Merge remote-tracking branch 'upstream/main' into feat/native-shader-params

# Conflicts:
#	docs/native-mods.md

Cargo.lock

@@ -1334,6 +1334,9 @@ dependencies = [
  "log",
  "miniz_oxide 0.8.9",
  "naga",
+ "objc2 0.6.5",
+ "objc2-app-kit 0.3.2",
+ "objc2-foundation 0.3.2",
  "open",
  "png",
  "pollster",
@@ -1506,6 +1509,13 @@ dependencies = [
  "windows 0.62.2",
 ]
 
+[[package]]
+name = "horizon-optifine"
+version = "0.1.0"
+dependencies = [
+ "regex",
+]
+
 [[package]]
 name = "horizon-port-pack"
 version = "0.1.0"

Cargo.toml

@@ -30,6 +30,7 @@ members = [
     "crates/cargo-horizon-mod",
     "crates/horizon-port-pack",
     "crates/horizon-shaders",
+    "crates/horizon-optifine",
     "crates/horizon-shader-api",
     "crates/horizon-release-sign",
     "xtask",

crates/horizon-anticheat/src/lib.rs

@@ -8,12 +8,16 @@
 //! check, off. A check that fails *flags* the player: its violation level (VL) rises by the flag's
 //! weight and falls back by `decay` a second. From `setback` on, the move or action is cancelled (the
 //! player is sent back where the server last had them); from `alert` on, online operators and the
-//! console are told; from `kick` on, the player is disconnected. Nothing bans. Any threshold at 0 turns
-//! that action off.
+//! console are told; from `kick` on, the player is disconnected. A check's kicks are counted per player
+//! across sessions ([`Strikes`]), and the kick that reaches its `ban_after` bans the player instead
+//! (`banned-players.json`, reason "Horizon anticheat: <check>"). Any threshold at 0 turns that action
+//! off.
 //!
 //! The checks are written from vanilla 26.3's own rules and from what cheats are publicly described to
 //! do, never from another anticheat's code.
 
+use std::collections::BTreeMap;
+
 use serde::{Deserialize, Serialize};
 
 pub mod combat;
@@ -28,12 +32,14 @@ pub struct Actions {
     pub kick: f32,
     /// Violation level lost each second.
     pub decay: f32,
+    /// The kick, counting this check's earlier ones for the player, that bans instead; 0: never.
+    pub ban_after: u32,
 }
 
 macro_rules! checks {
     ($(
         $(#[$doc:meta])*
-        $field:ident: $Check:ident => $Config:ident [$setback:expr, $alert:expr, $kick:expr, $decay:expr] {
+        $field:ident: $Check:ident => $Config:ident [$setback:expr, $alert:expr, $kick:expr, $decay:expr, $ban_after:expr] {
             $( $(#[$xdoc:meta])* $extra:ident: $ty:ty = $default:expr, )*
         }
     )*) => {
@@ -59,6 +65,7 @@ macro_rules! checks {
                 pub alert: f32,
                 pub kick: f32,
                 pub decay: f32,
+                pub ban_after: u32,
                 $( $(#[$xdoc])* pub $extra: $ty, )*
             }
 
@@ -70,6 +77,7 @@ macro_rules! checks {
                         alert: $alert,
                         kick: $kick,
                         decay: $decay,
+                        ban_after: $ban_after,
                         $($extra: $default,)*
                     }
                 }
@@ -87,6 +95,9 @@ macro_rules! checks {
             pub alert_level: u8,
             /// Every flag, one line each, relative to the server's folder; empty: no file.
             pub log: String,
+            /// The players' kicks by check ([`Strikes`]), relative to the server's folder; empty: kept
+            /// only while the server runs.
+            pub strikes: String,
             $(pub $field: $Config,)*
         }
 
@@ -97,6 +108,7 @@ macro_rules! checks {
                     alerts: true,
                     alert_level: 2,
                     log: "logs/anticheat.log".into(),
+                    strikes: "anticheat-strikes.json".into(),
                     $($field: $Config::default(),)*
                 }
             }
@@ -112,7 +124,13 @@ macro_rules! checks {
                 match check {
                     $(Check::$Check => {
                         let c = &self.$field;
-                        Actions { setback: c.setback, alert: c.alert, kick: c.kick, decay: c.decay }
+                        Actions {
+                            setback: c.setback,
+                            alert: c.alert,
+                            kick: c.kick,
+                            decay: c.decay,
+                            ban_after: c.ban_after,
+                        }
                     })*
                 }
             }
@@ -125,7 +143,7 @@ checks! {
     /// every tick with ServerboundClientTickEndPacket, at the server's tick rate; each one spends a tick's
     /// time from a balance that wall-clock time fills, capped so a pause can't be saved up for a burst.
     /// It logs only by default; once trusted: `setback = 2`, `alert = 5`, `kick = 20`.
-    timer: Timer => TimerConfig [0.0, 0.0, 0.0, 0.02] {
+    timer: Timer => TimerConfig [0.0, 0.0, 0.0, 0.02, 0] {
         /// How far ahead of the clock, in milliseconds, a client may get before it is flagged.
         tolerance_ms: f64 = 300.0,
         /// The most time, in milliseconds, a quiet connection banks for the ticks that follow (a lag
@@ -135,9 +153,12 @@ checks! {
 
     /// Ground: a move that says it ends on the ground with nothing there to stand on: no-fall (claiming
     /// the ground to skip fall damage) and walking on water. The claim is dropped, so vanilla's
-    /// fall damage follows; from `setback` on the player is also sent back. Logging only (`setback = 0`,
-    /// the default), the claim stands. Once trusted: `setback = 5`, `alert = 15`, `kick = 60`.
-    ground: Ground => GroundConfig [0.0, 0.0, 0.0, 2.0] {}
+    /// fall damage follows (the player is never sent back: `setback = 0` makes the check log only), and
+    /// a player that keeps claiming is kicked, then banned at the second kick (`ban_after = 2`). A claim standing still isn't
+    /// judged (no fall to skip). On the official server's first two hours (67 players), every player who
+    /// wasn't flying or walking on water peaked at level 7 (4 claims standing still in one second); the
+    /// ones who were, at 113 to 3749.
+    ground: Ground => GroundConfig [10.0, 15.0, 30.0, 2.0, 2] {}
 
     /// Prediction: each move played again from the client's own inputs with vanilla's movement code,
     /// and compared (speed, step, fly, jesus...). Each player's client ticks are recorded
@@ -149,7 +170,7 @@ checks! {
     /// a chunk the client doesn't have, a riptide launch) is excused, and so are the ticks after it
     /// until the moves agree again. It logs only by default; once trusted: `setback = 5`, `alert = 15`,
     /// `kick = 60`.
-    prediction: Prediction => PredictionConfig [0.0, 0.0, 0.0, 2.0] {
+    prediction: Prediction => PredictionConfig [0.0, 0.0, 0.0, 2.0, 0] {
         /// How far, in blocks, a move may land from where the replay puts it.
         tolerance: f64 = 0.03,
     }
@@ -157,8 +178,9 @@ checks! {
     /// Combat: attacks vanilla's client can't send (`combat`): one with no swing after it (a kill aura
     /// that hides its swing), or a second entity attacked in the same client tick (vanilla attacks the
     /// one entity under the crosshair, picked once a tick). Each flags once; from `setback` on the
-    /// player's attacks are dropped. A vanilla client never trips it, so it acts by default.
-    combat: Combat => CombatConfig [2.0, 5.0, 20.0, 0.5] {}
+    /// player's attacks are dropped. A vanilla client never trips it, so it acts by default: the first
+    /// kick warns, the second bans (`ban_after = 2`).
+    combat: Combat => CombatConfig [2.0, 5.0, 20.0, 0.5, 2] {}
 }
 
 /// How many checks there are.
@@ -207,6 +229,33 @@ impl Config {
     }
 }
 
+/// How many times each check kicked each player, kept across sessions (`strikes`, a JSON object of
+/// players' UUIDs to check names to counts): the kick that reaches a check's `ban_after` is a ban.
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+#[serde(transparent)]
+pub struct Strikes(pub BTreeMap<String, BTreeMap<String, u32>>);
+
+impl Strikes {
+    /// Player `uuid` was kicked by `check`: its kicks by it so far, this one included, and whether this
+    /// one bans. A ban starts the count again, so a player an operator pardons is kicked before the
+    /// next ban.
+    pub fn kick(&mut self, uuid: &str, check: Check, ban_after: u32) -> (u32, bool) {
+        let count = self
+            .0
+            .entry(uuid.to_owned())
+            .or_default()
+            .entry(check.name().to_owned())
+            .or_default();
+        *count = count.saturating_add(1);
+        let kicks = *count;
+        let ban = ban_after > 0 && kicks >= ban_after;
+        if ban {
+            *count = 0;
+        }
+        (kicks, ban)
+    }
+}
+
 /// What a flag leads to.
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
 pub struct Verdict {
@@ -277,14 +326,19 @@ mod tests {
     }
 
     #[test]
-    fn on_by_default_but_only_combat_acts() {
+    fn on_by_default_but_only_combat_and_ground_act() {
         let c = Config::from_server_toml("[server]\nport = 25565\n").unwrap();
         assert_eq!(c, Config::default());
         for &check in Check::ALL {
             assert!(c.runs(check), "{}", check.name());
             let a = c.actions(check);
             let acts = [a.setback, a.alert, a.kick] != [0.0; 3];
-            assert_eq!(acts, check == Check::Combat, "{}", check.name());
+            assert_eq!(
+                acts,
+                matches!(check, Check::Combat | Check::Ground),
+                "{}",
+                check.name()
+            );
         }
         let off = Config::from_server_toml("[anticheat]\nenabled = false\n").unwrap();
         assert!(Check::ALL.iter().all(|&check| !off.runs(check)));
@@ -336,6 +390,25 @@ mod tests {
         assert!(v.kick && v.alert);
     }
 
+    #[test]
+    fn the_kick_that_reaches_ban_after_bans() {
+        let c = Config::default();
+        assert_eq!(c.actions(Check::Combat).ban_after, 2);
+        assert_eq!(c.actions(Check::Prediction).ban_after, 0);
+        let mut s = Strikes::default();
+        assert_eq!(s.kick("a", Check::Combat, 2), (1, false));
+        // Another player, another check: their own counts.
+        assert_eq!(s.kick("b", Check::Combat, 2), (1, false));
+        assert_eq!(s.kick("a", Check::Timer, 2), (1, false));
+        assert_eq!(s.kick("a", Check::Combat, 2), (2, true));
+        // Pardoned, the player is kicked once more before the next ban.
+        assert_eq!(s.kick("a", Check::Combat, 2), (1, false));
+        // 0 never bans; 1 bans at the first kick.
+        assert_eq!(s.kick("c", Check::Timer, 0), (1, false));
+        assert_eq!(s.kick("c", Check::Timer, 0), (2, false));
+        assert_eq!(s.kick("d", Check::Ground, 1), (1, true));
+    }
+
     #[test]
     fn zero_turns_an_action_off() {
         let mut c = on();

crates/horizon-client-input/src/interaction_input.rs

@@ -81,6 +81,19 @@ impl InteractionInput {
     }
 }
 
+/// The sentence of `Minecraft.handleKeybinds` that follows a key which opened
+/// a screen: `Gui.setScreen` has already run `KeyMapping.releaseAll()`, so
+/// `key.use` reads up and the same call releases an active use
+/// (`player.isUsingItem() && !keyUse.isDown()` → `MultiPlayerGameMode.releaseUsingItem`).
+/// Only the screens opened from the keybinds do this (the inventory, chat and
+/// advancements); the pause menu, server containers, mount inventories and
+/// dialogs release on the first tick after closing instead, as vanilla does.
+pub fn release_on_screen_open(world: &mut impl InteractionWorld) {
+    if world.using_item() {
+        world.release_using();
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/horizon-client-render/src/block_entity_render.rs

@@ -885,25 +885,26 @@ impl BlockEntityRenderer {
         let mut renderer = Self::new(models, registry);
         renderer.visibility = Some(Mutex::new(visibility));
         // Sherd items: provides_pottery_pattern -> decorated_pot_pattern asset id.
-        if let Ok(bytes) = std::fs::read(root.join("items.json")) {
-            let items: Value = serde_json::from_slice(&bytes)?;
-            for (item, components) in items.as_object().into_iter().flatten() {
-                let Some(pattern) = components["minecraft:provides_pottery_pattern"].as_str()
-                else {
-                    continue;
-                };
-                let name = pattern.strip_prefix("minecraft:").unwrap_or(pattern);
-                let file = root.join(format!("data/minecraft/decorated_pot_pattern/{name}.json"));
-                let Ok(def) = std::fs::read(file) else {
-                    continue;
-                };
-                let def: Value = serde_json::from_slice(&def)?;
-                if let Some(asset) = def["asset_id"].as_str() {
-                    let asset = asset.strip_prefix("minecraft:").unwrap_or(asset);
-                    renderer
-                        .pot_patterns
-                        .insert(item.clone(), format!("entity/decorated_pot/{asset}"));
-                }
+        let items = match horizon_world::item_defaults::read(root) {
+            Ok(items) => items,
+            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Default::default(),
+            Err(e) => return Err(e.into()),
+        };
+        for (item, components) in &items {
+            let Some(pattern) = components["minecraft:provides_pottery_pattern"].as_str() else {
+                continue;
+            };
+            let name = pattern.strip_prefix("minecraft:").unwrap_or(pattern);
+            let file = root.join(format!("data/minecraft/decorated_pot_pattern/{name}.json"));
+            let Ok(def) = std::fs::read(file) else {
+                continue;
+            };
+            let def: Value = serde_json::from_slice(&def)?;
+            if let Some(asset) = def["asset_id"].as_str() {
+                let asset = asset.strip_prefix("minecraft:").unwrap_or(asset);
+                renderer
+                    .pot_patterns
+                    .insert(item.clone(), format!("entity/decorated_pot/{asset}"));
             }
         }
         Ok(renderer)

crates/horizon-client-render/src/chunk/block_entity.rs

@@ -291,11 +291,19 @@ pub struct Beacon {
 }
 #[derive(Clone, Debug, Default)]
 pub struct Jukebox {
-    pub record: Option<ItemStack>,
+    /// `JukeboxBlockEntity`'s one slot (`ContainerSingleItem`), so a hopper or
+    /// a dropper reaches it as it reaches any container.
+    pub items: [Option<ItemStack>; 1],
     /// `ticks_since_song_started`, while a song plays.
     pub ticks: i64,
     pub playing: bool,
 }
+impl Jukebox {
+    /// `JukeboxBlockEntity.getTheItem`: the disc it holds.
+    pub fn record(&self) -> Option<&ItemStack> {
+        self.items[0].as_ref()
+    }
+}
 /// `BrewingStandBlockEntity` state. Slots: 0-2 bottles, 3 ingredient, 4 fuel.
 #[derive(Clone, Debug, Default)]
 pub struct BrewingStand {

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

@@ -421,7 +421,7 @@ impl BlockEntity {
             Self::Furnace(f) => f.items.iter().flatten().cloned().collect(),
             Self::Brewing(b) => b.items.iter().flatten().cloned().collect(),
             Self::Sign(_) => Vec::new(),
-            Self::Jukebox(j) => j.record.iter().cloned().collect(),
+            Self::Jukebox(j) => j.items.iter().flatten().cloned().collect(),
             Self::Beacon(_)
             | Self::CreakingHeart(_)
             | Self::Spawner(_)
@@ -454,7 +454,6 @@ impl BlockEntity {
             Self::Furnace(f) => &f.items,
             Self::Brewing(b) => &b.items,
             Self::Sign(_)
-            | Self::Jukebox(_)
             | Self::Beacon(_)
             | Self::Lectern(_)
             | Self::Sculk(_)
@@ -468,6 +467,7 @@ impl BlockEntity {
             | Self::TestInstanceBlock(_)
             | Self::DaylightDetector
             | Self::Brushable(_) => &[],
+            Self::Jukebox(j) => &j.items,
             Self::Crafter(c) => &c.items,
             Self::ChiseledBookshelf(b) => &b.items,
             Self::Shelf(b) => &b.items,
@@ -488,7 +488,6 @@ impl BlockEntity {
             Self::Furnace(f) => &mut f.items,
             Self::Brewing(b) => &mut b.items,
             Self::Sign(_)
-            | Self::Jukebox(_)
             | Self::Beacon(_)
             | Self::Lectern(_)
             | Self::Sculk(_)
@@ -502,6 +501,7 @@ impl BlockEntity {
             | Self::TestInstanceBlock(_)
             | Self::DaylightDetector
             | Self::Brushable(_) => &mut [],
+            Self::Jukebox(j) => &mut j.items,
             Self::Crafter(c) => &mut c.items,
             Self::ChiseledBookshelf(b) => &mut b.items,
             Self::Shelf(b) => &mut b.items,
@@ -645,6 +645,26 @@ mod tests {
         assert_eq!(fifth.count, 1);
     }
 
+    /// `JukeboxBlockEntity`'s single slot is a `Container` slot, so a hopper
+    /// (`HopperBlockEntity.getContainerAt`) can reach the disc in it.
+    #[test]
+    fn a_jukebox_offers_its_record_as_its_one_container_slot() {
+        let mut entity = BlockEntity::Jukebox(Jukebox::default());
+        assert_eq!(entity.slots().len(), 1);
+        assert!(entity.slots()[0].is_none(), "empty until a disc lands");
+        let disc = ItemStack::new("minecraft:cat", 1);
+        entity.slots_mut()[0] = Some(disc.clone());
+        let slots = entity.slots();
+        assert_eq!(slots[0].as_ref().map(|s| &*s.item), Some("minecraft:cat"));
+        match &entity {
+            BlockEntity::Jukebox(j) => {
+                assert_eq!(j.record().map(|s| &*s.item), Some("minecraft:cat"));
+            }
+            _ => panic!("a jukebox"),
+        }
+        assert_eq!(entity.contents().len(), 1);
+    }
+
     /// A whole amount pays itself without a draw; a fraction is a chance of one more.
     #[test]
     fn create_experience_rounds_the_fraction_by_chance() {

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

@@ -331,6 +331,11 @@ pub struct Frame<'a> {
     /// (`crate::camera::spinning_effect_matrix`), not the hand's.
     pub spin: Mat4,
     pub sky: Sky,
+    /// Block edits and chunk membership that can change the shader pack's shadow map.
+    pub shadow_scene_revision: (u64, u64),
+    /// Opt-in reuse of the shader pack's last shadow map when the key still matches
+    /// (`horizon-graphics.txt` `shadowCache`; off by default).
+    pub shadow_cache: bool,
     /// Render distance in blocks (fog end).
     pub distance: f32,
     /// Full-detail terrain distance in blocks; distant LODs bypass the cave graph.
@@ -475,6 +480,9 @@ pub struct ScreenshotRequest {
     /// `GameRenderer.takeAutoScreenshot`: centre-crop the frame to a square
     /// and average it down to this size. `None` saves the frame as drawn.
     pub size: Option<[u32; 2]>,
+    /// F2's: drawn at the game's resolution (Resolution Scale above 100%) times
+    /// `Renderer::screenshot_quality`, not the window's.
+    pub scaled: bool,
 }
 pub struct Renderer {
     instance: wgpu::Instance,
@@ -489,6 +497,9 @@ pub struct Renderer {
     offscreen: Option<wgpu::Texture>,
     /// Offscreen submissions still on the GPU: at most two frames run ahead.
     in_flight: std::collections::VecDeque<wgpu::SubmissionIndex>,
+    /// Splitscreen: the caller waits for the GPU once every player has submitted
+    /// (`wait_in_flight`), so one player's work overlaps the GPU drawing another's.
+    pub paced_elsewhere: bool,
     /// Which steps of the first frame on this device still go to the log
     /// (see `startup_step`).
     first_frame: FirstFrame,
@@ -511,6 +522,9 @@ pub struct Renderer {
     window: Arc<Window>,
     pub device: wgpu::Device,
     pub queue: wgpu::Queue,
+    /// Set by the device's lost callback. wgpu reports nothing else when an
+    /// operation fails on a lost device (no error scope sees it).
+    device_lost: Arc<std::sync::atomic::AtomicBool>,
     pub config: wgpu::SurfaceConfiguration,
     solid: wgpu::RenderPipeline,
     translucent: wgpu::RenderPipeline,
@@ -593,9 +607,11 @@ pub struct Renderer {
     group: wgpu::BindGroup,
     globals: wgpu::Buffer,
     lightmap: wgpu::Texture,
-    /// The block sprites, [`SPRITE_SPLIT`] layers per array (the first is
+    /// The block sprites, `sprite_split` layers per array (the first is
     /// `sprites` in terrain.wgsl, the others `sprites_1`...).
     sprite_textures: Vec<wgpu::Texture>,
+    /// Block sprite layers per array on this device ([`layer_split`]).
+    sprite_split: u32,
     /// A 1-layer array bound where a pack needs fewer arrays.
     sprite_unused: wgpu::TextureView,
     mip_levels: u32,
@@ -728,6 +744,10 @@ pub struct Renderer {
     /// first gets the swapchain a fresh configuration; later ones reattach
     /// the window, as a lost surface does.
     acquire_validation_failures: u32,
+    /// A surface from `recreate_surface` whose configuration failed. wgpu
+    /// panics when such a surface is acquired from (it never had one that
+    /// worked), so frames configure it again first and skip until it takes.
+    surface_unconfigured: bool,
     pub drawn_sections: usize,
     /// Last frame's section draws (face ranges and translucent sections),
     /// and the draw calls the backend issued for them.
@@ -739,6 +759,12 @@ pub struct Renderer {
     pub screenshot: Option<ScreenshotRequest>,
     /// Outcome of the last screenshot: frame size, or the error.
     pub screenshot_result: Option<std::result::Result<[u32; 2], String>>,
+    /// Screenshot Quality (Horizon setting): a `scaled` screenshot's frame is this many
+    /// times the game's resolution (1, 2, 4 or 8).
+    pub screenshot_quality: u32,
+    /// How many times the pending scaled screenshot ran out of video memory: each
+    /// halves its size, down to the window's.
+    screenshot_halvings: u32,
     /// Brightness option (lightmap gamma), 0..1.
     pub gamma: f32,
     /// Optional full-light lightmap (Horizon Extras).
@@ -753,18 +779,45 @@ pub struct Renderer {
 }
 /// Every layer's mip levels, layer major (`first` is the first layer's
 /// index into `settings`), made by `MipmapGenerator`.
-/// Block sprite layers per texture array: the smallest
-/// `max_texture_array_layers` of the GPUs Horizon runs on. Mods add sprites
-/// past it into more arrays (terrain.wgsl's `sprite`).
+/// Block sprite layers per texture array at most: the
+/// `max_texture_array_layers` of most GPUs. Mods add sprites past it into more
+/// arrays (terrain.wgsl's `sprite`); a GPU with fewer layers per array gets a
+/// smaller split ([`layer_split`]).
 pub(crate) const SPRITE_SPLIT: u32 = 2048;
-/// [`SPRITE_SPLIT`], or a smaller split from `HORIZON_SPRITE_SPLIT` (dev
-/// only: vanilla's sprites drawn from several arrays must look the same).
-fn sprite_split() -> u32 {
+/// A smaller split from `HORIZON_SPRITE_SPLIT` (dev only: vanilla's sprites
+/// drawn from several arrays must look the same).
+fn requested_split() -> Option<u32> {
     std::env::var("HORIZON_SPRITE_SPLIT")
         .ok()
         .and_then(|v| v.parse().ok())
         .filter(|&n| (1..=SPRITE_SPLIT).contains(&n))
-        .unwrap_or(SPRITE_SPLIT)
+}
+/// The split the CPU mip chains are cut by before the adapter is known.
+fn sprite_split() -> u32 {
+    requested_split().unwrap_or(SPRITE_SPLIT)
+}
+/// The block sprite layers per texture array on an adapter that holds
+/// `max_layers` layers per array: [`SPRITE_SPLIT`], `requested`
+/// (`HORIZON_SPRITE_SPLIT`) or `max_layers`, whichever is smallest, with a full
+/// array still fitting once [`array_layers`] pads it for OpenGL. Errors when
+/// `layers` sprites need more than the [`SPRITE_ARRAYS`] arrays terrain.wgsl binds.
+fn layer_split(
+    max_layers: u32,
+    gl: bool,
+    requested: Option<u32>,
+    layers: u32,
+) -> std::result::Result<u32, String> {
+    let mut split = requested.unwrap_or(SPRITE_SPLIT).min(max_layers).max(1);
+    if split > 1 && array_layers(split, gl) > max_layers {
+        split -= 1;
+    }
+    if layers > split * SPRITE_ARRAYS {
+        return Err(format!(
+            "GPU supports {max_layers} texture layers per array; {layers} block textures need \
+             more than the {SPRITE_ARRAYS} arrays of {split} Horizon draws from"
+        ));
+    }
+    Ok(split)
 }
 /// Sprite arrays terrain.wgsl binds (`sprites`, `sprites_1`...).
 const SPRITE_ARRAYS: u32 = 8;
@@ -867,6 +920,8 @@ fn terrain_group(
 /// construction so the temporary mip chains are released after GPU upload.
 pub struct PreparedTextures {
     sprites: Vec<(Vec<u8>, u32)>,
+    /// The sprite layers per array `sprites` is cut by.
+    split: u32,
     forcefield: (Vec<u8>, u32),
 }
 impl PreparedTextures {
@@ -898,9 +953,33 @@ impl PreparedTextures {
                     mip_chain(&pixels[start..], size, settings, first, count)
                 })
                 .collect(),
+            split,
             forcefield: mip_chain(forcefield.0, forcefield.1, &[], 0, 1),
         }
     }
+
+    /// The same mip chains cut by `split` layers per array: chains made before
+    /// the adapter was known, for a GPU with fewer layers per array.
+    fn resplit(mut self, layers: u32, split: u32) -> Self {
+        if self.split == split || layers <= split.min(self.split) {
+            self.split = split;
+            return self;
+        }
+        let levels = self.sprites[0].1;
+        let all: Vec<u8> = self
+            .sprites
+            .drain(..)
+            .flat_map(|(bytes, _)| bytes)
+            .collect();
+        // Every layer's mip levels are contiguous (layer major).
+        let layer_bytes = all.len() / layers as usize;
+        self.sprites = all
+            .chunks(layer_bytes * split as usize)
+            .map(|chunk| (chunk.to_vec(), levels))
+            .collect();
+        self.split = split;
+        self
+    }
 }
 
 fn mip_chain(
@@ -1039,6 +1118,7 @@ struct Opened {
     adapter: wgpu::Adapter,
     device: wgpu::Device,
     queue: wgpu::Queue,
+    device_lost: Arc<std::sync::atomic::AtomicBool>,
 }
 /// Logs the adapter and records it for telemetry and crash reports.
 fn describe_adapter(adapter: &wgpu::Adapter) {
@@ -1068,16 +1148,13 @@ fn describe_adapter(adapter: &wgpu::Adapter) {
 }
 /// Whether an adapter's texture arrays hold the block textures Horizon puts
 /// in one array.
-fn check_layers(limits: &wgpu::Limits, layers: u32) -> Result<()> {
-    let needed = layers.min(sprite_split());
-    if limits.max_texture_array_layers < needed {
-        return Err(format!(
-            "GPU supports {} texture layers; {needed} required",
-            limits.max_texture_array_layers
-        )
-        .into());
-    }
-    Ok(())
+fn check_layers(adapter: &wgpu::Adapter, layers: u32) -> Result<u32> {
+    Ok(layer_split(
+        adapter.limits().max_texture_array_layers,
+        adapter.get_info().backend == wgpu::Backend::Gl,
+        requested_split(),
+        layers,
+    )?)
 }
 /// Whether the swapchain can take a window of `width` x `height`: each side from 1 to the
 /// device's `max_texture_dimension_2d` (`max`), else `Surface::configure` panics. 0 is a
@@ -1248,7 +1325,7 @@ async fn open_backend(
     describe_adapter(&adapter);
     let info = adapter.get_info();
     let limits = adapter.limits();
-    if let Err(e) = check_layers(&limits, layers) {
+    if let Err(e) = check_layers(&adapter, layers) {
         return Err(NoDevice::Failed(format!("{name}: {e}")));
     }
     // Mappable primary buffers: section pages that no longer fit in
@@ -1300,13 +1377,28 @@ async fn open_backend(
         None => adapter.request_device(&desc).await,
     };
     match opened {
-        Ok((device, queue)) => Ok(Opened {
-            instance,
-            surface,
-            adapter,
-            device,
-            queue,
-        }),
+        Ok((device, queue)) => {
+            let device_lost = Arc::new(std::sync::atomic::AtomicBool::new(false));
+            let lost = device_lost.clone();
+            device.set_device_lost_callback(move |reason, message| {
+                // A device destroyed on purpose was not lost.
+                if reason == wgpu::DeviceLostReason::Destroyed {
+                    return;
+                }
+                log::warn!(
+                    "Horizon renderer: the graphics device was lost ({reason:?}: {message})"
+                );
+                lost.store(true, std::sync::atomic::Ordering::Relaxed);
+            });
+            Ok(Opened {
+                instance,
+                surface,
+                adapter,
+                device,
+                queue,
+                device_lost,
+            })
+        }
         Err(e) => Err(NoDevice::Failed(format!("{name} device: {e}"))),
     }
 }
@@ -1397,27 +1489,20 @@ impl Renderer {
         previous: Option<&Self>,
         api: GraphicsApi,
     ) -> Result<Self> {
-        let split = sprite_split();
-        if layers > split * SPRITE_ARRAYS {
-            return Err(format!(
-                "{layers} block textures; Horizon draws at most {}",
-                split * SPRITE_ARRAYS
-            )
-            .into());
-        }
         let Opened {
             instance,
             surface,
             adapter,
             device,
             queue,
+            device_lost,
         } = match previous {
             // Reload resources on the same device; replacing live Vulkan
             // devices can invalidate the driver's swapchain state on the same
             // window.
             Some(renderer) => {
                 describe_adapter(&renderer.adapter);
-                check_layers(&renderer.adapter.limits(), layers)?;
+                check_layers(&renderer.adapter, layers)?;
                 Opened {
                     surface: if offscreen {
                         None
@@ -1436,10 +1521,17 @@ impl Renderer {
                     adapter: renderer.adapter.clone(),
                     device: renderer.device.clone(),
                     queue: renderer.queue.clone(),
+                    device_lost: renderer.device_lost.clone(),
                 }
             }
             None => open_device(&window, offscreen, api, layers).await?,
         };
+        // Computed once: the sprite arrays, the shaders' constants and the
+        // shader pack atlas all cut the sprites by it.
+        let split = check_layers(&adapter, layers)?;
+        if split < sprite_split() {
+            log::info!("Horizon: {split} block textures per array (the GPU's limit)");
+        }
         let info = adapter.get_info();
         crate::graphics::suggest_reduced_far_detail(crate::graphics::lod_capped(&info));
         let size = window.inner_size();
@@ -1817,9 +1909,17 @@ impl Renderer {
             usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
             mapped_at_creation: false,
         });
-        let prepared = prepared.unwrap_or_else(|| {
-            PreparedTextures::new(sprite_pixels, sprite_size, layers, sprite_mips, forcefield)
-        });
+        let prepared = match prepared {
+            Some(prepared) => prepared.resplit(layers, split),
+            None => PreparedTextures::with_split(
+                sprite_pixels,
+                sprite_size,
+                layers,
+                sprite_mips,
+                forcefield,
+                split,
+            ),
+        };
         let mut mip_levels = 1;
         let gl = adapter.get_info().backend == wgpu::Backend::Gl;
         let sprite_textures: Vec<wgpu::Texture> = prepared
@@ -2399,10 +2499,13 @@ impl Renderer {
             alpha_blend,
             true,
         );
-        // RenderPipelines.TEXT_SEE_THROUGH: translucent, no depth test or writes.
+        // RenderPipelines.TEXT_SEE_THROUGH: translucent, no depth test or
+        // writes, culled like every world text pipeline (TEXT_SNIPPET keeps
+        // RenderPipeline.Builder's default): a name tag or text display hides
+        // its back.
         let see_through_pipeline = entity_pipeline(
             "See-through text",
-            None,
+            Some(wgpu::Face::Back),
             false,
             wgpu::CompareFunction::Always,
             Default::default(),
@@ -2410,10 +2513,11 @@ impl Renderer {
             false,
         );
         // RenderPipelines.TEXT_POLYGON_OFFSET: a text display's text and
-        // background win against the surface they lie on (bias 1, 10).
+        // background win against the surface they lie on (bias 1, 10), from
+        // the front only.
         let text_polygon_offset_pipeline = entity_pipeline(
             "Polygon offset text",
-            None,
+            Some(wgpu::Face::Back),
             true,
             wgpu::CompareFunction::GreaterEqual,
             wgpu::DepthBiasState {
@@ -2984,6 +3088,7 @@ impl Renderer {
             spare_surface: std::sync::Mutex::new(None),
             offscreen,
             in_flight: std::collections::VecDeque::new(),
+            paced_elsewhere: false,
             first_frame: if previous.is_none() {
                 FirstFrame::Acquire
             } else {
@@ -2997,6 +3102,7 @@ impl Renderer {
             window,
             device,
             queue,
+            device_lost,
             config,
             solid,
             translucent,
@@ -3067,6 +3173,7 @@ impl Renderer {
             mipmaps: mip_levels - 1,
             terrain_layout: bindings,
             terrain_sprites: sprite_constants.map(|(_, v)| v),
+            sprite_split: split,
             sprite_sampler,
             texture_filtering: 0,
             max_anisotropy: 1,
@@ -3138,6 +3245,7 @@ impl Renderer {
             info,
             suspended: !drawable_size(size.width, size.height, max_side),
             acquire_validation_failures: 0,
+            surface_unconfigured: false,
             drawn_sections: 0,
             section_draws: 0,
             section_draw_calls: 0,
@@ -3145,6 +3253,8 @@ impl Renderer {
             started: Instant::now(),
             screenshot: None,
             screenshot_result: None,
+            screenshot_quality: 1,
+            screenshot_halvings: 0,
             gamma: 0.5,
             improved_transparency: false,
             oit: None,
@@ -3223,12 +3333,19 @@ impl Renderer {
             Some(surface) => surface,
             None => self.instance.create_surface(self.window.clone())?,
         };
-        Self::configure(
+        let configured = Self::configure(
             &self.device,
             &surface,
             &self.surface_config(),
             self.hdr.as_ref(),
+            &self.device_lost,
         );
+        if let Err(e) = &configured {
+            log::warn!(
+                "Horizon renderer: the new window surface did not configure ({e}); retrying"
+            );
+        }
+        self.surface_unconfigured = configured.is_err();
         self.surface = Some(surface);
         Ok(())
     }
@@ -3283,16 +3400,9 @@ impl Renderer {
             Some(PresentMode::Immediate) => wgpu::PresentMode::Immediate,
             _ => wgpu::PresentMode::Fifo,
         };
-        if self.config.present_mode != mode
-            && let Some(surface) = &self.surface
-        {
+        if self.config.present_mode != mode && self.surface.is_some() {
             self.config.present_mode = mode;
-            Self::configure(
-                &self.device,
-                surface,
-                &self.surface_config(),
-                self.hdr.as_ref(),
-            );
+            self.configure_surface();
         }
     }
     /// Follows the window to `width` x `height`. A size the swapchain can't take
@@ -3305,13 +3415,8 @@ impl Renderer {
         }
         self.config.width = width;
         self.config.height = height;
-        if let Some(surface) = &self.surface {
-            Self::configure(
-                &self.device,
-                surface,
-                &self.surface_config(),
-                self.hdr.as_ref(),
-            );
+        if self.surface.is_some() {
+            self.configure_surface();
         } else {
             self.offscreen = Some(Self::offscreen_target(&self.device, &self.config));
         }
@@ -3568,6 +3673,64 @@ impl Renderer {
         self.arena
             .release(s.page, s.start, u64::from(s.solid + s.translucent) * 4);
     }
+    /// Video memory the arena keeps because fragmentation holds its pages
+    /// partly used (a render distance that went down, far tiles that were
+    /// replaced): moves the meshes off the sparsest page, a few MiB a frame,
+    /// and `Arena::trim` returns the page once it is empty. Frames with the
+    /// arena in system memory (video memory full) are slow, so this is what
+    /// keeps the terrain in video memory.
+    fn compact_arena(&mut self) {
+        // Copied per frame: a page empties over a few frames, with no hitch.
+        const BUDGET: u64 = 32 << 20;
+        if self.arena.closing().is_none()
+            && let Some(page) = self.arena.sparsest()
+        {
+            self.arena.close(page);
+        }
+        let Some(page) = self.arena.closing() else {
+            return;
+        };
+        let stride = std::mem::size_of::<TerrainVertex>() as u64;
+        let mut budget = BUDGET;
+        let encoder = self.section_copies.get_or_insert_with(|| {
+            self.device
+                .create_command_encoder(&wgpu::CommandEncoderDescriptor {
+                    label: Some("Section uploads"),
+                })
+        });
+        let meshes = self
+            .sections
+            .values_mut()
+            .chain(self.lods.values_mut().flat_map(|tile| tile.meshes_mut()));
+        for s in meshes.filter(|s| s.page == page) {
+            let vertices = u64::from(s.solid + s.translucent) * 4;
+            if vertices * stride > budget {
+                break;
+            }
+            let Some(to) = self.arena.alloc_moved(vertices) else {
+                // The other pages have no room after all.
+                self.arena.reopen();
+                return;
+            };
+            self.arena.copy(encoder, (s.page, s.start), to, vertices);
+            self.arena.release(s.page, s.start, vertices);
+            if let (Some(flat), Some(id)) = (&mut self.flat, s.flat_id) {
+                flat.remove(id);
+                s.flat_id = Some(flat.add(
+                    &self.device,
+                    encoder,
+                    &mut self.section_uploads,
+                    to.0,
+                    to.1,
+                    vertices,
+                ));
+            }
+            (s.page, s.start) = to;
+            budget -= vertices * stride;
+        }
+        // With every mesh moved off, the page stays closed so this frame's
+        // uploads can't refill it: `trim` returns it and clears `closing`.
+    }
     /// Block-entity blocks of every meshed section (see `SectionMesh::block_entities`).
     pub fn block_entities(&self) -> impl Iterator<Item = &([i32; 3], u32)> {
         self.block_entities.values().flatten()
@@ -3745,14 +3908,26 @@ impl Renderer {
     }
     /// Horizon's resolution scale (world pixels per window pixel) and FXAA.
     /// Configures `surface` and, while HDR output is on, sends its HDR metadata
-    /// again: a new swapchain starts without it.
+    /// again: a new swapchain starts without it. Errs when `surface` was left
+    /// unconfigured (a validation error, or a lost device, which wgpu reports
+    /// to no error scope).
     fn configure(
         device: &wgpu::Device,
         surface: &wgpu::Surface<'_>,
         config: &wgpu::SurfaceConfiguration,
         hdr: Option<&hdr::Hdr>,
-    ) {
+        device_lost: &std::sync::atomic::AtomicBool,
+    ) -> std::result::Result<(), String> {
+        let validation = device.push_error_scope(wgpu::ErrorFilter::Validation);
+        let memory = device.push_error_scope(wgpu::ErrorFilter::OutOfMemory);
         surface.configure(device, config);
+        let memory = pollster::block_on(memory.pop());
+        if let Some(e) = memory.or(pollster::block_on(validation.pop())) {
+            return Err(e.to_string());
+        }
+        if device_lost.load(std::sync::atomic::Ordering::Relaxed) {
+            return Err("the graphics device was lost".into());
+        }
         if let Some(hdr) = hdr {
             horizon_hdr::set_metadata(
                 device,
@@ -3762,15 +3937,21 @@ impl Renderer {
                 hdr.black,
             );
         }
+        Ok(())
     }
+    /// Configures the window surface again. One that fails is still the one
+    /// wgpu configured before, which acquisition reports as a validation error.
     fn configure_surface(&self) {
-        if let Some(surface) = &self.surface {
-            Self::configure(
+        if let Some(surface) = &self.surface
+            && let Err(e) = Self::configure(
                 &self.device,
                 surface,
                 &self.surface_config(),
                 self.hdr.as_ref(),
-            );
+                &self.device_lost,
+            )
+        {
+            log::warn!("Horizon renderer: the window surface did not configure ({e})");
         }
     }
     /// HDR calibration's test picture (`crate::hdr_calibration`) while it runs, else None.
@@ -4057,7 +4238,7 @@ impl Renderer {
                 &self.device,
                 &mut encoder,
                 &self.sprite_textures,
-                sprite_split(),
+                self.sprite_split,
                 layers,
                 self.sprite_textures[0].width(),
             );
@@ -4280,7 +4461,11 @@ impl Renderer {
         }
     }
     pub fn render(&mut self, frame: &Frame) -> Result<bool> {
-        let rendered = self.draw_frame(frame);
+        let scaled = self.screenshot_size();
+        let rendered = match scaled {
+            Some(size) => self.draw_scaled_frame(frame, size),
+            None => self.draw_frame(frame, None),
+        };
         // A frame that was not drawn still submits the section copies and
         // atlas patches (glyphs, skins, maps), which the caller already took.
         if !matches!(rendered, Ok(true)) && !frame.hud.patches.is_empty() {
@@ -4303,10 +4488,76 @@ impl Renderer {
         } else if let Some(copies) = self.take_section_copies() {
             self.queue.submit([copies]);
         }
-        rendered
+        // A scaled screenshot's frame never reached the window.
+        rendered.map(|drawn| drawn && scaled.is_none())
     }
-    fn draw_frame(&mut self, frame: &Frame) -> Result<bool> {
+    /// The frame size of the pending `scaled` screenshot when it is larger than the
+    /// window: the window's times the Resolution Scale (when above 100%) and
+    /// `screenshot_quality`, cut down to what one texture and one readback buffer hold,
+    /// and halved for each time it ran out of video memory.
+    fn screenshot_size(&self) -> Option<[u32; 2]> {
+        let request = self.screenshot.as_ref()?;
+        if !request.scaled || request.size.is_some() || self.suspended {
+            return None;
+        }
+        let window = [self.config.width, self.config.height];
+        let limits = self.device.limits();
+        let factor = scaled_screenshot_factor(
+            window,
+            self.world_post.scale,
+            self.screenshot_quality,
+            limits.max_texture_dimension_2d,
+            limits.max_buffer_size,
+        ) / 2f32.powi(self.screenshot_halvings as i32);
+        (factor > 1.0).then(|| window.map(|side| (side as f32 * factor) as u32))
+    }
+    /// Draws one frame at `size` into a texture of its own, for the pending screenshot:
+    /// every pass sizes itself by `config`, which says `size` for this frame, the HUD
+    /// keeps its layout at a larger scale, and the world is drawn at `size` (a Resolution
+    /// Scale below 100% stays as low). The window keeps its last frame.
+    fn draw_scaled_frame(&mut self, frame: &Frame, size: [u32; 2]) -> Result<bool> {
+        let window = [self.config.width, self.config.height];
+        let mut config = self.config.clone();
+        [config.width, config.height] = size;
+        config.usage |= wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::COPY_SRC;
+        // Out of video memory (an invalid texture's view is a validation error):
+        // tried again at half the size next frame; the window keeps its last one.
+        let checks = GpuChecks::push(&self.device);
+        let target = Self::offscreen_target(&self.device, &config);
+        let depth = Self::depth(&self.device, &config);
+        if let Some(e) = checks.pop() {
+            log::warn!(
+                "Horizon renderer: no memory for a {}x{} screenshot ({e}); trying half the size",
+                size[0],
+                size[1]
+            );
+            self.screenshot_halvings += 1;
+            return Ok(false);
+        }
+        let scale = self.world_post.scale;
+        self.world_post.scale = scale / scale.max(1.0);
+        self.hud.zoom = size[0] as f32 / window[0] as f32;
+        [self.config.width, self.config.height] = size;
+        let surface = self.surface.take();
+        // HDR presents to the swapchain; this frame goes to a file.
+        let hdr = self.hdr.take();
+        let offscreen = self.offscreen.replace(target);
+        let window_depth = std::mem::replace(&mut self.depth, depth);
+        // The frame's own targets at `size` can run out of memory too.
+        let drawn = self.draw_frame(frame, Some(GpuChecks::push(&self.device)));
+        self.depth = window_depth;
+        self.offscreen = offscreen;
+        self.hdr = hdr;
+        self.surface = surface;
+        [self.config.width, self.config.height] = window;
+        self.hud.zoom = 1.0;
+        self.world_post.scale = scale;
+        drawn
+    }
+    /// `checks`: the error scopes of a scaled screenshot's frame, checked before its PNG is written.
+    fn draw_frame(&mut self, frame: &Frame, checks: Option<GpuChecks>) -> Result<bool> {
         self.arena.trim();
+        self.compact_arena();
         self.sorted_indices.trim();
         if let Some(flat) = &mut self.flat {
             flat.trim(|page| self.arena.has_page(page));
@@ -4320,6 +4571,27 @@ impl Renderer {
             startup_step(format_args!("acquiring the first frame"));
             self.first_frame = FirstFrame::Submit;
         }
+        if self.surface_unconfigured
+            && let Some(surface) = &self.surface
+        {
+            // Acquiring from it would panic: configure it again, or skip the
+            // frame. A lost device never configures it.
+            if self.device_lost.load(std::sync::atomic::Ordering::Relaxed) {
+                return Err("the graphics device was lost".into());
+            }
+            if Self::configure(
+                &self.device,
+                surface,
+                &self.surface_config(),
+                self.hdr.as_ref(),
+                &self.device_lost,
+            )
+            .is_err()
+            {
+                return Ok(false);
+            }
+            self.surface_unconfigured = false;
+        }
         let acquire = Instant::now();
         let acquired = self.surface.as_ref().map(|s| s.get_current_texture());
         self.last_wait = acquire.elapsed();
@@ -4331,14 +4603,7 @@ impl Renderer {
                 return Ok(false);
             }
             Some(wgpu::CurrentSurfaceTexture::Outdated) => {
-                if let Some(surface) = &self.surface {
-                    Self::configure(
-                        &self.device,
-                        surface,
-                        &self.surface_config(),
-                        self.hdr.as_ref(),
-                    );
-                }
+                self.configure_surface();
                 return Ok(false);
             }
             Some(wgpu::CurrentSurfaceTexture::Lost) => {
@@ -4353,14 +4618,7 @@ impl Renderer {
                 // window like a Lost one — a fullscreen loading screen then
                 // skips frames instead of failing every one of them.
                 if self.acquire_validation_failures == 0 {
-                    if let Some(surface) = &self.surface {
-                        Self::configure(
-                            &self.device,
-                            surface,
-                            &self.surface_config(),
-                            self.hdr.as_ref(),
-                        );
-                    }
+                    self.configure_surface();
                 } else {
                     self.recreate_surface()?;
                 }
@@ -5944,10 +6202,6 @@ impl Renderer {
                 );
                 pass.set_bind_group(0, &self.group, &[]);
             }
-            if !pack_draws_weather && !oit_on {
-                self.weather.draw(&mut pass, &self.entity_group);
-            }
-            pass.set_bind_group(0, &self.group, &[]);
             if crumbling_quads > 0 && !oit_on {
                 pass.set_pipeline(&self.crumbling_pipeline);
                 pass.set_bind_group(0, &self.entity_group, &[]);
@@ -6297,19 +6551,6 @@ impl Renderer {
             if outline_edges > 0 && frame.outline_after_terrain {
                 self.draw_outline(&mut pass, outline_edges as u32, frame.outline_high_contrast);
             }
-            pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
-            // LevelRenderer: the world border after translucent terrain and weather.
-            if let Some(b) = frame.border.as_ref().filter(|_| !frame.title && !oit_on) {
-                pass.set_pipeline(&self.border_pipeline);
-                pass.set_bind_group(0, &self.border_group, &[]);
-                pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
-                pass.set_vertex_buffer(0, self.border_vertices.slice(..));
-                for &side in &b.sides {
-                    let first = side as u32 * 6;
-                    pass.draw_indexed(first..first + 6, 0, 0..1);
-                }
-                pass.set_bind_group(0, &self.group, &[]);
-            }
             if translucent_crumbling_quads > 0 && !oit_on {
                 pass.set_pipeline(&self.crumbling_pipeline);
                 pass.set_bind_group(0, &self.entity_group, &[]);
@@ -6327,6 +6568,25 @@ impl Renderer {
                 pass.set_vertex_buffer(0, self.cloud_buffer.slice(..));
                 pass.draw_indexed(0..cloud_quads * 6, 0, 0..1);
             }
+            // LevelRenderer.executeClassicTransparency: weather after translucent
+            // terrain and clouds, so the water behind the rain is drawn first.
+            pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
+            if !pack_draws_weather && !oit_on {
+                self.weather.draw(&mut pass, &self.entity_group);
+                pass.set_bind_group(0, &self.group, &[]);
+            }
+            // LevelRenderer: the world border after translucent terrain and weather.
+            if let Some(b) = frame.border.as_ref().filter(|_| !frame.title && !oit_on) {
+                pass.set_pipeline(&self.border_pipeline);
+                pass.set_bind_group(0, &self.border_group, &[]);
+                pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
+                pass.set_vertex_buffer(0, self.border_vertices.slice(..));
+                for &side in &b.sides {
+                    let first = side as u32 * 6;
+                    pass.draw_indexed(first..first + 6, 0, 0..1);
+                }
+                pass.set_bind_group(0, &self.group, &[]);
+            }
             // LevelRenderer.executeSeeThrough, after the rest of the world.
             if see_through_quads > 0 {
                 pass.set_pipeline(&self.see_through_pipeline);
@@ -6715,21 +6975,34 @@ impl Renderer {
         if let Some(Some(timer)) = Self::pass_timer(&mut self.pack_post, &mut self.native) {
             timer.submitted(&self.queue);
         }
+        let failed = checks.and_then(GpuChecks::pop);
         if let Some((request, buffer)) = readback {
-            if let Some(hdr_buffer) = hdr_readback {
-                let hdr_path = hdr_screenshot_path(&request.path);
-                match self.write_hdr_screenshot(&hdr_path, &hdr_buffer) {
-                    Ok(()) => log::info!("Saved HDR screenshot to {}", hdr_path.display()),
-                    Err(e) => log::warn!(
-                        "Horizon renderer: HDR screenshot {}: {e}",
-                        hdr_path.display()
-                    ),
+            // Out of memory on the way: the PNG would be black; taken again at half the size.
+            if let Some(e) = failed {
+                log::warn!(
+                    "Horizon renderer: a {}x{} screenshot failed ({e}); trying half the size",
+                    self.config.width,
+                    self.config.height
+                );
+                self.screenshot_halvings += 1;
+                self.screenshot = Some(request);
+            } else {
+                self.screenshot_halvings = 0;
+                if let Some(hdr_buffer) = hdr_readback {
+                    let hdr_path = hdr_screenshot_path(&request.path);
+                    match self.write_hdr_screenshot(&hdr_path, &hdr_buffer) {
+                        Ok(()) => log::info!("Saved HDR screenshot to {}", hdr_path.display()),
+                        Err(e) => log::warn!(
+                            "Horizon renderer: HDR screenshot {}: {e}",
+                            hdr_path.display()
+                        ),
+                    }
                 }
+                self.screenshot_result = Some(
+                    self.write_screenshot(&request, &buffer)
+                        .map_err(|e| e.to_string()),
+                );
             }
-            self.screenshot_result = Some(
-                self.write_screenshot(&request, &buffer)
-                    .map_err(|e| e.to_string()),
-            );
         }
         let present = Instant::now();
         if let Some(surface_frame) = surface_frame {
@@ -6749,23 +7022,13 @@ impl Renderer {
                 let _ = std::fs::remove_file(marker);
                 log::info!("Horizon renderer: HDR output presented its first frame");
             }
-            if reconfigure && let Some(surface) = &self.surface {
-                Self::configure(
-                    &self.device,
-                    surface,
-                    &self.surface_config(),
-                    self.hdr.as_ref(),
-                );
+            if reconfigure {
+                self.configure_surface();
             }
         } else {
-            // No swapchain paces offscreen frames: keep two on the GPU at most.
             self.in_flight.push_back(submission);
-            while self.in_flight.len() > 2 {
-                let index = self.in_flight.pop_front();
-                let _ = self.device.poll(wgpu::PollType::Wait {
-                    submission_index: index,
-                    timeout: Some(std::time::Duration::from_secs(5)),
-                });
+            if !self.paced_elsewhere {
+                self.wait_in_flight();
             }
         }
         self.last_wait += present.elapsed();
@@ -6777,6 +7040,41 @@ impl Renderer {
         Ok(true)
     }
 }
+/// Out-of-memory and validation error scopes, popped together: the first error either caught.
+struct GpuChecks {
+    memory: wgpu::ErrorScopeGuard,
+    validation: wgpu::ErrorScopeGuard,
+}
+impl GpuChecks {
+    fn push(device: &wgpu::Device) -> Self {
+        let memory = device.push_error_scope(wgpu::ErrorFilter::OutOfMemory);
+        let validation = device.push_error_scope(wgpu::ErrorFilter::Validation);
+        Self { memory, validation }
+    }
+    fn pop(self) -> Option<wgpu::Error> {
+        let validation = pollster::block_on(self.validation.pop());
+        let memory = pollster::block_on(self.memory.pop());
+        memory.or(validation)
+    }
+}
+/// How many times the window's size a scaled screenshot is: the Resolution Scale
+/// `world_scale` when above 1, times `quality`, as far as a side fits in
+/// `max_side` pixels and the readback in `max_buffer` bytes.
+fn scaled_screenshot_factor(
+    [width, height]: [u32; 2],
+    world_scale: f32,
+    quality: u32,
+    max_side: u32,
+    max_buffer: u64,
+) -> f32 {
+    let wanted = world_scale.max(1.0) * quality.max(1) as f32;
+    let (w, h) = (f64::from(width.max(1)), f64::from(height.max(1)));
+    let side = f64::from(max_side) / w.max(h);
+    // padded_row(w * f) * h * f <= (4 * w * f + 256) * h * f <= max_buffer.
+    let (a, b) = (4.0 * w * h, 256.0 * h);
+    let buffer = ((b * b + 4.0 * a * max_buffer as f64).sqrt() - b) / (2.0 * a);
+    wanted.min(side.min(buffer) as f32)
+}
 /// Bytes per row of a `width`-pixel frame read back at 4 bytes a pixel.
 fn padded_row(width: u32) -> u32 {
     (width * 4).next_multiple_of(wgpu::COPY_BYTES_PER_ROW_ALIGNMENT)
@@ -6813,6 +7111,16 @@ pub(crate) fn copy_frame(
     buffer
 }
 impl Renderer {
+    /// No swapchain paces offscreen frames: keep two on the GPU at most.
+    pub fn wait_in_flight(&mut self) {
+        while self.in_flight.len() > 2 {
+            let index = self.in_flight.pop_front();
+            let _ = self.device.poll(wgpu::PollType::Wait {
+                submission_index: index,
+                timeout: Some(std::time::Duration::from_secs(5)),
+            });
+        }
+    }
     /// Take a screenshot request: queue the frame's copy, or report why the
     /// frame cannot be read back.
     fn take_readback(
@@ -7185,6 +7493,30 @@ mod tests {
         );
     }
     #[test]
+    fn scaled_screenshots_follow_resolution_scale_and_quality_within_limits() {
+        use super::scaled_screenshot_factor as factor;
+        let big = u64::MAX / 2;
+        // The window's size at 100% and 1x; Resolution Scale below 100% stays the window's.
+        assert_eq!(factor([1920, 1080], 1.0, 1, 16384, big), 1.0);
+        assert_eq!(factor([1920, 1080], 0.5, 1, 16384, big), 1.0);
+        // The game's resolution, times the quality.
+        assert_eq!(factor([1920, 1080], 2.0, 1, 16384, big), 2.0);
+        assert_eq!(factor([1920, 1080], 1.5, 4, 16384, big), 6.0);
+        assert_eq!(factor([1920, 1080], 0.5, 8, 16384, big), 8.0);
+        // Cut to the largest texture side: 3840 * 4.266 = 16384.
+        let f = factor([3840, 2160], 1.0, 8, 16384, big);
+        assert!(
+            (3840.0 * f) as u32 <= 16384 && (3840.0 * f) as u32 > 16300,
+            "{f}"
+        );
+        // Cut to the largest buffer: 256 MiB holds about 3.8x of 1080p's readback.
+        let max = 256 << 20;
+        let f = factor([1920, 1080], 1.0, 8, 16384, max);
+        let [w, h] = [1920, 1080].map(|s| (s as f32 * f) as u32);
+        assert!(u64::from(super::padded_row(w)) * u64::from(h) <= max, "{f}");
+        assert!(f > 3.7, "{f}");
+    }
+    #[test]
     fn drawable_size_skips_minimized_and_oversized_windows() {
         use super::drawable_size;
         assert!(drawable_size(1280, 720, 8192));
@@ -7793,9 +8125,52 @@ mod sprite_upload_tests {
                 .collect();
             assert_eq!(actual, expected.0);
             assert_eq!(prepared.forcefield, mip_chain(&border, size, &[], 0, 1));
+            // Chains cut before the adapter was known, cut again for it.
+            for to in [1, 2, 3, 5, 8] {
+                let direct = PreparedTextures::with_split(
+                    &pixels,
+                    size,
+                    layers,
+                    &settings,
+                    (&border, size),
+                    to,
+                );
+                let resplit = PreparedTextures::with_split(
+                    &pixels,
+                    size,
+                    layers,
+                    &settings,
+                    (&border, size),
+                    split,
+                )
+                .resplit(layers, to);
+                assert_eq!(resplit.split, to);
+                assert_eq!(resplit.sprites, direct.sprites, "{split} -> {to}");
+            }
         }
     }
 
