        let rules = [
-            rule("a", "layer=2"),
-            rule("b", "layer=0"),
-            rule("c", "layer=2"),
-            rule("d", "layer=-1"),
-        ];
-        // Priority order a, b, c, d: c loses layer 2 to a.
-        let g = StackGlint::new(&rules, &[0, 1, 2, 3], &SWORD, &Global::default());
-        assert_eq!(rules_of(&g), [3, 1, 0]);
-        let g = StackGlint::new(&rules, &[2, 0], &SWORD, &Global::default());
-        assert_eq!(rules_of(&g), [2]);
-    }
-
-    #[test]
-    fn average_and_layered_shares() {
-        let rules = [
-            rule("sharp", "enchantments=sharpness smite"),
-            rule("unb", "layer=1\nenchantments=unbreaking"),
-            rule("any", "layer=2"),
-            rule("fire", "layer=3\nenchantments=fire_aspect"),
-        ];
-        let weights = |method: &str| {
-            let g = StackGlint::new(&rules, &[0, 1, 2, 3], &SWORD, &global(method));
-            g.layers.iter().map(|l| l.weight).collect::<Vec<_>>()
-        };
-        // Sharpness III and Unbreaking I: 3 / 4 and 1 / 4; against the highest, 3 / 3 and 1 / 3.
-        // A rule naming no enchantment is at full strength, one the stack lacks at none.
-        assert_eq!(weights("method=average"), [0.75, 0.25, 1.0, 0.0]);
-        assert_eq!(weights("method=layered"), [1.0, 1.0 / 3.0, 1.0, 0.0]);
-        assert_eq!(weights("method=cycle"), [1.0; 4]);
-        assert_eq!(weights("method=none"), [1.0; 4]);
-    }
-
-    #[test]
-    fn the_level_is_one_the_rules_levels_allow() {
-        let rules = [rule(
-            "holy",
-            "enchantments=sharpness smite\nenchantmentLevels=1-2",
-        )];
-        // Sharpness V is out of range, so Smite I sets the share: 1 / 5 of the highest level.
-        let stack = [("minecraft:sharpness", 5), ("minecraft:smite", 1)];
-        let g = StackGlint::new(&rules, &[0], &stack, &global("method=layered"));
-        assert_eq!(g.layers[0].weight, 1.0 / 5.0);
-    }
-
-    #[test]
-    fn cap_keeps_the_topmost_layers() {
-        let rules = [
-            rule("a", "layer=0"),
-            rule("b", "layer=1"),
-            rule("c", "layer=2"),
-        ];
-        let g = StackGlint::new(&rules, &[0, 1, 2], &SWORD, &global("cap=2"));
-        assert_eq!(rules_of(&g), [1, 2]);
-        let g = StackGlint::new(&rules, &[0, 1, 2], &SWORD, &global("cap=0"));
-        assert!(g.is_empty());
-        let g = StackGlint::new(&rules, &[0, 1, 2], &SWORD, &global("cap=1\nmethod=none"));
-        assert_eq!(rules_of(&g), [2]);
-        // Cycles show every layer in turn.
-        let g = StackGlint::new(&rules, &[0, 1, 2], &SWORD, &global("cap=1\nmethod=cycle"));
-        assert_eq!(rules_of(&g), [0, 1, 2]);
-    }
-
-    #[test]
-    fn vanilla_glint() {
-        let plain = rule("plain", "");
-        let keep = rule("keep", "layer=1\nuseGlint=true");
-        let rules = [plain, keep];
-        let vanilla = |matched: &[usize], text: &str| {
-            StackGlint::new(&rules, matched, &SWORD, &global(text)).vanilla
-        };
-        assert!(vanilla(&[], ""), "no rule: vanilla's glint");
-        assert!(!vanilla(&[0], ""), "a rule replaces it");
-        assert!(vanilla(&[0, 1], ""), "unless one keeps it");
-        assert!(!vanilla(&[], "useGlint=false"));
-        assert!(!vanilla(&[1], "useGlint=false"), "the pack's word is final");
-        // Only the layers `cap` keeps count.
-        let rules = [rule("keep", "useGlint=true"), rule("top", "layer=1")];
-        let g = StackGlint::new(&rules, &[0, 1], &SWORD, &global("cap=1"));
-        assert!(!g.vanilla);
-        let g = StackGlint::new(&rules, &[0, 1], &SWORD, &global("cap=0"));
-        assert!(g.is_empty() && g.vanilla);
-        let g = StackGlint::new(&rules, &[0, 1], &SWORD, &global("cap=0\nuseGlint=false"));
-        assert!(!g.vanilla);
-    }
-
-    #[test]
-    fn cycles_take_turns_and_fade() {
-        let rules = [
-            rule("a", "duration=2"),
-            rule("b", "layer=1\nduration=1"),
-            rule("c", "layer=2\nduration=1"),
-        ];
-        let g = StackGlint::new(
-            &rules,
-            &[0, 1, 2],
-            &SWORD,
-            &global("method=cycle\nfade=0.5"),
-        );
-        // a 0-2, a→b 2-2.5, b 2.5-3.5, b→c 3.5-4, c 4-5, c→a 5-5.5, then again.
-        let at = |t: f64| [0, 1, 2].map(|i| g.intensity(i, t));
-        assert_eq!(at(1.0), [1.0, 0.0, 0.0]);
-        assert_eq!(at(2.125), [0.75, 0.25, 0.0]);
-        assert_eq!(at(3.0), [0.0, 1.0, 0.0]);
-        assert_eq!(at(3.75), [0.0, 0.5, 0.5]);
-        assert_eq!(at(4.5), [0.0, 0.0, 1.0]);
-        assert_eq!(at(5.25), [0.5, 0.0, 0.5]);
-        assert_eq!(at(5.5 + 3.0), [0.0, 1.0, 0.0]);
-        // One layer always shows.
-        let one = StackGlint::new(&rules, &[1], &SWORD, &global("method=cycle"));
-        assert_eq!(one.intensity(0, 0.7), 1.0);
-    }
-
-    #[test]
-    fn a_cycle_always_shows_a_whole_layer() {
-        let rules = [
-            rule("a", "duration=0.1"),
-            rule("b", "layer=1\nduration=0.7"),
-            rule("c", "layer=2\nduration=0.2"),
-        ];
-        let g = StackGlint::new(
-            &rules,
-            &[0, 1, 2],
-            &SWORD,
-            &global("method=cycle\nfade=0.3"),
-        );
-        // Every millisecond of the first two seconds, and just under a period, the last fade's
-        // end. (Rounding has not been seen to leave time past it; the last fade's clamp is
-        // defensive.)
-        let period: f64 = [0.1f32, 0.7, 0.2]
-            .map(|d| f64::from(d) + f64::from(0.3f32))
-            .iter()
-            .sum();
-        let last = f64::from_bits(period.to_bits() - 1);
-        for t in (0..2000_i32)
-            .map(|i| f64::from(i) * 0.001)
-            .chain([last, period + last])
-        {
-            let sum: f32 = (0..3).map(|i| g.intensity(i, t)).sum();
-            assert!((sum - 1.0).abs() < 1e-5, "{sum} at {t}");
-        }
-        // No time at all: the bottom layer alone, never NaN.
-        let still = [rule("a", "duration=0"), rule("b", "layer=1\nduration=0")];
-        let g = StackGlint::new(&still, &[0, 1], &SWORD, &global("method=cycle\nfade=0"));
-        for t in [0.0, 0.5, 7.25] {
-            assert_eq!([0, 1].map(|i| g.intensity(i, t)), [1.0, 0.0]);
-        }
-    }
-
-    #[test]
-    fn the_first_global_file_wins() {
-        let root = std::env::temp_dir().join(format!("horizon-cit-glint-{}", std::process::id()));
-        let _ = std::fs::remove_dir_all(&root);
-        assert_eq!(load_global(&root), Global::default());
-        let write = |path: &str, text: &[u8]| {
-            let file = root.join(path);
-            std::fs::create_dir_all(file.parent().unwrap()).unwrap();
-            std::fs::write(file, text).unwrap();
-        };
-        // Saved as Latin-1 (`é` is not UTF-8 alone), in the OptiFine doc's `cit/` folder.
-        write(
-            "assets/minecraft/optifine/cit/cit.properties",
-            b"# caf\xE9\nmethod=cycle",
-        );
-        assert_eq!(load_global(&root).method, Method::Cycle);
-        write("assets/minecraft/mcpatcher/cit.properties", b"method=none");
-        assert_eq!(load_global(&root).method, Method::Cycle);
-        write(
-            "assets/minecraft/optifine/cit.properties",
-            b"method=layered",
-        );
-        assert_eq!(load_global(&root).method, Method::Layered);
-        write("assets/minecraft/citresewn/cit.properties", b"cap=1");
-        let g = load_global(&root);
-        let _ = std::fs::remove_dir_all(&root);
-        assert_eq!((g.method, g.cap), (Method::Average, Some(1)));
-    }
-}
@@ -121,8 +121,8 @@ impl CommandBlock {
            condition_met: flag("conditionMet", false),
        }
    }
-    /// `CommandBlockEntity.saveAdditional`. The last output is written as a
-    /// plain string component.
+    /// `CommandBlockEntity.saveAdditional`. The last output is the component
+    /// itself (`ComponentSerialization.CODEC`), styles and click events kept.
    pub fn save(&self) -> Vec<(&'static str, Tag)> {
        let mut out = vec![
            ("Command", Tag::String(self.command.as_str().into())),
@@ -135,7 +135,7 @@ impl CommandBlock {
        if self.track_output
            && let Some(last) = &self.last_output
        {
-            out.push(("LastOutput", Tag::String(last.plain().as_str().into())));
+            out.push(("LastOutput", scoreboard::component_tag(&last.component())));
        }
        out.push((
            "UpdateLastExecution",
@@ -43,6 +43,11 @@ pub fn enter_native_mod(call: NativeModCall) -> NativeModGuard {
    }
 }

+/// The native mod call this thread is currently inside, if any.
+pub fn current_native_mod() -> Option<NativeModCall> {
+    IN_NATIVE_MOD.with(Cell::get)
+}
+
 /// Puts back the call that `enter_native_mod` found.
 #[must_use]
 pub struct NativeModGuard {
@@ -244,7 +249,7 @@ fn arch_label(build: &str, machine: &str) -> String {
 }

 /// `PRETTY_NAME` of /etc/os-release and the kernel, or the system's own version string.
-fn operating_system() -> String {
+pub(crate) fn operating_system() -> String {
    let arch = arch_label(std::env::consts::ARCH, machine_arch());
    let version = if cfg!(target_os = "linux") {
        let name = read("/etc/os-release").and_then(|t| {
@@ -1,27 +1,34 @@
-//! OptiFine custom skies (`horizon_optifine::sky`) as the game draws them: a pack's layers with
-//! their decoded textures, read once with the pack, and each frame's choice of layers, their
-//! brightness and rotation ([`CustomSky::draws`]), which `gfx::custom_sky` draws over the
-//! vanilla sky. A pack without `optifine/sky` gives an empty [`CustomSky`] and the sky stays
-//! vanilla.
+//! Custom sky layers: skyboxes a pack draws over the vanilla sky, in a format vanilla doesn't read
+//! (OptiFine's), which the platform's pack formats fill ([`crate::pack_hooks`]). The layers'
+//! textures are read once with the pack; each frame the game asks for the layers to draw, their
+//! brightness and rotation ([`SkyLayers::draws`]), and `gfx::custom_sky` draws them over the
+//! vanilla sky. A pack without layers keeps the vanilla sky.

 use std::path::Path;
+use std::sync::Arc;

-use glam::{Mat4, Vec3};
-use horizon_optifine::sky::{Blend, Conditions, Skies, SkyLayer, Transition};
+use glam::Mat4;

-/// A layer's texture, RGBA8.
+/// A layer's texture, RGBA8: the skybox's six faces in a 3x2 grid, bottom, top and south in the
+/// top row, west, north and east below (`gfx::custom_sky`'s faces).
 pub struct Image {
    pub width: u32,
    pub height: u32,
    pub rgba: Vec<u8>,
 }

-/// The pack's layers, by world, with one texture per layer (`images[i]` for the `i`th layer
-/// over all worlds, in `worlds` order).
-#[derive(Default)]
-pub struct CustomSky {
-    worlds: Vec<(i32, Vec<SkyLayer>)>,
-    pub images: Vec<Image>,
+/// How a layer mixes with what is drawn below it.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Blend {
+    Add,
+    Subtract,
+    Multiply,
+    Dodge,
+    Burn,
+    Screen,
+    Replace,
+    Overlay,
+    Alpha,
 }

 /// One layer of a frame: which texture, with which blend, how bright and turned how.
@@ -34,62 +41,44 @@ pub struct Draw {
    pub rotation: Mat4,
 }

+/// The weather of a frame: thunder is a storm's rain, so it is only `Thunder`.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Weather {
+    Clear,
+    Rain,
+    Thunder,
+}
+
+/// What a frame's layers may depend on.
+#[derive(Clone, Copy, Debug)]
+pub struct Conditions<'a> {
+    /// Ticks of the day, counting the days.
+    pub day_time: i64,
+    pub weather: Weather,
+    /// The biome at the camera, namespaced.
+    pub biome: &'a str,
+    /// The camera's block height.
+    pub y: i32,
+}
+
 /// The eased brightness of each layer, kept by the game between frames.
 #[derive(Default)]
 pub struct State {
-    world: Option<i32>,
-    eased: Vec<Transition>,
+    /// The world the layers were last drawn for.
+    pub world: Option<i32>,
+    /// Each layer's eased visibility, 0 to 1.
+    pub eased: Vec<f32>,
 }

-/// Textures past this many texels in all are left out (a skybox is a few megapixels at most).
-const TEXEL_BUDGET: u64 = 64 << 20;
-
-impl CustomSky {
-    /// The custom skies of the overlay at `root`. A layer whose texture does not decode is
-    /// dropped with a warning.
-    pub fn load(root: &Path) -> Self {
-        let skies = Skies::scan(root);
-        let mut out = Self::default();
-        let mut texels = 0u64;
-        for (world, sky) in skies.worlds {
-            let mut layers = Vec::new();
-            for layer in sky.layers {
-                match crate::hud::decode(&root.join(&layer.source)) {
-                    Ok((width, height, rgba))
-                        if texels + u64::from(width) * u64::from(height) <= TEXEL_BUDGET =>
-                    {
-                        texels += u64::from(width) * u64::from(height);
-                        out.images.push(Image {
-                            width,
-                            height,
-                            rgba,
-                        });
-                        layers.push(layer);
-                    }
-                    Ok(_) => log::warn!("{}: past the custom sky's texture budget", layer.source),
-                    Err(e) => log::warn!("{}: {e:#}", layer.source),
-                }
-            }
-            if !layers.is_empty() {
-                out.worlds.push((world, layers));
-            }
-        }
-        out
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.worlds.is_empty()
-    }
-
-    /// Whether `world` has layers (`0` the Overworld, `1` the End).
-    pub fn has(&self, world: i32) -> bool {
-        self.worlds.iter().any(|(w, _)| *w == world)
-    }
-
-    /// This frame's layers of `world` into `out` (cleared first), in drawing order: those whose
-    /// conditions hold, eased over their `transition` by `seconds` since the last frame, at the
-    /// brightness of their fade times. `sun_turns` is the sun's angle over 360° (`0` at noon).
-    pub fn draws(
+/// A pack's custom sky layers, by world (`0` the Overworld, `1` the End).
+pub trait SkyLayers: Send + Sync {
+    /// Every layer's texture: [`Draw::image`] indexes it.
+    fn images(&self) -> &[Image];
+    /// Whether `world` has layers.
+    fn has(&self, world: i32) -> bool;
+    /// This frame's layers of `world` into `out` (cleared first), in drawing order, eased by
+    /// `seconds` since the last frame. `sun_turns` is the sun's angle over 360° (`0` at noon).
+    fn draws(
        &self,
        world: i32,
        conditions: &Conditions,
@@ -97,147 +86,30 @@ impl CustomSky {
        seconds: f32,
        state: &mut State,
        out: &mut Vec<Draw>,
-    ) {
+    );
+}
+
+/// No layers: the vanilla sky.
+struct NoLayers;
+
+impl SkyLayers for NoLayers {
+    fn images(&self) -> &[Image] {
+        &[]
+    }
+
+    fn has(&self, _: i32) -> bool {
+        false
+    }
+
+    fn draws(&self, _: i32, _: &Conditions, _: f32, _: f32, s: &mut State, out: &mut Vec<Draw>) {
        out.clear();
-        let mut first = 0;
-        let mut found = None;
-        for (w, layers) in &self.worlds {
-            if *w == world {
-                found = Some(layers);
-                break;
-            }
-            first += layers.len();
-        }
-        let Some(layers) = found else {
-            state.world = None;
-            return;
-        };
-        // A new world (or pack) starts each layer where its conditions put it: no fade in.
-        let snap = state.world != Some(world) || state.eased.len() != layers.len();
-        if snap {
-            state.world = Some(world);
-            state.eased.clear();
-            state.eased.resize(layers.len(), Transition::default());
-        }
-        for (i, (layer, eased)) in layers.iter().zip(&mut state.eased).enumerate() {
-            let target = if layer.shows(conditions) { 1.0 } else { 0.0 };
-            let shown = if snap {
-                eased.value = target;
-                target
-            } else {
-                eased.step(target, seconds, layer.transition)
-            };
-            let brightness = shown * layer.brightness(conditions.day_time);
-            if brightness <= 0.0 {
-                continue;
-            }
-            let turns = layer.turns(conditions.day_time, sun_turns);
-            let rotation = if turns == 0.0 {
-                Mat4::IDENTITY
-            } else {
-                Mat4::from_axis_angle(Vec3::from_array(layer.axis), turns * std::f32::consts::TAU)
-            };
-            out.push(Draw {
-                image: (first + i) as u16,
-                blend: layer.blend,
-                brightness,
-                rotation,
-            });
-        }
+        s.world = None;
    }
 }

-#[cfg(test)]
-mod tests {
-    use super::*;
-    use horizon_optifine::sky::Now;
-
-    fn pack(files: &[(&str, &str)]) -> (std::path::PathBuf, CustomSky) {
-        let root = std::env::temp_dir().join(format!(
-            "horizon-custom-sky-{}-{}",
-            std::process::id(),
-            files.len()
-        ));
-        let _ = std::fs::remove_dir_all(&root);
-        let dir = root.join("assets/minecraft/optifine/sky/world0");
-        std::fs::create_dir_all(&dir).unwrap();
-        let png = {
-            let mut bytes = Vec::new();
-            let mut encoder = png::Encoder::new(&mut bytes, 6, 4);
-            encoder.set_color(png::ColorType::Rgba);
-            encoder.set_depth(png::BitDepth::Eight);
-            let mut writer = encoder.write_header().unwrap();
-            writer
-                .write_image_data(&[255, 0, 0, 255].repeat(24))
-                .unwrap();
-            writer.finish().unwrap();
-            bytes
-        };
-        for (name, text) in files {
-            std::fs::write(dir.join(format!("{name}.properties")), text).unwrap();
-            std::fs::write(dir.join(format!("{name}.png")), &png).unwrap();
-        }
-        let sky = CustomSky::load(&root);
-        (root, sky)
-    }
-
-    fn noon(biome: &str) -> Conditions<'_> {
-        Conditions {
-            day_time: 6000,
-            weather: Now::Clear,
-            biome,
-            y: 64,
-        }
-    }
-
-    #[test]
-    fn layers_ease_in_at_a_biome_border_but_not_on_arrival() {
-        let (root, sky) = pack(&[
-            ("sky1", "biomes=desert\ntransition=2"),
-            ("sky2", "blend=alpha\nrotate=false"),
-        ]);
-        let _ = std::fs::remove_dir_all(root);
-        assert!(sky.has(0) && !sky.has(1));
-        assert_eq!(sky.images[0].width, 6);
-        let (mut state, mut out) = (State::default(), Vec::new());
-        sky.draws(
-            0,
-            &noon("minecraft:desert"),
-            0.0,
-            0.05,
-            &mut state,
-            &mut out,
-        );
-        assert_eq!(
-            out.iter().map(|d| d.brightness).collect::<Vec<_>>(),
-            [1.0, 1.0]
-        );
-        // Out of the desert: the first layer fades over its two seconds.
-        sky.draws(0, &noon("minecraft:plains"), 0.0, 0.5, &mut state, &mut out);
-        assert_eq!(out[0].brightness, 0.75);
-        assert_eq!(out[1].blend, Blend::Alpha);
-        sky.draws(0, &noon("minecraft:plains"), 0.0, 2.0, &mut state, &mut out);
-        assert_eq!(out.len(), 1, "a dark layer is not drawn");
-        assert_eq!(out[0].image, 1);
-        // Into the End, which has no layers, and back: no fade.
-        sky.draws(1, &noon("minecraft:desert"), 0.0, 0.0, &mut state, &mut out);
-        assert!(out.is_empty());
-        sky.draws(0, &noon("minecraft:desert"), 0.0, 0.0, &mut state, &mut out);
-        assert_eq!(out.len(), 2);
-    }
-
-    #[test]
-    fn a_layer_turns_west_like_the_sun() {
-        let (root, sky) = pack(&[("sky1", "")]);
-        let _ = std::fs::remove_dir_all(root);
-        let (mut state, mut out) = (State::default(), Vec::new());
-        // A quarter turn after noon (sunset): the skybox's zenith has gone down to the west.
-        let c = Conditions {
-            day_time: 12000,
-            ..noon("minecraft:plains")
-        };
-        sky.draws(0, &c, 0.25, 0.0, &mut state, &mut out);
-        let up = out[0].rotation.transform_vector3(Vec3::Y);
-        assert!((up - Vec3::NEG_X).length() < 1e-5, "{up}");
-    }
+/// The custom sky layers of the overlay at `root`, from the installed pack formats.
+pub fn load(root: &Path) -> Arc<dyn SkyLayers> {
+    crate::pack_hooks::formats()
+        .custom_sky(root)
+        .unwrap_or_else(|| Arc::new(NoLayers))
 }
@@ -0,0 +1,271 @@
+//! Entity textures a pack format vanilla doesn't read changes (OptiFine's random entities, ETF's
+//! blinking and emissive textures): the variants of each texture and how an entity picks one,
+//! the blink frames a texture shows now and then, and the overlays that glow over a texture.
+//! The platform's pack formats fill them once per pack load ([`crate::pack_hooks`]); drawing
+//! only looks them up in these tables.
+//!
+//! Textures have the names the entity atlas gives them (`entity/zombie/zombie`,
+//! `<ns>:<path>`); files outside `textures/` are listed with the name they take
+//! ([`RandomTextures::files`], [`Blinks::files`], [`Emissive::files`]) for the atlas to pack.
+
+use std::collections::{BTreeMap, HashMap};
+use std::path::Path;
+
+/// A pack's entity texture changes: variants, blinks and emissive overlays.
+#[derive(Debug, Default)]
+pub struct EntityTextures {
+    pub random: RandomTextures,
+    pub blinks: Blinks,
+    pub emissive: Emissive,
+}
+
+impl EntityTextures {
+    /// The changes of the overlay at `root`, from the installed pack formats.
+    pub fn load(root: &Path) -> Self {
+        crate::pack_hooks::formats()
+            .entity_textures(root)
+            .unwrap_or_default()
+    }
+}
+
+/// What a variant rule can ask about an entity. `None` is a fact the entity doesn't have (a
+/// creeper's profession): a rule asking for it doesn't match.
+#[derive(Clone, Debug, Default)]
+pub struct Facts<'a> {
+    /// Where the entity was first seen: its biome (`minecraft:plains`) and block height.
+    pub biome: Option<&'a str>,
+    pub y: Option<i32>,
+    /// The block it stood on and the block it stood in when first seen; empty when unknown.
+    pub blocks: &'a [Block<'a>],
+    /// Its custom name, with `§` formatting codes where the name has them.
+    pub name: Option<&'a str>,
+    /// Villager profession (`minecraft:farmer`) and level.
+    pub profession: Option<(&'a str, i32)>,
+    /// Collar, wool, carpet or shell colour, as a dye name (`light_blue`).
+    pub color: Option<&'a str>,
+    pub baby: Option<bool>,
+    /// Health and max health.
+    pub health: Option<(f32, f32)>,
+    /// When first seen: moon phase (0-7), time of day (0-23999) and weather.
+    pub moon_phase: Option<i32>,
+    pub day_time: Option<i32>,
+    pub weather: Option<Weather>,
+    /// Slime, magma cube or phantom size: 0 small, 1 medium, 3 big.
+    pub size: Option<i32>,
+}
+
+/// A block and the values of its state properties.
+#[derive(Clone, Copy, Debug)]
+pub struct Block<'a> {
+    pub id: &'a str,
+    pub states: &'a [(&'a str, &'a str)],
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Weather {
+    Clear,
+    Rain,
+    Thunder,
+}
+
+/// How a pack format's rule files choose a variant.
+pub trait VariantRules: Send + Sync {
+    /// The variant rule file `rules` ([`Entry::rules`]) gives an entity with these facts and
+    /// seed, `None` when no rule matches.
+    fn matching(&self, rules: usize, facts: &Facts, seed: i32) -> Option<u32>;
+}
+
+/// Every texture a pack varies, by its atlas name.
+#[derive(Default)]
+pub struct RandomTextures {
+    entries: HashMap<String, Entry>,
+    /// Every variant's file (from the resource root) and atlas name.
+    files: Vec<(String, String)>,
+    rules: Option<Box<dyn VariantRules>>,
+    generation: u64,
+}
+
+impl std::fmt::Debug for RandomTextures {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("RandomTextures")
+            .field("entries", &self.entries)
+            .field("generation", &self.generation)
+            .finish_non_exhaustive()
+    }
+}
+
+/// One texture's variants.
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct Entry {
+    /// The rule file that chooses this texture's variant ([`RandomTextures::matching`]).
+    pub rules: Option<usize>,
+    /// The atlas name of each variant, by its number.
+    pub variants: BTreeMap<u32, String>,
+}
+
+impl RandomTextures {
+    /// `entries` by atlas name, their variants' `files` (file, atlas name), the rule files
+    /// `rules` that choose, and `generation`: different for every load (never 0), so choices
+    /// made from another load's rules are known to be stale.
+    pub fn new(
+        entries: HashMap<String, Entry>,
+        files: Vec<(String, String)>,
+        rules: Box<dyn VariantRules>,
+        generation: u64,
+    ) -> Self {
+        Self {
+            entries,
+            files,
+            rules: Some(rules),
+            generation,
+        }
+    }
+
+    /// This load's number; 0 for the empty set.
+    pub fn generation(&self) -> u64 {
+        self.generation
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.entries.is_empty()
+    }
+
+    /// The variants of the texture with this atlas name.
+    pub fn get(&self, texture: &str) -> Option<&Entry> {
+        self.entries.get(texture)
+    }
+
+    /// [`VariantRules::matching`].
+    pub fn matching(&self, rules: usize, facts: &Facts, seed: i32) -> Option<u32> {
+        self.rules.as_ref()?.matching(rules, facts, seed)
+    }
+
+    /// Every variant's file (its path from the resource root) and atlas name, for the entity
+    /// atlas to pack.
+    pub fn files(&self) -> impl Iterator<Item = (&str, &str)> {
+        self.files.iter().map(|(f, n)| (f.as_str(), n.as_str()))
+    }
+}
+
+impl Entry {
+    /// The atlas name of variant `index`, or `None` for the texture itself.
+    pub fn texture(&self, index: u32) -> Option<&str> {
+        self.variants.get(&index).map(String::as_str)
+    }
+
+    /// The even choice of an entity with this seed when no rules apply: the texture and its
+    /// variants 2, 3... up to the first missing one.
+    pub fn even(&self, seed: i32) -> u32 {
+        let mut count = 1;
+        while self.variants.contains_key(&(count + 1)) {
+            count += 1;
+        }
+        seed.unsigned_abs() % count + 1
+    }
+}
+
+/// An entity's seed from its UUID (most then least significant 64 bits): Java's
+/// `UUID.hashCode`, so it is fixed for the entity's whole life, on every client.
+pub fn seed(most: i64, least: i64) -> i32 {
+    let x = most ^ least;
+    ((x >> 32) ^ x) as i32
+}
+
+/// The pack's blinking textures, by the atlas name of the texture they replace.
+#[derive(Debug, Default)]
+pub struct Blinks {
+    blinks: HashMap<String, Blink>,
+    /// The blink frames outside `textures/`: file and atlas name.
+    files: Vec<(String, String)>,
+}
+
+/// A texture's blink.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Blink {
+    /// The atlas names of the shut and half-shut frames.
+    pub shut: String,
+    pub half: Option<String>,
+    /// Ticks a blink lasts (at least 1) and ticks from one blink to the next (more).
+    pub length: u32,
+    pub frequency: u32,
+}
+
+impl Blinks {
+    /// `blinks` by the atlas name of the texture they replace, and the frames outside
+    /// `textures/` (file, atlas name).
+    pub fn new(blinks: HashMap<String, Blink>, files: Vec<(String, String)>) -> Self {
+        Self { blinks, files }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.blinks.is_empty()
+    }
+
+    pub fn get(&self, texture: &str) -> Option<&Blink> {
+        self.blinks.get(texture)
+    }
+
+    /// The frames outside `textures/`: file and atlas name, for the entity atlas to pack (it
+    /// walks `textures/` itself).
+    pub fn files(&self) -> impl Iterator<Item = (&str, &str)> {
+        self.files.iter().map(|(f, n)| (f.as_str(), n.as_str()))
+    }
+}
+
+impl Blink {
+    /// The frame an entity shows `tick` ticks into its life: `None` with its eyes open. `phase`
+    /// spreads entities' blinks apart. With a half-shut frame, the first and last ticks of a
+    /// blink of 3 or more show it.
+    pub fn frame(&self, tick: u32, phase: u32) -> Option<&str> {
+        let t = (u64::from(tick) + u64::from(phase)) % u64::from(self.frequency);
+        let t = t as u32;
+        if t >= self.length {
+            return None;
+        }
+        match &self.half {
+            Some(half) if self.length >= 3 && (t == 0 || t == self.length - 1) => Some(half),
+            _ => Some(&self.shut),
+        }
+    }
+}
+
+/// The pack's emissive overlays, by the atlas name of the texture they glow over.
+#[derive(Debug, Default)]
+pub struct Emissive {
+    /// The name ending of the pack's emissive textures (`_e`).
+    pub suffix: String,
+    overlays: HashMap<String, String>,
+    /// Overlays outside `textures/`: file and atlas name.
+    files: Vec<(String, String)>,
+}
+
+impl Emissive {
+    /// `overlays` (texture → overlay, atlas names) with name ending `suffix`, and those outside
+    /// `textures/` (file, atlas name).
+    pub fn new(
+        suffix: String,
+        overlays: HashMap<String, String>,
+        files: Vec<(String, String)>,
+    ) -> Self {
+        Self {
+            suffix,
+            overlays,
+            files,
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.overlays.is_empty()
+    }
+
+    /// The atlas name of the overlay that glows over `texture`.
+    pub fn overlay(&self, texture: &str) -> Option<&str> {
+        self.overlays.get(texture).map(String::as_str)
+    }
+
+    /// The overlays outside `textures/`: file (from the resource root) and atlas name, for the
+    /// entity atlas to pack (it walks `textures/` itself).
+    pub fn files(&self) -> impl Iterator<Item = (&str, &str)> {
+        self.files.iter().map(|(f, n)| (f.as_str(), n.as_str()))
+    }
+}
@@ -265,7 +265,7 @@ impl horizon_polytone::expr::Host for FrameHost<'_> {
            ("config", [horizon_polytone::expr::Value::Str(id)]) => self
                .configs
                .get(id)
-                .map(horizon_polytone::pack::ConfigValue::to_value)
+                .map(horizon_polytone::pack::config_value)
                .ok_or_else(|| format!("no config {id}")),
            _ => Err(format!(
                "{name} is not available in an attribute expression"
@@ -305,6 +305,9 @@ pub(crate) struct Colormap {
    /// (`temperature`, `downfall`, `biome_id`) blend: Polytone 6.8.6's water by `biome_id`
    /// fades over a biome edge.
    pub(crate) biome_blend: bool,
+    /// Its axes read nothing that changes up a column of one biome (no `o.y`): a section of
+    /// one biome can sample it once per column.
+    pub(crate) column: bool,
    width: u32,
    height: u32,
    rgba: Vec<u8>,
@@ -323,6 +326,18 @@ enum Axis {
 }

 impl Axis {
+    /// Whether the axis reads only what stays the same up a column of one biome.
+    fn column(&self) -> bool {
+        use horizon_polytone::expr::Root;
+        let flat = |root: Root, name: &str| match root {
+            Root::Object => matches!(name, "x" | "z" | "biome" | "temperature" | "downfall"),
+            Root::Random => name == "noise",
+            _ => false,
+        };
+        match self {
+            Self::Expr(program) | Self::BiomeId(_, program) => program.reads_only(&flat),
+        }
+    }
    fn value(&self, host: &mut dyn horizon_polytone::expr::Host) -> Option<f64> {
        match self {
            Self::Expr(program) => Some(program.eval(host).ok()?.num()),
@@ -373,6 +388,23 @@ fn biome_id_mapper(pack_root: &Path, json: &Json) -> HashMap<String, f64> {
 }

 impl Colormap {
+    /// One colour wherever it samples (a `biome_colors` flat colour, RGB).
+    pub(crate) fn flat(rgb: u32) -> Self {
+        let zero = || Axis::Expr(horizon_polytone::expr::Program::compile("0").expect("a number"));
+        let [_, r, g, b] = rgb.to_be_bytes();
+        Self {
+            x: zero(),
+            y: zero(),
+            triangular: false,
+            rounds: true,
+            biome_blend: false,
+            column: true,
+            width: 1,
+            height: 1,
+            rgba: vec![r, g, b, 255],
+        }
+    }
+
    /// `assets/<namespace>/polytone/colormaps/<path>.png` and its optional `.json` (without
    /// one, the axes are the biome's temperature and downfall).
    pub(crate) fn load(pack_root: &Path, id: &str) -> Option<Self> {
@@ -424,9 +456,11 @@ impl Colormap {
            axis("x_axis", "o.temperature")?,
            axis("y_axis", "o.downfall")?,
        );
+        let column = [&x, &y].iter().all(|axis| axis.column());
        Some(Self {
            x,
            y,
+            column,
            biome_blend: json["biome_blend"].as_bool().unwrap_or(by_biome),
            triangular: json["triangular"].as_bool() == Some(true),
            rounds: json["rounds"].as_bool() != Some(false),
@@ -1050,6 +1084,7 @@ mod tests {
        for (path, text) in pack {
            write(&format!("pack/{path}"), text);
        }
+        crate::pack_formats::install();
        let modifiers = PackModifiers::read(&dir.join("pack")).with_configs(
            crate::packs::polytone_configs(&crate::packs::Source::Dir(dir.join("pack"))),
        );
@@ -482,13 +482,16 @@ impl Extras {
        true
    }
    /// Written only once something differs from the defaults, so a vanilla
-    /// setup gains no file.
+    /// setup gains no file. The settings stores of this file follow these lines
+    /// (`horizon_hooks::settings`).
    pub fn save(&self, dir: &Path) {
        let path = dir.join(FILE);
-        if *self == Self::default() && !path.exists() {
+        let mut text = self.serialize();
+        let stores_default = horizon_hooks::settings::engine::append(FILE, &mut text);
+        if *self == Self::default() && stores_default && !path.exists() {
            return;
        }
-        let _ = fs::write(path, self.serialize());
+        let _ = fs::write(path, text);
    }
 }

@@ -231,8 +231,8 @@ pub struct FogInputs<'a> {
    /// `GameRenderer.nightVisionScale` while Night Vision is on without
    /// Darkness, else 0 (`FogRenderer.computeFogColor`'s brightenFactor).
    pub night_vision: f32,
-    /// The packs' Polytone `environment` fog settings.
-    pub environment: horizon_polytone::colors::Environment,
+    /// The packs' `environment` fog settings (Polytone's).
+    pub environment: crate::pack_palette::Environment,
 }

 /// `FogRenderer.setupFog` + `computeFogColor`.
@@ -581,7 +581,7 @@ mod tests {
        let tables = FogTables {
            water_fog_end: vec![1.0],
        };
-        let environment = horizon_polytone::colors::Environment {
+        let environment = crate::pack_palette::Environment {
            powder_snow_fog: Some(0xFF0000),
            blindness_fog_distance: 40.0,
            water_fog_brightening: 0.0,
@@ -613,7 +613,7 @@ mod tests {
    }
    fn inputs_with<'a>(
        input: &FogInputs<'a>,
-        environment: horizon_polytone::colors::Environment,
+        environment: crate::pack_palette::Environment,
    ) -> FogInputs<'a> {
        FogInputs {
            environment,
@@ -179,7 +179,7 @@ fn packed_wanted() -> bool {
    std::env::var("HORIZON_PACKED_QUADS").as_deref() != Ok("0")
 }

-mod animate;
+pub(crate) mod animate;
 mod arena;
 pub mod capture;
 pub mod compositor;
@@ -194,6 +194,7 @@ mod frame_gen;
 mod gpu_culling;
 mod hdr;
 mod hdr_icc;
+mod hdr_start;
 mod hdr_stats;
 pub(crate) mod hud_coverage;
 pub use hdr::{Calibration as HdrCalibration, Output as HdrOutput};
@@ -215,6 +216,7 @@ mod occlusion;
 mod oit;
 mod oit_features;
 pub(crate) mod output;
+mod output_apply;
 mod pack_atlas;
 mod pack_center_depth;
 pub mod pack_draw;
@@ -1327,7 +1329,7 @@ pub struct Renderer {
    celestial_buffer: wgpu::Buffer,
    end_sky: end_sky::EndSky,
    stars: stars::Stars,
-    /// OptiFine custom sky layers (`crate::custom_sky`), and the frame's from the game.
+    /// Custom sky layers (`crate::custom_sky`), and the frame's from the game.
    custom_sky: custom_sky::CustomSky,
    custom_sky_draws: Vec<crate::custom_sky::Draw>,
    /// The glowing entities' outline (`LevelRenderer.entityOutlineTarget`).
@@ -1526,6 +1528,10 @@ pub struct Renderer {
    emission_stats: hdr_stats::EmissionStats,
    /// What this renderer's destination offers and its device draws.
    output_caps: output::OutputCapabilities,
+    /// An output that failed to apply, not tried again until something it needs changes.
+    output_rejected: Option<output_apply::Rejected>,
+    /// Since when Auto keeps HDR on through the display's loss of its report.
+    auto_off_since: Option<std::time::Instant>,
    /// The output applied (`update_output`), with the frame every pipeline that draws it
    /// targets: the swapchain's 8-bit format, or `Rgba16Unorm` when the renderer was made with
    /// HDR output on and Smooth Gradients and the device draws and blends into it, or
@@ -1538,6 +1544,8 @@ pub struct Renderer {
    /// The marker file of an HDR output that has not presented a frame yet
    /// (`graphics::HDR_MARKER`).
    hdr_marker: Option<std::path::PathBuf>,
+    /// The window's graphics driver (`hdr_start`); `None` offscreen.
+    hdr_driver: Option<String>,
    /// The HDR Lighting setting, kept for the HDR output made when HDR turns on.
    hdr_lighting_setting: bool,
    /// The shader pack's post-processing, and the dimension (legacy id) it was loaded for.
@@ -2985,11 +2993,13 @@ impl Renderer {
            adapter.get_downlevel_capabilities().flags,
            adapter.get_texture_format_features(hud_coverage::FORMAT),
        );
+        let hdr_driver = surface.is_some().then(|| output::window_driver(&info));
        let output_caps = output::OutputCapabilities {
            hdr: hdr_output,
            wide_frame: wide_ok,
            float_frame: float_ok,
            hud_layer: coverage_ok,
+            held: output::held(settings, hdr_driver.as_deref()),
        };
        let frame = output::resolve_frame(settings, request, output_caps, display, config.format);
        let (frame_format, hud_coverage, overlay_format) =
@@ -4239,16 +4249,13 @@ impl Renderer {
            CRUMBLING_BLEND,
            false,
        );
-        // RenderPipelines.ENTITY_SHADOW: translucent, back-face culled, depth
-        // test without writes. The quads lie exactly on the block tops like
-        // vanilla's, facing +Y so looking up from below culls them, but
-        // terrain and shadows are separate draw paths, so their fp32 depth
-        // interpolations disagree by a few dozen ulps of the fragment depth
-        // and the shadow's rim z-fights with the block top (speckle that
-        // re-rolls as the camera drifts a subpixel). A constant bias of 128
-        // ulps covers that spread at any resolution while staying far below
-        // the 0.001 a model's feet sit higher, so shadows never bleed onto
-        // the feet.
+        // RenderPipelines.ENTITY_SHADOW: translucent, back-face culled, depth test without writes.
+        // The quads lie exactly on the block tops like vanilla's, facing +Y so looking up from
+        // below culls them, but terrain and shadows are separate draw paths, so their fp32 depth
+        // interpolations disagree by a few dozen ulps of the fragment depth and the shadow's rim
+        // z-fights with the block top (speckle that re-rolls as the camera drifts a subpixel). A
+        // constant bias of 128 ulps covers that spread at any resolution while staying far below
+        // the 0.001 a model's feet sit higher, so shadows never bleed onto the feet.
        let shadow_blob_pipeline = entity_pipeline_with(
            "Entity shadows",
            Some(wgpu::Face::Back),
@@ -5346,10 +5353,13 @@ impl Renderer {
            hdr_lighting_setting: true,
            emission_stats,
            output_caps,
+            output_rejected: None,
+            auto_off_since: None,
            // Nothing is presented as HDR yet: `update_output` applies the settings.
            output: output::resolve_output(settings, output_caps, display, frame, false),
            frame_kept_logged: false,
            hdr_marker: None,
+            hdr_driver,
            pack_post: None,
            pack_loading: None,
            native: None,
@@ -5507,18 +5517,18 @@ impl Renderer {
            ))
        });
    }
-    /// The pack's OptiFine custom sky layer textures (`crate::custom_sky::CustomSky::load`).
-    pub fn set_custom_sky(&mut self, pack: &crate::custom_sky::CustomSky) {
+    /// The pack's custom sky layer textures (`crate::custom_sky::load`).
+    pub fn set_custom_sky(&mut self, pack: &dyn crate::custom_sky::SkyLayers) {
        self.custom_sky.set_pack(&self.device, &self.queue, pack);
    }
-    /// The custom sky layers the next frame draws (`CustomSky::draws`): the game refills it each
+    /// The custom sky layers the next frame draws (`SkyLayers::draws`): the game refills it each
    /// frame, empty when the world's sky has none.
    pub fn custom_sky_draws(&mut self) -> &mut Vec<crate::custom_sky::Draw> {
        &mut self.custom_sky_draws
    }
    /// The resource packs' `core/rendertype_lines` (`HudAtlas::lines_shader`) for the block
    /// outline, or the built-in one.
-    pub fn set_lines_shader(&mut self, program: Option<&horizon_shaders::CoreProgram>) {
+    pub fn set_lines_shader(&mut self, program: Option<&crate::core_shader::CoreProgram>) {
        let format = self.output.frame.format;
        self.core_lines =
            program.and_then(|program| core_lines::CoreLines::new(&self.device, format, program));
@@ -5527,8 +5537,8 @@ impl Renderer {
    /// `stars_shader`), or the built-in sky and stars.
    pub fn set_sky_shaders(
        &mut self,
-        disc: Option<&horizon_shaders::CoreProgram>,
-        stars: Option<&horizon_shaders::CoreProgram>,
+        disc: Option<&crate::core_shader::CoreProgram>,
+        stars: Option<&crate::core_shader::CoreProgram>,
    ) {
        self.core_sky = core_sky::CoreSky::new(&self.device, self.output.frame.format, disc, stars);
    }
@@ -5631,6 +5641,7 @@ impl Renderer {
        }
        self.surface_unconfigured = configured.is_err();
        self.surface = Some(Arc::new(surface));
+        self.surface_recreated();
        Ok(())
    }
    /// The world's depth, which occlusion culling's test and post effects may read.
@@ -7083,18 +7094,6 @@ impl Renderer {
            horizon_hdr::set_metadata(&self.device, surface, hdr.declared_peak(), hdr.black);
        }
    }
-    /// The swapchain's configuration: `config` (what every pipeline draws in), or
-    /// HDR10 or scRGB while HDR output is on.
-    fn surface_config(&self) -> wgpu::SurfaceConfiguration {
-        let mut config = self.config.clone();
-        if let Some(hdr) = &self.hdr {
-            config.format = hdr.output.format();
-            config.view_formats = vec![hdr.output.format()];
-            config.color_space = hdr.output.color_space();
-            config.usage = wgpu::TextureUsages::RENDER_ATTACHMENT;
-        }
-        config
-    }
    /// This renderer's output as applied, with what its destination offers and reports.
    pub fn output(&self) -> &output::EffectiveOutput {
        &self.output
@@ -7149,106 +7148,11 @@ impl Renderer {
        output::resolve_frame(
            settings,
            request,
-            self.output_caps,
-            self.reading,
+            self.caps_for(settings),
+            output_apply::graced(self.auto_off_since, self.reading, &self.output),
            self.config.format,
        )
    }
-    /// Follows the selected mode even when Auto currently wants SDR. Off never asks
-    /// the system about the display; selecting On or Auto starts a fresh watch.
-    fn watch_hdr(&mut self, mode: crate::graphics::HdrMode) {
-        if mode == crate::graphics::HdrMode::Off {
-            self.display = None;
-            self.display_fresh = false;
-            self.reading.stop_watching();
-        } else if self.display.is_none() {
-            let (watch, now) =
-                DisplayWatch::new(&self.window, self.surface.as_deref(), &self.adapter);
-            self.display = Some(watch);
-            self.refresh_hdr_offer();
-            self.reading = now;
-            self.display_fresh = true;
-        }
-    }
-    /// What the window's surface offers now: Vulkan's offered formats can change with desktop
-    /// HDR or the window's output.
-    fn refresh_hdr_offer(&mut self) {
-        if let Some(surface) = &self.surface {
-            self.output_caps.hdr = hdr::output(&surface.get_capabilities(&self.adapter));
-        }
-    }
-    /// HDR output (Horizon setting) as `settings` ask for it on this renderer's frame
-    /// (`output::resolve_output`): HDR10 or scRGB at paper white, the world's highlights
-    /// expanded up to the peak. Off where the surface can't present it. Offscreen
-    /// (`hdr::offscreen_output`) the frame is drawn the same and its HDR screenshot taken,
-    /// but nothing is presented, and Auto takes its defaults: no display reports.
-    pub fn update_output(
-        &mut self,
-        settings: &crate::graphics::Graphics,
-        marker: &std::path::Path,
-    ) {
-        self.watch_hdr(settings.hdr);
-        let next = output::resolve_output(
-            settings,
-            self.output_caps,
-            self.reading,
-            self.output.frame,
-            self.surface.is_some() || self.offscreen.is_some(),
-        );
-        let [paper_white, peak, black] = next.nits;
-        if next.encoding.is_some() != self.hdr.is_some() {
-            // If the game dies before HDR output shows a frame, the marker is still there at
-            // the next start, which then comes up with HDR off.
-            if next.encoding.is_some() {
-                if self.surface.is_some() {
-                    let _ = std::fs::write(marker, "HDR output was being switched on\n");
-                    self.hdr_marker = Some(marker.to_owned());
-                }
-            } else if let Some(marker) = self.hdr_marker.take() {
-                let _ = std::fs::remove_file(marker);
-            }
-            let frame = self.output.frame;
-            self.hdr = next.encoding.map(|output| {
-                hdr::Hdr::new(
-                    &self.device,
-                    &self.queue,
-                    frame.format,
-                    output,
-                    frame.hud_layer,
-                )
-            });
-            if let Some(hdr) = &mut self.hdr {
-                hdr.look = self.hdr_lighting_setting;
-            }
-            self.configure_surface();
-            match next.encoding {
-                Some(output) => log::info!(
-                    "Horizon renderer: HDR on: {} ({:?}), {paper_white}/{peak} nits",
-                    output.name(),
-                    output.format()
-                ),
-                None => log::info!("Horizon renderer: HDR off"),
-            }
-            self.measure_emission();
-        }
-        if let Some(hdr) = &mut self.hdr {
-            hdr.ui = next.ui_brightness;
-        }
-        if let Some(hdr) = &mut self.hdr
-            && (hdr.paper_white, hdr.peak, hdr.black) != (paper_white, peak, black)
-        {
-            hdr.paper_white = paper_white;
-            hdr.peak = peak;
-            hdr.black = black;
-            self.send_hdr_metadata();
-        }
-        // An output of another encoding than the one presented doesn't replace it yet, only
-        // Off does: the snapshot says what is presented.
-        self.output = output::EffectiveOutput {
-            encoding: self.hdr.as_ref().map(|hdr| hdr.output),
-            ..next
-        };
-    }
    /// Measures which pixels of each block sprite may shine (`hdr_stats`), at the current
    /// masks. Only with HDR output on: without it the frame's alpha is never read.
    pub fn measure_emission(&mut self) {
@@ -7258,24 +7162,6 @@ impl Renderer {
                .measure(&self.device, &self.queue, &views, hdr.masks);
        }
    }
-    /// Whether what the system reports for the display changed (another output, the
-    /// player recalibrating the desktop): the settings' Auto values follow it then, so
-    /// apply them again.
-    pub fn display_changed(&mut self) -> bool {
-        flush_display_log();
-        if std::mem::take(&mut self.display_fresh) {
-            return true;
-        }
-        let Some(watch) = self.display.as_mut() else {
-            return false;
-        };
-        let Some(now) = watch.changed(self.reading, self.surface.as_deref(), &self.adapter) else {
-            return false;
-        };
-        self.refresh_hdr_offer();
-        self.reading = now;
-        true
-    }
    /// The share of real frames frame generation shows a made frame before (1 while it
    /// keeps up), `None` while it isn't running.
    /// The posed models' store size (`SkinFrame::base`), with entity skinning.
@@ -7661,7 +7547,7 @@ impl Renderer {
    ) -> std::result::Result<Vec<String>, String> {
        let linear = pack
            .as_ref()
-            .is_some_and(|p| p.0.manifest.api == horizon_render_pipeline::Api::V0_2);
+            .is_some_and(|p| p.0.manifest.api == horizon_shader_api::Api::V0_2);
        if (linear || self.output.frame.format == LINEAR_FRAME)
            && linear != (self.output.frame.format == LINEAR_FRAME)
            && !std::mem::replace(&mut self.frame_kept_logged, true)
@@ -7714,7 +7600,7 @@ impl Renderer {
                inputs.declarations.push_str(
                    "layout(set = 5, binding = 0) readonly buffer HzIndices { uint hz_indices[]; };\n",
                );
-                horizon_render_pipeline::GeometryInputs {
+                horizon_shaders::GeometryInputs {
                    inputs,
                    pull: pack_atlas::PULL.to_owned(),
                    index: "hz_indices[@]".to_owned(),
@@ -7737,7 +7623,7 @@ impl Renderer {
        }
    }