+    #[test]
+    fn sprite_split_follows_the_adapters_layer_limit() {
+        // The Discord report: 512 layers per array, 1291 block textures (3 arrays).
+        assert_eq!(layer_split(512, false, None, 1291), Ok(512));
+        assert_eq!(layer_split(512, true, None, 1291), Ok(512));
+        assert_eq!(layer_split(2048, false, None, 1291), Ok(SPRITE_SPLIT));
+        assert_eq!(layer_split(8192, false, None, 1291), Ok(SPRITE_SPLIT));
+        // HORIZON_SPRITE_SPLIT only lowers it.
+        assert_eq!(layer_split(2048, false, Some(512), 1291), Ok(512));
+        assert_eq!(layer_split(256, false, Some(512), 1291), Ok(256));
+        // OpenGL pads a multiple of 6 by a layer: a full array must still fit.
+        assert_eq!(layer_split(600, true, None, 1291), Ok(599));
+        assert_eq!(layer_split(600, false, None, 1291), Ok(600));
+        assert_eq!(array_layers(599, true), 599);
+        // Past the arrays terrain.wgsl binds.
+        assert_eq!(layer_split(256, false, None, 256 * SPRITE_ARRAYS), Ok(256));
+        let err = layer_split(128, false, None, 1291).unwrap_err();
+        assert!(err.contains("128 texture layers per array"), "{err}");
+        assert!(layer_split(512, false, None, 512 * SPRITE_ARRAYS + 1).is_err());
+    }
+
     #[test]
     fn mip_chain_allocates_exactly_its_size() {
         for size in [16, 64] {

crates/horizon-client-render/src/gfx/arena.rs

@@ -76,8 +76,22 @@ struct Page {
     /// Capacity in vertices.
     capacity: u64,
     free: FreeList,
+    /// The buffer went to system memory (`Arena::create`'s fallback): meshes
+    /// are never moved into it, and it is the first to empty.
+    host: bool,
 }
 
+impl Page {
+    /// Vertices in the page's free ranges.
+    fn free_vertices(&self) -> u64 {
+        self.free.0.values().sum()
+    }
+}
+
+/// An arena with this many bytes in free ranges, at least half of its pages,
+/// has a page worth emptying (`Arena::sparsest`).
+const COMPACT_MIN_FREE: u64 = 128 << 20;
+
 /// Terrain vertices in pages of at most `page_limit` vertices (devices cap
 /// buffer sizes): a section's vertices sit in one page.
 pub struct Arena {
@@ -86,6 +100,8 @@ pub struct Arena {
     page_limit: u64,
     initial_capacity: u64,
     usage: wgpu::BufferUsages,
+    /// A page being emptied (`Arena::close`): nothing is placed in it.
+    closing: Option<u32>,
     /// A page had to go to system memory (logged once).
     spilled: bool,
     /// Tests: GPU-local pages fail as if video memory were full.
@@ -129,6 +145,7 @@ impl Arena {
             page_limit,
             initial_capacity: capacity,
             usage,
+            closing: None,
             spilled: false,
             #[cfg(test)]
             video_memory_full: false,
@@ -138,7 +155,7 @@ impl Arena {
     /// and the device allows it, in system memory: Vulkan drivers fail an
     /// allocation rather than page like OpenGL ones, and wgpu's default error
     /// handler panics. `None` when neither has room.
-    fn create(&mut self, device: &wgpu::Device, capacity: u64) -> Option<wgpu::Buffer> {
+    fn create(&mut self, device: &wgpu::Device, capacity: u64) -> Option<(wgpu::Buffer, bool)> {
         let usage = self.usage | wgpu::BufferUsages::COPY_DST | wgpu::BufferUsages::COPY_SRC;
         #[cfg(test)]
         let local = (!self.video_memory_full)
@@ -146,6 +163,7 @@ impl Arena {
             .flatten();
         #[cfg(not(test))]
         let local = try_create(device, capacity * self.stride, usage);
+        let local = local.map(|buffer| (buffer, false));
         local.or_else(|| {
             // Mappable buffers are placed in host-visible memory, which the
             // allocator takes from system memory once video memory is full.
@@ -166,7 +184,7 @@ impl Arena {
                      (lower the render distance if frames slow down)"
                 );
             }
-            Some(buffer)
+            Some((buffer, true))
         })
     }
     /// The rounded length a request of `vertices` occupies.
@@ -207,16 +225,13 @@ impl Arena {
         vertices: u64,
     ) -> Option<(u32, u64)> {
         let len = Self::span(vertices).min(self.page_limit);
-        for (i, page) in self.pages.iter_mut().enumerate() {
-            if let Some(page) = page
-                && let Some(start) = page.free.take(len)
-            {
-                return Some((i as u32, start));
-            }
+        if let Some(found) = self.alloc_existing(len) {
+            return Some(found);
         }
         let last = self.pages.len().saturating_sub(1);
         if let Some(page) = self.pages.last().and_then(Option::as_ref)
             && page.capacity < self.page_limit
+            && self.closing != Some(last as u32)
         {
             let current = page.capacity;
             let grown = (current * 2).max(current + len).min(self.page_limit);
@@ -235,7 +250,7 @@ impl Arena {
         .max(len)
         .min(self.page_limit);
         // A page just large enough when memory is short.
-        let (buffer, capacity) = match self.create(device, capacity) {
+        let ((buffer, host), capacity) = match self.create(device, capacity) {
             Some(buffer) => (buffer, capacity),
             None if capacity > len => (self.create(device, len)?, len),
             None => return None,
@@ -246,6 +261,7 @@ impl Arena {
             buffer,
             capacity,
             free,
+            host,
         };
         let index = self
             .pages
@@ -258,6 +274,96 @@ impl Arena {
         self.pages[index] = Some(page);
         Some((index as u32, start))
     }
+    /// A range of `vertices` in a page that exists already and is not being
+    /// emptied: never grows the arena.
+    pub fn alloc_existing(&mut self, vertices: u64) -> Option<(u32, u64)> {
+        let len = Self::span(vertices).min(self.page_limit);
+        let closing = self.closing;
+        self.pages
+            .iter_mut()
+            .enumerate()
+            .filter(|(i, _)| closing != Some(*i as u32))
+            .find_map(|(i, page)| Some((i as u32, page.as_mut()?.free.take(len)?)))
+    }
+    /// `alloc_existing` for a mesh moved off the closing page: only pages in
+    /// video memory, so compaction never pushes terrain into system memory.
+    pub fn alloc_moved(&mut self, vertices: u64) -> Option<(u32, u64)> {
+        let len = Self::span(vertices).min(self.page_limit);
+        let closing = self.closing;
+        self.pages
+            .iter_mut()
+            .enumerate()
+            .filter(|(i, p)| closing != Some(*i as u32) && p.as_ref().is_some_and(|p| !p.host))
+            .find_map(|(i, page)| Some((i as u32, page.as_mut()?.free.take(len)?)))
+    }
+    /// The page to empty when much of the arena is free ranges (video memory
+    /// that fragmentation keeps: a page goes back only once all of it is free):
+    /// the one with the fewest vertices in use that the other pages' free
+    /// ranges can take. `None` when the arena is dense enough or already
+    /// emptying a page.
+    pub fn sparsest(&self) -> Option<u32> {
+        self.sparsest_from(COMPACT_MIN_FREE)
+    }
+    /// `sparsest` for an arena with at least `min_free` bytes in free ranges.
+    fn sparsest_from(&self, min_free: u64) -> Option<u32> {
+        if self.closing.is_some() {
+            return None;
+        }
+        let pages = || {
+            self.pages
+                .iter()
+                .enumerate()
+                .filter_map(|(i, p)| Some((i, p.as_ref()?)))
+        };
+        let free: u64 = pages().map(|(_, p)| p.free_vertices()).sum();
+        let capacity: u64 = pages().map(|(_, p)| p.capacity).sum();
+        if free * self.stride < min_free || free * 2 < capacity {
+            return None;
+        }
+        // Moves only go to video-memory pages (`alloc_moved`).
+        let local_free: u64 = pages()
+            .filter(|(_, p)| !p.host)
+            .map(|(_, p)| p.free_vertices())
+            .sum();
+        pages()
+            .filter_map(|(i, p)| {
+                let used = p.capacity - p.free_vertices();
+                let own = if p.host { 0 } else { p.free_vertices() };
+                // The room elsewhere, less a quarter for first fit's gaps.
+                let elsewhere = (local_free - own) / 4 * 3;
+                // A page in system memory is emptied first.
+                (used > 0 && used <= elsewhere).then_some((!p.host, used, i as u32))
+            })
+            .min()
+            .map(|(_, _, i)| i)
+    }
+    /// Stops placing vertices in `page` until `reopen`.
+    pub fn close(&mut self, page: u32) {
+        self.closing = Some(page);
+    }
+    pub fn reopen(&mut self) {
+        self.closing = None;
+    }
+    pub fn closing(&self) -> Option<u32> {
+        self.closing
+    }
+    /// Records the copy of `vertices` from one range to another of other pages.
+    pub fn copy(
+        &self,
+        encoder: &mut wgpu::CommandEncoder,
+        from: (u32, u64),
+        to: (u32, u64),
+        vertices: u64,
+    ) {
+        debug_assert_ne!(from.0, to.0);
+        encoder.copy_buffer_to_buffer(
+            self.buffer(from.0),
+            from.1 * self.stride,
+            self.buffer(to.0),
+            to.1 * self.stride,
+            vertices * self.stride,
+        );
+    }
     pub fn release(&mut self, page: u32, start: u64, vertices: u64) {
         let len = Self::span(vertices).min(self.page_limit);
         self.pages[page as usize]
@@ -296,7 +402,7 @@ impl Arena {
         capacity: u64,
     ) -> bool {
         let capacity = capacity.next_multiple_of(GRAIN).min(self.page_limit);
-        let Some(buffer) = self.create(device, capacity) else {
+        let Some((buffer, host)) = self.create(device, capacity) else {
             return false;
         };
         let old = self.pages[page].as_mut().expect("live arena page");
@@ -304,6 +410,7 @@ impl Arena {
         encoder.copy_buffer_to_buffer(&old.buffer, 0, &buffer, 0, old.capacity * self.stride);
         let previous = old.capacity;
         old.buffer = buffer;
+        old.host = host;
         old.capacity = capacity;
         old.free.give(previous, capacity - previous);
         true
@@ -318,6 +425,9 @@ impl Arena {
                 *page = None;
             }
         }
+        if self.closing.is_some_and(|page| !self.has_page(page)) {
+            self.closing = None;
+        }
         // Keep live page indices stable; later allocations reuse interior holes.
         while self.pages.last().is_some_and(Option::is_none) {
             self.pages.pop();
@@ -325,6 +435,7 @@ impl Arena {
     }
     pub fn clear(&mut self) {
         self.pages.clear();
+        self.closing = None;
     }
 }
 
@@ -407,6 +518,76 @@ mod tests {
         assert_eq!(read(&device, &queue, arena.buffer(page), next * 4), 9);
     }
 
+    #[test]
+    fn a_sparse_page_empties_into_the_others_and_is_reclaimed() {
+        let Some((device, queue)) = device() else {
+            eprintln!("no GPU adapter: skipped");
+            return;
+        };
+        let mut arena = Arena::new(&device, 4, GRAIN, false);
+        arena.page_limit = 4 * GRAIN;
+        // Eight ranges fill two pages, each holding its own number.
+        let ranges: Vec<(u32, u64)> = (0..8)
+            .map(|i| {
+                let range = alloc(&mut arena, &device, &queue, GRAIN).unwrap();
+                queue.write_buffer(
+                    arena.buffer(range.0),
+                    range.1 * 4,
+                    &(100 + i as u32).to_le_bytes(),
+                );
+                range
+            })
+            .collect();
+        assert_eq!(arena.pages.iter().flatten().count(), 2);
+        let (first, second) = (ranges[0].0, ranges[7].0);
+        assert_ne!(first, second);
+        // Fragmented: one range live in the first page, two in the second.
+        for (i, &(page, start)) in ranges.iter().enumerate() {
+            if ![0, 6, 7].contains(&i) {
+                arena.release(page, start, GRAIN);
+            }
+        }
+        // Dense enough arenas, and ones without room elsewhere, are left alone.
+        assert_eq!(arena.sparsest_from(u64::MAX), None);
+        assert_eq!(arena.sparsest_from(0), Some(first));
+        arena.close(first);
+        assert_eq!(
+            arena.sparsest_from(0),
+            None,
+            "one page is emptied at a time"
+        );
+        // New ranges avoid the closing page though it has room.
+        let (page, extra) = alloc(&mut arena, &device, &queue, GRAIN).unwrap();
+        assert_eq!(page, second);
+        arena.release(page, extra, GRAIN);
+        // Its live range moves, data included, and the page goes back.
+        let (page, start) = ranges[0];
+        let to = arena.alloc_existing(GRAIN).unwrap();
+        assert_eq!(to.0, second);
+        let mut encoder = device.create_command_encoder(&Default::default());
+        arena.copy(&mut encoder, (page, start), to, GRAIN);
+        queue.submit([encoder.finish()]);
+        arena.release(page, start, GRAIN);
+        assert_eq!(read(&device, &queue, arena.buffer(to.0), to.1 * 4), 100);
+        // Emptied but not trimmed yet: it stays closed, so uploads can't refill it.
+        assert_eq!(arena.closing(), Some(page));
+        let refill = alloc(&mut arena, &device, &queue, GRAIN).unwrap();
+        assert_ne!(refill.0, page);
+        arena.release(refill.0, refill.1, GRAIN);
+        let before = arena.bytes();
+        arena.trim();
+        assert_eq!(arena.bytes(), before - 4 * GRAIN * 4);
+        assert_eq!(arena.closing(), None);
+        // The others kept their ranges.
+        for i in [6, 7] {
+            let (page, start) = ranges[i];
+            assert_eq!(
+                read(&device, &queue, arena.buffer(page), start * 4),
+                100 + i as u32
+            );
+        }
+    }
+
     #[test]
     fn empty_pages_are_reclaimed_without_moving_live_ranges() {
         let Some((device, queue)) = device() else {
@@ -572,6 +753,9 @@ mod tests {
         queue.write_buffer(arena.buffer(grown), next * 4, &9u32.to_le_bytes());
         assert_eq!(read(&device, &queue, arena.buffer(page), start * 4), 7);
         assert_eq!(read(&device, &queue, arena.buffer(grown), next * 4), 9);
+        // Compaction never moves terrain into a page in system memory.
+        assert!(arena.pages[page as usize].as_ref().unwrap().host);
+        assert_eq!(arena.alloc_moved(GRAIN), None);
     }
 
     #[test]

crates/horizon-client-render/src/gfx/lod.rs

@@ -152,6 +152,10 @@ impl Tile {
             None => &mut self.mesh,
         }
     }
+    /// Both meshes it holds in the arena: its own and the stand-in, if any.
+    pub fn meshes_mut(&mut self) -> impl Iterator<Item = &mut SectionGpu> {
+        std::iter::once(&mut self.mesh).chain(self.previous.as_mut().map(|(mesh, _)| mesh))
+    }
     pub fn visible(
         &self,
         key: TileKey,

crates/horizon-client-render/src/gfx/oit_features.rs

@@ -176,7 +176,7 @@ impl Features {
                 &entity_module,
                 entities,
                 &entity_buffers,
-                kind("text", "entity", None, offset),
+                kind("text", "entity", Some(wgpu::Face::Back), offset),
             ),
             crumbling: set(
                 &entity_module,

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

@@ -13,6 +13,7 @@
 
 use std::collections::HashMap;
 
+use glam::{DMat4, DVec3};
 use horizon_shaders::{Format, Group, Kind, Post, Val};
 
 use super::pack_draw::DrawUniforms;
@@ -434,9 +435,33 @@ pub(super) struct Weather {
     pub generation: u64,
 }
 
+/// Shadow cache: the key of the shadow map the shadow targets hold. Only the
+/// shadow passes write those targets, so while the key matches they still hold
+/// it and the pass is skipped.
+#[derive(Default)]
+struct ShadowCache {
+    key: Option<ShadowCacheKey>,
+}
+
+/// Key for validating the shadow cache.
+/// Must match the cache state exactly to be considered valid.
+#[derive(Clone, Copy, Debug, PartialEq)]
+struct ShadowCacheKey {
+    sun_angle: f32,
+    moon_angle: f32,
+    snapped_camera: Option<DVec3>,
+    shadow_settings_hash: u64,
+    shadow_scene_revision: (u64, u64),
+    ticks: u64,
+    day_time: i64,
+    shadow_uniforms_hash: u64,
+}
+
 pub struct PackPost {
     pub notes: Vec<String>,
     passes: Vec<Pass>,
+    /// Shadow cache for temporal reprojection.
+    shadow_cache: ShadowCache,
     /// What draws terrain (`gbuffers_terrain` or its fallback), between `prepare` and `deferred`.
     terrain: Option<Pass>,
     /// What draws translucent terrain (`gbuffers_water` or its fallback), after `deferred`.
@@ -2330,6 +2355,7 @@ impl PackPost {
                 u.shadow = shadow_config;
                 u
             },
+            shadow_cache: Default::default(),
         }
     }
 
@@ -3322,6 +3348,45 @@ impl PackPost {
         queue: &wgpu::Queue,
         encoder: &mut wgpu::CommandEncoder,
         terrain: &mut TerrainDraw<'_>,
+        frame: &super::Frame,
+    ) {
+        // Opt-in only (`horizon-graphics.txt` shadowCache). Off: always redraw, drop any cache.
+        if !frame.shadow_cache {
+            self.shadow_cache = ShadowCache::default();
+            self.draw_shadow_pass(device, queue, encoder, terrain);
+            return;
+        }
+
+        // Compute the current frame's cache key before borrowing shadow_targets mutably.
+        let cache_key = self.compute_shadow_cache_key(frame);
+
+        // Entity vertices are interpolated each frame, so their shadows cannot be reused.
+        let has_shadow_entities = self
+            .entities
+            .as_ref()
+            .is_some_and(|entities| entities.geometry.draws.iter().any(|draw| draw.shadow));
+        // Custom images are cleared each frame (`pack_images::clear`) before the
+        // shadow pass writes them, so a pack with any redraws it too.
+        let cache_hit = !has_shadow_entities
+            && self.images.is_empty()
+            && self.shadow_cache.key == Some(cache_key)
+            && self.shadow_targets.is_some();
+        if cache_hit {
+            // The targets still hold this map (and `main`, the A/B side
+            // `shadowcomp` left current).
+            return;
+        }
+        self.draw_shadow_pass(device, queue, encoder, terrain);
+        self.shadow_cache.key = self.shadow_targets.is_some().then_some(cache_key);
+    }
+
+    /// The shadow pass body: terrain, entities, clears, and `shadowcomp`.
+    fn draw_shadow_pass(
+        &mut self,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        encoder: &mut wgpu::CommandEncoder,
+        terrain: &mut TerrainDraw<'_>,
     ) {
         let Some(t) = &mut self.shadow_targets else {
             return;
@@ -3397,6 +3462,106 @@ impl PackPost {
         self.shadow_comp = comp;
     }
 
+    /// Computes the cache key for the current frame.
+    fn compute_shadow_cache_key(&self, frame: &super::Frame) -> ShadowCacheKey {
+        let shadow = &self.uniforms.shadow;
+        // Use the same logic as shadow_camera to compute the light direction and snapped camera.
+        // Use the public shadow_light function which returns the normalized light direction.
+        let light = super::pack_uniforms::shadow_light(frame, shadow);
+        let light = light.as_dvec3();
+        let up = if light.z.abs() > 0.99 {
+            DVec3::Y
+        } else {
+            DVec3::Z
+        };
+        let rotation = DMat4::look_to_rh(DVec3::ZERO, -light, up);
+        let at = rotation.transform_vector3(frame.camera);
+        let step = f64::from(shadow.interval);
+        let snapped_camera = if step > 0.0 {
+            Some((at / step).floor() * step)
+        } else {
+            Some(at)
+        };
+
+        // Hash the shadow settings that affect the shadow map.
+        use std::hash::{Hash, Hasher};
+        let mut hasher = std::collections::hash_map::DefaultHasher::new();
+        shadow.resolution.hash(&mut hasher);
+        shadow.distance.to_bits().hash(&mut hasher);
+        shadow.render_mul.to_bits().hash(&mut hasher);
+        shadow.interval.to_bits().hash(&mut hasher);
+        shadow.sun_path_rotation.to_bits().hash(&mut hasher);
+        shadow.fov.map(|f| f.to_bits()).hash(&mut hasher);
+        shadow.near.to_bits().hash(&mut hasher);
+        shadow.far.to_bits().hash(&mut hasher);
+        for hf in &shadow.hardware_filtering {
+            hf.hash(&mut hasher);
+        }
+        for color in &shadow.colors {
+            format!("{:?}", color.format).hash(&mut hasher);
+            color.clear.hash(&mut hasher);
+            if let Some(cc) = color.clear_color {
+                for c in cc {
+                    c.to_bits().hash(&mut hasher);
+                }
+            }
+            color.mipmap.hash(&mut hasher);
+        }
+        let shadow_settings_hash = hasher.finish();
+        let shadow_uniforms_hash = self.shadow_uniforms_hash();
+
+        ShadowCacheKey {
+            sun_angle: frame.sky.sun_angle,
+            moon_angle: frame.sky.moon_angle,
+            snapped_camera,
+            shadow_settings_hash,
+            shadow_scene_revision: frame.shadow_scene_revision,
+            ticks: frame.ticks,
+            day_time: frame.pack.day_time,
+            shadow_uniforms_hash,
+        }
+    }
+
+    fn shadow_uniforms_hash(&self) -> u64 {
+        use std::hash::{Hash, Hasher};
+
+        let mut hasher = std::collections::hash_map::DefaultHasher::new();
+        let passes = self
+            .shadow_terrain
+            .iter()
+            .chain(self.shadow_water.iter())
+            .chain(self.shadow_comp.iter())
+            .chain(
+                self.entities
+                    .iter()
+                    .flat_map(|entities| entities.shadow.iter().flatten()),
+            );
+        for pass in passes {
+            pass.name.hash(&mut hasher);
+            for (index, ty, offset) in &pass.uniforms {
+                index.hash(&mut hasher);
+                ty.hash(&mut hasher);
+                offset.hash(&mut hasher);
+                let Some(value) = index.and_then(|index| self.uniforms.values.get(index)) else {
+                    continue;
+                };
+                match value {
+                    pack_uniforms::Value::F(values) => {
+                        0u8.hash(&mut hasher);
+                        for value in values {
+                            value.to_bits().hash(&mut hasher);
+                        }
+                    }
+                    pack_uniforms::Value::I(values) => {
+                        1u8.hash(&mut hasher);
+                        values.hash(&mut hasher);
+                    }
+                }
+            }
+        }
+        hasher.finish()
+    }
+
     /// Runs the pack over the world drawn into `world` (colour) and `world_depth`, then draws
     /// the result onto `screen`.
     #[allow(clippy::too_many_arguments)]
@@ -3464,7 +3629,7 @@ impl PackPost {
             self.gpu.clear,
             &mut self.zeros,
         );
-        self.run_shadow(device, queue, encoder, terrain);
+        self.run_shadow(device, queue, encoder, terrain, frame);
         let Some(targets) = &self.targets else { return };
         let main = |m: u16, i: usize| usize::from(m & 1 << i != 0);
         let view = |m: u16, i: usize, alt: bool| {
@@ -3720,6 +3885,36 @@ mod tests {
     use super::*;
     use wgpu::TextureFormat as T;
 
+    #[test]
+    fn shadow_cache_key_tracks_world_and_time_changes() {
+        let key = ShadowCacheKey {
+            sun_angle: 0.0,
+            moon_angle: 180.0,
+            snapped_camera: Some(DVec3::ZERO),
+            shadow_settings_hash: 1,
+            shadow_scene_revision: (2, 3),
+            ticks: 4,
+            day_time: 5,
+            shadow_uniforms_hash: 6,
+        };
+
+        assert_ne!(
+            key,
+            ShadowCacheKey {
+                shadow_scene_revision: (8, 3),
+                ..key
+            }
+        );
+        assert_ne!(key, ShadowCacheKey { day_time: 9, ..key });
+        assert_ne!(
+            key,
+            ShadowCacheKey {
+                shadow_uniforms_hash: 10,
+                ..key
+            }
+        );
+    }
+
     /// Two textures with a sampler each become two textures sharing one sampler variable.
     #[test]
     fn samplers_of_a_kind_share_one_variable() {

crates/horizon-client-render/src/gfx/resident.rs

@@ -61,6 +61,9 @@ impl<T> Resident<T> {
     pub fn values(&self) -> impl Iterator<Item = &T> {
         self.items.iter().map(|(_, v)| v)
     }
+    pub fn values_mut(&mut self) -> impl Iterator<Item = &mut T> {
+        self.items.iter_mut().map(|(_, v)| v)
+    }
     /// `key`'s value, when it is resident.
     pub fn find(&self, key: SectionKey) -> Option<&T> {
         self.slots.get(&key).map(|&slot| self.get(slot))

crates/horizon-client-render/src/gfx/weather.rs

@@ -53,13 +53,7 @@ impl Weather {
                 topology: wgpu::PrimitiveTopology::TriangleList,
                 ..Default::default()
             },
-            depth_stencil: Some(wgpu::DepthStencilState {
-                format: wgpu::TextureFormat::Depth32Float,
-                depth_write_enabled: Some(true),
-                depth_compare: Some(wgpu::CompareFunction::GreaterEqual),
-                stencil: Default::default(),
-                bias: Default::default(),
-            }),
+            depth_stencil: Some(depth_stencil()),
             multisample: Default::default(),
             fragment: Some(wgpu::FragmentState {
                 module: shader,
@@ -157,11 +151,33 @@ impl Weather {
     }
 }
 
+/// RenderPipelines.WEATHER: depth-tested, but no depth write, so the water
+/// and glass drawn behind the rain still show through it.
+fn depth_stencil() -> wgpu::DepthStencilState {
+    wgpu::DepthStencilState {
+        format: wgpu::TextureFormat::Depth32Float,
+        depth_write_enabled: Some(false),
+        depth_compare: Some(wgpu::CompareFunction::GreaterEqual),
+        stencil: Default::default(),
+        bias: Default::default(),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::weather::{Parameters, Time};
     use wgpu::util::DeviceExt;
 
+    #[test]
+    fn weather_writes_no_depth() {
+        let depth = super::depth_stencil();
+        assert_eq!(depth.depth_write_enabled, Some(false));
+        assert_eq!(
+            depth.depth_compare,
+            Some(wgpu::CompareFunction::GreaterEqual)
+        );
+    }
+
     #[repr(C)]
     #[derive(Clone, Copy, bytemuck::Pod, bytemuck::Zeroable)]
     struct Case {

crates/horizon-client-render/src/graphics.rs

@@ -313,6 +313,8 @@ pub fn reduced_far_detail_suggested() -> bool {
 
 /// 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];
 static HDR_OFFERED: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
 /// Whether the display path offers HDR output (HDR10 or scRGB): set when the renderer
 /// opens its surface; the settings open HDR's screen only then.
@@ -379,6 +381,8 @@ pub struct Graphics {
     pub taa: bool,
     /// TAA upscaling; anything but `Native` comes with `taa` on.
     pub upscaling: Upscaling,
+    /// F2 screenshots at this many times the game's resolution: 1, 2, 4 or 8.
+    pub screenshot_quality: u32,
     /// HDR output (HDR10, or scRGB), where the display path offers it.
     pub hdr: bool,
     /// HDR paper white (where SDR white sits), in nits; 0 is Auto: the desktop's SDR
@@ -399,6 +403,10 @@ pub struct Graphics {
     /// 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.
     pub battery: bool,
+    /// Reuse the shader pack's last shadow map when sun, view, scene revision and
+    /// pack uniforms still match. Off by default: vanilla loaders redraw every frame
+    /// (or every `shadowInterval`), and a hit with a stale key shows old shadows.
+    pub shadow_cache: bool,
     /// The graphics API (Windows only; see `GraphicsApi`).
     pub api: GraphicsApi,
     /// The shader pack picked in `shaderpacks/` (`shader_pack_list`); empty: none. Its key is
@@ -428,6 +436,7 @@ impl Default for Graphics {
             fxaa: false,
             taa: false,
             upscaling: Upscaling::Native,
+            screenshot_quality: 1,
             hdr: false,
             hdr_paper_white: 0,
             hdr_peak: 0,
@@ -435,6 +444,7 @@ impl Default for Graphics {
             hdr_ui_brightness: 100,
             hdr_key: "key.keyboard.unknown".into(),
             battery: false,
+            shadow_cache: false,
             api: GraphicsApi::Auto,
             shader_pack: String::new(),
         }
@@ -497,6 +507,11 @@ impl Graphics {
                 "fxaa" => g.fxaa = flag(g.fxaa),
                 "taa" => g.taa = flag(g.taa),
                 "upscaling" => g.upscaling = Upscaling::parse(value),
+                "screenshotQuality" => {
+                    g.screenshot_quality = Some(number(0))
+                        .filter(|q| SCREENSHOT_QUALITIES.contains(q))
+                        .unwrap_or(1)
+                }
                 "hdr" => g.hdr = flag(g.hdr),
                 "hdrPaperWhite" => {
                     g.hdr_paper_white = match number(g.hdr_paper_white) {
@@ -516,6 +531,7 @@ impl Graphics {
                 }
                 "hdrKey" if value.starts_with("key.") => g.hdr_key = value.to_owned(),
                 "batteryMode" => g.battery = flag(g.battery),
+                "shadowCache" => g.shadow_cache = flag(g.shadow_cache),
                 "graphicsApi" => g.api = GraphicsApi::from_name(value).unwrap_or_default(),
                 "pickedShaderPack" => g.shader_pack = value.to_owned(),
                 "overlay" => {
@@ -532,7 +548,7 @@ impl Graphics {
     }
     pub fn serialize(&self) -> String {
         format!(
-            "preset:{}\nlodDistance:{}\nfarDetail:{}\ncaveCulling:{}\nentityCulling:{}\nchunkUpdates:{}\nuploadBudgetKiB:{}\nsky:{}\nfog:{}\nweather:{}\nanimatedTextures:{}\npresentMode:{}\nframePacing:{}\nworkers:{}\noverlay:{}\nresolutionScale:{}\nfxaa:{}\ntaa:{}\nupscaling:{}\nhdr:{}\nhdrPaperWhite:{}\nhdrPeak:{}\nhdrBlackLevel:{}\nhdrUiBrightness:{}\nhdrKey:{}\nbatteryMode:{}\ngraphicsApi:{}\npickedShaderPack:{}\n",
+            "preset:{}\nlodDistance:{}\nfarDetail:{}\ncaveCulling:{}\nentityCulling:{}\nchunkUpdates:{}\nuploadBudgetKiB:{}\nsky:{}\nfog:{}\nweather:{}\nanimatedTextures:{}\npresentMode:{}\nframePacing:{}\nworkers:{}\noverlay:{}\nresolutionScale:{}\nfxaa:{}\ntaa:{}\nupscaling:{}\nscreenshotQuality:{}\nhdr:{}\nhdrPaperWhite:{}\nhdrPeak:{}\nhdrBlackLevel:{}\nhdrUiBrightness:{}\nhdrKey:{}\nbatteryMode:{}\nshadowCache:{}\ngraphicsApi:{}\npickedShaderPack:{}\n",
             self.preset.name(),
             self.lod_distance,
             self.far_detail.name(),
@@ -559,6 +575,7 @@ impl Graphics {
             bool_text(self.fxaa),
             bool_text(self.taa),
             self.upscaling.name(),
+            self.screenshot_quality,
             bool_text(self.hdr),
             self.hdr_paper_white,
             self.hdr_peak,
@@ -566,6 +583,7 @@ impl Graphics {
             self.hdr_ui_brightness,
             self.hdr_key,
             bool_text(self.battery),
+            bool_text(self.shadow_cache),
             self.api.name(),
             self.shader_pack,
         )
@@ -703,6 +721,7 @@ mod tests {
             fxaa: true,
             taa: true,
             upscaling: Upscaling::Balanced,
+            screenshot_quality: 4,
             hdr: true,
             hdr_paper_white: 240,
             hdr_peak: 1400,
@@ -710,6 +729,7 @@ mod tests {
             hdr_ui_brightness: 60,
             hdr_key: "key.keyboard.h".into(),
             battery: true,
+            shadow_cache: true,
             api: GraphicsApi::Dx12,
             shader_pack: "Golden Hour".into(),
         };
@@ -720,6 +740,19 @@ mod tests {
         assert_eq!(Graphics::parse("hdrPeak:50\n").hdr_peak, 200);
         assert_eq!(Graphics::parse("hdrPaperWhite:0\n").hdr_paper_white, 0);
         assert_eq!(Graphics::parse("hdrPaperWhite:5\n").hdr_paper_white, 10);
+        // Only the button's choices.
+        assert_eq!(
+            Graphics::parse("screenshotQuality:8\n").screenshot_quality,
+            8
+        );
+        assert_eq!(
+            Graphics::parse("screenshotQuality:3\n").screenshot_quality,
+            1
+        );
+        assert_eq!(
+            Graphics::parse("screenshotQuality:16\n").screenshot_quality,
+            1
+        );
         // The old menus' Simple / Advanced choice is ignored, and so is the
         // shader pack older versions saved.
         assert_eq!(Graphics::parse("level:advanced\n"), Graphics::default());

crates/horizon-client-render/src/graphics_ui.rs

@@ -40,6 +40,7 @@ pub enum H {
     ResolutionScale,
     Antialiasing,
     Upscaling,
+    ScreenshotQuality,
     Hdr,
     /// Opens `Level::Hdr`.
     HdrSettings,
@@ -52,6 +53,7 @@ pub enum H {
     HdrPaperWhite,
     HdrUiBrightness,
     BatteryMode,
+    ShadowCache,
     GraphicsApi,
 }
 
@@ -278,6 +280,11 @@ pub fn rows(level: Level) -> Vec<Row> {
                 High,
                 "Renders the world smaller and rebuilds it with TAA. Faster, softer.",
             ),
+            h(
+                H::ScreenshotQuality,
+                None,
+                "F2 screenshots at this many times the game's resolution. Higher takes longer.",
+            ),
             h(
                 H::HdrSettings,
                 None,
@@ -313,6 +320,11 @@ pub fn rows(level: Level) -> Vec<Row> {
                 None,
                 "60 FPS cap (30 in menus or unfocused), half the workers: less power.",
             ),
+            h(
+                H::ShadowCache,
+                Saves,
+                "Reuses the pack shadow map when sun, view and world match. Off by default.",
+            ),
             h(
                 H::Workers,
                 None,
@@ -538,6 +550,9 @@ impl H {
                 },
             ),
             H::Upscaling => labelled("Upscaling", g.upscaling.label()),
+            H::ScreenshotQuality => {
+                labelled("Screenshot Quality", format!("{}x", g.screenshot_quality))
+            }
             H::Hdr => labelled("HDR", on_off(g.hdr)),
             H::HdrSettings => Text::literal(lang::get("HDR Settings...")),
             H::HdrCalibrate => Text::literal(lang::get(match setup(s) {
@@ -571,6 +586,7 @@ impl H {
                 Text::literal("Shortcut: ").append(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)),
             H::GraphicsApi => labelled("Graphics API", g.api.label()),
             H::Overlay => labelled(
                 "Performance Overlay",
@@ -647,8 +663,16 @@ impl H {
                     (g.fxaa, g.taa) = (false, true);
                 }
             }
+            H::ScreenshotQuality => {
+                g.screenshot_quality = step(
+                    &crate::graphics::SCREENSHOT_QUALITIES,
+                    g.screenshot_quality,
+                    back,
+                )
+            }
             H::Hdr => g.hdr = !g.hdr,
             H::BatteryMode => g.battery = !g.battery,
+            H::ShadowCache => g.shadow_cache = !g.shadow_cache,
             H::GraphicsApi => g.api = step(GraphicsApi::choices(), g.api, back),
             H::Pacing => {
                 g.pacing = match g.pacing {
@@ -711,6 +735,7 @@ impl Item {
             Item::Horizon(H::AnimatedTextures) => g.animated_textures,
             Item::Horizon(H::Hdr) => g.hdr,
             Item::Horizon(H::BatteryMode) => g.battery,
+            Item::Horizon(H::ShadowCache) => g.shadow_cache,
             Item::Vanilla(Opt::ViewBobbing) => s.view_bobbing,
             Item::Vanilla(Opt::Vsync) => s.vsync,
             Item::Vanilla(Opt::Fullscreen) => s.fullscreen,
@@ -766,10 +791,12 @@ impl Item {
             Item::Horizon(
                 H::Preset
                     | H::Overlay
+                    | H::ScreenshotQuality
                     | H::Pacing
                     | H::PresentMode
                     | H::Workers
                     | H::BatteryMode
+                    | H::ShadowCache
                     | H::GraphicsApi
             ) | Item::Vanilla(
                 Opt::GuiScale
@@ -1733,6 +1760,21 @@ mod tests {
         assert_eq!(s.horizon.preset, Preset::Ultra);
     }
 