-    fn pack_terrain_inputs(&mut self) -> Option<horizon_render_pipeline::GbuffersInputs> {
+    fn pack_terrain_inputs(&mut self) -> Option<horizon_shaders::GbuffersInputs> {
        // Flat draws whenever the device has them (`render` keeps them on with a pack).
        let flat = self.flat.is_some() && self.flat_on;
        // Flat draws read each sprite's place from a table: the atlas is stitched as the game's.
@@ -8463,8 +8349,12 @@ impl Renderer {
            t.begin(&self.device, &self.queue);
        }
        if self.animated_textures {
-            self.hud
-                .animate_sprites(&mut self.uploads, &mut encoder, frame.ticks);
+            self.hud.animate(
+                &mut self.uploads,
+                &mut encoder,
+                frame.ticks,
+                &self.animations,
+            );
        }
        self.update_lightmap(
            &mut encoder,
@@ -9402,13 +9292,11 @@ impl Renderer {
        }
        // Near water and distant water share one back-to-front draw order.
        if self.translucent_draws.len() > section_translucent {
-            // Distant water goes after the near chunks', and replaced tiles'
-            // after all: each is a hair behind the one before, so depth leaves
-            // it only where that one has none. Back to front together, a far
-            // tile's water under a near chunk's (one fading in, or brought
-            // into view by a longer render distance) blended twice and looked
-            // opaque. The cost: far water just behind near water shows no
-            // surface of its own there.
+            // Distant water goes after the near chunks', and replaced tiles' after all: each is a
+            // hair behind the one before, so depth leaves it only where that one has none. Back to
+            // front together, a far tile's water under a near chunk's (one fading in, or brought
+            // into view by a longer render distance) blended twice and looked opaque. The cost: far
+            // water just behind near water shows no surface of its own there.
            let tier = |instance: usize| match instance.checked_sub(visible.len()) {
                None => 0,
                Some(tile) if visible_lods[tile].old => 2,
@@ -10410,7 +10298,7 @@ impl Renderer {
                self.own_timing.as_mut(),
            );
            pass.set_bind_group(0, &self.group, &[]);
-            pass.set_bind_group(horizon_render_pipeline::stages::GROUP, &shadow.group, &[]);
+            pass.set_bind_group(horizon_shader_api::stages::GROUP, &shadow.group, &[]);
            if flat_frame
                && let Some(flat) = &self.flat
                && let Some(pipeline) = &shadow.flat
@@ -10443,7 +10331,7 @@ impl Renderer {
                self.own_timing.as_mut(),
            );
            pass.set_bind_group(0, &self.group, &[]);
-            pass.set_bind_group(horizon_render_pipeline::stages::GROUP, &shadow.group, &[]);
+            pass.set_bind_group(horizon_shader_api::stages::GROUP, &shadow.group, &[]);
            if flat_frame
                && let Some(flat) = &self.flat
                && let Some(pipeline) = &shadow.flat_translucent
@@ -10475,7 +10363,7 @@ impl Renderer {
                    .begin_entities(&mut encoder, "Native shader pack entity shadow");
                pass.set_pipeline(&shadow.entity);
                pass.set_bind_group(0, &self.entity_group, &[]);
-                pass.set_bind_group(horizon_render_pipeline::stages::GROUP, &shadow.group, &[]);
+                pass.set_bind_group(horizon_shader_api::stages::GROUP, &shadow.group, &[]);
                pass.set_vertex_buffer(0, self.entity_buffer.slice(..));
                pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
                pass.draw_indexed(0..entity_quads * 6, 0, 0..1);
@@ -10696,7 +10584,7 @@ impl Renderer {
        let gpu_occluding = gpu_frame && self.gpu_culling.as_ref().is_some_and(|g| g.occluding());
        let pack_frame = |pass: &mut wgpu::RenderPass<'_>| {
            if let Some((_, group)) = material {
-                pass.set_bind_group(horizon_render_pipeline::stages::GROUP, group, &[]);
+                pass.set_bind_group(horizon_shader_api::stages::GROUP, group, &[]);
            }
        };
        // A pack's solid terrain that calls `set_surface` also writes the surface target, in
@@ -12084,7 +11972,7 @@ impl Renderer {
            && self
                .native
                .as_ref()
-                .is_none_or(|n| n.frame.api == horizon_render_pipeline::Api::V0_1);
+                .is_none_or(|n| n.frame.api == horizon_shader_api::Api::V0_1);
        match (&self.hdr, &surface_frame) {
            (Some(hdr), Some(f)) => hdr.present(
                &self.queue,
@@ -15399,6 +15287,10 @@ struct DisplayWatch {
 }

 impl DisplayReading {
+    /// What wgpu reads from the OS for `surface`'s display; nothing without one.
+    fn read(surface: Option<&wgpu::Surface>, adapter: &wgpu::Adapter) -> Self {
+        surface.map_or_else(Self::default, |s| Self::os(&s.display_hdr_info(adapter)))
+    }
    fn os(info: &wgpu::DisplayHdrInfo) -> Self {
        #[cfg(target_os = "macos")]
        let hdr = macos_hdr(info);
@@ -15439,9 +15331,7 @@ impl DisplayWatch {
            return (watch, wayland_reading(now));
        }
        let _ = window;
-        let now = surface.map_or_else(DisplayReading::default, |surface| {
-            DisplayReading::os(&surface.display_hdr_info(adapter))
-        });
+        let now = DisplayReading::read(surface, adapter);
        log_os_reported(now.luminance);
        let watch = Self {
            #[cfg(target_os = "linux")]
@@ -15450,30 +15340,28 @@ impl DisplayWatch {
        };
        (watch, now)
    }
-    /// What the system reports, if that changed from `last`.
-    fn changed(
+    /// What the system reports at each poll that is due at `time` (`read`; on Wayland, at each
+    /// event), whether or not it is `last` again: the surface's capabilities are read with it.
+    fn poll(
        &mut self,
        last: DisplayReading,
-        surface: Option<&wgpu::Surface>,
-        adapter: &wgpu::Adapter,
+        time: std::time::Instant,
+        read: impl FnOnce() -> DisplayReading,
    ) -> Option<DisplayReading> {
        #[cfg(target_os = "linux")]
        if let Some(wayland) = &mut self.wayland {
            return wayland.changed().map(wayland_reading);
        }
        let next = self.polled.as_mut()?;
-        let time = std::time::Instant::now();
        if time < *next {
            return None;
        }
        *next = time + DISPLAY_POLL;
-        let now = surface.map_or_else(DisplayReading::default, |surface| {
-            DisplayReading::os(&surface.display_hdr_info(adapter))
-        });
-        (now != last).then(|| {
+        let now = read();
+        if now != last {
            log_os_reported(now.luminance);
-            now
-        })
+        }
+        Some(now)
    }
 }

@@ -64,7 +64,7 @@ enum Writer {
    },
 }

-pub(super) struct SpriteAnimator {
+pub(crate) struct SpriteAnimator {
    sprites: Vec<Sprite>,
    groups: Vec<Group>,
    writer: Writer,
@@ -86,6 +86,9 @@ struct AnimationModes {
    day_time: i64,
    weather: f32,
    values: std::collections::HashMap<String, f64>,
+    /// The open screen (an identity the game picks) and the ticks it has been open.
+    screen: Option<u64>,
+    screen_time: i64,
 }

 impl AnimationModes {
@@ -116,8 +119,15 @@ impl super::Renderer {
        day_time: i64,
        [rain, thunder]: [f32; 2],
        frame: Option<&crate::environment::Frame>,
+        screen: Option<u64>,
    ) {
        let modes = &mut self.animations.modes;
+        // `screen_time`: a tick more while the same screen stays open, from 0 on a new one.
+        modes.screen_time = match (screen, modes.screen) {
+            (Some(open), Some(was)) if open == was => modes.screen_time + 1,
+            _ => 0,
+        };
+        modes.screen = screen;
        modes.day_time = day_time;
        modes.weather = rain + thunder;
        modes.values.clear();
@@ -133,6 +143,16 @@ impl super::Renderer {
 }

 impl SpriteAnimator {
+    /// What the modes read this frame, for the GUI atlas's sprites (their expressions aren't
+    /// compiled: those run on ticks).
+    pub(crate) fn mode_inputs(&self) -> horizon_assets::animation::ModeInputs<'static> {
+        horizon_assets::animation::ModeInputs {
+            day_time: self.modes.day_time,
+            screen_time: self.modes.screen_time,
+            weather: self.modes.weather,
+            expression: &|_| None,
+        }
+    }
    /// `textures` are the sprite arrays, `split` layers each, `size` pixels
    /// wide; `animations` hold their frames at that size. `compute`: whether
    /// the device says it runs compute shaders writing storage textures.
@@ -361,6 +381,7 @@ impl SpriteAnimator {
        let expression = |source: &str| values.get(source).copied();
        let inputs = horizon_assets::animation::ModeInputs {
            day_time: self.modes.day_time,
+            screen_time: self.modes.screen_time,
            weather: self.modes.weather,
            expression: &expression,
        };
@@ -2,8 +2,8 @@
 //! and `secondaryBlockOutline` under a high contrast one): an outline its fragment shader colours
 //! or animates. Without one the outline draws natively (`vs_line` in terrain.wgsl).

+use crate::core_shader::{CoreProgram, Glue};
 use glam::Mat4;
-use horizon_shaders::{CoreProgram, Glue};

 /// The outline's edges (`pack_lines::layout`: start, end, ARGB colour and width per instance) as
 /// vanilla's lines: four vertices an edge, the start twice and the end twice, the side
@@ -425,7 +425,7 @@ mod tests {
            eprintln!("no GPU: skipping");
            return;
        };
-        let program = horizon_shaders::translate_core(LINES_VSH, RGB_FSH, &[], &include, &GLUE)
+        let program = crate::core_shader::translate_core(LINES_VSH, RGB_FSH, &[], &include, &GLUE)
            .expect("the shaders translate");
        assert_pack_coloured(&draw_edge(&device, &queue, &program));
    }
@@ -441,7 +441,7 @@ mod tests {
            include(id)
                .map(|text| text.replace("vec3 ModelOffset;", "vec3 ModelOffset;\n    vec4 More;"))
        };
-        let program = horizon_shaders::translate_core(LINES_VSH, RGB_FSH, &[], &bigger, &GLUE)
+        let program = crate::core_shader::translate_core(LINES_VSH, RGB_FSH, &[], &bigger, &GLUE)
            .expect("the shaders translate");
        assert!(CoreLines::new(&device, wgpu::TextureFormat::Rgba8Unorm, &program).is_none());
    }
@@ -470,11 +470,11 @@ mod tests {
            let (namespace, path) = id.split_once(':')?;
            std::fs::read_to_string(root.join(format!("assets/{namespace}/{path}"))).ok()
        };
-        let program = horizon_shaders::translate_core(&vertex, RGB_FSH, &[], &include, &GLUE)
+        let program = crate::core_shader::translate_core(&vertex, RGB_FSH, &[], &include, &GLUE)
            .expect("vanilla's vertex shader translates");
        // A pack that replaces only the vertex shader runs vanilla's fragment shader.
        let fragment = include("minecraft:shaders/core/rendertype_lines.fsh").unwrap();
-        let vanilla = horizon_shaders::translate_core(&vertex, &fragment, &[], &include, &GLUE)
+        let vanilla = crate::core_shader::translate_core(&vertex, &fragment, &[], &include, &GLUE)
            .expect("vanilla's fragment shader translates");
        let Some((device, queue)) = device() else {
            eprintln!("no GPU: skipping the draw");
@@ -3,8 +3,8 @@
 //! to the horizon or tints the night sky expects. Without one the sky draws natively (`fs_sky` in
 //! terrain.wgsl, stars.rs).

+use crate::core_shader::{CoreProgram, Glue};
 use glam::Mat4;
-use horizon_shaders::{CoreProgram, Glue};
 use wgpu::util::DeviceExt;

 /// `DefaultVertexFormat.POSITION`: the disc's and the stars' vertices.
@@ -325,7 +325,7 @@ mod tests {
        let fragment = "#version 330\n#include <minecraft:dynamictransforms.glsl>\n\
            layout(location = 0) out vec4 fragColor;\n\
            void main() {\n    fragColor = ColorModulator;\n}\n";
-        let program = horizon_shaders::translate_core(&vertex, fragment, &[], &include, &GLUE)
+        let program = crate::core_shader::translate_core(&vertex, fragment, &[], &include, &GLUE)
            .expect("the sky shaders translate");
        let instance = crate::gfx::test_gpu::instance();
        let Some((device, queue)) =
@@ -1,12 +1,11 @@
-//! OptiFine custom sky layers on the GPU: one texture per layer, kept with the renderer (its pack),
+//! Custom sky layers (`crate::custom_sky`) on the GPU: one texture per layer, kept with the renderer (its pack),
 //! a static skybox mesh of the 3x2 grid's six faces, and one pipeline per blend mode. A frame
 //! uploads one small uniform per drawn layer ([`crate::custom_sky::Draw`]) and draws 36 vertices
 //! each, after the vanilla sky's disc and sunrise and before the sun, moon and stars.
 use glam::Mat4;
-use horizon_optifine::sky::{Blend, Face};
 use wgpu::util::DeviceExt;

-use crate::custom_sky::{CustomSky as Pack, Draw};
+use crate::custom_sky::{Blend, Draw, SkyLayers};

 /// The blend modes in the shader's `mode` order (custom_sky.wgsl).
 const MODES: [Blend; 9] = [
@@ -85,6 +84,76 @@ fn blend(mode: Blend) -> wgpu::BlendComponent {
    }
 }

+/// A face of the skybox, as the 3x2 grid of its texture holds them: `Bottom`, `Top`, `South` in
+/// the top row, `West`, `North`, `East` below.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum Face {
+    Bottom,
+    Top,
+    South,
+    West,
+    North,
+    East,
+}
+
+impl Face {
+    const ALL: [Self; 6] = [
+        Self::Bottom,
+        Self::Top,
+        Self::South,
+        Self::West,
+        Self::North,
+        Self::East,
+    ];
+
+    /// The face's cell of the texture, `[u0, v0, u1, v1]` in 0..1.
+    fn cell(self) -> [f32; 4] {
+        let (col, row) = match self {
+            Self::Bottom => (0, 0),
+            Self::Top => (1, 0),
+            Self::South => (2, 0),
+            Self::West => (0, 1),
+            Self::North => (1, 1),
+            Self::East => (2, 1),
+        };
+        let (u, v) = (col as f32 / 3.0, row as f32 / 2.0);
+        [u, v, u + 1.0 / 3.0, v + 0.5]
+    }
+
+    /// The face's corners (on the unit cube around the camera; x east, y up, z south) in the
+    /// order of its cell's `(u0, v0)`, `(u1, v0)`, `(u1, v1)`, `(u0, v1)`. The side faces are
+    /// seen from inside with up at the top of their cell; the top face has north at the bottom of
+    /// its cell, the bottom face north at the top (the template's `N` marks).
+    fn corners(self) -> [[f32; 3]; 4] {
+        match self {
+            // Seen looking north: west on the left.
+            Self::North => [
+                [-1., 1., -1.],
+                [1., 1., -1.],
+                [1., -1., -1.],
+                [-1., -1., -1.],
+            ],
+            Self::South => [[1., 1., 1.], [-1., 1., 1.], [-1., -1., 1.], [1., -1., 1.]],
+            Self::East => [[1., 1., -1.], [1., 1., 1.], [1., -1., 1.], [1., -1., -1.]],
+            Self::West => [
+                [-1., 1., 1.],
+                [-1., 1., -1.],
+                [-1., -1., -1.],
+                [-1., -1., 1.],
+            ],
+            // Looking up with north toward the cell's bottom edge: east on the right.
+            Self::Top => [[-1., 1., 1.], [1., 1., 1.], [1., 1., -1.], [-1., 1., -1.]],
+            // Looking down with north toward the cell's top edge: east on the right.
+            Self::Bottom => [
+                [-1., -1., -1.],
+                [1., -1., -1.],
+                [1., -1., 1.],
+                [-1., -1., 1.],
+            ],
+        }
+    }
+}
+
 /// The skybox's 36 vertices: two triangles per face, each corner with its cell's UV.
 fn mesh() -> Vec<Vertex> {
    let mut out = Vec::with_capacity(36);
@@ -256,10 +325,15 @@ impl CustomSky {
    }

    /// The pack's layer textures, replacing any before.
-    pub(super) fn set_pack(&mut self, device: &wgpu::Device, queue: &wgpu::Queue, pack: &Pack) {
+    pub(super) fn set_pack(
+        &mut self,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        pack: &dyn SkyLayers,
+    ) {
        let limit = device.limits().max_texture_dimension_2d;
        self.groups = pack
-            .images
+            .images()
            .iter()
            .map(|image| {
                // Too large for this GPU: a 1x1 transparent texel, so the layer draws nothing.
@@ -413,6 +487,38 @@ impl CustomSky {
 mod tests {
    use super::*;

+    #[test]
+    fn the_grid_holds_each_face_once_and_faces_point_out() {
+        let mut cells: Vec<_> = Face::ALL
+            .iter()
+            .map(|f| f.cell().map(|x| (x * 6.0) as i32))
+            .collect();
+        cells.dedup();
+        assert_eq!(cells.len(), 6);
+        assert_eq!(Face::East.cell(), [2.0 / 3.0, 0.5, 1.0, 1.0]);
+        for face in Face::ALL {
+            let c = face.corners();
+            let sub = |a: [f32; 3], b: [f32; 3]| [a[0] - b[0], a[1] - b[1], a[2] - b[2]];
+            let (a, b) = (sub(c[1], c[0]), sub(c[3], c[0]));
+            let n = [
+                a[1] * b[2] - a[2] * b[1],
+                a[2] * b[0] - a[0] * b[2],
+                a[0] * b[1] - a[1] * b[0],
+            ];
+            let centre: [f32; 3] =
+                std::array::from_fn(|i| c.iter().map(|p| p[i]).sum::<f32>() / 4.0);
+            // Seen from inside, u runs right and v down, so u x v points away from the camera.
+            let dot: f32 = (0..3).map(|i| n[i] * centre[i]).sum();
+            assert!(dot > 0.0, "{face:?} is mirrored");
+        }
+        // The top cell's bottom edge (v1) is north: its corners 2 and 3 have z = -1.
+        assert_eq!(Face::Top.corners()[2][2], -1.0);
+        assert_eq!(Face::Top.corners()[3][2], -1.0);
+        // The bottom cell's top edge (v0) is north.
+        assert_eq!(Face::Bottom.corners()[0][2], -1.0);
+        assert_eq!(Face::Bottom.corners()[1][2], -1.0);
+    }
+
    /// What a blend leaves a sky texel of `dst` with when the shader outputs `src`
    /// (custom_sky.wgsl) for a layer texel `t` at brightness `b`, per channel.
    fn mix(mode: Blend, dst: f32, t: f32, a: f32, b: f32) -> f32 {
@@ -6,7 +6,7 @@ struct Layer {
    // Projection * view (camera-relative) * the layer's rotation.
    clip_from_sky: mat4x4<f32>,
    brightness: f32,
-    // horizon_optifine::sky::Blend, in gfx/custom_sky.rs's MODES order.
+    // crate::custom_sky::Blend, in gfx/custom_sky.rs's MODES order.
    mode: u32,
    pad: vec2<u32>,
    hdr_settings: vec4<f32>,
@@ -1,3 +1,25 @@
+// This file is part of the FidelityFX SDK.
+//
+// Copyright (C) 2024 Advanced Micro Devices, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files(the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and /or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions :
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
 //! FSR 3.1's frame interpolation (AMD FidelityFX SDK 1.1.4, `ffx_frameinterpolation*`,
 //! MIT), ported to WGSL (`interpolation.wgsl`): the frame halfway between the previous
 //! real frame and this one, from the camera's motion vectors, the optical flow
@@ -185,7 +185,7 @@ pub struct Hdr {
    /// The display's black level, in nits: shadows are lifted onto it (`hdr.wgsl`).
    pub black: f32,
    pub tiers: [Tier; 4],
-    /// The HUD and menus' brightness, as a share of paper white (0.25..=1).
+    /// The HUD and menus' brightness, as a share of paper white: above 1 brighter than it.
    pub ui: f32,
    /// Which pixels of a light source shine (`Masks`).
    pub masks: Masks,
@@ -419,6 +419,26 @@ impl Hdr {
        }
    }

+    /// The same HDR output presenting `output` instead (`output_apply`): the same frame and
+    /// HUD layer, and the player's tuning as it is (HDR Lighting, the world's lighting, the UI
+    /// brightness, the masks and tiers, the debug view, calibration and the luminance). Its
+    /// targets are made again on the next frame.
+    pub fn retargeted(&self, device: &wgpu::Device, queue: &wgpu::Queue, output: Output) -> Self {
+        Self {
+            debug: self.debug,
+            paper_white: self.paper_white,
+            peak: self.peak,
+            black: self.black,
+            tiers: self.tiers,
+            ui: self.ui,
+            masks: self.masks,
+            lighting: self.lighting,
+            look: self.look,
+            calibration: self.calibration,
+            ..Self::new(device, queue, self.format, output, self.layered.is_some())
+        }
+    }
+
    /// The frame every pass draws into this frame, sized like the window.
    pub fn frame(&mut self, device: &wgpu::Device, size: [u32; 2]) -> wgpu::Texture {
        if self.targets.as_ref().is_none_or(|t| t.size != size) {
@@ -936,7 +956,7 @@ impl Hdr {
            f32::from(u8::from(pq)),
        ]);
        params[5] = self.black.clamp(0.0, paper);
-        params[6] = self.ui.clamp(0.25, 1.0);
+        params[6] = self.ui;
        params[7] = if self.lighting {
            scene_gain(self.peak, self.paper_white)
        } else {
@@ -1541,6 +1561,93 @@ struct ReferenceParams { peak: f32, scene: f32, world: f32, debug: f32, share: v
        assert!(r == 1.0 && near(g, 0.5) && near(b, 0.2), "{r} {g} {b}");
    }

+    /// HDR output switched from HDR10 to scRGB and back (`output_apply`): the player's tuning
+    /// stays, each swapchain gets the same light in its own encoding, and the HDR10 capture
+    /// and the HDR10 picture after the switch back are the ones before it.
+    #[test]
+    fn a_switched_encoding_keeps_the_tuning_and_shows_the_same_light() {
+        let Some((device, queue)) = gpu() else {
+            eprintln!("HDR encoding switch GPU skipped: no adapter");
+            return;
+        };
+        let mut hdr = Hdr::with_debug(&device, &queue, F::Rgba16Float, Output::Pq, true, None);
+        (hdr.paper_white, hdr.peak, hdr.black) = (250.0, 800.0, 0.0);
+        (hdr.ui, hdr.look, hdr.lighting) = (0.5, false, false);
+        hdr.masks.parts = 0.4;
+        hdr.tiers[1].share = 0.7;
+        hdr.debug = true;
+        hdr.calibration = Some(super::Calibration {
+            step: 2,
+            nits: 700.0,
+            band: 0.6,
+        });
+        let tuning = |h: &Hdr| {
+            (
+                [h.paper_white, h.peak, h.black, h.ui],
+                (h.look, h.lighting, h.debug, h.layered.is_some(), h.format),
+                (h.masks, h.tiers, h.calibration),
+            )
+        };
+        let switched = hdr.retargeted(&device, &queue, Output::ScRgb);
+        assert_eq!(switched.output, Output::ScRgb);
+        assert_eq!(tuning(&switched), tuning(&hdr));
+        hdr.calibration = None;
+        hdr.debug = false;
+        // The swapchain's first texel (`capture`: the HDR10 screenshot's) for light 2 times
+        // paper white, grey, as the layered frame stores it.
+        let shot = |hdr: &mut Hdr, capture: bool| {
+            let frame = hdr.frame(&device, [1, 1]);
+            let mut encoder = device.create_command_encoder(&Default::default());
+            let g = 2f64.powf(1.0 / 2.2);
+            fill(&mut encoder, &frame, [g, g, g, 1.0]);
+            hdr.begin(&queue, true);
+            hdr.keep_world(&mut encoder, None);
+            super::super::hud_coverage::clear(&mut encoder, &hdr.coverage_view().unwrap());
+            let target = if capture {
+                hdr.capture(&device, &queue, &mut encoder, true).unwrap()
+            } else {
+                device.create_texture(&wgpu::TextureDescriptor {
+                    label: None,
+                    size: frame.size(),
+                    mip_level_count: 1,
+                    sample_count: 1,
+                    dimension: wgpu::TextureDimension::D2,
+                    format: hdr.output.format(),
+                    usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::COPY_SRC,
+                    view_formats: &[],
+                })
+            };
+            if !capture {
+                hdr.present(&queue, &mut encoder, &target, true, None);
+            }
+            texel(&device, &queue, encoder, &target)
+        };
+        // BT.2100's PQ EOTF: a 10-bit code's nits.
+        let pq_nits = |code: f32| {
+            let (m1, m2) = (2610.0 / 16384.0, 2523.0 / 4096.0 * 128.0);
+            let (c1, c2, c3) = (3424.0 / 4096.0, 2413.0 / 128.0, 2392.0 / 128.0);
+            let p = (code / 1023.0f32).powf(1.0 / m2);
+            ((p - c1).max(0.0) / (c2 - c3 * p)).powf(1.0 / m1) * 10000.0
+        };
+        let pq = shot(&mut hdr, false);
+        let pq_capture = shot(&mut hdr, true);
+        let mut scrgb = hdr.retargeted(&device, &queue, Output::ScRgb);
+        let linear = shot(&mut scrgb, false);
+        assert_eq!(shot(&mut scrgb, true), pq_capture);
+        // Two times paper white in both: 500 nits, as HDR10's code and as scRGB's 80-nit units.
+        let near = |got: f32| (got - 500.0).abs() <= 0.015 * 500.0;
+        assert!(
+            near(pq_nits(pq[0])) && pq[..3].iter().all(|&c| c == pq[0]),
+            "{pq:?}"
+        );
+        assert!(near(linear[0] * 80.0), "{linear:?}");
+        let mut back = scrgb.retargeted(&device, &queue, Output::Pq);
+        assert_eq!(
+            (shot(&mut back, false), shot(&mut back, true)),
+            (pq, pq_capture)
+        );
+    }
+
    /// ITU-R BT.2390's black level lift on grey light, in HDR10 and in scRGB, against values
    /// worked out apart from the shader, in f64 from SMPTE ST 2084: E3 = E2 + b (1 - E2)^4 on
    /// the PQ signal, for a source from 0 to the peak and b the black level's share of it.
@@ -1799,9 +1906,11 @@ struct ReferenceParams { peak: f32, scene: f32, world: f32, debug: f32, share: v
            // Covered: the HUD as drawn, at UI Brightness.
            (2.0, 0.3, 1.0, 1.0, 0.3),
            (2.0, 0.3, 1.0, 0.5, 0.3 * 0.5f32.powf(1.0 / 2.2)),
+            // UI Brightness above paper white: brighter than drawn.
+            (2.0, 0.3, 1.0, 2.0, 0.3 * 2f32.powf(1.0 / 2.2)),
            // Added over the world (the text highlight), which it doesn't hide.
            (0.6, 0.8, 0.0, 1.0, 0.8),
-            // At or below white, at 100%: the HUD's picture as drawn.
+            // At or below white, at paper white: the HUD's picture as drawn.
            (0.7, 0.45, 0.5, 1.0, 0.45),
        ] {
            hdr.ui = ui;
@@ -1821,6 +1930,50 @@ struct ReferenceParams { peak: f32, scene: f32, world: f32, debug: f32, share: v
        }
    }

+    /// On the frame without the HUD's layer, the HUD at UI Brightness reaches its nits, and
+    /// above the peak stops there, as on the layered frame.
+    #[test]
+    fn the_hud_at_ui_brightness_stops_at_the_peak() {
+        let Some((device, queue)) = gpu() else {
+            return;
+        };
+        let mut hdr = Hdr::with_debug(&device, &queue, F::Rgba8Unorm, Output::ScRgb, false, None);
+        (hdr.paper_white, hdr.peak) = (200.0, 300.0);
+        let target = device.create_texture(&wgpu::TextureDescriptor {
+            label: None,
+            size: wgpu::Extent3d {
+                width: 1,
+                height: 1,
+                depth_or_array_layers: 1,
+            },
+            mip_level_count: 1,
+            sample_count: 1,
+            dimension: wgpu::TextureDimension::D2,
+            format: Output::ScRgb.format(),
+            usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::COPY_SRC,
+            view_formats: &[],
+        });
+        // UI Brightness (a share of paper white) and the white HUD's nits.
+        for (ui, want) in [(0.5, 100.0), (1.25, 250.0), (2.0, 300.0)] {
+            hdr.ui = ui;
+            let frame = hdr.frame(&device, [1, 1]);
+            let mut encoder = device.create_command_encoder(&Default::default());
+            fill(&mut encoder, &frame, [0.2, 0.2, 0.2, 1.0]);
+            hdr.keep_world(&mut encoder, None);
+            // Opaque white HUD over the world: alpha 1 is full coverage.
+            fill(&mut encoder, &frame, [1.0; 4]);
+            hdr.begin(&queue, true);
+            hdr.present(&queue, &mut encoder, &target, true, None);
+            let got = texel(&device, &queue, encoder, &target);
+            for c in &got[..3] {
+                assert!(
+                    (c * 80.0 - want).abs() < 0.5,
+                    "UI {ui}: {got:?}, not {want} nits"
+                );
+            }
+        }
+    }
+
    #[test]
    fn the_menu_blur_keeps_the_light_it_blurs() {
        let Some((device, queue)) = gpu() else {
@@ -0,0 +1,65 @@
+//! A window's HDR output start and what a failed one leaves (`graphics::HDR_MARKER`). Turning
+//! HDR output on writes a marker naming the window's graphics driver (`output::window_driver`);
+//! the first frame presented, turning HDR output off and a clean exit remove it. A start that
+//! finds it holds HDR output back on that driver (`output::held`) until a mode is chosen on the
+//! HDR page or the driver changes. Offscreen renderers have no driver: they never write the
+//! marker or hold HDR output back.
+use super::{Renderer, output};
+
+impl Renderer {
+    /// What this renderer's destination offers for `settings`: HDR output held back on a window
+    /// whose graphics driver a start failed on (`output::held`).
+    pub(super) fn caps_for(
+        &self,
+        settings: &crate::graphics::Graphics,
+    ) -> output::OutputCapabilities {
+        output::OutputCapabilities {
+            held: output::held(settings, self.hdr_driver.as_deref()),
+            ..self.output_caps
+        }
+    }
+
+    /// Takes the hold `settings` put on this window's driver into the capabilities, and says it
+    /// once per start.
+    pub(super) fn hold_hdr_back(&mut self, settings: &crate::graphics::Graphics) {
+        self.output_caps = self.caps_for(settings);
+        if self.output_caps.held
+            && let Some(driver) = &self.hdr_driver
+        {
+            static LOGGED: std::sync::Once = std::sync::Once::new();
+            LOGGED.call_once(|| {
+                log::warn!(
+                    "Horizon renderer: HDR output is held back: the last start with this graphics driver ({driver}) ended before HDR output showed a frame. Choose an HDR mode on the HDR page to try again (or remove hdrFailedStart from {})",
+                    crate::graphics::FILE
+                )
+            });
+        }
+    }
+
+    /// Writes the marker at `marker` as a window's HDR output turns on (`on`), and removes this
+    /// renderer's marker as it turns off.
+    pub(super) fn mark_hdr_start(&mut self, on: bool, marker: &std::path::Path) {
+        if !on {
+            self.drop_hdr_marker();
+        } else if self.surface.is_some()
+            && let Some(driver) = &self.hdr_driver
+        {
+            let _ = std::fs::write(marker, crate::graphics::hdr_marker_text(driver));
+            self.hdr_marker = Some(marker.to_owned());
+        }
+    }
+
+    /// The graphics driver this window's HDR output starts on (`output::window_driver`);
+    /// `None` offscreen.
+    pub fn hdr_driver(&self) -> Option<&str> {
+        self.hdr_driver.as_deref()
+    }
+
+    /// Removes this renderer's marker of an HDR output that hasn't presented a frame yet, for a
+    /// clean exit: only a crash may leave it.
+    pub fn drop_hdr_marker(&mut self) {
+        if let Some(marker) = self.hdr_marker.take() {
+            let _ = std::fs::remove_file(marker);
+        }
+    }
+}
@@ -8,8 +8,7 @@
 //! colour. They read the terrain's group 0, the flat draws' group 1 where those run, and the
 //! pack's frame at group 3.

-use horizon_render_pipeline::stages::GROUP;
-use horizon_shader_api::check::CheckedStage;
+use horizon_shader_api::{check::CheckedStage, stages::GROUP};

 use super::native_post::{NativeFrame, present_constants};
 use super::wgsl_prefix::{TERRAIN, prefixed, section};
@@ -370,7 +369,7 @@ fn shader_source(
    tags: &[(u32, u32)],
    materials: &[(u32, u32)],
    (vertex, displaced): (bool, bool),
-    api: horizon_render_pipeline::Api,
+    api: horizon_shader_api::Api,
 ) -> String {
    format!(
        "{source}\n// Horizon's terrain (terrain.wgsl)\n{}{}{}{}{}{ENTRIES}{}{}",
@@ -399,7 +398,7 @@ fn module(
    materials: &[(u32, u32)],
    vertex: bool,
    displaced: bool,
-    api: horizon_render_pipeline::Api,
+    api: horizon_shader_api::Api,
 ) -> Result<naga::Module, String> {
    let text = shader_source(&stage.source, tags, materials, (vertex, displaced), api);
    naga::front::wgsl::parse_str(&text)
@@ -418,7 +417,7 @@ impl NativeMaterial {
        vertex: bool,
        displaced: Option<&DisplacedShape<'_>>,
    ) -> Result<Self, String> {
-        let writes_surface = horizon_render_pipeline::stages::calls_set_surface(&stage.source);
+        let writes_surface = horizon_shader_api::stages::calls_set_surface(&stage.source);
        let module = module(
            stage,
            shape.sprite_tags,
@@ -587,7 +586,7 @@ impl NativeMaterial {
 }

 #[cfg(test)]
-pub(super) fn coverage_test_shader(api: horizon_render_pipeline::Api) -> String {
+pub(super) fn coverage_test_shader(api: horizon_shader_api::Api) -> String {
    use horizon_shader_api::{MANIFEST, Pack, StageKind, check};
    let manifest = format!(
        "schema = 1\nid = \"coverage\"\nname = \"Coverage\"\nversion = \"1\"\napi = \"{api}\"\n[material]\nfile = \"material.wgsl\"\n[displacement]\n"
@@ -830,7 +829,7 @@ mod tests {
                .into();
            let report = check(&Pack::from_files(files).unwrap()).unwrap();
            let source = report.stages[0].source.clone()
-                + horizon_render_pipeline::stages::PBR_STUB
+                + horizon_shader_api::stages::PBR_STUB
                + super::super::native_post::line_helpers(api)
                + entry;
            let module = device.create_shader_module(wgpu::ShaderModuleDescriptor {
@@ -1,8 +1,7 @@
 //! One of Horizon's own shader packs while it runs (docs/shaders.md): the frame its stages
 //! read, its sky, material and post stages, and the timer of their passes.

-use horizon_render_pipeline::StageKind;
-use horizon_shader_api::Report;
+use horizon_shader_api::{Report, StageKind};

 use super::displace::Displacement;
 use super::native_material::{DisplacedShape, NativeMaterial, TerrainShape};
@@ -254,7 +253,7 @@ impl NativePack {
            .transpose()?;
        // A 0.2 pack always has one: its decode and tonemap run without a chain too.
        let tonemap = others.iter().find(|s| s.kind == StageKind::Tonemap);
-        let post = (!post.is_empty() || api == horizon_render_pipeline::Api::V0_2)
+        let post = (!post.is_empty() || api == horizon_shader_api::Api::V0_2)
            .then(|| {
                let manifest = &report.manifest;
                NativePost::new(device, post, manifest, constants, format, &frame, tonemap)
@@ -7,9 +7,9 @@
 //! (`NativeFrame`).

 use glam::{Mat4, Vec3};
-use horizon_render_pipeline::stages::{GROUP, POST_TARGET_BINDING};
-use horizon_render_pipeline::{Api, Frame as FrameInputs, StageKind};
-use horizon_shader_api::check::CheckedStage;
+use horizon_shader_api::{
+    Api, Frame as FrameInputs, StageKind, check::CheckedStage, stages::GROUP,
+};

 use super::Frame;

@@ -1014,9 +1014,10 @@ impl NativePost {
            texture_entry(11, wgpu::TextureSampleType::Uint),
        ];
        entries.extend(pack_texture_entries(frame.textures.len()));
-        entries.extend(
-            (0..targets.len() as u32).map(|j| texture_entry(POST_TARGET_BINDING + j, float)),
-        );
+        entries
+            .extend((0..targets.len() as u32).map(|j| {
+                texture_entry(horizon_shader_api::stages::POST_TARGET_BINDING + j, float)
+            }));
        let layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
            label: Some("Native shader pack post"),
            entries: &entries,
@@ -1345,7 +1346,7 @@ impl NativePost {
                        view
                    };
                    wgpu::BindGroupEntry {
-                        binding: POST_TARGET_BINDING + j as u32,
+                        binding: horizon_shader_api::stages::POST_TARGET_BINDING + j as u32,
                        resource: wgpu::BindingResource::TextureView(view),
                    }
                }));
@@ -1654,7 +1655,7 @@ pub fn pack_textures(

 /// Layout entries of `count` pack textures and their samplers.
 pub(super) fn pack_texture_entries(count: usize) -> Vec<wgpu::BindGroupLayoutEntry> {
-    use horizon_render_pipeline::stages::{TEXTURE_BINDING, TEXTURE_SAMPLER_BINDING};
+    use horizon_shader_api::stages::{TEXTURE_BINDING, TEXTURE_SAMPLER_BINDING};
    (0..count as u32)
        .flat_map(|i| {
            [
@@ -1683,7 +1684,7 @@ pub(super) fn pack_texture_entries(count: usize) -> Vec<wgpu::BindGroupLayoutEnt
 pub(super) fn pack_texture_group_entries(
    textures: &[(wgpu::TextureView, wgpu::Sampler)],
 ) -> Vec<wgpu::BindGroupEntry<'_>> {
-    use horizon_render_pipeline::stages::{TEXTURE_BINDING, TEXTURE_SAMPLER_BINDING};
+    use horizon_shader_api::stages::{TEXTURE_BINDING, TEXTURE_SAMPLER_BINDING};
    textures
        .iter()
        .enumerate()
@@ -2676,7 +2677,8 @@ file = \"b.wgsl\"

    /// On the layered HDR frame a 0.2 pack's light is tone mapped once: by Horizon's curve,
    /// the one HDR without a pack uses, when the pack has no `[tonemap]`, else by the pack's
-    /// alone, held to the headroom. In SDR Horizon's is a clip at white.
+    /// alone, held to the headroom. In SDR Horizon's is a clip at white. An HDR output switched
+    /// to scRGB and back to HDR10 (`Hdr::retargeted`) maps it once all the same.
    #[test]
    fn a_0_2_pack_is_tone_mapped_once_by_its_own_curve_or_horizons() {
        let Some((device, queue)) = device() else {
@@ -2686,8 +2688,9 @@ file = \"b.wgsl\"
        let light = 8.0f32;
        let (paper, peak) = (203.0, 1000.0);
        let headroom = peak / paper;
-        // The picture shown for that light, in linear light: (a pack's [tonemap], HDR).
-        let shown = |pack_curve: bool, hdr: bool| {
+        // The picture shown for that light, in linear light: (a pack's [tonemap], HDR, the
+        // output switched).
+        let shown = |pack_curve: bool, hdr: bool, switched: bool| {
            let (stage, file, source) = if pack_curve {
                (
                    "[tonemap]",
@@ -2745,6 +2748,11 @@ file = \"b.wgsl\"
                true,
            );
            (display.paper_white, display.peak) = (paper, peak);
+            if switched {
+                use super::super::hdr::Output::{Pq, ScRgb};
+                display = display.retargeted(&device, &queue, ScRgb);
+                display = display.retargeted(&device, &queue, Pq);
+            }
            let screen = display.frame(&device, [4, 4]);
            let usage =
                wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::TEXTURE_BINDING;
@@ -2812,14 +2820,16 @@ file = \"b.wgsl\"
        // Horizon's curve once: BT.2390's EETF at 203 and 1000 nits puts light 8 at 4.82
        // (worked out apart from the shader, as in the HDR tone curve's own test). Clipped at
        // the headroom first, or mapped twice, it would land lower.
-        let horizon = shown(false, true);
-        assert!(near(horizon, 4.82043), "{horizon}");
-        // The pack's identity curve alone: the light held to the headroom, not eased again.
-        let pack = shown(true, true);
-        assert!(near(pack, headroom), "{pack}");
+        for switched in [false, true] {
+            let horizon = shown(false, true, switched);
+            assert!(near(horizon, 4.82043), "{switched}: {horizon}");
+            // The pack's identity curve alone: the light held to the headroom, not eased again.
+            let pack = shown(true, true, switched);
+            assert!(near(pack, headroom), "{switched}: {pack}");
+        }
        // SDR: a clip at white, the pack's or Horizon's.
        for pack_curve in [false, true] {
-            let sdr = shown(pack_curve, false);
+            let sdr = shown(pack_curve, false, false);
            assert!(near(sdr, 1.0), "{pack_curve}: {sdr}");
        }
    }
@@ -11,9 +11,9 @@ use std::sync::{
    atomic::{AtomicBool, Ordering},
 };

-mod generated {
-    include!(concat!(env!("OUT_DIR"), "/native_render_generated.rs"));
-}
+/// The hooks' trait and dispatch, made from `native-hooks.json` by `cargo run -p xtask -- mod-api`;
+/// the game's build checks that the file is current.
+mod generated;
 pub use generated::{
    HandDrawnEvent, RenderHooks, RenderNeedsEvent, WorldDrawnEvent, WorldWarpEvent,
 };
@@ -0,0 +1,71 @@
+// @generated by cargo run -p xtask -- mod-api; do not edit.
+use super::*;
+pub trait RenderHooks: Send + Sync {
+    /// The world is drawn (see [`WorldDrawn`]). Not called on the title screen's panorama.
+    fn world_drawn(&self, event: &mut WorldDrawnEvent<'_, '_>) {
+        let _ = event;
+    }
+    /// Asked as a frame is built and drawn: set what your mod needs.
+    ///
+    /// Every mod gets `event.needs` in order and may add, change or remove needs.
+    fn render_needs(&self, event: &mut RenderNeedsEvent<'_>) {
+        let _ = event;
+    }
+    /// The first-person hand is drawn (see [`HandDrawn`]), on every frame [`native_world_drawn`]
+    /// runs, with no hand too. API 364.
+    fn hand_drawn(&self, event: &mut HandDrawnEvent<'_, '_>) {
+        let _ = event;
+    }
+    /// Asked once a frame, before the world is drawn (not on the title screen's panorama): set
+    /// [`WorldWarp`] to have the frame drawn through your warp. Mods are asked in order and one warp
+    /// draws: the last one set. Keep it cheap: compare and reuse your `Arc<str>`.
+    ///
+    /// Every mod gets `event.warp` in order and may add, change or remove warp.
+    fn world_warp(&self, event: &mut WorldWarpEvent<'_>) {
+        let _ = event;
+    }
+}
+/// What [`RenderHooks::world_drawn`] is told. Fields may be added: the struct is `#[non_exhaustive]`.
+#[non_exhaustive]
+pub struct WorldDrawnEvent<'a, 'b> {
+    pub world: &'a mut WorldDrawn<'b>,
+}
+pub fn dispatch_world_drawn(mods: &[&dyn RenderHooks], world: &mut WorldDrawn<'_>) {
+    let mut event = WorldDrawnEvent { world };
+    for mod_hook in mods {
+        mod_hook.world_drawn(&mut event);
+    }
+}
+/// What [`RenderHooks::render_needs`] is told. Fields may be added: the struct is `#[non_exhaustive]`.
+#[non_exhaustive]
+pub struct RenderNeedsEvent<'a> {
+    pub needs: &'a mut RenderNeeds,
+}
+pub fn dispatch_render_needs(mods: &[&dyn RenderHooks], needs: &mut RenderNeeds) {
+    let mut event = RenderNeedsEvent { needs };
+    for mod_hook in mods {
+        mod_hook.render_needs(&mut event);
+    }
+}
+/// What [`RenderHooks::hand_drawn`] is told. Fields may be added: the struct is `#[non_exhaustive]`.
+#[non_exhaustive]
+pub struct HandDrawnEvent<'a, 'b> {
+    pub hand: &'a mut HandDrawn<'b>,
+}
+pub fn dispatch_hand_drawn(mods: &[&dyn RenderHooks], hand: &mut HandDrawn<'_>) {
+    let mut event = HandDrawnEvent { hand };
+    for mod_hook in mods {
+        mod_hook.hand_drawn(&mut event);
+    }
+}
+/// What [`RenderHooks::world_warp`] is told. Fields may be added: the struct is `#[non_exhaustive]`.
+#[non_exhaustive]
+pub struct WorldWarpEvent<'a> {
+    pub warp: &'a mut WorldWarp,
+}
+pub fn dispatch_world_warp(mods: &[&dyn RenderHooks], warp: &mut WorldWarp) {
+    let mut event = WorldWarpEvent { warp };
+    for mod_hook in mods {
+        mod_hook.world_warp(&mut event);
+    }
+}
@@ -7,8 +7,7 @@
 //! prelude's `shadow_position` undoes.

 use horizon_render_pipeline::Shadow;
-use horizon_render_pipeline::{Api, Frame as FrameInputs, stages::GROUP};
-use horizon_shader_api::manifest::Shadow as Settings;
+use horizon_shader_api::{Api, Frame as FrameInputs, manifest::Shadow as Settings, stages::GROUP};

 use super::native_material::TerrainShape;
 use super::wgsl_prefix::{TERRAIN, prefixed, section};
@@ -388,7 +387,7 @@ fn entity_source() -> String {
    format!(
        "{}@group({GROUP}) @binding(0) var<uniform> frame: Frame;\n{}{ENTITY_ENTRIES}",
        FrameInputs::WGSL.wgsl(),
-        horizon_render_pipeline::stages::SHADOW_HELPERS,
+        horizon_shader_api::stages::SHADOW_HELPERS,
    )
 }

@@ -487,7 +486,7 @@ fn shader_source(
        (Some(material), _) => (
            format!(
                "{material}{}{table}{}{}{GRID_ENTRIES}",
-                horizon_render_pipeline::stages::PBR_STUB,
+                horizon_shader_api::stages::PBR_STUB,
                super::displace::RELIEF,
                super::displace::GRID,
            ),
@@ -505,7 +504,7 @@ fn shader_source(
            format!(
                "{}@group({GROUP}) @binding(0) var<uniform> frame: Frame;\n{}{UNTAKEN}",
                FrameInputs::WGSL.wgsl(),
-                horizon_render_pipeline::stages::SHADOW_HELPERS,
+                horizon_shader_api::stages::SHADOW_HELPERS,
            ),
            super::native_material::DISPLACE_VANILLA,
        ),
@@ -6,8 +6,7 @@
 //! names). It reads the renderer's globals (group 0) and the pack's frame (group 3), and
 //! draws where vanilla's sky draws; the sun, moon, stars and the dark disc are drawn over it.

-use horizon_render_pipeline::stages::GROUP;
-use horizon_shader_api::check::CheckedStage;
+use horizon_shader_api::{check::CheckedStage, stages::GROUP};

 use super::native_post::{NativeFrame, present_constants};
 use super::wgsl_prefix::{TERRAIN, prefixed, section};
@@ -41,7 +40,7 @@ fn vanilla_sky() -> String {
 }

 /// The sky shader for the pack's sky stage `source`.
-fn shader_source(source: &str, api: horizon_render_pipeline::Api) -> String {
+fn shader_source(source: &str, api: horizon_shader_api::Api) -> String {
    format!(
        "{source}\n// Horizon's sky (terrain.wgsl)\n{}{}{PACK_ENTRY}",
        vanilla_sky(),
@@ -199,7 +198,7 @@ mod tests {
        // A pack may use the renderer's names for its own things.
        let own = "override gain: f32;\nconst PI: f32 = 3.0;\nfn view_ray() -> f32 { return PI; }\n\
            fn sky(input: SkyInput) -> vec4<f32> { return input.color * gain * view_ray(); }\n";
-        let text = shader_source(&stage(own).source, horizon_render_pipeline::Api::V0_1);
+        let text = shader_source(&stage(own).source, horizon_shader_api::Api::V0_1);
        let module = naga::front::wgsl::parse_str(&text).unwrap_or_else(|e| {
            panic!("{}", e.emit_to_string(&text));
        });
@@ -262,7 +261,7 @@ mod tests {
            Vec::new(),
            Default::default(),
            None,
-            horizon_render_pipeline::Api::V0_1,
+            horizon_shader_api::Api::V0_1,
        );
        queue.write_buffer(
            &frame.buffer,
@@ -18,6 +18,43 @@ pub(crate) struct OutputCapabilities {
    pub float_frame: bool,
    /// The device keeps the HUD on a layer of its own (`hud_coverage::supported`).
    pub hud_layer: bool,
+    /// HDR output is held back: the last start on this window's graphics driver ended before
+    /// HDR output showed a frame ([`held`]). The mode stays; the output is SDR.
+    pub held: bool,
+}
+
+/// Whether HDR output is held back on a renderer whose window's graphics driver is `driver`
+/// (`None` offscreen, which never holds it back: only a window writes the marker).
+pub(crate) fn held(settings: &Graphics, driver: Option<&str>) -> bool {
+    driver.is_some_and(|driver| settings.hdr_held(driver))
+}
+
+/// The graphics driver this window's HDR output starts on ([`driver_fingerprint`]), with the
+/// system's version as crash reports name it (`crash::operating_system`), read once a run.
+pub(crate) fn window_driver(info: &wgpu::AdapterInfo) -> String {
+    static OS: std::sync::OnceLock<String> = std::sync::OnceLock::new();
+    driver_fingerprint(info, OS.get_or_init(crate::crash::operating_system))
+}
+
+/// The graphics driver a window's HDR output starts on, in one line: the backend, the
+/// adapter's vendor and device IDs and its name, the driver's name and its version, and the
+/// system's version `os`. Another GPU, a driver update or a system update reads differently:
+/// Metal names no driver, so on macOS the driver updates with the system.
+pub fn driver_fingerprint(info: &wgpu::AdapterInfo, os: &str) -> String {
+    let adapter = format!(
+        "{:?} {:04x}:{:04x} {}",
+        info.backend, info.vendor, info.device, info.name
+    );
+    [adapter.as_str(), &info.driver, &info.driver_info, os]
+        .map(|field| {
+            field
+                .chars()
+                .map(|c| if c.is_control() { ' ' } else { c })
+                .collect::<String>()
+                .trim()
+                .to_owned()
+        })
+        .join("; ")
 }

 /// What the system last reported for a renderer's display: its luminance, and whether it
@@ -97,13 +134,15 @@ pub struct EffectiveOutput {
    pub(crate) reported: Option<Reported>,
    /// The device draws the 16-bit frame (Smooth Gradients).
    pub(crate) wide_frame_supported: bool,
+    /// HDR output is held back on this window's graphics driver (`OutputCapabilities::held`).
+    pub(crate) held: bool,
    /// The HDR output presented; `None` is SDR.
    pub(crate) encoding: Option<Output>,
    pub(crate) frame: FrameConfiguration,
    /// Paper white, peak and black level in nits, as HDR output's last pass and its
    /// metadata take them, while it is on.
    pub(crate) nits: [f32; 3],
-    /// The HUD and menus' brightness, as a share of paper white.
+    /// The HUD and menus' brightness, as a share of paper white: their nits over its.
    pub(crate) ui_brightness: f32,
 }
 impl Default for EffectiveOutput {
@@ -118,6 +157,7 @@ impl EffectiveOutput {
        system_hdr: None,
        reported: None,
        wide_frame_supported: false,
+        held: false,
        encoding: None,
        frame: FrameConfiguration {
            format: wgpu::TextureFormat::Bgra8Unorm,
@@ -136,9 +176,10 @@ impl EffectiveOutput {
        self.encoding.is_some()
    }
    /// Whether `mode` asks for HDR here: On always, Auto where the destination offers it and
-    /// the display reports HDR. The output still needs an offer and a frame that can take it.
+    /// the display reports HDR, neither while HDR output is held back. The output still needs
+    /// an offer and a frame that can take it.
    pub fn requests_hdr(&self, mode: HdrMode) -> bool {
-        requests_hdr(mode, self.offered.is_some(), self.system_hdr)
+        !self.held && requests_hdr(mode, self.offered.is_some(), self.system_hdr)
    }
    /// What a 0.2 pack's `Frame` describes: the HDR display on the layered frame, whose
    /// picture is light; SDR otherwise, where the frame holds SDR's picture, the one HDR
@@ -169,6 +210,10 @@ fn requests_hdr(mode: HdrMode, offered: bool, system: Option<bool>) -> bool {
        HdrMode::Auto => offered && system == Some(true),
    }
 }
+/// Whether `settings` ask for HDR on a destination of `caps` whose display reports `reading`.
+fn wanted(settings: &Graphics, caps: OutputCapabilities, reading: DisplayReading) -> bool {
+    !caps.held && requests_hdr(settings.hdr, caps.hdr.is_some(), reading.hdr)
+}

 /// The frame a renderer made now draws in, for `settings`, the pack's `request`, what the
 /// destination and device can do (`caps`) and what the display reports.
@@ -179,7 +224,7 @@ pub(crate) fn resolve_frame(
    reading: DisplayReading,
    swapchain: wgpu::TextureFormat,
 ) -> FrameConfiguration {
-    let wanted = requests_hdr(settings.hdr, caps.hdr.is_some(), reading.hdr);
+    let wanted = wanted(settings, caps, reading);
    let (format, hud_layer) = super::frame_configuration(
        wanted && settings.hdr_smooth_gradients,
        (
@@ -210,12 +255,13 @@ pub(crate) fn resolve_output(
    frame: FrameConfiguration,
    presents: bool,
 ) -> EffectiveOutput {
-    let wanted = requests_hdr(settings.hdr, caps.hdr.is_some(), reading.hdr);
+    let wanted = wanted(settings, caps, reading);
    EffectiveOutput {
        offered: caps.hdr,
        system_hdr: reading.hdr,
        reported: reading.luminance,
        wide_frame_supported: caps.wide_frame,
+        held: caps.held,
        encoding: caps
            .hdr
            .filter(|_| wanted && presents && frame.overlay_format == frame.format),
@@ -225,7 +271,8 @@ pub(crate) fn resolve_output(
            settings.peak_nits(reading.luminance) as f32,
            settings.black_level_nits(),
        ],
-        ui_brightness: settings.hdr_ui_brightness as f32 / 100.0,
+        ui_brightness: settings.ui_nits(reading.luminance) as f32
+            / settings.paper_white_nits(reading.luminance) as f32,
    }
 }

@@ -247,6 +294,7 @@ pub(crate) mod tests {
                wide_frame: true,
                float_frame: true,
                hud_layer: true,
+                held: false,
            },
            DisplayReading {
                luminance: Some(Reported {
@@ -378,6 +426,118 @@ pub(crate) mod tests {
        assert_eq!(settings.hdr, HdrMode::On);
    }

+    /// A window on the driver a start failed on stays SDR, on an SDR frame, whatever the
+    /// mode, and the mode stays as chosen; another driver tries HDR again, and an offscreen
+    /// renderer (no driver) never holds HDR back.
+    #[test]
+    fn a_failed_start_holds_hdr_back_on_its_driver_only() {
+        let failed = "Vulkan 10de:2684 GPU; driver; 1.0";
+        for mode in [HdrMode::On, HdrMode::Auto] {
+            let settings = Graphics {
+                hdr: mode,
+                hdr_failed_start: Some(failed.into()),
+                ..Graphics::default()
+            };
+            let request = FrameRequest {
+                linear_pack: false,
+                hdr_float: true,
+            };
+            let on = |driver: Option<&str>| {
+                let (mut caps, reading) = window(Some(Output::Pq), Some(true));
+                caps.held = held(&settings, driver);
+                snapshot(&settings, request, caps, reading)
+            };
+            let out = on(Some(failed));
+            assert_eq!(out.encoding, None, "{mode:?}");
+            assert_eq!(out.frame.format, Bgra8Unorm, "{mode:?}");
+            assert!(!out.frame.hud_layer && out.held && !out.requests_hdr(mode));
+            // Still offered: the page lets the player pick a mode to try again.
+            assert!(out.hdr_offered());
+            assert_eq!(settings.hdr, mode);
+            for driver in [Some("Vulkan 10de:2684 GPU; driver; 1.1"), None] {
+                let out = on(driver);
+                assert_eq!(out.encoding, Some(Output::Pq), "{mode:?} {driver:?}");
+                assert_eq!(out.frame.format, LINEAR_FRAME, "{mode:?} {driver:?}");
+                assert!(!out.held && out.requests_hdr(mode));
+            }
+        }
+        // A marker that named no driver holds on whichever window comes first.
+        let legacy = Graphics {
+            hdr: HdrMode::On,
+            hdr_failed_start: Some(String::new()),
+            ..Graphics::default()
+        };
+        assert!(held(&legacy, Some(failed)));
+        assert!(!held(&legacy, None));
+    }
+
+    /// The fingerprint tells another GPU, backend, driver version or system version apart, in
+    /// one line.
+    #[test]
+    fn the_driver_fingerprint_is_one_line_that_changes_with_the_driver() {
+        let os = "windows (x86_64) version Windows 11 (26200.7019)";
+        let info = wgpu::AdapterInfo {
+            name: "NVIDIA GeForce RTX 4090".into(),
+            vendor: 0x10de,
+            device: 0x2684,
+            device_type: wgpu::DeviceType::DiscreteGpu,
+            device_pci_bus_id: "0000:01:00.0".into(),
+            driver: "NVIDIA".into(),
+            driver_info: "581.57\n".into(),
+            backend: wgpu::Backend::Vulkan,
+            subgroup_min_size: 32,
+            subgroup_max_size: 32,
+            transient_saves_memory: None,
+            limit_bucket: None,
+        };
+        let fingerprint = driver_fingerprint(&info, os);
+        assert_eq!(
+            fingerprint,
+            "Vulkan 10de:2684 NVIDIA GeForce RTX 4090; NVIDIA; 581.57; \
+             windows (x86_64) version Windows 11 (26200.7019)"
+        );
+        assert_ne!(
+            driver_fingerprint(&info, "windows (x86_64) version Windows 11 (26200.7171)"),
+            fingerprint
+        );
+        // Metal names no driver: a macOS update is what changes it.
+        let metal = wgpu::AdapterInfo {
+            name: "Apple M3".into(),
+            vendor: 0,
+            device: 0,
+            driver: String::new(),
+            driver_info: String::new(),
+            backend: wgpu::Backend::Metal,
+            ..info.clone()
+        };
+        let sonoma = driver_fingerprint(&metal, "macos (aarch64) version macOS 14.6");
+        assert_eq!(
+            sonoma,
+            "Metal 0000:0000 Apple M3; ; ; macos (aarch64) version macOS 14.6"
+        );
+        assert_ne!(
+            driver_fingerprint(&metal, "macos (aarch64) version macOS 15.1"),
+            sonoma
+        );
+        let other = [
+            wgpu::AdapterInfo {
+                driver_info: "582.02".into(),
+                ..info.clone()
+            },
+            wgpu::AdapterInfo {
+                backend: wgpu::Backend::Dx12,
+                ..info.clone()
+            },
+            wgpu::AdapterInfo {
+                device: 0x2704,
+                ..info.clone()
+            },
+        ];
+        for other in other {
+            assert_ne!(driver_fingerprint(&other, os), fingerprint, "{other:?}");
+        }
+    }
+
    /// Auto's paper white and peak are this display's report; the player's own values win.
    #[test]
    fn auto_levels_follow_this_renderers_report() {
@@ -407,6 +567,39 @@ pub(crate) mod tests {
        );
    }

+    /// UI Brightness reaches HDR output as its nits over paper white's: 1 on Auto, whatever
+    /// paper white is; a value set by hand holds its nits, Paper White on Auto or set by hand.
+    #[test]
+    fn ui_brightness_is_its_nits_over_paper_whites() {
+        let (caps, reading) = window(Some(Output::Pq), Some(true));
+        let share = |paper_white, ui_nits, reading| {
+            let settings = Graphics {
+                hdr: HdrMode::On,
+                hdr_paper_white: paper_white,
+                hdr_ui_nits: ui_nits,
+                ..Graphics::default()
+            };
+            let frame = resolve_frame(
+                &settings,
+                FrameRequest::default(),
+                caps,
+                reading,
+                Bgra8Unorm,
+            );
+            resolve_output(&settings, caps, reading, frame, true).ui_brightness
+        };
+        // Auto: the report's 400 nits, 203 without one, or the player's 250.
+        let unreported = DisplayReading::default();
+        for (paper_white, reading) in [(0, reading), (0, unreported), (250, reading)] {
+            assert_eq!(share(paper_white, 0, reading), 1.0);
+        }
+        assert_eq!(share(0, 100, reading), 0.25);
+        assert_eq!(share(0, 480, reading), 1.2);
+        assert_eq!(share(0, 406, unreported), 2.0);
+        assert_eq!(share(250, 100, reading), 0.4);
+        assert_eq!(share(250, 480, reading), 1.92);
+    }
+
    /// Two renderers' states, a window's and an offscreen one's, made and changed in turn:
    /// neither's offer or report shows in the other's snapshot, and the offscreen one
    /// stopping its watch (HDR Off) leaves the window's report alone.
@@ -0,0 +1,942 @@
+//! Applying the output a renderer resolves (`output::resolve_output`). Each observation of the
+//! settings, the destination's capabilities and the display resolves one candidate. One that
+//! changes only values (the luminance, the UI brightness, what the display reports) updates
+//! them in place. Another encoding or frame is built and the swapchain configured for it before
+//! the snapshot says so. One that fails is never published as active, and is not tried again
+//! until the request, the capabilities or the surface change. Auto keeps HDR on through a
+//! moment's loss of the display's report ([`auto_grace`]).
+use super::{DisplayReading, DisplayWatch, Renderer, hdr, output};
+use crate::graphics::HdrMode;
+use output::{EffectiveOutput, OutputCapabilities};
+use std::time::{Duration, Instant};
+
+/// What an output's resources are made for: the encoding presented and the frame.
+type Key = (Option<hdr::Output>, output::FrameConfiguration);
+fn key(output: &EffectiveOutput) -> Key {
+    (output.encoding, output.frame)
+}
+
+/// An output whose resources or swapchain configuration failed, with the capabilities it
+/// failed on.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(super) struct Rejected {
+    key: Key,
+    caps: OutputCapabilities,
+}
+
+/// What applying an output changes in a renderer.
+trait Present {
+    /// Builds what `output` presents and configures the swapchain for it, then swaps the new
+    /// resources in. On an error the resources stay as they were, and the swapchain may be
+    /// configured for neither output.
+    fn present(&mut self, output: &EffectiveOutput) -> std::result::Result<(), String>;
+    /// Presents SDR whatever happens: a swapchain that doesn't configure now is configured
+    /// again before the next frame (`surface_unconfigured`).
+    fn present_sdr(&mut self);
+}
+
+/// The snapshot to publish for `candidate` after `applied`, on `caps`. The same resources
+/// take the candidate's values as they are. Other ones are presented first and published only
+/// once that worked. On a failure the output applied stays where it presents again, else
+/// SDR, and the failed one is kept in `rejected` until the candidate's resources or the
+/// capabilities change.
+fn commit(
+    target: &mut impl Present,
+    applied: &EffectiveOutput,
+    candidate: EffectiveOutput,
+    caps: OutputCapabilities,
+    rejected: &mut Option<Rejected>,
+) -> EffectiveOutput {
+    let wanted = key(&candidate);
+    if rejected.is_some_and(|r| r.key != wanted || r.caps != caps) {
+        *rejected = None;
+    }
+    if wanted == key(applied) {
+        return candidate;
+    }
+    let kept = EffectiveOutput {
+        encoding: applied.encoding,
+        ..candidate
+    };
+    if rejected.is_some() {
+        return kept;
+    }
+    let Err(e) = target.present(&candidate) else {
+        return candidate;
+    };
+    log::warn!(
+        "Horizon renderer: {} could not be presented ({e}); keeping {}",
+        name(candidate.encoding),
+        name(applied.encoding)
+    );
+    *rejected = Some(Rejected { key: wanted, caps });
+    if target.present(&kept).is_ok() {
+        return kept;
+    }
+    log::warn!(
+        "Horizon renderer: {} no longer presents; SDR",
+        name(kept.encoding)
+    );
+    target.present_sdr();
+    EffectiveOutput {
+        encoding: None,
+        ..candidate
+    }
+}
+
+fn name(encoding: Option<hdr::Output>) -> &'static str {
+    encoding.map_or("SDR", hdr::Output::name)
+}
+
+/// The swapchain's configuration for `encoding`: `config` (what every pipeline draws in), or
+/// HDR10 or scRGB.
+pub(super) fn surface_config(
+    config: &wgpu::SurfaceConfiguration,
+    encoding: Option<hdr::Output>,
+) -> wgpu::SurfaceConfiguration {
+    let mut config = config.clone();
+    if let Some(output) = encoding {
+        config.format = output.format();
+        config.view_formats = vec![output.format()];
+        config.color_space = output.color_space();
+        config.usage = wgpu::TextureUsages::RENDER_ATTACHMENT;
+    }
+    config
+}
+
+/// How long Auto keeps HDR on once the display stops reporting it. A fixed window that
+/// coalesces the report's churn as a display wakes or the window moves to another one; not a
+/// measured sleep/wake time.
+const AUTO_OFF_DELAY: Duration = Duration::from_millis(500);
+
+/// The display's report `update_output` resolves Auto with at `now`. While Auto presents HDR
+/// and the surface still offers that encoding, a report that turns false or unknown starts
+/// the timer `since`, once, and HDR stays on at the values last applied until it has held
+/// for [`AUTO_OFF_DELAY`]; a positive report before then clears it. Off and On, a changed
+/// offer, and entering HDR take `raw` at once.
+fn auto_grace(
+    now: Instant,
+    mode: HdrMode,
+    offered: Option<hdr::Output>,
+    raw: DisplayReading,
+    applied: &EffectiveOutput,
+    since: &mut Option<Instant>,
+) -> DisplayReading {
+    let lost = mode == HdrMode::Auto
+        && applied.encoding.is_some()
+        && offered == applied.encoding
+        && raw.hdr != Some(true);
+    if !lost {
+        if since.take().is_some() && raw.hdr == Some(true) {
+            log::info!("Horizon renderer: the display reports HDR again; HDR stays on");
+        }
+    } else if since.is_none() {
+        log::info!(
+            "Horizon renderer: the display stopped reporting HDR; Auto keeps it on for {} ms",
+            AUTO_OFF_DELAY.as_millis()
+        );
+        *since = Some(now);
+    } else if grace_over(*since, now) {
+        *since = None;
+    }
+    graced(*since, raw, applied)
+}
+
+fn grace_over(since: Option<Instant>, now: Instant) -> bool {
+    since.is_some_and(|since| now.saturating_duration_since(since) >= AUTO_OFF_DELAY)
+}
+
+/// What the display reports as the output takes it: during Auto's grace (`since`), HDR at the
+/// luminance `applied` was resolved with; `raw` otherwise.
+pub(super) fn graced(
+    since: Option<Instant>,
+    raw: DisplayReading,
+    applied: &EffectiveOutput,
+) -> DisplayReading {
+    match since {
+        Some(_) => DisplayReading {
+            luminance: applied.reported,
+            hdr: Some(true),
+        },
+        None => raw,
+    }
+}
+
+/// Whether the output resolves again at `now`: a due poll (`read`, with the surface's
+/// `offer`; on Wayland, an event) changed `reading` or `caps`, or Auto's grace `since` is
+/// over. Its end reads the display once more first, however long until the next poll, unless
+/// a read since the deadline did (the last read is a `DISPLAY_POLL` before the next).
+fn poll_display(
+    watch: Option<&mut DisplayWatch>,
+    reading: &mut DisplayReading,
+    caps: &mut OutputCapabilities,
+    since: Option<Instant>,
+    now: Instant,
+    read: impl FnOnce() -> DisplayReading,
+    offer: impl FnOnce() -> Option<Option<hdr::Output>>,
+) -> bool {
+    let over = grace_over(since, now);
+    let Some(watch) = watch else {
+        return over;
+    };
+    if let (Some(since), Some(next)) = (since.filter(|_| over), &mut watch.polled)
+        && *next < since + AUTO_OFF_DELAY + super::DISPLAY_POLL
+    {
+        *next = now;
+    }
+    let Some(read) = watch.poll(*reading, now, read) else {
+        return over;
+    };
+    observe(reading, caps, read, offer()) || over
+}
+
+/// What `surface` offers now (`None` offscreen): Vulkan's offered formats can change with
+/// desktop HDR or the window's output, and a display can offer the other encoding.
+fn offer(surface: Option<&wgpu::Surface>, adapter: &wgpu::Adapter) -> Option<Option<hdr::Output>> {
+    Some(hdr::output(&surface?.get_capabilities(adapter)))
+}
+
+/// Takes what a due poll read into `reading` and `caps`: the display's report `now`, and what
+/// the surface offers (`offer`, `None` without a surface). Whether either changed, the offer
+/// alone included.
+fn observe(
+    reading: &mut DisplayReading,
+    caps: &mut OutputCapabilities,
+    now: DisplayReading,
+    offer: Option<Option<hdr::Output>>,
+) -> bool {
+    let before = (*reading, caps.hdr);
+    *reading = now;
+    if let Some(offer) = offer {
+        caps.hdr = offer;
+    }
+    before != (*reading, caps.hdr)
+}
+
+/// A renderer applying an output, with the marker its HDR output's start writes.
+struct Applying<'a> {
+    renderer: &'a mut Renderer,
+    marker: &'a std::path::Path,
+}
+
+impl Present for Applying<'_> {
+    fn present(&mut self, output: &EffectiveOutput) -> std::result::Result<(), String> {
+        let r = &mut *self.renderer;
+        let current = r.hdr.as_ref().map(|hdr| hdr.output);
+        let switching = output.encoding.is_some_and(|e| current != Some(e));
+        // If the game dies before HDR output shows a frame, its pipelines' build included, the
+        // marker is still there at the next start, which then holds HDR output back on this
+        // driver.
+        if output.encoding.is_none() || switching {
+            r.mark_hdr_start(output.encoding.is_some(), self.marker);
+        }
+        let built = match output.encoding {
+            Some(encoding) if switching => Some(r.build_hdr(encoding, output)?),
+            _ => None,
+        };
+        if let Some(surface) = &r.surface {
+            r.frame_gen.stop();
+            // The submit thread may still present to the old swapchain.
+            r.queue.wait();
+            let hdr = built.as_ref().or(r.hdr.as_ref());
+            Renderer::configure(
+                &r.device,
+                surface,
+                &surface_config(&r.config, output.encoding),
+                hdr.filter(|_| output.encoding.is_some()),
+                &r.device_lost,
+            )?;
+            r.surface_unconfigured = false;
+        }
+        if output.encoding.is_none() {
+            r.hdr = None;
+        } else if built.is_some() {
+            r.hdr = built;
+        }
+        Ok(())
+    }
+
+    fn present_sdr(&mut self) {
+        let r = &mut *self.renderer;
+        r.hdr = None;
+        r.mark_hdr_start(false, self.marker);
+        if let Some(surface) = &r.surface {
+            r.frame_gen.stop();
+            r.queue.wait();
+            r.surface_unconfigured =
+                Renderer::configure(&r.device, surface, &r.config, None, &r.device_lost).is_err();
+        }
+    }
+}
+
+impl Renderer {
+    /// HDR output presenting `encoding` for `output`, made apart from the one presented: from
+    /// it where there is one, keeping the player's tuning (`Hdr::retargeted`). An error is
+    /// the device's, caught here rather than left for the next frame.
+    fn build_hdr(
+        &self,
+        encoding: hdr::Output,
+        output: &EffectiveOutput,
+    ) -> std::result::Result<hdr::Hdr, String> {
+        let validation = self.device.push_error_scope(wgpu::ErrorFilter::Validation);
+        let memory = self.device.push_error_scope(wgpu::ErrorFilter::OutOfMemory);
+        let mut hdr = match &self.hdr {
+            Some(hdr) => hdr.retargeted(&self.device, &self.queue, encoding),
+            None => {
+                let mut hdr = hdr::Hdr::new(
+                    &self.device,
+                    &self.queue,
+                    output.frame.format,
+                    encoding,
+                    output.frame.hud_layer,
+                );
+                hdr.look = self.hdr_lighting_setting;
+                hdr
+            }
+        };
+        let memory = pollster::block_on(memory.pop());
+        if let Some(e) = memory.or(pollster::block_on(validation.pop())) {
+            return Err(e.to_string());
+        }
+        // The metadata the swapchain's configuration sends.
+        [hdr.paper_white, hdr.peak, hdr.black] = output.nits;
+        hdr.ui = output.ui_brightness;
+        Ok(hdr)
+    }
+
+    /// HDR output (Horizon setting) as `settings` ask for it on this renderer's frame
+    /// (`output::resolve_output`): HDR10 or scRGB at paper white, the world's highlights
+    /// expanded up to the peak. Off where the surface can't present it. Offscreen
+    /// (`hdr::offscreen_output`) the frame is drawn the same and its HDR screenshot taken,
+    /// but nothing is presented, and Auto takes its defaults: no display reports.
+    pub fn update_output(
+        &mut self,
+        settings: &crate::graphics::Graphics,
+        marker: &std::path::Path,
+    ) {
+        let now = Instant::now();
+        self.watch_hdr(settings.hdr);
+        // Auto's grace ends on a fresh read, also where a settings change comes before the
+        // frame's `display_changed`.
+        if grace_over(self.auto_off_since, now) {
+            self.read_display(now);
+        }
+        self.hold_hdr_back(settings);
+        let reading = auto_grace(
+            now,
+            settings.hdr,
+            self.output_caps.hdr,
+            self.reading,
+            &self.output,
+            &mut self.auto_off_since,
+        );
+        let candidate = output::resolve_output(
+            settings,
+            self.output_caps,
+            reading,
+            self.output.frame,
+            self.surface.is_some() || self.offscreen.is_some(),
+        );
+        let (applied, caps) = (self.output, self.output_caps);
+        let mut rejected = self.output_rejected.take();
+        let renderer = &mut Applying {
+            renderer: self,
+            marker,
+        };
+        let next = commit(renderer, &applied, candidate, caps, &mut rejected);
+        self.output_rejected = rejected;
+        let [paper_white, peak, black] = next.nits;
+        if next.encoding != applied.encoding {
+            match next.encoding {
+                Some(output) => log::info!(
+                    "Horizon renderer: HDR on: {} ({:?}), {paper_white}/{peak} nits",
+                    output.name(),
+                    output.format()
+                ),
+                None => log::info!("Horizon renderer: HDR off"),
+            }
+            self.measure_emission();
+        }
+        if let Some(hdr) = &mut self.hdr {
+            hdr.ui = next.ui_brightness;
+            if (hdr.paper_white, hdr.peak, hdr.black) != (paper_white, peak, black) {
+                (hdr.paper_white, hdr.peak, hdr.black) = (paper_white, peak, black);
+                self.send_hdr_metadata();
+            }
+        }
+        self.output = next;
+    }
+
+    /// Follows the selected mode even when Auto currently wants SDR. Off never asks
+    /// the system about the display; selecting On or Auto starts a fresh watch.
+    fn watch_hdr(&mut self, mode: crate::graphics::HdrMode) {
+        if mode == crate::graphics::HdrMode::Off {
+            self.display = None;
+            self.display_fresh = false;
+            self.reading.stop_watching();
+        } else if self.display.is_none() {
+            let (watch, now) =
+                DisplayWatch::new(&self.window, self.surface.as_deref(), &self.adapter);
+            self.display = Some(watch);
+            let offer = offer(self.surface.as_deref(), &self.adapter);
+            self.output_caps.hdr = offer.unwrap_or(self.output_caps.hdr);
+            self.reading = now;
+            self.display_fresh = true;
+        }
+    }
+
+    /// The swapchain's configuration: `config` (what every pipeline draws in), or
+    /// HDR10 or scRGB while HDR output is on.
+    pub(super) fn surface_config(&self) -> wgpu::SurfaceConfiguration {
+        surface_config(&self.config, self.hdr.as_ref().map(|hdr| hdr.output))
+    }
+
+    /// After a new window surface: what it offers, and an output that failed on the old one
+    /// may be tried again. The settings apply again.
+    pub(super) fn surface_recreated(&mut self) {
+        let offer = offer(self.surface.as_deref(), &self.adapter);
+        self.output_caps.hdr = offer.unwrap_or(self.output_caps.hdr);
+        self.display_fresh = true;
+        self.output_rejected = None;
+    }
+
+    /// Whether what the system reports for the display, or what the surface offers, changed
+    /// (another output, the player recalibrating the desktop, desktop HDR offering the other
+    /// encoding): the settings' Auto values and the output follow it then, so apply them
+    /// again. Each due poll reads the surface's capabilities as well, even when the display
+    /// reports the same. So does the end of Auto's grace (`auto_grace`), with or without a
+    /// poll or an event then.
+    pub fn display_changed(&mut self) -> bool {
+        super::flush_display_log();
+        if std::mem::take(&mut self.display_fresh) {
+            return true;
+        }
+        self.read_display(Instant::now())
+    }
+
+    /// The display read where a poll is due or Auto's grace is over (`poll_display`).
+    fn read_display(&mut self, now: Instant) -> bool {
+        let (surface, adapter) = (self.surface.as_deref(), &self.adapter);
+        poll_display(
+            self.display.as_mut(),
+            &mut self.reading,
+            &mut self.output_caps,
+            self.auto_off_since,
+            now,
+            || DisplayReading::read(surface, adapter),
+            || offer(surface, adapter),
+        )
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::graphics::{Graphics, HdrMode, Reported};
+    use hdr::Output::{Pq, ScRgb};
+    use output::FrameRequest;
+    use output::tests::{snapshot, window};
+
+    /// A swapchain that records what it was asked to present, and fails `fails`.
+    #[derive(Default)]
+    struct Swapchain {
+        fails: Vec<Option<hdr::Output>>,
+        /// Each encoding presented, with the luminance its metadata sends.
+        asked: Vec<(Option<hdr::Output>, [f32; 3])>,
+        sdr: usize,
+    }
+    impl Present for Swapchain {
+        fn present(&mut self, output: &EffectiveOutput) -> std::result::Result<(), String> {
+            self.asked.push((output.encoding, output.nits));
+            if self.fails.contains(&output.encoding) {
+                return Err("unsupported".into());
+            }
+            Ok(())
+        }
+        fn present_sdr(&mut self) {
+            self.sdr += 1;
+        }
+    }
+
+    const NO_PACK: FrameRequest = FrameRequest {
+        linear_pack: false,
+        hdr_float: true,
+    };
+    fn on() -> Graphics {
+        Graphics {
+            hdr: HdrMode::On,
+            ..Graphics::default()
+        }
+    }
+    /// The candidate on a renderer whose frame is `applied`'s.
+    fn candidate(
+        settings: &Graphics,
+        caps: OutputCapabilities,
+        reading: DisplayReading,
+        applied: &EffectiveOutput,
+    ) -> EffectiveOutput {
+        output::resolve_output(settings, caps, reading, applied.frame, true)
+    }
+
+    /// HDR stays on while the display offers scRGB instead of HDR10 and then HDR10 again:
+    /// the swapchain, its metadata and the snapshot follow each, with no Off between.
+    #[test]
+    fn the_output_follows_pq_to_scrgb_and_back_while_hdr_stays_on() {
+        let settings = on();
+        let (mut caps, reading) = window(Some(Pq), Some(true));
+        let mut applied = snapshot(&settings, NO_PACK, caps, reading);
+        assert_eq!(applied.encoding, Some(Pq));
+        let (mut swapchain, mut rejected) = (Swapchain::default(), None);
+        for encoding in [ScRgb, Pq] {
+            caps.hdr = Some(encoding);
+            let next = candidate(&settings, caps, reading, &applied);
+            applied = commit(&mut swapchain, &applied, next, caps, &mut rejected);
+            assert_eq!(
+                (applied.encoding, applied.offered),
+                (Some(encoding), Some(encoding))
+            );
+            assert_eq!(
+                applied.frame,
+                snapshot(&settings, NO_PACK, caps, reading).frame
+            );
+        }
+        let metadata = [400.0, 1000.0, 0.0];
+        assert_eq!(
+            swapchain.asked,
+            [(Some(ScRgb), metadata), (Some(Pq), metadata)]
+        );
+        assert_eq!((rejected, swapchain.sdr), (None, 0));
+    }
+
+    /// The display reports the same luminance and HDR, but the surface now offers scRGB: the
+    /// next due poll reads it, and the output follows with the same nits and report.
+    #[test]
+    fn a_change_of_offer_alone_is_seen_at_the_next_poll() {
+        let settings = on();
+        let (mut caps, mut reading) = window(Some(Pq), Some(true));
+        let applied = snapshot(&settings, NO_PACK, caps, reading);
+        let start = std::time::Instant::now();
+        let mut watch = DisplayWatch {
+            #[cfg(target_os = "linux")]
+            wayland: None,
+            polled: Some(start + super::super::DISPLAY_POLL),
+        };
+        let same = reading;
+        assert_eq!(watch.poll(reading, start, || unreachable!()), None);
+        let due = start + super::super::DISPLAY_POLL;
+        assert_eq!(watch.poll(reading, due, || same), Some(same));
+        assert_eq!(watch.polled, Some(due + super::super::DISPLAY_POLL));
+        assert!(observe(&mut reading, &mut caps, same, Some(Some(ScRgb))));
+        // Nothing changed at the next poll, and offscreen nothing is offered to read.
+        assert!(!observe(&mut reading, &mut caps, same, Some(Some(ScRgb))));
+        assert!(!observe(&mut reading, &mut caps, same, None));
+        let next = candidate(&settings, caps, reading, &applied);
+        let published = commit(&mut Swapchain::default(), &applied, next, caps, &mut None);
+        assert_eq!(published.encoding, Some(ScRgb));
+        assert_eq!(
+            (published.nits, published.reported, published.system_hdr),
+            (applied.nits, applied.reported, applied.system_hdr)
+        );
+    }
+
+    /// The display's luminance or the UI brightness change on the same output: the values
+    /// follow, and nothing is built or configured again.
+    #[test]
+    fn new_nits_on_the_same_output_build_nothing() {
+        let mut settings = on();
+        let (caps, mut reading) = window(Some(Pq), Some(true));
+        let applied = snapshot(&settings, NO_PACK, caps, reading);
+        reading.luminance = Some(Reported {
+            paper_white: 250,
+            peak: 600,
+        });
+        // 150 nits under the reported paper white of 250: 0.6 of it.
+        settings.hdr_ui_nits = 150;
+        let mut swapchain = Swapchain::default();
+        let next = candidate(&settings, caps, reading, &applied);
+        let published = commit(&mut swapchain, &applied, next, caps, &mut None);
+        assert_eq!(published, next);
+        assert_eq!(published.nits, [250.0, 600.0, 0.0]);
+        assert_eq!(published.ui_brightness, 0.6);
+        assert!(swapchain.asked.is_empty());
+    }
+
+    /// An encoding that fails is never the snapshot's: the output applied stays where it
+    /// presents again, else SDR. It is not tried again each frame, nor for new nits, only
+    /// once the request or the capabilities change.
+    #[test]
+    fn an_output_that_fails_is_never_active_nor_tried_every_frame() {
+        let settings = on();
+        let (mut caps, mut reading) = window(Some(Pq), Some(true));
+        let pq = snapshot(&settings, NO_PACK, caps, reading);
+        caps.hdr = Some(ScRgb);
+        let mut swapchain = Swapchain {
+            fails: vec![Some(ScRgb)],
+            ..Default::default()
+        };
+        let mut rejected = None;
+        let next = candidate(&settings, caps, reading, &pq);
+        let published = commit(&mut swapchain, &pq, next, caps, &mut rejected);
+        assert_eq!(published.encoding, Some(Pq));
+        assert_eq!(swapchain.asked.len(), 2, "scRGB, then HDR10 again");
+        // Frames after, and a new luminance: no new attempt.
+        for paper_white in [400, 400, 300] {
+            reading.luminance = Some(Reported {
+                paper_white,
+                peak: 1000,
+            });
+            let next = candidate(&settings, caps, reading, &published);
+            let again = commit(&mut swapchain, &published, next, caps, &mut rejected);
+            assert_eq!(again.encoding, Some(Pq));
+            assert_eq!(again.nits[0], paper_white as f32);
+        }
+        assert_eq!(swapchain.asked.len(), 2);
+        // Another request (HDR Off, then On) tries it again.
+        let off = Graphics::default();
+        let sdr = commit(
+            &mut swapchain,
+            &published,
+            candidate(&off, caps, reading, &published),
+            caps,
+            &mut rejected,
+        );
+        assert_eq!((sdr.encoding, rejected), (None, None));
+        let next = candidate(&settings, caps, reading, &sdr);
+        assert_eq!(
+            commit(&mut swapchain, &sdr, next, caps, &mut rejected).encoding,
+            None
+        );
+        assert_eq!(
+            swapchain.asked.iter().map(|a| a.0).collect::<Vec<_>>(),
+            [Some(ScRgb), Some(Pq), None, Some(ScRgb), None]
+        );
+        // So does another capability (the hold lifted here stands for any).
+        caps.held = true;
+        let held = candidate(&settings, caps, reading, &sdr);
+        assert_eq!(held.encoding, None);
+        commit(&mut swapchain, &sdr, held, caps, &mut rejected);
+        caps.held = false;
+        let asked = swapchain.asked.len();
+        let next = candidate(&settings, caps, reading, &sdr);
+        commit(&mut swapchain, &sdr, next, caps, &mut rejected);
+        assert_eq!(swapchain.asked.len(), asked + 2);
+        // The output applied failing too: SDR, never the failed one.
+        let mut broken = Swapchain {
+            fails: vec![Some(ScRgb), Some(Pq)],
+            ..Default::default()
+        };
+        let next = candidate(&settings, caps, reading, &pq);
+        let published = commit(&mut broken, &pq, next, caps, &mut None);
+        assert_eq!((published.encoding, broken.sdr), (None, 1));
+        assert_eq!(settings.hdr, HdrMode::On, "the mode stays");
+        // A new surface forgets the failure (`surface_recreated`): the same request on the
+        // same capabilities is tried again.
+        let mut swapchain = Swapchain {
+            fails: vec![Some(ScRgb)],
+            ..Default::default()
+        };
+        let mut rejected = None;
+        let next = candidate(&settings, caps, reading, &pq);
+        for _ in 0..2 {
+            commit(&mut swapchain, &pq, next, caps, &mut rejected);
+        }
+        assert_eq!(swapchain.asked.len(), 2);
+        rejected = None;
+        commit(&mut swapchain, &pq, next, caps, &mut rejected);
+        assert_eq!(swapchain.asked.len(), 4);
+    }
+
+    /// A window in Auto presenting HDR10 at 400/1000 nits on the layered frame, followed on
+    /// fake time as the game follows a renderer each frame: `display_changed`, then
+    /// `update_output` where it says so.
+    struct Auto {
+        settings: Graphics,
+        start: Instant,
+        watch: DisplayWatch,
+        reading: DisplayReading,
+        caps: OutputCapabilities,
+        applied: EffectiveOutput,
+        since: Option<Instant>,
+        swapchain: Swapchain,
+        /// What the system reports when it is read, and when (ms) it was.
+        report: DisplayReading,
+        reads: Vec<u64>,
+    }
+    impl Auto {
+        /// `polled`: the system is read every `DISPLAY_POLL` from 0, else it sends events
+        /// (`event`), as on Wayland.
+        fn new(polled: bool) -> Self {
+            let settings = Graphics {
+                hdr: HdrMode::Auto,
+                ..Graphics::default()
+            };
+            let (caps, reading) = window(Some(Pq), Some(true));
+            let applied = snapshot(&settings, NO_PACK, caps, reading);
+            assert!(applied.encoding == Some(Pq) && applied.frame.hud_layer);
+            let start = Instant::now();
+            Self {
+                settings,
+                start,
+                watch: DisplayWatch {
+                    #[cfg(target_os = "linux")]
+                    wayland: None,
+                    polled: polled.then_some(start),
+                },
+                reading,
+                caps,
+                applied,
+                since: None,
+                swapchain: Swapchain::default(),
+                report: reading,
+                reads: Vec::new(),
+            }
+        }
+        /// A frame at `ms`.
+        fn frame(&mut self, ms: u64) {
+            if self.read_display(ms) {
+                self.update(ms);
+            }
+        }
+        /// `Renderer::read_display` at `ms`.
+        fn read_display(&mut self, ms: u64) -> bool {
+            let now = self.start + Duration::from_millis(ms);
+            let (report, offer, reads) = (self.report, Some(self.caps.hdr), &mut self.reads);
+            let read = || {
+                reads.push(ms);
+                report
+            };
+            let (reading, caps) = (&mut self.reading, &mut self.caps);
+            poll_display(
+                Some(&mut self.watch),
+                reading,
+                caps,
+                self.since,
+                now,
+                read,
+                || offer,
+            )
+        }
+        /// Frames from `from` to `to` ms, every 10 ms.
+        fn frames(&mut self, from: u64, to: u64) {
+            for ms in (from..=to).step_by(10) {
+                self.frame(ms);
+            }
+        }
+        /// What the system reports from `ms` on: HDR `hdr`, with no luminance unless it is
+        /// HDR, at 300/800 nits then.
+        fn reports(&mut self, hdr: Option<bool>, offer: Option<hdr::Output>) {
+            self.report = DisplayReading {
+                luminance: (hdr == Some(true)).then_some(Reported {
+                    paper_white: 300,
+                    peak: 800,
+                }),
+                hdr,
+            };
+            self.caps.hdr = offer;
+        }
+        /// The system's event at `ms`, with what it now `reports`.
+        fn event(&mut self, ms: u64, hdr: Option<bool>, offer: Option<hdr::Output>) {
+            self.reports(hdr, offer);
+            self.reading = self.report;
+            self.update(ms);
+        }
+        /// `update_output` at `ms`, in its order.
+        fn update(&mut self, ms: u64) {
+            let now = self.start + Duration::from_millis(ms);
+            if grace_over(self.since, now) {
+                self.read_display(ms);
+            }
+            let applied = &self.applied;
+            let reading = auto_grace(
+                now,
+                self.settings.hdr,
+                self.caps.hdr,
+                self.reading,
+                applied,
+                &mut self.since,
+            );
+            let next = candidate(&self.settings, self.caps, reading, applied);
+            self.applied = commit(&mut self.swapchain, applied, next, self.caps, &mut None);
+            // While HDR stays on, the frame the game asks for (`Renderer::requested_frame`) is
+            // this one: no new renderer.
+            let reading = graced(self.since, self.reading, &self.applied);
+            let frame = output::resolve_frame(
+                &self.settings,
+                NO_PACK,
+                self.caps,
+                reading,
+                wgpu::TextureFormat::Bgra8UnormSrgb,
+            );
+            assert_eq!(
+                frame == self.applied.frame,
+                self.applied.hdr_on(),
+                "{ms} ms"
+            );
+        }
+        fn presented(&self) -> Vec<Option<hdr::Output>> {
+            self.swapchain.asked.iter().map(|a| a.0).collect()
+        }
+    }
+
+    /// The display's report flickers off and back, false or unknown: HDR stays on, nothing
+    /// is presented again, and the shader `Frame`, what the settings show as active and the
+    /// nits stay as they were applied, even while the report says nothing of them.
+    #[test]
+    fn a_report_that_flickers_off_and_back_swaps_nothing() {
+        for lost in [Some(false), None] {
+            let mut auto = Auto::new(false);
+            let before = auto.applied;
+            auto.event(0, Some(true), Some(Pq));
+            auto.frames(0, 90);
+            let fresh = auto.applied;
+            assert_eq!(fresh.nits, [300.0, 800.0, 0.0], "a positive report applies");
+            auto.event(100, lost, Some(Pq));
+            auto.frames(100, 390);
+            assert_eq!(auto.applied, fresh, "{lost:?}");
+            assert!(auto.applied.requests_hdr(HdrMode::Auto) && auto.applied.display().hdr);
+            auto.event(400, Some(true), Some(Pq));
+            auto.frames(400, 1500);
+            assert_eq!((auto.applied, auto.since), (fresh, None), "{lost:?}");
+            assert!(auto.presented().is_empty(), "{lost:?}");
+            assert_eq!(auto.applied.frame, before.frame);
+        }
+    }
+
+    /// A loss held through 600 ms turns HDR off once, at 500 ms, and on an event-driven
+    /// display with no event then. The same loss reported again doesn't restart the timer.
+    #[test]
+    fn a_loss_held_turns_hdr_off_once_at_the_deadline() {
+        for lost in [Some(false), None] {
+            let mut auto = Auto::new(false);
+            auto.event(0, lost, Some(Pq));
+            auto.frames(0, 190);
+            auto.event(200, lost, Some(Pq));
+            auto.frames(200, 490);
+            assert_eq!(auto.applied.encoding, Some(Pq), "{lost:?}");
+            auto.frame(500);
+            assert_eq!(auto.applied.encoding, None, "{lost:?}");
+            auto.frames(500, 3000);
+            assert_eq!(auto.presented(), [None], "{lost:?}");
+            assert_eq!(auto.since, None);
+        }
+    }
+
+    /// Where the system is polled, a false read by the poll that starts the timer is read
+    /// again at the deadline, not two seconds after, before it counts: the display came back
+    /// meanwhile, so HDR stays; where it didn't, HDR turns off then. The two-second cadence
+    /// stays otherwise.
+    #[test]
+    fn a_polled_false_is_read_again_at_the_deadline() {
+        for back in [true, false] {
+            let mut auto = Auto::new(true);
+            auto.frames(0, 1990);
+            auto.reports(Some(false), Some(Pq));
+            auto.frame(2000);
+            assert_eq!(
+                (auto.applied.encoding, auto.since.is_some()),
+                (Some(Pq), true)
+            );
+            if back {
+                auto.reports(Some(true), Some(Pq));
+            }
+            auto.frames(2010, 2490);
+            assert_eq!(auto.applied.encoding, Some(Pq), "never before the deadline");
+            auto.frames(2500, 4990);
+            assert_eq!(auto.reads, [0, 2000, 2500, 4500], "back {back}");
+            let after = if back { vec![] } else { vec![None] };
+            assert_eq!(auto.presented(), after, "back {back}");
+        }
+    }
+
+    /// A settings change at the deadline, before the frame's poll (a slider, F11), reads the
+    /// display before the grace ends, and the frame after reads it no more: the display came
+    /// back meanwhile, so HDR stays; where it didn't, HDR turns off then, once.
+    #[test]
+    fn a_settings_change_at_the_deadline_reads_the_display_first() {
+        for back in [true, false] {
+            let mut auto = Auto::new(true);
+            auto.frames(0, 1990);
+            auto.reports(Some(false), Some(Pq));
+            auto.frame(2000);
+            if back {
+                auto.reports(Some(true), Some(Pq));
+            }
+            auto.frames(2010, 2490);
+            auto.update(2500);
+            assert_eq!(auto.applied.hdr_on(), back, "back {back}");
+            auto.frames(2500, 4990);
+            assert_eq!(auto.reads, [0, 2000, 2500, 4500], "back {back}");
+            let after = if back { vec![] } else { vec![None] };
+            assert_eq!(auto.presented(), after, "back {back}");
+        }
+    }
+
+    /// A positive report clears the timer: a later loss has its own 500 ms.
+    #[test]
+    fn a_positive_report_clears_the_timer() {
+        let mut auto = Auto::new(false);
+        auto.event(100, Some(false), Some(Pq));
+        auto.event(300, Some(true), Some(Pq));
+        auto.event(700, Some(false), Some(Pq));
+        auto.frames(700, 1190);
+        assert_eq!(auto.applied.encoding, Some(Pq));
+        auto.frame(1200);
+        assert_eq!(auto.presented(), [None]);
+    }
+
+    /// Off acts at once, and On or Off clear the timer: Auto again starts it anew.
+    #[test]
+    fn off_and_on_take_no_grace() {
+        let mut auto = Auto::new(false);
+        auto.event(100, Some(false), Some(Pq));
+        auto.settings.hdr = HdrMode::Off;
+        auto.update(200);
+        assert_eq!((auto.presented(), auto.since), (vec![None], None));
+        let mut auto = Auto::new(false);
+        auto.event(100, Some(false), Some(Pq));
+        auto.settings.hdr = HdrMode::On;
+        auto.update(200);
+        assert_eq!((auto.applied.encoding, auto.since), (Some(Pq), None));
+        auto.settings.hdr = HdrMode::Auto;
+        auto.update(300);
+        auto.frames(300, 790);
+        assert_eq!(auto.applied.encoding, Some(Pq));
+        auto.frame(800);
+        assert_eq!(auto.presented(), [None]);
+    }
+
+    /// The surface no longer offering the encoding presented ends the grace at once: SDR
+    /// without a report, the other encoding with one.
+    #[test]
+    fn an_encoding_no_longer_offered_is_not_kept() {
+        for offer in [None, Some(ScRgb)] {
+            let mut auto = Auto::new(false);
+            auto.event(100, Some(false), Some(Pq));
+            auto.event(200, Some(false), offer);
+            assert_eq!((auto.presented(), auto.since), (vec![None], None));
+            let mut auto = Auto::new(false);
+            auto.event(100, None, offer);
+            assert_eq!(auto.presented(), [None], "{offer:?}");
+        }
+        let mut auto = Auto::new(false);
+        auto.event(100, Some(false), Some(Pq));
+        auto.event(200, Some(true), Some(ScRgb));
+        assert_eq!(auto.presented(), [Some(ScRgb)]);
+    }
+
+    /// Two windows' timers run apart.
+    #[test]
+    fn two_renderers_keep_their_own_timer() {
+        let (mut a, mut b) = (Auto::new(false), Auto::new(false));
+        b.start = a.start;
+        a.event(100, Some(false), Some(Pq));
+        b.event(300, Some(false), Some(Pq));
+        a.event(400, Some(true), Some(Pq));
+        for ms in (300..=900).step_by(10) {
+            a.frame(ms);
+            b.frame(ms);
+            assert_eq!(b.applied.hdr_on(), ms < 800, "{ms} ms");
+        }
+        assert_eq!((a.presented(), b.presented()), (vec![], vec![None]));
+    }
+}
@@ -597,9 +597,9 @@ const FACE: &str = "    uint hz_q = (uint(gl_VertexIndex) & ~3u) * 6u;\n    \
 /// quad lands whole in one part. The colour's alpha can't decide it, as with `separateAo` it
 /// holds each vertex's own ambient occlusion.
 pub fn terrain_parts(
-    terrain: &horizon_render_pipeline::GbuffersInputs,
+    terrain: &horizon_shaders::GbuffersInputs,
    lava: &[u16],
-) -> [horizon_render_pipeline::GbuffersInputs; 2] {
+) -> [horizon_shaders::GbuffersInputs; 2] {
    let opaque = crate::mesher::OPAQUE_LAYER;
    let lava: String = lava
        .iter()
@@ -619,7 +619,7 @@ pub fn terrain_parts(
 impl PackAtlas {
    /// The vertex inputs of a gbuffers program drawing terrain (`TerrainVertex`, terrain.wgsl's
    /// `vs_terrain` or, for `flat` draws, `vs_terrain_flat`), in atlas coordinates.
-    pub fn terrain_inputs(&self, flat: bool) -> horizon_render_pipeline::GbuffersInputs {
+    pub fn terrain_inputs(&self, flat: bool) -> horizon_shaders::GbuffersInputs {
        let mut declarations = String::from(
            "layout(location = 0) in vec3 hz_v_pos;\nlayout(location = 1) in uvec2 hz_v_uv;\n\
             layout(location = 2) in uint hz_v_layer;\nlayout(location = 3) in vec4 hz_v_color;\n\
@@ -753,7 +753,7 @@ impl PackAtlas {
            ("vaColor", "hz_Color"),
            ("vaNormal", "hz_Normal"),
        ];
-        horizon_render_pipeline::GbuffersInputs {
+        horizon_shaders::GbuffersInputs {
            declarations,
            body,
            attributes: attributes
@@ -2,7 +2,7 @@
 //! translator's `DRAW_UNIFORMS`): one slot per render stage of a uniform buffer, picked with a
 //! dynamic offset at each draw.