+    #[test]
+    fn screenshot_quality_cycles_1_2_4_8_and_keeps_the_preset() {
+        let mut s = Settings::default();
+        Item::Horizon(H::Preset).cycle(&mut s, false, [854, 480]);
+        let mut seen = Vec::new();
+        for _ in 0..4 {
+            Item::Horizon(H::ScreenshotQuality).cycle(&mut s, false, [854, 480]);
+            seen.push(s.horizon.screenshot_quality);
+        }
+        assert_eq!(seen, [2, 4, 8, 1]);
+        Item::Horizon(H::ScreenshotQuality).cycle(&mut s, true, [854, 480]);
+        assert_eq!(s.horizon.screenshot_quality, 8);
+        assert_eq!(s.horizon.preset, Preset::Performance);
+    }
+
     #[test]
     fn upload_budget_slider_steps() {
         let mut s = Settings::default();

crates/horizon-client-render/src/hud.rs

@@ -528,14 +528,16 @@ impl HudAtlas {
         for folder in folders {
             walk(&textures.join(folder), &mut files);
         }
-        // Content mods' equipment textures, which their equipment assets name as
-        // `<ns>:<path>`, and their mob effects' icons, `<ns>:mob_effect/<path>`.
+        // Content mods' entity textures: their equipment assets name them as
+        // `<ns>:<path>`, and native mods draw their block entities with them
+        // (`native_draw_quad`: `<ns>:entity/...`); and their mob effects'
+        // icons, `<ns>:mob_effect/<path>`.
         let namespaces = horizon_items::content_namespaces::namespaces(root);
-        for (folder, textures) in [("entity", "entity/equipment"), ("mob_effect", "mob_effect")] {
+        for folder in ["entity", "mob_effect"] {
             if folders.contains(&folder) {
                 for namespace in &namespaces {
                     walk(
-                        &root.join(format!("assets/{namespace}/textures/{textures}")),
+                        &root.join(format!("assets/{namespace}/textures/{folder}")),
                         &mut files,
                     );
                 }
@@ -1604,6 +1606,9 @@ pub struct HudRenderer {
     atlas_view: wgpu::TextureView,
     /// The resource pack's text shader, when it has one that works.
     pack_text: Option<pack_text::PackText>,
+    /// Target pixels per window pixel: above 1 for a screenshot drawn larger than the
+    /// window (`Renderer::screenshot_quality`).
+    pub zoom: f32,
 }
 impl HudRenderer {
     pub fn new(
@@ -1833,6 +1838,7 @@ impl HudRenderer {
             format,
             atlas_view: view.clone(),
             pack_text: None,
+            zoom: 1.0,
         })
     }
     /// Draw the GUI's text with `shader` (`HudAtlas::text_shader`), or natively.
@@ -1968,14 +1974,14 @@ impl HudRenderer {
                 [
                     size[0] as f32,
                     size[1] as f32,
-                    batch.scale,
+                    batch.scale * self.zoom,
                     batch.glint_alpha,
                 ],
                 batch.end_portal,
             )),
         );
         if let Some(pack_text) = &self.pack_text {
-            pack_text.prepare(uploads, encoder, batch, size);
+            pack_text.prepare(uploads, encoder, batch, size, batch.scale * self.zoom);
         }
     }
     /// Draw the batch `prepare` staged.
@@ -2048,7 +2054,8 @@ impl HudRenderer {
             });
             pass.set_bind_group(0, &self.group, &[]);
             pass.set_vertex_buffer(0, self.buffer.slice(..));
-            if let Some([x, y, w, h]) = clip {
+            if let Some(clip) = clip {
+                let [x, y, w, h] = clip.map(|v| (v as f32 * self.zoom) as u32);
                 let (x, y) = (x.min(size[0]), y.min(size[1]));
                 let (w, h) = (w.min(size[0] - x), h.min(size[1] - y));
                 if w == 0 || h == 0 {
@@ -2186,7 +2193,7 @@ mod tests {
         atlas.pixels[at..at + 4].try_into().unwrap()
     }
     #[test]
-    fn content_mod_equipment_textures_pack_under_their_namespace() {
+    fn content_mod_entity_textures_pack_under_their_namespace() {
         let root = std::env::temp_dir().join(format!("horizon-atlas-equip-{}", std::process::id()));
         let _ = fs::remove_dir_all(&root);
         let equipment = root.join("assets/gems/textures/entity/equipment/humanoid");
@@ -2206,10 +2213,17 @@ mod tests {
             br#"["gems"]"#,
         )
         .unwrap();
+        // A block entity's texture, for a native mod's renderer.
+        let machine = root.join("assets/gems/textures/entity/machine");
+        fs::create_dir_all(&machine).unwrap();
+        write_strip(&machine.join("cog.png"), 32, 32, &[[0, 0, 200, 255]], None);
         let atlas = HudAtlas::build(&root).unwrap();
         let rect = atlas.sprites["gems:entity/equipment/humanoid/ruby"];
         assert_eq!(texel_at(&atlas, rect, 0, 0), [200, 0, 0, 255]);
-        // Only equipment: the mods' other textures reach the atlas through atlas definitions.
+        let rect = atlas.sprites["gems:entity/machine/cog"];
+        assert_eq!(rect.texels((atlas.width, atlas.height)), (32, 32));
+        assert_eq!(texel_at(&atlas, rect, 0, 0), [0, 0, 200, 255]);
+        // Only entity textures: the mods' others reach the atlas through atlas definitions.
         assert!(!atlas.sprites.contains_key("gems:item/ruby"));
         fs::remove_dir_all(&root).unwrap();
     }

crates/horizon-client-render/src/hud/pack_text.rs

@@ -216,8 +216,9 @@ impl PackText {
         encoder: &mut wgpu::CommandEncoder,
         batch: &HudBatch,
         size: [u32; 2],
+        scale: f32,
     ) {
-        uploads.buffer(encoder, &self.uniform, 0, &uniforms(batch, size));
+        uploads.buffer(encoder, &self.uniform, 0, &uniforms(batch, size, scale));
     }
 
     /// Draw `range` (whole glyph quads) with the pack's shader; the caller sets its own
@@ -233,7 +234,8 @@ impl PackText {
 /// `GlintAlpha`, `GameTime`, `ScreenSize`), `Projection` (`GuiRenderer`'s orthographic GUI
 /// projection, 1000 to 11000 deep, in GL's depth range), `DynamicTransforms` (the GUI's model view
 /// moving 11000 back, colour modulator white) and an empty `Fog`.
-fn uniforms(batch: &HudBatch, size: [u32; 2]) -> Vec<u8> {
+/// `scale`: target pixels per GUI pixel (`batch.scale`, times `HudRenderer::zoom`).
+fn uniforms(batch: &HudBatch, size: [u32; 2], scale: f32) -> Vec<u8> {
     let mut data = vec![0f32; 256];
     let globals = 0;
     data[globals + 3] = batch.glint_alpha;
@@ -241,7 +243,7 @@ fn uniforms(batch: &HudBatch, size: [u32; 2]) -> Vec<u8> {
     data[globals + 8] = size[0] as f32;
     data[globals + 9] = size[1] as f32;
     // Matrix4f.setOrtho(0, width, height, 0, near, far) with the GUI's scale, columns.
-    let (w, h) = (size[0] as f32 / batch.scale, size[1] as f32 / batch.scale);
+    let (w, h) = (size[0] as f32 / scale, size[1] as f32 / scale);
     let (near, far) = (1000.0f32, 11000.0f32);
     let projection = 64;
     data[projection] = 2.0 / w;
@@ -287,7 +289,8 @@ mod tests {
     fn the_gui_projection_maps_gui_pixels_to_the_screen() {
         let mut batch = HudBatch::new([1920, 1080]);
         batch.scale = 4.0;
-        let data: Vec<f32> = bytemuck::cast_slice(&uniforms(&batch, [1920, 1080])).to_vec();
+        let data: Vec<f32> =
+            bytemuck::cast_slice(&uniforms(&batch, [1920, 1080], batch.scale)).to_vec();
         let column = |matrix: usize, c: usize| &data[matrix + 4 * c..matrix + 4 * c + 4];
         let apply = |matrix: usize, v: [f32; 4]| -> [f32; 4] {
             std::array::from_fn(|r| (0..4).map(|c| column(matrix, c)[r] * v[c]).sum())

crates/horizon-client-render/src/level_loading.rs

@@ -385,9 +385,40 @@ pub fn draw(
     }
 }
 
+/// `LoadingOverlay.MOJANG_STUDIOS_LOGO_LOCATION`, from the player's own resources.
+pub const MOJANG_STUDIOS_LOGO: &str = "gui/title/mojangstudios";
+
+/// `LoadingOverlay.extractRenderState`'s logo on a GUI `w` x `h`: the left
+/// half's corner, then each half's width and height.
+pub fn logo_layout(w: f32, h: f32) -> (i32, i32, i32, i32) {
+    let (w, h) = (f64::from(w), f64::from(h));
+    let (content_x, logo_y) = ((w * 0.5) as i32, (h * 0.5) as i32);
+    let logo_height = (w * 0.75).min(h) * 0.25;
+    let half_height = (logo_height * 0.5) as i32;
+    let half_width = (logo_height * 4.0 * 0.5) as i32;
+    (
+        content_x - half_width,
+        logo_y - half_height,
+        half_width,
+        logo_height as i32,
+    )
+}
+
+/// `GuiGraphicsExtractor.fill(x0, y0, x1, y1, color)`: the corners in either order.
+fn fill_corners(batch: &mut HudBatch, atlas: &HudAtlas, [x0, y0, x1, y1]: [i32; 4], color: u32) {
+    let (left, right) = (x0.min(x1), x0.max(x1));
+    let (top, bottom) = (y0.min(y1), y0.max(y1));
+    let (w, h) = ((right - left) as f32, (bottom - top) as f32);
+    batch.fill(atlas, left as f32, top as f32, w, h, color);
+}
+
 /// `LoadingOverlay.extractRenderState`: fills the frame with `BRAND_BACKGROUND`
-/// (Mojang red, or black when `darkMojangStudiosBackground` is set) and draws the
-/// progress line and bar.
+/// (Mojang red, or black when `darkMojangStudiosBackground` is set), draws the
+/// Mojang Studios logo as its two halves side by side, and the progress bar
+/// at 83.25% of the height (`extractProgressBar`, unfaded), with the stage's
+/// line above it. The logo's `MOJANG_LOGO` pipeline adds it (`SRC_ALPHA, ONE`):
+/// its texels are white, which alpha blending matches but for the red channel
+/// of the logo's soft edges, a 16/255 difference at most.
 pub fn draw_loading_overlay(
     batch: &mut HudBatch,
     atlas: &HudAtlas,
@@ -395,15 +426,58 @@ pub fn draw_loading_overlay(
     progress: f32,
     dark: bool,
 ) {
-    batch.fill(
+    let (w, h) = (batch.width, batch.height);
+    batch.fill(atlas, 0.0, 0.0, w, h, brand_background(dark));
+    let (x, y, half_width, logo_height) = logo_layout(w, h);
+    if let Some(r) = atlas.sprites.get(MOJANG_STUDIOS_LOGO).copied() {
+        // blit(.., u, v, width, height, 120, 60, 120, 120): the left half
+        // samples the texture's top half from u = -0.0625, the right half its
+        // bottom half from u = 0.0625 (clamped, as the logo's sampler is).
+        let at = |u: f32, v: f32| {
+            let (u, v) = ((u / 120.0).clamp(0.0, 1.0), v / 120.0);
+            (r.u0 + (r.u1 - r.u0) * u, r.v0 + (r.v1 - r.v0) * v)
+        };
+        for (i, (u, v)) in [(-0.0625, 0.0), (0.0625, 60.0)].into_iter().enumerate() {
+            let (u0, v0) = at(u, v);
+            let (u1, v1) = at(u + 120.0, v + 60.0);
+            let half = crate::hud::Rect {
+                u0,
+                v0,
+                u1,
+                v1,
+                ..r
+            };
+            let left = x + i as i32 * half_width;
+            let (lw, lh) = (half_width as f32, logo_height as f32);
+            batch.rect_uv(left as f32, y as f32, lw, lh, half, u32::MAX);
+        }
+    }
+    let bar_y = (f64::from(h) * 0.8325) as i32;
+    let x_center = (w as i32) / 2;
+    let [x0, y0, x1, y1] = [
+        x_center - half_width,
+        bar_y - 5,
+        x_center + half_width,
+        bar_y + 5,
+    ];
+    let filled = (((x1 - x0) - 2) as f32 * progress.clamp(0.0, 1.0)).ceil() as i32;
+    let white = u32::MAX;
+    fill_corners(batch, atlas, [x0 + 2, y0 + 2, x0 + filled, y1 - 2], white);
+    fill_corners(batch, atlas, [x0 + 1, y0, x1 - 1, y0 + 1], white);
+    fill_corners(batch, atlas, [x0 + 1, y1, x1 - 1, y1 - 1], white);
+    fill_corners(batch, atlas, [x0, y0, x0 + 1, y1], white);
+    fill_corners(batch, atlas, [x1, y0, x1 - 1, y1], white);
+    let text = Text::literal(line);
+    let tw = atlas.font.width_text(&text) as i32;
+    let text_top = (y0 - 9 - 3) as f32;
+    batch.text_styled(
         atlas,
-        0.0,
-        0.0,
-        batch.width,
-        batch.height,
-        brand_background(dark),
+        &text,
+        (x_center - tw / 2) as f32,
+        text_top,
+        white,
+        true,
     );
-    draw_progress(batch, atlas, line, progress);
 }
 
 /// The startup loading screen: the stage's line and a progress bar, centred
@@ -572,6 +646,14 @@ pub fn draw_file_fixer(
 mod tests {
     use super::*;
 
+    #[test]
+    fn the_mojang_logo_is_a_quarter_of_the_shorter_side_and_four_times_as_wide() {
+        // 320x240: min(240, 240) / 4 = 60 high, two halves of 120.
+        assert_eq!(logo_layout(320.0, 240.0), (40, 90, 120, 60));
+        // A tall frame sizes the logo by three quarters of its width.
+        assert_eq!(logo_layout(400.0, 500.0), (50, 213, 150, 75));
+    }
+
     #[test]
     fn progress_weighs_the_prepared_server_and_the_player_chunks() {
         assert_eq!(progress(0), 10.0 / 59.0);

crates/horizon-client-render/src/mesher/sides.rs

@@ -13,9 +13,10 @@
 //!
 //! The buckets lie one after another in the mesh, in an order chosen so that
 //! the buckets an eye can see are usually one or two runs of quads: one draw
-//! each. Inside a bucket quads keep their model order, so coplanar quads
-//! facing one way (an overlay on its base) still draw in that order.
-use super::TerrainVertex;
+//! each. Coplanar quads facing one way keep their model order, so an overlay
+//! on its base still draws in that order. Solid cutout quads are otherwise
+//! ordered from the outside toward the section interior to reduce overdraw.
+use super::{OPAQUE_LAYER, TerrainVertex};
 
 /// The buckets in mesh order: +X, +Z, other, +Y, -Z, -X, -Y. Seen from
 /// above (+Y, the commonest case), each pair of horizontal sides with a
@@ -138,11 +139,14 @@ fn bucket(quad: &[TerrainVertex; 4]) -> usize {
     OTHER
 }
 
-/// Reorders `solid`'s quads by bucket, keeping their order inside each.
+/// Reorders `solid`'s quads by bucket. Solid cutout quads are also ordered
+/// front to back within each axis-facing bucket; stable sorting preserves the
+/// mesher's order for coplanar overlays.
 pub fn sort(solid: &mut Vec<TerrainVertex>) -> Sides {
     let (quads, rest) = solid.as_chunks::<4>();
     debug_assert!(rest.is_empty(), "solid vertices come in quads");
     let buckets: Vec<u8> = quads.iter().map(|q| bucket(q) as u8).collect();
+    let has_cutout = quads.iter().any(|q| q[0].layer & OPAQUE_LAYER == 0);
     let mut counts = [0u32; 7];
     let mut planes = [0f32; 7];
     for (quad, &b) in quads.iter().zip(&buckets) {
@@ -163,7 +167,7 @@ pub fn sort(solid: &mut Vec<TerrainVertex>) -> Sides {
         total += count;
         *end = total;
     }
-    if counts.iter().filter(|&&c| c > 0).count() > 1 {
+    if has_cutout || counts.iter().filter(|&&c| c > 0).count() > 1 {
         let mut next: [u32; 7] = std::array::from_fn(|b| ends[b] - counts[b]);
         let mut sorted = vec![quads[0]; quads.len()];
         for (quad, &b) in quads.iter().zip(&buckets) {
@@ -171,6 +175,25 @@ pub fn sort(solid: &mut Vec<TerrainVertex>) -> Sides {
             sorted[*slot as usize] = *quad;
             *slot += 1;
         }
+        if has_cutout {
+            let mut start = 0;
+            for (i, bucket) in BUCKETS.iter().enumerate() {
+                let end = ends[i] as usize;
+                let slice = &mut sorted[start..end];
+                if let Bucket::Side(axis, positive) = *bucket {
+                    slice.sort_by(|a, b| {
+                        let a = a[0].pos[axis];
+                        let b = b[0].pos[axis];
+                        if positive {
+                            b.total_cmp(&a)
+                        } else {
+                            a.total_cmp(&b)
+                        }
+                    });
+                }
+                start = end;
+            }
+        }
         *solid = sorted.into_flattened();
     }
     Sides { ends, planes }
@@ -368,4 +391,46 @@ mod tests {
             before.iter().map(|v| v.layer).collect::<Vec<_>>()
         );
     }
+
+    #[test]
+    fn front_to_back_sort_orders_positive_faces_and_keeps_ties_stable() {
+        let mut solid: Vec<_> = [(1.0, 10), (3.0, 30), (3.0, 31)]
+            .into_iter()
+            .flat_map(|(x, layer)| {
+                quad(
+                    [[x, 0.0, 0.0], [x, 1.0, 0.0], [x, 1.0, 1.0], [x, 0.0, 1.0]],
+                    layer,
+                )
+            })
+            .collect();
+        sort(&mut solid);
+        let layers: Vec<u16> = solid
+            .as_chunks::<4>()
+            .0
+            .iter()
+            .map(|q| q[0].layer)
+            .collect();
+        assert_eq!(layers, [30, 31, 10]);
+    }
+
+    #[test]
+    fn front_to_back_sort_orders_negative_faces_toward_the_eye() {
+        let mut solid: Vec<_> = [(3.0, 30), (1.0, 10), (2.0, 20)]
+            .into_iter()
+            .flat_map(|(x, layer)| {
+                quad(
+                    [[x, 0.0, 0.0], [x, 0.0, 1.0], [x, 1.0, 1.0], [x, 1.0, 0.0]],
+                    layer,
+                )
+            })
+            .collect();
+        sort(&mut solid);
+        let layers: Vec<u16> = solid
+            .as_chunks::<4>()
+            .0
+            .iter()
+            .map(|q| q[0].layer)
+            .collect();
+        assert_eq!(layers, [10, 20, 30]);
+    }
 }

crates/horizon-client-render/src/options_ui.rs

@@ -1236,6 +1236,8 @@ pub enum Page {
     NativeMod(usize),
     /// Horizon's shader packs, either kind (`shader_pack_list`).
     ShaderPacks,
+    /// The options of `s.shader_packs[.0]`, a Horizon pack.
+    NativePackOptions(usize),
     /// The picked `shaders/` pack's options (`shader_options`), one of its screens at a time.
     ShaderOptions,
     /// Horizon's graphics settings (`graphics_ui`).
@@ -1282,6 +1284,12 @@ enum Act {
     OpenShaderPackFolder,
     /// Open the picked pack's Shader Options page.
     ShaderOptions,
+    /// Open the options page of the Horizon pack `s.shader_packs[.0]`.
+    NativePackOptions(usize),
+    /// Option `.1` of that pack: its next value.
+    NativePackOption(usize, usize),
+    /// Every option of that pack back to its default.
+    NativePackReset(usize),
     /// Shader Options: the next value of an option, a screen of the pack, the next profile,
     /// every option back to its default.
     ShaderOption(String),
@@ -1411,6 +1419,9 @@ pub enum Event {
     OpenShaderOptions,
     /// The Shader Options page closed with changes: save them and load the pack again.
     ShaderOptions,
+    /// The options of `shader_packs[.0]`, a Horizon pack, changed: save them (the pack reloads
+    /// with them).
+    NativePackOptions(usize),
     /// Native mod `.0`'s page opened: the game asks the mod for its labels
     /// again (they were made with the list, maybe in another language).
     NativeSettings(usize),
@@ -1627,6 +1638,27 @@ fn horizon_page_tooltip(page: Page) -> Option<&'static str> {
 }
 /// The open screen of the picked pack: its title, then its items two to a row (one when the
 /// pack asks for a single column).
+/// The options of the Horizon pack `s.shader_packs[i]`, two a row.
+fn native_pack_option_rows(s: &Settings, i: usize) -> Vec<Row> {
+    let Some(pack) = s.shader_packs.get(i) else {
+        return Vec::new();
+    };
+    let mut widgets = pack
+        .options
+        .iter()
+        .zip(&pack.values)
+        .enumerate()
+        .map(|(o, (option, v))| {
+            let value = crate::shader_pack_list::show_value(&option.kind, *v);
+            let label = Text::literal(format!("{}: {value}", option.name));
+            button(0.0, 0.0, 150.0, label, Act::NativePackOption(i, o))
+        });
+    let mut rows = vec![Row::Note(pack.title.clone())];
+    while let Some(a) = widgets.next() {
+        rows.push(Row::Buttons(a, widgets.next()));
+    }
+    rows
+}
 fn shader_option_rows(s: &Settings) -> Vec<Row> {
     let Some(options) = &s.shader_options else {
         return vec![Row::Header("horizon.shader_options.loading")];
@@ -1712,6 +1744,14 @@ enum Row {
 /// A widget's tooltip (`setTooltip`), unwrapped: drawn while hovered, and
 /// its narration's hint.
 fn tooltip_text(s: &Settings, wd: &Widget) -> Option<Text> {
+    if let WKind::Button {
+        act: Act::NativePackOption(pack, option),
+        ..
+    } = &wd.kind
+    {
+        let option = s.shader_packs.get(*pack)?.options.get(*option)?;
+        return (!option.description.is_empty()).then(|| Text::literal(&option.description));
+    }
     let WKind::Button { act, .. } = &wd.kind else {
         let WKind::Slider { opt, .. } = &wd.kind else {
             return None;
@@ -2073,7 +2113,7 @@ impl OptionsUi {
             Page::Mods => "horizon.pages.mods",
             Page::NativeMod(_) => "Mod Settings",
             Page::ShaderPacks => "horizon.pages.shader_packs",
-            Page::ShaderOptions => "horizon.pages.shader_options",
+            Page::ShaderOptions | Page::NativePackOptions(_) => "horizon.pages.shader_options",
             Page::Graphics | Page::GraphicsAdvanced | Page::GraphicsHdr | Page::HdrCalibration => {
                 "options.videoTitle"
             }
@@ -2502,13 +2542,19 @@ impl OptionsUi {
                 if s.shader_packs.is_empty() {
                     return vec![Row::Header("horizon.shader_packs.empty")];
                 }
-                let options = s.shader_packs.iter().any(|p| {
-                    p.file == s.horizon.shader_pack
-                        && p.kind == crate::shader_pack_list::Kind::Classic
-                });
-                let options = options.then(|| {
+                let picked = s
+                    .shader_packs
+                    .iter()
+                    .position(|p| p.file == s.horizon.shader_pack);
+                let options = picked.and_then(|i| {
+                    let pack = &s.shader_packs[i];
+                    let act = match pack.kind {
+                        crate::shader_pack_list::Kind::Classic => Act::ShaderOptions,
+                        _ if pack.options.is_empty() => return None,
+                        crate::shader_pack_list::Kind::Horizon => Act::NativePackOptions(i),
+                    };
                     let label = tr("horizon.shader_options.open");
-                    Row::Buttons(button(0.0, 0.0, 310.0, label, Act::ShaderOptions), None)
+                    Some(Row::Buttons(button(0.0, 0.0, 310.0, label, act), None))
                 });
                 options
                     .into_iter()
@@ -2526,6 +2572,7 @@ impl OptionsUi {
                     .collect()
             }
             Page::ShaderOptions => shader_option_rows(s),
+            Page::NativePackOptions(i) => native_pack_option_rows(s, i),
             _ => {
                 let _ = s;
                 Vec::new()
@@ -3062,6 +3109,7 @@ impl OptionsUi {
                     Page::Mods => Some(("horizon.mods.open_folder", Act::OpenModFolder)),
                     Page::ShaderPacks => Some(("pack.openFolder", Act::OpenShaderPackFolder)),
                     Page::ShaderOptions => Some(("controls.reset", Act::ShaderReset)),
+                    Page::NativePackOptions(i) => Some(("controls.reset", Act::NativePackReset(i))),
                     _ => None,
                 };
                 if let Some((label, act)) = folder {
@@ -3722,6 +3770,25 @@ impl OptionsUi {
                 options.cycle(&name, true);
                 events.push(Event::ButtonClick);
             }
+            let native = widgets.iter().find_map(|wd| match wd.kind {
+                WKind::Button {
+                    active: true,
+                    act: Act::NativePackOption(pack, option),
+                    ..
+                } if ui::hovered((x, y), wd.x, wd.y, wd.w, wd.h)
+                    && !(wd.list && (y < top || y >= bottom)) =>
+                {
+                    Some((pack, option))
+                }
+                _ => None,
+            });
+            if let Some((pack, option)) = native
+                && let Some(entry) = s.shader_packs.get_mut(pack)
+                && entry.step_option(option, true, false)
+            {
+                events.push(Event::ButtonClick);
+                events.push(Event::NativePackOptions(pack));
+            }
             return events;
         }
         if ui::scrollbar_thumb(top, bottom, content, self.scroll).is_some()
@@ -3838,6 +3905,22 @@ impl OptionsUi {
                                 options.reset();
                             }
                         }
+                        Act::NativePackOptions(i) => {
+                            self.push(Page::NativePackOptions(i));
+                        }
+                        Act::NativePackOption(pack, option) => {
+                            if let Some(entry) = s.shader_packs.get_mut(pack)
+                                && entry.step_option(option, false, self.shift)
+                            {
+                                events.push(Event::NativePackOptions(pack));
+                            }
+                        }
+                        Act::NativePackReset(pack) => {
+                            if let Some(entry) = s.shader_packs.get_mut(pack) {
+                                entry.reset_options();
+                                events.push(Event::NativePackOptions(pack));
+                            }
+                        }
                         Act::Credits => events.push(Event::Credits),
                         Act::CopyAgentDetails => events.push(Event::CopyAgentDetails),
                         Act::None => {}
@@ -4745,6 +4828,22 @@ impl OptionsUi {
                                 options.reset();
                             }
                         }
+                        Act::NativePackOptions(i) => {
+                            self.push(Page::NativePackOptions(i));
+                        }
+                        Act::NativePackOption(pack, option) => {
+                            if let Some(entry) = s.shader_packs.get_mut(pack)
+                                && entry.step_option(option, false, shift)
+                            {
+                                events.push(Event::NativePackOptions(pack));
+                            }
+                        }
+                        Act::NativePackReset(pack) => {
+                            if let Some(entry) = s.shader_packs.get_mut(pack) {
+                                entry.reset_options();
+                                events.push(Event::NativePackOptions(pack));
+                            }
+                        }
                         Act::Credits => events.push(Event::Credits),
                         Act::CopyAgentDetails => events.push(Event::CopyAgentDetails),
                         Act::None => {}
@@ -5032,6 +5131,54 @@ mod tests {
         HudAtlas::build(std::path::Path::new("/nonexistent/horizon-test-assets")).unwrap()
     }
 
+    #[test]
+    fn a_horizon_packs_options_step_both_ways_from_the_picked_packs_button() {
+        let atlas = atlas();
+        let size = (960.0, 540.0);
+        let mut s = Settings::default();
+        s.horizon.shader_pack = "p".into();
+        s.shader_packs = vec![crate::shader_pack_list::Entry {
+            file: "p".into(),
+            title: "P".into(),
+            kind: crate::shader_pack_list::Kind::Horizon,
+            options: vec![horizon_shader_api::PackOption {
+                id: "a".into(),
+                name: "A".into(),
+                description: String::new(),
+                kind: horizon_shader_api::OptionKind::Float {
+                    default: 1.0,
+                    min: 0.0,
+                    max: 2.0,
+                    step: 0.5,
+                },
+            }],
+            values: vec![1.0],
+        }];
+        let mut ui = OptionsUi::default();
+        ui.show(Page::ShaderPacks);
+        let find = |ui: &mut OptionsUi, s: &Settings, want: &Act| {
+            let (widgets, ..) = ui.layout(s, size.0, size.1);
+            let w = widgets
+                .into_iter()
+                .find(|w| matches!(&w.kind, WKind::Button { act, .. } if act == want))
+                .expect("button");
+            (w.x + w.w / 2.0, w.y + w.h / 2.0)
+        };
+        let (x, y) = find(&mut ui, &s, &Act::NativePackOptions(0));
+        ui.click(&mut s, &atlas, x, y, size, [854, 480], false, false);
+        assert_eq!(ui.page(), Page::NativePackOptions(0));
+        let (x, y) = find(&mut ui, &s, &Act::NativePackOption(0, 0));
+        let events = ui.click(&mut s, &atlas, x, y, size, [854, 480], false, false);
+        assert!(events.contains(&Event::NativePackOptions(0)));
+        assert_eq!(s.shader_packs[0].values, [1.5]);
+        ui.click(&mut s, &atlas, x, y, size, [854, 480], false, true);
+        ui.click(&mut s, &atlas, x, y, size, [854, 480], false, true);
+        assert_eq!(s.shader_packs[0].values, [0.5]);
+        let (x, y) = find(&mut ui, &s, &Act::NativePackReset(0));
+        ui.click(&mut s, &atlas, x, y, size, [854, 480], false, false);
+        assert_eq!(s.shader_packs[0].values, [1.0]);
+    }
+
     #[test]
     fn resource_reload_error_blocks_options_until_dismissed() {
         use winit::keyboard::KeyCode;

crates/horizon-client-render/src/shader_pack_list.rs

@@ -2,7 +2,9 @@
 //! Settings > Shader Packs lists them: Horizon's own (docs/shaders.md) and those in the
 //! `shaders/` format, side by side.
 
-use std::path::Path;
+use std::path::{Path, PathBuf};
+
+use horizon_shader_api::{OptionKind, PackOption};
 
 pub const DIR: &str = "shaderpacks";
 
@@ -14,13 +16,46 @@ pub enum Kind {
     Classic,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct Entry {
     /// The folder's or file's name in `shaderpacks`: what the pick saves.
     pub file: String,
     /// The pack's own name for Horizon's packs, else `file`.
     pub title: String,
     pub kind: Kind,
+    /// A Horizon pack's `[[options]]`, and the value of each the player set (`values_path`).
+    pub options: Vec<PackOption>,
+    pub values: Vec<f64>,
+}
+
+impl Entry {
+    /// Saves the player's option values, for the pack in the folder `dir`.
+    pub fn save_values(&self, dir: &Path) {
+        let path = dir.join(&self.file);
+        if let Err(e) = save_values(&path, &self.options, &self.values) {
+            log::warn!("shader pack options of {}: {e}", self.file);
+        }
+    }
+
+    /// The option `i` one value on (`back`: one before), or at its default (`reset`). Whether
+    /// the pack has that option.
+    pub fn step_option(&mut self, i: usize, back: bool, reset: bool) -> bool {
+        let (Some(o), Some(v)) = (self.options.get(i), self.values.get_mut(i)) else {
+            return false;
+        };
+        *v = if reset {
+            o.kind.default_constant()
+        } else {
+            step_value(&o.kind, *v, back)
+        };
+        true
+    }
+
+    /// Every option back to its default.
+    pub fn reset_options(&mut self) {
+        let defaults = self.options.iter().map(|o| o.kind.default_constant());
+        self.values = defaults.collect();
+    }
 }
 
 /// The packs in `dir`, Horizon's first, each kind by title. A missing folder has none.
@@ -53,11 +88,15 @@ fn entry(path: &Path) -> Option<Entry> {
                 .ok()
                 .map(|p| p.manifest)
         };
-        let title = manifest.map_or_else(|| file.clone(), |m| m.name);
+        let (title, options) =
+            manifest.map_or_else(|| (file.clone(), Vec::new()), |m| (m.name, m.options));
+        let values = load_values(path, &options);
         return Some(Entry {
             file,
             title,
             kind: Kind::Horizon,
+            options,
+            values,
         });
     }
     let zip = path.is_file()
@@ -68,9 +107,127 @@ fn entry(path: &Path) -> Option<Entry> {
         title: file.clone(),
         file,
         kind: Kind::Classic,
+        options: Vec::new(),
+        values: Vec::new(),
     })
 }
 
+/// Where the option values of the Horizon pack at `pack` are kept: `<pack>.txt` beside it,
+/// one `id=value` a line.
+pub fn values_path(pack: &Path) -> PathBuf {
+    let mut path = pack.as_os_str().to_owned();
+    path.push(".txt");
+    PathBuf::from(path)
+}
+
+/// The value of each of `options` saved for the pack at `pack`, else its default; a value
+/// out of the option's range is brought into it.
+pub fn load_values(pack: &Path, options: &[PackOption]) -> Vec<f64> {
+    let text = std::fs::read_to_string(values_path(pack)).unwrap_or_default();
+    let saved: std::collections::HashMap<&str, f64> = text
+        .lines()
+        .filter_map(|l| l.split_once('='))
+        .filter_map(|(k, v)| Some((k.trim(), v.trim().parse().ok()?)))
+        .collect();
+    options
+        .iter()
+        .map(|o| {
+            saved
+                .get(o.id.as_str())
+                .map_or_else(|| o.kind.default_constant(), |&v| clamp(&o.kind, v))
+        })
+        .collect()
+}
+
+/// Saves `values` of `options`; values at their defaults are left out, and with none left
+/// the file goes.
+fn save_values(pack: &Path, options: &[PackOption], values: &[f64]) -> std::io::Result<()> {
+    let text: String = options
+        .iter()
+        .zip(values)
+        .filter(|(o, v)| o.kind.default_constant() != **v)
+        .map(|(o, v)| format!("{}={v}\n", o.id))
+        .collect();
+    let path = values_path(pack);
+    if text.is_empty() {
+        match std::fs::remove_file(&path) {
+            Err(e) if e.kind() != std::io::ErrorKind::NotFound => Err(e),
+            _ => Ok(()),
+        }
+    } else {
+        std::fs::write(path, text)
+    }
+}
+
+fn clamp(kind: &OptionKind, v: f64) -> f64 {
+    match kind {
+        OptionKind::Bool { .. } => f64::from(u8::from(v != 0.0)),
+        OptionKind::Float { min, max, .. } => v.clamp(f64::from(*min), f64::from(*max)),
+        OptionKind::Int { min, max, .. } => v.round().clamp(f64::from(*min), f64::from(*max)),
+        OptionKind::Choice { values, .. } => v.round().clamp(0.0, values.len() as f64 - 1.0),
+    }
+}
+
+/// The option's next value (`back`: the one before), wrapping around at the ends.
+fn step_value(kind: &OptionKind, v: f64, back: bool) -> f64 {
+    let dir = if back { -1.0 } else { 1.0 };
+    match kind {
+        OptionKind::Bool { .. } => f64::from(u8::from(v == 0.0)),
+        OptionKind::Float { min, max, step, .. } => {
+            let (min, max, step) = (f64::from(*min), f64::from(*max), f64::from(*step));
+            if !back && v >= max - step * 0.01 {
+                min
+            } else if back && v <= min + step * 0.01 {
+                max
+            } else {
+                // On the grid of steps from the minimum, so float error never piles up.
+                let n = ((v - min) / step).round() + dir;
+                (min + n * step).clamp(min, max)
+            }
+        }
+        OptionKind::Int { min, max, .. } => {
+            let (min, max) = (f64::from(*min), f64::from(*max));
+            let n = v.round() + dir;
+            if n > max {
+                min
+            } else if n < min {
+                max
+            } else {
+                n
+            }
+        }
+        OptionKind::Choice { values, .. } => {
+            let n = values.len() as f64;
+            (v.round() + dir).rem_euclid(n)
+        }
+    }
+}
+
+/// The value as the settings page shows it.
+pub fn show_value(kind: &OptionKind, v: f64) -> String {
+    match kind {
+        OptionKind::Bool { .. } => crate::lang::get(if v != 0.0 {
+            "options.on"
+        } else {
+            "options.off"
+        }),
+        OptionKind::Float { step, .. } => {
+            let digits = if *step >= 1.0 {
+                0
+            } else if *step >= 0.1 {
+                1
+            } else {
+                2
+            };
+            format!("{v:.digits$}")
+        }
+        OptionKind::Int { .. } => format!("{v:.0}"),
+        OptionKind::Choice { values, .. } => {
+            values.get(v.round() as usize).cloned().unwrap_or_default()
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -106,4 +263,59 @@ mod tests {
         assert!(scan(&d.join("missing")).is_empty());
         std::fs::remove_dir_all(d).unwrap();
     }
+
+    fn option(id: &str, kind: OptionKind) -> PackOption {
+        PackOption {
+            id: id.into(),
+            name: id.into(),
+            description: String::new(),
+            kind,
+        }
+    }
+
+    #[test]
+    fn values_step_wrap_and_round_trip() {
+        let float = OptionKind::Float {
+            default: 1.0,
+            min: 0.0,
+            max: 2.0,
+            step: 0.5,
+        };
+        assert_eq!(step_value(&float, 1.0, false), 1.5);
+        assert_eq!(step_value(&float, 2.0, false), 0.0);
+        assert_eq!(step_value(&float, 0.0, true), 2.0);
+        assert_eq!(show_value(&float, 1.5), "1.5");
+        let choice = OptionKind::Choice {
+            values: vec!["a".into(), "b".into(), "c".into()],
+            default: 0,
+        };
+        assert_eq!(step_value(&choice, 2.0, false), 0.0);
+        assert_eq!(step_value(&choice, 0.0, true), 2.0);
+        assert_eq!(show_value(&choice, 1.0), "b");
+        let int = OptionKind::Int {
+            default: 0,
+            min: -1,
+            max: 1,
+        };
+        assert_eq!(step_value(&int, 1.0, false), -1.0);
+        let on = OptionKind::Bool { default: true };
+        assert_eq!(step_value(&on, 1.0, false), 0.0);
+
+        let dir =
+            std::env::temp_dir().join(format!("horizon-shader-values-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(&dir).unwrap();
+        let pack = dir.join("p.hshader");
+        let options = [option("a", float), option("b", choice)];
+        // Only what differs from the defaults is written; out of range comes back clamped.
+        save_values(&pack, &options, &[1.0, 2.0]).unwrap();
+        let text = std::fs::read_to_string(values_path(&pack)).unwrap();
+        assert_eq!(text, "b=2\n");
+        std::fs::write(values_path(&pack), "a=9\nb=1\nzzz=4\n").unwrap();
+        assert_eq!(load_values(&pack, &options), [2.0, 1.0]);
+        save_values(&pack, &options, &[1.0, 0.0]).unwrap();
+        assert!(!values_path(&pack).exists());
+        assert_eq!(load_values(&pack, &options), [1.0, 0.0]);
+        std::fs::remove_dir_all(&dir).unwrap();
+    }
 }

crates/horizon-client-render/src/split_layout.rs

@@ -25,6 +25,30 @@ const ROWS: [&[u32]; MAX_PLAYERS - 4] = [
     &[4, 4, 4, 4],
 ];
 
+/// Where a window is.
+#[derive(Clone, Debug, PartialEq)]
+pub enum Placement {
+    /// A normal window: its corner on the desktop and its size in pixels (`None`: a new one,
+    /// where the system opens it).
+    Free(Option<([i32; 2], [u32; 2])>),
+    /// Borderless over the monitor of this name.
+    Fill(String),
+}
+
+/// How far window `number` opens right and down of the centre, in logical pixels: Window 2
+/// centred, each next one a step further, as systems cascade new windows (back to the centre
+/// after six), so new windows never open exactly on one another.
+pub fn cascade(number: u8) -> f64 {
+    f64::from(number.saturating_sub(2) % 6) * 32.0
+}
+
+/// A window: its number (1 is the game's own) and where it is.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Window {
+    pub number: u8,
+    pub placement: Placement,
+}
+
 /// `order` made a whole order of `n` players: those it names (once, if there are), then the
 /// others, P1 first.
 pub fn ordered(order: &[usize], n: usize) -> Vec<usize> {

crates/horizon-client-render/src/ui.rs

@@ -34,9 +34,16 @@ fn parse_nine_slice(v: &serde_json::Value) -> Option<NineSlice> {
         let g = |k: &str| border[k].as_u64().unwrap_or(0) as u32;
         [g("left"), g("top"), g("right"), g("bottom")]
     };
+    let (width, height) = (size("width")?, size("height")?);
+    // `NineSlice.validate`: borders that meet leave no centre slice, so the
+    // sprite has no nine-slice metadata (vanilla draws it as a stretch).
+    let [l, t, r, b] = border;
+    if l.saturating_add(r) >= width || t.saturating_add(b) >= height {
+        return None;
+    }
     Some(NineSlice {
-        width: size("width")?,
-        height: size("height")?,
+        width,
+        height,
         border,
         stretch_inner: s["stretch_inner"].as_bool().unwrap_or(false),
     })
@@ -1458,6 +1465,17 @@ mod tests {
         assert_quad(q[1], ([32.0, 5.0, 40.0, 7.0], [0.0, 0.0, 0.25, 1.0]));
     }
     #[test]
+    fn a_border_that_leaves_no_centre_slice_is_no_metadata() {
+        // NineSlice.validate rejects 12 + 12 >= 20, so the sprite has none.
+        let json = serde_json::json!({"gui": {"scaling": {
+            "type": "nine_slice", "width": 20, "height": 20, "border": 12}}});
+        assert!(parse_nine_slice(&json).is_none());
+        // 9 + 9 < 20 still leaves a centre slice.
+        let json = serde_json::json!({"gui": {"scaling": {
+            "type": "nine_slice", "width": 20, "height": 20, "border": 9}}});
+        assert_eq!(parse_nine_slice(&json).unwrap().border, [9; 4]);
+    }
+    #[test]
     fn a_high_resolution_button_slices_in_its_gui_units() {
         // Faithful 32x's widget/button: 400x40 texels, gui.scaling 200x20.
         let n = faithful(

crates/horizon-client-render/src/widgets.rs

@@ -98,6 +98,25 @@ thread_local! {
     static TARGETS: RefCell<(Vec<Target>, Vec<Target>, u64)> = const { RefCell::new((Vec::new(), Vec::new(), 0)) };
 }
 
+/// Splitscreen: one player's buttons and focus targets, kept aside while another player's game
+/// runs on this thread ([`take`] and [`put`] around each turn).
+#[derive(Default)]
+pub struct Saved(
+    (Vec<Widget>, Vec<Widget>, u64),
+    (Vec<Target>, Vec<Target>, u64),
+);
+
+/// This thread's buttons and targets, leaving none.
+pub fn take() -> Saved {
+    Saved(WIDGETS.take(), TARGETS.take())
+}
+
+/// Bring back what [`take`] kept.
+pub fn put(saved: Saved) {
+    WIDGETS.set(saved.0);
+    TARGETS.set(saved.1);
+}
+
 /// An interactive rectangle (GUI pixels) a controller can focus and click.
 pub fn target(rect: [f32; 4]) {
     target_as(rect, Kind::Button);

crates/horizon-client/Cargo.toml

@@ -83,6 +83,13 @@ open = { version = "5.4.5", features = ["shellexecute-on-windows"] }
 # on the PATH.
 wgpu = { version = "30.0.1", default-features = false, features = ["dx12"] }
 
+[target.'cfg(target_os = "macos")'.dependencies]
+# Splitscreen: a window filling a monitor goes over its menu bar (game/split/windows.rs
+# `above_menu_bar`); all already in the tree through winit and wgpu.
+objc2 = "0.6"
+objc2-app-kit = { version = "0.3", default-features = false, features = ["std", "NSApplication", "NSResponder", "NSWindow", "NSScreen"] }
+objc2-foundation = { version = "0.3", default-features = false, features = ["std", "NSArray", "NSString"] }
+
 [target.'cfg(not(target_os = "macos"))'.dependencies]
 # OpenGL (WGL on Windows, EGL on Linux), the last fallback, for GPUs with no Vulkan or
 # DirectX 12 driver (`graphicsApi`, graphics.rs).