-use horizon_render_pipeline::{RENDER_STAGES, render_stage};
+use horizon_shaders::{RENDER_STAGES, render_stage};

 /// Where a run of `Frame::entities` begins, and what it is (slice 7): the run lasts until the
 /// next span. Recorded only while a shader pack draws entities, so Horizon's own frames carry
@@ -6,7 +6,7 @@

 use std::ops::Range;

-use horizon_render_pipeline::render_stage;
+use horizon_shaders::render_stage;

 use super::Vertex;
 use super::pack_draw::EntitySpan;
@@ -31,7 +31,7 @@ pub fn buffers() -> [Option<wgpu::VertexBufferLayout<'static>>; 1] {
 /// position, the shared atlas's UV, colour, light (block, sky in 16ths) and the world-oriented
 /// normal. The quad's corners, read from the same vertices at set 1, give the face normal where
 /// the vertex has none (custom geometry) and `at_tangent` along the texture's u, as for terrain.
-pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
+pub fn inputs() -> horizon_shaders::GbuffersInputs {
    let words = std::mem::size_of::<Vertex>() / 4;
    let mut declarations = "layout(location = 0) in vec3 hz_v_pos;\nlayout(location = 1) in vec2 hz_v_uv;\n\
         layout(location = 2) in uint hz_v_overlay;\nlayout(location = 3) in vec4 hz_v_color;\n\
@@ -112,7 +112,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
        // bright.
        ("horizonTier", "float((hz_v_overlay >> 16u) & 255u)"),
    ];
-    horizon_render_pipeline::GbuffersInputs {
+    horizon_shaders::GbuffersInputs {
        declarations,
        body,
        attributes: attributes
@@ -121,7 +121,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
            .collect(),
        after: String::new(),
        // Cutout, as vanilla's entity types mostly are (OQ-23): the loader's test at 0.1.
-        alpha_test: Some(horizon_render_pipeline::AlphaTest {
+        alpha_test: Some(horizon_shaders::AlphaTest {
            op: ">",
            reference: 0.1,
        }),
@@ -138,7 +138,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
 /// inputs of [`inputs`], each vertex read from set 1 (`hz_entity_vertices`), as `Vertex` lays
 /// it out. The draw's corners walk its quads two triangles each, as `quad_indices` does: corner
 /// `c` of a draw from vertex `first` (a whole quad) is drawn as vertex `first / 4 * 6 + c`.
-pub fn geometry_inputs() -> horizon_render_pipeline::GeometryInputs {
+pub fn geometry_inputs() -> horizon_shaders::GeometryInputs {
    let words = std::mem::size_of::<Vertex>() / 4;
    let pull = format!(
        "        uint hz_pw = hz_vertex_index * {words}u;\n        \
@@ -150,7 +150,7 @@ pub fn geometry_inputs() -> horizon_render_pipeline::GeometryInputs {
         hz_v_light = uvec4(hz_pl & 255u, (hz_pl >> 8u) & 255u, (hz_pl >> 16u) & 255u, hz_pl >> 24u);\n        \
         hz_v_normal = unpackSnorm4x8(hz_entity_vertices[hz_pw + 8u]);\n"
    );
-    horizon_render_pipeline::GeometryInputs {
+    horizon_shaders::GeometryInputs {
        inputs: inputs(),
        pull,
        // Quad `c / 6`, corner 0, 1, 2, 0, 2, 3 of it.
@@ -163,7 +163,7 @@ pub fn geometry_inputs() -> horizon_render_pipeline::GeometryInputs {
 /// What `gbuffers_clouds` reads from the clouds' mesh (entity vertices, `vs_cloud`): the
 /// position moved by the clouds' offset, the colour of the face's shade from their palette,
 /// full light, the face's normal. Set 1 holds the clouds' uniform (`clouds::Uniform`).
-pub fn cloud_inputs() -> horizon_render_pipeline::GbuffersInputs {
+pub fn cloud_inputs() -> horizon_shaders::GbuffersInputs {
    let declarations = "layout(location = 0) in vec3 hz_v_pos;\nlayout(location = 1) in vec2 hz_v_uv;\n\
         layout(location = 2) in uint hz_v_overlay;\nlayout(location = 3) in vec4 hz_v_color;\n\
         layout(location = 4) in uvec4 hz_v_light;\nlayout(location = 5) in vec4 hz_v_normal;\n\
@@ -183,7 +183,7 @@ pub fn cloud_inputs() -> horizon_render_pipeline::GbuffersInputs {
        ("vaColor", "hz_Color"),
        ("vaNormal", "hz_Normal"),
    ];
-    horizon_render_pipeline::GbuffersInputs {
+    horizon_shaders::GbuffersInputs {
        declarations,
        body,
        attributes: attributes
@@ -17,7 +17,7 @@ const UNIFORM: u64 = 2 * 64;
 const SLOT: u64 = 32;

 /// What `gbuffers_hand` reads: the entity inputs, and the hand's projection from set 1.
-pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
+pub fn inputs() -> horizon_shaders::GbuffersInputs {
    let mut inputs = super::pack_entities::inputs();
    // No last frame's hand to measure from: the hand's `at_velocity` reads zero (and its set 1
    // has no previous vertices).
@@ -270,7 +270,7 @@ fn translucent_quad(quad: &[Vertex]) -> bool {
 /// outside block entities, and `currentRenderedItemId`.
 fn draw_slot(id: i32, translucent: bool) -> [u8; SLOT as usize] {
    let mut bytes = [0u8; SLOT as usize];
-    let stage = horizon_render_pipeline::render_stage(if translucent {
+    let stage = horizon_shaders::render_stage(if translucent {
        "HAND_TRANSLUCENT"
    } else {
        "HAND_SOLID"
@@ -8,7 +8,7 @@
 /// width in pixels. The strip's corners 0 and 1 are at the start, 2 and 3 at the end (six
 /// vertices per edge: pack pipelines draw triangle lists); the
 /// width is applied in screen space after the pack's transform.
-pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
+pub fn inputs() -> horizon_shaders::GbuffersInputs {
    let declarations =
        "layout(location = 0) in vec3 hz_l_start;\nlayout(location = 1) in vec3 hz_l_end;\n\
         layout(location = 2) in vec4 hz_l_argb;\nlayout(location = 3) in float hz_l_width;\n\
@@ -41,7 +41,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
         if ((hz_l_c & 1) != 0) hz_l_o = -hz_l_o;\n        \
         gl_Position.xy += hz_l_o * gl_Position.w;\n    }\n"
        .to_owned();
-    horizon_render_pipeline::GbuffersInputs {
+    horizon_shaders::GbuffersInputs {
        declarations,
        body,
        attributes: attributes
@@ -55,6 +55,10 @@ mod sky_disc_blend_tests;
 #[cfg(test)]
 mod undrawn_terrain_tests;

+mod image_formats;
+use image_formats::{image_format, storage_formats_of};
+#[cfg(test)]
+mod full_outputs_tests;
 #[cfg(test)]
 mod shadow_faces_tests;

@@ -125,7 +129,7 @@ enum Source {
    ShadowDepth(usize, bool),
    /// `shadowcolor0/1` read outside the shadow programs (in them they are `Color`).
    ShadowColor(usize),
-    /// The boats' water patches' depth (`horizon_render_pipeline::WATER_MASK`), for translucent terrain.
+    /// The boats' water patches' depth (`horizon_shaders::WATER_MASK`), for translucent terrain.
    WaterMask,
 }

@@ -883,7 +887,7 @@ fn fits(ty: &str, sample_type: wgpu::TextureSampleType) -> bool {
 /// `hz_depth_linear` for a program: 1 for each of shadowtex0, shadowtex1, `shadow` and
 /// `watershadow` whose depth filters (`linear`, bit n: shadowtex n). `shadow` is shadowtex1 in a
 /// program that also declares `watershadow` (6.3).
-fn depth_linear(interface: &horizon_render_pipeline::Interface, linear: u8) -> [f32; 4] {
+fn depth_linear(interface: &horizon_shaders::Interface, linear: u8) -> [f32; 4] {
    let watershadow = interface.samplers.iter().any(|s| s.name == "watershadow");
    [0, 1, usize::from(watershadow), 0].map(|n| f32::from(linear >> n & 1))
 }
@@ -921,7 +925,7 @@ fn source(name: &str, shadow_space: bool, shadow_pass: bool, watershadow: bool)
        "lightmap" => Source::Lightmap,
        "normals" => Source::Normals,
        "specular" => Source::Specular,
-        horizon_render_pipeline::WATER_MASK => Source::WaterMask,
+        horizon_shaders::WATER_MASK => Source::WaterMask,
        n => horizon_render_pipeline::buffer_index(n).map_or(Source::Dummy, Source::Color),
    }
 }
@@ -1503,7 +1507,7 @@ fn owned_buffers(
 #[allow(clippy::too_many_arguments, clippy::type_complexity)]
 fn bindings(
    features: wgpu::Features,
-    interface: &horizon_render_pipeline::Interface,
+    interface: &horizon_shaders::Interface,
    name: &str,
    group: Group,
    buffers: &[u32],
@@ -1574,7 +1578,7 @@ fn bindings(
            // pack of ours (#9064) bound it over `gaux2` and `noisetex` but not over names of its
            // own, where a raw texture was bound; this rule is a fit to those cases.
            let unbound = t.png
-                && t.stage != horizon_render_pipeline::textures::EVERY_STAGE
+                && t.stage != horizon_shaders::EVERY_STAGE
                && source(&s.name, false, true, false) == Source::Dummy;
            !unbound
                && (t.stage != pack_textures::stage(group)
@@ -1826,98 +1830,6 @@ fn bindings(
    Some((entries, samplers, slots, reads, shadow_reads, images))
 }

-/// Makes each storage image of `module` in group 0 declare the format its layout entry binds:
-/// a `layout(r11f_g11f_b10f)` image whose texture is the `RGBA16F` stand-in (`bindings`).
-fn storage_formats_of(module: &mut naga::Module, entries: &[wgpu::BindGroupLayoutEntry]) {
-    let globals: Vec<_> = module.global_variables.iter().map(|(h, _)| h).collect();
-    for handle in globals {
-        let var = &module.global_variables[handle];
-        let Some(naga::ResourceBinding { group: 0, binding }) = var.binding else {
-            continue;
-        };
-        let naga::TypeInner::Image {
-            dim,
-            arrayed,
-            class: naga::ImageClass::Storage { format, access },
-        } = module.types[var.ty].inner
-        else {
-            continue;
-        };
-        let bound = entries.iter().find_map(|e| match e.ty {
-            wgpu::BindingType::StorageTexture { format, .. } if e.binding == binding => {
-                Some(format)
-            }
-            _ => None,
-        });
-        if format == naga::StorageFormat::Rg11b10Ufloat
-            && bound == Some(wgpu::TextureFormat::Rgba16Float)
-        {
-            let ty = module.types.insert(
-                naga::Type {
-                    name: module.types[var.ty].name.clone(),
-                    inner: naga::TypeInner::Image {
-                        dim,
-                        arrayed,
-                        class: naga::ImageClass::Storage {
-                            format: naga::StorageFormat::Rgba16Float,
-                            access,
-                        },
-                    },
-                },
-                naga::Span::UNDEFINED,
-            );
-            module.global_variables[handle].ty = ty;
-        }
-    }
-}
-
-/// The wgpu format of an image's format qualifier.
-fn image_format(qualifier: &str) -> Option<wgpu::TextureFormat> {
-    use wgpu::TextureFormat as T;
-    Some(match qualifier {
-        "rgba32f" => T::Rgba32Float,
-        "rgba16f" => T::Rgba16Float,
-        "rg32f" => T::Rg32Float,
-        "rg16f" => T::Rg16Float,
-        "r11f_g11f_b10f" => T::Rg11b10Ufloat,
-        "r32f" => T::R32Float,
-        "r16f" => T::R16Float,
-        "rgba16" => T::Rgba16Unorm,
-        "rgb10_a2" => T::Rgb10a2Unorm,
-        "rgba8" => T::Rgba8Unorm,
-        "rg16" => T::Rg16Unorm,
-        "rg8" => T::Rg8Unorm,
-        "r16" => T::R16Unorm,
-        "r8" => T::R8Unorm,
-        "rgba16_snorm" => T::Rgba16Snorm,
-        "rgba8_snorm" => T::Rgba8Snorm,
-        "rg16_snorm" => T::Rg16Snorm,
-        "rg8_snorm" => T::Rg8Snorm,
-        "r16_snorm" => T::R16Snorm,
-        "r8_snorm" => T::R8Snorm,
-        "rgba32i" => T::Rgba32Sint,
-        "rgba16i" => T::Rgba16Sint,
-        "rgba8i" => T::Rgba8Sint,
-        "rg32i" => T::Rg32Sint,
-        "rg16i" => T::Rg16Sint,
-        "rg8i" => T::Rg8Sint,
-        "r32i" => T::R32Sint,
-        "r16i" => T::R16Sint,
-        "r8i" => T::R8Sint,
-        "rgba32ui" => T::Rgba32Uint,
-        "rgba16ui" => T::Rgba16Uint,
-        "rgb10_a2ui" => T::Rgb10a2Uint,
-        "rgba8ui" => T::Rgba8Uint,
-        "rg32ui" => T::Rg32Uint,
-        "rg16ui" => T::Rg16Uint,
-        "rg8ui" => T::Rg8Uint,
-        "r32ui" => T::R32Uint,
-        "r16ui" => T::R16Uint,
-        "r8ui" => T::R8Uint,
-        _ => return None,
-    })
-}
-
 /// The value slot of the pack's custom uniform `name` for a program declaring it as GLSL type
 /// `ty`: after the frame's uniforms, in the order of `custom` (each with the type
 /// `shaders.properties` gives it). A `float`, `int`, `vec2`, `vec3` or `vec4` custom uniform
@@ -2283,7 +2195,7 @@ fn build_compute(
    device: &wgpu::Device,
    name: String,
    group: Group,
-    c: horizon_render_pipeline::ComputeProgram,
+    c: horizon_shaders::ComputeProgram,
    formats: &[wgpu::TextureFormat; BUFFERS],
    shadow: Option<&[wgpu::TextureFormat; SHADOW_COLORS]>,
    notes: &mut Vec<String>,
@@ -2805,10 +2717,21 @@ impl PackPost {
            .shadow
            .zip(shadow_geometry.as_ref())
            .and_then(|(p, g)| build(p, Some(g)));
+        // A GPU that refuses translucent terrain's program with the boats' water patches gets it
+        // without them (`Post::shadow_water_plain`), rather than no translucent shadows at all.
+        let mut plain = post.shadow_water_plain;
        let shadow_water = post
            .shadow_water
            .zip(shadow_geometry.as_ref())
            .and_then(|(p, g)| build(p, Some(g)));
+        let unpatched = shadow_water.is_none().then(|| plain.take()).flatten();
+        let unpatched_name = unpatched.as_ref().map(|p| p.name.clone());
+        let shadow_water = shadow_water.or_else(|| {
+            unpatched
+                .zip(shadow_geometry.as_ref())
+                .and_then(|(p, g)| build(p, Some(g)))
+        });
+        let water_unpatched = unpatched_name.filter(|_| shadow_water.is_some());
        let (hides_sky, hides_celestial) = (post.sky.is_some(), post.sky_textured.is_some());
        let sky = (post.sky.is_some() || post.sky_textured.is_some()).then(|| {
            let geometry = PackSky::new(device);
@@ -3365,6 +3288,17 @@ impl PackPost {
        let white = [255u8; 4];
        let black = [0u8; 4];
        let flat_normal = [128u8, 128, 255, 255];
+        // Said as what it is, not as a program skipped.
+        if let Some(name) = water_unpatched {
+            let skipped = format!("{name}: skipped: ");
+            if let Some(n) = notes.iter_mut().rev().find(|n| n.starts_with(&skipped)) {
+                *n = format!(
+                    "{name}: translucent terrain without the boats' water patches, as the GPU \
+                     refused it with them ({})",
+                    &n[skipped.len()..]
+                );
+            }
+        }
        let jobs = (pack.jobs.as_ref())
            .map(std::cell::RefCell::take)
            .unwrap_or_default();
@@ -6065,7 +5999,7 @@ mod tests {
            texture("composite", "tr", false),
            texture("composite", "gaux2", true),
            texture("composite", "noisetex", true),
-            texture(horizon_render_pipeline::textures::EVERY_STAGE, "cp", true),
+            texture(horizon_shaders::EVERY_STAGE, "cp", true),
        ];
        let names = ["tp", "tr", "gaux2", "noisetex", "cp"];
        let interface = horizon_shaders::Interface {
@@ -0,0 +1,109 @@
+//! A shadow program writing as many vertex outputs as the GPU takes leaves no room for the boats'
+//! water patches (`GbuffersInputs::water_patches`, one output more): translucent terrain gets
+//! the program without them, not no shadow program. The programs here are original.
+use super::destination_tests::Fixture;
+use super::*;
+use std::io::{Cursor, Write};
+
+fn pack(outputs: u32) -> Post {
+    let mut zip = zip::ZipWriter::new(Cursor::new(Vec::new()));
+    let mut add = |name: &str, source: &str| {
+        zip.start_file(
+            format!("shaders/{name}"),
+            zip::write::SimpleFileOptions::default(),
+        )
+        .unwrap();
+        zip.write_all(source.as_bytes()).unwrap();
+    };
+    let declared: String = (0..outputs)
+        .map(|i| format!("varying vec4 v{i};\n"))
+        .collect();
+    let written: String = (0..outputs).map(|i| format!("v{i}=vec4({i}.0);")).collect();
+    let read: String = (0..outputs).map(|i| format!("+v{i}")).collect();
+    add(
+        "shadow.vsh",
+        &format!(
+            "#version 120\n{declared}void main() {{ gl_Position=vec4(gl_Vertex.xy,0.5,1.0); {written} }}\n"
+        ),
+    );
+    add(
+        "shadow.fsh",
+        &format!("#version 120\n{declared}void main() {{ gl_FragData[0]=vec4(0.0){read}; }}\n"),
+    );
+    add(
+        "final.vsh",
+        "#version 120\nvarying vec2 uv;\nvoid main() { uv=gl_MultiTexCoord0.xy; gl_Position=ftransform(); }\n",
+    );
+    add(
+        "final.fsh",
+        "#version 120\nconst int shadowMapResolution=16;\nuniform sampler2D shadowcolor0;\n\
+         varying vec2 uv;\nvoid main() { gl_FragColor=texture2D(shadowcolor0,uv); }\n",
+    );
+    let pack = horizon_shaders::Pack::from_zip_bytes(
+        "original-full-outputs",
+        zip.finish().unwrap().into_inner(),
+    )
+    .unwrap();
+    let mut macros = horizon_shaders::Macros::standard();
+    let (properties, _) = horizon_shaders::read_properties(&pack, &mut macros);
+    let inputs = horizon_shaders::GameInputs {
+        terrain: Some(horizon_shaders::GbuffersInputs {
+            item_id_declared: false,
+            far_depth: false,
+            paged_maps: false,
+            water_mask: false,
+            water_patches: false,
+            declarations: "layout(location=0)in vec3 fixture_position;\n".into(),
+            body: "hz_Vertex=vec4(fixture_position,1.0);hz_Color=vec4(1.0);\
+                   hz_MultiTexCoord0=vec4(0.0);hz_MultiTexCoord1=vec4(240.0);\
+                   hz_MultiTexCoord2=vec4(240.0);hz_Normal=vec3(0.0,0.0,1.0);\n"
+                .into(),
+            attributes: vec![],
+            after: String::new(),
+            alpha_test: None,
+        }),
+        ..Default::default()
+    };
+    horizon_shaders::load_post(&pack, "", &properties, &macros, &inputs)
+}
+
+#[test]
+fn a_shadow_program_with_every_output_drops_the_boats_patches_not_its_water() {
+    let Some(gpu) = Fixture::new() else { return };
+    const ATTRS: [wgpu::VertexAttribute; 1] = wgpu::vertex_attr_array![0=>Float32x3];
+    let layouts = [Some(wgpu::VertexBufferLayout {
+        array_stride: 12,
+        step_mode: wgpu::VertexStepMode::Vertex,
+        attributes: &ATTRS,
+    })];
+    let geometry = || {
+        Some(Geometry {
+            material_maps: false,
+            buffers: &layouts,
+            table: None,
+            depth_write: true,
+            atlas: None,
+            ids: None,
+            cull: true,
+        })
+    };
+    let outputs = gpu.device.limits().max_inter_stage_shader_variables;
+    let post = gpu.build_with_terrain(pack(outputs), geometry());
+    assert!(post.has_shadow(), "{:?}", post.notes);
+    assert!(post.shadow_water.is_some(), "{:?}", post.notes);
+    assert!(
+        post.notes
+            .iter()
+            .any(|n| n.contains("without the boats' water patches")),
+        "{:?}",
+        post.notes
+    );
+    // With room for them, the patches stay and nothing is said.
+    let post = gpu.build_with_terrain(pack(outputs - 1), geometry());
+    assert!(post.shadow_water.is_some(), "{:?}", post.notes);
+    assert!(
+        !post.notes.iter().any(|n| n.contains("water patches")),
+        "{:?}",
+        post.notes
+    );
+}
@@ -0,0 +1,97 @@
+//! Image formats: a storage image's format qualifier as wgpu's, and the stand-in a module's
+//! storage images declare.
+
+/// Makes each storage image of `module` in group 0 declare the format its layout entry binds:
+/// a `layout(r11f_g11f_b10f)` image whose texture is the `RGBA16F` stand-in (`bindings`).
+pub(super) fn storage_formats_of(
+    module: &mut naga::Module,
+    entries: &[wgpu::BindGroupLayoutEntry],
+) {
+    let globals: Vec<_> = module.global_variables.iter().map(|(h, _)| h).collect();
+    for handle in globals {
+        let var = &module.global_variables[handle];
+        let Some(naga::ResourceBinding { group: 0, binding }) = var.binding else {
+            continue;
+        };
+        let naga::TypeInner::Image {
+            dim,
+            arrayed,
+            class: naga::ImageClass::Storage { format, access },
+        } = module.types[var.ty].inner
+        else {
+            continue;
+        };
+        let bound = entries.iter().find_map(|e| match e.ty {
+            wgpu::BindingType::StorageTexture { format, .. } if e.binding == binding => {
+                Some(format)
+            }
+            _ => None,
+        });
+        if format == naga::StorageFormat::Rg11b10Ufloat
+            && bound == Some(wgpu::TextureFormat::Rgba16Float)
+        {
+            let ty = module.types.insert(
+                naga::Type {
+                    name: module.types[var.ty].name.clone(),
+                    inner: naga::TypeInner::Image {
+                        dim,
+                        arrayed,
+                        class: naga::ImageClass::Storage {
+                            format: naga::StorageFormat::Rgba16Float,
+                            access,
+                        },
+                    },
+                },
+                naga::Span::UNDEFINED,
+            );
+            module.global_variables[handle].ty = ty;
+        }
+    }
+}
+
+/// The wgpu format of an image's format qualifier.
+pub(super) fn image_format(qualifier: &str) -> Option<wgpu::TextureFormat> {
+    use wgpu::TextureFormat as T;
+    Some(match qualifier {
+        "rgba32f" => T::Rgba32Float,
+        "rgba16f" => T::Rgba16Float,
+        "rg32f" => T::Rg32Float,
+        "rg16f" => T::Rg16Float,
+        "r11f_g11f_b10f" => T::Rg11b10Ufloat,
+        "r32f" => T::R32Float,
+        "r16f" => T::R16Float,
+        "rgba16" => T::Rgba16Unorm,
+        "rgb10_a2" => T::Rgb10a2Unorm,
+        "rgba8" => T::Rgba8Unorm,
+        "rg16" => T::Rg16Unorm,
+        "rg8" => T::Rg8Unorm,
+        "r16" => T::R16Unorm,
+        "r8" => T::R8Unorm,
+        "rgba16_snorm" => T::Rgba16Snorm,
+        "rgba8_snorm" => T::Rgba8Snorm,
+        "rg16_snorm" => T::Rg16Snorm,
+        "rg8_snorm" => T::Rg8Snorm,
+        "r16_snorm" => T::R16Snorm,
+        "r8_snorm" => T::R8Snorm,
+        "rgba32i" => T::Rgba32Sint,
+        "rgba16i" => T::Rgba16Sint,
+        "rgba8i" => T::Rgba8Sint,
+        "rg32i" => T::Rg32Sint,
+        "rg16i" => T::Rg16Sint,
+        "rg8i" => T::Rg8Sint,
+        "r32i" => T::R32Sint,
+        "r16i" => T::R16Sint,
+        "r8i" => T::R8Sint,
+        "rgba32ui" => T::Rgba32Uint,
+        "rgba16ui" => T::Rgba16Uint,
+        "rgb10_a2ui" => T::Rgb10a2Uint,
+        "rgba8ui" => T::Rgba8Uint,
+        "rg32ui" => T::Rg32Uint,
+        "rg16ui" => T::Rg16Uint,
+        "rg8ui" => T::Rg8Uint,
+        "r32ui" => T::R32Uint,
+        "r16ui" => T::R16Uint,
+        "r8ui" => T::R8Uint,
+        _ => return None,
+    })
+}
@@ -58,7 +58,7 @@ pub(super) const ATTRIBUTES: [wgpu::VertexAttribute; 2] =
    wgpu::vertex_attr_array![0 => Float32x3, 1 => Uint32];

 /// What `gbuffers_skybasic` reads from these vertices.
-pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
+pub fn inputs() -> horizon_shaders::GbuffersInputs {
    let declarations =
        "layout(location = 0) in vec3 hz_v_pos;\nlayout(location = 1) in uint hz_v_kind;\n\
         layout(set = 1, binding = 0) uniform HzSky { mat4 hz_sky_stars; vec4 hz_sky_color; \
@@ -90,7 +90,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
         hz_MultiTexCoord2 = hz_MultiTexCoord1;\n    \
         hz_Normal = vec3(0.0, 0.0, 1.0);\n"
    );
-    horizon_render_pipeline::GbuffersInputs {
+    horizon_shaders::GbuffersInputs {
        declarations,
        body,
        attributes: vec![
@@ -111,8 +111,8 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
 }

 /// What `gbuffers_skytextured` reads from the sun and moon's vertices.
-pub fn celestial_inputs() -> horizon_render_pipeline::GbuffersInputs {
-    horizon_render_pipeline::GbuffersInputs {
+pub fn celestial_inputs() -> horizon_shaders::GbuffersInputs {
+    horizon_shaders::GbuffersInputs {
        declarations:
            "layout(location = 0) in vec3 hz_v_pos;\nlayout(location = 1) in vec2 hz_v_uv;\n\
             layout(location = 2) in vec4 hz_v_color;\n"
@@ -2,10 +2,7 @@
 //! which of them a program's sampler reads.

 use horizon_render_pipeline::Kind;
-use horizon_render_pipeline::textures::{
-    CustomTexture, Dim as TextureDim, EVERY_STAGE, Texels, Texture, TextureSource,
-};
-use horizon_shaders::Group;
+use horizon_shaders::{CustomTexture, Group, Texels, Texture, TextureDim, TextureSource};

 /// What a custom texture is once uploaded: an image of ours, or one the game already has.
 pub(super) enum Image {
@@ -130,16 +127,16 @@ pub(super) fn find(textures: &[PackTexture], group: Group, ty: &str, name: &str)
                || buffer.is_some() && horizon_render_pipeline::buffer_index(&t.name) == buffer)
    });
    staged.or_else(|| {
-        textures
-            .iter()
-            .position(|t| t.stage == EVERY_STAGE && t.dimension == dimension && t.name == name)
+        textures.iter().position(|t| {
+            t.stage == horizon_shaders::EVERY_STAGE && t.dimension == dimension && t.name == name
+        })
    })
 }

 /// The `shaders.properties` key a texture came from, for notes.
 fn key(stage: &str, name: &str) -> String {
    match stage {
-        EVERY_STAGE => format!("customTexture.{name}"),
+        horizon_shaders::EVERY_STAGE => format!("customTexture.{name}"),
        _ => format!("texture.{stage}.{name}"),
    }
 }
@@ -354,7 +351,7 @@ mod tests {
    #[test]
    fn custom_textures_reach_every_program() {
        use wgpu::TextureViewDimension as D;
-        let every = EVERY_STAGE;
+        let every = horizon_shaders::EVERY_STAGE;
        let textures = [
            lightmap(every, "texClouds", D::D3),
            lightmap("composite", "texClouds", D::D3),
@@ -2717,7 +2717,7 @@ pub(super) mod initial_history_tests {
 /// `horizonWaterPatch<k>`'s `k`: patch `k / 2`, its corner and y range (even) or edges (odd).
 fn water_patch_index(name: &str) -> Option<usize> {
    let k: usize = name.strip_prefix("horizonWaterPatch")?.parse().ok()?;
-    (k < 2 * horizon_render_pipeline::WATER_PATCHES).then_some(k)
+    (k < 2 * horizon_shaders::WATER_PATCHES).then_some(k)
 }

 /// The boats' water patches among the frame's entity quads (`WATER_MASK_OVERLAY`), the first
@@ -2729,7 +2729,7 @@ pub(super) fn water_patches(entities: &[super::Vertex]) -> Vec<[[f32; 4]; 2]> {
    let mut points: Vec<[f32; 3]> = Vec::new();
    let flush = |points: &mut Vec<[f32; 3]>, out: &mut Vec<[[f32; 4]; 2]>| {
        if let Some(b) = patch_box(points)
-            && out.len() < horizon_render_pipeline::WATER_PATCHES
+            && out.len() < horizon_shaders::WATER_PATCHES
        {
            out.push(b);
        }
@@ -11,7 +11,7 @@ use super::pack_post::Weather;
 /// What `gbuffers_weather` reads from a weather vertex: camera-relative position, the UV in
 /// repeats of the sprite, colour (with vanilla's fade) and light. Weather has no normal; the
 /// pack sees straight up.
-pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
+pub fn inputs() -> horizon_shaders::GbuffersInputs {
    let declarations =
        "layout(location = 0) in vec3 hz_v_pos;\nlayout(location = 1) in vec2 hz_v_uv;\n\
         layout(location = 2) in uint hz_v_overlay;\nlayout(location = 3) in vec4 hz_v_color;\n\
@@ -31,7 +31,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
        ("vaColor", "hz_Color"),
        ("vaNormal", "hz_Normal"),
    ];
-    horizon_render_pipeline::GbuffersInputs {
+    horizon_shaders::GbuffersInputs {
        declarations,
        body,
        attributes: attributes
@@ -40,7 +40,7 @@ pub fn inputs() -> horizon_render_pipeline::GbuffersInputs {
            .collect(),
        after: String::new(),
        // Vanilla's weather drops texels below 0.1, as Horizon's own weather shader does.
-        alpha_test: Some(horizon_render_pipeline::AlphaTest {
+        alpha_test: Some(horizon_shaders::AlphaTest {
            op: ">",
            reference: 0.1,
        }),
@@ -158,7 +158,7 @@ impl Weather {
        match native {
            Some((pipeline, frame)) => {
                pass.set_pipeline(pipeline);
-                pass.set_bind_group(horizon_render_pipeline::stages::GROUP, frame, &[]);
+                pass.set_bind_group(horizon_shader_api::stages::GROUP, frame, &[]);
            }
            None => pass.set_pipeline(&self.pipeline),
        }
@@ -225,7 +225,7 @@ struct HorizonWeatherOut {
 ";

 /// The shader of a native pack's weather stage `source`.
-fn native_source(source: &str, api: horizon_render_pipeline::Api) -> String {
+fn native_source(source: &str, api: horizon_shader_api::Api) -> String {
    format!(
        "{source}\n// Horizon's weather (entity.wgsl)\n{}{}{NATIVE_ENTRIES}",
        super::wgsl_prefix::prefixed(&super::entity_shader(), "horizon_entity_"),
@@ -245,7 +245,7 @@ pub(super) fn native_pipeline(
    stage: &horizon_shader_api::check::CheckedStage,
    constants: &[(String, f64)],
 ) -> Result<wgpu::RenderPipeline, String> {
-    use horizon_render_pipeline::stages::GROUP;
+    use horizon_shader_api::stages::GROUP;
    let text = native_source(&stage.source, frame.api);
    let module = naga::front::wgsl::parse_str(&text)
        .map_err(|e| format!("{}: {}", stage.file, e.emit_to_string(&text)))?;
@@ -322,7 +322,7 @@ mod tests {

    #[test]
    fn a_native_weather_stage_validates() {
-        use horizon_render_pipeline::{Api, StageKind};
+        use horizon_shader_api::{Api, stages::StageKind};
        for api in [Api::V0_1, Api::V0_2] {
            let source = StageKind::Weather.prelude(api)
                + "fn weather(input: WeatherInput) -> vec4<f32> {\n    \
@@ -50,6 +50,98 @@ struct TaaResources {
    uniform: wgpu::Buffer,
 }

+/// One frame handed to an upscaler backend: the jittered world at `render_size` and what
+/// it needs to rebuild it at `output_size`. The motion is the camera's alone (`reproject`);
+/// objects that move on their own carry no motion vectors yet.
+// Only TAA reads it so far; a vendor backend reads the rest (#12918).
+#[allow(dead_code)]
+pub(super) struct UpscaleFrame<'a> {
+    /// The world's colour, rendered with this frame's jitter.
+    pub color: &'a wgpu::TextureView,
+    /// The world's depth, at `render_size`.
+    pub depth: &'a wgpu::TextureView,
+    pub render_size: [u32; 2],
+    pub output_size: [u32; 2],
+    /// The jitter in clip space, as added to the projection.
+    pub jitter_clip: [f32; 2],
+    /// The same jitter in rendered pixels, y down.
+    pub jitter_pixels: [f32; 2],
+    /// This frame's unjittered clip space to the previous frame's.
+    pub reproject: [[f32; 4]; 4],
+    /// The history is unusable: a cut, a resize, a frame without the upscaler.
+    pub reset: bool,
+    /// Frames jittered so far.
+    pub index: u32,
+}
+
+/// Something that turns the jittered low-resolution world into the output picture.
+/// TAA (`TaaResources`) is the only backend; `Target` is the per-size state a backend
+/// keeps beside the world target (TAA's history textures).
+pub(super) trait UpscalerBackend {
+    type Target;
+    /// The name its GPU timing is shown under.
+    fn name(&self) -> &'static str;
+    /// Write this frame's output and return the bind group that shows it (`draw_onto`).
+    fn resolve<'t>(
+        &self,
+        queue: &wgpu::Queue,
+        encoder: &mut wgpu::CommandEncoder,
+        frame: &UpscaleFrame<'_>,
+        target: &'t Self::Target,
+        timing: Option<&mut super::pack_timing::PassTiming>,
+    ) -> &'t wgpu::BindGroup;
+}
+
+impl UpscalerBackend for TaaResources {
+    type Target = History;
+
+    fn name(&self) -> &'static str {
+        "TAA"
+    }
+
+    fn resolve<'t>(
+        &self,
+        queue: &wgpu::Queue,
+        encoder: &mut wgpu::CommandEncoder,
+        frame: &UpscaleFrame<'_>,
+        taa: &'t History,
+        timing: Option<&mut super::pack_timing::PassTiming>,
+    ) -> &'t wgpu::BindGroup {
+        // The resolve bind group already samples `frame.color` and `frame.depth`.
+        let i = (frame.index % 2) as usize;
+        let uniform = TaaUniform {
+            reproject: frame.reproject,
+            jitter: [
+                frame.jitter_clip[0],
+                frame.jitter_clip[1],
+                if frame.reset { 1.0 } else { 0.0 },
+                0.0,
+            ],
+        };
+        queue.write_buffer(&self.uniform, 0, bytemuck::bytes_of(&uniform));
+        let attachments = [Some(wgpu::RenderPassColorAttachment {
+            view: &taa.history[i],
+            resolve_target: None,
+            depth_slice: None,
+            ops: wgpu::Operations {
+                load: wgpu::LoadOp::Clear(wgpu::Color::BLACK),
+                store: wgpu::StoreOp::Store,
+            },
+        })];
+        let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+            label: Some("Horizon TAA"),
+            timestamp_writes: timing.and_then(|t| t.writes(self.name())),
+            color_attachments: &attachments,
+            ..Default::default()
+        });
+        pass.set_pipeline(&self.pipeline);
+        pass.set_bind_group(0, &taa.resolve[i], &[]);
+        pass.draw(0..3, 0..1);
+        drop(pass);
+        &taa.show[i]
+    }
+}
+
 pub struct Post {
    layout: wgpu::BindGroupLayout,
    sampler: wgpu::Sampler,
@@ -563,33 +655,25 @@ impl Post {
            self.finish_with(encoder, screen, &target.group, timing.as_deref_mut());
            return;
        };
-        let i = (self.taa_frame % 2) as usize;
-        queue.write_buffer(&res.uniform, 0, bytemuck::bytes_of(&self.taa_this_frame));
-        let attachments = [Some(wgpu::RenderPassColorAttachment {
-            view: &taa.history[i],
-            resolve_target: None,
-            depth_slice: None,
-            ops: wgpu::Operations {
-                load: wgpu::LoadOp::Clear(wgpu::Color::BLACK),
-                store: wgpu::StoreOp::Store,
-            },
-        })];
-        let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
-            label: Some("Horizon TAA"),
-            timestamp_writes: timing.as_deref_mut().and_then(|t| t.writes("TAA")),
-            color_attachments: &attachments,
-            ..Default::default()
-        });
-        pass.set_pipeline(&res.pipeline);
-        pass.set_bind_group(0, &taa.resolve[i], &[]);
-        pass.draw(0..3, 0..1);
-        drop(pass);
+        let size = self.size().unwrap_or([1, 1]);
+        let frame = UpscaleFrame {
+            color: &target.color,
+            depth: &target.depth,
+            render_size: size,
+            output_size: taa.size,
+            jitter_clip: [self.taa_this_frame.jitter[0], self.taa_this_frame.jitter[1]],
+            jitter_pixels: self.jitter_pixels(),
+            reproject: self.taa_this_frame.reproject,
+            reset: self.taa_this_frame.jitter[2] > 0.5,
+            index: self.taa_frame,
+        };
+        let shown = res.resolve(queue, encoder, &frame, taa, timing.as_deref_mut());
        let pipeline = if self.upscale > 1.0 {
            &self.sharpen
        } else {
            &self.copy
        };
-        self.draw_onto(encoder, screen, &taa.show[i], pipeline, timing);
+        self.draw_onto(encoder, screen, shown, pipeline, timing);
    }

    /// Draw what `group` binds (`bind`) onto `screen`.
@@ -5,9 +5,23 @@
 use std::{fs, path::Path};

 pub const FILE: &str = "horizon-graphics.txt";
-/// Written beside it before HDR output is switched on and removed once the first HDR frame is
-/// presented. Found at the next start, it means HDR output took the game down, so HDR starts off.
+/// Written beside it before a window's HDR output is switched on, naming the graphics driver it
+/// starts on ([`hdr_marker_text`]), and removed once the first HDR frame is presented. Found at
+/// the next start, it means HDR output took the game down there: HDR output is held back on
+/// that driver ([`Graphics::hdr_failed_start`]), and the mode stays as the player chose it.
 pub const HDR_MARKER: &str = "horizon-hdr-pending";
+/// The marker's text for a window whose HDR output starts on `driver`
+/// (`gfx::output::window_driver`).
+pub fn hdr_marker_text(driver: &str) -> String {
+    format!("driver:{driver}\n")
+}
+/// The driver a marker names; empty for one written before markers named it.
+fn marker_driver(text: &str) -> &str {
+    text.lines()
+        .find_map(|line| line.strip_prefix("driver:"))
+        .unwrap_or_default()
+        .trim()
+}

 /// What the system reports for the display HDR output goes to, in nits in HDR output's
 /// scale: where its SDR white sits (the desktop's white) and the peak. Each renderer keeps its
@@ -38,6 +52,23 @@ pub fn peak_step_of(nits: f32) -> f32 {
    };
    step.clamp(0.0, PEAK_STEPS as f32)
 }
+/// The steps of Paper White's and UI Brightness's scale: Auto (0), then 10 to 480 nits by 10.
+pub const NITS_STEPS: u32 = 48;
+/// Paper White's or UI Brightness's setting at slider position `v`, 0 to 1 ([`NITS_STEPS`]).
+pub fn nits_at(v: f32) -> u32 {
+    (v * NITS_STEPS as f32).round() as u32 * 10
+}
+/// Where a Paper White or UI Brightness setting sits on its slider, 0 to 1.
+pub fn nits_position(nits: u32) -> f32 {
+    nits as f32 / (NITS_STEPS * 10) as f32
+}
+/// A saved Paper White or UI Brightness: Auto (0), or 10 to 480 nits.
+fn nits_setting(nits: u32) -> u32 {
+    match nits {
+        0 => 0,
+        n => n.clamp(10, 480),
+    }
+}

 /// Simple-level presets. `Custom` leaves every option as the player set it.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
@@ -490,8 +521,6 @@ pub fn reduced_far_detail_suggested() -> bool {
    REDUCED_SUGGESTED.load(std::sync::atomic::Ordering::Relaxed)
 }

-/// The name the options screen waits on to bind `Graphics::hdr_key`.
-pub const HDR_KEY: &str = "horizon.hdrSettings";
 /// The Screenshot Quality choices, times the game's resolution.
 pub const SCREENSHOT_QUALITIES: [u32; 4] = [1, 2, 4, 8];
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
@@ -801,14 +830,17 @@ pub struct Graphics {
    /// HDR black level: the display's darkest black, in hundredths of a nit; 0, the default,
    /// lifts nothing. Shadows are lifted onto it, and the HDR metadata says it.
    pub hdr_black_level: u32,
-    /// HDR brightness of the HUD and menus, in percent of paper white (25..=100); the
-    /// first-person hand stays at the world's.
-    pub hdr_ui_brightness: u32,
+    /// HDR brightness of the HUD and menus, in nits; 0 is Auto: at paper white
+    /// ([`Graphics::ui_nits`]). The first-person hand stays at the world's.
+    pub hdr_ui_nits: u32,
    /// HDR Lighting: Horizon's own HDR look, light sources, the sun and sunlight above paper
    /// white. Off, HDR output shows the same picture as SDR, for shader packs or the vanilla look.
    pub hdr_lighting: bool,
-    /// A vanilla key name (`HDR_KEY`): opens HDR's settings from the game. Unbound by default.
-    pub hdr_key: String,
+    /// The graphics driver whose last start ended before HDR output showed a frame (the
+    /// marker found, [`HDR_MARKER`]): a window on it stays SDR whatever the mode, until the
+    /// mode is changed or the window starts on another driver ([`Graphics::hdr_held`]).
+    /// Empty for a marker that named no driver: the first one seen holds it.
+    pub hdr_failed_start: Option<String>,
    /// Battery mode: at most 60 frames per second in a world and 30 in menus
    /// or behind other windows, and half the worker threads. Off by default;
    /// it changes when frames are drawn, never what they show or the ticks.
@@ -881,9 +913,9 @@ impl Default for Graphics {
            hdr_paper_white: 0,
            hdr_peak: 0,
            hdr_black_level: 0,
-            hdr_ui_brightness: 100,
+            hdr_ui_nits: 0,
            hdr_lighting: true,
-            hdr_key: "key.keyboard.unknown".into(),
+            hdr_failed_start: None,
            battery: false,
            shadow_cache: false,
            api: GraphicsApi::Auto,
@@ -909,17 +941,54 @@ impl Graphics {
                Vec::new()
            }
        };
-        if fs::remove_file(dir.join(HDR_MARKER)).is_ok() && g.hdr != HdrMode::Off {
-            g.hdr = HdrMode::Off;
+        let marker = dir.join(HDR_MARKER);
+        if let Ok(text) = fs::read_to_string(&marker)
+            && fs::remove_file(&marker).is_ok()
+            && g.hdr != HdrMode::Off
+        {
+            g.hdr_failed_start = Some(marker_driver(&text).to_owned());
            g.save(dir);
            log::warn!(
-                "the last start ended before HDR output showed a frame; HDR is off now (graphics option hdr, in {FILE})"
+                "the last start ended before HDR output showed a frame; HDR output stays off with that graphics driver until the HDR mode is changed (graphics option hdrFailedStart, in {FILE})"
            );
        }
        g
    }
+    /// Whether HDR output is held back on a window whose graphics driver is `driver`
+    /// (`gfx::output::window_driver`): the last start on it ended before HDR output
+    /// showed a frame ([`Graphics::hdr_failed_start`]).
+    pub fn hdr_held(&self, driver: &str) -> bool {
+        self.hdr_failed_start
+            .as_deref()
+            .is_some_and(|failed| failed.is_empty() || failed == driver)
+    }
+    /// The window's renderer runs on `driver`: a failed start that named no driver is this
+    /// one's now, and another driver's (a driver update, another GPU) is dropped, so HDR output
+    /// is tried again. True when it changed.
+    pub fn settle_failed_start(&mut self, driver: &str) -> bool {
+        match self.hdr_failed_start.as_deref() {
+            Some("") => self.hdr_failed_start = Some(driver.to_owned()),
+            Some(failed) if failed != driver => self.hdr_failed_start = None,
+            _ => return false,
+        }
+        true
+    }
+    /// `before`, as Undo brings it back, but never the hold on a driver HDR output failed to
+    /// start on: that stays as it is now, and goes when Undo changes the mode, as any change of
+    /// the mode drops it.
+    pub fn undone_to(&self, before: &Self) -> Self {
+        Self {
+            hdr_failed_start: self
+                .hdr_failed_start
+                .clone()
+                .filter(|_| self.hdr == before.hdr),
+            ..before.clone()
+        }
+    }
    pub fn parse(text: &str) -> Self {
        let mut g = Self::default();
+        // UI Brightness: `hdrUiNits`, else an older file's share of Paper White.
+        let (mut ui_nits, mut ui_share) = (None, None);
        for line in text.lines() {
            let Some((key, value)) = line.split_once(':') else {
                continue;
@@ -1009,12 +1078,9 @@ impl Graphics {
                "frameGeneration" => g.frame_generation = FrameGeneration::parse(value),
                "hdr" => g.hdr = HdrMode::parse(value, g.hdr),
                "hdrLighting" => g.hdr_lighting = flag(g.hdr_lighting),
-                "hdrPaperWhite" => {
-                    g.hdr_paper_white = match number(g.hdr_paper_white) {
-                        0 => 0,
-                        n => n.clamp(10, 480),
-                    }
-                }
+                "hdrPaperWhite" => g.hdr_paper_white = nits_setting(number(g.hdr_paper_white)),
+                "hdrUiNits" => ui_nits = value.parse().ok().map(nits_setting),
+                "hdrUiBrightness" => ui_share = value.parse::<u32>().ok(),
                "hdrPeak" => {
                    g.hdr_peak = match number(g.hdr_peak) {
                        0 => 0,
@@ -1022,10 +1088,7 @@ impl Graphics {
                    }
                }
                "hdrBlackLevel" => g.hdr_black_level = number(g.hdr_black_level).min(100),
-                "hdrUiBrightness" => {
-                    g.hdr_ui_brightness = number(g.hdr_ui_brightness).clamp(25, 100)
-                }
-                "hdrKey" if value.starts_with("key.") => g.hdr_key = value.to_owned(),
+                "hdrFailedStart" => g.hdr_failed_start = Some(value.to_owned()),
                "batteryMode" => g.battery = flag(g.battery),
                "shadowCache" => g.shadow_cache = flag(g.shadow_cache),
                "batchTranslucent" => g.translucent_batching = flag(g.translucent_batching),
@@ -1042,11 +1105,20 @@ impl Graphics {
                _ => {}
            }
        }
+        // The share was 25 to 100% of Paper White. 100% is Auto, and so is any share of an
+        // Auto Paper White, whose nits the file doesn't hold; another share of a Paper White set
+        // by hand is its nits, to the nearest step.
+        g.hdr_ui_nits = ui_nits.unwrap_or(match (ui_share, g.hdr_paper_white) {
+            (Some(share), paper) if share < 100 && paper != 0 => {
+                ((paper * share.max(25) + 500) / 1000).max(1) * 10
+            }
+            _ => 0,
+        });
        g
    }
    pub fn serialize(&self) -> String {
        let mut text = format!(
-            "preset:{}\nlodDistance:{}\nfarDetail:{}\ncaveCulling:{}\nentityCulling:{}\nentityCullingPrecheck:{}\nparticleCulling:{}\nleafCulling:{}\nopaqueIce:{}\nblockEntityCacheShulkerBoxes:{}\nblockEntityCacheSigns:{}\nblockEntityCacheDecoratedPots:{}\nblockEntityCacheBells:{}\nblockEntityCacheChests:{}\nblockEntityCacheBanners:{}\nblockEntityCacheCopperGolemStatues:{}\nchunkUpdates:{}\nuploadBudgetKiB:{}\ntextureBudgetMiB:{}\nsky:{}\nfog:{}\nweather:{}\nanimatedTextures:{}\nditherCutoutMips:{}\npresentMode:{}\nframePacing:{}\nworkers:{}\noverlay:{}\nresolutionScale:{}\nfxaa:{}\ntaa:{}\nupscaling:{}\nupscalingSharpness:{}\nscreenshotQuality:{}\nframeGeneration:{}\nhdr:{}\nhdrPaperWhite:{}\nhdrPeak:{}\nhdrBlackLevel:{}\nhdrUiBrightness:{}\nhdrLighting:{}\nhdrKey:{}\nbatteryMode:{}\nshadowCache:{}\ngraphicsApi:{}\npickedShaderPack:{}\nbatchTranslucent:{}\nhdrSmoothGradients:{}\ngpuCulling:{}\n",
+            "preset:{}\nlodDistance:{}\nfarDetail:{}\ncaveCulling:{}\nentityCulling:{}\nentityCullingPrecheck:{}\nparticleCulling:{}\nleafCulling:{}\nopaqueIce:{}\nblockEntityCacheShulkerBoxes:{}\nblockEntityCacheSigns:{}\nblockEntityCacheDecoratedPots:{}\nblockEntityCacheBells:{}\nblockEntityCacheChests:{}\nblockEntityCacheBanners:{}\nblockEntityCacheCopperGolemStatues:{}\nchunkUpdates:{}\nuploadBudgetKiB:{}\ntextureBudgetMiB:{}\nsky:{}\nfog:{}\nweather:{}\nanimatedTextures:{}\nditherCutoutMips:{}\npresentMode:{}\nframePacing:{}\nworkers:{}\noverlay:{}\nresolutionScale:{}\nfxaa:{}\ntaa:{}\nupscaling:{}\nupscalingSharpness:{}\nscreenshotQuality:{}\nframeGeneration:{}\nhdr:{}\nhdrPaperWhite:{}\nhdrPeak:{}\nhdrBlackLevel:{}\nhdrUiNits:{}\nhdrLighting:{}\nbatteryMode:{}\nshadowCache:{}\ngraphicsApi:{}\npickedShaderPack:{}\nbatchTranslucent:{}\nhdrSmoothGradients:{}\ngpuCulling:{}\n",
            self.preset.name(),
            self.lod_distance,
            self.far_detail.name(),
@@ -1093,9 +1165,8 @@ impl Graphics {
            self.hdr_paper_white,
            self.hdr_peak,
            self.hdr_black_level,
-            self.hdr_ui_brightness,
+            self.hdr_ui_nits,
            bool_text(self.hdr_lighting),
-            self.hdr_key,
            bool_text(self.battery),
            bool_text(self.shadow_cache),
            self.api.name(),
@@ -1104,17 +1175,12 @@ impl Graphics {
            bool_text(self.hdr_smooth_gradients),
            self.gpu_culling.key(),
        );
+        if let Some(driver) = &self.hdr_failed_start {
+            text += &format!("hdrFailedStart:{driver}\n");
+        }
        text += &self.blue_map.serialize();
        text
    }
-    /// Binds Horizon's graphics key `name` (`HDR_KEY`); false for another name.
-    pub fn set_key(&mut self, name: &str, value: String) -> bool {
-        match name {
-            HDR_KEY => self.hdr_key = value,
-            _ => return false,
-        }
-        true
-    }
    pub fn save(&self, dir: &Path) {
        let _ = fs::write(dir.join(FILE), self.serialize());
    }
@@ -1126,6 +1192,13 @@ impl Graphics {
            n => n,
        }
    }
+    /// The HUD and menus' brightness, in nits: the player's, or on Auto paper white's.
+    pub fn ui_nits(&self, reported: Option<Reported>) -> u32 {
+        match self.hdr_ui_nits {
+            0 => self.paper_white_nits(reported),
+            n => n,
+        }
+    }
    /// The peak the world's highlights reach, in nits: the player's, or on Auto
    /// what the system `reported`, else 1000.
    pub fn peak_nits(&self, reported: Option<Reported>) -> u32 {
@@ -1206,6 +1279,55 @@ pub fn apply_preset(preset: Preset, s: &mut crate::settings::Settings) {
 mod tests {
    use super::*;

+    /// UI Brightness is saved in nits, 0 for Auto. An older file's share of Paper White reads
+    /// as Auto at 100% or with Paper White on Auto, else as that share of it to the nearest step.
+    #[test]
+    fn ui_brightness_round_trips_in_nits_and_reads_older_shares() {
+        for (file, nits) in [
+            ("", 0),
+            ("hdrUiNits:0\n", 0),
+            ("hdrUiNits:160\n", 160),
+            ("hdrUiNits:5\n", 10),
+            ("hdrUiNits:9000\n", 480),
+            ("hdrUiNits:x\n", 0),
+            // Older files: 100% is Auto,
+            ("hdrPaperWhite:200\nhdrUiBrightness:100\n", 0),
+            // any share of Paper White's Auto too,
+            ("hdrUiBrightness:60\n", 0),
+            ("hdrPaperWhite:0\nhdrUiBrightness:25\n", 0),
+            // and another share of a Paper White set by hand is its nits.
+            ("hdrPaperWhite:200\nhdrUiBrightness:60\n", 120),
+            ("hdrUiBrightness:50\nhdrPaperWhite:203\n", 100),
+            ("hdrPaperWhite:250\nhdrUiBrightness:75\n", 190),
+            ("hdrPaperWhite:10\nhdrUiBrightness:25\n", 10),
+            ("hdrPaperWhite:480\nhdrUiBrightness:10\n", 120),
+            // The new key wins over the old one.
+            (
+                "hdrPaperWhite:200\nhdrUiBrightness:60\nhdrUiNits:300\n",
+                300,
+            ),
+            ("hdrUiNits:0\nhdrPaperWhite:200\nhdrUiBrightness:60\n", 0),
+        ] {
+            let g = Graphics::parse(file);
+            assert_eq!(g.hdr_ui_nits, nits, "{file}");
+            let saved = g.serialize();
+            assert!(!saved.contains("hdrUiBrightness"), "{file}");
+            assert!(saved.contains(&format!("\nhdrUiNits:{nits}\n")), "{file}");
+            assert_eq!(Graphics::parse(&saved), g, "{file}");
+        }
+        let mut g = Graphics::default();
+        assert_eq!(g.ui_nits(None), 203);
+        let reported = Some(Reported {
+            paper_white: 300,
+            peak: 1000,
+        });
+        assert_eq!(g.ui_nits(reported), 300);
+        g.hdr_paper_white = 120;
+        assert_eq!(g.ui_nits(reported), 120);
+        g.hdr_ui_nits = 400;
+        assert_eq!((g.ui_nits(None), g.ui_nits(reported)), (400, 400));
+    }
+
    #[test]
    fn hdr_modes_keep_boolean_files_and_round_trip_auto() {
        assert_eq!(Graphics::parse("").hdr, HdrMode::Off);
@@ -1243,6 +1365,85 @@ mod tests {
        }
    }

+    fn scratch(name: &str) -> std::path::PathBuf {
+        let dir = std::env::temp_dir().join(format!(
+            "horizon-{name}-{}-{:?}",
+            std::process::id(),
+            std::thread::current().id()
+        ));
+        let _ = fs::remove_dir_all(&dir);
+        fs::create_dir_all(&dir).unwrap();
+        dir
+    }
+
+    /// A start that finds the marker (HDR output took the last one down) keeps the mode the
+    /// player chose and saves the driver the marker names; HDR Off saves nothing.
+    #[test]
+    fn a_marker_keeps_the_mode_and_holds_the_driver_it_names() {
+        let driver = "Vulkan 10de:2684 NVIDIA GeForce RTX 4090; NVIDIA; 581.57";
+        for mode in HdrMode::ALL {
+            let dir = scratch(&format!("hdr-marker-{mode:?}"));
+            let saved = Graphics {
+                hdr: mode,
+                ..Graphics::default()
+            };
+            saved.save(&dir);
+            fs::write(dir.join(HDR_MARKER), hdr_marker_text(driver)).unwrap();
+            let g = Graphics::load(&dir);
+            let failed = (mode != HdrMode::Off).then(|| driver.to_owned());
+            assert_eq!((g.hdr, &g.hdr_failed_start), (mode, &failed), "{mode:?}");
+            assert!(!dir.join(HDR_MARKER).exists(), "{mode:?}");
+            // Saved for good: the next start, without a marker, reads the same.
+            let again = Graphics::load(&dir);
+            assert_eq!((again.hdr, again.hdr_failed_start), (mode, failed));
+            let _ = fs::remove_dir_all(&dir);
+        }
+    }
+
+    /// Today's marker names no driver: it holds whichever driver the window starts on first,
+    /// and is that driver's from then on.
+    #[test]
+    fn a_marker_without_a_driver_holds_the_first_one_seen() {
+        let dir = scratch("hdr-marker-legacy");
+        Graphics {
+            hdr: HdrMode::Auto,
+            ..Graphics::default()
+        }
+        .save(&dir);
+        fs::write(dir.join(HDR_MARKER), "HDR output was being switched on\n").unwrap();
+        let mut g = Graphics::load(&dir);
+        assert_eq!(
+            (g.hdr, g.hdr_failed_start.as_deref()),
+            (HdrMode::Auto, Some(""))
+        );
+        let (first, second) = (
+            "Vulkan 10de:2684 GPU; NVIDIA; 1",
+            "Dx12 1002:744c GPU; AMD; 2",
+        );
+        assert!(g.hdr_held(first) && g.hdr_held(second));
+        assert!(g.settle_failed_start(first));
+        assert!(g.hdr_held(first) && !g.hdr_held(second));
+        assert!(!g.settle_failed_start(first));
+        let _ = fs::remove_dir_all(&dir);
+    }
+
+    /// The window starting on another driver (an update, another GPU) drops the hold, so HDR
+    /// output is tried again; on the same driver it stays.
+    #[test]
+    fn another_driver_drops_the_hold() {
+        let held = "Vulkan 10de:2684 GPU; NVIDIA; 581.57";
+        let mut g = Graphics {
+            hdr: HdrMode::On,
+            hdr_failed_start: Some(held.into()),
+            ..Graphics::default()
+        };
+        assert!(!g.settle_failed_start(held));
+        assert!(g.hdr_held(held));
+        assert!(g.settle_failed_start("Vulkan 10de:2684 GPU; NVIDIA; 582.02"));
+        assert_eq!((g.hdr, g.hdr_failed_start), (HdrMode::On, None));
+        assert!(!Graphics::default().hdr_held(held));
+    }
+
    #[test]
    fn round_trips() {
        let g = Graphics {
@@ -1292,9 +1493,11 @@ mod tests {
            hdr_paper_white: 240,
            hdr_peak: 1400,
            hdr_black_level: 12,
-            hdr_ui_brightness: 60,
+            hdr_ui_nits: 160,
            hdr_lighting: false,
-            hdr_key: "key.keyboard.h".into(),
+            hdr_failed_start: Some(
+                "Vulkan 10de:2684 NVIDIA GeForce RTX 4090; NVIDIA; 581.57".into(),
+            ),
            battery: true,
            shadow_cache: true,
            api: GraphicsApi::Dx12,
@@ -1303,6 +1506,15 @@ mod tests {
            shader_pack: "Golden Hour".into(),
        };
        assert_eq!(Graphics::parse(&g.serialize()), g);
+        // A legacy marker's hold, which names no driver, round-trips too; none writes no line.
+        for failed in [Some(String::new()), None] {
+            let graphics = Graphics {
+                hdr_failed_start: failed,
+                ..Graphics::default()
+            };
+            assert_eq!(Graphics::parse(&graphics.serialize()), graphics);
+        }
+        assert!(!Graphics::default().serialize().contains("hdrFailedStart"));
        for mode in EntityCullingMode::ALL {
            let graphics = Graphics {
                entity_culling: mode,
@@ -1424,6 +1636,10 @@ mod tests {
            Graphics::parse("shaderPack:Pack.zip\n"),
            Graphics::default()
        );
+        // The HDR page's old shortcut key loads as nothing, and the next save drops it.
+        let old = Graphics::parse("hdr:true\nhdrKey:key.keyboard.h\nhdrPeak:1000\n");
+        assert_eq!((old.hdr, old.hdr_peak), (HdrMode::On, 1000));
+        assert!(!old.serialize().contains("hdrKey"));
        assert_eq!(
            Graphics::parse(
                "workers:abc\nsky:maybe\ncullLeaves:true\nentityCulling:maybe\nleafCulling:maybe\n"
@@ -14,7 +14,7 @@ use crate::{
    lang,
    options_ui::{Event, Page as OptionsPage},
    settings::{Opt, Settings},
-    settings_shell::{self as shell, Binding, Group, Output, Row, Screen, Sheet, Value},
+    settings_shell::{self as shell, Group, Output, Row, Screen, Sheet, Value},
    text::Text,
 };

@@ -106,8 +106,6 @@ pub enum H {
    FrameGeneration,
    Hdr,
    HdrBlackLevel,
-    /// Binds `Graphics::hdr_key`.
-    HdrKey,
    /// Starts HDR calibration (`crate::hdr_calibration`).
    HdrCalibrate,
    HdrPeak,
@@ -614,7 +612,7 @@ pub fn rows() -> Vec<(Page, Vec<(&'static str, Vec<Setting>)>)> {
                        h(
                            H::HdrUiBrightness,
                            None,
-                            "How bright the HUD and menus are, against paper white.",
+                            "How bright the HUD and menus are. Auto: at paper white.",
                        ),
                        h(
                            H::HdrLighting,
@@ -623,14 +621,6 @@ pub fn rows() -> Vec<(Page, Vec<(&'static str, Vec<Setting>)>)> {
                        ),
                    ],
                ),
-                (
-                    "Shortcut",
-                    vec![h(
-                        H::HdrKey,
-                        None,
-                        "A key that opens this screen from the game. Not bound at first.",
-                    )],
-                ),
            ],
        ),
    ];
@@ -708,6 +698,10 @@ fn setup_of(g: &crate::graphics::Graphics, reported: bool) -> Setup {
        Setup::Changed
    }
 }
+/// What the HDR page says while HDR output is held back on this window's graphics driver
+/// (`EffectiveOutput::held`): picking a mode tries again (`H::cycle`).
+const HDR_HELD: &str = "HDR output stopped the game the last time it started with this graphics driver. Choose a mode to try again.";
+
 /// The description beside `item` where it depends on [`setup`]; `text` otherwise.
 fn description(
    item: Item,
@@ -716,6 +710,7 @@ fn description(
    text: &'static str,
 ) -> &'static str {
    match (item, setup(s, out)) {
+        (Item::Horizon(H::Hdr), _) if out.held => HDR_HELD,
        (Item::Horizon(H::HdrCalibrate), Setup::Unknown) => {
            "Your display didn't say how bright it gets: calibrate to set it up."
        }
@@ -814,14 +809,14 @@ impl H {
            H::ResolutionScale => Some((g.resolution_scale as f32 - 50.0) / 150.0),
            H::UpscalingSharpness => Some(g.upscaling_sharpness as f32 / 100.0),
            // Auto, then 10..480 by 10.
-            H::HdrPaperWhite => Some(g.hdr_paper_white as f32 / 480.0),
+            H::HdrPaperWhite => Some(crate::graphics::nits_position(g.hdr_paper_white)),
+            H::HdrUiBrightness => Some(crate::graphics::nits_position(g.hdr_ui_nits)),
            // Auto, then the peak's scale.
            H::HdrPeak => Some(match g.hdr_peak {
                0 => 0.0,
                n => (1.0 + crate::graphics::peak_step_of(n as f32)) / PEAK_POSITIONS as f32,
            }),
            H::HdrBlackLevel => Some(g.hdr_black_level as f32 / 100.0),
-            H::HdrUiBrightness => Some((g.hdr_ui_brightness as f32 - 25.0) / 75.0),
            _ => None,
        }
    }
@@ -833,13 +828,26 @@ impl H {
            H::Workers => Some(max_workers()),
            H::ResolutionScale => Some(30),
            H::UpscalingSharpness => Some(20),
-            H::HdrPaperWhite => Some(48),
+            H::HdrPaperWhite | H::HdrUiBrightness => Some(crate::graphics::NITS_STEPS),
            H::HdrPeak => Some(PEAK_POSITIONS),
            H::HdrBlackLevel => Some(100),
-            H::HdrUiBrightness => Some(15),
            _ => None,
        }
    }
+    /// "Paper White: Auto (203)" or "Paper White: 160": a setting in nits, 0 for Auto, which
+    /// shows the nits Auto gives.
+    fn nits_label(self, s: &Settings, out: &EffectiveOutput) -> Text {
+        let (g, r) = (&s.horizon, out.reported);
+        let (caption, set, auto) = match self {
+            H::HdrPaperWhite => ("Paper White", g.hdr_paper_white, g.paper_white_nits(r)),
+            H::HdrPeak => ("Peak Brightness", g.hdr_peak, g.peak_nits(r)),
+            _ => ("UI Brightness", g.hdr_ui_nits, g.ui_nits(r)),
+        };
+        match set {
+            0 => labelled(caption, lang::tr("Auto (%s)", &[&auto])),
+            n => labelled(caption, n),
+        }
+    }
    fn label(self, s: &Settings, out: &EffectiveOutput) -> Text {
        let g = &s.horizon;
        match self {
@@ -940,26 +948,9 @@ impl H {
                Setup::Automatic => "Calibrate Anyway...",
                Setup::Changed => "Use Automatic Setup",
            })),
-            H::HdrPaperWhite => match g.hdr_paper_white {
-                0 => labelled(
-                    "Paper White",
-                    lang::tr("Auto (%s)", &[&g.paper_white_nits(out.reported)]),
-                ),
-                n => labelled("Paper White", n.to_string()),
-            },
-            H::HdrPeak => match g.hdr_peak {
-                0 => labelled(
-                    "Peak Brightness",
-                    lang::tr("Auto (%s)", &[&g.peak_nits(out.reported)]),
-                ),
-                n => labelled("Peak Brightness", n.to_string()),
-            },
+            H::HdrPaperWhite | H::HdrPeak | H::HdrUiBrightness => self.nits_label(s, out),
            H::HdrBlackLevel => labelled("Black Level", format!("{:.2}", g.black_level_nits())),
-            H::HdrUiBrightness => labelled_percent("UI Brightness", g.hdr_ui_brightness),
            H::HdrLighting => labelled("HDR Lighting", on_off(g.hdr_lighting)),
-            H::HdrKey => {
-                Text::translate("Shortcut: %s", &[crate::keybinds::display_name(&g.hdr_key)])
-            }
            H::BatteryMode => labelled("Battery Mode", on_off(g.battery)),
            H::ShadowCache => labelled("Shadow Cache", on_off(g.shadow_cache)),
            // A press across the row, as Calibrate...: the list it opens shows the pick.
@@ -1000,7 +991,8 @@ impl H {
            H::Workers => g.workers = (v * max_workers() as f32).round() as u32,
            H::ResolutionScale => g.resolution_scale = (50.0 + (v * 30.0).round() * 5.0) as u32,
            H::UpscalingSharpness => g.upscaling_sharpness = (v * 20.0).round() as u32 * 5,
-            H::HdrPaperWhite => g.hdr_paper_white = (v * 48.0).round() as u32 * 10,
+            H::HdrPaperWhite => g.hdr_paper_white = crate::graphics::nits_at(v),
+            H::HdrUiBrightness => g.hdr_ui_nits = crate::graphics::nits_at(v),
            H::HdrPeak => {
                g.hdr_peak = match (v * PEAK_POSITIONS as f32).round() as u32 {
                    0 => 0,
@@ -1008,7 +1000,6 @@ impl H {
                }
            }
            H::HdrBlackLevel => g.hdr_black_level = (v * 100.0).round() as u32,
-            H::HdrUiBrightness => g.hdr_ui_brightness = (25.0 + (v * 15.0).round() * 5.0) as u32,
            _ => {}
        }
    }
@@ -1086,7 +1077,9 @@ impl H {
            H::FrameGeneration => {
                g.frame_generation = step(&FrameGeneration::ALL, g.frame_generation, back)
            }
+            // Any choice tries HDR output again on a driver a start failed on.
            H::Hdr => {
+                g.hdr_failed_start = None;
                g.hdr = step(&HdrMode::ALL, g.hdr, back);
                if g.hdr == HdrMode::On && !out.hdr_offered() {
                    g.hdr = step(&HdrMode::ALL, g.hdr, back);
@@ -1155,7 +1148,11 @@ impl Item {
                | H::HdrUiBrightness
                | H::HdrLighting
                | H::HdrSmoothGradients,
-            ) if !out.requests_hdr(s.horizon.hdr) => Some("Turn HDR on to use it."),
+            ) if !out.requests_hdr(s.horizon.hdr) => Some(if out.held {
+                HDR_HELD
+            } else {
+                "Turn HDR on to use it."
+            }),
            Item::Horizon(H::TranslucentBatching)
                if !crate::graphics::translucent_batching_offered() =>
            {
@@ -1178,10 +1175,7 @@ impl Item {
    fn steps(self, s: &Settings, out: &EffectiveOutput) -> bool {
        self.switch(s, out).is_none()
            && self.slider(s).is_none()
-            && !matches!(
-                self,
-                Item::Horizon(H::HdrKey | H::HdrCalibrate | H::ShaderPacks)
-            )
+            && !matches!(self, Item::Horizon(H::HdrCalibrate | H::ShaderPacks))
    }
    /// On/off settings and their value.
    pub fn switch(self, s: &Settings, out: &EffectiveOutput) -> Option<bool> {
@@ -1336,12 +1330,6 @@ fn shown(item: Item, s: &Settings) -> bool {
 }
 /// A control's label as its name and its value ("Render Distance" and "12 chunks").
 fn parts(item: Item, s: &Settings, out: &EffectiveOutput) -> (String, Option<String>) {
-    // The shortcut's label is one translated "Shortcut: %s"; the row shows its key apart, as
-    // KeyBindsScreen does ("> key <" while it waits, `settings_shell::Value::Binding`).
-    if item == Item::Horizon(H::HdrKey) {
-        let key = crate::keybinds::display_name(&s.horizon.hdr_key).plain();
-        return (lang::get("Shortcut"), Some(key));
-    }
    shell::name_and_value(&item.label(s, out).plain())
 }

@@ -1350,13 +1338,9 @@ fn parts(item: Item, s: &Settings, out: &EffectiveOutput) -> (String, Option<Str
 fn row(setting: Setting, s: &Settings, out: &EffectiveOutput) -> Row<Item> {
    let item = setting.item;
    let (name, value) = parts(item, s, out);
-    let value = match (item, item.switch(s, out), item.slider(s)) {
-        (Item::Horizon(H::HdrKey), ..) => Value::Binding(Binding::key(
-            crate::graphics::HDR_KEY,
-            value.unwrap_or_default(),
-        )),
-        (_, Some(on), _) => Value::Switch(on),
-        (_, None, Some(position)) => Value::Slider {
+    let value = match (item.switch(s, out), item.slider(s)) {
+        (Some(on), _) => Value::Switch(on),
+        (None, Some(position)) => Value::Slider {
            position,
            steps: item.slider_steps(),
            text: value.unwrap_or_default(),
@@ -1522,7 +1506,7 @@ impl Screen for GraphicsScreen {
    /// one `horizon-ctl options-set` changed meanwhile), nor fullscreen, which F11 and the
    /// window manager change.
    fn undo(&mut self, s: &mut Settings, b: &Settings) -> Vec<Output> {
-        s.horizon = b.horizon.clone();
+        s.horizon = s.horizon.undone_to(&b.horizon);
        s.render_distance = b.render_distance;
        s.simulation_distance = b.simulation_distance;
        s.gamma = b.gamma;
@@ -1572,7 +1556,7 @@ mod tests {
    use super::*;
    use crate::{
        graphics_style as style,
-        settings_shell::{Capture, Columns, Hosted, Shell, Target},
+        settings_shell::{Columns, Hosted, Shell, Target},
    };
    use winit::keyboard::KeyCode as K;

@@ -2038,10 +2022,6 @@ mod tests {
            precheck.why.as_deref(),
            Some("Only applies to asynchronous entity culling.")
        );
-        let key = find(&s, Item::Horizon(H::HdrKey));
-        assert_eq!(key.name, "Shortcut");
-        let waits = Capture::Key(crate::graphics::HDR_KEY);
-        assert!(matches!(key.value, Value::Binding(ref b) if b.capture == waits));
        let calibrate = find(&s, Item::Horizon(H::HdrCalibrate));
        assert_eq!(calibrate.value, Value::Press);
    }
@@ -2726,7 +2706,7 @@ mod tests {
            H::HdrPaperWhite => s.horizon.hdr_paper_white,
            H::HdrPeak => s.horizon.hdr_peak,
            H::HdrBlackLevel => s.horizon.hdr_black_level,
-            H::HdrUiBrightness => s.horizon.hdr_ui_brightness,
+            H::HdrUiBrightness => s.horizon.hdr_ui_nits,
            _ => unreachable!(),
        };
        let fresh = || {
@@ -2,7 +2,7 @@
 //! reports.
 use super::tests::{CHANGED, CLICK, DRAGGED, FB, NONE, SIZE, Ui, offering, press, row, ui};
 use super::*;
-use crate::settings_shell::{Capture, Columns, Hosted};
+use crate::settings_shell::{Columns, Hosted};
 use winit::keyboard::KeyCode as K;

 #[test]
@@ -64,17 +64,12 @@ fn hdr_auto_can_be_selected_before_querying_and_brightness_waits_for_output() {
    let peak = row(&mut ui, &s, Item::Horizon(H::HdrPeak));
    assert_eq!(press(&mut ui, &mut s, (tx + 2.0, peak[1] + 4.0)), [DRAGGED]);
    ui.release();
-    // Calibrate starts the calibration; the shortcut row waits for a key.
+    // Calibrate starts the calibration.
    let calibrate = row(&mut ui, &s, Item::Horizon(H::HdrCalibrate));
    assert_eq!(
        press(&mut ui, &mut s, at(calibrate)),
        [CLICK, Output::Push(OptionsPage::HdrCalibration)]
    );
-    let key = row(&mut ui, &s, Item::Horizon(H::HdrKey));
-    assert_eq!(
-        press(&mut ui, &mut s, at(key)),
-        [CLICK, Output::Bind(Capture::Key(crate::graphics::HDR_KEY))]
-    );
    assert!(ui.changed());
 }