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

@@ -205,5 +205,9 @@
   "Frame rate and frame times over the game, with a graph.": "Frame rate and frame times over the game, with a graph.",
   "horizon.multiplayer.finding_friend": "Finding your friend's world...",
   "horizon.loading.opening_world": "Opening world",
-  "horizon.loading.cancelling_world": "Cancelling world"
+  "horizon.loading.cancelling_world": "Cancelling world",
+  "horizon.multiplayer.not_signed_in": "This server is in online mode. Sign in with your Microsoft account in the Horizon launcher to join it.",
+  "horizon.multiplayer.invalid_address": "Invalid server address: %s",
+  "horizon.multiplayer.connected_friend_direct": "Connected straight to your friend...",
+  "horizon.multiplayer.connected_friend_relay": "Connected to your friend through the relay..."
 }

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

@@ -199,5 +199,9 @@
   "Frame rate and frame times over the game, with a graph.": "Fotogramas por segundo y tiempos de fotograma sobre el juego, con un gráfico.",
   "horizon.multiplayer.finding_friend": "Buscando el mundo de tu amigo…",
   "horizon.loading.opening_world": "Abriendo el mundo",
-  "horizon.loading.cancelling_world": "Cancelando"
+  "horizon.loading.cancelling_world": "Cancelando",
+  "horizon.multiplayer.not_signed_in": "Este servidor está en modo en línea. Inicia sesión con tu cuenta de Microsoft en el launcher de Horizon para unirte.",
+  "horizon.multiplayer.invalid_address": "Dirección de servidor no válida: %s",
+  "horizon.multiplayer.connected_friend_direct": "Conectado directamente con tu amigo…",
+  "horizon.multiplayer.connected_friend_relay": "Conectado con tu amigo a través del relé…"
 }

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

@@ -14,5 +14,9 @@
   "horizon.options.on_screen_keyboard": "Klawiatura ekranowa",
   "horizon.multiplayer.finding_friend": "Szukanie świata znajomego…",
   "horizon.loading.opening_world": "Otwieranie świata",
-  "horizon.loading.cancelling_world": "Anulowanie"
+  "horizon.loading.cancelling_world": "Anulowanie",
+  "horizon.multiplayer.not_signed_in": "Ten serwer działa w trybie online. Zaloguj się kontem Microsoft w launcherze Horizon, aby dołączyć.",
+  "horizon.multiplayer.invalid_address": "Nieprawidłowy adres serwera: %s",
+  "horizon.multiplayer.connected_friend_direct": "Połączono bezpośrednio ze znajomym…",
+  "horizon.multiplayer.connected_friend_relay": "Połączono ze znajomym przez przekaźnik…"
 }

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

@@ -198,5 +198,9 @@
   "Frame rate and frame times over the game, with a graph.": "Частота кадров и их время поверх игры, с графиком.",
   "horizon.multiplayer.finding_friend": "Ищем мир друга…",
   "horizon.loading.opening_world": "Открытие мира",
-  "horizon.loading.cancelling_world": "Отмена"
+  "horizon.loading.cancelling_world": "Отмена",
+  "horizon.multiplayer.not_signed_in": "Этот сервер работает в онлайн-режиме. Войдите с помощью аккаунта Microsoft в лаунчере Horizon, чтобы присоединиться.",
+  "horizon.multiplayer.invalid_address": "Недействительный адрес сервера: %s",
+  "horizon.multiplayer.connected_friend_direct": "Установлено прямое соединение с другом…",
+  "horizon.multiplayer.connected_friend_relay": "Соединение с другом через релей…"
 }

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

@@ -14,5 +14,9 @@
   "horizon.options.on_screen_keyboard": "Екранна клавіатура",
   "horizon.multiplayer.finding_friend": "Шукаємо світ друга…",
   "horizon.loading.opening_world": "Відкриття світу",
-  "horizon.loading.cancelling_world": "Скасування"
+  "horizon.loading.cancelling_world": "Скасування",
+  "horizon.multiplayer.not_signed_in": "Цей сервер працює в онлайн-режимі. Увійдіть за допомогою акаунта Microsoft у лаунчері Horizon, щоб приєднатися.",
+  "horizon.multiplayer.invalid_address": "Недійсна адреса сервера: %s",
+  "horizon.multiplayer.connected_friend_direct": "Пряме з'єднання з другом встановлено…",
+  "horizon.multiplayer.connected_friend_relay": "З'єднання з другом через ретранслятор…"
 }

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

@@ -199,5 +199,9 @@
   "Frame rate and frame times over the game, with a graph.": "游戏运行时的帧率与帧时间，附带图表。",
   "horizon.multiplayer.finding_friend": "正在查找好友的世界…",
   "horizon.loading.opening_world": "正在打开世界",
-  "horizon.loading.cancelling_world": "正在取消"
+  "horizon.loading.cancelling_world": "正在取消",
+  "horizon.multiplayer.not_signed_in": "该服务器为在线模式服务器。请先在 Horizon 启动器中登录 Microsoft 账户再加入。",
+  "horizon.multiplayer.invalid_address": "无效的服务器地址：%s",
+  "horizon.multiplayer.connected_friend_direct": "已直连好友的世界…",
+  "horizon.multiplayer.connected_friend_relay": "已通过中继连接好友的世界…"
 }

crates/horizon-client/build.rs

@@ -5,6 +5,15 @@ fn main() {
     let dir = std::env::var("CARGO_MANIFEST_DIR").unwrap_or_default();
     let ico = format!("{dir}/../../packaging/icons/horizon.ico");
     println!("cargo:rerun-if-changed={ico}");
+    // The game's main thread gets 8 MB of stack on Windows as on macOS and Linux (Windows gives 1
+    // MB): splitscreen builds a joining player's `Game`, ~67 KB, deep in the event loop.
+    if std::env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("windows") {
+        let arg = match std::env::var("CARGO_CFG_TARGET_ENV").as_deref() {
+            Ok("msvc") => "/STACK:8388608",
+            _ => "-Wl,--stack,8388608",
+        };
+        println!("cargo:rustc-link-arg-bin=horizon-client={arg}");
+    }
     #[cfg(windows)]
     if std::env::var("CARGO_CFG_TARGET_OS").as_deref() == Ok("windows") {
         let mut resource = winresource::WindowsResource::new();

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

@@ -291,6 +291,8 @@ pub fn main() -> horizon_client::Result<()> {
             for d in items {
                 let _ = match d {
                     drops::Drop::Item(s) => writeln!(out, "{}", line(&s)),
+                    // The fixture's mobs keep no whole stacks.
+                    drops::Drop::Stack(s) => writeln!(out, "drop {} {}", s.item, s.count),
                     drops::Drop::CarriedBlock(state) => {
                         let stacks = enderman::carried_block_drops(
                             &block_items,

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

@@ -1,5 +1,6 @@
 use horizon_client::interaction_input::{
-    Button, InteractionInput, InteractionWorld, TargetUseWorld, use_on_target,
+    Button, InteractionInput, InteractionWorld, TargetUseWorld, release_on_screen_open,
+    use_on_target,
 };
 use serde_json::Value;
 use std::io::{BufRead, Write};
@@ -103,14 +104,23 @@ pub fn main() -> Result<(), Box<dyn std::error::Error>> {
             passing: row["passing"].as_bool().unwrap_or(false),
         };
         let mut input = InteractionInput::default();
-        for button in row["clicks"].as_array().unwrap() {
-            input.press(match button.as_u64().unwrap() {
-                0 => Button::Attack,
-                1 => Button::Use,
-                _ => Button::Pick,
-            });
+        let screen = row["screen"].as_bool().unwrap_or(false);
+        if screen {
+            // A keybind opened a screen: Gui.setScreen already ran
+            // KeyMapping.releaseAll, so the same handleKeybinds call releases an
+            // active use; with the screen open nothing else acts this tick.
+            release_on_screen_open(&mut world);
+            input.tick(&mut world, false, false);
+        } else {
+            for button in row["clicks"].as_array().unwrap() {
+                input.press(match button.as_u64().unwrap() {
+                    0 => Button::Attack,
+                    1 => Button::Use,
+                    _ => Button::Pick,
+                });
+            }
+            input.tick(&mut world, flag("attack_down"), flag("use_down"));
         }
-        input.tick(&mut world, flag("attack_down"), flag("use_down"));
         writeln!(out, "== {i}")?;
         for event in world.events {
             writeln!(out, "{event}")?;

crates/horizon-client/src/arrows.rs

@@ -1071,6 +1071,15 @@ impl Ticker<'_, '_, '_, '_> {
             }
             effects.advance(step);
             let name = &*self.scene.facts.get(state).name;
+            crate::block_contact::emit(crate::block_contact::Event::Inside(
+                crate::block_contact::Contact {
+                    entity: self.p.id as i32,
+                    kind: self.p.kind.id(),
+                    block: name,
+                    state,
+                    position: p,
+                },
+            ));
             if matches!(name, "minecraft:fire" | "minecraft:soul_fire") {
                 // BaseFireBlock.entityInside (its inFire hurt does nothing to arrows).
                 effects.apply(Effect::ClearFreeze);

crates/horizon-client/src/banner.rs

@@ -92,9 +92,7 @@ impl Banners {
             });
         }
         banners.no_item_required = read_tag(root, "no_item_required", 0);
-        if let Some(raw) = fs::read(root.join("items.json")).ok().and_then(|b| {
-            serde_json::from_slice::<std::collections::BTreeMap<String, Value>>(&b).ok()
-        }) {
+        if let Ok(raw) = horizon_world::item_defaults::read(root) {
             for (item, c) in raw {
                 let id: Arc<str> = Arc::from(item.as_str());
                 if let Some(dye) = c["minecraft:dye"].as_str() {

crates/horizon-client/src/bin/horizon-ctl/commands.rs

@@ -194,7 +194,8 @@ pub const COMMANDS: &[Cmd] = &[
         &[flag("world", Ty::Str, "world folder to open or create"), flag("seed", Ty::Str, "seed for a new world"), flag("creative", Ty::Bool, "creative mode for a new world"),
           flag("version", Ty::Str, "an installed launcher version tag such as v2026.10.13"), flag("game", Ty::Str, "path to a horizon-client binary"),
           flag("wait", Ty::Bool, "also wait until the world is ready (default in MCP)"),
-          flag("offscreen", Ty::Bool, "render without showing a window (screenshots still work): locked or headless sessions")],
+          flag("offscreen", Ty::Bool, "render without showing a window (screenshots still work): locked or headless sessions"),
+          flag("headless", Ty::Bool, "no display, window or GPU: a player that plays through these commands only (no screenshots)")],
         mcp: true, local: true),
     cmd!("wait-for", Session, "wait-for screen NAME|widget ID|loaded|chat TEXT|event KIND [--timeout S] [--since SEQ]", "wait until the game reaches a state, then reply",
         "screen takes the names state shows (playing, inventory, paused, dead, title...); widget an id from ui; loaded means a world is open, the player is in it and no chunk is pending; chat a new line containing TEXT; event a kind from events (death, respawn, item, screen...). chat and event count from --since SEQ (take last from events before acting), else from now. A timeout (default 30 s) is an error with kind timeout.",

crates/horizon-client/src/block_contact.rs

@@ -0,0 +1,201 @@
+//! Synchronous mod-block contacts from the server's simulation code.
+use horizon_core::position::BlockPos;
+use horizon_world::registry::BlockStateId;
+use std::{
+    cell::Cell,
+    sync::{
+        OnceLock,
+        atomic::{AtomicBool, Ordering},
+    },
+};
+
+#[derive(Clone, Copy, Debug)]
+pub struct Contact<'a> {
+    pub entity: i32,
+    pub kind: &'a str,
+    pub block: &'a str,
+    pub state: BlockStateId,
+    pub position: BlockPos,
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum Event<'a> {
+    StepOn(Contact<'a>),
+    Inside(Contact<'a>),
+    FallOn(Contact<'a>, f64),
+}
+
+pub static HOOK: OnceLock<fn(&str, Event<'_>, &mut f32)> = OnceLock::new();
+/// Whether the loaded blocks hold one outside `minecraft:` (a content mod's).
+/// Without one no contact can dispatch, so the item and projectile sweeps
+/// skip their per-tick work: every item and thrown thing on a server would
+/// otherwise sweep its blocks each tick for nothing.
+static MOD_BLOCKS: AtomicBool = AtomicBool::new(false);
+
+/// Called when the block tables load.
+pub fn set_mod_blocks(any: bool) {
+    MOD_BLOCKS.store(any, Ordering::Relaxed);
+}
+thread_local! {
+    static LEVEL: Cell<Option<&'static str>> = const { Cell::new(None) };
+}
+
+/// Scope authority to this thread and restore it even on an error or panic.
+/// Nested guest actions may temporarily enter a different dimension.
+pub fn in_level<R>(dimension: Option<&'static str>, f: impl FnOnce() -> R) -> R {
+    struct Restore(Option<&'static str>);
+    impl Drop for Restore {
+        fn drop(&mut self) {
+            LEVEL.set(self.0);
+        }
+    }
+    let _restore = Restore(LEVEL.replace(dimension));
+    f()
+}
+
+pub fn emit(event: Event<'_>) {
+    dispatch(event, &mut 0.0);
+}
+
+/// Damage is the calculated fall damage, before hurt handling and fall sounds.
+pub fn fall(contact: Contact<'_>, distance: f64, mut damage: f32) -> f32 {
+    dispatch(Event::FallOn(contact, distance), &mut damage);
+    damage
+}
+
+fn dispatch(event: Event<'_>, damage: &mut f32) {
+    let contact = match event {
+        Event::StepOn(c) | Event::Inside(c) | Event::FallOn(c, _) => c,
+    };
+    if contact.block.starts_with("minecraft:") {
+        return;
+    }
+    if let Some(dimension) = LEVEL.get()
+        && let Some(hook) = HOOK.get()
+    {
+        let original = *damage;
+        hook(dimension, event, damage);
+        if !damage.is_finite() {
+            *damage = original;
+        }
+        *damage = damage.max(0.0);
+    }
+}
+
+/// Reuse the entity block sweep for item and projectile ticks without an effect collector.
+pub fn swept_inside<'a>(
+    entity: i32,
+    kind: &str,
+    from: horizon_core::geometry::Vec3,
+    to: horizon_core::geometry::Vec3,
+    bounds: horizon_core::geometry::Aabb,
+    mut block: impl FnMut(BlockPos) -> (BlockStateId, &'a str),
+) {
+    if !MOD_BLOCKS.load(Ordering::Relaxed) || LEVEL.get().is_none() || HOOK.get().is_none() {
+        return;
+    }
+    let bounds = bounds.deflate(horizon_core::geometry::Vec3::new(1e-5, 1e-5, 1e-5));
+    let mut visited = std::collections::HashSet::new();
+    let _ =
+        horizon_core::geometry::sweep_intersected_blocks(from, to, bounds, 1_000_000, |p, step| {
+            if step >= 16 {
+                return false;
+            }
+            if visited.insert(p) {
+                let (state, name) = block(p);
+                emit(Event::Inside(Contact {
+                    entity,
+                    kind,
+                    block: name,
+                    state,
+                    position: p,
+                }));
+            }
+            true
+        });
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    thread_local! {
+        static SEEN: Cell<usize> = const { Cell::new(0) };
+    }
+    fn hook(dimension: &str, event: Event<'_>, damage: &mut f32) {
+        assert_eq!(dimension, "minecraft:the_nether");
+        let c = match event {
+            Event::FallOn(c, distance) => {
+                assert_eq!(distance, 12.0);
+                *damage = match *damage {
+                    99.0 => f32::NAN,
+                    98.0 => -1.0,
+                    _ => *damage * 0.2,
+                };
+                c
+            }
+            Event::Inside(c) | Event::StepOn(c) => c,
+        };
+        assert_eq!(
+            (c.entity, c.kind, c.state, c.position),
+            (
+                17,
+                "minecraft:zombie",
+                BlockStateId(9),
+                BlockPos::new(1, 2, 3)
+            )
+        );
+        SEEN.set(SEEN.get() + 1);
+    }
+    #[test]
+    fn contacts_require_server_scope_and_mod_blocks_and_restore_nested_levels() {
+        HOOK.set(hook).unwrap();
+        let c = Contact {
+            entity: 17,
+            kind: "minecraft:zombie",
+            block: "test:hay",
+            state: BlockStateId(9),
+            position: BlockPos::new(1, 2, 3),
+        };
+        assert_eq!(fall(c, 12.0, 10.0), 10.0);
+        in_level(Some("minecraft:the_nether"), || {
+            emit(Event::StepOn(c));
+            emit(Event::Inside(c));
+            assert_eq!(fall(c, 12.0, 10.0), 2.0);
+            in_level(None, || assert_eq!(fall(c, 12.0, 10.0), 10.0));
+            assert_eq!(fall(c, 12.0, 0.0), 0.0);
+            emit(Event::Inside(Contact {
+                block: "minecraft:hay_block",
+                ..c
+            }));
+        });
+        assert_eq!(fall(c, 12.0, 10.0), 10.0);
+        assert_eq!(SEEN.get(), 4);
+        in_level(Some("minecraft:the_nether"), || {
+            assert_eq!(fall(c, 12.0, 99.0), 99.0);
+            assert_eq!(fall(c, 12.0, 98.0), 0.0);
+            use horizon_core::geometry::{Aabb, Vec3};
+            let to = Vec3::new(2.5, 2.0, 3.5);
+            let bounds = Aabb::new(Vec3::new(2.25, 2.0, 3.25), Vec3::new(2.75, 2.5, 3.75));
+            let block = |p| {
+                (
+                    BlockStateId(9),
+                    if p == c.position {
+                        "test:hay"
+                    } else {
+                        "minecraft:air"
+                    },
+                )
+            };
+            set_mod_blocks(true);
+            swept_inside(17, c.kind, Vec3::new(0.5, 2.0, 3.5), to, bounds, block);
+            assert_eq!(SEEN.get(), 7, "a block crossed mid-move is notified once");
+            let at = Vec3::new(1.5, 2.0, 3.5);
+            let bounds = bounds.move_by(Vec3::new(-1.0, 0.0, 0.0));
+            swept_inside(17, c.kind, at, at, bounds, block);
+            assert_eq!(SEEN.get(), 8, "stationary overlap still notifies");
+        });
+        let _ =
+            std::panic::catch_unwind(|| in_level(Some("minecraft:the_nether"), || panic!("test")));
+        assert_eq!(fall(c, 12.0, 10.0), 10.0);
+    }
+}

crates/horizon-client/src/content_identity.rs

@@ -1,6 +1,6 @@
 //! Identity of the ordered block-state registry used by chunk packets, and of
-//! the item and mob effect registries once content mods add to them (item
-//! stacks and effect packets carry their network ids).
+//! the item, mob effect and entity type registries once content mods add to
+//! them (item stacks, effect and entity packets carry their network ids).
 use horizon_protocol::registry::Builtin;
 use serde::{Deserialize, Serialize, de::IgnoredAny};
 use sha2::{Digest, Sha256};
@@ -76,6 +76,21 @@ pub fn identity(root: &Path) -> Result<[u8; 32], IdentityError> {
         .collect();
     if !components.is_empty() {
         hash = hash_entries(hash, "horizon:nbt_components/v1", &components);
+        // Defaults are not sent in a stack patch. Both peers must therefore
+        // agree on their values as well as the registered wire IDs, native
+        // mods' changes included.
+        let items = horizon_world::item_defaults::read(root).map_err(IdentityError::Read)?;
+        let mut defaults = Vec::new();
+        for (item, components) in items {
+            for (name, value) in components.as_object().into_iter().flatten() {
+                if horizon_protocol::item::custom::id(name).is_some() {
+                    defaults.push((defaults.len() as u64, format!("{item}\0{name}\0{value}")));
+                }
+            }
+        }
+        if !defaults.is_empty() {
+            hash = hash_entries(hash, "horizon:nbt_component_defaults/v1", &defaults);
+        }
     }
     identities.insert(root.to_owned(), hash);
     Ok(hash)
@@ -93,7 +108,11 @@ fn hash_facts(bytes: &[u8]) -> Result<[u8; 32], IdentityError> {
 }
 
 /// The built-in registries whose network ids content mods extend besides blocks.
-const REGISTRIES: [&str; 2] = ["minecraft:item", "minecraft:mob_effect"];
+const REGISTRIES: [&str; 3] = [
+    "minecraft:item",
+    "minecraft:mob_effect",
+    "minecraft:entity_type",
+];
 
 fn parse_registries(bytes: &[u8]) -> Result<Builtin, IdentityError> {
     let text = std::str::from_utf8(bytes).map_err(|e| IdentityError::Registries(e.to_string()))?;

crates/horizon-client/src/entities.rs

@@ -182,47 +182,14 @@ impl ItemEntity {
     /// up) without a full collision cube, at `speed` (`nextFloat() * 0.2 +
     /// 0.1`).
     pub fn move_towards_closest_space(&mut self, world: &World, facts: &BlockFacts, speed: f32) {
-        let bounds = self.bounds();
-        let at = Vec3::new(
-            self.position.x,
-            (bounds.min_position().y + bounds.max_position().y) / 2.0,
-            self.position.z,
+        self.velocity = towards_closest_space(
+            self.position,
+            self.bounds(),
+            self.velocity,
+            world,
+            facts,
+            speed,
         );
-        let pos = [
-            at.x.floor() as i32,
-            at.y.floor() as i32,
-            at.z.floor() as i32,
-        ];
-        let delta = [
-            at.x - f64::from(pos[0]),
-            at.y - f64::from(pos[1]),
-            at.z - f64::from(pos[2]),
-        ];
-        // (axis, step): NORTH, SOUTH, WEST, EAST, UP.
-        let mut closest = (1, 1);
-        let mut nearest = f64::MAX;
-        for (axis, step) in [(2, -1), (2, 1), (0, -1), (0, 1), (1, 1)] {
-            let mut n = pos;
-            n[axis] += step;
-            if !facts.get(world.block(n[0], n[1], n[2])).full_collision {
-                let d = if step > 0 {
-                    1.0 - delta[axis]
-                } else {
-                    delta[axis]
-                };
-                if d < nearest {
-                    nearest = d;
-                    closest = (axis, step);
-                }
-            }
-        }
-        let push = f64::from(closest.1 as f32 * speed);
-        let v = self.velocity.scale(0.75);
-        self.velocity = match closest.0 {
-            0 => Vec3::new(push, v.y, v.z),
-            1 => Vec3::new(v.x, push, v.z),
-            _ => Vec3::new(v.x, v.y, push),
-        };
     }
     /// Returns false when the item should be removed. `no_physics`: the item
     /// moves through blocks this tick ([`ItemEntity::inside_block`]).
@@ -339,6 +306,37 @@ impl ItemEntity {
                 &mut self.velocity,
             );
         }
+        if !no_physics {
+            // Entity.applyEffectsFromBlocks: stepOn, then checkInsideBlocks.
+            if self.on_ground {
+                let p = BlockPos::containing(self.position.add_vector(Vec3::new(
+                    0.0,
+                    -f64::from(0.2_f32),
+                    0.0,
+                )));
+                let state = world.block(p.x, p.y, p.z);
+                crate::block_contact::emit(crate::block_contact::Event::StepOn(
+                    crate::block_contact::Contact {
+                        entity: self.id as i32,
+                        kind: "minecraft:item",
+                        block: &facts.get(state).name,
+                        state,
+                        position: p,
+                    },
+                ));
+            }
+            crate::block_contact::swept_inside(
+                self.id as i32,
+                "minecraft:item",
+                self.previous,
+                self.position,
+                self.bounds(),
+                |p| {
+                    let state = world.block(p.x, p.y, p.z);
+                    (state, &facts.get(state).name)
+                },
+            );
+        }
         if self.velocity.subtract(old_velocity).length_squared() > 0.01 {
             self.needs_sync = true;
         }
@@ -638,6 +636,7 @@ impl ExperienceOrb {
         facts: &BlockFacts,
         collision: &BlockCollisionRegistry<'_>,
         player: Option<[f64; 3]>,
+        server: bool,
         next_float: &mut dyn FnMut() -> f32,
     ) -> bool {
         self.ticks += 1;
@@ -647,13 +646,22 @@ impl ExperienceOrb {
             self.position.y.floor() as i32,
             self.position.z.floor() as i32,
         );
+        let bounds = self.bounds();
+        let mut scene = SceneCollisions {
+            world,
+            binding: collision,
+            subject: None,
+        };
+        // `boolean colliding = !level.noCollision(getBoundingBox())`: an orb
+        // inside blocks takes no gravity until it is pushed out below.
+        let colliding = !crate::collisions::no_collision_empty(&mut scene, bounds);
         if facts.get(block).fluid == Fluid::Water {
             self.velocity = Vec3::new(
                 self.velocity.x * 0.99,
                 (self.velocity.y + 5.0e-4).min(0.06),
                 self.velocity.z * 0.99,
             );
-        } else {
+        } else if !colliding {
             self.velocity.y -= 0.03;
         }
         if facts.get(block).fluid == Fluid::Lava {
@@ -681,12 +689,18 @@ impl ExperienceOrb {
                 );
             }
         }
-        let bounds = self.bounds();
-        let mut scene = SceneCollisions {
-            world,
-            binding: collision,
-            subject: None,
-        };
+        if player.is_none() && server && colliding {
+            // `followingPlayer == null && !level().isClientSide() && colliding`: an orb that would still
+            // be stuck at its next position gets
+            // `Entity.moveTowardsClosestSpace`, a nudge towards the nearest
+            // free side of its block.
+            if !crate::collisions::no_collision_empty(&mut scene, bounds.move_by(self.velocity)) {
+                let speed = next_float() * 0.2 + 0.1;
+                self.move_towards_closest_space(world, facts, speed);
+            }
+        }
+        // `double fallSpeed = getDeltaMovement().y`, taken after the stuck
+        // push and before the move.
         let wanted = self.velocity;
         let moved = scene
             .resolve(bounds, wanted, 0.0, self.on_ground)
@@ -697,26 +711,114 @@ impl ExperienceOrb {
             self.position.z + moved.z,
         );
         self.on_ground = wanted.y < 0.0 && moved.y != wanted.y;
-        let mut friction = 0.98;
+        // Entity.move's restituteMovementAfterCollisions, an orb's bounciness
+        // 0: each collided axis's velocity is zeroed — x and z by Mth.equal's
+        // 1.0E-5, y exactly.
+        if (wanted.x - moved.x).abs() >= 1.0e-5 {
+            self.velocity.x = 0.0;
+        }
+        if (wanted.z - moved.z).abs() >= 1.0e-5 {
+            self.velocity.z = 0.0;
+        }
+        if moved.y != wanted.y {
+            self.velocity.y = 0.0;
+        }
+        // `float friction = getAirDrag()` (0.98F), the ground's block
+        // friction multiplied in as a float, widened once for the scale.
+        let mut friction = 0.98_f32;
         if self.on_ground {
             let below = world.block(
                 self.position.x.floor() as i32,
-                (self.position.y - 1.0).floor() as i32,
+                (self.position.y - 0.999_999).floor() as i32,
                 self.position.z.floor() as i32,
             );
-            friction = f64::from(facts.get(below).friction) * 0.98;
+            friction *= facts.get(below).friction;
         }
+        let friction = f64::from(friction);
+        // The drag scales every axis by the same friction, the ground's
+        // block friction included.
         self.velocity = Vec3::new(
             self.velocity.x * friction,
-            self.velocity.y * 0.98,
+            self.velocity.y * friction,
             self.velocity.z * friction,
         );
-        if self.on_ground {
-            self.velocity.y *= -0.9;
+        // `if (verticalCollisionBelow && fallSpeed < -getGravity())`: the
+        // landing bounce is 0.4 of the pre-move speed, not a fixed
+        // restitution.
+        if self.on_ground && wanted.y < -0.03 {
+            self.velocity.y = -wanted.y * 0.4;
         }
         self.age += 1;
         self.age < 6000
     }
+    /// `Entity.moveTowardsClosestSpace` from the middle of the orb's box:
+    /// towards the nearest side of its block (north, south, west, east or
+    /// up) without a full collision cube, at `speed` (the orb's own
+    /// random, `nextFloat() * 0.2 + 0.1`).
+    fn move_towards_closest_space(&mut self, world: &World, facts: &BlockFacts, speed: f32) {
+        self.velocity = towards_closest_space(
+            self.position,
+            self.bounds(),
+            self.velocity,
+            world,
+            facts,
+            speed,
+        );
+    }
+}
+/// `Entity.moveTowardsClosestSpace` from the middle of an entity's box
+/// (`bounds`, its feet at `position`): the velocity pushed towards the
+/// nearest side of its block (north, south, west, east or up) without a full
+/// collision cube, at `speed` (`nextFloat() * 0.2 + 0.1`). Items and
+/// experience orbs share it.
+fn towards_closest_space(
+    position: Vec3,
+    bounds: Aabb,
+    velocity: Vec3,
+    world: &World,
+    facts: &BlockFacts,
+    speed: f32,
+) -> Vec3 {
+    let at = Vec3::new(
+        position.x,
+        (bounds.min_position().y + bounds.max_position().y) / 2.0,
+        position.z,
+    );
+    let pos = [
+        at.x.floor() as i32,
+        at.y.floor() as i32,
+        at.z.floor() as i32,
+    ];
+    let delta = [
+        at.x - f64::from(pos[0]),
+        at.y - f64::from(pos[1]),
+        at.z - f64::from(pos[2]),
+    ];
+    // (axis, step): NORTH, SOUTH, WEST, EAST, UP.
+    let mut closest = (1, 1);
+    let mut nearest = f64::MAX;
+    for (axis, step) in [(2, -1), (2, 1), (0, -1), (0, 1), (1, 1)] {
+        let mut n = pos;
+        n[axis] += step;
+        if !facts.get(world.block(n[0], n[1], n[2])).full_collision {
+            let d = if step > 0 {
+                1.0 - delta[axis]
+            } else {
+                delta[axis]
+            };
+            if d < nearest {
+                nearest = d;
+                closest = (axis, step);
+            }
+        }
+    }
+    let push = f64::from(closest.1 as f32 * speed);
+    let v = velocity.scale(0.75);
+    match closest.0 {
+        0 => Vec3::new(push, v.y, v.z),
+        1 => Vec3::new(v.x, push, v.z),
+        _ => Vec3::new(v.x, v.y, push),
+    }
 }
 /// `ExperienceOrb.scanForMerges`, run by each orb on `tickCount % 20 == 1`:
 /// it absorbs the orbs that `canMerge` within 0.5 blocks of its box,
@@ -947,9 +1049,15 @@ pub struct ArmorStand {
     pub health: f32,
     pub id: u32,
     pub position: Vec3,
+    /// `Entity.xo`, `yo`, `zo`: the position at the start of the tick, which
+    /// the renderer blends toward `position` by the partial tick.
+    pub previous: Vec3,
     pub velocity: Vec3,
     pub on_ground: bool,
+    /// `yRot`, which the body follows (`ArmorStand.tickHeadTurn`: `yBodyRot`).
     pub yaw: f32,
+    /// `yBodyRotO`: the body's yaw at the start of the tick.
+    pub previous_yaw: f32,
     /// mainhand, offhand, feet, legs, chest, head (EquipmentSlot order).
     pub equipment: [Option<crate::items::ItemStack>; 6],
     pub small: bool,
@@ -970,6 +1078,9 @@ pub struct ArmorStand {
     /// rides, which seats it every tick (`positionRider`), as NPC plugins hang
     /// a second name over a player's head.
     pub vehicle: Option<u32>,
+    /// `ArmorStand.disabledSlots`: bit `filterFlag` locks a slot, bit
+    /// `filterFlag + 8` takes from it and bit `filterFlag + 16` puts into it.
+    pub disabled_slots: i32,
 }
 impl ArmorStand {
     pub const SLOTS: [&'static str; 6] = ["mainhand", "offhand", "feet", "legs", "chest", "head"];
@@ -985,15 +1096,50 @@ impl ArmorStand {
         [-1.0, 0.0, -1.0],
         [1.0, 0.0, 1.0],
     ];
+    /// Where the renderer draws the stand `alpha` of the way through the tick
+    /// (`EntityRenderer`'s `Mth.lerp(partialTick, xo, x)` and so on).
+    pub fn render_position(&self, alpha: f64) -> Vec3 {
+        self.previous.lerp(self.position, alpha)
+    }
+    /// The body's yaw `alpha` of the way through the tick
+    /// (`LivingEntityRenderer.solveBodyRot`: `Mth.rotLerp(partialTick,
+    /// yBodyRotO, yBodyRot)`).
+    pub fn render_yaw(&self, alpha: f32) -> f32 {
+        self.previous_yaw + alpha * crate::camera::wrap_degrees(self.yaw - self.previous_yaw)
+    }
+    /// A server's stand on its client, each tick:
+    /// `setOldPosAndRot` (`ClientLevel.tickNonPassenger`), then the step of
+    /// its `SteppedInterpolationHandler` (`step`: the position and yaw it is
+    /// put at, when one is due). The yaw
+    /// turns the short way and stays continuous, so a frame between ticks
+    /// never spins it.
+    pub fn interpolate(&mut self, step: Option<(Vec3, f32)>) {
+        self.previous = self.position;
+        self.previous_yaw = self.yaw;
+        if let Some((at, yaw)) = step {
+            self.position = at;
+            self.yaw += crate::camera::wrap_degrees(yaw - self.yaw);
+        }
+    }
+    /// Put there at once, with nothing to blend from
+    /// (`Entity.snapTo`).
+    pub fn snap(&mut self, at: Vec3, yaw: f32) {
+        self.position = at;
+        self.previous = at;
+        self.yaw = yaw;
+        self.previous_yaw = yaw;
+    }
     pub fn new(id: u32, position: Vec3, yaw: f32) -> Self {
         Self {
             fire_ticks: 0,
             health: 20.0,
             id,
             position,
+            previous: position,
             velocity: Vec3::ZERO,
             on_ground: true,
             yaw,
+            previous_yaw: yaw,
             equipment: Default::default(),
             small: false,
             show_arms: false,
@@ -1005,8 +1151,29 @@ impl ArmorStand {
             last_hit: i64::MIN / 2,
             pose: Self::DEFAULT_POSE,
             vehicle: None,
+            disabled_slots: 0,
         }
     }
+    /// `EquipmentSlot.getFilterFlag` of an `equipment` index (main hand, off
+    /// hand, feet, legs, chest, head).
+    fn filter_flag(slot: usize) -> u32 {
+        [0, 5, 1, 2, 3, 4][slot]
+    }
+    /// `ArmorStand.isDisabled`: the slot is locked, or it is a hand and the
+    /// stand has no arms.
+    pub fn is_disabled(&self, slot: usize) -> bool {
+        self.disabled_slots & (1 << Self::filter_flag(slot)) != 0 || (slot < 2 && !self.show_arms)
+    }
+    /// The `swapItem` locks: taking from a filled slot or putting into an
+    /// empty one can each be disabled.
+    pub fn swap_locked(&self, slot: usize) -> bool {
+        let offset = if self.equipment[slot].is_some() {
+            8
+        } else {
+            16
+        };
+        self.disabled_slots & (1 << (Self::filter_flag(slot) + offset)) != 0
+    }
     pub fn environment_tick(
         &mut self,
         world: &World,
@@ -1296,6 +1463,53 @@ mod fire_environment_tests {
     }
 }
 #[cfg(test)]
+mod armor_stand_render_tests {
+    use super::*;
+
+    /// A falling stand is drawn between last tick's position and this one's,
+    /// so it slides down every frame instead of jumping once a tick (#4416).
+    #[test]
+    fn a_falling_stand_is_drawn_between_its_ticks() {
+        let mut stand = ArmorStand::new(1, Vec3::new(0.5, 70.0, 0.5), 0.0);
+        // A new stand has no move behind it.
+        assert_eq!(stand.render_position(0.5), stand.position);
+        let fall = |s: &ArmorStand| Some((Vec3::new(0.5, s.position.y - 1.0, 0.5), 0.0));
+        stand.interpolate(fall(&stand));
+        assert_eq!(stand.render_position(0.0).y, 70.0);
+        assert_eq!(stand.render_position(0.25).y, 69.75);
+        assert_eq!(stand.render_position(1.0).y, 69.0);
+        stand.interpolate(fall(&stand));
+        assert_eq!(stand.render_position(0.5).y, 68.5);
+        // Landed: no step is due, so it stays put, and so does every frame.
+        stand.interpolate(None);
+        assert_eq!(stand.render_position(0.5).y, 68.0);
+    }
+
+    /// A turning stand's body turns between ticks too, the short way round.
+    #[test]
+    fn a_turning_stand_is_drawn_between_its_ticks() {
+        let mut stand = ArmorStand::new(1, Vec3::ZERO, 170.0);
+        assert_eq!(stand.render_yaw(0.5), 170.0);
+        // To -170 is 20 degrees on through 180, not 340 back through 0.
+        stand.interpolate(Some((Vec3::ZERO, -170.0)));
+        assert_eq!(stand.render_yaw(0.0), 170.0);
+        assert_eq!(stand.render_yaw(0.5), 180.0);
+        assert_eq!(stand.render_yaw(1.0), 190.0);
+        stand.interpolate(None);
+        assert_eq!(stand.render_yaw(0.5), 190.0);
+    }
+
+    /// A snap (a move too far to interpolate) leaves nothing to blend from.
+    #[test]
+    fn a_snapped_stand_is_drawn_where_it_landed() {
+        let mut stand = ArmorStand::new(1, Vec3::new(0.5, 70.0, 0.5), 0.0);
+        stand.interpolate(Some((Vec3::new(0.5, 69.0, 0.5), 0.0)));
+        stand.snap(Vec3::new(200.5, 64.0, 0.5), 90.0);
+        assert_eq!(stand.render_position(0.5), Vec3::new(200.5, 64.0, 0.5));
+        assert_eq!(stand.render_yaw(0.5), 90.0);
+    }
+}
+#[cfg(test)]
 mod merge_tests {
     use super::*;
 

crates/horizon-client/src/entity_nbt.rs

@@ -1141,6 +1141,25 @@ pub fn mob_to_nbt(
                 equipment.insert(slot.into(), crate::save::item_to_nbt(&stack));
                 continue;
             }
+            // A worn piece or held item that kept its damage, name or
+            // components is saved with them.
+            if slot != "mainhand"
+                && item.is_some()
+                && let Some(stack) = crate::mobs::finalize::stored_stack(
+                    m,
+                    [
+                        crate::mobs::finalize::MAINHAND,
+                        crate::mobs::finalize::OFFHAND,
+                        crate::mobs::finalize::HEAD,
+                        crate::mobs::finalize::CHEST,
+                        crate::mobs::finalize::LEGS,
+                        crate::mobs::finalize::FEET,
+                    ][index],
+                )
+            {
+                equipment.insert(slot.into(), crate::save::item_to_nbt(&stack));
+                continue;
+            }
             // Enchanted or trimmed gear is saved with its components.
             if let (Some(id), Some(g)) = (item, crate::mobs::gear::gear(m))
                 && (!g.slots[index].is_empty() || g.trims[index].is_some())
@@ -1405,6 +1424,10 @@ pub fn mob_from_nbt(
                 crate::mobs::gear::set(&mut m, index, stack.enchantments().to_vec());
                 let trim = stack.data().and_then(|d| d.trim.clone());
                 crate::mobs::gear::set_trim(&mut m, index, trim);
+                // The damage, name and components stay with the slot.
+                if index != crate::mobs::gear::MAIN {
+                    crate::mobs::gear::set_stack(&mut m, index, stack);
+                }
             }
         }
     } else {
@@ -2155,6 +2178,7 @@ pub fn arrow_from_nbt(
     p.velocity = motion(tag);
     [p.yaw, p.pitch] = rotation(tag);
     p.left_owner = flag(tag, "LeftOwner");
+    p.owner_uuid = owner;
     let a = p.arrow.as_mut()?;
     a.life = number(tag.get("life")).unwrap_or(0) as i16 as i32;
     a.shake = (number(tag.get("shake")).unwrap_or(0) as i8 as u8).into();
@@ -2198,26 +2222,106 @@ pub fn fireball_to_nbt(
         "acceleration_power",
         Tag::Double(p.acceleration.to_bits()),
     );
-    // Projectile: LeftOwner only when set; HasBeenShot once it has ticked
-    // (a fireball saved before its first tick keeps what it was loaded with).
-    if let Tag::Compound(map) = &mut tag {
-        map.remove(&"LeftOwner".into());
-    }
-    if p.left_owner {
-        put(&mut tag, "LeftOwner", Tag::Byte(1));
-    }
-    if p.age > 0 || tag.get("HasBeenShot").is_none() {
-        put(&mut tag, "HasBeenShot", Tag::Byte(i8::from(p.age > 0)));
-    }
+    put_projectile(&mut tag, p, owner);
     if let Some(power) = power {
         put(&mut tag, "ExplosionPower", Tag::Byte(power as i8));
     }
+    Some(tag)
+}
+
+/// `Projectile.addAdditionalSaveData`: Owner, LeftOwner only when set, and
+/// HasBeenShot once it has ticked (one saved before its first tick keeps
+/// what it was loaded with).
+fn put_projectile(tag: &mut Tag, p: &Projectile, owner: Option<[i32; 4]>) {
+    if let Tag::Compound(map) = tag {
+        map.remove(&"LeftOwner".into());
+    }
+    if p.left_owner {
+        put(tag, "LeftOwner", Tag::Byte(1));
+    }
+    if p.age > 0 || tag.get("HasBeenShot").is_none() {
+        put(tag, "HasBeenShot", Tag::Byte(i8::from(p.age > 0)));
+    }
     if let Some(owner) = owner {
-        put(&mut tag, "Owner", Tag::IntArray(owner.to_vec()));
+        put(tag, "Owner", Tag::IntArray(owner.to_vec()));
+    }
+}
+
+/// The thrown item projectiles Horizon saves: each entity type's id is also
+/// the item it saves when none was loaded (`getDefaultItem`).
+const THROWABLES: [(ProjectileKind, &str); 3] = [
+    (ProjectileKind::Snowball, "minecraft:snowball"),
+    (ProjectileKind::Egg, "minecraft:egg"),
+    (ProjectileKind::EnderPearl, "minecraft:ender_pearl"),
+];
+fn throwable_item(kind: &ProjectileKind) -> Option<&'static str> {
+    THROWABLES
+        .iter()
+        .find(|(k, _)| k == kind)
+        .map(|&(_, id)| id)
+}
+
+/// Whether its chunk saves it: the kinds `arrow_to_nbt`, `fireball_to_nbt`
+/// and [`throwable_to_nbt`] write.
+pub fn saved_with_chunk(p: &Projectile) -> bool {
+    matches!(
+        p.kind,
+        ProjectileKind::LargeFireball { .. } | ProjectileKind::SmallFireball
+    ) || (p.arrow.is_some() && matches!(p.kind, ProjectileKind::Arrow { .. }))
+        || throwable_item(&p.kind).is_some()
+}
+
+/// `ThrowableItemProjectile.addAdditionalSaveData`: `Projectile`'s keys and
+/// the `Item` it flies as.
+pub fn throwable_to_nbt(
+    p: &Projectile,
+    uuid: [i32; 4],
+    owner: Option<[i32; 4]>,
+    raw: Option<&Tag>,
+) -> Option<Tag> {
+    let item = throwable_item(&p.kind)?;
+    let base = Base {
+        id: p.kind.id(),
+        uuid,
+        position: p.position,
+        motion: p.velocity,
+        rotation: [p.yaw, p.pitch],
+        on_ground: false,
+        fall_distance: 0.0,
+    };
+    let mut tag = base.tag(raw);
+    put_projectile(&mut tag, p, owner);
+    // the loaded item stays (a blue egg's, a renamed one's).
+    if tag.get("Item").is_none() {
+        put(
+            &mut tag,
+            "Item",
+            item_to_nbt(&crate::items::ItemStack::new(item, 1)),
+        );
     }
     Some(tag)
 }
 
+/// `ThrowableItemProjectile.readAdditionalSaveData` for the kinds
+/// [`throwable_to_nbt`] writes; the owner is the player when it is theirs.
+pub fn throwable_from_nbt(tag: &Tag, player: Option<[i32; 4]>) -> Option<Projectile> {
+    let id = kind(tag)?;
+    let (kind, _) = THROWABLES.iter().find(|(_, i)| *i == id)?.clone();
+    let owner = owner_uuid(tag);
+    let from_player = player.is_some() && owner == player;
+    let mut p = Projectile::new(kind, position(tag)?, from_player.then_some(Who::Player));
+    p.velocity = motion(tag);
+    [p.yaw, p.pitch] = rotation(tag);
+    p.left_owner = flag(tag, "LeftOwner");
+    p.owner_uuid = owner;
+    Some(p)
+}
+
+/// `Projectile`'s `Owner`.
+pub fn owner_uuid(tag: &Tag) -> Option<[i32; 4]> {
+    uuid_from_tag(tag.get("Owner"))
+}
+
 pub fn fireball_from_nbt(tag: &Tag, player: Option<[i32; 4]>) -> Option<Projectile> {
     let kind = match kind(tag)?.as_str() {
         "minecraft:fireball" => ProjectileKind::LargeFireball {
@@ -2234,6 +2338,7 @@ pub fn fireball_from_nbt(tag: &Tag, player: Option<[i32; 4]>) -> Option<Projecti
     p.velocity = motion(tag);
     [p.yaw, p.pitch] = rotation(tag);
     p.left_owner = flag(tag, "LeftOwner");
+    p.owner_uuid = owner;
     p.acceleration = float(tag.get("acceleration_power")).unwrap_or(0.1);
     Some(p)
 }
@@ -2498,6 +2603,7 @@ pub fn armor_stand_to_nbt(a: &ArmorStand, uuid: [i32; 4], raw: Option<&Tag>) ->
     } else {
         put(&mut tag, "equipment", Tag::compound(equipment));
     }
+    put(&mut tag, "DisabledSlots", Tag::Int(a.disabled_slots));
     for (key, value) in [
         ("Small", a.small),
         ("ShowArms", a.show_arms),
@@ -2572,6 +2678,7 @@ pub fn armor_stand_from_nbt(tag: &Tag, id: u32) -> Option<ArmorStand> {
     }
     a.small = flag(tag, "Small");
     a.show_arms = flag(tag, "ShowArms");
+    a.disabled_slots = number(tag.get("DisabledSlots")).unwrap_or(0) as i32;
     a.no_base_plate = flag(tag, "NoBasePlate");
     a.invisible = flag(tag, "Invisible");
     a.marker = flag(tag, "Marker");
@@ -4084,6 +4191,69 @@ mod fireball_nbt_tests {
             assert_eq!(fireball_from_nbt(&tag, None).unwrap().kind, kind);
         }
     }
+
+    #[test]
+    fn thrown_item_projectiles_round_trip_their_flight_item_and_owner() {
+        let player = Some([5, 6, 7, 8]);
+        for (kind, id) in [
+            (ProjectileKind::Snowball, "minecraft:snowball"),
+            (ProjectileKind::Egg, "minecraft:egg"),
+            (ProjectileKind::EnderPearl, "minecraft:ender_pearl"),
+        ] {
+            let mut p =
+                Projectile::new(kind.clone(), Vec3::new(1.5, 70.0, -2.5), Some(Who::Player));
+            (p.velocity, p.left_owner, p.age) = (Vec3::new(0.3, -0.1, 1.2), true, 4);
+            [p.yaw, p.pitch] = [30.0, -10.0];
+            let tag = throwable_to_nbt(&p, [1, 2, 3, 4], player, None).unwrap();
+            assert_eq!(super::kind(&tag).as_deref(), Some(id));
+            // ThrowableItemProjectile: the item it flies as, by its default.
+            let item = tag.get("Item").and_then(item_from_nbt).unwrap();
+            assert_eq!((&*item.item, item.count), (id, 1));
+            assert_eq!(number(tag.get("HasBeenShot")), Some(1));
+            assert_eq!(uuid_from_tag(tag.get("Owner")), player);
+            let back = throwable_from_nbt(&tag, player).unwrap();
+            assert_eq!((back.kind, back.owner), (kind, Some(Who::Player)));
+            assert_eq!((back.position, back.velocity), (p.position, p.velocity));
+            assert_eq!(
+                ([back.yaw, back.pitch], back.left_owner),
+                ([30.0, -10.0], true)
+            );
+            // an owner who is not here keeps their UUID through a moved resave.
+            let mut away = throwable_from_nbt(&tag, Some([9; 4])).unwrap();
+            assert_eq!((away.owner, away.owner_uuid), (None, player));
+            away.position.y += 3.0;
+            let resaved = throwable_to_nbt(&away, [1; 4], away.owner_uuid, None).unwrap();
+            assert_eq!(uuid_from_tag(resaved.get("Owner")), player);
+        }
+        // the chunk saves arrows, fireballs and these, and so takes them with it.
+        let kinds = [
+            (ProjectileKind::SmallFireball, true),
+            (ProjectileKind::Snowball, true),
+            (ProjectileKind::WindCharge, false),
+            (ProjectileKind::Trident, false),
+        ];
+        for (kind, saved) in kinds {
+            let p = Projectile::new(kind, Vec3::ZERO, None);
+            assert_eq!(saved_with_chunk(&p), saved, "{:?}", p.kind);
+        }
+        // a loaded item stays, and a new projectile leaves LeftOwner out.
+        let raw = Tag::compound([
+            ("id", Tag::String("minecraft:egg".into())),
+            ("Pos", doubles(&[0.0, 64.0, 0.0])),
+            (
+                "Item",
+                item_to_nbt(&crate::items::ItemStack::new("minecraft:blue_egg", 1)),
+            ),
+        ]);
+        let egg = throwable_from_nbt(&raw, None).unwrap();
+        let tag = throwable_to_nbt(&egg, [1; 4], None, Some(&raw)).unwrap();
+        let item = tag.get("Item").and_then(item_from_nbt).unwrap();
+        assert_eq!(&*item.item, "minecraft:blue_egg");
+        assert!(tag.get("LeftOwner").is_none() && tag.get("Owner").is_none());
+        assert_eq!(number(tag.get("HasBeenShot")), Some(0));
+        let wind = Projectile::new(ProjectileKind::WindCharge, Vec3::ZERO, None);
+        assert!(throwable_to_nbt(&wind, [1; 4], None, None).is_none());
+    }
 }
 
 #[cfg(test)]
@@ -4136,6 +4306,43 @@ mod neutral_anger_tests {
 mod held_item_name_tests {
     use super::*;
 
+    #[test]
+    fn a_worn_piece_keeps_its_damage_and_name_through_the_save() {
+        let root = std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("../../.local/horizon-client")
+            .join(horizon_core::VANILLA_VERSION);
+        if !root.join("items.json").exists() {
+            return;
+        }
+        let data = crate::mobs::MobTypes::load(&root).unwrap();
+        let types: HashMap<_, _> = data
+            .types
+            .into_iter()
+            .map(|(id, kind)| (id, Arc::new(kind)))
+            .collect();
+        let mut mob = Mob::new(1, Arc::clone(&types["minecraft:zombie"]), Vec3::ZERO, 0.0);
+        let mut helmet = crate::items::ItemStack::new("minecraft:iron_helmet", 1);
+        helmet.damage = 40;
+        helmet.data_mut().custom_name = Some(horizon_world::nbt::Tag::String("Hat".into()));
+        crate::mobs::finalize::set_item_stack(&mut mob, crate::mobs::finalize::HEAD, helmet);
+        let raw = mob_to_nbt(&mob, [1, 2, 3, 4], None, None);
+        let loaded = mob_from_nbt(&raw, &types, 2, None).unwrap();
+        let worn = crate::mobs::finalize::item_stack(&loaded, crate::mobs::finalize::HEAD).unwrap();
+        assert_eq!(worn.damage, 40);
+        assert_eq!(worn.custom_name().as_deref(), Some("Hat"));
+        // Replacing the item forgets the old stack.
+        let mut loaded = loaded;
+        crate::mobs::finalize::set_item(
+            &mut loaded,
+            crate::mobs::finalize::HEAD,
+            "minecraft:iron_helmet",
+        );
+        let fresh =
+            crate::mobs::finalize::item_stack(&loaded, crate::mobs::finalize::HEAD).unwrap();
+        assert_eq!(fresh.damage, 0);
+        assert!(fresh.custom_name().is_none());
+    }
+
     #[test]
     fn replacing_a_named_item_does_not_restore_its_old_name_on_save() {
         let root = std::path::Path::new(env!("CARGO_MANIFEST_DIR"))

crates/horizon-client/src/flatgen.rs

@@ -150,6 +150,52 @@ impl FlatTerrain {
             void_platform,
         })
     }
+    /// The settings of a superflat overworld that lets structure sets generate
+    /// (`FlatLevelSource.createState`): its layers, biome and `structure_overrides`
+    /// (no key means every set; `[]` none). `None` for anything else, a world with no
+    /// structure set to generate, the Void preset's biome (its platform is a feature
+    /// this generator places) or one that is not superflat.
+    pub fn structure_settings(
+        settings: &Tag,
+    ) -> Option<horizon_world::worldgen::generator::FlatSettings> {
+        let generator = settings
+            .get("dimensions")?
+            .get("minecraft:overworld")?
+            .get("generator")?;
+        if crate::save::text(generator.get("type"))?.trim_start_matches("minecraft:") != "flat" {
+            return None;
+        }
+        let s = generator.get("settings")?;
+        let biome = crate::save::text(s.get("biome")).unwrap_or_else(|| "minecraft:plains".into());
+        if biome == "minecraft:the_void" {
+            return None;
+        }
+        let mut layers = Vec::new();
+        if let Some(Tag::List(list)) = s.get("layers") {
+            for layer in list {
+                let block = crate::save::text(layer.get("block"))?;
+                let height = crate::save::number(layer.get("height")).unwrap_or(0).max(0) as i32;
+                layers.push((block, height));
+            }
+        }
+        let structure_overrides = match s.get("structure_overrides") {
+            Some(Tag::List(sets)) => Some(
+                sets.iter()
+                    .filter_map(|set| crate::save::text(Some(set)))
+                    .collect::<Vec<_>>(),
+            ),
+            Some(Tag::String(set)) => Some(vec![set.to_string_lossy()]),
+            _ => None,
+        };
+        if structure_overrides.as_ref().is_some_and(Vec::is_empty) {
+            return None;
+        }
+        Some(horizon_world::worldgen::generator::FlatSettings {
+            layers,
+            biome,
+            structure_overrides,
+        })
+    }
     /// FlatLevelSource.getSpawnHeight: the top of the layers.
     pub fn spawn_height(&self) -> i32 {
         self.shape.min_y + self.layers.len().min(self.shape.height as usize) as i32
@@ -479,4 +525,67 @@ mod tests {
             (None, vec!["Sum of layer heights is > 4064".into()])
         );
     }
+
+    /// `FlatLevelSource.createState`: the settings a flat world's structure sets run with.
+    #[test]
+    fn a_flat_world_names_the_structure_sets_that_may_generate() {
+        let world = |generator: Tag| {
+            Tag::compound([(
+                "dimensions",
+                Tag::compound([(
+                    "minecraft:overworld",
+                    Tag::compound([("generator", generator)]),
+                )]),
+            )])
+        };
+        let flat = |extra: Vec<(&str, Tag)>, biome: &str| {
+            let mut settings = vec![
+                ("biome", Tag::String(biome.into())),
+                (
+                    "layers",
+                    Tag::List(vec![Tag::compound([
+                        ("block", Tag::String("minecraft:stone".into())),
+                        ("height", Tag::Int(3)),
+                    ])]),
+                ),
+            ];
+            settings.extend(extra);
+            world(Tag::compound([
+                ("type", Tag::String("minecraft:flat".into())),
+                ("settings", Tag::compound(settings)),
+            ]))
+        };
+        // No key: every set. A list: those. An empty list: none. The void and a noise world: none.
+        let all = FlatTerrain::structure_settings(&flat(vec![], "minecraft:plains")).unwrap();
+        assert_eq!(all.structure_overrides, None);
+        assert_eq!(all.layers, [("minecraft:stone".to_owned(), 3)]);
+        let some = FlatTerrain::structure_settings(&flat(
+            vec![(
+                "structure_overrides",
+                Tag::List(vec![Tag::String("minecraft:villages".into())]),
+            )],
+            "minecraft:desert",
+        ))
+        .unwrap();
+        assert_eq!(
+            some.structure_overrides,
+            Some(vec!["minecraft:villages".to_owned()])
+        );
+        assert_eq!(some.biome, "minecraft:desert");
+        assert!(
+            FlatTerrain::structure_settings(&flat(
+                vec![("structure_overrides", Tag::List(vec![]))],
+                "minecraft:plains"
+            ))
+            .is_none()
+        );
+        assert!(FlatTerrain::structure_settings(&flat(vec![], "minecraft:the_void")).is_none());
+        assert!(
+            FlatTerrain::structure_settings(&world(Tag::compound([(
+                "type",
+                Tag::String("minecraft:noise".into())
+            )])))
+            .is_none()
+        );
+    }
 }

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

@@ -457,6 +457,8 @@ impl Game<'_> {
         EntityView {
             kind: "minecraft:player".into(),
             position: [p.position.x, p.position.y, p.position.z],
+            // Entity.isOnFire on a server: remainingFireTicks (players aren't fire immune).
+            on_fire: p.fire_ticks > 0,
             sneaking: p.pose == horizon_client::pose::Pose::Crouching,
             // Input.shift: the held key, as `BlockItem.place`'s sneaking reads it.
             input_sneak: self.keys.contains(&winit::keyboard::KeyCode::ShiftLeft),

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

@@ -522,7 +522,9 @@ impl Game<'_> {
         let slot = match &held {
             Some(h) => {
                 let slot = self.equipment_slot(h);
-                if slot < 2 && !a.show_arms {
+                // ArmorStand.interactAt: a disabled slot, or a hand without
+                // arms, is FAIL.
+                if a.is_disabled(slot) {
                     return true;
                 }
                 slot
@@ -550,6 +552,18 @@ impl Game<'_> {
                 }
             }
         };
+        // An empty hand takes from the main hand when the clicked slot is
+        // disabled (`isDisabled(clickedSlot) ? slot : clickedSlot`).
+        let slot = if held.is_none() && a.is_disabled(slot) {
+            0
+        } else {
+            slot
+        };
+        // ArmorStand.swapItem: taking from a filled slot or putting into an
+        // empty one can be disabled; the click then passes.
+        if a.swap_locked(slot) {
+            return false;
+        }
         let current = self.armor_stands[i].equipment[slot].clone();
         if held.is_none() && current.is_none() {
             return false;
@@ -722,6 +736,8 @@ impl Game<'_> {
         // ServerLevel.tick: only entities in entity-ticking chunks tick.
         let ticking = self.entity_ticking_area();
         for (i, a) in self.armor_stands.iter_mut().enumerate() {
+            a.previous = a.position;
+            a.previous_yaw = a.yaw;
             if !ticking(a.position.x.floor() as i32, a.position.z.floor() as i32) {
                 continue;
             }
@@ -785,11 +801,10 @@ impl Game<'_> {
             let dragon = a.equipment[5]
                 .as_ref()
                 .is_some_and(|i| &*i.item == "minecraft:dragon_head");
-            let position = super::entity_culling::at(a.position);
             if !self.standing_entity_in_view(
                 camera,
-                position,
-                position,
+                super::entity_culling::at(a.previous),
+                super::entity_culling::at(a.position),
                 alpha,
                 width,
                 height,
@@ -798,7 +813,9 @@ impl Game<'_> {
             ) {
                 continue;
             }
-            let p = glam::DVec3::new(a.position.x, a.position.y, a.position.z) - camera;
+            // EntityRenderer: drawn between last tick's position and this one's.
+            let at = a.render_position(alpha);
+            let p = super::entity_culling::at(at) - camera;
             // setupRotations: 180 - body yaw, plus the wobble for 5 ticks after a hit.
             let wiggle = (self.world.game_time - a.last_hit) as f32 + alpha as f32;
             let wobble = if wiggle < 5.0 {
@@ -807,13 +824,15 @@ impl Game<'_> {
                 0.0
             };
             let base = glam::Mat4::from_translation(p.as_vec3())
-                * glam::Mat4::from_rotation_y((180.0 - a.yaw + wobble).to_radians())
+                * glam::Mat4::from_rotation_y(
+                    (180.0 - a.render_yaw(alpha as f32) + wobble).to_radians(),
+                )
                 * glam::Mat4::from_scale(glam::Vec3::new(-1.0, -1.0, 1.0))
                 * glam::Mat4::from_translation(glam::Vec3::new(0.0, -1.501, 0.0));
             let light = self.world.light(
-                a.position.x.floor() as i32,
-                (a.position.y + 0.5).floor() as i32,
-                a.position.z.floor() as i32,
+                at.x.floor() as i32,
+                (at.y + 0.5).floor() as i32,
+                at.z.floor() as i32,
             );
             let packed = (u32::from(light >> 4) * 16) | ((u32::from(light & 15) * 16) << 8);
             self.armor_stand_vertices(a, base, packed, out);
@@ -1322,6 +1341,26 @@ mod swap_tests {
         ItemStack::new(item, count)
     }
     #[test]
+    fn disabled_slots_lock_by_filter_flag() {
+        let mut a = ArmorStand::new(1, horizon_core::geometry::Vec3::ZERO, 0.0);
+        // Hands need arms.
+        assert!(a.is_disabled(0) && a.is_disabled(1));
+        a.show_arms = true;
+        assert!(!a.is_disabled(0) && !a.is_disabled(1));
+        // Bit 4 locks the head (equipment index 5), bit 5 the off hand (1).
+        a.disabled_slots = (1 << 4) | (1 << 5);
+        assert!(a.is_disabled(5) && a.is_disabled(1));
+        assert!(!a.is_disabled(4) && !a.is_disabled(0));
+        // Taking (+8) from a filled slot and putting (+16) into an empty one.
+        a.disabled_slots = (1 << (3 + 8)) | (1 << (1 + 16));
+        assert!(!a.swap_locked(4), "an empty chest slot is not take-locked");
+        a.equipment[4] = Some(stack("minecraft:iron_chestplate", 1));
+        assert!(a.swap_locked(4));
+        assert!(a.swap_locked(2), "an empty feet slot is put-locked");
+        a.equipment[2] = Some(stack("minecraft:iron_boots", 1));
+        assert!(!a.swap_locked(2));
+    }
+    #[test]
     fn creative_swap_gives_the_worn_piece_to_the_hand() {
         let swap = swap_with_equipment_slot(
             &stack("minecraft:diamond_chestplate", 1),

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

@@ -14,7 +14,7 @@ use horizon_client::{
         leash::{Holder, Pending},
         riders,
     },
-    motion::RiddenBoat,
+    motion::{BubbleColumn, RiddenBoat, bubble_column_at},
 };
 use horizon_core::{
     geometry::{Aabb, ShapeOp, Vec3, VoxelShape},
@@ -48,6 +48,25 @@ pub(super) struct Boat {
     water_level: f64,
     land_friction: f32,
     out_of_control: f32,
+    /// `AbstractBoat.DATA_ID_BUBBLE_TIME` (synched): the ticks of `BUBBLE_TIME`
+    /// left before a bubble column lifts or drags the boat; 0 when it is not
+    /// over one.
+    pub bubble_time: i32,
+    /// `AbstractBoat.isAboveBubbleColumn`, set by `onAboveBubbleColumn` and
+    /// cleared by `tickBubbleColumn` (the server's).
+    above_bubble_column: bool,
+    /// `AbstractBoat.bubbleColumnDirectionIsDown`.
+    bubble_down: bool,
+    /// A bubble column's drag asked a rider the server can't move itself (a
+    /// player) to get out: `guest_vehicle_tick` takes it (`ejectPassengers`).
+    pub eject_riders: bool,
+    /// `Entity.tickCount`, counted where the wobble is (a client's tick).
+    tick_count: i32,
+    /// `AbstractBoat.bubbleMultiplier`, `bubbleAngle` and `bubbleAngleO`
+    /// (a client's).
+    bubble_multiplier: f32,
+    bubble_angle: f32,
+    bubble_angle_old: f32,
     pub hurt_time: i32,
     pub hurt_dir: i32,
     pub damage: f32,
@@ -72,6 +91,13 @@ pub(super) struct Boat {
 }
 /// `ChestBoat.CONTAINER_SIZE`.
 pub(super) const CHEST_SLOTS: usize = 27;
+/// `AbstractBoat.BUBBLE_TIME`: the ticks over a bubble column before it
+/// lifts or drags the boat.
+const BUBBLE_TIME: i32 = 60;
+/// `EntityEvent` 71 and 72, which `AbstractBoat.tickBubbleColumn` broadcasts
+/// for a down and an up column.
+pub(super) const BUBBLE_DOWN_EVENT: i8 = 71;
+pub(super) const BUBBLE_UP_EVENT: i8 = 72;
 pub(super) const WIDTH: f64 = 1.375;
 pub(super) const HEIGHT: f64 = 0.5625;
 impl Boat {
@@ -90,6 +116,14 @@ impl Boat {
             water_level: 0.0,
             land_friction: 0.0,
             out_of_control: 0.0,
+            bubble_time: 0,
+            above_bubble_column: false,
+            bubble_down: false,
+            eject_riders: false,
+            tick_count: 0,
+            bubble_multiplier: 0.0,
+            bubble_angle: 0.0,
+            bubble_angle_old: 0.0,
             hurt_time: 0,
             hurt_dir: 1,
             damage: 0.0,
@@ -174,6 +208,42 @@ impl Boat {
             yaw,
         )
     }
+    /// `AbstractBoat.getBubbleAngle`: the wobble, in degrees, `a` of the way
+    /// from the last tick's to this one's.
+    pub fn bubble_angle(&self, a: f32) -> f32 {
+        self.bubble_angle_old + a * (self.bubble_angle - self.bubble_angle_old)
+    }
+    /// `AbstractBoat.tickBubbleColumn`: on a client, the wobble grows by 0.05 a
+    /// tick while the synched bubble time runs and fades by 0.1 otherwise.
+    pub(super) fn tick_bubble_wobble(&mut self) {
+        self.tick_count += 1;
+        if self.bubble_time > 0 {
+            self.bubble_multiplier += 0.05;
+        } else {
+            self.bubble_multiplier -= 0.1;
+        }
+        self.bubble_multiplier = self.bubble_multiplier.clamp(0.0, 1.0);
+        self.bubble_angle_old = self.bubble_angle;
+        self.bubble_angle =
+            10.0 * (0.5 * f64::from(self.tick_count)).sin() as f32 * self.bubble_multiplier;
+    }
+    /// `AbstractBoat.tickBubbleColumn`'s countdown on the server: the bubble
+    /// time drops while the boat stays over a column and resets when it leaves.
+    /// `Some(down)` on the tick it runs out: the boat is thrown up (`false`) or
+    /// pulled down (`true`).
+    pub(super) fn tick_bubble_countdown(&mut self) -> Option<bool> {
+        if !self.above_bubble_column {
+            self.bubble_time = 0;
+        }
+        if self.bubble_time <= 0 {
+            return None;
+        }
+        self.bubble_time -= 1;
+        let diff = BUBBLE_TIME - self.bubble_time - 1;
+        let fired = (diff > 0 && self.bubble_time == 0).then_some(self.bubble_down);
+        self.above_bubble_column = false;
+        fired
+    }
     /// `getRowingTime`.
     pub fn rowing_time(&self, side: usize, a: f32) -> f32 {
         if self.paddling[side] {
@@ -684,9 +754,194 @@ impl Game<'_> {
             if self.boats[i].out_of_control >= 60.0 {
                 self.eject_boat_mobs(i, false);
             }
+            self.boat_bubble_tick(i);
             self.boat_contacts(i);
         }
     }
+    /// `Entity.canSimulateMovement`: for a boat (`AUTHORITATIVE_SIDE`) a
+    /// server leaves the boat its player drives to that player's client, and a
+    /// client moves only the boat its player drives.
+    fn boat_can_simulate_movement(&self, id: u32) -> bool {
+        if self.remote.is_some() {
+            self.riding == Some(id)
+        } else {
+            !self.guest_vehicles().contains(&id)
+        }
+    }
+    /// `AbstractBoat.tick`: `status = getStatus()` for a boat this window
+    /// does not tick (`tick_boat` sets it for the others): a client's boats
+    /// other than the one it drives, and a server's boats its players drive.
+    pub(super) fn refresh_boat_status(&mut self, i: usize) {
+        let b = &self.boats[i];
+        let mut probe = Boat::new(b.id, b.wood.clone(), b.position, b.yaw);
+        let status = self.boat_status(&mut probe);
+        self.boats[i].status = status;
+    }
+    /// `BubbleColumnBlock.entityInside`: the bubble columns boat `i` touches
+    /// (its box deflated by 1e-5 as `Entity.checkInsideBlocks` does), in x, y,
+    /// z order.
+    pub(super) fn boat_bubble_columns(&self, i: usize) -> Vec<BubbleColumn> {
+        let b = self.boats[i].bounds().deflate(Vec3::new(
+            f64::from(1.0e-5f32),
+            f64::from(1.0e-5f32),
+            f64::from(1.0e-5f32),
+        ));
+        let (lo, hi) = (b.min_position(), b.max_position());
+        let mut columns = Vec::new();
+        for x in lo.x.floor() as i32..=(hi.x.ceil() as i32 - 1) {
+            for y in lo.y.floor() as i32..=(hi.y.ceil() as i32 - 1) {
+                for z in lo.z.floor() as i32..=(hi.z.ceil() as i32 - 1) {
+                    if let Some(column) = bubble_column_at(
+                        &self.world,
+                        self.pack.assets.registry,
+                        self.res.facts(),
+                        self.collision,
+                        BlockPos::new(x, y, z),
+                    ) {
+                        columns.push(column);
+                    }
+                }
+            }
+        }
+        columns
+    }
+    /// `Entity.handleOnInsideBubbleColumn`: a column under more water lifts
+    /// boat `i` up to 0.7 or drags it down to -0.3 (`AbstractBoat` does not
+    /// override `onInsideBubbleColumn`), applied by the column's own push below
+    /// the surface.
+    pub(super) fn boat_inside_bubble_column(&mut self, i: usize, column: BubbleColumn) {
+        if !self.boat_can_simulate_movement(self.boats[i].id) {
+            return;
+        }
+        column.push(&mut self.boats[i].velocity);
+    }
+    /// `AbstractBoat.onAboveBubbleColumn`: whether the splash comes up, one
+    /// time in a hundred for a boat that is not under water.
+    pub(super) fn boat_splash_roll(&mut self, i: usize) -> bool {
+        !self.boats[i].under_water() && self.world.random.next_int_bound(100).unwrap_or(1) == 0
+    }
+    /// `AbstractBoat.onAboveBubbleColumn`: the client's half after the roll,
+    /// the splash sound and particle at the boat.
+    pub(super) fn boat_bubble_splash(&mut self, i: usize) {
+        use horizon_client::particles::{ParticleOptions, ParticleType};
+        let p = self.boats[i].position;
+        let pitch = 0.8 + 0.4 * self.world.random.next_float();
+        self.audio.play(
+            "minecraft:entity.generic.splash",
+            Some([p.x, p.y, p.z]),
+            1.0,
+            pitch,
+        );
+        let x = p.x + f64::from(self.world.random.next_float());
+        let z = p.z + f64::from(self.world.random.next_float());
+        self.particles.add(
+            &ParticleOptions::simple(ParticleType::Splash),
+            [x, p.y + 0.7, z],
+            [0.0; 3],
+        );
+    }
+    /// `AbstractBoat.onAboveBubbleColumn`: on the server (this window
+    /// simulates the boat) the column is remembered, the countdown starts and
+    /// the splash's game event goes to the listeners (its sound and particle
+    /// are the client's).
+    fn boat_above_bubble_column(&mut self, i: usize, drag_down: bool) {
+        let b = &mut self.boats[i];
+        b.above_bubble_column = true;
+        b.bubble_down = drag_down;
+        if b.bubble_time == 0 {
+            b.bubble_time = BUBBLE_TIME;
+        }
+        if !self.boat_splash_roll(i) {
+            return;
+        }
+        // A window that is its own client hears and sees the splash too.
+        if self.options.execution_role.is_client() {
+            self.boat_bubble_splash(i);
+        }
+        let (id, p) = (self.boats[i].id, self.boats[i].position);
+        // Entity.gameEvent(SPLASH, getControllingPassenger()): the window's
+        // own player when it drives the boat.
+        let ctx = if self.riding == Some(id) && self.player.is_some() {
+            self.player_context(None)
+        } else {
+            self.who_context(None, None)
+        };
+        self.post_game_event("minecraft:splash", [p.x, p.y, p.z], ctx);
+    }
+    /// `AbstractBoat.handleBubbleColumnEffect`: an up column throws the boat
+    /// up at 0.6, a down column pulls it down by 0.7.
+    pub(super) fn handle_bubble_column_effect(&mut self, i: usize, drag_down: bool) {
+        if !self.boat_can_simulate_movement(self.boats[i].id) {
+            return;
+        }
+        let v = &mut self.boats[i].velocity;
+        if drag_down {
+            // movement.add(0.0, -0.7, 0.0)
+            v.y += -0.7;
+        } else {
+            v.y = 0.6;
+        }
+    }
+    /// `Entity.ejectPassengers`: for a down column the mobs get out here, this
+    /// window's player gets out, and a server's player is asked to
+    /// (`guest_vehicle_tick` lets it out through its client).
+    fn eject_boat_riders(&mut self, i: usize) {
+        self.eject_boat_mobs(i, false);
+        let id = self.boats[i].id;
+        if self.riding == Some(id) && self.player.is_some() {
+            self.dismount(i);
+        } else if self.guest_rides(id) {
+            self.boats[i].eject_riders = true;
+        }
+    }
+    /// `AbstractBoat.tickBubbleColumn`: on the server, a boat that stays over
+    /// a column for `BUBBLE_TIME` ticks is thrown up or pulled down (a down
+    /// column lets the riders out first), and every client is told.
+    fn tick_boat_bubble_column(&mut self, i: usize) {
+        if let Some(down) = self.boats[i].tick_bubble_countdown() {
+            let (id, p) = (self.boats[i].id, self.boats[i].position);
+            let event = if down {
+                BUBBLE_DOWN_EVENT
+            } else {
+                BUBBLE_UP_EVENT
+            };
+            if down {
+                self.eject_boat_riders(i);
+            }
+            self.lan_entity_event(id as i32, event, [p.x, p.y, p.z]);
+            self.handle_bubble_column_effect(i, down);
+        }
+    }
+    /// `AbstractBoat.tick`: the end of it on the server for boat `i`, the two
+    /// `applyEffectsFromBlocks` that reach bubble columns (the lava is
+    /// `boat_lava_tick`'s), then `tickBubbleColumn`; and the wobble when this
+    /// window is its own client.
+    fn boat_bubble_tick(&mut self, i: usize) {
+        let id = self.boats[i].id;
+        // The boat a server's player drives is not ticked here: its status is.
+        if self.guest_vehicles().contains(&id) {
+            self.refresh_boat_status(i);
+        }
+        // An ejection nobody took (its player left the boat first) is void.
+        if !self.guest_rides(id) {
+            self.boats[i].eject_riders = false;
+        }
+        let touches = self.boat_bubble_columns(i);
+        // AbstractBoat.tick calls applyEffectsFromBlocks twice.
+        for _ in 0..2 {
+            for &column in &touches {
+                if column.surface {
+                    self.boat_above_bubble_column(i, column.drag);
+                } else {
+                    self.boat_inside_bubble_column(i, column);
+                }
+            }
+        }
+        self.tick_boat_bubble_column(i);
+        if self.options.execution_role.is_client() {
+            self.boats[i].tick_bubble_wobble();
+        }
+    }
     /// `LavaFluid.entityInside` (`lavaHurt`) from the two
     /// `applyEffectsFromBlocks` calls in `AbstractBoat.tick`: twice 40
     /// damage, so lava breaks a boat on its first tick inside, and the fire
@@ -1053,6 +1308,8 @@ impl Game<'_> {
         let destroyed = creative || b.damage > 40.0;
         if destroyed {
             self.eject_boat_mobs(i, true);
+            let id = self.boats[i].id;
+            self.release_vehicle_container(id);
             let b = self.boats.remove(i);
             let at = [b.position.x, b.position.y, b.position.z];
             // AbstractBoat.remove: a destroyed boat drops its lead.
@@ -1132,6 +1389,16 @@ impl Game<'_> {
                     (hurt.sin() * hurt * damage / 10.0 * b.hurt_dir as f32).to_radians(),
                 );
             }
+            // AbstractBoatRenderer.extractRenderState: bubbleAngle.
+            let wobble = b.bubble_angle(a);
+            // AbstractBoatRenderer.submit: a boat above water wobbles in a
+            // bubble column, about the axis (1, 0, 1).
+            if !b.under_water() && wobble.abs() >= 1.0e-5 {
+                base *= glam::Mat4::from_axis_angle(
+                    glam::Vec3::new(1.0, 0.0, 1.0).normalize(),
+                    wobble * (std::f64::consts::PI / 180.0) as f32,
+                );
+            }
             base *= glam::Mat4::from_scale(glam::Vec3::new(-1.0, -1.0, 1.0))
                 * glam::Mat4::from_rotation_y(90f32.to_radians());
             let mut poses = Poses::new(model);
@@ -1186,3 +1453,95 @@ impl Game<'_> {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn boat() -> Boat {
+        Boat::new(1, Arc::from("oak"), Vec3::ZERO, 0.0)
+    }
+
+    /// `AbstractBoat.tickBubbleColumn` on a client: the wobble grows while the
+    /// bubble time runs and fades after.
+    #[test]
+    fn the_wobble_grows_while_the_bubble_time_runs_and_fades_after() {
+        let mut b = boat();
+        b.bubble_time = BUBBLE_TIME;
+        for _ in 0..30 {
+            b.tick_bubble_wobble();
+        }
+        // 0.05 a tick, capped at 1.
+        assert_eq!(b.bubble_multiplier, 1.0);
+        // 10 * sin(0.5 * tickCount) * multiplier.
+        let expected = 10.0 * (0.5 * 30.0f64).sin() as f32;
+        assert!((b.bubble_angle - expected).abs() < 1.0e-4);
+        // The render angle lerps between the last two ticks.
+        let mid = b.bubble_angle(0.5);
+        assert!((mid - (b.bubble_angle_old + b.bubble_angle) / 2.0).abs() < 1.0e-5);
+        // Once the bubble time is 0 the multiplier fades by 0.1 a tick.
+        b.bubble_time = 0;
+        for _ in 0..4 {
+            b.tick_bubble_wobble();
+        }
+        assert!((b.bubble_multiplier - 0.6).abs() < 1.0e-5);
+        for _ in 0..10 {
+            b.tick_bubble_wobble();
+        }
+        assert_eq!(b.bubble_multiplier, 0.0);
+        assert_eq!(b.bubble_angle, 0.0);
+    }
+
+    /// `AbstractBoat.tickBubbleColumn` on the server: a boat held over a
+    /// column fires on the 60th tick, with the column's direction, then the
+    /// time restarts.
+    #[test]
+    fn the_bubble_countdown_fires_every_sixty_ticks_over_a_column() {
+        for down in [false, true] {
+            let mut b = boat();
+            let mut fired = Vec::new();
+            for tick in 1..=130 {
+                // What boat_above_bubble_column does each tick.
+                b.above_bubble_column = true;
+                b.bubble_down = down;
+                if b.bubble_time == 0 {
+                    b.bubble_time = BUBBLE_TIME;
+                }
+                if let Some(d) = b.tick_bubble_countdown() {
+                    fired.push((tick, d));
+                }
+                assert!(!b.above_bubble_column);
+            }
+            assert_eq!(fired, vec![(60, down), (120, down)]);
+        }
+    }
+
+    /// Leaving the column resets the time: nothing fires, and a boat with no
+    /// time left does nothing over a column until the column sets it.
+    #[test]
+    fn leaving_the_column_resets_the_bubble_countdown() {
+        let mut b = boat();
+        b.bubble_time = BUBBLE_TIME;
+        for _ in 0..30 {
+            b.above_bubble_column = true;
+            assert_eq!(b.tick_bubble_countdown(), None);
+        }
+        assert_eq!(b.bubble_time, 30);
+        // A tick away from the column.
+        assert_eq!(b.tick_bubble_countdown(), None);
+        assert_eq!(b.bubble_time, 0);
+        b.above_bubble_column = true;
+        assert_eq!(b.tick_bubble_countdown(), None);
+        assert!(b.above_bubble_column);
+    }
+
+    #[test]
+    fn a_boat_that_never_saw_a_column_does_not_wobble() {
+        let mut b = boat();
+        for _ in 0..10 {
+            b.tick_bubble_wobble();
+        }
+        assert_eq!(b.bubble_angle, 0.0);
+        assert_eq!(b.bubble_angle(0.5), 0.0);
+    }
+}

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

@@ -1432,6 +1432,7 @@ impl Game<'_> {
         renderer.screenshot = Some(horizon_client::gfx::ScreenshotRequest {
             path: path.clone(),
             size: None,
+            scaled: true,
         });
         self.ui.screenshot_message = Some(path);
     }

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

@@ -1227,21 +1227,11 @@ impl Game<'_> {
         static RARITY: std::sync::OnceLock<std::collections::HashMap<String, String>> =
             std::sync::OnceLock::new();
         let map = RARITY.get_or_init(|| {
-            let v: serde_json::Value = serde_json::from_slice(
-                &std::fs::read(self.options.resources.join("items.json")).unwrap_or_default(),
-            )
-            .unwrap_or_default();
-            v.as_object()
-                .map(|o| {
-                    o.iter()
-                        .filter_map(|(k, c)| {
-                            c["minecraft:rarity"]
-                                .as_str()
-                                .map(|r| (k.clone(), r.to_owned()))
-                        })
-                        .collect()
-                })
+            horizon_world::item_defaults::read(&self.options.resources)
                 .unwrap_or_default()
+                .into_iter()
+                .filter_map(|(k, c)| c["minecraft:rarity"].as_str().map(|r| (k, r.to_owned())))
+                .collect()
         });
         map.get(item).cloned().unwrap_or_else(|| "common".into())
     }
@@ -1951,11 +1941,15 @@ impl Game<'_> {
             Target::Boat(id) => {
                 // AbstractBoat.remove: a killed boat drops its lead.
                 if let Some(i) = self.boats.iter().position(|b| b.id == id) {
+                    self.release_vehicle_container(id);
                     let b = self.boats.remove(i);
                     self.boat_removed(&b);
                 }
             }
-            Target::Cart(id) => self.carts.retain(|c| c.id != id),
+            Target::Cart(id) => {
+                self.release_vehicle_container(id);
+                self.carts.retain(|c| c.id != id);
+            }
             Target::Other(id) => self.others.retain(|o| o.id != id),
             Target::Crystal(id) => self.kill_crystal(id),
             Target::Dragon(id) => self.kill_dragon(id),

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

@@ -26,6 +26,8 @@ pub(in crate::game) enum Slot {
     /// An armor stand's equipment (`ArmorStand::SLOTS` index).
     Stand(u32, usize),
     Frame(u32),
+    /// A chest or hopper minecart's slot (`ContainerEntity.getChestVehicleSlot`).
+    Cart(u32, usize),
     Block([i32; 3], usize),
     /// A slot of another player (`for_player`): reached with their state in place.
     Guest(u32, Box<Slot>),
@@ -168,6 +170,19 @@ impl Game<'_> {
                     add(Slot::Frame(*id));
                 }
             }
+            // `getChestVehicleSlot` takes any index below `getContainerSize`.
+            Owner::Entity(Target::Cart(id)) => {
+                let size = self
+                    .carts
+                    .iter()
+                    .find(|c| c.id == *id)
+                    .map_or(0, |c| c.kind.slots());
+                for i in 0..size {
+                    if matches_name(name, &format!("container.{i}")) {
+                        add(Slot::Cart(*id, i));
+                    }
+                }
+            }
             Owner::Entity(_) => {}
         }
         out
@@ -209,6 +224,7 @@ impl Game<'_> {
                 .cloned()
                 .flatten(),
             Slot::Frame(id) => self.item_frames.iter().find(|f| f.id == *id)?.item.clone(),
+            Slot::Cart(id, i) => self.cart_slots(*id)?.get(*i).cloned().flatten(),
             Slot::Block(p, i) => match self.world.block_entities.get(&(p[0], p[1], p[2])) {
                 Some(horizon_client::containers::BlockEntity::Chest(items)) => {
                     items.get(*i).cloned().flatten()
@@ -296,6 +312,13 @@ impl Game<'_> {
                 }
                 None => false,
             },
+            Slot::Cart(id, i) => match self.cart_slots(*id).and_then(|c| c.get_mut(*i)) {
+                Some(slot) => {
+                    *slot = stack;
+                    true
+                }
+                None => false,
+            },
             Slot::Block(p, i) => match self.world.block_entities.get_mut(&(p[0], p[1], p[2])) {
                 Some(horizon_client::containers::BlockEntity::Chest(items)) => {
                     match items.get_mut(*i) {

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

@@ -61,7 +61,11 @@ impl Game<'_> {
             .unwrap_or(Target::Player)
     }
 
-    /// `PlayerList.getPlayerByName`: names are not case sensitive.
+    /// `PlayerList.getPlayerByName`: names are not case sensitive. Horizon:
+    /// on a server where a mod gave players nicknames
+    /// (`native_set_nickname`), a name no player has finds the player going
+    /// by it, without its `~` or with it (quoted), so `/msg` and `/tell`
+    /// reach a player by the name chat shows. No nickname, no change.
     pub(super) fn player_named(&self, name: &str) -> Option<Target> {
         if self.player.is_some() && name.eq_ignore_ascii_case(self.acting_player_name()) {
             return Some(Target::Player);
@@ -69,6 +73,21 @@ impl Game<'_> {
         self.command_players()
             .find(|g| g.name.eq_ignore_ascii_case(name))
             .map(|g| Target::Guest(g.conn))
+            .or_else(|| self.player_nicknamed(name))
+    }
+
+    /// The player whose nickname is `name` (any case, a leading `~` either
+    /// side ignored).
+    fn player_nicknamed(&self, name: &str) -> Option<Target> {
+        let bare = |s: &str| s.strip_prefix('~').unwrap_or(s).to_ascii_lowercase();
+        let wanted = bare(name);
+        let hub = &self.lan.as_ref()?.hub;
+        let uuid = hub
+            .nicknames
+            .iter()
+            .find(|(_, nick)| bare(nick) == wanted)?
+            .0;
+        self.target_by_uuid(*uuid)
     }
 
     /// `EntitySelector.findEntities` with a UUID: the player with it, else

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

@@ -644,6 +644,7 @@ impl Game<'_> {
                 renderer.screenshot = Some(horizon_client::gfx::ScreenshotRequest {
                     path: path.trim().into(),
                     size: None,
+                    scaled: false,
                 });
                 self.pending_screenshot = Some(reply.clone());
                 Ok(None)
@@ -895,6 +896,15 @@ impl Game<'_> {
                 );
                 ok()
             }
+            // A splitscreen player leaves splitscreen; only P1's game ends the process.
+            "quit" if self.options.split_guest => {
+                if self.remote.is_some() {
+                    self.leave_server(None)?;
+                } else if let Some(title) = self.title.as_mut() {
+                    title.escape();
+                }
+                ok()
+            }
             "quit" => {
                 self.begin_closing_save(true)?;
                 ok()

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

@@ -89,6 +89,12 @@ pub(super) struct ProjWorld<'a, 'w> {
     pub targets: Vec<(Who, Aabb)>,
 }
 impl ProjectileWorld for ProjWorld<'_, '_> {
+    fn block_contacts(&self, entity: i32, kind: &str, from: Vec3, to: Vec3, bounds: Aabb) {
+        horizon_client::block_contact::swept_inside(entity, kind, from, to, bounds, |p| {
+            let state = self.w.world.block(p.x, p.y, p.z);
+            (state, &self.w.facts.get(state).name)
+        });
+    }
     fn clip(&self, from: Vec3, to: Vec3) -> Option<(Vec3, [i32; 3], [i32; 3])> {
         let mut scene = SceneCollisions {
             world: self.w.world,
@@ -1201,7 +1207,13 @@ impl Game<'_> {
         self.villager_murdered(m, slain_by_player, killer.flatten());
         let pos = [m.position.x, m.position.y + 0.5, m.position.z];
         let killer_entity = self.killer_loot_entity(killer.flatten());
-        self.drop_death_loot(&mut dying, by_player, killer_entity, consumed, pos);
+        // LAST_DAMAGE_PLAYER only while the player-hurt memory lasts
+        // (LivingEntity.dropFromLootTable's playerKilled): a mob that dies to
+        // the environment long after a player's hit names no player.
+        let player = killer
+            .filter(|_| m.ai.last_hurt_by_player > 0)
+            .and_then(|conn| self.killer_uuid(conn));
+        self.drop_death_loot(&mut dying, player, by_player, killer_entity, consumed, pos);
         self.create_wither_rose(m);
         if m.species() == Species::CopperGolem {
             // CopperGolem.dropEquipment: the preserved equipment too.
@@ -1318,9 +1330,26 @@ impl Game<'_> {
         }
         own(self)
     }
+    /// The UUID of the player `last_hurt_by_player` keeps: the guest on
+    /// connection `conn` (None once they left), else the player in place
+    /// (None on a server, which has none of its own).
+    fn killer_uuid(&mut self, conn: Option<u32>) -> Option<u128> {
+        match conn {
+            // During that guest's own turn, the hub is out of `lan`.
+            Some(conn) if self.lan_acting != Some(conn) => {
+                Some(self.lan.as_ref()?.hub.guest(conn)?.uuid)
+            }
+            Some(_) => Some(self.native_acting_id()),
+            None if self.lan_acting.is_none() && self.player.is_some() => {
+                Some(self.native_acting_id())
+            }
+            None => None,
+        }
+    }
     fn drop_death_loot(
         &mut self,
         m: &mut Mob,
+        player_uuid: Option<u128>,
         by_player: bool,
         killer: horizon_world::loot::LootEntity,
         consumed: bool,
@@ -1403,22 +1432,48 @@ impl Game<'_> {
             }
         }
         let raider = horizon_client::mobs::raider::is_raider(m.species());
+        // The item drops come before the carried block and the orbs, so the
+        // mods get them all at once and they still spawn in that order.
+        let mut stacks = Vec::new();
+        let mut rest = Vec::new();
         for d in items {
             match d {
-                drops::Drop::Item(stack) => {
-                    let item = if raider && stack.item == horizon_client::mobs::raider::BANNER {
+                drops::Drop::Item(stack) => stacks.push(
+                    if raider && stack.item == horizon_client::mobs::raider::BANNER {
                         horizon_client::mobs::raider::ominous_banner()
                     } else {
                         from_loot(&stack)
-                    };
-                    // Every death drop is its own ItemEntity, and the drop
-                    // entity's own random (not the level's) gives it the
-                    // constructor's horizontal push (its motion otherwise
-                    // stays [0, 0.2, 0] and the drops land stacked at the
-                    // mob's centre, without disturbing the level random that
-                    // the orbs' merge ids and block ticks read next).
-                    self.spawn_item(item, pos, dispenser::new_item_motion(), 10);
-                }
+                    },
+                ),
+                drops::Drop::Stack(stack) => stacks.push(stack),
+                other => rest.push(other),
+            }
+        }
+        let kind = super::native_hooks::mob_kind(m);
+        let table = drops::death_loot_table(m, death.mob_drops).filter(|t| loot.has_table(t));
+        let context = super::native_hooks::NativeLootDrops {
+            table: table.as_deref().unwrap_or_default(),
+            dimension: self.dim.id(),
+            origin: [m.position.x, m.position.y, m.position.z],
+            block: None,
+            entity: Some((m.id, &kind)),
+            player: player_uuid,
+            tool: None,
+            explosion: None,
+        };
+        self.native_loot_drops(&context, &mut stacks);
+        stacks.retain(|stack| stack.count > 0 && &*stack.item != "minecraft:air");
+        for item in stacks {
+            // Every death drop is its own ItemEntity, and the drop entity's
+            // own random (not the level's) gives it the constructor's
+            // horizontal push (its motion otherwise stays [0, 0.2, 0] and
+            // the drops land stacked at the mob's centre, without disturbing
+            // the level random that the orbs' merge ids and block ticks read
+            // next).
+            self.spawn_item(item, pos, dispenser::new_item_motion(), 10);
+        }
+        for d in rest {
+            match d {
                 drops::Drop::CarriedBlock(state) => {
                     // Enderman.dropCustomDeathLoot: spawnAtLocation for each
                     // of the carried block's silk-touch drops.
@@ -1434,7 +1489,7 @@ impl Game<'_> {
                     }
                 }
                 drops::Drop::Orb(value) if !consumed => self.spawn_orbs(pos, value as u32),
-                drops::Drop::Orb(_) => {}
+                drops::Drop::Item(_) | drops::Drop::Stack(_) | drops::Drop::Orb(_) => {}
             }
         }
     }
@@ -1599,6 +1654,15 @@ impl Game<'_> {
             self.next_entity += 1;
             p.id = self.next_entity;
         }
+        // Projectile.setOwner: the acting player's or the mob's UUID, which
+        // its save keeps even once the owner is gone.
+        if p.owner_uuid.is_none() {
+            p.owner_uuid = match p.owner {
+                Some(Who::Player) => Some(self.acting_player_uuid()),
+                Some(Who::Mob(id)) => Some(self.uuid_for(id)),
+                None => None,
+            };
+        }
         self.creatures.projectiles.push(p);
     }
     pub(super) fn handle_mob_events(&mut self, events: Vec<MobEvent>) -> Result<()> {
@@ -2218,13 +2282,14 @@ impl Game<'_> {
                         self.destroy_particles(pos, old);
                     }
                     if drop {
-                        let drops = world_items!(self).block_drops_in(
+                        let mut drops = world_items!(self).block_drops_in(
                             self.pack.assets.registry,
                             old,
                             None,
                             &mut self.world.random,
                             Some((&mut self.rand_sequences, self.level.seed)),
                         );
+                        self.native_block_drops(pos, old, None, None, None, &mut drops);
                         for d in drops {
                             self.pop_resource(pos, d);
                         }
@@ -3096,7 +3161,7 @@ impl Game<'_> {
             });
         }
         if raised {
-            self.after_block(outcome, amount, attacker, projectile);
+            self.after_block(outcome, attacker, projectile);
         }
         outcome.hurt
     }
@@ -3411,9 +3476,10 @@ impl Game<'_> {
                 } = hit
                     && let Some(j) = wind_charge_hit(id)
                 {
-                    let (owner, guest) = (p.owner, p.guest);
+                    let (owner, owner_uuid, guest) = (p.owner, p.owner_uuid, p.guest);
                     let look = self.owner_look(owner, guest);
-                    super::deflect::aim_deflect(&mut projectiles[j], look, owner, guest);
+                    let wind = &mut projectiles[j];
+                    super::deflect::aim_deflect(wind, look, owner, owner_uuid, guest);
                 }
             }
             let mut idx = 0;
@@ -3564,6 +3630,7 @@ impl Game<'_> {
             ProjectileKind::Arrow { .. }
                 | ProjectileKind::Trident
                 | ProjectileKind::Snowball
+                | ProjectileKind::Thrown(_)
                 | ProjectileKind::Egg
                 | ProjectileKind::SmallFireball
                 | ProjectileKind::LargeFireball { .. }
@@ -3860,6 +3927,7 @@ impl Game<'_> {
             let amount = match p.kind {
                 ProjectileKind::SmallFireball => 5.0,
                 ProjectileKind::LargeFireball { .. } => 6.0,
+                ProjectileKind::Thrown(t) => t.damage,
                 _ => 0.0,
             };
             let kind = match p.kind {
@@ -3880,6 +3948,7 @@ impl Game<'_> {
                 ProjectileKind::EnderPearl
                     | ProjectileKind::Egg
                     | ProjectileKind::Snowball
+                    | ProjectileKind::Thrown(_)
                     | ProjectileKind::LargeFireball { .. }
             ) {
                 return Ok(());
@@ -4133,6 +4202,47 @@ impl Game<'_> {
                 self.thrown_break_event(p.id, atp);
                 self.item_burst(atp, "minecraft:snowball");
             }
+            // a mod's copy of Snowball: its damage to anything it hits.
+            (ProjectileKind::Thrown(t), hit) => {
+                match hit {
+                    Hit::Entity {
+                        who: Who::Mob(id), ..
+                    } => {
+                        let push = [p.velocity.x, p.velocity.z];
+                        let hurt = self
+                            .mobs
+                            .iter_mut()
+                            .find(|m| m.id == id)
+                            .is_some_and(|m| m.damage_projectile(t.damage, source, aim, push));
+                        if hurt {
+                            self.player_hurt_mob(p, id);
+                        }
+                        // LivingEntity.hurtServer: PLAYER_HURT_ENTITY.
+                        if hurt
+                            && p.owner == Some(Who::Player)
+                            && let Some(m) = self.mobs.iter().find(|m| m.id == id)
+                        {
+                            let victim = self.mob_entity(m);
+                            let direct = horizon_client::advancements::EntityView {
+                                kind: t.id.into(),
+                                position: [p.position.x, p.position.y, p.position.z],
+                                ..Default::default()
+                            };
+                            self.player_hit(&victim, "minecraft:thrown", Some(direct), t.damage);
+                        }
+                    }
+                    // Player.hurtServer takes no 0 damage.
+                    Hit::Entity {
+                        who: Who::Player, ..
+                    } if t.damage > 0.0 => {
+                        let from = [p.previous.x, p.previous.y, p.previous.z];
+                        self.mob_hits_player(t.damage, from, "minecraft:thrown");
+                    }
+                    _ => {}
+                }
+                self.thrown_break_event(p.id, atp);
+                self.item_burst(atp, t.item);
+            }
             (ProjectileKind::Egg, hit) => {
                 if let Hit::Entity {
                     who: Who::Mob(id), ..
@@ -4450,7 +4560,7 @@ impl Game<'_> {
     /// client entity's random (the particle engine's here) for an egg.
     pub(super) fn item_burst(&mut self, at: [f64; 3], item: &str) {
         let options = self.item_particle(&horizon_client::items::ItemStack::new(item, 1));
-        let egg = item != "minecraft:snowball";
+        let egg = item == "minecraft:egg";
         for _ in 0..8 {
             let v = if egg {
                 let r = self.particles.random();
@@ -5450,7 +5560,10 @@ impl Game<'_> {
                 return Ok(thrown);
             }
             _ if item.ends_with("_spawn_egg") => return self.use_spawn_egg(stack),
-            _ => return Ok(false),
+            _ => match horizon_client::projectiles::thrown_by_item(item) {
+                Some(t) => ProjectileKind::Thrown(t),
+                None => return Ok(false),
+            },
         };
         let Some(eye) = self.eye_position() else {
             return Ok(false);
@@ -5480,7 +5593,9 @@ impl Game<'_> {
         // second is the `use_cooldown` component, as for any thrown item.
         self.apply_use_cooldown(stack);
         let sound = match kind {
-            ProjectileKind::Snowball => "minecraft:entity.snowball.throw",
+            ProjectileKind::Snowball | ProjectileKind::Thrown(_) => {
+                "minecraft:entity.snowball.throw"
+            }
             ProjectileKind::Egg => "minecraft:entity.egg.throw",
             _ => "minecraft:entity.ender_pearl.throw",
         };
@@ -6080,8 +6195,8 @@ impl Game<'_> {
                 }
                 continue;
             }
-            if let Some(stack) = a.potion_item() {
-                let owner = super::item_draw::owner_at(at, 0.0, "minecraft:splash_potion");
+            if let Some(stack) = a.drawn_item() {
+                let owner = super::item_draw::owner_at(at, 0.0, a.kind.id());
                 let state = self.resolve_item(&stack, DisplayContext::Ground, Some(&owner), 0);
                 let pose = glam::Mat4::from_translation(c)
                     * glam::Mat4::from_quat(self.camera_orientation());