@@ -134,3 +129,107 @@ fn hdr_setup_follows_what_the_system_reported() {
    assert_eq!(setup_of(&g, true), Setup::Changed);
    assert_eq!(setup_of(&g, false), Setup::Unknown);
 }
+
+/// UI Brightness reads as Paper White does, in nits apart from it: Auto shows the paper white
+/// in use, and a value set by hand its own nits, whatever Paper White is. Its slider has Paper
+/// White's steps: Auto, then 10 to 480 nits by 10.
+#[test]
+fn ui_brightness_reads_in_nits_on_paper_whites_steps() {
+    let mut s = Settings::default();
+    s.horizon.hdr = HdrMode::On;
+    let reporting = offering(true, Some(true));
+    let label = |s: &Settings, out| Item::Horizon(H::HdrUiBrightness).label(s, out).plain();
+    assert_eq!(label(&s, &reporting), "UI Brightness: Auto (400)");
+    assert_eq!(label(&s, &NONE), "UI Brightness: Auto (203)");
+    s.horizon.hdr_paper_white = 250;
+    assert_eq!(label(&s, &reporting), "UI Brightness: Auto (250)");
+    s.horizon.hdr_ui_nits = 160;
+    for paper_white in [0, 80, 250] {
+        s.horizon.hdr_paper_white = paper_white;
+        assert_eq!(label(&s, &reporting), "UI Brightness: 160");
+    }
+    let item = Item::Horizon(H::HdrUiBrightness);
+    assert_eq!(
+        H::HdrUiBrightness.slider_steps(),
+        H::HdrPaperWhite.slider_steps()
+    );
+    H::HdrUiBrightness.set_slider(&mut s, 0.0);
+    let mut reached = vec![s.horizon.hdr_ui_nits];
+    for _ in 0..H::HdrUiBrightness.slider_steps().unwrap() {
+        item.step_slider(&mut s, true, 200.0, &reporting);
+        reached.push(s.horizon.hdr_ui_nits);
+    }
+    let paper: Vec<u32> = std::iter::once(0).chain((10..=480).step_by(10)).collect();
+    assert_eq!(reached, paper);
+    // Each value sits where Paper White's same value does.
+    for nits in paper {
+        s.horizon.hdr_ui_nits = nits;
+        s.horizon.hdr_paper_white = nits;
+        assert_eq!(item.slider(&s), Item::Horizon(H::HdrPaperWhite).slider(&s));
+    }
+}
+
+/// While HDR output is held back on this window's driver, the HDR row says so and keeps
+/// the mode; any change of the mode drops the hold, and HDR is asked for again.
+#[test]
+fn a_held_hdr_start_is_said_on_the_page_and_a_mode_change_tries_again() {
+    use crate::gfx::{HdrOutput, output::tests};
+    let mut s = Settings::default();
+    s.horizon.hdr = HdrMode::Auto;
+    s.horizon.hdr_failed_start = Some("Vulkan 10de:2684 GPU; driver; 1.0".into());
+    let (mut caps, reading) = tests::window(Some(HdrOutput::Pq), Some(true));
+    caps.held = true;
+    let out = tests::snapshot(&s.horizon, Default::default(), caps, reading);
+    let hdr = Item::Horizon(H::Hdr);
+    let setting = h(
+        H::Hdr,
+        Cost::None,
+        "Lava, fire and sunlight shine brighter than white.",
+    );
+    let held = super::row(setting, &s, &out);
+    assert_eq!(held.chosen.as_deref(), Some(HDR_HELD));
+    assert_eq!(held.why, None);
+    assert_eq!(hdr.label(&s, &out).plain(), "HDR: Auto");
+    assert_eq!(Item::Horizon(H::HdrPeak).blocked(&s, &out), Some(HDR_HELD));
+    // Not held, the row says what HDR does.
+    caps.held = false;
+    let free = tests::snapshot(&s.horizon, Default::default(), caps, reading);
+    assert_eq!(super::row(setting, &s, &free).chosen, None);
+    // Any step of the mode, either way, tries again.
+    for back in [false, true] {
+        let mut s = s.clone();
+        hdr.cycle(&mut s, back, FB, &out);
+        assert_ne!(s.horizon.hdr, HdrMode::Auto);
+        assert_eq!(s.horizon.hdr_failed_start, None);
+    }
+}
+
+/// Undo never brings the hold back: held Auto, changed to On (HDR tried again), then
+/// undone, is Auto without the hold. With the mode left alone, it keeps the hold as it is.
+#[test]
+fn undo_never_restores_a_held_hdr_start() {
+    let mut screen = GraphicsScreen {
+        framebuffer: FB,
+        output: NONE,
+    };
+    let mut opened = Settings::default();
+    opened.horizon.hdr = HdrMode::Auto;
+    opened.horizon.hdr_failed_start = Some("Vulkan 10de:2684 GPU; driver; 1.0; os".into());
+    let mut s = opened.clone();
+    let out = offering(true, Some(true));
+    Item::Horizon(H::Hdr).cycle(&mut s, true, FB, &out);
+    assert_eq!(
+        (s.horizon.hdr, &s.horizon.hdr_failed_start),
+        (HdrMode::On, &None)
+    );
+    screen.undo(&mut s, &opened);
+    assert_eq!(
+        (s.horizon.hdr, &s.horizon.hdr_failed_start),
+        (HdrMode::Auto, &None)
+    );
+    // Another row changed and undone: the hold stays.
+    let mut s = opened.clone();
+    s.horizon.fxaa = !s.horizon.fxaa;
+    screen.undo(&mut s, &opened);
+    assert_eq!(s.horizon, opened.horizon);
+}
@@ -206,8 +206,9 @@ fn display(light: vec3<f32>) -> vec4<f32> {
    let shows = params.world > 0.5 && params.peak > 1.0
        && (hand || (!covered && shows_world(f.rgb, w.rgb)));
    var light = lit(f.rgb, w.a, shows, true).light;
-    // The HUD and menus at their own brightness, by how much they cover.
-    light *= mix(1.0, params.ui, ui);
+    // The HUD and menus at their own brightness, by how much they cover, no brighter than the
+    // peak (as `fs_hdr_layered`): UI Brightness can pass paper white.
+    light = min(light * mix(1.0, params.ui, ui), vec3(params.peak));
    return display(light);
 }

@@ -275,8 +276,8 @@ fn backdrop(w: vec3<f32>) -> vec3<f32> {

 // The HUD over the world in gamma, the space the HUD blends in: its own part, what its backdrop
 // B doesn't explain (H = P - (1 - c) B, exact for the layering blends), at UI Brightness, over
-// (1 - c) of the world, light above white included. Where the world is at or below white, at
-// 100%, that is the HUD's picture as drawn.
+// (1 - c) of the world, light above white included. Where the world is at or below white, with
+// UI Brightness at paper white, that is the HUD's picture as drawn.
 fn layered(at: vec2<i32>) -> vec3<f32> {
    let w = max(textureLoad(frame, at, 0).rgb, vec3(0.0));
    let p = textureLoad(hud, at, 0).rgb;
@@ -17,6 +17,7 @@
 //! Nothing changes until Save, which writes the three into Horizon's settings; Cancel
 //! or Escape leaves them as they were.
 use crate::{
+    font::Font,
    hud::{HudAtlas, HudBatch, rgba},
    lang,
    settings::Settings,
@@ -33,6 +34,10 @@ pub enum Step {
 }
 const STEPS: [Step; 3] = [Step::Black, Step::Peak, Step::PaperWhite];

+/// A step's test picture for HDR output: the step, its nits and where the controls start (a
+/// share of the height).
+pub type Picture = (Step, f32, f32);
+
 /// What the options screen does after an input here.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Outcome {
@@ -43,6 +48,30 @@ pub enum Outcome {
    Cancel,
 }

+/// The window as calibration found it: calibration turns it fullscreen for its test pictures,
+/// and gives it back as it was.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum WindowState {
+    Fullscreen,
+    Maximized,
+    Windowed,
+}
+
+impl WindowState {
+    pub fn of(fullscreen: bool, maximized: bool) -> Self {
+        match (fullscreen, maximized) {
+            (true, _) => Self::Fullscreen,
+            (false, true) => Self::Maximized,
+            (false, false) => Self::Windowed,
+        }
+    }
+    /// On leaving calibration: whether the window leaves fullscreen, and whether it is
+    /// maximized again after (leaving fullscreen gives back its restored size on Windows).
+    pub fn leaving(self) -> (bool, bool) {
+        (self != Self::Fullscreen, self == Self::Maximized)
+    }
+}
+
 pub struct Calibration {
    step: usize,
    /// Nits, in the order of `STEPS`.
@@ -53,8 +82,11 @@ pub struct Calibration {
    dragging: bool,
 }

-/// Height of the band of controls at the bottom, in GUI pixels.
+/// Height of the band of controls at the bottom with a hint of one line, in GUI pixels.
 const BAND: f32 = 84.0;
+/// Each further line of the hint, which wraps within the window less this at each side.
+const HINT_LINE: f32 = 10.0;
+const HINT_MARGIN: f32 = 10.0;

 impl Step {
    /// The slider's steps past its first: the settings' own.
@@ -115,18 +147,24 @@ impl Step {

 struct Layout {
    top: f32,
+    hint: Vec<Text>,
    slider: (f32, f32, f32),
    cancel: (f32, f32, f32),
    back: (f32, f32, f32),
    next: (f32, f32, f32),
 }
-fn layout(w: f32, h: f32) -> Layout {
-    let top = (h - BAND).floor();
+/// The band grows up by the lines `step`'s hint takes past its first.
+fn layout(font: &Font, step: Step, (w, h): (f32, f32)) -> Layout {
+    let hint = Text::literal(lang::get(step.hint_key()));
+    let hint = font.split(&hint, w - 2.0 * HINT_MARGIN);
+    let more = hint.len().saturating_sub(1) as f32 * HINT_LINE;
+    let top = (h - BAND - more).floor();
    let cx = (w / 2.0).floor();
-    let by = top + 58.0;
+    let by = top + more + 58.0;
    Layout {
        top,
-        slider: (cx - 100.0, top + 32.0, 200.0),
+        hint,
+        slider: (cx - 100.0, top + more + 32.0, 200.0),
        cancel: (cx - 152.0, by, 98.0),
        back: (cx - 49.0, by, 98.0),
        next: (cx + 54.0, by, 98.0),
@@ -159,6 +197,9 @@ impl Calibration {
    fn current(&self) -> Step {
        STEPS[self.step]
    }
+    fn layout(&self, font: &Font, size: (f32, f32)) -> Layout {
+        layout(font, self.current(), size)
+    }
    /// The slider's position, 0..=1.
    fn position(&self) -> f32 {
        let step = self.current();
@@ -184,18 +225,17 @@ impl Calibration {
        };
        Text::literal(format!("{}: {}", step.name(), value))
    }
-    /// The step, its nits and where the controls start (a share of the height), for
-    /// HDR output's test picture.
-    pub fn picture(&self, h: f32) -> (Step, f32, f32) {
+    /// The current step's test picture in a GUI of `size`.
+    pub fn picture(&self, font: &Font, size: (f32, f32)) -> Picture {
        (
            self.current(),
            self.values[self.step],
-            layout(0.0, h).top / h.max(1.0),
+            self.layout(font, size).top / size.1.max(1.0),
        )
    }
    pub fn draw(&self, batch: &mut HudBatch, atlas: &HudAtlas, cursor: (f32, f32)) {
        let (w, h) = (batch.width, batch.height);
-        let l = layout(w, h);
+        let l = self.layout(&atlas.font, (w, h));
        // Above the band HDR output draws the test picture over whatever is here.
        batch.fill(atlas, 0.0, 0.0, w, h, rgba(0, 0, 0, 255));
        batch.fill(atlas, 0.0, l.top, w, h - l.top, rgba(24, 24, 24, 255));
@@ -205,16 +245,10 @@ impl Calibration {
            &[&(self.step + 1), &STEPS.len(), &step.name()],
        ));
        ui::centered_text(batch, atlas, &title, 0.0, l.top + 6.0, w, u32::MAX);
-        let hint = Text::literal(lang::get(step.hint_key()));
-        ui::centered_text(
-            batch,
-            atlas,
-            &hint,
-            0.0,
-            l.top + 18.0,
-            w,
-            rgba(160, 160, 160, 255),
-        );
+        for (i, line) in l.hint.iter().enumerate() {
+            let y = l.top + 18.0 + i as f32 * HINT_LINE;
+            ui::centered_text(batch, atlas, line, 0.0, y, w, rgba(160, 160, 160, 255));
+        }
        let (x, y, sw) = l.slider;
        ui::slider(
            batch,
@@ -261,8 +295,14 @@ impl Calibration {
        }
    }
    /// A press, or a drag with `drag`, at `cursor`.
-    pub fn click(&mut self, cursor: (f32, f32), (w, h): (f32, f32), drag: bool) -> Outcome {
-        let l = layout(w, h);
+    pub fn click(
+        &mut self,
+        font: &Font,
+        cursor: (f32, f32),
+        size: (f32, f32),
+        drag: bool,
+    ) -> Outcome {
+        let l = self.layout(font, size);
        let (x, _, sw) = l.slider;
        if drag {
            if !self.dragging {
@@ -336,6 +376,14 @@ mod tests {

    const NONE: EffectiveOutput = EffectiveOutput::NONE;

+    fn font() -> Font {
+        Font::metrics(std::path::Path::new("/nonexistent/horizon-test-assets"))
+    }
+    /// At the default GUI scale of the game's first window (854 x 480 at 2).
+    fn picture(c: &Calibration) -> Picture {
+        c.picture(&font(), (427.0, 240.0))
+    }
+
    #[test]
    fn calibration_saves_only_on_save() {
        let mut s = Settings::default();
@@ -344,14 +392,14 @@ mod tests {
        let mut c = Calibration::new(&s, &NONE);
        assert_eq!(c.key(KeyCode::ArrowLeft), Outcome::Changed);
        assert_eq!(c.key(KeyCode::ArrowLeft), Outcome::Changed);
-        assert!((c.picture(100.0).1 - 0.03).abs() < 1e-6);
+        assert!((picture(&c).1 - 0.03).abs() < 1e-6);
        assert_eq!(c.key(KeyCode::Escape), Outcome::Cancel);
        assert_eq!(s.horizon, before);
        // Black, then Peak (one step up), then Paper White, then Save.
        assert_eq!(c.key(KeyCode::Enter), Outcome::Click);
        assert_eq!(c.key(KeyCode::ArrowRight), Outcome::Changed);
        assert_eq!(c.key(KeyCode::Enter), Outcome::Click);
-        assert_eq!(c.picture(100.0).0, Step::PaperWhite);
+        assert_eq!(picture(&c).0, Step::PaperWhite);
        assert_eq!(c.key(KeyCode::Enter), Outcome::Save);
        c.save(&mut s);
        assert_eq!(s.horizon.hdr_black_level, 3);
@@ -370,10 +418,10 @@ mod tests {
        for (output, peak, paper_white) in [(&reporting, 1000.0, 400.0), (&NONE, 1000.0, 203.0)] {
            let mut c = Calibration::new(&s, output);
            c.key(KeyCode::Enter);
-            assert_eq!(c.picture(1.0).0, Step::Peak);
-            assert_eq!(c.picture(1.0).1, peak);
+            assert_eq!(picture(&c).0, Step::Peak);
+            assert_eq!(picture(&c).1, peak);
            c.key(KeyCode::Enter);
-            assert_eq!(c.picture(1.0).1, paper_white);
+            assert_eq!(picture(&c).1, paper_white);
        }
    }

@@ -392,14 +440,14 @@ mod tests {
        ];
        let mut c = Calibration::new(&Settings::default(), &NONE);
        for (i, expected) in expected.iter().enumerate() {
-            assert_eq!(c.picture(1.0).0, STEPS[i]);
+            assert_eq!(picture(&c).0, STEPS[i]);
            for _ in 0..200 {
                c.key(KeyCode::ArrowLeft);
            }
-            let mut seen = vec![c.picture(1.0).1];
+            let mut seen = vec![picture(&c).1];
            for _ in 0..200 {
                c.key(KeyCode::ArrowRight);
-                let v = c.picture(1.0).1;
+                let v = picture(&c).1;
                if seen.last() != Some(&v) {
                    seen.push(v);
                }
@@ -422,7 +470,7 @@ mod tests {
        assert_eq!(s.horizon.hdr_black_level, 2);
        // Calibrated back down, 0 is no lift: what the step showed.
        let mut c = Calibration::new(&s, &NONE);
-        assert!((c.picture(1.0).1 - 0.02).abs() < 1e-6);
+        assert!((picture(&c).1 - 0.02).abs() < 1e-6);
        c.key(KeyCode::ArrowLeft);
        c.key(KeyCode::ArrowLeft);
        c.key(KeyCode::Enter);
@@ -435,14 +483,89 @@ mod tests {
        assert_eq!(s.horizon.hdr_peak, 10_000);
        let mut c = Calibration::new(&s, &NONE);
        c.key(KeyCode::Enter);
-        assert_eq!(c.picture(1.0).1, 10_000.0);
+        assert_eq!(picture(&c).1, 10_000.0);
        // One step down from the top is 500 nits; from 2000, 50.
        c.key(KeyCode::ArrowLeft);
-        assert_eq!(c.picture(1.0).1, 9500.0);
+        assert_eq!(picture(&c).1, 9500.0);
        s.horizon.hdr_peak = 2000;
        let mut c = Calibration::new(&s, &NONE);
        c.key(KeyCode::Enter);
        c.key(KeyCode::ArrowLeft);
-        assert_eq!(c.picture(1.0).1, 1950.0);
+        assert_eq!(picture(&c).1, 1950.0);
+    }
+
+    /// A hint wider than the window less its margins wraps, the band grows up by the lines
+    /// it adds, and the test picture ends where the band drawn starts.
+    #[test]
+    fn the_hint_wraps_and_the_band_grows_by_its_lines() {
+        let font = font();
+        let mut c = Calibration::new(&Settings::default(), &NONE);
+        c.key(KeyCode::Enter);
+        c.key(KeyCode::Enter);
+        let hint = Text::literal(lang::get(Step::PaperWhite.hint_key()));
+        let wide = font.width_text(&hint);
+        let size = (wide + 2.0 * HINT_MARGIN, 240.0);
+        let one = c.layout(&font, size);
+        assert_eq!(one.hint.len(), 1);
+        assert_eq!(one.top, 240.0 - BAND);
+        let narrow = (wide * 0.6, 240.0);
+        let wrapped = c.layout(&font, narrow);
+        assert_eq!(wrapped.hint.len(), 2);
+        assert!(
+            wrapped
+                .hint
+                .iter()
+                .all(|l| font.width_text(l) <= narrow.0 - 2.0 * HINT_MARGIN)
+        );
+        assert_eq!(wrapped.top, 240.0 - BAND - HINT_LINE);
+        // Under the hint's lines, the controls keep their place in the band.
+        assert_eq!(
+            wrapped.slider.1 - wrapped.top,
+            one.slider.1 - one.top + HINT_LINE
+        );
+        assert_eq!(
+            wrapped.next.1 - wrapped.top,
+            one.next.1 - one.top + HINT_LINE
+        );
+        for size in [size, narrow] {
+            let (_, _, band) = c.picture(&font, size);
+            assert_eq!(band * size.1, c.layout(&font, size).top);
+        }
+    }
+
+    /// The Peak step's patch (a square of a tenth of the screen, centred above the band,
+    /// `hdr.wgsl`) stays above the band even on the narrowest GUI with every hint wrapped:
+    /// its side is no more than the band's top.
+    #[test]
+    fn the_test_pictures_stay_above_a_grown_band() {
+        let font = font();
+        let mut c = Calibration::new(&Settings::default(), &NONE);
+        for step in STEPS {
+            for (w, h) in [(320.0, 240.0), (200.0, 240.0), (427.0, 240.0)] {
+                let (shown, _, band) = c.picture(&font, (w, h));
+                assert_eq!(shown, step);
+                let side = (0.1 * w * h).sqrt();
+                assert!(
+                    side <= band * h,
+                    "{step:?} at {w}x{h}: {side} > {}",
+                    band * h
+                );
+            }
+            c.key(KeyCode::Enter);
+        }
+    }
+
+    /// Leaving calibration gives the window back as it found it.
+    #[test]
+    fn leaving_gives_the_window_back_as_it_was() {
+        use WindowState as W;
+        assert_eq!(W::of(true, false), W::Fullscreen);
+        assert_eq!(W::of(true, true), W::Fullscreen);
+        assert_eq!(W::of(false, true), W::Maximized);
+        assert_eq!(W::of(false, false), W::Windowed);
+        // (leave fullscreen, maximize again)
+        assert_eq!(W::Fullscreen.leaving(), (false, false));
+        assert_eq!(W::Maximized.leaving(), (true, true));
+        assert_eq!(W::Windowed.leaving(), (true, false));
    }
 }
@@ -12,6 +12,7 @@ use std::{
 };
 use wgpu::util::DeviceExt;

+mod animate;
 pub mod cit_glint;
 mod pack_text;
 pub mod pictures;
@@ -100,21 +101,21 @@ pub struct HudAtlas {
    pub glint_armor: (Vec<u8>, u32, u32),
    /// A resource pack's own `core/text` shader for the GUI's text, translated;
    /// none draws the text natively.
-    pub text_shader: Option<std::sync::Arc<horizon_shaders::CoreProgram>>,
+    pub text_shader: Option<std::sync::Arc<crate::core_shader::CoreProgram>>,
    /// A resource pack's own `core/rendertype_lines` shader for the block outline, translated;
    /// none draws the outline natively.
-    pub lines_shader: Option<std::sync::Arc<horizon_shaders::CoreProgram>>,
+    pub lines_shader: Option<std::sync::Arc<crate::core_shader::CoreProgram>>,
    /// The packs' `core/sky` and `core/stars`, when a pack replaces them.
-    pub sky_shader: Option<std::sync::Arc<horizon_shaders::CoreProgram>>,
-    pub stars_shader: Option<std::sync::Arc<horizon_shaders::CoreProgram>>,
+    pub sky_shader: Option<std::sync::Arc<crate::core_shader::CoreProgram>>,
+    pub stars_shader: Option<std::sync::Arc<crate::core_shader::CoreProgram>>,
    /// The packs' Polytone screen sprite modifiers.
    pub sprite_modifiers: std::sync::Arc<sprite_modifiers::SpriteModifiers>,
    /// The packs' OptiFine random entity textures, whose variants this atlas packs.
-    pub random_textures: horizon_optifine::random_textures::RandomTextures,
+    pub random_textures: crate::entity_textures::RandomTextures,
    /// Their emissive overlays (`_e`), packed here too.
-    pub emissive: std::sync::Arc<horizon_optifine::emissive::Emissive>,
+    pub emissive: std::sync::Arc<crate::entity_textures::Emissive>,
    /// ETF's blinking frames (`_blink`), packed here too.
-    pub blinks: horizon_optifine::blink::Blinks,
+    pub blinks: crate::entity_textures::Blinks,
    /// Of the shared atlas's textures, their LabPBR normal and specular maps as paged maps
    /// (`paged_maps.rs`), read while loading for shader packs (`sprites::labpbr_maps`).
    pub material_maps: std::sync::Arc<[Option<crate::paged_maps::PagedMap>; 2]>,
@@ -432,7 +433,7 @@ fn cit_sprites(
    packed: &[PackedImage],
 ) -> Vec<(PackedImage, Option<TextureFlags>, bool)> {
    let have: HashSet<&str> = packed.iter().map(|i| i.0.as_str()).collect();
-    let rules = crate::cit::load_rules(root);
+    let rules = crate::cit::CitRules::load(root).rules;
    let mut ids = crate::cit_assets::item_sprites(&rules);
    if !rules.is_empty() {
        let models = crate::cit_assets::load_models(root, &rules);
@@ -1203,25 +1204,18 @@ impl HudAtlas {
            let s = p.to_string_lossy().replace('\\', "/");
            !s.contains("title/background") && !s.contains("presets")
        });
-        // OptiFine random entity variants, under the names their scan gives them (those
-        // outside `textures/` are `<ns>:optifine/random/...`).
-        let random_textures = if folders.contains(&"entity") {
-            horizon_optifine::random_textures::RandomTextures::scan(root)
+        // Random entity variants, under the names their scan gives them (those outside
+        // `textures/` are `<ns>:optifine/random/...`), blink frames and emissive overlays.
+        let crate::entity_textures::EntityTextures {
+            random: random_textures,
+            blinks,
+            emissive,
+        } = if folders.contains(&"entity") {
+            crate::entity_textures::EntityTextures::load(root)
        } else {
            Default::default()
        };
-        let blinks = if folders.contains(&"entity") {
-            horizon_optifine::blink::Blinks::scan(root, &random_textures)
-        } else {
-            Default::default()
-        };
-        let emissive = std::sync::Arc::new(if folders.contains(&"entity") {
-            let mut e = horizon_optifine::emissive::Emissive::scan(root, &random_textures);
-            e.pair_beside(root, blinks.files());
-            e
-        } else {
-            Default::default()
-        });
+        let emissive = std::sync::Arc::new(emissive);
        let mut named: HashMap<PathBuf, String> = HashMap::new();
        let extra = random_textures
            .files()
@@ -1427,32 +1421,7 @@ impl HudAtlas {
        }
        if full {
            // Official Recipes artwork from Just Enough Items, under MIT.
-            for (name, png) in [
-                (
-                    "button_enabled_v2",
-                    include_bytes!("jei_recipes/button_enabled_v2.png").as_slice(),
-                ),
-                (
-                    "button_disabled_v2",
-                    include_bytes!("jei_recipes/button_disabled_v2.png").as_slice(),
-                ),
-                (
-                    "button_highlight_v2",
-                    include_bytes!("jei_recipes/button_highlight_v2.png").as_slice(),
-                ),
-                (
-                    "icons/arrow_previous_v2",
-                    include_bytes!("jei_recipes/icons/arrow_previous_v2.png").as_slice(),
-                ),
-                (
-                    "icons/arrow_next_v2",
-                    include_bytes!("jei_recipes/icons/arrow_next_v2.png").as_slice(),
-                ),
-                (
-                    "search_background_v2",
-                    include_bytes!("jei_recipes/search_background_v2.png").as_slice(),
-                ),
-            ] {
+            for (name, png) in crate::jei_sprites::SPRITES {
                let (width, height, rgba) = decode_bytes(png)?;
                images.push((format!("horizon/jei/{name}"), width, height, rgba));
            }
@@ -2895,65 +2864,12 @@ impl HudRenderer {
    pub fn set_text_shader(
        &mut self,
        device: &wgpu::Device,
-        shader: Option<&horizon_shaders::CoreProgram>,
+        shader: Option<&crate::core_shader::CoreProgram>,
    ) {
        self.pack_text = shader.and_then(|shader| {
            pack_text::PackText::new(device, self.format, &self.atlas_view, shader, self.coverage)
        });
    }
-    pub fn animate_sprites(
-        &mut self,
-        uploads: &mut crate::gfx::upload::Uploads,
-        encoder: &mut wgpu::CommandEncoder,
-        tick: u64,
-    ) {
-        let Some(texture) = &self.atlas_texture else {
-            return;
-        };
-        for (rect, animation, previous) in &mut self.sprite_animations {
-            // `SpriteContents.AnimationState`: the frame from the mcmeta's
-            // list, blended into the next one by the sub-frame's thousandths
-            // when the sprite interpolates.
-            let blend = animation.blend(tick);
-            let state = (blend.frame, blend.next, blend.millis);
-            if state == *previous {
-                continue;
-            }
-            let (w, h) = rect.texels((texture.width(), texture.height()));
-            let pixels = if blend.millis == 0 {
-                animation.resized_pixels(blend.frame, w, h)
-            } else {
-                let current = animation.resized_pixels(blend.frame, w, h);
-                let next = animation.resized_pixels(blend.next, w, h);
-                let millis = blend.millis;
-                current
-                    .iter()
-                    .zip(next)
-                    .map(|(&a, b)| {
-                        ((u32::from(a) * (1000 - millis) + u32::from(b) * millis + 500) / 1000)
-                            as u8
-                    })
-                    .collect()
-            };
-            uploads.texture(
-                encoder,
-                wgpu::TexelCopyTextureInfo {
-                    texture,
-                    mip_level: 0,
-                    origin: wgpu::Origin3d {
-                        x: (rect.u0 * texture.width() as f32).round() as u32,
-                        y: (rect.v0 * texture.height() as f32).round() as u32,
-                        z: 0,
-                    },
-                    aspect: wgpu::TextureAspect::All,
-                },
-                w,
-                h,
-                &pixels,
-            );
-            *previous = state;
-        }
-    }
    /// Stage `patches` into the shared atlas texture.
    pub fn upload_patches(
        &self,
@@ -3551,6 +3467,7 @@ mod tests {
    /// `RandomTextures` gives them; one beside its texture packs once, under its own.
    #[test]
    fn random_entity_variants_pack_under_their_scan_names() {
+        crate::pack_formats::install();
        let root =
            std::env::temp_dir().join(format!("horizon-atlas-random-{}", std::process::id()));
        let _ = fs::remove_dir_all(&root);
@@ -3573,6 +3490,7 @@ mod tests {
    /// A random variant's emissive overlay packs beside the variant, under its name.
    #[test]
    fn variant_overlays_pack_under_their_names() {
+        crate::pack_formats::install();
        let root =
            std::env::temp_dir().join(format!("horizon-atlas-overlay-{}", std::process::id()));
        let _ = fs::remove_dir_all(&root);
@@ -3887,6 +3805,7 @@ mod tests {
    }
    /// A resource root with one plain item texture and these CIT files (relative path, contents).
    fn cit_root(name: &str, files: &[(&str, &str)]) -> PathBuf {
+        crate::pack_formats::install();
        let root =
            std::env::temp_dir().join(format!("horizon-atlas-cit-{name}-{}", std::process::id()));
        let _ = fs::remove_dir_all(&root);
@@ -3976,7 +3895,7 @@ mod tests {
        );
        let cit = root.join("assets/minecraft/optifine/cit");
        write_strip(&cit.join("a.png"), 64, 32, &[[1, 2, 3, 255]], None);
-        let rules = crate::cit::load_rules(&root);
+        let rules = crate::cit::CitRules::load(&root).rules;
        assert_eq!(rules.len(), 1);
        let atlas = HudAtlas::build(&root).unwrap();
        let _ = fs::remove_dir_all(&root);
@@ -0,0 +1,61 @@
+//! The GUI atlas's animated sprites, frame by frame (vanilla's or a Polytone `mode`'s).
+
+impl super::HudRenderer {
+    /// Shows each animated sprite's frame: its mcmeta's, or what its Polytone `mode` picks.
+    pub(crate) fn animate(
+        &mut self,
+        uploads: &mut crate::gfx::upload::Uploads,
+        encoder: &mut wgpu::CommandEncoder,
+        tick: u64,
+        animator: &crate::gfx::animate::SpriteAnimator,
+    ) {
+        let inputs = animator.mode_inputs();
+        let inputs = Some(&inputs);
+        let Some(texture) = &self.atlas_texture else {
+            return;
+        };
+        for (rect, animation, previous) in &mut self.sprite_animations {
+            // `SpriteContents.AnimationState`: the frame from the mcmeta's
+            // list, blended into the next one by the sub-frame's thousandths
+            // when the sprite interpolates; or what a Polytone `mode` picks.
+            let blend = animation.blend_with(tick, inputs);
+            let state = (blend.frame, blend.next, blend.millis);
+            if state == *previous {
+                continue;
+            }
+            let (w, h) = rect.texels((texture.width(), texture.height()));
+            let pixels = if blend.millis == 0 {
+                animation.resized_pixels(blend.frame, w, h)
+            } else {
+                let current = animation.resized_pixels(blend.frame, w, h);
+                let next = animation.resized_pixels(blend.next, w, h);
+                let millis = blend.millis;
+                current
+                    .iter()
+                    .zip(next)
+                    .map(|(&a, b)| {
+                        ((u32::from(a) * (1000 - millis) + u32::from(b) * millis + 500) / 1000)
+                            as u8
+                    })
+                    .collect()
+            };
+            uploads.texture(
+                encoder,
+                wgpu::TexelCopyTextureInfo {
+                    texture,
+                    mip_level: 0,
+                    origin: wgpu::Origin3d {
+                        x: (rect.u0 * texture.width() as f32).round() as u32,
+                        y: (rect.v0 * texture.height() as f32).round() as u32,
+                        z: 0,
+                    },
+                    aspect: wgpu::TextureAspect::All,
+                },
+                w,
+                h,
+                &pixels,
+            );
+            *previous = state;
+        }
+    }
+}
@@ -1,12 +1,12 @@
-//! OptiFine CIT enchantment glints on GUI items (`type=enchantment`, see `crate::cit_glint` for
+//! Custom item texture enchantment glints on GUI items (`Kind::Enchantment`, see `crate::cit_glint` for
 //! which layers a stack draws): every rule's texture in one texture array, each layer an extra
 //! pass over the item's quads with its rule's blend. A layer's vertices carry its texture slot
 //! (red) and its intensity (alpha) in their colour; its scrolled UV is worked out on the CPU, as
 //! vanilla's glint's is. Without enchantment rules nothing here is made.

 use super::HudVertex;
+use crate::cit::{Blend, Factor, Kind, Rule};
 use crate::gfx::hud_coverage::Pipeline;
-use horizon_optifine::cit::{Blend, Factor, Kind, Rule};
 use std::path::Path;

 /// Slots the shader's table holds; rules past it draw no layer (and match no stack).
@@ -438,13 +438,11 @@ impl CitGlintPass {
 #[cfg(test)]
 mod tests {
    use super::*;
-    use horizon_optifine::Properties;
-    use horizon_optifine::cit::parse_blend;
+    use crate::pack_formats::cit::{parse_blend, parse_rule};

    fn rule(name: &str, text: &str) -> Rule {
        let path = format!("assets/minecraft/optifine/cit/{name}.properties");
-        let text = format!("texture=glint\n{text}");
-        Rule::parse(&path, &Properties::parse_equals_first(&text), |_| true).unwrap()
+        parse_rule(&path, &format!("texture=glint\n{text}")).unwrap()
    }

    #[test]
@@ -338,7 +338,7 @@ fn coverage_preserves_each_cit_blend_and_its_destination_alpha() {
    let Some(mut gpu) = Gpu::new() else {
        return;
    };
-    use horizon_optifine::cit::parse_blend;
+    use crate::pack_formats::cit::parse_blend;
    for (name, expected) in [
        ("alpha", 128),
        ("add", 0),
@@ -393,7 +393,7 @@ fn coverage_uses_pack_texts_final_alpha_and_discard() {
        return;
    };
    // A translated-style struct result and early return; no dependency on game resources.
-    let program = horizon_shaders::CoreProgram {
+    let program = crate::core_shader::CoreProgram {
        vertex: naga::front::wgsl::parse_str("@vertex fn main(@location(0) p: vec2<f32>) -> @builtin(position) vec4<f32> { return vec4(p.x / 2.0 - 1.0, 1.0 - p.y, 0.0, 1.0); }").unwrap(),
        fragment: naga::front::wgsl::parse_str("struct Result { @location(0) color: vec4<f32> } @fragment fn main(@builtin(position) p: vec4<f32>) -> Result { if p.x > 2.0 { discard; } return Result(vec4(0.4, 0.2, 0.1, 0.5)); }").unwrap(),
    };
@@ -414,7 +414,7 @@ fn a_pack_text_shader_without_a_colour_output_is_dropped_not_wrapped() {
    let Some(mut gpu) = Gpu::new() else {
        return;
    };
-    let program = horizon_shaders::CoreProgram {
+    let program = crate::core_shader::CoreProgram {
        vertex: naga::front::wgsl::parse_str("@vertex fn main(@location(0) p: vec2<f32>) -> @builtin(position) vec4<f32> { return vec4(p, 0.0, 1.0); }").unwrap(),
        fragment: naga::front::wgsl::parse_str("@fragment fn main() -> @location(1) vec4<f32> { return vec4(1.0); }").unwrap(),
    };
@@ -5,7 +5,7 @@
 use std::path::Path;
 use std::sync::Arc;

-use horizon_shaders::{CoreProgram, Glue};
+use crate::core_shader::{CoreProgram, Glue};