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

@@ -374,7 +374,7 @@ impl Game<'_> {
         let p = c.position;
         self.world.modified.insert((c.pos[0] >> 4, c.pos[2] >> 4));
         if self.riding == Some(c.id) {
-            self.riding = None;
+            self.dismount_removed_vehicle(p.y);
         }
         self.audio.play(
             "minecraft:entity.cushion.break",
@@ -468,6 +468,49 @@ impl Game<'_> {
         );
     }
 
+    /// `LivingEntity.dismountVehicle` from a removed vehicle (a broken
+    /// cushion) whose position was at `vehicle_y`: up to the higher of the
+    /// rider's and the vehicle's heights, then the free spot nearest there
+    /// (`findFreePosition` within the rider's own box). No get-up sound:
+    /// `Cushion.removePassenger` plays none once the cushion is removed.
+    pub(super) fn dismount_removed_vehicle(&mut self, vehicle_y: f64) {
+        self.riding = None;
+        let border = self.border_bounds();
+        let b = self.res.behaviours();
+        let Some(p) = self.player.as_ref() else {
+            return;
+        };
+        let (w, h) = (
+            f64::from(p.dimensions.width),
+            f64::from(p.dimensions.height),
+        );
+        let mut at = Vec3::new(p.position.x, p.position.y.max(vehicle_y), p.position.z);
+        // `getBbWidth() <= 4 && getBbHeight() <= 4`.
+        if w <= 4.0 && h <= 4.0 {
+            let center = at.add_vector(Vec3::new(0.0, h / 2.0, 0.0));
+            let size = Vec3::new(w, h, w);
+            let free = horizon_world::level::portal_travel::find_free_position(
+                Aabb::of_size(center, size),
+                center,
+                size,
+                &border,
+                |q| {
+                    b.collision_shape(self.world.block(q.x, q.y, q.z))
+                        .map(|s| s.moved(Vec3::new(f64::from(q.x), f64::from(q.y), f64::from(q.z))))
+                },
+            );
+            if let Some(free) = free {
+                at = free.add_vector(Vec3::new(0.0, -h / 2.0, 0.0));
+            }
+        }
+        if let Some(p) = self.player.as_mut() {
+            self.previous_position = p.position;
+            p.position = at;
+            p.velocity = Vec3::ZERO;
+            p.fall_distance = 0.0;
+        }
+    }
+
     /// `Player.rideTick` on a cushion: hold the seat, and get up on sneak.
     pub(super) fn tick_cushion_riding(&mut self, keys: super::Keys) -> bool {
         let Some(c) = self

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

@@ -954,6 +954,20 @@ impl Game<'_> {
             let p = c.position;
             g.entity_box(min, max, [p.x, p.y, p.z], 0.2125, false, (0.0, c.yaw));
         }
+        // Interaction: EntityDimensions.scalable(width, height), so its eyes
+        // are at 0.85 of the height. Its rotation is not kept here.
+        for i in self.interactions.values() {
+            let b = i.bounds();
+            let p = i.position;
+            g.entity_box(
+                [b.min(Axis::X), b.min(Axis::Y), b.min(Axis::Z)],
+                [b.max(Axis::X), b.max(Axis::Y), b.max(Axis::Z)],
+                [p.x, p.y, p.z],
+                i.height.max(0.0) * 0.85,
+                false,
+                (0.0, 0.0),
+            );
+        }
         for a in self.armor_stands.iter().filter(|a| !a.invisible) {
             // ArmorStand.getDimensions: a marker has none, a small one is
             // half scale with its eyes at 0.9875.
@@ -962,8 +976,13 @@ impl Game<'_> {
                 (_, true) => ((0.25, 0.9875), 0.9875),
                 _ => ((0.5, 1.975), 1.7775),
             };
-            let p = a.position;
-            g.hitbox([p.x, p.y, p.z], size, eye, true, (0.0, a.yaw));
+            g.hitbox(
+                at(a.previous, a.position),
+                size,
+                eye,
+                true,
+                (0.0, a.render_yaw(alpha)),
+            );
         }
         for b in &self.boats {
             let h = super::boats::HEIGHT as f32;
@@ -1023,9 +1042,12 @@ impl Game<'_> {
             use horizon_client::projectiles::ProjectileKind as K;
             let (size, eye) = match p.kind {
                 K::Arrow { .. } | K::Trident => (0.5, 0.13),
-                K::Snowball | K::Egg | K::EnderPearl | K::LlamaSpit | K::Potion { .. } => {
-                    (0.25, 0.2125)
-                }
+                K::Snowball
+                | K::Egg
+                | K::EnderPearl
+                | K::LlamaSpit
+                | K::Potion { .. }
+                | K::Thrown(_) => (0.25, 0.2125),
                 K::SmallFireball | K::ShulkerBullet { .. } | K::WitherSkull { .. } => {
                     (0.3125, 0.265_625)
                 }

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

@@ -1720,6 +1720,55 @@ impl Game<'_> {
         }
     }
 
+    /// The anticheat bans a player (`HostEvent::Ban`): `banned-players.json` gets it as `/ban` adds it,
+    /// with the anticheat as its source, and the player is sent away with the ban's message.
+    pub(super) fn anticheat_ban(
+        &mut self,
+        hub: &mut horizon_client::lan::hub::Hub,
+        uuid: u128,
+        name: &str,
+        reason: &str,
+    ) {
+        let Some(lists) = &self.server_lists else {
+            // No ban list to add to: the anticheat's kick, so a flagged cheater still doesn't stay.
+            log(
+                "WARN",
+                &format!("Can't ban {name} ({reason}): no ban list; kicked"),
+            );
+            let conns: Vec<u32> = hub
+                .guests
+                .iter()
+                .filter(|g| g.uuid == uuid)
+                .map(|g| g.conn)
+                .collect();
+            for conn in conns {
+                hub.anticheat_kick(conn);
+            }
+            return;
+        };
+        let user = NameAndId {
+            id: uuid,
+            name: name.to_owned(),
+        };
+        lists.lock().unwrap().bans.add(BanEntry::new(
+            user,
+            Some("Horizon anticheat".into()),
+            None,
+            Some(reason.to_owned()),
+        ));
+        log("INFO", &format!("Banned {name}: {reason}"));
+        let conns: Vec<u32> = hub
+            .guests
+            .iter()
+            .filter(|g| g.uuid == uuid)
+            .map(|g| g.conn)
+            .collect();
+        for conn in conns {
+            hub.kick(conn, translatable("multiplayer.disconnect.banned", &[]));
+        }
+        events::record("ban", name, uuid, serde_json::json!({ "reason": reason }));
+    }
+
     pub(super) fn kick_uuid(&mut self, uuid: u128, reason: Tag) {
         if let Some(h) = self.lan.as_mut() {
             let conns: Vec<u32> = h

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

@@ -34,14 +34,14 @@ pub(super) fn aim_deflect(
     p: &mut Projectile,
     look: Option<Vec3>,
     owner: Option<Who>,
+    owner_uuid: Option<[i32; 4]>,
     guest: Option<u32>,
 ) {
     if let Some(look) = look {
         p.velocity = look;
         p.needs_sync = true;
     }
-    p.owner = owner;
-    p.guest = guest;
+    (p.owner, p.owner_uuid, p.guest) = (owner, owner_uuid, guest);
     p.acceleration = 0.1;
 }
 
@@ -196,14 +196,14 @@ impl Game<'_> {
     /// `Projectile.deflect(AIM_DEFLECT, player, player, true)`.
     pub(super) fn deflect(&mut self, i: usize) {
         let dir = view_vector(self.yaw, self.pitch);
-        let guest = self.lan_acting;
+        let (guest, owner_uuid) = (self.lan_acting, Some(self.acting_player_uuid()));
         let p = &mut self.creatures.projectiles[i];
         p.velocity = Vec3::new(dir[0], dir[1], dir[2]);
         p.yaw = dir[0].atan2(dir[2]).to_degrees() as f32;
         p.pitch = dir[1].atan2(dir[0].hypot(dir[2])).to_degrees() as f32;
         p.owner = Some(Who::Player);
         // On a server, the guest who struck it (their projectile now).
-        p.guest = guest;
+        (p.guest, p.owner_uuid) = (guest, owner_uuid);
         // Not into the one who turned it on its way out.
         p.left_owner = false;
         // `AbstractHurtingProjectile.onDeflection` by an attack, and the
@@ -274,9 +274,9 @@ mod tests {
     fn a_redirected_wind_charge_flies_along_the_new_owners_look() {
         let mut p = wind_charge();
         let look = Vec3::new(0.0, -1.0, 0.0);
-        aim_deflect(&mut p, Some(look), Some(Who::Player), Some(3));
+        aim_deflect(&mut p, Some(look), Some(Who::Player), Some([4; 4]), Some(3));
         assert_eq!(p.velocity, look);
-        assert_eq!(p.owner, Some(Who::Player));
+        assert_eq!((p.owner, p.owner_uuid), (Some(Who::Player), Some([4; 4])));
         assert_eq!(p.guest, Some(3));
         assert_eq!(p.acceleration, 0.1);
         assert!(p.needs_sync);
@@ -285,9 +285,10 @@ mod tests {
     #[test]
     fn with_no_owner_here_it_keeps_its_movement_but_changes_hands() {
         let mut p = wind_charge();
-        aim_deflect(&mut p, None, None, None);
+        p.owner_uuid = Some([7; 4]);
+        aim_deflect(&mut p, None, None, None, None);
         assert_eq!(p.velocity, Vec3::new(0.0, 1.5, 0.0));
-        assert_eq!(p.owner, None);
+        assert_eq!((p.owner, p.owner_uuid), (None, None));
         assert_eq!(p.acceleration, 0.1);
         assert!(!p.needs_sync);
     }

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

@@ -5,6 +5,10 @@ use horizon_client::discord_presence::{self as presence, Dimension, Play, Status
 impl Game<'_> {
     /// Each frame: only a change reaches the presence thread.
     pub(super) fn update_discord_presence(&self) {
+        // One Discord status per computer: P1's, not a splitscreen player's.
+        if self.options.split_guest {
+            return;
+        }
         presence::set(self.discord_status());
     }
     fn discord_status(&self) -> Status {

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

@@ -357,7 +357,7 @@ impl Game<'_> {
         for p in containers {
             let entity = &self.world.block_entities[&p];
             let single = match entity {
-                BlockEntity::Jukebox(j) => std::slice::from_ref(&j.record),
+                BlockEntity::Jukebox(j) => &j.items,
                 _ => entity.slots(),
             };
             for (i, slot) in single.iter().enumerate() {
@@ -744,7 +744,7 @@ impl Game<'_> {
         let jukebox =
             &*self.res.facts().get(self.world.block(p.0, p.1, p.2)).name == "minecraft:jukebox";
         match self.world.block_entities.get_mut(&p) {
-            Some(BlockEntity::Jukebox(j)) => j.record = stack,
+            Some(BlockEntity::Jukebox(j)) => j.items[0] = stack,
             Some(BlockEntity::Lectern(l)) => l.book = stack,
             Some(BlockEntity::Campfire(c)) => {
                 if let Some(cell) = c.items.get_mut(slot) {
@@ -761,7 +761,7 @@ impl Game<'_> {
                 self.world.block_entities.insert(
                     p,
                     BlockEntity::Jukebox(horizon_client::containers::Jukebox {
-                        record: stack,
+                        items: [stack],
                         ticks: 0,
                         playing: false,
                     }),

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

@@ -67,6 +67,15 @@ fn y_rot(d: Direction) -> f32 {
         _ => 270.0,
     }
 }
+/// `DirectionalPlaceContext.getRotation`: `get2DDataValue() * 90`, so a
+/// vertical direction (`data2d = -1`) gives -90 where `toYRot` gives 270: the
+/// same horizontal facing, but the raw value a mod's placement hook reads.
+fn place_rotation(d: Direction) -> f32 {
+    match d {
+        Direction::Up | Direction::Down => -90.0,
+        _ => y_rot(d),
+    }
+}
 fn block_box(p: Pos) -> Aabb {
     Aabb::new(
         Vec3::new(f64::from(p.0), f64::from(p.1), f64::from(p.2)),
@@ -90,6 +99,15 @@ fn shrink(mut stack: ItemStack) -> Option<ItemStack> {
 /// A dispenser's answer: the slot's new content and the level event played.
 type Dispensed = (Option<ItemStack>, i32);
 
+/// A dispenser hook's answer: the slot's remainder (None empties it) and the
+/// level event to play, `CLICK` (1000), `FAIL` (1001) or 0 for none.
+pub(super) type NativeDispensed = (Option<ItemStack>, i32);
+
+/// None keeps vanilla's behaviour; an explicit empty remainder consumes the stack.
+fn mod_dispensed(answer: Option<NativeDispensed>) -> Option<Dispensed> {
+    answer.map(|(left, event)| (left.filter(|stack| stack.count > 0), event))
+}
+
 thread_local! {
     /// `OptionalDispenseItemBehavior.success` of the registered behaviours
     /// that leave it unset on some paths (brush, TNT, honeycomb, chest).
@@ -495,6 +513,29 @@ impl Game<'_> {
         self.spawn_dispensed(pos, facing, one, 6);
         (stack.count > 0).then_some(stack)
     }
+    /// Drop one item as DefaultDispenseItemBehavior does. For a dispenser hook:
+    /// return this remainder in its answer with `CLICK`; the caller plays the
+    /// answer's event and smoke once. A client, another dimension or an unloaded
+    /// chunk keeps the input stack unchanged. API @API:dispenser_behaviour@.
+    #[allow(dead_code)]
+    pub(super) fn native_dispense_default(
+        &mut self,
+        dimension: &str,
+        pos: [i32; 3],
+        facing: Direction,
+        stack: ItemStack,
+    ) -> Option<ItemStack> {
+        if !(self.serving.is_some() || self.options.dedicated.is_some())
+            || dimension != self.dim.id()
+            || !self.world.chunks.contains_key(&(pos[0] >> 4, pos[2] >> 4))
+        {
+            return Some(stack);
+        }
+        if stack.count == 0 {
+            return None;
+        }
+        self.default_execute((pos[0], pos[1], pos[2]), facing, stack)
+    }
     /// `new DefaultDispenseItemBehavior().dispense(..)` including its events.
     pub(super) fn dispense_default(
         &mut self,
@@ -584,6 +625,25 @@ impl Game<'_> {
         facing: Direction,
         stack: ItemStack,
     ) -> Result<Option<ItemStack>> {
+        let mut answer = None;
+        if self.serving.is_some() || self.options.dedicated.is_some() {
+            self.native_dispense_item(
+                self.dim.id(),
+                [pos.0, pos.1, pos.2],
+                facing,
+                &stack,
+                &mut answer,
+            );
+        }
+        if let Some((left, event)) = mod_dispensed(answer) {
+            // DefaultDispenseItemBehavior.dispense: playSound, then playAnimation;
+            // a NOOP behaviour (event 0) plays neither.
+            if event != 0 {
+                self.dispenser_event(event, pos, 0);
+                self.dispenser_event(2000, pos, data_value(facing));
+            }
+            return Ok(left);
+        }
         let item = stack.item.to_string();
         let (left, event) = match item.as_str() {
             "minecraft:arrow"
@@ -1530,7 +1590,7 @@ impl Game<'_> {
                 f64::from(front.2) + 0.5,
             ),
             inside: false,
-            yaw: y_rot(facing),
+            yaw: place_rotation(facing),
             pitch: 0.0,
             sneaking: false,
             item: stack.item.to_string(),
@@ -2148,3 +2208,27 @@ pub(super) fn tipped_effect(stack: &ItemStack) -> Option<(&'static str, i32)> {
                 })
         })
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn mod_dispenser_answers_preserve_fallback_and_own_consumption() {
+        assert!(
+            mod_dispensed(None).is_none(),
+            "no registered behaviour keeps vanilla"
+        );
+        assert_eq!(mod_dispensed(Some((None, CLICK))), Some((None, CLICK)));
+        let stack = ItemStack::new("minecraft:stone", 7);
+        let Some((Some(left), event)) = mod_dispensed(Some((Some(stack.clone()), FAIL))) else {
+            panic!("handled stack")
+        };
+        assert_eq!(left, stack, "the returned remainder is not consumed again");
+        assert_eq!(event, FAIL, "the answer chooses its sound");
+        assert_eq!(
+            mod_dispensed(Some((Some(ItemStack { count: 0, ..stack }), 0))),
+            Some((None, 0))
+        );
+    }
+}

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

@@ -175,6 +175,7 @@ impl Game<'_> {
         };
         let Some(m) = self.mobs.get(mob) else { return };
         let kind = m.kind.id.clone();
+        let victim = m.id;
         let ctx = EffectContext {
             this: Some(&kind),
             attacker: Some("minecraft:player"),
@@ -187,6 +188,7 @@ impl Game<'_> {
         // ignite (fire aspect) and apply_mob_effect (bane of arthropods).
         let mut ignite = 0.0f32;
         let mut mob_effects = Vec::new();
+        let mut hook_calls: Vec<(String, String, Value, u32)> = Vec::new();
         for (id, level) in held.enchantments() {
             let Some(def) = world_stations!(self).enchantments.get(id) else {
                 continue;
@@ -197,14 +199,17 @@ impl Game<'_> {
                 .flatten()
             {
                 let e = &effect["effect"];
-                let kind_of = e["type"].as_str();
-                if effect["enchanted"] != "attacker"
-                    || effect["affected"] != "victim"
-                    || !matches!(
-                        kind_of,
-                        Some("minecraft:ignite" | "minecraft:apply_mob_effect")
-                    )
-                {
+                if effect["enchanted"] != "attacker" || effect["affected"] != "victim" {
+                    continue;
+                }
+                // A bare type name is minecraft's own, as a bare item id is.
+                let kind_of = match e["type"].as_str() {
+                    Some(k) if k.contains(':') => k.to_owned(),
+                    Some(k) => format!("minecraft:{k}"),
+                    None => continue,
+                };
+                let own = !kind_of.starts_with("minecraft:");
+                if !own && !matches!(&*kind_of, "minecraft:ignite" | "minecraft:apply_mob_effect") {
                     continue;
                 }
                 let mut random = self.world.random.clone();
@@ -218,7 +223,11 @@ impl Game<'_> {
                 if !ok {
                     continue;
                 }
-                if kind_of == Some("minecraft:ignite") {
+                // A mod's own kind: its hook answers, after this loop (the
+                // stations borrow is held here).
+                if own {
+                    hook_calls.push((id.to_string(), kind_of, e.clone(), *level));
+                } else if kind_of == "minecraft:ignite" {
                     ignite =
                         ignite.max(horizon_client::enchant::level_value(&e["duration"], *level));
                 } else {
@@ -235,6 +244,9 @@ impl Game<'_> {
         for (effect, level) in mob_effects {
             self.apply_mob_effect(mob, &effect, level);
         }
+        for (id, kind_of, data, level) in hook_calls {
+            self.native_enchant_effect(&id, &kind_of, &data, level, victim);
+        }
         self.post_attack_bursts(&held, &kind);
     }
     /// `EnchantmentHelper.doPostPiercingAttackEffects`: the

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

@@ -435,7 +435,7 @@ impl Game<'_> {
             }
         }
         if raised {
-            self.after_block(outcome, amount, None, false);
+            self.after_block(outcome, None, false);
         }
         pushed
     }
@@ -941,7 +941,7 @@ impl Game<'_> {
             // tables' survives_explosion and explosion_decay draw from their
             // random sequence.
             let decay = (interaction == BlockInteraction::DestroyWithDecay).then_some(radius);
-            let drops = world_items!(self).block_drops_exploded(
+            let mut drops = world_items!(self).block_drops_exploded(
                 self.pack.assets.registry,
                 state,
                 None,
@@ -951,6 +951,7 @@ impl Game<'_> {
                 decay,
                 false,
             );
+            self.native_block_drops(pos, state, None, None, Some(radius), &mut drops);
             for mut stack in drops {
                 if &*stack.item == "minecraft:air" || stack.count == 0 {
                     continue;

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

@@ -93,13 +93,18 @@ impl Game<'_> {
     }
     /// Auto-reconnect's next attempt after a disconnect, when it is on and
     /// the reason allows one.
-    pub(super) fn reconnect_after(&mut self, reason: &str, from_server: bool) -> Option<Retry> {
+    pub(super) fn reconnect_after(
+        &mut self,
+        reason: &str,
+        key: Option<&str>,
+        from_server: bool,
+    ) -> Option<Retry> {
         if !self.settings.extras.auto_reconnect {
             self.extras.reconnect.reset();
             return None;
         }
         let now = std::time::Instant::now();
-        self.extras.reconnect.ended(reason, from_server, now)
+        self.extras.reconnect.ended(reason, key, from_server, now)
     }
     /// Show the attempt's countdown on the Disconnected screen.
     pub(super) fn offer_reconnect(&mut self, retry: Option<Retry>) {

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

@@ -14,7 +14,7 @@ use horizon_client::{
     pose::Pose,
 };
 use horizon_core::{
-    geometry::{Aabb, Vec3, trig},
+    geometry::{Aabb, Vec3, traverse_blocks, trig},
     position::BlockPos,
     random::RandomSource,
 };
@@ -68,6 +68,12 @@ fn bounds(p: Vec3) -> Aabb {
 fn triangle(r: &mut impl RandomSource, mode: f64, deviation: f64) -> f64 {
     mode + deviation * (f64::from(r.next_float()) - f64::from(r.next_float()))
 }
+/// `FishingHook.onHitBlock`: `getDeltaMovement().normalize().scale(hit.distanceTo(this))`,
+/// where `HitResult.distanceTo` is the *squared* distance to the hook: the bobber
+/// springs back a little off a wall instead of stopping dead.
+fn rebound(velocity: Vec3, hit: Vec3, at: Vec3) -> Vec3 {
+    velocity.normalize().scale(hit.distance_squared(at))
+}
 impl Game<'_> {
     fn holds_rod(&self) -> bool {
         self.held()
@@ -568,6 +574,28 @@ impl Game<'_> {
                     self.hook = Some(h);
                     return;
                 }
+                // checkCollision: the block the path hits before the move, then
+                // `onHitBlock`'s rebound.
+                let to = h.position.add_vector(h.velocity);
+                let mut scene = SceneCollisions {
+                    world: &self.world,
+                    binding: self.collision,
+                    subject: None,
+                };
+                let hit = traverse_blocks(h.position, to, 1024, |p: BlockPos| {
+                    let state = self.world.block(p.x, p.y, p.z);
+                    if self.res.facts().is_air(state) {
+                        return None;
+                    }
+                    let shape = self
+                        .collision
+                        .collision_shape(&mut scene, state, [p.x, p.y, p.z])
+                        .ok()?;
+                    shape.clip(h.position, to, p)
+                });
+                if let Some(hit) = hit.ok().flatten() {
+                    h.velocity = rebound(h.velocity, hit.location, h.position);
+                }
             }
             State::Hooked(id) => {
                 // updateHookedEntity: ride the hooked mob, player or item at 0.8 of its height.
@@ -1291,3 +1319,17 @@ impl Game<'_> {
             .collect()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::rebound;
+    use horizon_core::geometry::Vec3;
+
+    /// `HitResult.distanceTo` is squared: a hit 0.5 away rebounds at 0.25.
+    #[test]
+    fn a_block_hit_rebounds_by_the_squared_distance() {
+        let v = Vec3::new(0.0, 0.0, -2.0);
+        let hit = Vec3::new(0.0, 0.0, -0.5);
+        assert_eq!(rebound(v, hit, Vec3::ZERO), Vec3::new(0.0, 0.0, -0.25));
+    }
+}

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

@@ -0,0 +1,98 @@
+//! `--headless` (#4951): a client with no display, no window and no renderer.
+//!
+//! winit's event loop needs a display server even when no window is shown, so a headless game
+//! runs this loop instead. Each step is what winit's `about_to_wait` does (`Game::idle`: stop
+//! requests, the closing save, world entry, the control socket), and `idle` runs the frame
+//! (the client tick, nothing drawn) through the same `RedrawRequested` path a window's game
+//! takes. Input comes only from the control socket (`horizon-ctl`), as synthetic window events.
+
+use super::Game;
+use super::event_loop::EventLoopCtl;
+use std::{
+    cell::Cell,
+    time::{Duration, Instant},
+};
+use winit::event_loop::ControlFlow;
+
+/// Time between headless frames. The client ticks at 20 Hz whatever the frame rate (a frame
+/// runs the ticks its elapsed time owes), so one frame per tick does all the work there is
+/// without spending a core on frames nobody sees.
+const FRAME: Duration = Duration::from_millis(50);
+
+/// The loop's side of `EventLoopCtl`: what the game asked for during a step.
+struct HeadlessLoop {
+    exit: Cell<bool>,
+    flow: Cell<ControlFlow>,
+}
+
+impl EventLoopCtl for HeadlessLoop {
+    fn exit(&self) {
+        self.exit.set(true);
+    }
+    fn set_control_flow(&self, flow: ControlFlow) {
+        self.flow.set(flow);
+    }
+}
+
+impl HeadlessLoop {
+    /// When the step that started at `started` wants the next one: at the time the game asked
+    /// for (`WaitUntil`, as the closing save's polls do), else one frame later.
+    fn next_step(&self, started: Instant) -> Instant {
+        match self.flow.get() {
+            ControlFlow::WaitUntil(at) => at,
+            ControlFlow::Poll | ControlFlow::Wait => started + FRAME,
+        }
+    }
+}
+
+impl Game<'_> {
+    /// Runs the game until it asks to stop (`horizon-ctl quit`, a signal, an error), then
+    /// saves as a window's game does when its loop ends.
+    pub(super) fn run_headless(&mut self) {
+        let ctl = HeadlessLoop {
+            exit: Cell::new(false),
+            flow: Cell::new(ControlFlow::Poll),
+        };
+        self.previous = Instant::now();
+        while !ctl.exit.get() {
+            let started = Instant::now();
+            ctl.flow.set(ControlFlow::Poll);
+            self.idle(&ctl);
+            if let Some(wait) = ctl
+                .next_step(started)
+                .checked_duration_since(Instant::now())
+            {
+                std::thread::sleep(wait);
+            }
+        }
+        self.shut_down();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn ctl(flow: ControlFlow) -> HeadlessLoop {
+        HeadlessLoop {
+            exit: Cell::new(false),
+            flow: Cell::new(flow),
+        }
+    }
+
+    #[test]
+    fn steps_come_a_frame_apart_unless_the_game_asks_for_sooner() {
+        let started = Instant::now();
+        assert_eq!(ctl(ControlFlow::Poll).next_step(started), started + FRAME);
+        let soon = started + Duration::from_millis(4);
+        assert_eq!(ctl(ControlFlow::WaitUntil(soon)).next_step(started), soon);
+    }
+
+    #[test]
+    fn exit_is_remembered_for_the_loop() {
+        let c = ctl(ControlFlow::Poll);
+        assert!(!c.exit.get());
+        EventLoopCtl::exit(&c);
+        assert!(c.exit.get());
+    }
+}

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

@@ -60,6 +60,9 @@ struct Flags {
     entity_distance: AtomicU32,
     /// `MinecraftServer.isCurrentlySaving`: the server is autosaving.
     saving: AtomicBool,
+    /// Splitscreen players joined through memory (offline uuids): let in although the world is
+    /// not open to the LAN, and the game no longer pauses while they play.
+    split_players: Mutex<Vec<u128>>,
     /// The generators of the levels the server has run, by dimension: what
     /// F3's chunk generation entry asks `ServerChunkCache.getGenerator`.
     terrain: Mutex<
@@ -120,7 +123,42 @@ impl Integrated {
     }
     /// `IntegratedServer.tickServer` skips the world while the game is paused.
     pub fn set_paused(&self, paused: bool) {
-        self.flags.paused.store(paused, Ordering::Relaxed);
+        let split = !self.flags.split_players.lock().unwrap().is_empty();
+        self.flags.paused.store(paused && !split, Ordering::Relaxed);
+    }
+    /// Splitscreen: `name` left; the game pauses again once every such player has. The owner's
+    /// permissions it was given go with it (a LAN player could otherwise join under that name).
+    pub fn leave_split(&self, name: &str) {
+        let uuid = horizon_protocol::crypto::offline_uuid(name);
+        self.flags
+            .split_players
+            .lock()
+            .unwrap()
+            .retain(|&u| u != uuid);
+        self.call(move |g| {
+            if let Some(host) = g.lan.as_mut() {
+                host.hub.ops.remove(&uuid);
+            }
+        });
+    }
+    /// Splitscreen: a connection through memory for another player on this machine, who gets
+    /// the owner's permissions. `None` once the server has stopped.
+    pub fn join_split(&self, name: &str) -> Option<horizon_protocol::connection::Pipe> {
+        let uuid = horizon_protocol::crypto::offline_uuid(name);
+        self.flags.split_players.lock().unwrap().push(uuid);
+        let pipe = self
+            .call(move |g| {
+                let host = g.lan.as_mut()?;
+                let owner = host.owner.as_ref()?.uuid;
+                let level = host.hub.ops.get(&owner).copied().unwrap_or(0);
+                host.hub.ops.insert(uuid, level);
+                host.hub.lan.connect_local().ok()
+            })
+            .flatten();
+        if pipe.is_none() {
+            self.leave_split(name);
+        }
+        pipe
     }
     /// The window's render and simulation distances and its Entity Distance
     /// option, for the server to follow.
@@ -679,14 +717,25 @@ impl Game<'_> {
         };
         let owner = launch.owner;
         let published = flags.clone();
+        let local_players = flags.clone();
         let net = NetConfig {
             // No network until it is opened to the LAN; the memory connection
             // is not compressed (`Connection.isMemoryConnection`).
             listen: false,
             online: horizon_client::lan::OnlineMode::lan(),
-            gate: Some(Arc::new(move |_, uuid, _| {
-                (uuid != owner && published.published.load(Ordering::Relaxed) == 0)
-                    .then(|| translatable("multiplayer.disconnect.not_whitelisted", &[]))
+            // Registered local seats share this computer; the vanilla LAN capacity still
+            // applies to other connections when the world is published.
+            bypasses_limit: Some(Arc::new(move |uuid| {
+                local_players.split_players.lock().unwrap().contains(&uuid)
+            })),
+            gate: Some(Arc::new(move |address, uuid, _| {
+                refused(
+                    uuid == owner,
+                    published.published.load(Ordering::Relaxed) != 0,
+                    published.split_players.lock().unwrap().contains(&uuid),
+                    address == horizon_client::lan::conn::MEMORY_ADDRESS,
+                )
+                .then(|| translatable("multiplayer.disconnect.not_whitelisted", &[]))
             })),
             levels: self.level_shapes,
             owner_profile: launch.owner_profile.clone(),
@@ -1033,12 +1082,17 @@ impl Game<'_> {
     /// `IntegratedServer.setWorldAllowCommands`: the owner is an operator
     /// while the world allows commands; everyone's level is sent again.
     pub(super) fn owner_allow_commands(&mut self, allow: bool) {
-        let Some(owner) = self.serving.as_ref().map(|s| s.owner) else {
+        let Some((owner, flags)) = self.serving.as_ref().map(|s| (s.owner, s.flags.clone())) else {
             return;
         };
         let published = self.published_port().is_some();
         if let Some(host) = self.lan.as_mut() {
-            host.hub.ops.insert(owner, if allow { 4 } else { 0 });
+            let level = if allow { 4 } else { 0 };
+            host.hub.ops.insert(owner, level);
+            // Splitscreen seats have the owner's permissions (`join_split`): they follow it.
+            for &seat in flags.split_players.lock().unwrap().iter() {
+                host.hub.ops.insert(seat, level);
+            }
             if published {
                 host.hub.config.guest_commands = allow && host.settings.guest_commands;
             }
@@ -1144,10 +1198,38 @@ fn server_game(
     Game::new(res, pack, gui, options, settings, audio, None)
 }
 
+/// Who the integrated server turns away: anyone but the owner until it is opened to the LAN,
+/// except a splitscreen seat. A seat's name is let in only through memory, so a LAN player
+/// logging in under it never gets its place or the owner's permissions it holds.
+fn refused(owner: bool, published: bool, split_seat: bool, memory: bool) -> bool {
+    if split_seat {
+        !memory
+    } else {
+        !owner && !published
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn a_splitscreen_seat_is_let_in_only_through_memory() {
+        // (owner, published, seat, memory)
+        assert!(!refused(false, false, true, true), "a local seat joins");
+        assert!(
+            refused(false, true, true, false),
+            "a LAN player under a seat's name"
+        );
+        assert!(refused(false, false, true, false));
+        assert!(
+            !refused(false, true, false, false),
+            "anyone once open to the LAN"
+        );
+        assert!(refused(false, false, false, false), "nobody else before");
+        assert!(!refused(true, false, false, true), "the owner");
+    }
+
     #[test]
     fn shutdown_request_does_not_join_a_server_still_saving() {
         let flags = Arc::new(Flags::default());

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

@@ -53,6 +53,47 @@ impl Game<'_> {
         self.container_changed((pos[0], pos[1], pos[2]));
         self.world.modified.insert((pos[0] >> 4, pos[2] >> 4));
     }
+    /// `JukeboxBlockEntity.setTheItem` from a container (a hopper or a dropper
+    /// feeding the slot): a disc that lands in a jukebox that is not playing
+    /// starts its song, as the player's own use does, with the block state,
+    /// the song's level event and the neighbour and comparator updates.
+    pub(super) fn jukebox_inserted(&mut self, pos: [i32; 3]) {
+        let Some(song) = self
+            .jukebox(pos)
+            .filter(|j| !j.playing)
+            .and_then(|j| j.record())
+            .and_then(|record| self.res.items().get(&record.item))
+            .and_then(|info| info.jukebox_song.clone())
+        else {
+            return;
+        };
+        if let Some(BlockEntity::Jukebox(j)) =
+            self.world.block_entities.get_mut(&(pos[0], pos[1], pos[2]))
+        {
+            j.playing = true;
+            j.ticks = 0;
+        }
+        self.set_has_record(pos, true);
+        self.start_song(pos, &song);
+        self.jukebox_changed(pos);
+    }
+    /// `JukeboxBlockEntity.setTheItem(EMPTY)` from a container (a hopper
+    /// below taking the disc): the song stops, the block loses its record,
+    /// and the neighbours and comparators hear it.
+    pub(super) fn jukebox_taken(&mut self, pos: [i32; 3]) {
+        if let Some(BlockEntity::Jukebox(j)) =
+            self.world.block_entities.get_mut(&(pos[0], pos[1], pos[2]))
+        {
+            if j.record().is_some() {
+                return;
+            }
+            j.playing = false;
+            j.ticks = 0;
+        }
+        self.stop_song(pos);
+        self.set_has_record(pos, false);
+        self.jukebox_changed(pos);
+    }
     /// `JukeboxBlock.useItemOn` / `useWithoutItem` on the jukebox at `pos`.
     pub(super) fn use_jukebox(&mut self, pos: [i32; 3], held: Option<&ItemStack>) -> bool {
         if &*self
@@ -64,7 +105,7 @@ impl Game<'_> {
         {
             return false;
         }
-        if self.jukebox(pos).is_some_and(|j| j.record.is_some()) {
+        if self.jukebox(pos).is_some_and(|j| j.record().is_some()) {
             // TRY_WITH_EMPTY_HAND: only the main hand goes on to useWithoutItem.
             if self.hand != Hand::Main {
                 return false;
@@ -95,7 +136,7 @@ impl Game<'_> {
         self.world.block_entities.insert(
             (pos[0], pos[1], pos[2]),
             BlockEntity::Jukebox(Jukebox {
-                record: Some(record),
+                items: [Some(record)],
                 ticks: 0,
                 playing: true,
             }),
@@ -200,7 +241,7 @@ impl Game<'_> {
             Some(BlockEntity::Jukebox(j)) => {
                 j.playing = false;
                 j.ticks = 0;
-                j.record.take()
+                j.items[0].take()
             }
             _ => None,
         };
@@ -224,7 +265,7 @@ impl Game<'_> {
     /// `JukeboxSongPlayer.tick` of the jukebox at `key`, while it plays.
     pub(super) fn tick_jukebox(&mut self, key: (i32, i32, i32)) {
         let playing = match self.world.block_entities.get(&key) {
-            Some(BlockEntity::Jukebox(j)) if j.playing => j.record.as_ref().and_then(|r| {
+            Some(BlockEntity::Jukebox(j)) if j.playing => j.record().and_then(|r| {
                 let song = self.items().get(&r.item)?.jukebox_song.clone()?;
                 Some((song, j.ticks))
             }),
@@ -314,8 +355,7 @@ pub(super) fn jukebox_signals(
     match world.block_entities.get(&(pos.x, pos.y, pos.z)) {
         Some(BlockEntity::Jukebox(j)) => {
             let comparator = j
-                .record
-                .as_ref()
+                .record()
                 .and_then(|r| items.get(&r.item)?.jukebox_song.as_ref())
                 .and_then(|s| items.songs.get(s))
                 .map_or(0, |s| s.comparator);

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

@@ -1482,6 +1482,25 @@ impl Game<'_> {
     /// `PlayerList.removeAll`: every guest leaves in turn, the vehicle it
     /// alone rides with it (`PlayerList.remove`), and is saved.
     pub(super) fn save_leaving_guests(&mut self, host: &mut LanHost) {
+        // Every open menu closes first, in its guest's level
+        // (`ServerPlayer.disconnect` -> `doCloseContainer`), so the cursor,
+        // the trade and the inputs are back in the file that is saved.
+        let back = self.dim;
+        let open: Vec<(u32, super::Dim)> = host
+            .hub
+            .guests
+            .iter()
+            .filter(|g| g.placed)
+            .map(|g| (g.conn, super::Dim::from_id(&g.dimension)))
+            .collect();
+        for (conn, dim) in open {
+            if self.enter_level(Some(host), dim).is_ok() {
+                self.guest_close_all(host, conn);
+            }
+        }
+        if let Err(e) = self.enter_level(Some(host), back) {
+            log::error!("could not reopen {}: {e}", back.id());
+        }
         for i in 0..host.hub.guests.len() {
             let mut g = host.hub.guests.remove(i);
             self.take_parent_vehicle(host, &mut g);
@@ -1490,15 +1509,13 @@ impl Game<'_> {
         }
     }
     /// Save a guest when they leave or the world closes (after
-    /// `take_parent_vehicle`): an integrated server's owner with the world
-    /// (`save_game`), anyone else in their file.
+    /// `take_parent_vehicle`, `PlayerList.save`): an integrated server's owner
+    /// into the level (`/data`) and both its files (`playerdata::save_owner`),
+    /// anyone else into their own file.
     pub(super) fn save_guest(&mut self, host: &LanHost, guest: &horizon_client::lan::guest::Guest) {
-        if host.owner.as_ref().is_some_and(|o| o.uuid == guest.uuid) && guest.placed {
-            // The world's own player state rides in the level (`/data`).
-            playerdata::store(guest, &mut self.level, None);
-        }
-        if guest.placed {
-            // PlayerList.save/remove: every player saves to their own file.
+        if guest.placed && host.owner.as_ref().is_some_and(|o| o.uuid == guest.uuid) {
+            playerdata::save_owner(guest, &mut self.level, &self.world_root);
+        } else if guest.placed {
             playerdata::save(guest, &self.world_root);
         }
         self.save_guest_records(host, guest);
@@ -1900,6 +1917,9 @@ impl Game<'_> {
                 event @ (HostEvent::Chat { .. } | HostEvent::Warn(_) | HostEvent::Error(_)) => {
                     self.lan_log_event(event);
                 }
+                HostEvent::Ban { uuid, name, reason } => {
+                    self.anticheat_ban(&mut host.hub, uuid, &name, &reason);
+                }
                 HostEvent::ChatFiltered {
                     sender,
                     name,
@@ -1976,15 +1996,17 @@ impl Game<'_> {
                     }
                 }
                 HostEvent::Left(mut guest) => {
-                    // The container they had open loses an opener.
-                    if let Some(pos) = guest.menu.as_ref().and_then(|m| m.pos)
-                        && !guest.spectator()
-                    {
-                        // In the level they were in.
+                    // The menu they had open closes, in the level they were in
+                    // (`ServerPlayer.disconnect` -> `doCloseContainer`).
+                    if guest.placed {
                         let back = self.dim;
                         let theirs = super::Dim::from_id(&guest.dimension);
                         if self.enter_level(Some(&mut host), theirs).is_ok() {
-                            self.container_openers_changed(pos, false);
+                            let conn = guest.conn;
+                            let at = host.hub.guests.len();
+                            host.hub.guests.push(*guest);
+                            self.guest_close_all(&mut host, conn);
+                            *guest = host.hub.guests.remove(at);
                         }
                         if let Err(e) = self.enter_level(Some(&mut host), back) {
                             log::error!("could not reopen {}: {e}", back.id());
@@ -2349,28 +2371,15 @@ impl Game<'_> {
         let force = host.hub.config.force_game_mode;
         let root = self.world_root.clone();
         let in_place = host.hub.config.dimension.clone();
-        let mut owner = host.owner.as_mut();
+        let owner = host.owner.as_mut();
         let Some(g) = host.hub.guest_mut(conn) else {
             return;
         };
-        let is_owner = owner.as_ref().is_some_and(|o| o.uuid == g.uuid);
-        // PlayerDataStorage.load: the player's own file first; the world's
-        // own player state is the fallback for a first join.
-        let known = if is_owner && playerdata::load(g, &root) {
-            true
-        } else {
-            let saved = if is_owner {
-                owner.as_mut().and_then(|o| o.saved.take())
-            } else {
-                None
-            };
-            match saved {
-                Some(level) => {
-                    playerdata::apply(g, &level);
-                    level.position.is_some()
-                }
-                None => playerdata::load(g, &root),
-            }
+        // PlayerList.loadPlayerData: the owner gets the world's player file,
+        // everyone else their own.
+        let known = match owner.filter(|o| o.uuid == g.uuid) {
+            Some(o) => playerdata::load_owner(g, &root, o.saved.take().as_deref()),
+            None => playerdata::load(g, &root),
         };
         if !known || force {
             g.game_mode = default_mode;

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

@@ -295,7 +295,9 @@ impl Game<'_> {
         f: impl FnOnce(&mut Self) -> R,
     ) -> Option<R> {
         let swap = self.enter_guest(host, conn)?;
-        let result = f(self);
+        let dimension =
+            (self.serving.is_some() || self.options.dedicated.is_some()).then_some(self.dim.id());
+        let result = horizon_client::block_contact::in_level(dimension, || f(self));
         self.leave_guest(host, swap);
         Some(result)
     }
@@ -482,6 +484,9 @@ impl Game<'_> {
         if let Some(p) = self.player.as_mut() {
             p.is_passenger = g.vehicle.is_some();
         }
+        // Entity.collide: the guest's body collides with the level's world
+        // border too, as it is this turn (it moves with /worldborder).
+        self.player_border();
         let host_station = self.station.take();
         // The guest's bed, sleep counter and respawn point; the host's
         // respawn point, anchor and action bar stay theirs.
@@ -1179,8 +1184,7 @@ impl Game<'_> {
             return false;
         }
         // ServerPlayer.openMenu closes the menu that was open.
-        self.guest_container_closed(host, conn);
-        self.lan_station_closed(host, conn, None);
+        self.guest_close_all(host, conn);
         let hidden = self.native_hidden_slots(pos, items.len());
         host.hub
             .open_container(conn, menu, title, pos, slots, items);
@@ -1228,8 +1232,7 @@ impl Game<'_> {
             return false;
         };
         // ServerPlayer.openMenu closes the menu that was open.
-        self.guest_container_closed(host, conn);
-        self.lan_station_closed(host, conn, None);
+        self.guest_close_all(host, conn);
         host.hub
             .open_container(conn, menu, title, pos, slots, items);
         true
@@ -1250,6 +1253,38 @@ impl Game<'_> {
         }
     }
 
+    /// Closes whatever menu the guest has open, the way each `ContainerClose`
+    /// does (`ServerPlayer.doCloseContainer`, `AbstractContainerMenu.removed`):
+    /// the container's lid, a vehicle's stand-in (its items go back to the
+    /// vehicle), the trade (written back to the villager), the crafting table,
+    /// station and mount menus, and the cursor stack back to the inventory.
+    /// Nothing is sent to the client: this is for a guest who is leaving or
+    /// whose server is closing. The guest must be in `host.hub.guests` and the
+    /// level they are in must be the one in place.
+    pub(super) fn guest_close_all(&mut self, host: &mut LanHost, conn: u32) {
+        let Some(gi) = host.hub.guests.iter().position(|g| g.conn == conn) else {
+            return;
+        };
+        if let Some((window, slots)) = host.hub.guests[gi]
+            .menu
+            .as_ref()
+            .map(|m| (m.window, m.slots))
+        {
+            self.guest_container_closed(host, conn);
+            if let Slots::Block(key) = slots
+                && key.1 == super::minecarts::CART_KEY_Y
+            {
+                self.close_guest_vehicle_menu(host, conn, key);
+            }
+            host.hub.container_closed(conn, window);
+        }
+        self.lan_merchant_closed(host, conn, None);
+        self.lan_crafting_closed(host, conn, None);
+        self.lan_station_closed(host, conn, None);
+        self.lan_mount_closed(host, conn, None);
+        self.guest_carried_back(host, gi);
+    }
+
     /// `ContainerEntity`'s `Container.stopOpen` when a vehicle menu closes
     /// (`AbstractChestBoat.stopOpen` / `MinecartChest.stopOpen`): the menu's
     /// slots go back to the vehicle, the shared placeholder leaves
@@ -1294,15 +1329,7 @@ impl Game<'_> {
             .guests
             .iter()
             .filter(|g| host.hub.here(g))
-            .filter(|g| {
-                g.menu.as_ref().is_some_and(|m| {
-                    (m.slots.valid(&self.world) && !m.slots.still_valid(&self.world, g, m.pos))
-                        || m.pos.is_some_and(|k| {
-                            k.1 == super::minecarts::CART_KEY_Y
-                                && !self.chest_vehicle_still_valid(k.2, g)
-                        })
-                })
-            })
+            .filter(|g| !self.container_menu_valid(g))
             .map(|g| {
                 let vehicle = g.menu.as_ref().and_then(|m| match m.slots {
                     Slots::Block(key) if key.1 == super::minecarts::CART_KEY_Y => Some(key),
@@ -1323,6 +1350,78 @@ impl Game<'_> {
         }
     }
 
+    /// `stillValid` of the guest's open container: its blocks are still there
+    /// and in reach, or its vehicle exists and is in reach. True with none open.
+    fn container_menu_valid(&self, g: &horizon_client::lan::guest::Guest) -> bool {
+        g.menu.as_ref().is_none_or(|m| {
+            !(m.slots.valid(&self.world) && !m.slots.still_valid(&self.world, g, m.pos))
+                && !m.pos.is_some_and(|k| {
+                    k.1 == super::minecarts::CART_KEY_Y && !self.chest_vehicle_still_valid(k.2, g)
+                })
+        })
+    }
+
+    /// `AbstractContainerMenu.stillValid` of whatever menu the guest has open
+    /// (a container or vehicle, a trade, the crafting table, a station, a
+    /// lectern, a mount's inventory). True when none is open.
+    fn guest_menu_still_valid(&self, host: &LanHost, conn: u32) -> bool {
+        let Some(g) = host.hub.guest(conn) else {
+            return true;
+        };
+        if !self.container_menu_valid(g) {
+            return false;
+        }
+        let Some(p) = host.play.get(&conn) else {
+            return true;
+        };
+        p.crafting
+            .table
+            .as_ref()
+            .is_none_or(|t| self.lan_table_valid(g, t.3))
+            && p.station
+                .as_ref()
+                .is_none_or(|s| self.lan_station_valid(g, s))
+            && p.lectern
+                .as_ref()
+                .is_none_or(|l| self.lan_lectern_valid(g, l.key))
+            && p.merchant
+                .as_ref()
+                .and_then(|m| m.merchant.mob)
+                .is_none_or(|id| self.lan_merchant_valid(g, id))
+            && p.mount_window
+                .as_ref()
+                .is_none_or(|m| self.lan_mount_valid(g, m.mob))
+    }
+
+    /// The check before a menu click: a menu that is no longer valid closes
+    /// (returning what it held, as `ContainerClose` does) and the client's
+    /// window with it, so the click lands on nothing
+    /// (`ServerGamePacketListenerImpl.handleContainerClick` and the others
+    /// ask `stillValid` first).
+    fn guest_validate_menu(&mut self, host: &mut LanHost, conn: u32) {
+        if self.guest_menu_still_valid(host, conn) {
+            return;
+        }
+        let mut windows: Vec<i32> = host
+            .hub
+            .guest(conn)
+            .and_then(|g| g.menu.as_ref().map(|m| m.window))
+            .into_iter()
+            .collect();
+        if let Some(p) = host.play.get(&conn) {
+            windows.extend(p.crafting.table.as_ref().map(|t| t.0));
+            windows.extend(p.station.as_ref().map(|s| s.window));
+            windows.extend(p.lectern.as_ref().map(|l| l.window));
+            windows.extend(p.merchant.as_ref().map(|m| m.window));
+            windows.extend(p.mount_window.as_ref().map(|m| m.window));
+        }
+        self.guest_close_all(host, conn);
+        for container in windows {
+            host.hub
+                .send_to(conn, &C::ContainerClose(play::ContainerClose { container }));
+        }
+    }
+
     /// `ContainerEntity.isChestVehicleStillValid`: the chest minecart or chest
     /// boat is still there and within the guest's entity interaction range
     /// plus 4 of its box.
@@ -1434,6 +1533,19 @@ impl Game<'_> {
         {
             return;
         }
+        if matches!(
+            packet,
+            S::ContainerClick(_)
+                | S::ContainerButtonClick(_)
+                | S::ContainerSlotStateChanged(_)
+                | S::RenameItem(_)
+                | S::SetBeacon(_)
+                | S::SelectTrade(_)
+                | S::SelectBundleItem(_)
+                | S::PlaceRecipe(_)
+        ) {
+            self.guest_validate_menu(host, conn);
+        }
         let spectator = host.hub.guests[gi].spectator();
         match packet {
             S::PlayerAction(a) => match a.action {

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

@@ -186,9 +186,27 @@ impl Game<'_> {
             let targets: Vec<usize> = match (raw, &selector.player_name, selector.uuid) {
                 (Some("@s"), ..) => vec![i],
                 (Some("@a"), ..) => (0..guests.len()).filter(placed).collect(),
-                (_, Some(name), _) => (0..guests.len())
-                    .filter(|&k| placed(&k) && guests[k].name.eq_ignore_ascii_case(name))
-                    .collect(),
+                (_, Some(name), _) => {
+                    let named: Vec<usize> = (0..guests.len())
+                        .filter(|&k| placed(&k) && guests[k].name.eq_ignore_ascii_case(name))
+                        .collect();
+                    if named.is_empty() {
+                        // No player has that name: the one going by it as a nickname (`~` optional).
+                        let bare = |s: &str| s.strip_prefix('~').unwrap_or(s).to_ascii_lowercase();
+                        let wanted = bare(name);
+                        let nicknamed = |k: &usize| {
+                            host.hub
+                                .nicknames
+                                .get(&guests[*k].uuid)
+                                .is_some_and(|nick| bare(nick) == wanted)
+                        };
+                        (0..guests.len())
+                            .filter(|k| placed(k) && nicknamed(k))
+                            .collect()
+                    } else {
+                        named
+                    }
+                }
                 (_, None, Some(uuid)) => (0..guests.len())
                     .filter(|&k| placed(&k) && guests[k].uuid == uuid)
                     .collect(),

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

@@ -21,7 +21,7 @@ pub(super) struct GuestCrafting {
     /// The inventory menu; its grid lives in the hub's guest.
     inventory: Option<Box<Menu>>,
     /// The open crafting table: its window, state id, menu and block.
-    table: Option<(i32, i32, Box<Menu>, [i32; 3])>,
+    pub(super) table: Option<(i32, i32, Box<Menu>, [i32; 3])>,
     /// The open furnace's or brewing stand's window and menu (`AbstractFurnaceMenu`,
     /// `BrewingStandMenu`); its slots live in the block entity and the hub's
     /// container menu keeps the client in sync.
@@ -436,10 +436,8 @@ impl Game<'_> {
 
     /// The guest opened a crafting table (`CraftingTableBlock.getMenuProvider`).
     pub(super) fn lan_open_crafting(&mut self, host: &mut LanHost, conn: u32, pos: [i32; 3]) {
-        self.lan_crafting_closed(host, conn, None);
-        self.lan_station_closed(host, conn, None);
-        // The container it replaces loses its opener.
-        self.guest_container_closed(host, conn);
+        // ServerPlayer.openMenu closes the menu that was open.
+        self.guest_close_all(host, conn);
         let title = horizon_protocol::text::translatable("container.crafting", &[]);
         let Some(window) = host.hub.open_window(conn, "minecraft:crafting", title) else {
             return;
@@ -509,7 +507,7 @@ impl Game<'_> {
 
     /// `CraftingMenu.stillValid`: the block is still a crafting table and the
     /// guest is within reach of it.
-    fn lan_table_valid(&self, g: &Guest, pos: [i32; 3]) -> bool {
+    pub(super) fn lan_table_valid(&self, g: &Guest, pos: [i32; 3]) -> bool {
         let name = &self
             .res
             .facts()

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

@@ -12,6 +12,15 @@ use horizon_client::lan::{
 use horizon_protocol::entity_data::{Value, serializer};
 use horizon_world::{nbt::Tag, registry::BlockStateId};
 
+/// Allocate once: a native summon may need its id before the tracking tick.
+pub(super) fn assign_entity_id(next: &mut u32, id: &mut u32) -> u32 {
+    if *id == 0 {
+        *next += 1;
+        *id = *next;
+    }
+    *id
+}
+
 fn state(id: u32, kind: &str, position: [f64; 3], yaw: f32, on_ground: bool) -> EntityState {
     EntityState {
         id: id as i32,
@@ -125,6 +134,13 @@ impl Game<'_> {
                         .push((11 + k as u8, serializer::BOOLEAN, Value::Bool(true)));
                 }
             }
+            // AbstractBoat.DATA_ID_BUBBLE_TIME, back to 0 once the boat is off
+            // the column.
+            if b.bubble_time != 0 {
+                e.meta
+                    .push((13, serializer::INT, Value::Int(b.bubble_time)));
+            }
+            e.defaults.push((13, serializer::INT, Value::Int(0)));
             out.push(e);
         }
         for c in &self.carts {
@@ -443,10 +459,7 @@ impl Game<'_> {
         }
         let next = &mut self.next_entity;
         let mut give = |id: &mut u32| {
-            if *id == 0 {
-                *next += 1;
-                *id = *next;
-            }
+            assign_entity_id(next, id);
         };
         self.tnts.iter_mut().for_each(|t| give(&mut t.id));
         self.falling.iter_mut().for_each(|f| give(&mut f.id));
@@ -729,6 +742,22 @@ fn arrow_meta(
 mod tests {
     use super::*;
 
+    #[test]
+    fn summoned_ids_are_unique_and_survive_the_tracking_pass() {
+        let mut next = 40;
+        let mut roots = [0; 3];
+        let returned = roots.each_mut().map(|id| assign_entity_id(&mut next, id));
+        assert_eq!(returned, [41, 42, 43]);
+        // Tracking sees the same roots plus an unrelated deferred entity.
+        for id in &mut roots {
+            assign_entity_id(&mut next, id);
+        }
+        let mut later = 0;
+        assert_eq!(assign_entity_id(&mut next, &mut later), 44);
+        assert_eq!(roots, returned);
+        assert_eq!(next, 44);
+    }
+
     #[test]
     fn armor_stand_poses_send_only_what_differs() {
         let mut stand = horizon_client::entities::ArmorStand::new(1, Default::default(), 0.0);

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

@@ -15,8 +15,8 @@ use horizon_protocol::packets::play::{self, Clientbound as C};
 
 /// A guest's open mount menu.
 pub(super) struct GuestMount {
-    window: i32,
-    mob: u32,
+    pub(super) window: i32,
+    pub(super) mob: u32,
     columns: usize,
     state: i32,
     /// The menu's slots and the carried stack the client was last sent.
@@ -31,10 +31,8 @@ impl Game<'_> {
             return;
         };
         let columns = super::mount_menu::mount_columns(&self.mobs[index]);
-        self.lan_mount_closed(host, conn, None);
-        self.lan_station_closed(host, conn, None);
-        self.lan_crafting_closed(host, conn, None);
-        self.guest_container_closed(host, conn);
+        // ServerPlayer.openMenu closes the menu that was open.
+        self.guest_close_all(host, conn);
         let Some(window) = host.hub.open_mount_window(conn, columns as i32, mob as i32) else {
             return;
         };
@@ -182,10 +180,28 @@ impl Game<'_> {
         closed
     }
 
+    /// `AbstractMountInventoryMenu.stillValid`: the mount is alive and within
+    /// the entity interaction range (3) plus 4 of the guest's eyes.
+    pub(super) fn lan_mount_valid(&self, g: &horizon_client::lan::guest::Guest, mob: u32) -> bool {
+        let eye = [g.position[0], g.position[1] + g.eye_height(), g.position[2]];
+        self.mobs.iter().find(|m| m.id == mob).is_some_and(|m| {
+            let (w, h) = (f64::from(m.width()) / 2.0, f64::from(m.height()));
+            let p = [m.position.x, m.position.y, m.position.z];
+            let lo = [p[0] - w, p[1], p[2] - w];
+            let hi = [p[0] + w, p[1] + h, p[2] + w];
+            let d: f64 = (0..3)
+                .map(|k| (eye[k] - eye[k].clamp(lo[k], hi[k])).powi(2))
+                .sum();
+            m.alive() && d < 7.0 * 7.0
+        })
+    }
+
     /// Each tick: a mount menu whose mount died or is out of reach closes
     /// (`AbstractMountInventoryMenu.stillValid`: alive, within the entity
     /// interaction range plus 4 of the eyes), and the others follow the
-    /// mount's and the inventory's slots.
+    /// mount's and the inventory's slots. Only the level the player is in
+    /// checks its menu (`ServerPlayer.tick`): another level ticking has
+    /// none of its mobs (#5331).
     pub(super) fn tick_lan_mount_menus(&mut self, host: &mut LanHost) {
         let open: Vec<(u32, u32, i32)> = host
             .play
@@ -196,19 +212,10 @@ impl Game<'_> {
             let Some(g) = host.hub.guests.iter().find(|g| g.conn == conn) else {
                 continue;
             };
-            let eye = [g.position[0], g.position[1] + g.eye_height(), g.position[2]];
-            let valid = self.mobs.iter().find(|m| m.id == mob).is_some_and(|m| {
-                let (w, h) = (f64::from(m.width()) / 2.0, f64::from(m.height()));
-                let p = [m.position.x, m.position.y, m.position.z];
-                let lo = [p[0] - w, p[1], p[2] - w];
-                let hi = [p[0] + w, p[1] + h, p[2] + w];
-                let d: f64 = (0..3)
-                    .map(|k| (eye[k] - eye[k].clamp(lo[k], hi[k])).powi(2))
-                    .sum();
-                // Player.ENTITY_INTERACTION_RANGE 3, plus 4.
-                m.alive() && d < 7.0 * 7.0
-            });
-            if valid {
+            if !host.hub.here(g) {
+                continue;
+            }
+            if self.lan_mount_valid(g, mob) {
                 self.lan_send_mount(host, conn);
             } else {
                 self.lan_mount_closed(host, conn, Some(window));

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

@@ -16,12 +16,16 @@ use horizon_client::{
 use horizon_core::geometry::{Aabb, Vec3};
 
 /// The player projectiles that meet other players: arrows (their hurt), and
-/// snowballs and eggs, which break on them (`Player.hurtServer` takes no 0
-/// damage). Pearls, potions and wind charges fly past players as before.
+/// snowballs, eggs and mods' thrown types, which break on them
+/// (`Player.hurtServer` takes no 0 damage). Pearls, potions and wind charges
+/// fly past players as before.
 pub(super) fn meets_players(kind: &ProjectileKind) -> bool {
     matches!(
         kind,
-        ProjectileKind::Arrow { .. } | ProjectileKind::Snowball | ProjectileKind::Egg
+        ProjectileKind::Arrow { .. }
+            | ProjectileKind::Snowball
+            | ProjectileKind::Egg
+            | ProjectileKind::Thrown(_)
     )
 }
 

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

@@ -20,7 +20,7 @@ use horizon_protocol::packets::play::{self, Clientbound as C};
 
 /// A guest's open workstation menu.
 pub(super) struct GuestStation {
-    window: i32,
+    pub(super) window: i32,
     state: i32,
     kind: StationKind,
     pos: [i32; 3],
@@ -34,9 +34,9 @@ pub(super) struct GuestStation {
 /// A guest's open lectern: `LecternMenu` over the block entity, made on the
 /// menu engine for each click (`Game::lectern_menu`).
 pub(super) struct GuestLectern {
-    window: i32,
+    pub(super) window: i32,
     state: i32,
-    key: (i32, i32, i32),
+    pub(super) key: (i32, i32, i32),
     /// The book and page the client was last sent (`broadcastChanges`).
     sent: Option<(Option<ItemStack>, i32)>,
 }
@@ -69,10 +69,8 @@ impl Game<'_> {
         let Some((menu_type, kind, _)) = menu_of(station.kind) else {
             return false;
         };
-        self.lan_station_closed(host, conn, None);
-        self.lan_crafting_closed(host, conn, None);
-        // The container it replaces loses its opener.
-        self.guest_container_closed(host, conn);
+        // ServerPlayer.openMenu closes the menu that was open.
+        self.guest_close_all(host, conn);
         let title = horizon_protocol::text::translatable(station.kind.title_key(), &[]);
         let Some(window) = host.hub.open_window(conn, menu_type, title) else {
             return true;
@@ -151,9 +149,8 @@ impl Game<'_> {
     /// `LecternBlock.openScreen` for a guest: `minecraft:lectern` over the
     /// block entity, with its book and page.
     pub(super) fn lan_open_lectern(&mut self, host: &mut LanHost, conn: u32, key: (i32, i32, i32)) {
-        self.lan_station_closed(host, conn, None);
-        self.lan_crafting_closed(host, conn, None);
-        self.guest_container_closed(host, conn);
+        // ServerPlayer.openMenu closes the menu that was open.
+        self.guest_close_all(host, conn);
         let title = horizon_protocol::text::translatable("container.lectern", &[]);
         let Some(window) = host.hub.open_window(conn, "minecraft:lectern", title) else {
             return;
@@ -644,10 +641,7 @@ impl Game<'_> {
             let Some(gs) = host.play.get(&conn).and_then(|p| p.station.as_ref()) else {
                 continue;
             };
-            let [x, y, z] = gs.pos;
-            let name = &self.res.facts().get(self.world.block(x, y, z)).name;
-            let block = StationKind::from_block(name) == Some(gs.kind);
-            if !(block && g.within_block_range(gs.pos, 4.0)) {
+            if !self.lan_station_valid(g, gs) {
                 let window = gs.window;
                 self.lan_station_closed(host, conn, Some(window));
                 host.hub.send_to(
@@ -669,6 +663,32 @@ impl Game<'_> {
 }
 
 impl Game<'_> {
+    /// A station menu's `stillValid`: its block is still that station and the
+    /// guest is within `isWithinBlockInteractionRange(pos, 4)`.
+    pub(super) fn lan_station_valid(
+        &self,
+        g: &horizon_client::lan::guest::Guest,
+        gs: &GuestStation,
+    ) -> bool {
+        let [x, y, z] = gs.pos;
+        let name = &self.res.facts().get(self.world.block(x, y, z)).name;
+        StationKind::from_block(name) == Some(gs.kind) && g.within_block_range(gs.pos, 4.0)
+    }
+
+    /// `LecternMenu.stillValid` (`Container.stillValidBlockEntity`): the block
+    /// entity still holds a book and the guest is within the interaction
+    /// range and its buffer.
+    pub(super) fn lan_lectern_valid(
+        &self,
+        g: &horizon_client::lan::guest::Guest,
+        key: (i32, i32, i32),
+    ) -> bool {
+        matches!(
+            self.world.block_entities.get(&key),
+            Some(BlockEntity::Lectern(l)) if l.book.is_some()
+        ) && g.within_block_range([key.0, key.1, key.2], 4.0)
+    }
+
     /// The guests' lecterns each tick: `stillValid` (the block entity, its
     /// book, the reach) closes them, and `broadcastChanges` sends a book or
     /// page another player changed.
@@ -685,13 +705,7 @@ impl Game<'_> {
             if !host.hub.here(g) {
                 continue;
             }
-            let has_book = matches!(
-                self.world.block_entities.get(&key),
-                Some(BlockEntity::Lectern(l)) if l.book.is_some()
-            );
-            // Container.stillValidBlockEntity: the interaction range and its buffer.
-            let near = g.within_block_range([key.0, key.1, key.2], 4.0);
-            if has_book && near {
+            if self.lan_lectern_valid(g, key) {
                 self.lan_send_lectern(host, conn, false);
             } else {
                 self.lan_station_closed(host, conn, Some(window));

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

@@ -57,9 +57,8 @@ impl Game<'_> {
             state.session.update_special_prices();
         }
         let title = self.merchant_display_name(&state);
-        // The container or workstation the trading screen replaces is closed.
-        self.guest_container_closed(host, conn);
-        self.lan_station_closed(host, conn, None);
+        // ServerPlayer.openMenu closes the menu that was open.
+        self.guest_close_all(host, conn);
         let Some(window) = host.hub.open_merchant_window(conn, title) else {
             self.merchant_closed(&mut state);
             return;
@@ -350,28 +349,37 @@ impl Game<'_> {
         self.merchant_closed(&mut gm.merchant);
         true
     }
+    /// `Merchant.stillValid` for a trader: it is alive and the guest is within
+    /// the entity interaction range plus 4 of its box.
+    pub(super) fn lan_merchant_valid(
+        &self,
+        g: &horizon_client::lan::guest::Guest,
+        id: u32,
+    ) -> bool {
+        self.mobs
+            .iter()
+            .find(|m| m.id == id)
+            .is_some_and(|m| m.alive() && guest_within_entity_range(g, &m.bounds(), 4.0))
+    }
     /// `Villager.customServerAiStep` for the guests' trading villagers: the
     /// TRADE reputation event, then the prices follow.
     pub(super) fn lan_merchant_tick(&mut self, host: &mut LanHost) {
         // `AbstractVillager.stillValid`: the trade screen closes once the trader
         // is gone or dead, or the guest is more than 4 blocks past its reach.
-        let far: Vec<(u32, i32)> =
-            host.play
-                .iter()
-                .filter_map(|(conn, p)| {
-                    let gm = p.merchant.as_ref()?;
-                    let id = gm.merchant.mob?;
-                    let g = host
-                        .hub
-                        .guests
-                        .iter()
-                        .find(|g| g.conn == *conn && host.hub.here(g))?;
-                    let valid = self.mobs.iter().find(|m| m.id == id).is_some_and(|m| {
-                        m.alive() && guest_within_entity_range(g, &m.bounds(), 4.0)
-                    });
-                    (!valid).then_some((*conn, gm.window))
-                })
-                .collect();
+        let far: Vec<(u32, i32)> = host
+            .play
+            .iter()
+            .filter_map(|(conn, p)| {
+                let gm = p.merchant.as_ref()?;
+                let id = gm.merchant.mob?;
+                let g = host
+                    .hub
+                    .guests
+                    .iter()
+                    .find(|g| g.conn == *conn && host.hub.here(g))?;
+                (!self.lan_merchant_valid(g, id)).then_some((*conn, gm.window))
+            })
+            .collect();
         for (conn, window) in far {
             if self.lan_merchant_closed(host, conn, Some(window)) {
                 host.hub.send_to(

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

@@ -126,12 +126,15 @@ impl Game<'_> {
             (g.vehicle, g.vehicle_good) = (None, None);
             return;
         }
+        let mut ejected = false;
         if let Some(i) = boat {
             // AbstractBoat.tick on the server for a boat its rider drives:
             // only the hurt animation and the damage wear off here.
             let b = &mut self.boats[i];
             b.hurt_time = (b.hurt_time - 1).max(0);
             b.damage = (b.damage - 1.0).max(0.0);
+            // AbstractBoat.tickBubbleColumn: a down column ejects the rider.
+            ejected = std::mem::take(&mut b.eject_riders);
         }
         // ServerGamePacketListenerImpl.tick: the vehicle's last good position
         // is where it is now, so a move the server made (a piston, a push)
@@ -161,7 +164,7 @@ impl Game<'_> {
                 return Some([p.x, p.y, p.z]);
             }
             if let Some(i) = game.boats.iter().position(|b| Some(b.id) == game.riding) {
-                if keys.shift {
+                if keys.shift || ejected {
                     game.dismount(i);
                     return None;
                 }

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

@@ -246,7 +246,14 @@ impl Game<'_> {
                 return true;
             }
         }
-        if self.mobs[index].extra.leash == Some(Holder::Player) {
+        // Mob.checkAndHandleImportantInteractions: only the player the lead
+        // is tied to unties it (`getLeashHolder() == player`).
+        if self.mobs[index].extra.leash == Some(Holder::Player)
+            && self.mobs[index]
+                .extra
+                .leash_player
+                .is_none_or(|p| p == self.acting_player_uuid())
+        {
             let creative = self.creative;
             self.break_leash(id, !creative, false);
             self.lead_game_event("minecraft:entity_interact", at);
@@ -301,12 +308,31 @@ impl Game<'_> {
             .filter(|&i| self.mobs[i].extra.leash == Some(Holder::Knot(knot_pos)))
             .collect();
         let existing_boats = self.boats_on(Holder::Knot(knot_pos));
+        // `LeashFenceKnotEntity.interact` runs only when the ray meets the knot
+        // before the post: the knot's box (`recalculateBoundingBox`, 0.375 wide,
+        // y + 0.375 to y + 0.875) is wider than the post, so a hit point on the
+        // post inside that box went through the knot first. Any other click on
+        // the fence is `FenceBlock.useWithoutItem` / `LeadItem.useOn`, which only
+        // ties the player's own mobs (`LeadItem.bindPlayerMobs`).
+        let knot_hit = !(existing.is_empty() && existing_boats.is_empty()) && {
+            let box_ = leash::knot_state(knot_pos);
+            let half = box_.width / 2.0 + 1.0e-6;
+            (hit.point[0] - box_.position.x).abs() <= half
+                && (hit.point[2] - box_.position.z).abs() <= half
+                && hit.point[1] >= box_.position.y - 1.0e-6
+                && hit.point[1] <= box_.position.y + box_.height + 1.0e-6
+                // The knot is an entity: a hit on it counts only within the
+                // entity interaction range (`filterHitResult`), shorter than
+                // the block range the fence was hit at.
+                && self.eye_position().is_some_and(|eye| {
+                    let d = [0, 1, 2].map(|i| hit.point[i] - eye[i]);
+                    d[0] * d[0] + d[1] * d[1] + d[2] * d[2] <= self.entity_reach * self.entity_reach
+                })
+        };
         let held_item = self.held().map(|s| s.item.to_string());
         let sneaking = self.keys.contains(&winit::keyboard::KeyCode::ShiftLeft);
         // Shears snip every lead on the knot.
-        if held_item.as_deref() == Some("minecraft:shears")
-            && !(existing.is_empty() && existing_boats.is_empty())
-        {
+        if knot_hit && held_item.as_deref() == Some("minecraft:shears") {
             for i in existing {
                 let id = self.mobs[i].id;
                 self.break_leash(id, true, false);
@@ -335,7 +361,7 @@ impl Game<'_> {
                 attached = true;
             }
         }
-        if !attached && !sneaking {
+        if !attached && !sneaking && knot_hit {
             let player = self.player_center();
             let holder = self.acting_player_uuid();
             for i in existing {

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

@@ -82,6 +82,13 @@ impl Game<'_> {
                 }
             }
             None if &*facts.get(state).name == "minecraft:water" => (p, count * 3, 3.0, 1.0, false),
+            // A mod block the level answered bone meal for: the port knows no
+            // `BonemealableBlock.Type` for it, and vanilla's `GROWER` is the
+            // one a block growing itself has, so the sparks stay inside it
+            // rather than spreading over its neighbours.
+            None if !facts.get(state).name.starts_with("minecraft:") => {
+                (p, count, 0.5, self.block_shape_top(p), true)
+            }
             None => return,
         };
         self.spawn_particles(at, count, xz, height, floating, ParticleType::HappyVillager);

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

@@ -411,18 +411,23 @@ impl Game<'_> {
             }
             self.update_dedicated_streaming();
             self.update_world();
-            result = if paused {
-                self.tick_lan(true);
-                Ok(())
-            } else if k == 0 {
-                self.tick()
-            } else {
-                let running = running.unwrap_or_else(|| self.clock.world_runs());
-                if running {
-                    self.tick_weather_effects();
-                }
-                self.tick_world(running)
-            };
+            result = horizon_client::block_contact::in_level(
+                (self.serving.is_some() || self.options.dedicated.is_some()).then_some(dim.id()),
+                || {
+                    if paused {
+                        self.tick_lan(true);
+                        Ok(())
+                    } else if k == 0 {
+                        self.tick()
+                    } else {
+                        let running = running.unwrap_or_else(|| self.clock.world_runs());
+                        if running {
+                            self.tick_weather_effects();
+                        }
+                        self.tick_world(running)
+                    }
+                },
+            );
             if result.is_err() {
                 break;
             }

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

@@ -46,6 +46,8 @@ enum Kind {
     Brewing,
     /// `ChiseledBookShelfBlockEntity`: books only, one to a slot.
     Bookshelf,
+    /// `JukeboxBlockEntity`'s single slot: a playable disc only.
+    Jukebox,
     /// A mod block's block entity (`ModContainer`).
     Mod,
     /// `ShulkerBoxBlockEntity`: a shulker box doesn't go through a face into one.
@@ -209,6 +211,7 @@ impl Containers<'_> {
             (BlockEntity::Crafter(_), _) => Kind::Crafter,
             (BlockEntity::Brewing(_), _) => Kind::Brewing,
             (BlockEntity::ChiseledBookshelf(_), _) => Kind::Bookshelf,
+            (BlockEntity::Jukebox(_), _) => Kind::Jukebox,
             (_, "minecraft:hopper") => Kind::Hopper,
             (_, n) if is_shulker_box(n) => Kind::Shulker,
             _ => Kind::Generic,
@@ -302,6 +305,15 @@ impl Containers<'_> {
                 _ => false,
             };
         }
+        if view.kind == Kind::Jukebox {
+            // JukeboxBlockEntity.canPlaceItem: a playable disc, into the one
+            // slot, which has to be empty first (its maximum stack is 1).
+            return self
+                .items
+                .get(&stack.item)
+                .is_some_and(|i| i.jukebox_song.is_some())
+                && self.get(view, slot).is_none();
+        }
         if view.kind == Kind::Bookshelf {
             // ListBackedContainer.canPlaceItem: `acceptsItemType` (the books)
             // and a free slot, as `getMaxStackSize` is 1.
@@ -572,6 +584,12 @@ impl Game<'_> {
         let (rest, moved) = self.move_in_item(from_hopper, view, stack, slot);
         if moved {
             self.view_changed(view);
+            // JukeboxBlockEntity.setTheItem through a hopper's or a dropper's
+            // transfer: the disc it lands on starts playing.
+            if view.kind == Kind::Jukebox {
+                let (x, y, z) = view.parts[0].0;
+                self.jukebox_inserted([x, y, z]);
+            }
         }
         rest
     }
@@ -868,6 +886,12 @@ impl Game<'_> {
             match self.add_item(source_hopper, hopper, one, None) {
                 None => {
                     self.view_changed(source);
+                    // JukeboxBlockEntity.removeItem -> setTheItem(EMPTY): a
+                    // disc a hopper takes out stops the song.
+                    if source.kind == Kind::Jukebox {
+                        let (x, y, z) = source.parts[0].0;
+                        self.jukebox_taken([x, y, z]);
+                    }
                     return true;
                 }
                 Some(rest) => self.put_back(source, slot, rest),

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

@@ -56,7 +56,7 @@ impl CartKind {
             Self::CommandBlock => "minecraft:command_block_minecart",
         }
     }
-    fn slots(self) -> usize {
+    pub(super) fn slots(self) -> usize {
         match self {
             Self::Chest => 27,
             Self::Hopper => 5,
@@ -963,6 +963,7 @@ impl Game<'_> {
         if let Some(i) = self.carts.iter().position(|x| x.id == c.id) {
             self.eject_cart_mobs(i);
         }
+        self.release_vehicle_container(c.id);
         self.carts.retain(|x| x.id != c.id);
         // ExplosionInteraction.TNT: the tnt_explosion_drop_decay rule.
         let interaction = self.destroy_type("tnt_explosion_drop_decay");
@@ -1226,6 +1227,7 @@ impl Game<'_> {
                 }
             } else {
                 self.eject_cart_mobs(i);
+                self.release_vehicle_container(id);
                 self.carts.remove(i);
             }
         }
@@ -1331,6 +1333,7 @@ impl Game<'_> {
             self.push_from_cart(i);
         } else {
             self.eject_cart_mobs(i);
+            self.release_vehicle_container(c.id);
             self.carts.remove(i);
             self.riding = None;
         }
@@ -1453,6 +1456,22 @@ impl Game<'_> {
         }
         best
     }
+    /// The slots of the cart `id`, for a command: `getChestVehicleItem` and
+    /// `setChestVehicleItem` first unpack its loot table with no player, so
+    /// no `player_generates_container_loot` fires later. While its menu is
+    /// open the live slots are the placeholder copy (`open_cart_container`).
+    pub(super) fn cart_slots(&mut self, id: u32) -> Option<&mut Vec<Option<ItemStack>>> {
+        let c = self.carts.iter_mut().find(|c| c.id == id)?;
+        c.loot = None;
+        match self
+            .world
+            .block_entities
+            .get_mut(&(i32::MAX - 15, CART_KEY_Y, id as i32))
+        {
+            Some(BlockEntity::Chest(open)) => Some(open),
+            _ => Some(&mut c.items),
+        }
+    }
     /// `ContainerEntity.unpackChestVehicleLootTable` for a player who opens a
     /// chest minecart: a roll it still holds fires `player_generates_container_loot`
     /// for its table, and the cart keeps its items from then on.
@@ -1561,6 +1580,19 @@ impl Game<'_> {
         self.store_cart_items(key);
         self.world.block_entities.remove(&key);
     }
+    /// A chest or hopper minecart or a chest boat is about to be removed
+    /// (`Containers.dropContents` / `AbstractChestBoat.remove`): what an open
+    /// menu edited goes back to the vehicle, so it is what drops or travels
+    /// with it, and the menu's stand-in leaves the level. A menu that is
+    /// still open over it then has nothing left to take.
+    pub(super) fn release_vehicle_container(&mut self, id: u32) {
+        let key = (i32::MAX - 15, CART_KEY_Y, id as i32);
+        self.store_cart_items(key);
+        self.world.block_entities.remove(&key);
+        if self.container == Some(key) {
+            self.container = None;
+        }
+    }
     /// The menu of a chest or hopper minecart or a chest boat works on the
     /// vehicle's own items (`ContainerEntity`): the placeholder under `key`
     /// that the menu edits is copied back to the vehicle.
@@ -1628,6 +1660,8 @@ impl Game<'_> {
         }
         if burning && self.carts[i].kind == CartKind::Tnt {
             self.eject_cart_mobs(i);
+            let id = self.carts[i].id;
+            self.release_vehicle_container(id);
             let c = self.carts.remove(i);
             self.explode_cart(&c, arrow_velocity.length_squared());
             return;
@@ -1653,6 +1687,10 @@ impl Game<'_> {
             if !tnt_prime {
                 self.eject_cart_mobs(i);
             }
+            let id = self.carts[i].id;
+            if !tnt_prime {
+                self.release_vehicle_container(id);
+            }
             let mut c = self.carts.remove(i);
             if c.kind == CartKind::Tnt && (fire || speed >= f64::from(0.01f32)) {
                 // MinecartTNT.destroy: prime instead of breaking.

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

@@ -18,6 +18,28 @@ fn carried_block_matrix(base: glam::Mat4) -> glam::Mat4 {
         * glam::Mat4::from_rotation_y(90.0f32.to_radians())
 }
 
+/// Drops the quads of `out[first..]` whose face normal points away from the eye, which
+/// is the origin of camera-relative vertices. Each quad is four vertices carrying its
+/// face normal in `Vertex::normal`, as `block_model_vertices` writes for diffuse faces.
+fn cull_back_quads(out: &mut Vec<Vertex>, first: usize) {
+    let mut kept = first;
+    for quad in (first..out.len()).step_by(4) {
+        let vertices = &out[quad..quad + 4];
+        let n = vertices[0].normal;
+        let normal = glam::Vec3::new(f32::from(n[0]), f32::from(n[1]), f32::from(n[2]));
+        let centre = vertices.iter().fold(glam::Vec3::ZERO, |sum, v| {
+            sum + glam::Vec3::from_array(v.pos)
+        }) * 0.25;
+        // The eye is at the origin: the face is seen from its front when the eye is on the
+        // side its normal points to, that is when `normal . (eye - centre) > 0`.
+        if normal.dot(centre) < 0.0 {
+            out.copy_within(quad..quad + 4, kept);
+            kept += 4;
+        }
+    }
+    out.truncate(kept);
+}
+
 /// `CustomHeadLayer.translateToHead` and the banner's `head` display.
 fn banner_matrix(head: glam::Mat4) -> glam::Mat4 {
     head * glam::Mat4::from_translation(glam::Vec3::new(0.0, -0.25, 0.0))
@@ -30,6 +52,24 @@ fn banner_matrix(head: glam::Mat4) -> glam::Mat4 {
         * glam::Mat4::from_scale(glam::Vec3::new(2.0 / 3.0, -2.0 / 3.0, -2.0 / 3.0))
 }
 
+/// `BlockDecorationLayer.submit` and `CopperGolemModel.applyBlockOnAntennaTransform`, then the
+/// block model's own display transformation, which `BlockModelRenderState.submitModel` post-multiplies.
+fn antenna_block_matrix(head: glam::Mat4, flowerbed_shift: bool) -> glam::Mat4 {
+    // UNIT_CUBE_BOTTOM_CENTER_TO_ANTENNA_CENTER: translation(-0.5, 0, -0.5)
+    // then rotateAround(Z 180, 0.5, 0.5, 0.5), which JOML post-multiplies.
+    let unit = glam::Mat4::from_translation(glam::Vec3::new(-0.5, 0.0, -0.5))
+        * glam::Mat4::from_translation(glam::Vec3::splat(0.5))
+        * glam::Mat4::from_rotation_z(180.0f32.to_radians())
+        * glam::Mat4::from_translation(glam::Vec3::splat(-0.5));
+    let t = head * glam::Mat4::from_translation(glam::Vec3::new(0.0, -1.75, 0.0)) * unit;
+    if flowerbed_shift {
+        // `BuiltInBlockModels.createFlowerBedModel`'s Transformation(0.25, 0, 0.25).
+        t * glam::Mat4::from_translation(glam::Vec3::new(0.25, 0.0, 0.25))
+    } else {
+        t
+    }
+}
+
 /// `ElderGuardianParticle.lifetime`.
 pub(super) const APPARITION_TICKS: i32 = 30;
 
@@ -206,7 +246,13 @@ impl Game<'_> {
             let base = render::base_transform(mob, alpha as f32, camera);
             let t = carried_block_matrix(base);
             // Preserve cross models (flowers, fungi) and state properties (facing).
+            let first = out.len();
             self.block_model_vertices(state, 42, t, light, true, out);
+            // The carried block uses the item cutout render type, which culls back faces
+            // (RenderPipelines.ITEM_CUTOUT). Without that, both coplanar sides of a cross
+            // model are drawn and flicker. CULL_BACK would drop them too, but it turns off
+            // the normal lighting this model needs.
+            cull_back_quads(out, first);
         }
     }
     /// `BlockDecorationLayer.submit`: the block item in a copper golem's
@@ -222,7 +268,6 @@ impl Game<'_> {
         light: u32,
         out: &mut Vec<Vertex>,
     ) {
-        use glam::{Mat4, Vec3};
         if mob.species() != Species::CopperGolem || horizon_client::mobs::trader::is_invisible(mob)
         {
             return;
@@ -260,13 +305,12 @@ impl Game<'_> {
         else {
             return;
         };
-        // UNIT_CUBE_BOTTOM_CENTER_TO_ANTENNA_CENTER: translation(-0.5, 0, -0.5)
-        // then rotateAround(Z 180, 0.5, 0.5, 0.5), which JOML post-multiplies.
-        let unit = Mat4::from_translation(Vec3::new(-0.5, 0.0, -0.5))
-            * Mat4::from_translation(Vec3::splat(0.5))
-            * Mat4::from_rotation_z(180.0f32.to_radians())
-            * Mat4::from_translation(Vec3::splat(-0.5));
-        let t = head * Mat4::from_translation(Vec3::new(0.0, -1.75, 0.0)) * unit;
+        // Only wildflowers and pink petals carry the flowerbed display shift.
+        let flowerbeds = matches!(
+            &*stack.item,
+            "minecraft:wildflowers" | "minecraft:pink_petals"
+        );
+        let t = antenna_block_matrix(head, flowerbeds);
         self.block_model_vertices(state, 42, t, light, true, out);
     }
     /// `IronGolemFlowerLayer`: the poppy in the right arm while the golem
@@ -658,12 +702,13 @@ mod tests {
             (Vec3::ONE, Vec3::new(-0.3535534, 0.3938461, -0.85688126)),
             (Vec3::splat(0.5), Vec3::new(0.0, 0.6287693, -0.77137625)),
         ];
-        for base in [
+        let bases = [
             Mat4::IDENTITY,
             Mat4::from_translation(Vec3::new(3.0, 2.0, -7.0))
                 * Mat4::from_rotation_y(1.2)
                 * Mat4::from_scale(Vec3::new(-1.0, -1.0, 1.0)),
-        ] {
+        ];
+        for base in bases {
             let block = carried_block_matrix(base);
             for (point, expected) in samples {
                 let actual = block.transform_point3(point);
@@ -674,5 +719,32 @@ mod tests {
                 );
             }
         }
+        // `antenna_block_matrix` with an identity head, from the 26.3 expressions:
+        // `UNIT_CUBE_BOTTOM_CENTER_TO_ANTENNA_CENTER` (`translate(-0.5, 0, -0.5)`
+        // then `rotateAround(Z 180, 0.5, 0.5, 0.5)`) sends (x, y, z) to
+        // (0.5 - x, 1 - y, z - 0.5), the antenna drops it 1.75, and
+        // `createFlowerBedModel`'s quarter block lands on (-0.25, 0, 0.25) because
+        // the Z-180 turn flips it.
+        let antenna = [
+            (Vec3::ZERO, Vec3::new(0.5, -0.75, -0.5)),
+            (Vec3::X, Vec3::new(-0.5, -0.75, -0.5)),
+            (Vec3::Y, Vec3::new(0.5, -1.75, -0.5)),
+            (Vec3::Z, Vec3::new(0.5, -0.75, 0.5)),
+            (Vec3::ONE, Vec3::new(-0.5, -1.75, 0.5)),
+            (Vec3::splat(0.5), Vec3::new(0.0, -1.25, 0.0)),
+        ];
+        for (shifted, shift) in [(false, Vec3::ZERO), (true, Vec3::new(-0.25, 0.0, 0.25))] {
+            for base in bases {
+                let m = antenna_block_matrix(base, shifted);
+                for (point, expected) in antenna {
+                    let actual = m.transform_point3(point);
+                    let expected = base.transform_point3(expected + shift);
+                    assert!(
+                        actual.abs_diff_eq(expected, 1e-6),
+                        "{actual:?} != {expected:?}"
+                    );
+                }
+            }
+        }
     }
 }

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

@@ -14,10 +14,7 @@ use horizon_client::{
     mobs::{
         Mob, Species,
         equip::{self, Facts, ItemTags, Slot},
-        finalize::{
-            self, set_drop_chance, set_item, set_slot_enchantments, slot_enchantments,
-            stored_drop_chance,
-        },
+        finalize::{self, set_drop_chance, set_item_stack, stored_drop_chance},
     },
 };
 use horizon_core::{geometry::Vec3, random::RandomSource};
@@ -92,27 +89,29 @@ impl Game<'_> {
         if !replace {
             return None;
         }
-        // shortcut: a mob's equipment is one item per slot here, so a hand
-        // takes one item of a stack where vanilla takes the whole stack;
-        // upgrade with a per-slot count in `Extra`.
-        let taken = 1;
+        // `EquipmentSlot.limit`: an armour slot takes one item, a hand the
+        // whole stack.
+        let taken = if slot.is_armor() {
+            1
+        } else {
+            stack.count.max(1)
+        };
         let m = &mut self.mobs[index];
-        let old = finalize::item(m, slot.index());
+        let old = finalize::item_stack(m, slot.index());
         let chance = stored_drop_chance(m, slot.index());
-        let old_enchantments = slot_enchantments(m, slot.index());
         // `DropChances.byEquipment` against the roll the equip makes.
         let drop_old = old.is_some() && (m.random.next_float() - 0.1).max(0.0) < chance;
-        set_item(m, slot.index(), item);
-        // The stack's enchantments come with it: a Sharpness V sword stays sharp.
-        set_slot_enchantments(m, slot.index(), stack.enchantments().to_vec());
+        // The whole stack comes with it: its enchantments (a Sharpness V sword
+        // stays sharp), damage, name and components.
+        let mut equipped = stack.clone();
+        equipped.count = taken;
+        set_item_stack(m, slot.index(), equipped);
         // `setItemSlotAndDropWhenKilled`, then `persistenceRequired`.
         set_drop_chance(m, slot.index(), 2.0);
         m.persistent = true;
         let at = [m.position.x, m.position.y, m.position.z];
         if drop_old && let Some(old) = old {
-            let mut dropped = ItemStack::new(&old, 1);
-            dropped.set_crafting_enchantments(old_enchantments);
-            self.spawn_item(dropped, at, super::dispenser::new_item_motion(), 10);
+            self.spawn_item(old, at, super::dispenser::new_item_motion(), 10);
         }
         Some(taken)
     }
@@ -120,9 +119,10 @@ impl Game<'_> {
     /// `Mob.canReplaceCurrentItem` for what `m` wears or holds in `slot`.
     fn can_replace(&self, index: usize, stack: &ItemStack, slot: Slot) -> bool {
         let m = &self.mobs[index];
-        let Some(current) = finalize::item(m, slot.index()) else {
+        let Some(worn_stack) = finalize::item_stack(m, slot.index()) else {
             return true;
         };
+        let current = worn_stack.item.clone();
         let species = m.species();
         // `Drowned.canReplaceCurrentItem` never parts with a nautilus shell.
         if species == Species::Drowned && &*current == "minecraft:nautilus_shell" {
@@ -140,21 +140,15 @@ impl Game<'_> {
             // Binding's, the only enchantment that carries one.
             prevents_armor_change: stack.enchantment_level("minecraft:binding_curse") > 0,
         };
-        let worn_enchantments = slot_enchantments(m, slot.index());
         let (armor, toughness, attack) = self.attributes(m, &current, slot);
-        // shortcut: what a mob already wears keeps no damage value or name here
-        // (`Extra` records neither), so a worn piece always compares as fresh;
-        // upgrade with a stack per equipment slot.
         let worn = Facts {
             armor,
             armor_toughness: toughness,
             attack_damage: attack,
-            enchantments: worn_enchantments.len(),
-            damage: 0,
-            custom_name: false,
-            prevents_armor_change: worn_enchantments
-                .iter()
-                .any(|(id, level)| &**id == "minecraft:binding_curse" && *level > 0),
+            enchantments: worn_stack.enchantments().len(),
+            damage: worn_stack.damage as i32,
+            custom_name: worn_stack.custom_name().is_some(),
+            prevents_armor_change: worn_stack.enchantment_level("minecraft:binding_curse") > 0,
         };
         let preferred = equip::preferred_weapon_tag(species).map(|tag| {
             (