 use super::{HudBatch, HudVertex};
 use crate::gfx::hud_coverage::Pipeline;
@@ -64,7 +64,7 @@ pub(super) fn load_core(
        let path = format!("assets/{namespace}/{path}");
        read(root, &path).or_else(|| read(defaults, &path))
    };
-    match horizon_shaders::translate_core(&vertex, &fragment, defines, &include, glue) {
+    match crate::core_shader::translate_core(&vertex, &fragment, defines, &include, glue) {
        Ok(program) => {
            log::info!("the resource pack's {name} shader is used");
            Some(Arc::new(program))
@@ -132,7 +132,7 @@ impl PackText {
                count: None,
            })
            .collect();
-        for (_, binding) in horizon_shaders::SAMPLERS {
+        for (_, binding) in crate::core_shader::SAMPLERS {
            entries.push(wgpu::BindGroupLayoutEntry {
                binding,
                visibility,
@@ -175,7 +175,7 @@ impl PackText {
                }),
            })
            .collect();
-        for (_, binding) in horizon_shaders::SAMPLERS {
+        for (_, binding) in crate::core_shader::SAMPLERS {
            resources.push(wgpu::BindGroupEntry {
                binding,
                resource: wgpu::BindingResource::TextureView(atlas),
@@ -0,0 +1,55 @@
+//! The official Recipes viewer's artwork from Just Enough Items, under MIT (`jei_recipes/LICENSE.txt`,
+//! THIRD_PARTY_NOTICES.md): `HudAtlas` loads each as the sprite `horizon/jei/<name>`.
+
+/// Each sprite's name and its PNG.
+pub(crate) const SPRITES: &[(&str, &[u8])] = &[
+    (
+        "button_enabled_v2",
+        include_bytes!("jei_recipes/button_enabled_v2.png"),
+    ),
+    (
+        "button_disabled_v2",
+        include_bytes!("jei_recipes/button_disabled_v2.png"),
+    ),
+    (
+        "button_highlight_v2",
+        include_bytes!("jei_recipes/button_highlight_v2.png"),
+    ),
+    (
+        "icons/arrow_previous_v2",
+        include_bytes!("jei_recipes/icons/arrow_previous_v2.png"),
+    ),
+    (
+        "icons/arrow_next_v2",
+        include_bytes!("jei_recipes/icons/arrow_next_v2.png"),
+    ),
+    (
+        "search_background_v2",
+        include_bytes!("jei_recipes/search_background_v2.png"),
+    ),
+    ("slot", include_bytes!("jei_recipes/slot.png")),
+    (
+        "icons/list_badge",
+        include_bytes!("jei_recipes/icons/list_badge.png"),
+    ),
+    (
+        "interactive_ingredient_tooltip_background",
+        include_bytes!("jei_recipes/interactive_ingredient_tooltip_background.png"),
+    ),
+    (
+        "recipe_preview_background_v2",
+        include_bytes!("jei_recipes/recipe_preview_background_v2.png"),
+    ),
+    (
+        "ingredient_list_slot_background_v2",
+        include_bytes!("jei_recipes/ingredient_list_slot_background_v2.png"),
+    ),
+    (
+        "scrollbar_background_v2",
+        include_bytes!("jei_recipes/scrollbar_background_v2.png"),
+    ),
+    (
+        "scrollbar_marker_v2",
+        include_bytes!("jei_recipes/scrollbar_marker_v2.png"),
+    ),
+];
@@ -14,7 +14,6 @@ pub mod biome;
 pub mod block_edit;
 pub mod block_entities;
 pub mod block_entity_anim;
-pub mod block_entity_cem;
 pub mod block_entity_render;
 pub mod block_sprites;
 pub mod block_states;
@@ -38,11 +37,13 @@ pub mod command_block;
 pub mod connected;
 pub mod containers;
 pub mod controller_ui;
+pub mod core_shader;
 pub mod crash;
 pub mod custom_sky;
 pub mod datapack;
 pub mod dynamic_light;
 pub mod effects;
+pub mod entity_textures;
 pub mod environment;
 pub mod extras;
 pub(crate) mod extras_ui;
@@ -50,7 +51,6 @@ pub mod fast_hash;
 pub mod fluid_render;
 pub mod fog;
 pub mod font;
-pub mod fusion;
 pub mod gfx;
 pub mod graphics;
 pub mod graphics_style;
@@ -62,10 +62,11 @@ pub mod hud_layout;
 pub mod hud_overlays;
 pub mod inventory_effects;
 pub mod java_text;
+mod jei_sprites;
 pub mod jigsaw_block;
 pub mod keypad;
 pub mod terrain_model;
-pub use horizon_polytone::colors as polytone_colors;
+pub use horizon_polytone::creative_tabs as polytone_creative_tabs;
 pub use horizon_world::json_folder;
 pub mod level_loading;
 pub mod light;
@@ -86,6 +87,8 @@ pub mod options_fixes;
 pub mod options_ui;
 pub mod overlay;
 pub mod pack_browser;
+pub mod pack_formats;
+pub mod pack_hooks;
 pub mod pack_options_ui;
 pub mod pack_palette;
 pub mod pack_screen;
@@ -11,7 +11,7 @@ mod sides;
 #[cfg(test)]
 #[path = "mesher/source_tests.rs"]
 mod source_tests;
-use crate::connected::{Pick, TileLayer};
+use crate::connected::{ConnectedTextures, NoConnected, Pick, TileLayer};
 use crate::{
    assets::{Assets, RenderAssets},
    biome::{Biomes, GrassModifier},
@@ -24,7 +24,6 @@ use horizon_assets::model::Direction as ModelDirection;
 use horizon_core::{
    biome::BiomeZoom, geometry::Direction, position::BlockPos, random::position_seed,
 };
-use horizon_optifine::ctm::connect::{Axes as CtmAxes, Face as CtmFace};
 use horizon_world::{
    block_render::FaceVisibility,
    fluid::{FluidKind, FluidState},
@@ -761,6 +760,49 @@ pub struct MeshTables {
    colormaps: Vec<Arc<crate::environment::Colormap>>,
    water_colormap: Option<u16>,
 }
+/// Vanilla's four biome colour functions (`BiomeColors`) with what the packs replace them by:
+/// `biome_colors` (a colormap or a flat colour), else the colormap a block modifier gives
+/// `grass_block`, `oak_leaves` or `leaf_litter`, or a fluid modifier gives water, which Polytone
+/// spreads to every block of that function. Each with the tints that read it.
+fn biome_functions(
+    pack_root: &std::path::Path,
+    modifiers: &[(bool, horizon_polytone::Targets, String)],
+) -> Vec<(&'static [Tint], crate::environment::Colormap)> {
+    use crate::environment::Colormap;
+    use horizon_polytone::colors::BiomeColor;
+    const FUNCTIONS: [(&str, &str, &[Tint]); 4] = [
+        (
+            "grass",
+            "minecraft:grass_block",
+            &[
+                Tint::Grass,
+                Tint::GrassBlock,
+                Tint::TallGrassUpper,
+                Tint::SugarCane,
+            ],
+        ),
+        ("foliage", "minecraft:oak_leaves", &[Tint::Foliage]),
+        ("dry_foliage", "minecraft:leaf_litter", &[Tint::DryFoliage]),
+        ("water", "minecraft:water", &[Tint::Water]),
+    ];
+    let colors = horizon_polytone::colors::PackColors::read(pack_root);
+    FUNCTIONS
+        .into_iter()
+        .filter_map(|(function, block, tints)| {
+            let colormap = match colors.biome_color(function) {
+                Some(BiomeColor::Flat(rgb)) => Some(Colormap::flat(rgb)),
+                Some(BiomeColor::Colormap(id)) => Colormap::load(pack_root, &id),
+                None => modifiers
+                    .iter()
+                    .find(|(fluid, targets, _)| {
+                        *fluid == (function == "water") && targets.matches(block, |_| false)
+                    })
+                    .and_then(|(_, _, id)| Colormap::load(pack_root, id)),
+            }?;
+            Some((tints, colormap))
+        })
+        .collect()
+}
 fn stem_color(age: u8) -> u32 {
    let a = u32::from(age);
    (a * 32) << 16 | (255 - a * 8) << 8 | (a * 4)
@@ -945,7 +987,8 @@ impl MeshTables {
    }
    /// These tables with the colormaps of the Polytone block and fluid modifiers of the packs
    /// merged at `pack_root` (wiki "Colormaps"): a tinted block they target takes its colour
-    /// from the colormap, and its own tint where the colormap's pixel is transparent.
+    /// from the colormap, and its own tint where the colormap's pixel is transparent. Vanilla's
+    /// four biome colour functions take the packs' `biome_colors` first (wiki "Custom Colors").
    #[must_use]
    pub fn with_polytone_colormaps(
        mut self,
@@ -953,7 +996,8 @@ impl MeshTables {
        registry: &horizon_world::registry::BlockRegistry,
    ) -> Self {
        let modifiers = crate::environment::polytone_colormap_modifiers(pack_root);
-        if modifiers.is_empty() {
+        let biome_functions = biome_functions(pack_root, &modifiers);
+        if modifiers.is_empty() && biome_functions.is_empty() {
            return self;
        }
        let mut loaded: std::collections::HashMap<String, Option<u16>> = Default::default();
@@ -964,7 +1008,24 @@ impl MeshTables {
                Some((colormaps.len() - 1) as u16)
            })
        };
+        for (tints, colormap) in biome_functions {
+            self.colormaps.push(Arc::new(colormap));
+            let i = Some((self.colormaps.len() - 1) as u16);
+            if tints == [Tint::Water] {
+                self.water_colormap = i;
+            }
+            for info in &mut self.info {
+                let own = &info.tints[..usize::from(info.tint_count).min(2)];
+                if own.iter().any(|t| tints.contains(t)) {
+                    info.colormap = i;
+                }
+            }
+        }
+        let water_function = self.water_colormap;
        for (fluid, targets, id) in &modifiers {
+            if *fluid && water_function.is_some() {
+                continue;
+            }
            if *fluid {
                if targets.matches("minecraft:water", |_| false) {
                    self.water_colormap = index(id, &mut self.colormaps);
@@ -1495,9 +1556,9 @@ struct Tints<'a> {
    /// by colormap and section-local block.
    colormaps: &'a [Arc<crate::environment::Colormap>],
    water_colormap: Option<u16>,
-    sampled: std::collections::HashMap<(u16, [i32; 3]), Option<u32>>,
+    sampled: crate::fast_hash::FxHashMap<(u16, [i32; 3]), Option<u32>>,
    /// Each colormap's own colour by block, before the blend averages them.
-    cells: std::collections::HashMap<(u16, [i32; 3]), Option<u32>>,
+    cells: crate::fast_hash::FxHashMap<(u16, [i32; 3]), Option<u32>>,
 }
 impl<'a> Tints<'a> {
    fn new(
@@ -1518,8 +1579,8 @@ impl<'a> Tints<'a> {
            uniform: None,
            colormaps: &[],
            water_colormap: None,
-            sampled: std::collections::HashMap::new(),
-            cells: std::collections::HashMap::new(),
+            sampled: Default::default(),
+            cells: Default::default(),
        }
    }
    /// With the packs' colormaps of `tables`.
@@ -1531,10 +1592,16 @@ impl<'a> Tints<'a> {
    /// Colormap `index`'s colour at block `(x, y, z)` (section-local), `None` where its pixel
    /// is transparent.
    fn colormap(&mut self, index: u16, x: i32, y: i32, z: i32) -> Option<u32> {
+        let colormap = self.colormaps.get(usize::from(index))?.clone();
+        // A colormap that ignores the height, over one biome: one colour per column.
+        let y = if colormap.column && self.uniform_biome().is_some() {
+            0
+        } else {
+            y
+        };
        if let Some(&known) = self.sampled.get(&(index, [x, y, z])) {
            return known;
        }
-        let colormap = self.colormaps.get(usize::from(index))?.clone();
        // ClientLevel.calculateBlockTint: the mean of the (2r+1)^2 colours around the block, each
        // channel summed and divided. A transparent pixel in the square leaves the block's own.
        let r = if colormap.biome_blend { self.radius } else { 0 };
@@ -1573,7 +1640,11 @@ impl<'a> Tints<'a> {
        if let Some(&known) = self.cells.get(&(index, at)) {
            return known;
        }
-        let id = Self::biome_id(&self.zoom, self.region, self.plains, self.origin, at);
+        // One biome over the section and its blend margin: no zoom per block.
+        let id = match self.uniform_biome() {
+            Some(biome) => biome,
+            None => Self::biome_id(&self.zoom, self.region, self.plains, self.origin, at),
+        };
        let [cx, cz, base_y] = self.origin;
        let block = [cx * 16 + at[0], base_y + at[1], cz * 16 + at[2]];
        let mut host = crate::environment::BlockHost::new(block, self.biomes.get(id));
@@ -1800,11 +1871,27 @@ impl Mesher<'_> {
        )
    }
    /// The meshing workers' path: `out`'s buffers and `scratch` are reused
-    /// rather than allocated per section.
+    /// rather than allocated per section. A pack's connected textures mesh through their
+    /// format's entry point ([`crate::connected::Connected::mesh`]).
    pub fn mesh_reusing(
        &mut self,
        region: &[[Option<&Chunk>; 3]; 3],
        sy: i32,
+        out: SectionMesh,
+        scratch: &mut MeshScratch,
+    ) -> SectionMesh {
+        let render = self.render;
+        match &render.connected {
+            Some(connected) => (connected.mesh)(self, &*connected.rules, region, sy, out, scratch),
+            None => self.mesh_with(&NoConnected, region, sy, out, scratch),
+        }
+    }
+    /// [`Self::mesh_reusing`] with the connected textures `connected`.
+    pub fn mesh_with<C: ConnectedTextures>(
+        &mut self,
+        connected: &C,
+        region: &[[Option<&Chunk>; 3]; 3],
+        sy: i32,
        mut out: SectionMesh,
        scratch: &mut MeshScratch,
    ) -> SectionMesh {
@@ -1949,7 +2036,6 @@ impl Mesher<'_> {
                                )
                                .unwrap_or(true);
                    }
-                    let connected = &self.render.connected;
                    let start = [out.solid.len(), out.translucent.len()];
                    for model in &models {
                        for face in &model.faces {
@@ -1980,6 +2066,7 @@ impl Mesher<'_> {
                                }
                            }
                            self.face(
+                                connected,
                                pad,
                                &mut tints,
                                &mut out,
@@ -2030,8 +2117,9 @@ impl Mesher<'_> {
        })
    }
    #[allow(clippy::too_many_arguments)]
-    fn face(
+    fn face<C: ConnectedTextures>(
        &self,
+        connected: &C,
        pad: &Padded,
        tints: &mut Tints,
        out: &mut SectionMesh,
@@ -2091,55 +2179,40 @@ impl Mesher<'_> {
            }
            None => tint,
        };
-        // Fusion's and then OptiFine's connected textures: another sprite, or one per quarter,
-        // and the overlays drawn over it (a few per face at most; more are dropped).
-        let (fusion, connected) = (&self.render.fusion, &self.render.connected);
+        // Connected textures: another sprite, or one per quarter, and the overlays drawn over it
+        // (a few per face at most; more are dropped).
        let mut overlays = [None; 8];
        let mut count = 0;
-        let mut push = |overlay| {
-            if let Some(slot) = overlays.get_mut(count) {
-                *slot = Some(overlay);
-                count += 1;
-            }
-        };
-        let neighbour = |n: [i32; 3]| pad.blocks[(cell as isize + step_index(n)) as usize];
-        let fused = face.fusion.and_then(|rule| {
-            fusion.pick(
-                rule,
-                id,
-                CtmFace::ALL[q.facing as usize],
-                q.tint_index,
-                neighbour,
+        let pick = if connected.is_empty() {
+            Pick::Keep
+        } else {
+            let mut push = |overlay| {
+                if let Some(slot) = overlays.get_mut(count) {
+                    *slot = Some(overlay);
+                    count += 1;
+                }
+            };
+            let tints = &*tints;
+            connected.pick(
+                &crate::connected::Face {
+                    state: id,
+                    layer: face.layer as u16,
+                    facing: q.facing as u8,
+                    pos: [world.x, world.y, world.z],
+                    positions: &q.positions,
+                    uv: &q.uv,
+                    pane: state.pane,
+                    tint_index: q.tint_index,
+                    rule: face.fusion,
+                },
+                |n: [i32; 3]| pad.blocks[(cell as isize + step_index(n)) as usize],
                |s| {
                    self.tables
                        .info
                        .get(s as usize)
                        .is_some_and(|i| i.opaque_cube)
                },
-                &mut push,
-            )
-        });
-        let pick = if let Some(pick) = fused {
-            pick
-        } else if connected.is_empty() {
-            Pick::Keep
-        } else {
-            let tints = &*tints;
-            connected.pick(
-                id,
-                face.layer as u16,
-                CtmFace::ALL[q.facing as usize],
-                [world.x, world.y, world.z],
-                neighbour,
                || Some(tints.biome(pos[0], pos[1], pos[2])),
-                // A pane's tiles are drawn with the cube's UVs (below), so that is its texture.
-                || {
-                    if state.pane {
-                        Some(CtmAxes::cube(CtmFace::ALL[q.facing as usize]))
-                    } else {
-                        CtmAxes::texture(&q.positions, &q.uv)
-                    }
-                },
                &mut push,
            )
        };
@@ -100,8 +100,7 @@ fn fixture() -> (Scratch, Assets, RenderAssets, MeshTables, Biomes) {
        pbr_normals: vec![],
        pbr_specular: vec![],
        pbr_size: 1,
-        connected: Default::default(),
-        fusion: Default::default(),
+        connected: None,
        generation: 1,
    };
    let assets = Assets {
@@ -251,3 +251,117 @@ fn a_biome_colormap_blends_over_a_biome_edge_as_the_vanilla_water_tint_does() {
    }
    assert!(edge_differs, "the square must cross the edge somewhere");
 }
+
+#[test]
+fn biome_colors_and_a_grass_block_colormap_replace_their_whole_biome_function() {
+    let biomes = Biomes::from_jsons(&[(
+        "minecraft:plains",
+        serde_json::json!({"effects": {"water_color": 0x3F76E4}}),
+    )]);
+    // biome_colors gives water a flat green; a block modifier colours oak leaves with a map,
+    // which Polytone spreads to the whole foliage function.
+    let root = pack(&[
+        (
+            "assets/mypack/polytone/colors.json",
+            br#"{"biome_colors": {"water": "0x00ff00"}}"#.to_vec(),
+        ),
+        (
+            "assets/mypack/polytone/colormaps/leaves.png",
+            png_row(&[[0, 0, 255, 255]]),
+        ),
+        (
+            "assets/mypack/polytone/block_modifiers/oak.json",
+            br#"{"targets": ["minecraft:oak_leaves"], "colormap": "mypack:leaves"}"#.to_vec(),
+        ),
+    ]);
+    let modifiers = crate::environment::polytone_colormap_modifiers(&root);
+    let functions = biome_functions(&root, &modifiers);
+    let tints: Vec<_> = functions.iter().map(|(t, _)| *t).collect();
+    assert_eq!(tints.len(), 2);
+    assert!(tints[0] == [Tint::Foliage] && tints[1] == [Tint::Water]);
+    let colormaps: Vec<_> = functions.into_iter().map(|(_, c)| Arc::new(c)).collect();
+    let chunks: Vec<Vec<Chunk>> = (0..3)
+        .map(|rz| (0..3).map(|rx| filled(rx - 1, rz - 1, 0)).collect())
+        .collect();
+    let region: [[Option<&Chunk>; 3]; 3] =
+        std::array::from_fn(|rz| std::array::from_fn(|rx| Some(&chunks[rz][rx])));
+    let mut tints = Tints::new(&region, &biomes, BiomeZoom::new(0), 0, [0, 0, 64]);
+    tints.colormaps = &colormaps;
+    tints.water_colormap = Some(1);
+    assert_eq!(tints.water(3, 4, 5), 0x00_FF00);
+    std::fs::remove_dir_all(root).unwrap();
+}
+
+#[test]
+fn only_a_colormap_that_ignores_the_height_is_shared_up_a_column() {
+    let root = pack(&[
+        (
+            "assets/mypack/polytone/colormaps/flat.png",
+            png_row(&[[1, 2, 3, 255]]),
+        ),
+        (
+            "assets/mypack/polytone/colormaps/flat.json",
+            br#"{"x_axis": "biome_id", "y_axis": "r.noise(o.x/60, o.z/60)"}"#.to_vec(),
+        ),
+        (
+            "assets/mypack/polytone/colormaps/tall.png",
+            png_row(&[[1, 2, 3, 255]]),
+        ),
+        (
+            "assets/mypack/polytone/colormaps/tall.json",
+            br#"{"y_axis": "y_level"}"#.to_vec(),
+        ),
+    ]);
+    let load = |id| crate::environment::Colormap::load(&root, id).unwrap();
+    assert!(load("mypack:flat").column);
+    assert!(!load("mypack:tall").column);
+    std::fs::remove_dir_all(root).unwrap();
+}
+
+/// Times a section's colormap tints with the freepack's kind of grass colormap (a biome id
+/// column and a noise row) over the default Biome Blend: `cargo test --release ... -- --ignored
+/// --nocapture colormap_tint_cost`.
+#[test]
+#[ignore = "timing, not a check"]
+fn colormap_tint_cost() {
+    const RADIUS: i32 = 2;
+    const LAYERS: i32 = 16;
+    let biomes = Biomes::from_jsons(&[(
+        "minecraft:plains",
+        serde_json::json!({"effects": {"water_color": 0x3F76E4}}),
+    )]);
+    let pixels: Vec<[u8; 4]> = (0..16).map(|i| [i * 16, 200, 64, 255]).collect();
+    let root = pack(&[
+        ("assets/mypack/polytone/colormaps/grass.png", png_row(&pixels)),
+        (
+            "assets/mypack/polytone/colormaps/grass.json",
+            br#"{"x_axis": "biome_id", "y_axis": "0.5+(r.noise(o.x/60,5+o.z/60)*0.55)", "biome_id_mapper": {"minecraft:plains": 1, "texture_size": 16}}"#
+                .to_vec(),
+        ),
+    ]);
+    let colormaps = vec![Arc::new(
+        crate::environment::Colormap::load(&root, "mypack:grass").unwrap(),
+    )];
+    let chunks: Vec<Vec<Chunk>> = (0..3)
+        .map(|rz| (0..3).map(|rx| filled(rx - 1, rz - 1, 0)).collect())
+        .collect();
+    let region: [[Option<&Chunk>; 3]; 3] =
+        std::array::from_fn(|rz| std::array::from_fn(|rx| Some(&chunks[rz][rx])));
+    let rounds = 50;
+    let start = std::time::Instant::now();
+    let mut check = 0u64;
+    for _ in 0..rounds {
+        let mut tints = Tints::new(&region, &biomes, BiomeZoom::new(0), RADIUS, [0, 0, 64]);
+        tints.colormaps = &colormaps;
+        for y in 0..LAYERS {
+            for z in 0..16 {
+                for x in 0..16 {
+                    check += u64::from(tints.colormap(0, x, y, z).unwrap_or(0));
+                }
+            }
+        }
+    }
+    let per = start.elapsed() / rounds;
+    println!("{LAYERS} layers of 256 blended colormap tints: {per:?} (checksum {check})");
+    std::fs::remove_dir_all(root).unwrap();
+}
@@ -1,6 +1,7 @@
 //! Optional, texture-matched overlays drawn full bright over their base texture in the same
-//! terrain fragment: native mods' (`<ns>:emissive/...`) and OptiFine's emissive block textures
-//! (`block/stone_e.png` beside `block/stone.png`). No extra draw calls or world light changes.
+//! terrain fragment: native mods' (`<ns>:emissive/...`) and a pack's emissive block textures
+//! (OptiFine's `block/stone_e.png` beside `block/stone.png`, the suffix from the pack formats,
+//! [`crate::pack_hooks`]). No extra draw calls or world light changes.
 use crate::sprites::Sprites;
 use std::{collections::BTreeMap, path::Path};

@@ -35,14 +36,12 @@ fn tile_file(name: &str) -> Option<&str> {
    name.strip_suffix(".png")
 }

-/// OptiFine's emissive overlays of the block sprites already loaded (what the terrain draws;
-/// items draw from the HUD atlas): for each
-/// `<ns>:block/<name>`, or connected-texture tile `assets/<ns>/.../<name>.png`, whose
-/// `<name><suffix>.png` sits beside it, the overlay is loaded too and paired with it, blocks
-/// first, then tiles, each by name, at most [`MAX`] - [`NATIVE`] (native mods keep their share of
-/// the table). A pack without such files adds nothing.
-pub fn load_optifine(root: &Path, sprites: &mut Sprites) -> Vec<(String, String)> {
-    let suffix = horizon_optifine::emissive::suffix(root);
+/// A pack's emissive overlays of the block sprites already loaded (what the terrain draws;
+/// items draw from the HUD atlas): for each `<ns>:block/<name>`, or connected-texture tile
+/// `assets/<ns>/.../<name>.png`, whose `<name><suffix>.png` sits beside it, the overlay is loaded
+/// too and paired with it, blocks first, then tiles, each by name, at most [`MAX`] - [`NATIVE`]
+/// (native mods keep their share of the table). A pack without such files adds nothing.
+pub fn load_overlays(root: &Path, suffix: &str, sprites: &mut Sprites) -> Vec<(String, String)> {
    // Blocks with identical pixels share a layer (and the shader pairs by layer): a shared
    // base would glow on every block that shares it, so it gets no overlay.
    let mut sharing: BTreeMap<u32, usize> = BTreeMap::new();
@@ -56,8 +55,8 @@ pub fn load_optifine(root: &Path, sprites: &mut Sprites) -> Vec<(String, String)
            sharing[layer] == 1
                && (name
                    .split_once(':')
-                    .is_some_and(|(_, p)| p.starts_with("block/") && !p.ends_with(&suffix))
-                    || tile_file(name).is_some_and(|stem| !stem.ends_with(&suffix)))
+                    .is_some_and(|(_, p)| p.starts_with("block/") && !p.ends_with(suffix))
+                    || tile_file(name).is_some_and(|stem| !stem.ends_with(suffix)))
        })
        .map(|(name, _)| name.clone())
        .collect();
@@ -110,7 +109,7 @@ pub fn load_optifine(root: &Path, sprites: &mut Sprites) -> Vec<(String, String)
 pub const CUTOUT: u32 = 1 << 31;

 /// The frame's overlay table: native mods' pairs (at most [`NATIVE`] requested), then the packs'
-/// OptiFine pairs flagged [`CUTOUT`] (at most [`MAX`] - [`NATIVE`], as [`load_optifine`] loads),
+/// OptiFine pairs flagged [`CUTOUT`] (at most [`MAX`] - [`NATIVE`], as [`load_overlays`] loads),
 /// one per base layer with native mods' first, sorted by base layer for the shader's early exit.
 pub fn table<'a>(
    layers: &BTreeMap<String, u32>,
@@ -204,7 +203,7 @@ mod tests {
        // Items draw from the HUD atlas, not the terrain: no pair.
        sprites.insert(&root, "minecraft:item/stick").unwrap();
        // glowstone isn't loaded: its overlay pairs with nothing.
-        let pairs = load_optifine(&root, &mut sprites);
+        let pairs = load_overlays(&root, "_e", &mut sprites);
        assert_eq!(
            pairs,
            [(
@@ -215,9 +214,6 @@ mod tests {
        assert!(sprites.layers.contains_key("minecraft:block/stone_e"));
        assert!(!sprites.layers.contains_key("minecraft:block/granite_e"));
        // The pack's own suffix.
-        let props = root.join("assets/minecraft/optifine/emissive.properties");
-        std::fs::create_dir_all(props.parent().unwrap()).unwrap();
-        std::fs::write(&props, "suffix.emissive=_glow").unwrap();
        // Connected-texture tiles pair with the overlay beside them.
        let tiles = root.join("assets/minecraft/optifine/ctm/lamp");
        png(&tiles.join("0.png"), 230);
@@ -234,7 +230,7 @@ mod tests {
                .insert_file(&root, &format!("assets/minecraft/optifine/{tile}.png"))
                .unwrap();
        }
-        let pairs = load_optifine(&root, &mut sprites);
+        let pairs = load_overlays(&root, "_glow", &mut sprites);
        assert_eq!(
            pairs,
            // Blocks first, then tiles.
@@ -8,6 +8,7 @@ pub use crate::settings::Opt;

 use crate::{
    gamepad::{self, GlyphStyle},
+    hdr_calibration::Picture,
    hud::{HudAtlas, HudBatch, rgba},
    keybinds::{self, CATEGORIES, KeyBinds, all_mappings},
    lang::{self, LanguageInfo},
@@ -1492,7 +1493,7 @@ pub enum Event {
    /// ones that differ from their defaults (the others went back to theirs).
    PackOptions {
        entries: Vec<String>,
-        chosen: std::collections::BTreeMap<String, horizon_polytone::pack::ConfigValue>,
+        chosen: std::collections::BTreeMap<String, horizon_pack_options::ConfigValue>,
    },
    /// An accepted button press or the release of a slider.
    ButtonClick,
@@ -1678,12 +1679,12 @@ pub struct OptionsUi {
    /// The Pack Options page, and the packs' Polytone config entries by pack id (the game
    /// fills them beside `pack_infos`).
    pub pack_options: crate::pack_options_ui::PackOptionsUi,
-    pub pack_configs: std::collections::BTreeMap<String, horizon_polytone::pack::Configs>,
+    pub pack_configs: std::collections::BTreeMap<String, horizon_pack_options::Configs>,
    pub split_profiles: crate::split_profiles::SplitProfiles,
    /// HDR calibration while its page is open.
    pub calibration: Option<crate::hdr_calibration::Calibration>,
-    /// Whether the window was fullscreen before calibration made it so (the game keeps it).
-    pub calibration_fullscreen: Option<bool>,
+    /// The window as calibration found it before making it fullscreen (the game keeps it).
+    pub calibration_window: Option<crate::hdr_calibration::WindowState>,
    pub split_setup: crate::split_ui::SplitUi,
    pub studio: crate::studio_ui::StudioUi,
    /// The AI Agent page's status lines (set by the game while it shows).
@@ -1762,7 +1763,7 @@ impl Default for OptionsUi {
            pack_configs: Default::default(),
            split_profiles: Default::default(),
            calibration: None,
-            calibration_fullscreen: None,
+            calibration_window: None,
            split_setup: Default::default(),
            studio: Default::default(),
            agent_status: Vec::new(),
@@ -2582,43 +2583,6 @@ impl OptionsUi {
        }
        rows
    }
-    /// A native mod's page: its name, its keys as Key Binds rows (the
-    /// player's choice, else the default), then its buttons.
-    fn native_rows(&self, s: &Settings, i: usize) -> Vec<Row> {
-        let Some(m) = s.mods.installed.get(i) else {
-            return Vec::new();
-        };
-        let mut rows = vec![Row::Note(m.title.clone())];
-        let Some(page) = &m.native else {
-            return rows;
-        };
-        let chosen = s.mods.keys.get(&m.id);
-        for (k, [name, label, default]) in page.keys.iter().enumerate() {
-            let key = chosen.and_then(|c| c.get(name)).unwrap_or(default);
-            let mut message = keybinds::display_name(key);
-            if self.selected_native_key == Some((i, k)) {
-                message = Text::literal("> ")
-                    .append(message.with_color(text::WHITE))
-                    .append(" <")
-                    .with_color(text::YELLOW);
-            }
-            let caption = button(0.0, 0.0, 150.0, Text::literal(label.clone()), Act::None);
-            let change = button(0.0, 0.0, 150.0, message, Act::NativeKey(i, k));
-            rows.push(Row::Buttons(inactive(caption), Some(change)));
-        }
-        for (b, label) in page.buttons.iter().enumerate() {
-            let widget = button(
-                0.0,
-                0.0,
-                310.0,
-                Text::literal(label.clone()),
-                Act::NativeButton(i, b),
-            );
-            rows.push(Row::Buttons(widget, None));
-        }
-        rows
-    }
-
    fn list_rows(&self, s: &Settings) -> Vec<Row> {
        match self.page() {
            Page::SplitSetup => Vec::new(),
@@ -4030,7 +3994,7 @@ impl OptionsUi {
            if right {
                return Vec::new();
            }
-            let outcome = c.click((x, y), size, drag);
+            let outcome = c.click(&atlas.font, (x, y), size, drag);
            return self.calibration_outcome(s, outcome);
        }
        if self.shell().is_some() {
@@ -4098,7 +4062,7 @@ impl OptionsUi {
                    events.push(Event::DownloadPack(i));
                }
                crate::pack_screen::Action::Options(id) => {
-                    let mut configs = horizon_polytone::pack::Configs::default();
+                    let mut configs = horizon_pack_options::Configs::default();
                    if let Some(own) = self.pack_configs.get(&id) {
                        configs.merge(own);
                    }
@@ -4272,10 +4236,7 @@ impl OptionsUi {
                            self.push(Page::NativeMod(i));
                            events.push(Event::NativeSettings(i));
                        }
-                        Act::NativeKey(i, k) => {
-                            self.selected_key = Some(NATIVE_KEY);
-                            self.selected_native_key = Some((i, k));
-                        }
+                        Act::NativeKey(i, k) => self.wait_native_key(i, k),
                        Act::NativeButton(i, b) => events.push(Event::NativeButton(i, b)),
                        Act::OpenModFolder => events.push(Event::OpenModFolder),
                        Act::ModProject(i) => {
@@ -4632,13 +4593,12 @@ impl OptionsUi {
            }
        }
    }
-    /// HDR calibration's test picture, while its page is open: the step, its nits and
-    /// where the controls start (a share of the height `h`).
-    pub fn calibration_picture(&self, h: f32) -> Option<(crate::hdr_calibration::Step, f32, f32)> {
+    /// HDR calibration's test picture, while its page is open, in a GUI of `size`.
+    pub fn calibration_picture(&self, atlas: &HudAtlas, size: (f32, f32)) -> Option<Picture> {
        self.calibration
            .as_ref()
            .filter(|_| self.page() == Page::HdrCalibration)
-            .map(|c| c.picture(h))
+            .map(|c| c.picture(&atlas.font, size))
    }
    pub fn back(&mut self, s: &mut Settings) -> Vec<Event> {
        let mut events = Vec::new();
@@ -4782,18 +4742,9 @@ impl OptionsUi {
            return Vec::new();
        };
        if name == NATIVE_KEY {
-            let (i, k) = self.selected_native_key.take().unwrap_or_default();
-            let Some(m) = s.mods.installed.get(i) else {
-                return Vec::new();
-            };
-            let Some([key, ..]) = m.native.as_ref().and_then(|p| p.keys.get(k)) else {
-                return Vec::new();
-            };
-            let keys = s.mods.keys.entry(m.id.clone()).or_default();
-            keys.insert(key.clone(), value);
-            return vec![Event::Changed];
+            return self.bind_native_key(s, value);
        }
-        if !s.extras.set_key(name, value.clone()) && !s.horizon.set_key(name, value.clone()) {
+        if !s.extras.set_key(name, value.clone()) {
            s.keys.set(name, &value);
        }
        vec![Event::Changed]
@@ -5173,10 +5124,7 @@ impl OptionsUi {
                            self.push(Page::NativeMod(i));
                            events.push(Event::NativeSettings(i));
                        }
-                        Act::NativeKey(i, k) => {
-                            self.selected_key = Some(NATIVE_KEY);
-                            self.selected_native_key = Some((i, k));
-                        }
+                        Act::NativeKey(i, k) => self.wait_native_key(i, k),
                        Act::NativeButton(i, b) => events.push(Event::NativeButton(i, b)),
                        Act::OpenModFolder => events.push(Event::OpenModFolder),
                        Act::ModProject(i) => {
@@ -7348,7 +7296,7 @@ mod tests {
            MouseButton::Back,
            MouseButton::Forward,
        ] {
-            for name in [SORT_KEY, crate::graphics::HDR_KEY, "key.jump"] {
+            for name in [SORT_KEY, "key.jump"] {
                let mut ui = OptionsUi::default();
                let mut s = Settings::default();
                ui.selected_key = Some(name);
@@ -7357,7 +7305,6 @@ mod tests {
                let value = keybinds::mouse_name(button);
                match name {
                    SORT_KEY => assert_eq!(s.extras.sort_key, value),
-                    crate::graphics::HDR_KEY => assert_eq!(s.horizon.hdr_key, value),
                    _ => assert_eq!(s.keys.get(name), value),
                }
                assert_eq!(Extras::parse(&s.extras.serialize()), s.extras);
@@ -8439,3 +8386,5 @@ mod tests {
 #[cfg(test)]
 #[path = "options_ui_graphics_tests.rs"]
 mod graphics_tests;
+#[path = "options_ui_pages.rs"]
+mod pages;
@@ -143,3 +143,34 @@ fn the_graphics_screens_wheel_scrolls_even_over_a_slider_being_changed() {
    assert_eq!(s.horizon.chunk_updates, 16);
    assert!(ui.graphics.scroll_amount() > before);
 }
+
+/// A window holding HDR output back (a start failed on its driver) shows it on the HDR page
+/// as soon as the graphics screen opens, with no setting applied: the row's line, and
+/// Calibrate blocked, where the same window not holding it back calibrates.
+#[test]
+fn a_held_hdr_start_shows_as_the_graphics_screen_opens() {
+    use crate::gfx::output::tests::{snapshot, window};
+    let atlas = atlas();
+    let mut s = Settings::default();
+    s.horizon.hdr = crate::graphics::HdrMode::Auto;
+    s.horizon.hdr_failed_start = Some("Vulkan 10de:2684 GPU; driver; 1.0; os".into());
+    let (mut caps, reading) = window(Some(crate::gfx::HdrOutput::Pq), Some(true));
+    for held in [true, false] {
+        caps.held = held;
+        let mut ui = OptionsUi {
+            size: (427.0, 240.0),
+            ..Default::default()
+        };
+        let output = snapshot(&s.horizon, Default::default(), caps, reading);
+        ui.draw(
+            &s,
+            output,
+            &mut HudBatch::new([427, 240]),
+            &atlas,
+            (-1.0, -1.0),
+        );
+        ui.show(Page::Graphics);
+        assert!(calibrates(&mut ui, &mut s, &atlas) != held, "held {held}");
+        assert_eq!(ui.graphics.screen.output.held, held);
+    }
+}
@@ -0,0 +1,62 @@
+//! The pages crates add to the options screens: a native mod's settings page (its keys and
+//! buttons). Kept out of options_ui.rs, which may not grow (tools/check_file_size.py).
+use super::*;
+
+impl OptionsUi {
+    /// A native mod's page: its name, its keys as Key Binds rows (the
+    /// player's choice, else the default), then its buttons.
+    pub(super) fn native_rows(&self, s: &Settings, i: usize) -> Vec<Row> {
+        let Some(m) = s.mods.installed.get(i) else {
+            return Vec::new();
+        };
+        let mut rows = vec![Row::Note(m.title.clone())];
+        let Some(page) = &m.native else {
+            return rows;
+        };
+        let chosen = s.mods.keys.get(&m.id);
+        for (k, [name, label, default]) in page.keys.iter().enumerate() {
+            let key = chosen.and_then(|c| c.get(name)).unwrap_or(default);
+            let mut message = keybinds::display_name(key);
+            if self.selected_native_key == Some((i, k)) {
+                message = Text::literal("> ")
+                    .append(message.with_color(text::WHITE))
+                    .append(" <")
+                    .with_color(text::YELLOW);
+            }
+            let caption = button(0.0, 0.0, 150.0, Text::literal(label.clone()), Act::None);
+            let change = button(0.0, 0.0, 150.0, message, Act::NativeKey(i, k));
+            rows.push(Row::Buttons(inactive(caption), Some(change)));
+        }
+        for (b, label) in page.buttons.iter().enumerate() {
+            let widget = button(
+                0.0,
+                0.0,
+                310.0,
+                Text::literal(label.clone()),
+                Act::NativeButton(i, b),
+            );
+            rows.push(Row::Buttons(widget, None));
+        }
+        rows
+    }
+
+    /// A native mod's key waits for the next key or button pressed.
+    pub(super) fn wait_native_key(&mut self, i: usize, k: usize) {
+        self.selected_key = Some(NATIVE_KEY);
+        self.selected_native_key = Some((i, k));
+    }
+
+    /// The key pressed for the native mod's key that waited for one.
+    pub(super) fn bind_native_key(&mut self, s: &mut Settings, value: String) -> Vec<Event> {
+        let (i, k) = self.selected_native_key.take().unwrap_or_default();
+        let Some(m) = s.mods.installed.get(i) else {
+            return Vec::new();
+        };
+        let Some([key, ..]) = m.native.as_ref().and_then(|p| p.keys.get(k)) else {
+            return Vec::new();
+        };
+        let keys = s.mods.keys.entry(m.id.clone()).or_default();
+        keys.insert(key.clone(), value);
+        vec![Event::Changed]
+    }
+}
@@ -12,6 +12,7 @@
 //! block models here, so their files are not read; copper golem statues have no CEM name.

 use crate::block_entity_render::ModelPart;
+use crate::pack_hooks::Reshaped;
 use horizon_optifine::cem::{
    files::{atlas_name, jem_files, load_jem},
    model::{Bone, EntityModel},
@@ -140,12 +141,6 @@ const TARGETS: &[Target] = &[
    model("decorated_pot_sides", &["decorated_pot"], POT_SIDES),
 ];

-/// Every model, reshaped or vanilla's, and the atlas names of the `.jem` textures by model.
-pub type Reshaped = (
-    HashMap<&'static str, ModelPart>,
-    HashMap<&'static str, String>,
-);
-
 /// The models the packs under `root` reshape, over `vanilla`'s; None when no block entity has
 /// a `.jem` there.
 pub fn reshape(root: &Path, vanilla: &HashMap<&'static str, ModelPart>) -> Option<Reshaped> {
@@ -0,0 +1,969 @@
+//! OptiFine's Custom Item Textures (and CIT Resewn's): the rules of the enabled packs'
+//! `optifine/cit/**/*.properties`, read from the overlay resource root, and which of them a stack
+//! matches ([`crate::cit::Matcher`]). The rules themselves are `horizon_optifine::cit`'s; the
+//! engine gets them as [`crate::cit::Rule`]s.
+
+use super::cit_glint::{load_global, stack_glint};
+use crate::cit::{self as engine, CitRules};
+use crate::cit_glint::StackGlint;
+use horizon_client_core::component::name_text;
+use horizon_client_core::scoreboard::comp_text;
+use horizon_items::item_data::{canon_tag, encode_components};
+use horizon_items::items::ItemStack;
+use horizon_optifine::cit::{
+    Blend, ComponentTest, Factor, Glint, Global, Hand, Kind, Rule, Source, ValueTest,
+};
+use horizon_optifine::{Properties, properties_files_in};
+use horizon_world::nbt::{JavaString, Tag, parse_snbt};
+use std::borrow::Cow;
+use std::collections::HashMap;
+use std::fs;
+use std::hash::{DefaultHasher, Hash, Hasher};
+use std::path::Path;
+use std::sync::{Arc, Mutex};
+
+/// Every rule under the root's `optifine/cit/`, `mcpatcher/cit/` and CIT Resewn's
+/// `citresewn/cit/` folders, the one chosen first when several match first (`Rule::priority`).
+/// The pack's global `cit.properties` is not a rule.
+pub fn load_rules(root: &Path) -> Vec<Rule> {
+    let tops = ["optifine", "mcpatcher", "citresewn"];
+    let mut rules: Vec<Rule> = properties_files_in(root, &tops, "cit")
+        .into_iter()
+        .filter(|path| !path.ends_with("/cit.properties"))
+        .filter_map(|path| {
+            let props = read_properties(&root.join(&path))?;
+            let rule = Rule::parse(&path, &props, |p| root.join(p).is_file());
+            if rule.is_none() {
+                log::warn!("custom item textures: {path} is not a rule Horizon can read");
+            }
+            rule
+        })
+        .collect();
+    rules.sort_by(Rule::priority);
+    rules
+}
+
+/// A `.properties` file as CIT Resewn reads them (`Properties::parse_equals_first`): UTF-8,
+/// else Latin-1 as Java reads them, so a pack saved that way still loads. `None` when it can't
+/// be read.
+pub fn read_properties(path: &Path) -> Option<Properties> {
+    let bytes = fs::read(path).ok()?;
+    let text = String::from_utf8(bytes)
+        .unwrap_or_else(|e| e.into_bytes().iter().map(|&b| char::from(b)).collect());
+    Some(Properties::parse_equals_first(&text))
+}
+
+/// The rules at `root` with the pack's `cit.properties`, as the engine draws and matches them.
+pub fn load(root: &Path) -> CitRules {
+    cit_rules(load_rules(root), load_global(root))
+}
+
+/// `rules` (in priority order, the winner first) under `global`, for the engine.
+pub fn cit_rules(rules: Vec<Rule>, global: Global) -> CitRules {
+    let drawn = rules.iter().map(rule).collect();
+    let use_glint = global.use_glint;
+    CitRules::new(drawn, use_glint, Box::new(Matcher::new(rules, global)))
+}
+
+/// A rule's file as the engine draws it: `text` read as the `.properties` file at `path`, every
+/// file it names taken to exist. For tests and tools.
+pub fn parse_rule(path: &str, text: &str) -> Option<engine::Rule> {
+    Rule::parse(path, &Properties::parse_equals_first(text), |_| true).map(|r| rule(&r))
+}
+
+/// [`parse_rule`] for a rule in the pack at `root`, whose files it looks for there.
+pub fn parse_rule_in(root: &Path, path: &str, text: &str) -> Option<engine::Rule> {
+    let props = Properties::parse_equals_first(text);
+    Rule::parse(path, &props, |p| root.join(p).is_file()).map(|r| rule(&r))
+}
+
+/// Rules from (path, `.properties` text) under the global `cit.properties` text `global`, in
+/// priority order, every file they name taken to exist. For tests and tools.
+pub fn parse_rules(files: &[(&str, &str)], global: &str) -> CitRules {
+    let mut rules: Vec<Rule> = files
+        .iter()
+        .filter_map(|(path, text)| {
+            Rule::parse(path, &Properties::parse_equals_first(text), |_| true)
+        })
+        .collect();
+    rules.sort_by(Rule::priority);
+    cit_rules(
+        rules,
+        Global::parse(&Properties::parse_equals_first(global)),
+    )
+}
+
+/// A `blend=` value as the engine draws it ([`horizon_optifine::cit::parse_blend`]). For tests
+/// and tools.
+pub fn parse_blend(value: &str) -> Option<Option<engine::Blend>> {
+    horizon_optifine::cit::parse_blend(value).map(|b| b.map(blend))
+}
+
+fn rule(r: &Rule) -> engine::Rule {
+    engine::Rule {
+        path: r.path.clone(),
+        kind: kind(r.kind),
+        texture: r.texture.clone(),
+        textures: r.textures.clone(),
+        model: r.model.clone(),
+        models: r.models.clone(),
+        glint: glint(&r.glint),
+    }
+}
+
+fn kind(k: Kind) -> engine::Kind {
+    match k {
+        Kind::Item => engine::Kind::Item,
+        Kind::Armor => engine::Kind::Armor,
+        Kind::Elytra => engine::Kind::Elytra,
+        Kind::Enchantment => engine::Kind::Enchantment,
+    }
+}
+
+fn of_kind(k: engine::Kind) -> Kind {
+    match k {
+        engine::Kind::Item => Kind::Item,
+        engine::Kind::Armor => Kind::Armor,
+        engine::Kind::Elytra => Kind::Elytra,
+        engine::Kind::Enchantment => Kind::Enchantment,
+    }
+}
+
+fn of_hand(h: engine::Hand) -> Hand {
+    match h {
+        engine::Hand::Any => Hand::Any,
+        engine::Hand::Main => Hand::Main,
+        engine::Hand::Off => Hand::Off,
+    }
+}
+
+fn glint(g: &Glint) -> engine::Glint {
+    engine::Glint {
+        layer: g.layer,
+        blend: g.blend.map(blend),
+        speed: g.speed,
+        rotation: g.rotation,
+        duration: g.duration,
+        rgba: g.rgba,
+        use_glint: g.use_glint,
+        blur: g.blur,
+    }
+}
+
+fn blend(b: Blend) -> engine::Blend {
+    engine::Blend {
+        src: factor(b.src),
+        dst: factor(b.dst),
+        src_alpha: factor(b.src_alpha),
+        dst_alpha: factor(b.dst_alpha),
+    }
+}
+
+fn factor(f: Factor) -> engine::Factor {
+    use engine::Factor as F;
+    match f {
+        Factor::Zero => F::Zero,
+        Factor::One => F::One,
+        Factor::SrcColor => F::SrcColor,
+        Factor::OneMinusSrcColor => F::OneMinusSrcColor,
+        Factor::SrcAlpha => F::SrcAlpha,
+        Factor::OneMinusSrcAlpha => F::OneMinusSrcAlpha,
+        Factor::DstAlpha => F::DstAlpha,
+        Factor::OneMinusDstAlpha => F::OneMinusDstAlpha,
+        Factor::DstColor => F::DstColor,
+        Factor::OneMinusDstColor => F::OneMinusDstColor,
+        Factor::SrcAlphaSaturate => F::SrcAlphaSaturate,
+    }
+}
+
+/// The rules with an index by item and a cache of what each stack matched.
+#[derive(Debug, Default)]
+struct Matcher {
+    rules: Vec<Rule>,
+    /// The pack's `cit.properties`.
+    global: Global,
+    /// Per kind (`Kind as usize`), the rules naming each item, in priority order.
+    by_item: [HashMap<String, Vec<u32>>; 4],
+    /// Enchantment rules without `items`, in priority order.
+    any_item: Vec<u32>,
+    /// Per rule, per component test: its literal read as SNBT and as a JSON text component.
+    literals: Vec<Vec<Prepared>>,
+    selected: Mutex<HashMap<u64, Option<u32>>>,
+    enchanted: Mutex<HashMap<u64, Vec<u32>>>,
+    glints: Mutex<HashMap<u64, Arc<StackGlint>>>,
+}
+
+#[derive(Debug, Default)]
+struct Prepared {
+    snbt: Option<Tag>,
+    json: Option<String>,
+}
+
+/// Cache entries kept before the cache starts over.
+const CACHE_LIMIT: usize = 4096;
+
+impl Matcher {
+    /// `rules` in priority order, the winner first.
+    fn new(rules: Vec<Rule>, global: Global) -> Self {
+        let mut by_item: [HashMap<String, Vec<u32>>; 4] = Default::default();
+        let mut any_item = Vec::new();
+        for (i, rule) in rules.iter().enumerate() {
+            let i = i as u32;
+            if rule.kind == Kind::Enchantment && rule.items.is_empty() {
+                any_item.push(i);
+            }
+            for item in &rule.items {
+                let list = by_item[rule.kind as usize].entry(item.clone()).or_default();
+                if list.last() != Some(&i) {
+                    list.push(i);
+                }
+            }
+        }
+        let literals = rules
+            .iter()
+            .map(|r| r.components.iter().map(prepare).collect())
+            .collect();
+        Self {
+            rules,
+            global,
+            by_item,
+            any_item,
+            literals,
+            ..Default::default()
+        }
+    }
+
+    /// Whether rule `i` matches the stack drawn in `hand`.
+    fn matches(
+        &self,
+        i: u32,
+        stack: &ItemStack,
+        hand: Hand,
+        max_damage: u32,
+        comps: Option<&Tag>,
+    ) -> bool {
+        let rule = &self.rules[i as usize];
+        if rule.hand != Hand::Any && rule.hand != hand {
+            return false;
+        }
+        let count = i32::try_from(stack.count).unwrap_or(i32::MAX);
+        if rule.stack_size.as_ref().is_some_and(|r| !r.contains(count)) {
+            return false;
+        }
+        // CIT Resewn: only damageable items have damage.
+        let damage = if max_damage > 0 { stack.damage } else { 0 };
+        if rule
+            .damage
+            .as_ref()
+            .is_some_and(|d| !d.matches(damage, max_damage))
+        {
+            return false;
+        }
+        let enchantments = stack.crafting_enchantments();
+        let listed = |id: &str| rule.enchantments.iter().any(|e| e == id);
+        if !rule.enchantments.is_empty() && !enchantments.iter().any(|(id, _)| listed(id)) {
+            return false;
+        }
+        if let Some(levels) = &rule.enchantment_levels {
+            let level_in_range = enchantments.iter().any(|(id, level)| {
+                (rule.enchantments.is_empty() || listed(id))
+                    && levels.contains(i32::try_from(*level).unwrap_or(i32::MAX))
+            });
+            if !level_in_range {
+                return false;
+            }
+        }
+        let literals = &self.literals[i as usize];
+        rule.components
+            .iter()
+            .zip(literals)
+            .all(|(test, lit)| component_test(test, lit, stack, comps) != test.negate)
+    }
+}
+
+impl engine::Matcher for Matcher {
+    fn keep_glints(&mut self, keep: &dyn Fn(usize) -> bool) {
+        self.any_item.retain(|&i| keep(i as usize));
+        let named = &mut self.by_item[Kind::Enchantment as usize];
+        for list in named.values_mut() {
+            list.retain(|&i| keep(i as usize));
+        }
+        named.retain(|_, list| !list.is_empty());
+        lock(&self.enchanted).clear();
+        lock(&self.glints).clear();
+    }
+
+    fn select(
+        &self,
+        kind: engine::Kind,
+        stack: &ItemStack,
+        hand: engine::Hand,
+        max_damage: u32,
+    ) -> Option<usize> {
+        let (kind, hand) = (of_kind(kind), of_hand(hand));
+        let candidates = self.by_item[kind as usize].get(&*stack.item)?;
+        let comps = encode_components(stack);
+        let key = cache_key((0, kind, hand), stack, max_damage, comps.as_ref());
+        if let Some(hit) = lock(&self.selected).get(&key) {
+            return hit.map(|i| i as usize);
+        }
+        let found = candidates
+            .iter()
+            .copied()
+            .find(|&i| self.matches(i, stack, hand, max_damage, comps.as_ref()));
+        remember(&self.selected, key, found);
+        found.map(|i| i as usize)
+    }
+
+    fn enchantments(&self, stack: &ItemStack, hand: engine::Hand, max_damage: u32) -> Vec<usize> {
+        let hand = of_hand(hand);
+        let named = self.by_item[Kind::Enchantment as usize]
+            .get(&*stack.item)
+            .map_or(&[][..], Vec::as_slice);
+        if named.is_empty() && self.any_item.is_empty() {
+            return Vec::new();
+        }
+        let comps = encode_components(stack);
+        let key = cache_key(
+            (1, Kind::Enchantment, hand),
+            stack,
+            max_damage,
+            comps.as_ref(),
+        );
+        let hit = lock(&self.enchanted).get(&key).cloned();
+        let found = hit.unwrap_or_else(|| {
+            let mut all: Vec<u32> = named.iter().chain(&self.any_item).copied().collect();
+            all.sort_unstable();
+            all.retain(|&i| self.matches(i, stack, hand, max_damage, comps.as_ref()));
+            remember(&self.enchanted, key, all.clone());
+            all
+        });
+        found.into_iter().map(|i| i as usize).collect()
+    }
+
+    /// Worked out once per stack and hand.
+    fn glint(
+        &self,
+        stack: &ItemStack,
+        hand: engine::Hand,
+        max_damage: u32,
+        foil: bool,
+    ) -> Option<Arc<StackGlint>> {
+        let no_rules =
+            self.any_item.is_empty() && self.by_item[Kind::Enchantment as usize].is_empty();
+        // Before the cache, which `foil` is not part of.
+        if !foil || (no_rules && self.global.use_glint) {
+            return None;
+        }
+        let comps = encode_components(stack);
+        let key = cache_key(
+            (2, Kind::Enchantment, of_hand(hand)),
+            stack,
+            max_damage,
+            comps.as_ref(),
+        );
+        if let Some(hit) = lock(&self.glints).get(&key) {
+            return Some(hit.clone());
+        }
+        let matched = self.enchantments(stack, hand, max_damage);
+        let glint = Arc::new(stack_glint(
+            &self.rules,
+            &matched,
+            stack.crafting_enchantments(),
+            &self.global,
+        ));
+        remember(&self.glints, key, glint.clone());
+        Some(glint)
+    }
+}
+
+fn lock<T>(m: &Mutex<T>) -> std::sync::MutexGuard<'_, T> {
+    m.lock().unwrap_or_else(|e| e.into_inner())
+}
+
+fn remember<V>(cache: &Mutex<HashMap<u64, V>>, key: u64, value: V) {
+    let mut cache = lock(cache);
+    if cache.len() >= CACHE_LIMIT {
+        cache.clear();
+    }
+    cache.insert(key, value);
+}
+
+/// What a cached answer depends on; `query` tells `select`, `enchantments` and `glint` apart.
+fn cache_key(query: (u8, Kind, Hand), stack: &ItemStack, max: u32, comps: Option<&Tag>) -> u64 {
+    let mut h = DefaultHasher::new();
+    (query.0, query.1 as u8, query.2 as u8, &*stack.item).hash(&mut h);
+    (stack.count, stack.damage, max, comps).hash(&mut h);
+    h.finish()
+}
+
+fn prepare(test: &ComponentTest) -> Prepared {
+    let ValueTest::Literal(lit) = &test.value else {
+        return Prepared::default();
+    };
+    let text = lit.text.trim();
+    let snbt = match parse_snbt(text) {
+        Ok((tag, read)) if read == text.len() && text.starts_with(['{', '[']) => Some(tag),
+        _ => None,
+    };
+    let json = json_plain(text);
+    Prepared { snbt, json }
+}
+
+/// The plain text of `s` read as a JSON text component.
+fn json_plain(s: &str) -> Option<String> {
+    if !s.starts_with(['{', '[', '"']) {
+        return None;
+    }
+    let value: serde_json::Value = serde_json::from_str(s).ok()?;
+    Some(comp_text(&value).plain())
+}
+
+/// Whether one test passes, before its `negate`.
+fn component_test(
+    test: &ComponentTest,
+    lit: &Prepared,
+    stack: &ItemStack,
+    comps: Option<&Tag>,
+) -> bool {
+    let legacy;
+    let (root, text_depth) = match &test.source {
+        Source::Component(id) => {
+            let depth = match id.as_str() {
+                "minecraft:custom_name" | "minecraft:item_name" => Some(0),
+                "minecraft:lore" => Some(1),
+                _ => None,
+            };
+            (comps.and_then(|c| c.get(id)), depth)
+        }
+        Source::LegacyEnchantments { stored } => {
+            let levels = if *stored {
+                stack.stored_enchantments()
+            } else {
+                stack.enchantments()
+            };
+            legacy = Tag::List(
+                levels
+                    .iter()
+                    .map(|(id, lvl)| {
+                        let lvl = i16::try_from(*lvl).unwrap_or(i16::MAX);
+                        Tag::compound([
+                            ("id", Tag::String((&**id).into())),
+                            ("lvl", Tag::Short(lvl)),
+                        ])
+                    })
+                    .collect(),
+            );
+            (Some(&legacy), None)
+        }
+    };
+    // Fields the component leaves out when 0, which pre-1.20.5 items always wrote.
+    let defaulted;
+    let root = match (&test.source, root, test.path.first()) {
+        (Source::Component(id), Some(Tag::Compound(map)), Some(field))
+            if matches!(
+                (id.as_str(), field.as_str()),
+                ("minecraft:written_book_content", "generation")
+                    | ("minecraft:fireworks", "flight_duration")
+            ) && !map.contains_key(&JavaString::from(field.as_str())) =>
+        {
+            let mut map = map.clone();
+            map.insert(JavaString::from(field.as_str()), Tag::Int(0));
+            defaulted = Tag::Compound(map);
+            Some(&defaulted)
+        }
+        (_, root, _) => root,
+    };
+    let Some(root) = root else {
+        return matches!(test.value, ValueTest::Exists(false));
+    };
+    if let ValueTest::Exists(want) = test.value {
+        return walk(root, &test.path, 0, &mut |_, _| true) == want;
+    }
+    walk(root, &test.path, 0, &mut |tag, depth| {
+        value_test(&test.value, lit, tag, text_depth == Some(depth))
+    })
+}
+
+/// Visits what `path` reaches from `tag`, true once `visit` is.
+fn walk(
+    tag: &Tag,
+    path: &[String],
+    depth: usize,
+    visit: &mut dyn FnMut(&Tag, usize) -> bool,
+) -> bool {
+    let Some((seg, rest)) = path.split_first() else {
+        return visit(tag, depth);
+    };
+    let mut next = |t: &Tag| walk(t, rest, depth + 1, visit);
+    let len = match tag {
+        Tag::Compound(map) if seg == "*" => return map.values().any(&mut next),
+        Tag::Compound(map) => return map.get(&JavaString::from(seg.as_str())).is_some_and(next),
+        Tag::List(v) => v.len(),
+        Tag::ByteArray(v) => v.len(),
+        Tag::IntArray(v) => v.len(),
+        Tag::LongArray(v) => v.len(),
+        _ => return false,
+    };
+    let element = |i: usize| match tag {
+        Tag::List(v) => Cow::Borrowed(&v[i]),
+        Tag::ByteArray(v) => Cow::Owned(Tag::Byte(v[i] as i8)),
+        Tag::IntArray(v) => Cow::Owned(Tag::Int(v[i])),
+        Tag::LongArray(v) => Cow::Owned(Tag::Long(v[i])),
+        _ => Cow::Owned(Tag::End),
+    };
+    if seg == "count" {
+        return next(&Tag::Int(i32::try_from(len).unwrap_or(i32::MAX)));
+    }
+    if seg == "*" {
+        return (0..len).any(|i| next(&element(i)));
+    }
+    seg.parse::<usize>()
+        .ok()
+        .filter(|&i| i < len)
+        .is_some_and(|i| next(&element(i)))
+}
+
+fn int_value(tag: &Tag) -> Option<i64> {
+    match *tag {
+        Tag::Byte(v) => Some(v.into()),
+        Tag::Short(v) => Some(v.into()),
+        Tag::Int(v) => Some(v.into()),
+        Tag::Long(v) => Some(v),
+        _ => None,
+    }
+}
+
+/// A number as Java's `String.valueOf` writes it (`3`, `3.0`).
+fn decimal(tag: &Tag) -> Option<String> {
+    let s = match *tag {
+        Tag::Float(b) => f32::from_bits(b).to_string(),
+        Tag::Double(b) => f64::from_bits(b).to_string(),
+        _ => return int_value(tag).map(|v| v.to_string()),
+    };
+    Some(if s.contains(['.', 'e', 'N', 'i']) {
+        s
+    } else {
+        s + ".0"
+    })
+}
+
+/// `text` against a string, its JSON text, or the plain text of a text component.
+fn text_matches(tag: &Tag, is_text: bool, text: impl Fn(&str) -> bool) -> bool {
+    match tag {
+        Tag::String(s) => {
+            let s = s.to_string_lossy();
+            text(&s)
+                || (is_text && text(&name_text(tag).plain()))
+                || json_plain(&s).is_some_and(|p| text(&p))
+        }
+        Tag::Compound(_) | Tag::List(_) => is_text && text(&name_text(tag).plain()),
+        _ => false,
+    }
+}
+
+fn value_test(test: &ValueTest, lit: &Prepared, tag: &Tag, is_text: bool) -> bool {
+    match test {
+        ValueTest::Exists(_) => true,
+        ValueTest::Range(r) => {
+            int_value(tag).is_some_and(|v| i32::try_from(v).is_ok_and(|v| r.contains(v)))
+        }
+        ValueTest::Raw(name) => name.matches(&canon_tag(tag)),
+        ValueTest::Text(name) => match decimal(tag) {
+            Some(n) => name.matches(&n),
+            None => text_matches(tag, is_text, |s| name.matches(s)),
+        },
+        ValueTest::Literal(l) => match tag {
+            Tag::Float(b) => l.text.trim().parse::<f32>().ok() == Some(f32::from_bits(*b)),
+            Tag::Double(b) => l.float == Some(f64::from_bits(*b)),
+            Tag::Compound(_) | Tag::List(_)
+                if lit.snbt.as_ref().is_some_and(|e| contains(e, tag)) =>
+            {
+                true
+            }
+            _ => match int_value(tag) {
+                Some(v) => l.int == Some(v),
+                None => text_matches(tag, is_text, |s| {
+                    s == l.text || lit.json.as_deref() == Some(s)
+                }),
+            },
+        },
+    }
+}
+
+/// `NbtUtils.compareNbt(expected, actual, true)`: every key and element of `expected` found in
+/// `actual`.
+fn contains(expected: &Tag, actual: &Tag) -> bool {
+    match (expected, actual) {
+        (Tag::Compound(e), Tag::Compound(a)) => e
+            .iter()
+            .all(|(k, v)| a.get(k).is_some_and(|a| contains(v, a))),
+        (Tag::List(e), Tag::List(a)) if e.is_empty() => a.is_empty(),
+        (Tag::List(e), Tag::List(a)) => e.iter().all(|e| a.iter().any(|a| contains(e, a))),
+        _ => expected == actual,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::cit::{Hand, Kind};
+    use std::sync::Arc;
+
+    /// Rules from (file stem, properties), sorted as `load_rules` sorts them, under the global
+    /// `cit.properties` text `global`.
+    fn rules_under(files: &[(&str, &str)], global: &str) -> CitRules {
+        let files: Vec<(String, String)> = files
+            .iter()
+            .map(|(stem, text)| {
+                let path = format!("assets/minecraft/optifine/cit/{stem}.properties");
+                (path, format!("texture=x\n{text}"))
+            })
+            .collect();
+        let files: Vec<(&str, &str)> = files.iter().map(|(p, t)| (&**p, &**t)).collect();
+        let cit = parse_rules(&files, global);
+        assert_eq!(cit.rules.len(), files.len(), "every rule parses");
+        cit
+    }
+
+    fn rules(files: &[(&str, &str)]) -> CitRules {
+        rules_under(files, "")
+    }
+
+    fn stem(cit: &CitRules, i: Option<usize>) -> Option<&str> {
+        let path = &cit.rules[i?].path;
+        path.rsplit('/').next()?.strip_suffix(".properties")
+    }
+
+    fn item(cit: &CitRules, stack: ItemStack) -> Option<&str> {
+        stem(cit, cit.select(Kind::Item, &stack, Hand::Main, 0))
+    }
+
+    fn new(id: &str) -> ItemStack {
+        ItemStack::new(&format!("minecraft:{id}"), 1)
+    }
+
+    fn string(s: &str) -> Tag {
+        Tag::String(s.into())
+    }
+
+    fn with(id: &str, component: &str, tag: Tag) -> ItemStack {
+        let mut stack = new(id);
+        let component = format!("minecraft:{component}");
+        stack.data_mut().other.push((component, tag));
+        stack
+    }
+
+    fn enchanted(id: &str, levels: &[(&str, u32)]) -> ItemStack {
+        let mut stack = new(id);
+        let levels = levels
+            .iter()
+            .map(|(e, l)| (Arc::from(format!("minecraft:{e}")), *l));
+        stack.data_mut().enchantments = levels.collect();
+        stack
+    }
+
+    #[test]
+    fn heavier_rules_win_and_kinds_stay_apart() {
+        let cit = rules(&[
+            ("plain", "items=stick"),
+            ("heavy", "items=stick\nweight=2\nstackSize=2-"),
+            ("offhand", "items=stick\nweight=5\nhand=off"),
+            ("armor", "type=armor\nitems=stick"),
+            ("wings", "type=elytra"),
+        ]);
+        assert_eq!(item(&cit, new("stick")), Some("plain"));
+        assert_eq!(
+            item(&cit, ItemStack::new("minecraft:stick", 3)),
+            Some("heavy")
+        );
+        let pick = |kind, id, hand, max| stem(&cit, cit.select(kind, &new(id), hand, max));
+        assert_eq!(pick(Kind::Item, "stick", Hand::Off, 0), Some("offhand"));
+        assert_eq!(item(&cit, new("stone")), None);
+        assert_eq!(item(&cit, new("elytra")), None);
+        assert_eq!(pick(Kind::Elytra, "elytra", Hand::Main, 432), Some("wings"));
+        assert_eq!(pick(Kind::Armor, "stick", Hand::Main, 0), Some("armor"));
+    }
+
+    #[test]
+    fn names_match_by_their_plain_text() {
+        let cit = rules(&[
+            ("glob", "items=stick\nnbt.display.Name=ipattern:*sword"),
+            ("exact", "items=stone\ncomponents.custom_name=My Sword"),
+            ("json", "items=dirt\nnbt.display.Name=[\"My \",\"Sword\"]"),
+        ]);
+        let named = |id: &str, name: Tag| {
+            let mut stack = new(id);
+            stack.data_mut().custom_name = Some(name);
+            stack
+        };
+        let styled = Tag::compound([("text", string("My Sword")), ("color", string("red"))]);
+        assert_eq!(item(&cit, named("stick", styled.clone())), Some("glob"));
+        assert_eq!(item(&cit, named("stick", string("Blade"))), None);
+        assert_eq!(item(&cit, new("stick")), None);
+        assert_eq!(item(&cit, named("stone", styled.clone())), Some("exact"));
+        assert_eq!(item(&cit, named("dirt", styled)), Some("json"));
+    }
+
+    #[test]
+    fn lore_lines_and_list_counts() {
+        let cit = rules(&[
+            (
+                "any_line",
+                "items=stick\nnbt.display.Lore.*=ipattern:*legendary*",
+            ),
+            ("two_lines", "items=stone\ncomponents.lore.count=2"),
+        ]);
+        let bold = Tag::compound([("text", string("A LEGENDARY item")), ("bold", Tag::Byte(1))]);
+        let lore = Tag::List(vec![string("Common"), bold]);
+        assert_eq!(
+            item(&cit, with("stick", "lore", lore.clone())),
+            Some("any_line")
+        );
+        assert_eq!(item(&cit, with("stone", "lore", lore)), Some("two_lines"));
+        let one = Tag::List(vec![string("A legendary item")]);
+        assert_eq!(item(&cit, with("stone", "lore", one)), None);
+    }
+
+    #[test]
+    fn custom_data_existence_and_negation() {
+        let cit = rules(&[
+            (
+                "aote",
+                "items=stick\nweight=2\nnbt.ExtraAttributes.id=ASPECT_OF_THE_END",
+            ),
+            (
+                "not_hyp",
+                "items=stick\nweight=1\ncomponent.custom_data.ExtraAttributes.id=!HYP",
+            ),
+            ("unnamed", "items=stick\nnbt.display.Name=exists:false"),
+        ]);
+        let data = |id: &str| {
+            let attributes =
+                Tag::compound([("ExtraAttributes", Tag::compound([("id", string(id))]))]);
+            with("stick", "custom_data", attributes)
+        };
+        assert_eq!(item(&cit, data("ASPECT_OF_THE_END")), Some("aote"));
+        assert_eq!(item(&cit, data("MIDAS")), Some("not_hyp"));
+        assert_eq!(item(&cit, data("HYP")), Some("unnamed"));
+        let mut named = data("HYP");
+        named.data_mut().custom_name = Some(string("Hyperion"));
+        assert_eq!(item(&cit, named), None);
+    }
+
+    #[test]
+    fn legacy_enchantment_lists_and_model_data() {
+        let cit = rules(&[
+            (
+                "sharp",
+                "items=stick\nnbt.Enchantments.*.id=minecraft:sharpness\nnbt.Enchantments.0.lvl=5",
+            ),
+            ("cmd", "items=stone\nnbt.CustomModelData=3"),
+            (
+                "cmd_snbt",
+                "items=dirt\ncomponents.custom_model_data={floats:[3.0f]}",
+            ),
+        ]);
+        assert_eq!(
+            item(&cit, enchanted("stick", &[("sharpness", 5)])),
+            Some("sharp")
+        );
+        assert_eq!(item(&cit, enchanted("stick", &[("sharpness", 4)])), None);
+        let model = |id: &str, f: f32| {
+            let floats = Tag::List(vec![Tag::Float(f.to_bits()), Tag::Float(7f32.to_bits())]);
+            with(id, "custom_model_data", Tag::compound([("floats", floats)]))
+        };
+        assert_eq!(item(&cit, model("stone", 3.0)), Some("cmd"));
+        assert_eq!(item(&cit, model("stone", 3.5)), None);
+        assert_eq!(item(&cit, model("dirt", 3.0)), Some("cmd_snbt"));
+        assert_eq!(item(&cit, model("dirt", 2.0)), None);
+    }
+
+    #[test]
+    fn fields_left_out_at_zero_read_as_zero() {
+        let cit = rules(&[("zero", "items=firework_rocket\nnbt.Fireworks.Flight=0")]);
+        let mut rocket = new("firework_rocket");
+        rocket.data_mut().fireworks = Some((0, Vec::new()));
+        assert_eq!(item(&cit, rocket.clone()), Some("zero"));
+        rocket.data_mut().fireworks = Some((2, Vec::new()));
+        assert_eq!(item(&cit, rocket), None);
+    }
+
+    #[test]
+    fn damage_counts_only_for_damageable_items() {
+        let cit = rules(&[
+            ("worn", "items=diamond_sword\ndamage=50-100%"),
+            ("new", "items=stick\ndamage=0"),
+        ]);
+        let damaged = |id: &str, damage: u32, max: u32| {
+            let mut stack = new(id);
+            stack.damage = damage;
+            stem(&cit, cit.select(Kind::Item, &stack, Hand::Main, max))
+        };
+        // Half of 1561 is 780.5.
+        assert_eq!(damaged("diamond_sword", 780, 1561), None);
+        assert_eq!(damaged("diamond_sword", 781, 1561), Some("worn"));
+        assert_eq!(damaged("stick", 5, 0), Some("new"));
+    }
+
+    #[test]
+    fn enchantment_levels_and_rules_for_any_item() {
+        let cit = rules(&[
+            (
+                "sharp3",
+                "items=stick\nenchantments=sharpness\nenchantmentLevels=3-",
+            ),
+            ("any3", "items=stone\nenchantmentLevels=3-"),
+            ("glint", "type=enchantment\nenchantments=sharpness"),
+            (
+                "sword_glint",
+                "type=enchantment\nitems=diamond_sword\nweight=2",
+            ),
+        ]);
+        let mixed = [("sharpness", 2), ("unbreaking", 3)];
+        assert_eq!(item(&cit, enchanted("stick", &mixed)), None);
+        assert_eq!(
+            item(&cit, enchanted("stick", &[("sharpness", 4)])),
+            Some("sharp3")
+        );
+        assert_eq!(item(&cit, enchanted("stone", &mixed)), Some("any3"));
+        let glints = |stack: ItemStack| -> Vec<&str> {
+            let found = cit.enchantments(&stack, Hand::Main, 0).into_iter();
+            found.map(|i| stem(&cit, Some(i)).unwrap()).collect()
+        };
+        let sharp = [("sharpness", 1)];
+        assert_eq!(
+            glints(enchanted("diamond_sword", &sharp)),
+            ["sword_glint", "glint"]
+        );
+        assert_eq!(glints(enchanted("stick", &sharp)), ["glint"]);
+        assert!(glints(new("stick")).is_empty());
+        // Glints are never an item's texture.
+        assert_eq!(item(&cit, enchanted("diamond_sword", &sharp)), None);
+    }
+
+    /// `CitRules::glint` in the main hand, with the stack's own `has_foil` as callers pass it.
+    fn glint(cit: &CitRules, stack: &ItemStack, item_glint: bool) -> Option<Arc<StackGlint>> {
+        cit.glint(stack, Hand::Main, 0, stack.has_foil(item_glint))
+    }
+
+    /// `stack` with its `enchantment_glint_override` set to `on`.
+    fn overridden(mut stack: ItemStack, on: bool) -> ItemStack {
+        let flag = (
+            "minecraft:enchantment_glint_override".to_owned(),
+            Tag::Byte(on.into()),
+        );
+        stack.data_mut().other.push(flag);
+        stack
+    }
+
+    #[test]
+    fn a_stack_glint_reads_the_book_and_the_pack_file() {
+        let files = [
+            ("sharp", "type=enchantment\nenchantments=sharpness"),
+            (
+                "keep",
+                "type=enchantment\nlayer=1\nuseGlint=true\nenchantments=mending",
+            ),
+        ];
+        let cit = rules(&files);
+        // An enchanted book's glint follows its stored enchantments.
+        let mut book = new("enchanted_book");
+        book.data_mut().stored_enchantments = vec![
+            (Arc::from("minecraft:sharpness"), 3),
+            (Arc::from("minecraft:mending"), 1),
+        ];
+        let book = glint(&cit, &book, true).unwrap();
+        let weights: Vec<_> = book.layers.iter().map(|l| l.weight).collect();
+        assert_eq!(weights, [0.75, 0.25]);
+        assert!(book.vanilla);
+        let plain = glint(&cit, &enchanted("stick", &[("sharpness", 1)]), false).unwrap();
+        assert_eq!(plain.layers.len(), 1);
+        assert!(!plain.vanilla);
+        // No enchantment rules: nothing changes, unless the pack turns vanilla's glint off.
+        let bare = rules(&[("stick", "items=stick")]);
+        assert!(glint(&bare, &overridden(new("stick"), true), false).is_none());
+        let bare = rules_under(&[("stick", "items=stick")], "useGlint=false");
+        assert!(!bare.use_glint);
+        assert!(
+            !glint(&bare, &overridden(new("stick"), true), false)
+                .unwrap()
+                .vanilla
+        );
+        let cit = rules_under(&files, "useGlint=false");
+        assert!(
+            glint(&cit, &overridden(new("stick"), true), false)
+                .unwrap()
+                .is_empty()
+        );
+    }
+
+    #[test]
+    fn only_a_stack_with_a_glint_gets_layers() {
+        let cit = rules(&[("any", "type=enchantment")]);
+        assert!(glint(&cit, &new("stick"), false).is_none());
+        // The override turns an enchanted stack's glint off, and an unenchanted one's on.
+        let off = overridden(enchanted("stick", &[("sharpness", 1)]), false);
+        assert!(glint(&cit, &off, false).is_none());
+        let on = glint(&cit, &overridden(new("stick"), true), false).unwrap();
+        let weights: Vec<_> = on.layers.iter().map(|l| l.weight).collect();
+        assert_eq!(
+            weights,
+            [1.0],
+            "nothing to share: the rule at full strength"
+        );
+        // The same stack, asked again without its glint, is not answered from the cache.
+        assert!(
+            cit.glint(&overridden(new("stick"), true), Hand::Main, 0, false)
+                .is_none()
+        );
+    }
+
+    #[test]
+    fn a_rule_left_out_of_the_glints_matches_nothing() {
+        let mut cit = rules(&[
+            ("broken", "type=enchantment\nitems=diamond_sword\nweight=1"),
+            ("shown", "type=enchantment"),
+        ]);
+        let sword = enchanted("diamond_sword", &[("sharpness", 1)]);
+        let layers = |cit: &CitRules| -> Vec<String> {
+            let glint = glint(cit, &sword, false).unwrap();
+            let stems = glint
+                .layers
+                .iter()
+                .map(|l| stem(cit, Some(l.rule)).unwrap());
+            stems.map(str::to_owned).collect()
+        };
+        // The heavier rule wins the layer, until its texture is missing.
+        assert_eq!(layers(&cit), ["broken"]);
+        let broken = (0..cit.rules.len())
+            .find(|&i| stem(&cit, Some(i)) == Some("broken"))
+            .unwrap();
+        cit.keep_glints(|i| i != broken);
+        assert_eq!(layers(&cit), ["shown"]);
+        assert_eq!(cit.enchantments(&sword, Hand::Main, 0).len(), 1);
+        // None left: vanilla's glint stays.
+        cit.keep_glints(|_| false);
+        assert!(glint(&cit, &sword, false).is_none());
+    }
+
+    #[test]
+    fn an_off_hand_layer_draws_only_in_the_off_hand() {
+        let cit = rules(&[
+            ("left", "type=enchantment\nlayer=1\nhand=off"),
+            ("both", "type=enchantment"),
+        ]);
+        let sword = enchanted("diamond_sword", &[("sharpness", 1)]);
+        let layers = |hand| -> Vec<&str> {
+            let glint = cit.glint(&sword, hand, 0, true).unwrap();
+            glint
+                .layers
+                .iter()
+                .map(|l| stem(&cit, Some(l.rule)).unwrap())
+                .collect()
+        };
+        assert_eq!(layers(Hand::Off), ["both", "left"]);
+        // Asked in this order, a cache keyed without the hand would answer as for the off hand.
+        assert_eq!(layers(Hand::Main), ["both"]);
+    }
+}
@@ -0,0 +1,301 @@
+//! OptiFine's Custom Item Textures' enchantment glints (`type=enchantment`): which of a stack's
+//! matching rules draw, in which order and how strongly, and whether vanilla's glint still draws
+//! under them ([`crate::cit_glint::StackGlint`]). The pack's `cit.properties` (`Global`) says how
+//! layers share an item.
+//!
+//! Written from OptiFine's `cit.properties` doc and CIT Resewn's (MIT) `TypeEnchantment` of
+//! before its 1.21.11 port, which implemented `method`, `cap` and `fade`: the sums and the
+//! cycle's fading follow it, except where noted.
+
+use super::cit::read_properties;
+use crate::cit_glint::{GlintLayer, StackGlint};
+use horizon_optifine::cit::{Global, Method, Rule};
+use std::path::Path;
+
+/// The pack's global `cit.properties` under the overlay resource root: the first of
+/// `Global::PATHS` that exists, else the defaults.
+pub fn load_global(root: &Path) -> Global {
+    Global::PATHS
+        .iter()
+        .find_map(|path| read_properties(&root.join(path)))
+        .map(|props| Global::parse(&props))
+        .unwrap_or_default()
+}
+
+/// A stack's glint: the layers among `matched` (its matching enchantment rules, in priority
+/// order, as `CitRules::enchantments` gives them) that draw, for a stack with `enchantments`
+/// (`ItemStack::crafting_enchantments`).
+pub fn stack_glint(
+    rules: &[Rule],
+    matched: &[usize],
+    enchantments: &[(impl AsRef<str>, u32)],
+    global: &Global,
+) -> StackGlint {
+    // The highest priority rule of each layer.
+    let mut layers: Vec<usize> = Vec::new();
+    for &i in matched {
+        let layer = rules[i].glint.layer;
+        if !layers.iter().any(|&j| rules[j].glint.layer == layer) {
+            layers.push(i);
+        }
+    }
+    layers.sort_by_key(|&i| rules[i].glint.layer);
+    let cycle = global.method == Method::Cycle;
+    // OptiFine's doc: `cap` is for `average` and `layered`, and keeps the topmost layers.
+    // `none`, which OptiFine lacks, is capped too, as CIT Resewn caps every method (it keeps
+    // the bottom layers, though, and caps cycles as well).
+    if let Some(cap) = global.cap.filter(|_| !cycle) {
+        let cap = usize::try_from(cap).unwrap_or(usize::MAX);
+        layers = layers.split_off(layers.len().saturating_sub(cap));
+    }
+    // CIT Resewn: any layer left asking for vanilla's glint keeps it, and the global
+    // `useGlint=false` removes it everywhere, as OptiFine's doc says too. `cap=0` leaves no
+    // custom layer, and vanilla's glint only if the pack's `useGlint` allows it.
+    let vanilla =
+        global.use_glint && (layers.is_empty() || layers.iter().any(|&i| rules[i].glint.use_glint));
+    // CIT Resewn: shares are against every enchantment of the stack, not only those the
+    // layers name.
+    let levels = enchantments.iter().map(|(_, level)| *level as f32);
+    let total = match global.method {
+        Method::Average => levels.sum::<f32>(),
+        Method::Layered => levels.fold(0.0, f32::max),
+        Method::None | Method::Cycle => 0.0,
+    };
+    let shared = matches!(global.method, Method::Average | Method::Layered);
+    let layers = layers
+        .into_iter()
+        .map(|i| {
+            let rule = &rules[i];
+            let named = &rule.enchantments;
+            let weight = if !shared || named.is_empty() {
+                1.0
+            } else {
+                // The highest level among the enchantments the rule names whose level also
+                // passes its `enchantmentLevels` (CIT Resewn takes the first named one the
+                // stack has, whatever its level).
+                let in_range = |level: u32| {
+                    let level = i32::try_from(level).unwrap_or(i32::MAX);
+                    rule.enchantment_levels
+                        .as_ref()
+                        .is_none_or(|r| r.contains(level))
+                };
+                let level = enchantments
+                    .iter()
+                    .filter(|(id, level)| {
+                        let id: &str = id.as_ref();
+                        named.iter().any(|n| n == id) && in_range(*level)
+                    })
+                    .map(|(_, level)| *level as f32)
+                    .fold(0.0, f32::max);
+                if total > 0.0 { level / total } else { 0.0 }
+            };
+            GlintLayer::new(i, weight, rule.glint.duration)
+        })
+        .collect();
+    StackGlint::from_parts(layers, vanilla, cycle.then_some(global.fade))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use horizon_optifine::Properties;
+
+    const DIR: &str = "assets/minecraft/optifine/cit";
+
+    /// An enchantment rule named `name` with `text` after `type` and `texture`.
+    fn rule(name: &str, text: &str) -> Rule {
+        let text = format!("type=enchantment\ntexture=glint\n{text}");
+        let path = format!("{DIR}/{name}.properties");
+        Rule::parse(&path, &Properties::parse_equals_first(&text), |_| true).unwrap()
+    }
+
+    fn global(text: &str) -> Global {
+        Global::parse(&Properties::parse_equals_first(text))
+    }
+
+    fn rules_of(layers: &StackGlint) -> Vec<usize> {
+        layers.layers.iter().map(|l| l.rule).collect()
+    }
+
+    const SWORD: [(&str, u32); 2] = [("minecraft:sharpness", 3), ("minecraft:unbreaking", 1)];
+
+    #[test]
+    fn one_rule_per_layer_bottom_first() {
+        let rules = [
+            rule("a", "layer=2"),
+            rule("b", "layer=0"),
+            rule("c", "layer=2"),
+            rule("d", "layer=-1"),
+        ];
+        // Priority order a, b, c, d: c loses layer 2 to a.
+        let g = stack_glint(&rules, &[0, 1, 2, 3], &SWORD, &Global::default());
+        assert_eq!(rules_of(&g), [3, 1, 0]);
+        let g = stack_glint(&rules, &[2, 0], &SWORD, &Global::default());
+        assert_eq!(rules_of(&g), [2]);
+    }
+
+    #[test]
+    fn average_and_layered_shares() {
+        let rules = [
+            rule("sharp", "enchantments=sharpness smite"),
+            rule("unb", "layer=1\nenchantments=unbreaking"),
+            rule("any", "layer=2"),
+            rule("fire", "layer=3\nenchantments=fire_aspect"),
+        ];
+        let weights = |method: &str| {
+            let g = stack_glint(&rules, &[0, 1, 2, 3], &SWORD, &global(method));
+            g.layers.iter().map(|l| l.weight).collect::<Vec<_>>()
+        };
+        // Sharpness III and Unbreaking I: 3 / 4 and 1 / 4; against the highest, 3 / 3 and 1 / 3.
+        // A rule naming no enchantment is at full strength, one the stack lacks at none.
+        assert_eq!(weights("method=average"), [0.75, 0.25, 1.0, 0.0]);
+        assert_eq!(weights("method=layered"), [1.0, 1.0 / 3.0, 1.0, 0.0]);
+        assert_eq!(weights("method=cycle"), [1.0; 4]);
+        assert_eq!(weights("method=none"), [1.0; 4]);
+    }
+
+    #[test]
+    fn the_level_is_one_the_rules_levels_allow() {
+        let rules = [rule(
+            "holy",
+            "enchantments=sharpness smite\nenchantmentLevels=1-2",
+        )];
+        // Sharpness V is out of range, so Smite I sets the share: 1 / 5 of the highest level.
+        let stack = [("minecraft:sharpness", 5), ("minecraft:smite", 1)];
+        let g = stack_glint(&rules, &[0], &stack, &global("method=layered"));
+        assert_eq!(g.layers[0].weight, 1.0 / 5.0);
+    }
+
+    #[test]
+    fn cap_keeps_the_topmost_layers() {
+        let rules = [
+            rule("a", "layer=0"),
+            rule("b", "layer=1"),
+            rule("c", "layer=2"),
+        ];
+        let g = stack_glint(&rules, &[0, 1, 2], &SWORD, &global("cap=2"));
+        assert_eq!(rules_of(&g), [1, 2]);
+        let g = stack_glint(&rules, &[0, 1, 2], &SWORD, &global("cap=0"));
+        assert!(g.is_empty());
+        let g = stack_glint(&rules, &[0, 1, 2], &SWORD, &global("cap=1\nmethod=none"));
+        assert_eq!(rules_of(&g), [2]);
+        // Cycles show every layer in turn.
+        let g = stack_glint(&rules, &[0, 1, 2], &SWORD, &global("cap=1\nmethod=cycle"));
+        assert_eq!(rules_of(&g), [0, 1, 2]);
+    }
+
+    #[test]
+    fn vanilla_glint() {
+        let plain = rule("plain", "");
+        let keep = rule("keep", "layer=1\nuseGlint=true");
+        let rules = [plain, keep];
+        let vanilla = |matched: &[usize], text: &str| {
+            stack_glint(&rules, matched, &SWORD, &global(text)).vanilla
+        };
+        assert!(vanilla(&[], ""), "no rule: vanilla's glint");
+        assert!(!vanilla(&[0], ""), "a rule replaces it");
+        assert!(vanilla(&[0, 1], ""), "unless one keeps it");
+        assert!(!vanilla(&[], "useGlint=false"));
+        assert!(!vanilla(&[1], "useGlint=false"), "the pack's word is final");
+        // Only the layers `cap` keeps count.
+        let rules = [rule("keep", "useGlint=true"), rule("top", "layer=1")];
+        let g = stack_glint(&rules, &[0, 1], &SWORD, &global("cap=1"));
+        assert!(!g.vanilla);
+        let g = stack_glint(&rules, &[0, 1], &SWORD, &global("cap=0"));
+        assert!(g.is_empty() && g.vanilla);
+        let g = stack_glint(&rules, &[0, 1], &SWORD, &global("cap=0\nuseGlint=false"));
+        assert!(!g.vanilla);
+    }
+
+    #[test]
+    fn cycles_take_turns_and_fade() {
+        let rules = [
+            rule("a", "duration=2"),
+            rule("b", "layer=1\nduration=1"),
+            rule("c", "layer=2\nduration=1"),
+        ];
+        let g = stack_glint(
+            &rules,
+            &[0, 1, 2],
+            &SWORD,
+            &global("method=cycle\nfade=0.5"),
+        );
+        // a 0-2, a→b 2-2.5, b 2.5-3.5, b→c 3.5-4, c 4-5, c→a 5-5.5, then again.
+        let at = |t: f64| [0, 1, 2].map(|i| g.intensity(i, t));
+        assert_eq!(at(1.0), [1.0, 0.0, 0.0]);
+        assert_eq!(at(2.125), [0.75, 0.25, 0.0]);
+        assert_eq!(at(3.0), [0.0, 1.0, 0.0]);
+        assert_eq!(at(3.75), [0.0, 0.5, 0.5]);
+        assert_eq!(at(4.5), [0.0, 0.0, 1.0]);
+        assert_eq!(at(5.25), [0.5, 0.0, 0.5]);
+        assert_eq!(at(5.5 + 3.0), [0.0, 1.0, 0.0]);
+        // One layer always shows.
+        let one = stack_glint(&rules, &[1], &SWORD, &global("method=cycle"));
+        assert_eq!(one.intensity(0, 0.7), 1.0);
+    }
+
+    #[test]
+    fn a_cycle_always_shows_a_whole_layer() {
+        let rules = [
+            rule("a", "duration=0.1"),
+            rule("b", "layer=1\nduration=0.7"),
+            rule("c", "layer=2\nduration=0.2"),
+        ];
+        let g = stack_glint(
+            &rules,
+            &[0, 1, 2],
+            &SWORD,
+            &global("method=cycle\nfade=0.3"),
+        );
+        // Every millisecond of the first two seconds, and just under a period, the last fade's
+        // end. (Rounding has not been seen to leave time past it; the last fade's clamp is
+        // defensive.)
+        let period: f64 = [0.1f32, 0.7, 0.2]
+            .map(|d| f64::from(d) + f64::from(0.3f32))
+            .iter()
+            .sum();
+        let last = f64::from_bits(period.to_bits() - 1);
+        for t in (0..2000_i32)
+            .map(|i| f64::from(i) * 0.001)
+            .chain([last, period + last])
+        {
+            let sum: f32 = (0..3).map(|i| g.intensity(i, t)).sum();
+            assert!((sum - 1.0).abs() < 1e-5, "{sum} at {t}");
+        }
+        // No time at all: the bottom layer alone, never NaN.
+        let still = [rule("a", "duration=0"), rule("b", "layer=1\nduration=0")];
+        let g = stack_glint(&still, &[0, 1], &SWORD, &global("method=cycle\nfade=0"));
+        for t in [0.0, 0.5, 7.25] {
+            assert_eq!([0, 1].map(|i| g.intensity(i, t)), [1.0, 0.0]);
+        }
+    }
+
+    #[test]
+    fn the_first_global_file_wins() {
+        let root = std::env::temp_dir().join(format!("horizon-cit-glint-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&root);
+        assert_eq!(load_global(&root), Global::default());
+        let write = |path: &str, text: &[u8]| {
+            let file = root.join(path);
+            std::fs::create_dir_all(file.parent().unwrap()).unwrap();
+            std::fs::write(file, text).unwrap();
+        };
+        // Saved as Latin-1 (`é` is not UTF-8 alone), in the OptiFine doc's `cit/` folder.
+        write(
+            "assets/minecraft/optifine/cit/cit.properties",
+            b"# caf\xE9\nmethod=cycle",
+        );
+        assert_eq!(load_global(&root).method, Method::Cycle);
+        write("assets/minecraft/mcpatcher/cit.properties", b"method=none");
+        assert_eq!(load_global(&root).method, Method::Cycle);
+        write(
+            "assets/minecraft/optifine/cit.properties",
+            b"method=layered",
+        );
+        assert_eq!(load_global(&root).method, Method::Layered);
+        write("assets/minecraft/citresewn/cit.properties", b"cap=1");
+        let g = load_global(&root);
+        let _ = std::fs::remove_dir_all(&root);
+        assert_eq!((g.method, g.cap), (Method::Average, Some(1)));
+    }
+}
@@ -0,0 +1,67 @@
+//! Polytone's custom colours (`horizon_polytone::colors`, `colors.json` or `color.properties`)
+//! as the engine's pack colours ([`crate::pack_palette::PackColors`]).
+use std::path::Path;
+
+use horizon_polytone::colors::PackColors;
+
+use crate::block_entity_render::DYES;
+use crate::pack_palette::{self, Environment};
+
+/// The colours of every namespace's file under the pack overlay at `root`.
+pub fn read(root: &Path) -> pack_palette::PackColors {
+    let colors = PackColors::read(root);
+    let by_dye = |f: &dyn Fn(&str) -> Option<u32>| std::array::from_fn(|i| f(DYES[i].0));
+    let env = colors.env;
+    pack_palette::PackColors {
+        dye_diffuse: by_dye(&|name| colors.dye(name, "diffuse")),
+        dye_text: by_dye(&|name| colors.dye(name, "text")),
+        sheep: by_dye(&|name| colors.sheep(name)),
+        redstone: std::array::from_fn(|i| colors.redstone(i as u8)),
+        effects: colors.effects(),
+        entity_shadows: colors.entity_shadows(),
+        xp_bar: colors.xp_bar(),
+        env: Environment {
+            powder_snow_fog: env.powder_snow_fog,
+            blindness_fog_distance: env.blindness_fog_distance,
+            darkness_fog_distance: env.darkness_fog_distance,
+            boss_fog_distance: env.boss_fog_distance,
+            water_fog_brightening: env.water_fog_brightening,
+            water_fog_brightening_time: env.water_fog_brightening_time,
+            horizon_height: env.horizon_height,
+        },
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::pack_palette::{diffuse, redstone, sheep_wool, text};
+
+    #[test]
+    fn a_pack_recolours_only_what_it_names() {
+        // Dyes no other test draws: the table is process-wide.
+        let dir = std::env::temp_dir().join(format!("pack-dyes-{}", std::process::id()));
+        let polytone = dir.join("assets/obs/polytone");
+        std::fs::create_dir_all(&polytone).unwrap();
+        std::fs::write(
+            polytone.join("colors.json"),
+            r#"{"dye": {"cyan": {"diffuse": "00ff00", "text": "0000ff"}}, "sheep": {"pink": "2040ff"}, "redstone": {"7": "0x123456"}}"#,
+        )
+        .unwrap();
+        crate::pack_palette::set(&read(&dir));
+        let (cyan, pink, purple) = (9, 6, 10);
+        assert_eq!(diffuse(cyan), 0x00ff00);
+        assert_eq!(text(cyan), 0x0000ff);
+        assert_eq!(sheep_wool(pink as u8), 0x2040ff);
+        // Wool reads vanilla's dye, not the pack's diffuse: 75% of 0x169C9C.
+        assert_eq!(sheep_wool(cyan as u8), 0x107575);
+        assert_eq!(diffuse(purple), 0x8932B8);
+        assert_eq!(text(purple), 0xA020F0);
+        assert_eq!((redstone(7), redstone(15)), (Some(0x123456), None));
+        crate::pack_palette::set(&Default::default());
+        assert_eq!(redstone(7), None);
+        assert_eq!(diffuse(cyan), 0x169C9C);
+        assert_eq!(sheep_wool(pink as u8), 0xB6687F);
+        std::fs::remove_dir_all(&dir).ok();
+    }
+}
@@ -0,0 +1,136 @@
+//! OptiFine's and Fusion's connected textures as the mesher draws them
+//! ([`crate::connected::ConnectedTextures`]): a Fusion face first, then OptiFine's rules.
+
+use std::path::Path;
+use std::sync::Arc;
+
+use horizon_optifine::ctm::connect::{Axes, Face};
+use horizon_world::registry::{BlockRegistry, BlockStateId};
+
+use super::ctm::ConnectedTextures as Ctm;
+use super::fusion::FusionTextures;
+use crate::chunk::Chunk;
+use crate::connected::{self as engine, Connected, ConnectedTextures, Overlay, Pick};
+use crate::mesher::{MeshScratch, Mesher, SectionMesh};
+use crate::models::StateModels;
+use crate::sprites::Sprites;
+
+/// A pack's Fusion and OptiFine connected textures.
+pub struct Rules {
+    ctm: Ctm,
+    fusion: FusionTextures,
+}
+
+/// The connected textures under `root`: Fusion's models' tiles, native mods' sprites, then
+/// OptiFine's rules' tiles go into `sprites`, in that order. `None` without either format's files.
+pub fn load(
+    root: &Path,
+    registry: &BlockRegistry,
+    sprites: &mut Sprites,
+    models: &mut StateModels,
+    native_mods: &mut dyn FnMut(&mut Sprites),
+) -> Option<Connected> {
+    let fusion = {
+        let _step = crate::spans::startup::step("core.fusion");
+        FusionTextures::load(root, registry, sprites, models)
+    };
+    native_mods(sprites);
+    // A side's sprite, for rules that connect by tile: the first quad facing it.
+    let catalog = &*models;
+    let mut found = Vec::new();
+    let ctm = Ctm::load(
+        root,
+        registry,
+        sprites,
+        |state: BlockStateId, face: Face| {
+            let side = horizon_assets::model::Direction::ALL[face as usize];
+            catalog
+                .models_at(
+                    state,
+                    horizon_core::position::BlockPos::new(0, 0, 0),
+                    &mut found,
+                )
+                .ok()?;
+            found
+                .iter()
+                .flat_map(|m| &m.faces)
+                .find(|f| f.quad.facing == side)
+                .map(|f| f.layer)
+        },
+    );
+    let rules = Rules { ctm, fusion };
+    (!rules.is_empty()).then(|| Connected {
+        rules: Arc::new(rules),
+        mesh,
+    })
+}
+
+/// The mesher on [`Rules`].
+fn mesh(
+    mesher: &mut Mesher<'_>,
+    rules: &(dyn std::any::Any + Send + Sync),
+    region: &[[Option<&Chunk>; 3]; 3],
+    sy: i32,
+    out: SectionMesh,
+    scratch: &mut MeshScratch,
+) -> SectionMesh {
+    let rules = rules
+        .downcast_ref::<Rules>()
+        .expect("the connected textures this format loaded");
+    mesher.mesh_with(rules, region, sy, out, scratch)
+}
+
+impl ConnectedTextures for Rules {
+    fn is_empty(&self) -> bool {
+        self.ctm.is_empty() && self.fusion.is_empty()
+    }
+
+    fn stacked_pane_hides(&self, state: u32, other: u32, centre: [f32; 2]) -> bool {
+        !self.ctm.is_empty() && self.ctm.stacked_pane_hides(state, other, centre)
+    }
+
+    fn pick<'b>(
+        &self,
+        face: &engine::Face,
+        neighbour: impl Fn([i32; 3]) -> u32,
+        covers: impl Fn(u32) -> bool,
+        biome: impl Fn() -> Option<&'b str>,
+        mut overlay: impl FnMut(Overlay),
+    ) -> Pick {
+        let side = Face::ALL[usize::from(face.facing)];
+        let fused = face.rule.and_then(|rule| {
+            self.fusion.pick(
+                rule,
+                face.state,
+                side,
+                face.tint_index,
+                &neighbour,
+                covers,
+                &mut overlay,
+            )
+        });
+        if let Some(pick) = fused {
+            pick
+        } else if self.ctm.is_empty() {
+            Pick::Keep
+        } else {
+            self.ctm.pick(
+                face.state,
+                face.layer,
+                side,
+                face.pos,
+                &neighbour,
+                biome,
+                // A pane's tiles are drawn with the cube's UVs, so that is its texture.
+                || {
+                    if face.pane {
+                        Some(Axes::cube(side))
+                    } else {
+                        Axes::texture(face.positions, face.uv)
+                    }
+                },
+                &mut overlay,
+            )
+        }
+    }
+}