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

@@ -16,6 +16,27 @@ pub(super) struct ModsState {
     stopped: Vec<String>,
 }
 
+/// Freeze native component IDs before reading content or opening a connection.
+/// With no mod registering any, nothing is installed, which every reader
+/// treats as no custom components, and `registries.json` isn't read.
+pub(super) fn register_components(root: &std::path::Path) -> horizon_client::Result<()> {
+    let mut names = Vec::new();
+    Game::native_component_types(&mut names);
+    if names.is_empty() {
+        return Ok(());
+    }
+    let path =
+        horizon_protocol::registry::Builtin::find(root).ok_or("registries.json not found")?;
+    let builtin = horizon_protocol::registry::Builtin::load(&path)?;
+    let types = builtin
+        .get("minecraft:data_component_type")
+        .ok_or("missing data component registry")?;
+    let first = i32::try_from(types.names.len())?;
+    horizon_protocol::item::custom::install(first, names)
+        .map_err(|error| format!("invalid native component registration: {error}"))?;
+    Ok(())
+}
+
 /// `root` with the content mods that are on layered over it
 /// (docs/modpacks.md): their blocks, items, data and assets. Read once at
 /// start, before the resources load; a mod whose content is refused is left
@@ -31,6 +52,7 @@ pub(super) fn content_root(
     let mut paths = horizon_mods::find(&here.join(mod_list::DIR));
     paths.retain(|p| !dev.contains(p));
     paths.extend(dev.iter().cloned());
+    let mut known = None;
     let mut mods: Vec<ContentMod> = Vec::new();
     for path in &paths {
         let Ok(package) = Package::read(path) else {
@@ -44,23 +66,30 @@ pub(super) fn content_root(
         {
             continue;
         }
-        let content = Content::read(path, m).and_then(|content| {
-            // The first of two mods owning one namespace stays on.
-            let own = (m.id.as_str(), content.namespaces.as_slice());
-            match mods
-                .iter()
-                .find_map(|c| horizon_mods::content::clash((&c.id, &c.content.namespaces), own))
-            {
-                Some(e) => Err(e),
-                None => Ok(content),
+        let content = match Content::read(path, m) {
+            Ok(content) => content,
+            Err(e) => {
+                log::warn!("Horizon: mod {} content not loaded: {e}", m.id);
+                continue;
             }
-        });
-        match content {
-            Ok(content) => mods.push(ContentMod {
-                id: m.id.clone(),
-                content,
-            }),
-            Err(e) => log::warn!("Horizon: mod {} content not loaded: {e}", m.id),
+        };
+        let known = match &mut known {
+            Some(types) => types,
+            None => match mod_content::known_components(root) {
+                Ok(types) => known.insert(types),
+                Err(e) => {
+                    log::warn!("Horizon: content mods not loaded: {e}");
+                    register_mob_effects(&[]);
+                    return root.to_owned();
+                }
+            },
+        };
+        let candidate = ContentMod {
+            id: m.id.clone(),
+            content,
+        };
+        if let Err(e) = mod_content::accept_mod(&mut mods, candidate, known) {
+            log::warn!("Horizon: mod {} content not loaded: {e}", m.id);
         }
     }
     match mod_content::resource_root(root, &mods, &here.join(".horizon-cache")) {
@@ -73,11 +102,13 @@ pub(super) fn content_root(
                 );
             }
             register_mob_effects(&mods);
+            register_entity_types(&mods);
             out
         }
         Err(e) => {
             log::warn!("Horizon: content mods not loaded: {e}");
             register_mob_effects(&[]);
+            register_entity_types(&[]);
             root.to_owned()
         }
     }
@@ -110,6 +141,26 @@ fn register_mob_effects(mods: &[horizon_client::mod_content::ContentMod]) {
     }
 }
 
+/// the mods' thrown entity types, as their mob effects: set once, from the
+/// startup root.
+fn register_entity_types(mods: &[horizon_client::mod_content::ContentMod]) {
+    use horizon_client::projectiles;
+    let types = horizon_client::mod_content::entity_types(mods);
+    let set = projectiles::register_thrown_types(
+        types
+            .iter()
+            .map(|t| (t.id.clone(), t.item.clone(), t.damage)),
+    );
+    if !set
+        && projectiles::thrown_types()
+            .iter()
+            .map(|t| t.id)
+            .ne(types.iter().map(|t| t.id.as_str()))
+    {
+        log::warn!("Horizon: the mods' entity types changed; restart the game to use them");
+    }
+}
+
 /// What the launcher writes beside a game it built with native mods: their ids under `mods`.
 const BUILD_INFO: &str = "native-mods.json";
 

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

@@ -319,6 +319,16 @@ impl Game<'_> {
         v.extend((0..open.columns * 3).map(|i| CHEST + i));
         Some(v)
     }
+    /// How many slots `mount_slots` lists, counted without building it
+    /// (`Game::slot_count` asks every frame).
+    pub(super) fn mount_slot_count(&self) -> Option<usize> {
+        let open = self
+            .mount_menu
+            .open
+            .as_ref()
+            .filter(|_| self.mount_active())?;
+        Some(36 + usize::from(open.show_saddle) + usize::from(open.show_armor) + open.columns * 3)
+    }
     pub(super) fn mount_slot_position(&self, i: usize) -> Option<(f32, f32)> {
         let open = self
             .mount_menu

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

@@ -17,6 +17,15 @@ use horizon_core::{
     random::RandomSource,
 };
 
+fn steering_item(species: Species, main: Option<&str>, offhand: Option<&str>) -> bool {
+    let item = match species {
+        Species::Pig => "minecraft:carrot_on_a_stick",
+        Species::Strider => "minecraft:warped_fungus_on_a_stick",
+        _ => return false,
+    };
+    main == Some(item) || offhand == Some(item)
+}
+
 /// `passengerAttachments` minus the player's 0.6 vehicle attachment.
 fn seat(s: Species) -> f64 {
     let attach = match s {
@@ -367,12 +376,11 @@ impl Game<'_> {
         let strafe = f32::from(u8::from(keys.left)) - f32::from(u8::from(keys.right));
         let forward = f32::from(u8::from(keys.forward)) - f32::from(u8::from(keys.backward));
         // LocalPlayer.aiStep: the riding jump charges while space is held.
-        let held = self.held().map(|s| s.item.clone());
-        let steer = match self.mobs[i].species() {
-            Species::Pig => held.as_deref() == Some("minecraft:carrot_on_a_stick"),
-            Species::Strider => held.as_deref() == Some("minecraft:warped_fungus_on_a_stick"),
-            _ => false,
-        };
+        let steer = steering_item(
+            self.mobs[i].species(),
+            self.held().map(|s| s.item.as_ref()),
+            self.offhand.as_ref().map(|s| s.item.as_ref()),
+        );
         let jump = self.charge_mount_jump(i, keys);
         let m = &mut self.mobs[i];
         if jump > 0.0 {
@@ -839,6 +847,17 @@ mod tests {
     use super::*;
     use std::collections::HashMap;
 
+    #[test]
+    fn steering_accepts_the_correct_item_in_either_hand() {
+        let carrot = "minecraft:carrot_on_a_stick";
+        let fungus = "minecraft:warped_fungus_on_a_stick";
+        assert!(steering_item(Species::Pig, Some(carrot), None));
+        assert!(steering_item(Species::Pig, None, Some(carrot)));
+        assert!(steering_item(Species::Strider, None, Some(fungus)));
+        assert!(!steering_item(Species::Pig, Some(fungus), None));
+        assert!(!steering_item(Species::Horse, Some(carrot), Some(fungus)));
+    }
+
     /// A lava sea up to y 30 with full blocks placed in it; air above.
     struct Sea {
         blocks: HashMap<[i32; 3], ()>,

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

@@ -10,6 +10,10 @@ use horizon_client::{
 impl Game<'_> {
     /// `Minecraft.tick` -> `MusicManager.tick`, once per client tick.
     pub(super) fn tick_music(&mut self) {
+        // Splitscreen: one music, P1's.
+        if self.options.split_guest {
+            return;
+        }
         let (music, volume) = self.situational_music();
         // Options.musicFrequency's listener: MusicManager.setMinutesBetweenSongs.
         let frequency = MusicFrequency::parse(&self.settings.file.name("musicFrequency"));

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

@@ -287,13 +287,15 @@ impl Game<'_> {
                 lift = f64::from(9.0f32 * 1.15 * 0.025);
             }
             lines.push((shown, lift));
+            // The tag rides with the body, between last tick's position and this one's.
+            let at = a.render_position(alpha);
             let l = self.world.light(
-                a.position.x.floor() as i32,
-                (a.position.y + height).floor() as i32,
-                a.position.z.floor() as i32,
+                at.x.floor() as i32,
+                (at.y + height).floor() as i32,
+                at.z.floor() as i32,
             );
             tags.push(NameTag {
-                at: glam::DVec3::new(a.position.x, a.position.y + height + 0.5, a.position.z),
+                at: glam::DVec3::new(at.x, at.y + height + 0.5, at.z),
                 lines,
                 light: l,
                 discrete: false,

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

@@ -0,0 +1,391 @@
+//! Mod block entities drawn on the client: `native_block_entity_submit`
+//! (vanilla's `BlockEntityRenderer.submit`) gets a [`BlockEntityDraw`], whose
+//! pose stack (`PoseStack`) places what the helpers here add to the entity
+//! batch, as vanilla's block entity renderers draw.
+
+use super::{Dim, Game};
+use glam::{DVec3, Mat4, Quat, Vec3};
+use horizon_assets::{
+    bake::{bake_flat_face, default_uv},
+    model::{Direction, Material},
+};
+use horizon_client::{
+    block_entity_render::{diffuse, diffuse_lights, vertex_light},
+    containers::BlockEntity,
+    gfx::Cull,
+    hud::Rect,
+    mesher::Vertex,
+};
+use horizon_world::registry::BlockStateId;
+
+/// `BlockEntityRenderer.getViewDistance`'s default, in blocks.
+const VIEW_DISTANCE: f64 = 64.0;
+/// A mod block entity's bounds until its mod says otherwise: the block with
+/// the block of margin Horizon culls vanilla's block entities with.
+const DEFAULT_BOUNDS: [f32; 6] = [-1.0, -1.0, -1.0, 2.0, 2.0, 2.0];
+
+/// Whether `bounds` (min then max, in blocks from `origin`, the block's corner
+/// relative to the camera) meet the frustum; an infinite bound always does
+/// (NeoForge's `INFINITE_EXTENT_AABB`), as does a frame without a frustum.
+fn in_frustum(frustum: Option<&impl Cull>, origin: Vec3, bounds: [f32; 6]) -> bool {
+    if bounds.iter().any(|b| !b.is_finite()) {
+        return true;
+    }
+    let min = origin + Vec3::new(bounds[0], bounds[1], bounds[2]);
+    let max = origin + Vec3::new(bounds[3], bounds[4], bounds[5]);
+    frustum.is_none_or(|f| f.intersects(min, max))
+}
+
+/// One mod block entity's frame, as `submit` gets it: the render state's
+/// partial tick, game time and light, and the pose stack the helpers draw
+/// under (`native_draw_quad`, `native_draw_cube`, `native_draw_block`).
+// Native mods read and drive it; nothing in Horizon does.
+#[allow(dead_code)]
+pub struct BlockEntityDraw {
+    /// The frame's partial tick, 0 to 1 (`BlockEntityRenderState`).
+    pub partial: f32,
+    /// The level's game time, for animations.
+    pub game_time: i64,
+    /// The light the helpers draw with: the block's own
+    /// (`LevelRenderer.getLightCoords`), 16 times sky light in bits 0..8 and
+    /// 16 times block light in bits 8..16; set it to light a part otherwise.
+    pub light: u32,
+    poses: Vec<Mat4>,
+    lights: (Vec3, Vec3),
+    vertices: Vec<Vertex>,
+}
+
+#[allow(dead_code)]
+impl BlockEntityDraw {
+    /// `PoseStack.pushPose`: `pop` comes back to the pose as it is now.
+    pub fn push(&mut self) {
+        let pose = self.pose();
+        self.poses.push(pose);
+    }
+    /// `PoseStack.popPose`; the block's own pose is never popped.
+    pub fn pop(&mut self) {
+        if self.poses.len() > 1 {
+            self.poses.pop();
+        }
+    }
+    /// Moves what is drawn next by `by`, in blocks.
+    pub fn translate(&mut self, by: [f32; 3]) {
+        self.apply(Mat4::from_translation(Vec3::from_array(by)));
+    }
+    /// Turns what is drawn next by `degrees` about `axis` (counterclockwise
+    /// seen from the axis' positive end, as `Axis.rotationDegrees`) through
+    /// `pivot`, in blocks from the pose's origin: `[0.5; 3]` is the block's centre.
+    pub fn rotate_about(&mut self, axis: [f32; 3], degrees: f32, pivot: [f32; 3]) {
+        let axis = Vec3::from_array(axis).normalize_or(Vec3::Y);
+        let pivot = Vec3::from_array(pivot);
+        self.apply(
+            Mat4::from_translation(pivot)
+                * Mat4::from_quat(Quat::from_axis_angle(axis, degrees.to_radians()))
+                * Mat4::from_translation(-pivot),
+        );
+    }
+    /// Scales what is drawn next by `by` about the pose's origin.
+    pub fn scale(&mut self, by: [f32; 3]) {
+        self.apply(Mat4::from_scale(Vec3::from_array(by)));
+    }
+    fn apply(&mut self, m: Mat4) {
+        if let Some(pose) = self.poses.last_mut() {
+            *pose *= m;
+        }
+    }
+    fn pose(&self) -> Mat4 {
+        self.poses.last().copied().unwrap_or(Mat4::IDENTITY)
+    }
+    /// A quad of `corners` (blocks, under the pose) with unit UVs, shaded as
+    /// vanilla's block entity models are (`Lighting`'s two lights).
+    fn quad(&mut self, corners: [[f32; 3]; 4], uv: [[f32; 2]; 4], sprite: Rect, tint: u32) {
+        let pose = self.pose();
+        let at = corners.map(|c| pose.transform_point3(Vec3::from_array(c)));
+        let normal = (at[1] - at[0]).cross(at[2] - at[0]).normalize_or_zero();
+        let normal = if normal == Vec3::ZERO {
+            (at[2] - at[1]).cross(at[3] - at[1]).normalize_or(Vec3::Y)
+        } else {
+            normal
+        };
+        let color = shaded(tint, diffuse(normal, self.lights));
+        for (p, uv) in at.into_iter().zip(uv) {
+            self.vertices.push(Vertex {
+                pos: p.to_array(),
+                uv: [
+                    sprite.u0 + (sprite.u1 - sprite.u0) * uv[0],
+                    sprite.v0 + (sprite.v1 - sprite.v0) * uv[1],
+                ],
+                layer: 0,
+                color,
+                light: self.light,
+                normal: [0; 4],
+                glint_uv: [0.0, 0.0],
+            });
+        }
+    }
+}
+
+/// One face of a `native_draw_cube` box: its sprite (`mymod:entity/cog`,
+/// `mymod:block/casing`) and its UVs in texels of 16 per side, as a model
+/// face's `uv` (none takes the box's own, as a model's default).
+#[allow(dead_code)]
+#[derive(Clone, Copy, Debug)]
+pub struct CubeFace<'a> {
+    pub sprite: &'a str,
+    pub uv: Option<[f32; 4]>,
+}
+
+/// 0xRRGGBB `tint` times `brightness`, as an opaque vertex colour.
+fn shaded(tint: u32, brightness: f32) -> u32 {
+    let c = |shift: u32| (((tint >> shift) & 255) as f32 * brightness) as u32;
+    0xFF00_0000 | c(0) << 16 | c(8) << 8 | c(16)
+}
+
+impl Game<'_> {
+    /// `native_block_entity_submit` for each of `blocks` (in drawn sections,
+    /// drawn by no vanilla renderer) whose block entity is a mod's, closer than
+    /// `BlockEntityRenderer.getViewDistance` to the camera (`shouldRender`)
+    /// and with its bounds (`native_block_entity_render_bounding_box`) in the
+    /// frustum.
+    pub(super) fn mod_block_entity_geometry<'a>(
+        &self,
+        blocks: impl Iterator<Item = &'a ([i32; 3], u32)>,
+        camera: DVec3,
+        partial: f32,
+        out: &mut Vec<Vertex>,
+    ) {
+        let mut draw = BlockEntityDraw {
+            partial,
+            game_time: self.world.game_time,
+            light: 0,
+            poses: Vec::new(),
+            lights: diffuse_lights(self.dim == Dim::Nether),
+            vertices: std::mem::take(out),
+        };
+        for &(pos, state) in blocks {
+            let corner = DVec3::new(f64::from(pos[0]), f64::from(pos[1]), f64::from(pos[2]));
+            // Vec3.closerThan: strictly closer.
+            if (corner + 0.5).distance_squared(camera) >= VIEW_DISTANCE * VIEW_DISTANCE {
+                continue;
+            }
+            let Some(BlockEntity::Mod(entity)) =
+                self.world.block_entities.get(&(pos[0], pos[1], pos[2]))
+            else {
+                continue;
+            };
+            let id = BlockStateId(state);
+            let block = &*self.res.facts().get(id).name;
+            let origin = (corner - camera).as_vec3();
+            let mut bounds = DEFAULT_BOUNDS;
+            self.native_block_entity_render_bounding_box(pos, block, id, entity, &mut bounds);
+            if !in_frustum(self.view_frustum.as_ref(), origin, bounds) {
+                continue;
+            }
+            let start = draw.vertices.len();
+            self.mark_block_entity(start, state);
+            draw.poses.clear();
+            draw.poses.push(Mat4::from_translation(origin));
+            draw.light = vertex_light(self.world.light(pos[0], pos[1], pos[2]));
+            self.native_block_entity_submit(pos, block, id, entity, &mut draw);
+            self.cull_entity_vertices(&mut draw.vertices, start);
+        }
+        *out = draw.vertices;
+    }
+}
+
+/// Helpers for drawing mod block entities, kept as stable as the hook points.
+// Native mods use these; nothing in Horizon does.
+#[allow(dead_code)]
+impl Game<'_> {
+    /// Draws a quad with `corners` in blocks under `draw`'s pose, in a model
+    /// face's order (top left, bottom left, bottom right, top right as seen
+    /// from its front), textured with the `uv` rectangle (u0, v0, u1, v1 in
+    /// texels of 16 per side) of `sprite` (`mymod:entity/screen`,
+    /// `mymod:block/casing`, `block/stone`) times the 0xRRGGBB `tint`
+    /// (0xFFFFFF for none). False for an unknown sprite. API @API:block_entity_submit@.
+    pub(super) fn native_draw_quad(
+        &self,
+        draw: &mut BlockEntityDraw,
+        sprite: &str,
+        corners: [[f32; 3]; 4],
+        uv: [f32; 4],
+        tint: u32,
+    ) -> bool {
+        let Some(rect) = self.gui.atlas.sprites.get(sprite).copied() else {
+            return false;
+        };
+        let [u0, v0, u1, v1] = uv.map(|t| t / 16.0);
+        draw.quad(
+            corners,
+            [[u0, v0], [u0, v1], [u1, v1], [u1, v0]],
+            rect,
+            tint,
+        );
+        true
+    }
+
+    /// Draws a box from `from` to `to` (texels of 16 per block, as a block
+    /// model's element) under `draw`'s pose, with the faces given, by
+    /// `Direction` (down, up, north, south, west, east), baked as a model
+    /// element's are (`FaceBakery`), times the 0xRRGGBB `tint`. A turned box
+    /// is drawn under a turned pose (`BlockEntityDraw::rotate_about`). False
+    /// when a face's sprite is unknown; that face is left out. API @API:block_entity_submit@.
+    pub(super) fn native_draw_cube(
+        &self,
+        draw: &mut BlockEntityDraw,
+        from: [f32; 3],
+        to: [f32; 3],
+        faces: [Option<CubeFace<'_>>; 6],
+        tint: u32,
+    ) -> bool {
+        let mut all = true;
+        for (direction, face) in Direction::ALL.into_iter().zip(faces) {
+            let Some(face) = face else { continue };
+            let Some(rect) = self.gui.atlas.sprites.get(face.sprite).copied() else {
+                all = false;
+                continue;
+            };
+            let uv = face.uv.unwrap_or_else(|| default_uv(from, to, direction));
+            let material = Material {
+                sprite: String::new(),
+                force_translucent: false,
+            };
+            if let Ok(quad) = bake_flat_face(from, to, uv, direction, material, -1) {
+                draw.quad(quad.positions, quad.uv, rect, tint);
+            }
+        }
+        all
+    }
+
+    /// Draws block `block`'s model (`mymod:cog`, any block with a model) in
+    /// the state with `properties` (`[("axis", "x")]`, the rest default)
+    /// under `draw`'s pose, as vanilla's `submitBlockModel` draws a block in
+    /// an entity's place: a block's baked model, with its default tints. A
+    /// moving part is often a block of the mod's own, never placed. False for
+    /// an unknown block or property. API @API:block_entity_submit@.
+    pub(super) fn native_draw_block(
+        &self,
+        draw: &mut BlockEntityDraw,
+        block: &str,
+        properties: &[(&str, &str)],
+    ) -> bool {
+        let registry = &self.pack.assets.registry;
+        let Some(mut state) = registry
+            .default_state(block)
+            .and_then(|id| registry.state(id))
+            .cloned()
+        else {
+            return false;
+        };
+        for (key, value) in properties {
+            match state.properties.get_mut(*key) {
+                Some(v) => *v = (*value).to_owned(),
+                None => return false,
+            }
+        }
+        let Some(id) = registry.id(&state) else {
+            return false;
+        };
+        let pose = draw.pose();
+        self.block_model_vertices(id, 42, pose, draw.light, true, &mut draw.vertices);
+        true
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn draw() -> BlockEntityDraw {
+        BlockEntityDraw {
+            partial: 0.0,
+            game_time: 0,
+            light: 0xF0F0,
+            poses: vec![Mat4::from_translation(Vec3::new(10.0, 0.0, 0.0))],
+            lights: diffuse_lights(false),
+            vertices: Vec::new(),
+        }
+    }
+
+    fn sprite() -> Rect {
+        Rect {
+            u0: 0.5,
+            v0: 0.25,
+            u1: 0.75,
+            v1: 0.5,
+            w: 16,
+            h: 16,
+        }
+    }
+
+    #[test]
+    fn the_pose_stack_turns_about_its_pivot_and_pops_back() {
+        let mut d = draw();
+        d.push();
+        d.rotate_about([0.0, 1.0, 0.0], 90.0, [0.5, 0.5, 0.5]);
+        // (1, 0, 0.5) turns a quarter about the block's centre to (0.5, 0, 0).
+        let p = d.pose().transform_point3(Vec3::new(1.0, 0.0, 0.5));
+        assert!(p.abs_diff_eq(Vec3::new(10.5, 0.0, 0.0), 1e-5), "{p}");
+        d.pop();
+        d.pop();
+        // Popping past the block's own pose keeps it.
+        let p = d.pose().transform_point3(Vec3::ZERO);
+        assert_eq!(p, Vec3::new(10.0, 0.0, 0.0));
+        d.translate([0.0, 2.0, 0.0]);
+        d.scale([2.0, 2.0, 2.0]);
+        let p = d.pose().transform_point3(Vec3::ONE);
+        assert_eq!(p, Vec3::new(12.0, 4.0, 2.0));
+    }
+
+    #[test]
+    fn a_quad_lands_in_its_sprite_lit_and_shaded() {
+        let mut d = draw();
+        // An upward face: full brightness under vanilla's level lights is
+        // below 1 (two lights), so the colour is shaded but opaque.
+        d.quad(
+            [
+                [0.0, 1.0, 0.0],
+                [0.0, 1.0, 1.0],
+                [1.0, 1.0, 1.0],
+                [1.0, 1.0, 0.0],
+            ],
+            [[0.0, 0.0], [0.0, 1.0], [1.0, 1.0], [1.0, 0.0]],
+            sprite(),
+            0xFFFFFF,
+        );
+        assert_eq!(d.vertices.len(), 4);
+        let v = d.vertices[2];
+        assert_eq!(v.pos, [11.0, 1.0, 1.0]);
+        assert_eq!(v.uv, [0.75, 0.5]);
+        assert_eq!(v.light, 0xF0F0);
+        let up = diffuse(Vec3::Y, diffuse_lights(false));
+        assert_eq!(v.color, shaded(0xFFFFFF, up));
+        assert_eq!(v.color >> 24, 0xFF);
+    }
+
+    /// A frustum that sees nothing.
+    struct Blind;
+    impl Cull for Blind {
+        fn intersects(&self, _: Vec3, _: Vec3) -> bool {
+            false
+        }
+        fn contains(&self, _: Vec3, _: Vec3) -> bool {
+            false
+        }
+    }
+
+    #[test]
+    fn infinite_bounds_and_frames_without_a_frustum_are_never_culled() {
+        let origin = Vec3::new(1.0e6, 0.0, 0.0);
+        let infinite = [f32::NEG_INFINITY, 0.0, 0.0, f32::INFINITY, 1.0, 1.0];
+        assert!(!in_frustum(Some(&Blind), origin, DEFAULT_BOUNDS));
+        assert!(in_frustum(Some(&Blind), origin, infinite));
+        assert!(in_frustum(None::<&Blind>, origin, DEFAULT_BOUNDS));
+    }
+
+    #[test]
+    fn a_tint_keeps_its_channels_in_vertex_order() {
+        // The vertex colour is RGBA8 read little-endian: red in the low byte.
+        assert_eq!(shaded(0x10_20_30, 1.0), 0xFF_30_20_10);
+    }
+}

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

@@ -0,0 +1,93 @@
+//! Native item data component helpers.
+use super::Game;
+use horizon_client::items::ItemStack;
+use horizon_world::nbt::Tag;
+
+/// Failure to access a native item component.
+#[derive(Debug)]
+pub(crate) enum NativeComponentError {
+    UnknownType,
+    InvalidValue(horizon_protocol::Error),
+}
+impl std::fmt::Display for NativeComponentError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::UnknownType => f.write_str("unregistered component type"),
+            Self::InvalidValue(error) => write!(f, "invalid component value: {error}"),
+        }
+    }
+}
+impl std::error::Error for NativeComponentError {}
+
+// Native mods use these helpers.
+#[allow(dead_code)]
+impl Game<'_> {
+    /// Read a native component, including the item's default when not patched.
+    pub(super) fn native_component<'a>(
+        &'a self,
+        stack: &'a ItemStack,
+        id: &str,
+    ) -> Result<Option<&'a Tag>, NativeComponentError> {
+        if horizon_protocol::item::custom::id(id).is_none() {
+            return Err(NativeComponentError::UnknownType);
+        }
+        if let Some(data) = stack.data() {
+            if data.other(&format!("!{id}")).is_some() {
+                return Ok(None);
+            }
+            if let Some(value) = data.other(id) {
+                return Ok(Some(value));
+            }
+        }
+        Ok(self
+            .items()
+            .get(&stack.item)
+            .and_then(|item| item.custom_components.get(id)))
+    }
+
+    /// Set a registered native component after checking the network NBT limits.
+    pub(super) fn native_set_component(
+        &self,
+        stack: &mut ItemStack,
+        id: &str,
+        value: Tag,
+    ) -> Result<(), NativeComponentError> {
+        if horizon_protocol::item::custom::id(id).is_none() {
+            return Err(NativeComponentError::UnknownType);
+        }
+        horizon_protocol::item::custom::validate(&value)
+            .map_err(NativeComponentError::InvalidValue)?;
+        let default = self
+            .items()
+            .get(&stack.item)
+            .and_then(|item| item.custom_components.get(id));
+        let value = (default != Some(&value)).then_some(value);
+        let removed = format!("!{id}");
+        let data = stack.data_mut();
+        data.set_other(&removed, None);
+        data.set_other(id, value);
+        stack.tidy();
+        Ok(())
+    }
+
+    /// Remove a native component, including its item default.
+    pub(super) fn native_remove_component(
+        &self,
+        stack: &mut ItemStack,
+        id: &str,
+    ) -> Result<(), NativeComponentError> {
+        if horizon_protocol::item::custom::id(id).is_none() {
+            return Err(NativeComponentError::UnknownType);
+        }
+        let default = self
+            .items()
+            .get(&stack.item)
+            .is_some_and(|item| item.custom_components.contains_key(id));
+        let removed = format!("!{id}");
+        let data = stack.data_mut();
+        data.set_other(id, None);
+        data.set_other(&removed, default.then(|| Tag::Compound(Default::default())));
+        stack.tidy();
+        Ok(())
+    }
+}

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

@@ -0,0 +1,215 @@
+//! A mod's own advancement criteria triggers (docs/native-mods.md,
+//! "Advancement triggers"). An advancement of a content mod or a world's data
+//! pack names a trigger of the mod's (`mymod:pipe_connected`); the tree keeps
+//! it as it keeps vanilla's, and the mod fires it where its event happens, as
+//! a NeoForge mod calls its own `SimpleCriterionTrigger.trigger`.
+use super::{Game, advancements::item_view, commands::Target};
+use horizon_client::{
+    advancements::{self as adv, EntityView},
+    items::ItemStack,
+};
+use serde_json::Value;
+
+/// One open criterion of a mod's trigger, as the mod's test sees it.
+pub(crate) struct NativeCriterion<'a> {
+    /// The criterion's `conditions`, `Null` when it has none. Its `player`
+    /// predicate is the game's to test, as vanilla's `SimpleInstance.player`.
+    pub(crate) conditions: &'a Value,
+    world: &'a dyn adv::World,
+}
+
+#[allow(dead_code)]
+impl NativeCriterion<'_> {
+    /// Whether `stack` passes the item predicate under `key` in the
+    /// conditions, as the game's own triggers read an `ItemPredicate`:
+    /// `items` (an id, a list or a `#tag`), `count`, the `potion_contents`
+    /// and `damage` components, and the `enchantments` and `damage`
+    /// predicates; other components and predicates aren't checked. A missing
+    /// key passes, as an absent `Optional<ItemPredicate>` does.
+    pub(crate) fn item(&self, key: &str, stack: &ItemStack) -> bool {
+        adv::item(&self.conditions[key], &item_view(stack), self.world)
+    }
+}
+
+/// Whether a mod may fire `trigger`: a namespaced id outside `minecraft`,
+/// whose triggers the game fires from its own events.
+fn mod_trigger(trigger: &str) -> bool {
+    trigger
+        .split_once(':')
+        .is_some_and(|(ns, path)| !ns.is_empty() && !path.is_empty() && ns != "minecraft")
+}
+
+/// Helpers for server mods, kept as stable as the hook points.
+// Native mods use these; nothing in Horizon does.
+#[allow(dead_code)]
+impl Game<'_> {
+    /// Fires the mod's criteria trigger `trigger` (`mymod:pipe_connected`)
+    /// for the player with that UUID: vanilla's
+    /// `SimpleCriterionTrigger.trigger`. Each criterion of theirs with that
+    /// trigger, not yet granted, of an advancement not yet done, is tested
+    /// by `test` and then by its `player` predicate; those that pass are
+    /// granted, and an advancement they complete is awarded with its toast,
+    /// chat line and rewards, as the game's own triggers award.
+    ///
+    /// The acting player is reached inside their hook; any player on the
+    /// server, in their own level, only where no player's state is swapped in
+    /// (`native_tick`, `native_menu_clicked`), as `native_run_command`. True
+    /// when the player was reached, whether or not anything was granted;
+    /// false off a server, when the player isn't on or can't be reached from
+    /// here, and for a `minecraft:` trigger or a name without a namespace.
+    /// API @API:native_criteria@.
+    pub(super) fn native_trigger_criterion(
+        &mut self,
+        uuid: u128,
+        trigger: &str,
+        test: impl Fn(&NativeCriterion<'_>) -> bool,
+    ) -> bool {
+        if !mod_trigger(trigger) || self.remote.is_some() {
+            return false;
+        }
+        if self.lan_acting_uuid == Some(uuid) {
+            self.trigger_mod_criteria(trigger, &test);
+            return true;
+        }
+        if self.lan_acting.is_some() {
+            return false;
+        }
+        let Some(conn) = self.lan.as_ref().and_then(|host| {
+            host.hub
+                .guests
+                .iter()
+                .find(|g| g.placed && g.uuid == uuid)
+                .map(|g| g.conn)
+        }) else {
+            return false;
+        };
+        // In their level: the predicates read where they are, and a reward
+        // that doesn't fit drops there.
+        self.for_player(Target::Guest(conn), |g| {
+            g.trigger_mod_criteria(trigger, &test)
+        })
+        .is_some()
+    }
+
+    /// `trigger` for a mod's trigger, for the player in place.
+    fn trigger_mod_criteria(&mut self, trigger: &str, test: &dyn Fn(&NativeCriterion<'_>) -> bool) {
+        let me = self.player_entity();
+        self.trigger(trigger, |conditions, world| {
+            passes(conditions, &me, world, test)
+        });
+    }
+}
+
+/// `SimpleCriterionTrigger.trigger`'s test of one criterion for the player
+/// `me`: the mod's matcher, then the `player` predicate, in the player's own
+/// context (`EntityPredicate.createContext(player, player)`).
+fn passes(
+    conditions: &Value,
+    me: &EntityView,
+    world: &dyn adv::World,
+    test: &dyn Fn(&NativeCriterion<'_>) -> bool,
+) -> bool {
+    let player = adv::Entities {
+        this: Some(me),
+        origin: me.position,
+        tool: None,
+        block_pos: None,
+    };
+    test(&NativeCriterion { conditions, world })
+        && adv::conditions(&conditions["player"], &player, world)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+    use std::collections::BTreeMap;
+
+    struct Plains;
+    impl adv::World for Plains {
+        fn dimension(&self) -> &str {
+            "minecraft:overworld"
+        }
+        fn biome(&self, _: [i32; 3]) -> String {
+            "minecraft:plains".into()
+        }
+        fn structures(&self, _: [i32; 3]) -> Vec<String> {
+            Vec::new()
+        }
+        fn block(&self, _: [i32; 3]) -> (String, BTreeMap<String, String>) {
+            ("minecraft:air".into(), BTreeMap::new())
+        }
+        fn fluid(&self, _: [i32; 3]) -> Option<String> {
+            None
+        }
+        fn can_see_sky(&self, _: [i32; 3]) -> bool {
+            true
+        }
+        fn light(&self, _: [i32; 3]) -> i32 {
+            15
+        }
+        fn smokey(&self, _: [i32; 3]) -> bool {
+            false
+        }
+        fn in_tag(&self, registry: &str, tag: &str, id: &str) -> bool {
+            registry == "item" && tag == "c:ingots/copper" && id == "minecraft:copper_ingot"
+        }
+    }
+
+    /// A mod's `pipe_connected` criterion: the pipe's item by a convention
+    /// tag, and only for a player on fire (a loot condition list, as
+    /// vanilla's advancements write `player`).
+    fn criterion() -> Value {
+        json!({
+            "pipe": {"items": "#c:ingots/copper", "count": {"min": 2}},
+            "player": [{
+                "condition": "minecraft:entity_properties",
+                "entity": "this",
+                "predicate": {"flags": {"is_on_fire": true}}
+            }]
+        })
+    }
+
+    #[test]
+    fn a_mods_criterion_takes_its_own_test_and_the_player_predicate() {
+        let burning = EntityView {
+            kind: "minecraft:player".into(),
+            on_fire: true,
+            ..EntityView::default()
+        };
+        let calm = EntityView {
+            on_fire: false,
+            ..burning.clone()
+        };
+        let copper = ItemStack::new("minecraft:copper_ingot", 2);
+        let pipe = |stack: &ItemStack| {
+            let stack = stack.clone();
+            move |c: &NativeCriterion<'_>| c.item("pipe", &stack)
+        };
+        let c = criterion();
+        assert!(passes(&c, &burning, &Plains, &pipe(&copper)));
+        assert!(
+            !passes(&c, &calm, &Plains, &pipe(&copper)),
+            "the player predicate"
+        );
+        let one = ItemStack::new("minecraft:copper_ingot", 1);
+        assert!(
+            !passes(&c, &burning, &Plains, &pipe(&one)),
+            "the item's count"
+        );
+        let iron = ItemStack::new("minecraft:iron_ingot", 2);
+        assert!(!passes(&c, &burning, &Plains, &pipe(&iron)), "the tag");
+        // A criterion without the key or any conditions passes the item test.
+        let any = |c: &NativeCriterion<'_>| c.item("filter", &iron);
+        assert!(passes(&c, &burning, &Plains, &any));
+        assert!(passes(&Value::Null, &calm, &Plains, &any));
+    }
+
+    #[test]
+    fn mods_fire_only_their_own_namespaced_triggers() {
+        assert!(mod_trigger("mymod:pipe_connected"));
+        assert!(!mod_trigger("minecraft:inventory_changed"));
+        assert!(!mod_trigger("inventory_changed"));
+        assert!(!mod_trigger(":pipe_connected"));
+    }
+}

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

@@ -117,7 +117,7 @@ impl Game<'_> {
     /// client's copy of the world, for another dimension, a position outside
     /// `/summon`'s bounds, a chunk that isn't loaded, a kind Horizon can't
     /// load, or one a mod kept out (`native_entity_join_level`). API
-    /// @API:native_entities@.
+    /// 59.
     pub(super) fn native_summon(
         &mut self,
         dimension: &str,
@@ -139,15 +139,25 @@ impl Game<'_> {
             Tag::List(pos.map(|v| Tag::Double(v.to_bits())).to_vec()),
         );
         let from = self.mobs.len();
+        let deferred = (self.tnts.len(), self.falling.len(), self.rockets.len());
         let target = self.spawn_entity_from_nbt(Tag::Compound(tag));
+        // These roots load with id 0 and have no command Target variant.
+        // Select the newly appended root, never an older waiting entity.
+        let root = match kind {
+            "minecraft:tnt" => self.tnts.get_mut(deferred.0).map(|e| &mut e.id),
+            "minecraft:falling_block" => self.falling.get_mut(deferred.1).map(|e| &mut e.id),
+            "minecraft:firework_rocket" => self.rockets.get_mut(deferred.2).map(|e| &mut e.id),
+            _ => None,
+        };
+        let root = root.map(|id| super::lan_entities::assign_entity_id(&mut self.next_entity, id));
         self.native_mobs_joined(from, false);
-        target.and_then(target_id)
+        root.or_else(|| target.and_then(target_id))
     }
     /// Moves entity `id`, one Horizon keeps without simulating (a display, a
     /// marker, an interaction), to `pos` facing `yaw` and `pitch` in degrees;
     /// a display eases there over its `teleport` ticks. False for no such
     /// entity, another dimension or a position outside `/summon`'s bounds.
-    /// Mobs move with `native_teleport_mob`. API @API:native_entities@.
+    /// Mobs move with `native_teleport_mob`. API 59.
     pub(super) fn native_move_entity(
         &mut self,
         dimension: &str,
@@ -175,7 +185,7 @@ impl Game<'_> {
     /// `block_display`, `item_display` or `text_display`): players see it
     /// ease from what it showed over `interpolation` ticks. False for no such
     /// display, another dimension, or a value that isn't finite, a zero
-    /// quaternion, or a duration out of range. API @API:native_entities@.
+    /// quaternion, or a duration out of range. API 59.
     pub(super) fn native_set_display(
         &mut self,
         dimension: &str,
@@ -209,7 +219,7 @@ impl Game<'_> {
     /// Removes entity `id`, one Horizon keeps without simulating, as `/kill`
     /// does (it drops nothing and isn't saved). False for no such entity or
     /// another dimension. Mobs go with `native_remove_mob`. API
-    /// @API:native_entities@.
+    /// 59.
     pub(super) fn native_remove_entity(&mut self, dimension: &str, id: u32) -> bool {
         if !self.native_entity_level(dimension) || !self.others.iter().any(|o| o.id == id) {
             return false;

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

@@ -0,0 +1,138 @@
+//! Explosions for native server mods (docs/native-mods.md, "Explosions"): a mod
+//! sets one off as `Level.explode` does, in the level in place, which it names
+//! by its `dimension` (`minecraft:overworld`) as `native_set_block` does.
+use super::{Game, explosion::BlockInteraction};
+
+/// The largest radius `native_explode` takes. A blast's cost grows with its
+/// radius (its 1352 rays walk `radius * 1.3` blocks at most); vanilla's
+/// largest is the wither's charged spawn, 7.
+pub(super) const NATIVE_EXPLOSION_MAX_RADIUS: f32 = 32.0;
+
+/// What a mod's blast does to blocks (`Level.ExplosionInteraction`). Built by
+/// mods only.
+#[allow(dead_code)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub(super) enum NativeBlast {
+    /// Blocks stay; entities are hurt and pushed (`ExplosionInteraction.NONE`).
+    Keep,
+    /// Blocks break and drop by the `block_explosion_drop_decay` rule
+    /// (`ExplosionInteraction.BLOCK`).
+    #[default]
+    Block,
+    /// Blocks break and drop by the `tnt_explosion_drop_decay` rule
+    /// (`ExplosionInteraction.TNT`).
+    Tnt,
+}
+
+/// Whether `native_explode` takes this centre and radius.
+fn blast_ok(center: [f64; 3], radius: f32) -> bool {
+    center
+        .into_iter()
+        .all(|v| v.is_finite() && v.abs() <= 30_000_000.0)
+        && radius.is_finite()
+        && radius > 0.0
+        && radius <= NATIVE_EXPLOSION_MAX_RADIUS
+}
+
+#[allow(dead_code)]
+impl Game<'_> {
+    /// Explodes at `center` in the level in place, `dimension`, as
+    /// `Level.explode(null, x, y, z, radius, fire, interaction)` does: the
+    /// blocks it reaches break (`native_explosion_detonate` sees them first),
+    /// entities are hurt and pushed, `fire` lights a third of the air above
+    /// solid blocks, and everyone near hears and sees it. False, with nothing
+    /// done, on a client's copy of the world, for another dimension, a chunk
+    /// that isn't loaded, or a radius that isn't in `0 < radius <= 32`. Call
+    /// it from a server hook; a blast inside `native_explosion_detonate`
+    /// starts that hook again. API @API:native_explode@.
+    pub(super) fn native_explode(
+        &mut self,
+        dimension: &str,
+        center: [f64; 3],
+        radius: f32,
+        fire: bool,
+        blast: NativeBlast,
+    ) -> bool {
+        if (self.serving.is_none() && self.options.dedicated.is_none())
+            || dimension != self.dim.id()
+            || !blast_ok(center, radius)
+        {
+            return false;
+        }
+        let chunk = (
+            (center[0].floor() as i32) >> 4,
+            (center[2].floor() as i32) >> 4,
+        );
+        if !self.world.chunks.contains_key(&chunk) {
+            return false;
+        }
+        let interaction = match blast {
+            NativeBlast::Keep => BlockInteraction::Keep,
+            NativeBlast::Block => self.destroy_type("block_explosion_drop_decay"),
+            NativeBlast::Tnt => self.destroy_type("tnt_explosion_drop_decay"),
+        };
+        // `Level.explode(null, ...)`: no source. Called from inside another
+        // blast (`native_explosion_detonate`), it must not take that blast's
+        // source, owner or flags, and that blast gets them back after.
+        let outer = self.take_blast_state();
+        let done = self
+            .server_explode(center, radius, interaction, fire)
+            .is_ok();
+        self.restore_blast_state(outer);
+        done
+    }
+
+    /// The blast going off now, cleared to a sourceless one.
+    fn take_blast_state(&mut self) -> BlastState {
+        let c = &mut self.combat;
+        BlastState {
+            source: c.explosion_source.take(),
+            cause: c.explosion_cause.take(),
+            source_named: std::mem::take(&mut c.explosion_source_named),
+            in_water: std::mem::take(&mut c.explosion_in_water),
+            hive_emptying: std::mem::take(&mut c.hive_emptying_blast),
+            rail_proof: std::mem::take(&mut c.rail_proof_blast),
+            owner: c.explosion_owner.take(),
+        }
+    }
+
+    /// Puts back what `take_blast_state` cleared.
+    fn restore_blast_state(&mut self, s: BlastState) {
+        let c = &mut self.combat;
+        c.explosion_source = s.source;
+        c.explosion_cause = s.cause;
+        c.explosion_source_named = s.source_named;
+        c.explosion_in_water = s.in_water;
+        c.hive_emptying_blast = s.hive_emptying;
+        c.rail_proof_blast = s.rail_proof;
+        c.explosion_owner = s.owner;
+    }
+}
+
+/// The fields of `CombatTracker` that describe the blast going off now.
+struct BlastState {
+    source: Option<u32>,
+    cause: Option<horizon_client::advancements::EntityView>,
+    source_named: bool,
+    in_water: bool,
+    hive_emptying: bool,
+    rail_proof: bool,
+    owner: Option<u32>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn a_blast_needs_a_finite_centre_and_a_radius_in_range() {
+        assert!(blast_ok([0.5, 64.0, 0.5], 4.0));
+        assert!(blast_ok([0.5, 64.0, 0.5], NATIVE_EXPLOSION_MAX_RADIUS));
+        assert!(!blast_ok([0.5, 64.0, 0.5], 0.0));
+        assert!(!blast_ok([0.5, 64.0, 0.5], -1.0));
+        assert!(!blast_ok([0.5, 64.0, 0.5], 33.0));
+        assert!(!blast_ok([0.5, 64.0, 0.5], f32::NAN));
+        assert!(!blast_ok([f64::INFINITY, 64.0, 0.5], 4.0));
+        assert!(!blast_ok([0.5, 64.0, 4.0e7], 4.0));
+    }
+}

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

@@ -6,6 +6,19 @@
 //! Horizon's own HUD extras do, and keep a mod's settings where the
 //! WebAssembly mod of the same id kept them.
 //!
+//! API 62 adds nicknames for server mods: `native_set_nickname` shows a name in place of a player's in chat and
+//! the Tab list (the real one on hover), and `native_text_allowed` asks the server's chat filter, in
+//! `native_server.rs`.
+//!
+//! API 61 adds mods' own sound events in `native_play_sound`: another
+//! namespace's event is sent by name, as vanilla sends an unregistered sound.
+//!
+//! API 60 adds the small bar under an item (`native_item_bar`): `GuiGraphicsExtractor.itemDecorations`
+//! hands it vanilla's choice (the damage bar, or a bundle's fullness already applied), to replace or hide.
+//!
+//! API 59 adds entities for server mods (`native_summon`, `native_move_entity`,
+//! `native_set_display`, `native_remove_entity`, in `native_entities.rs`).
+//!
 //! API 58 adds the renderer's hook points, in `horizon-client-render`'s
 //! `gfx/native_render.rs`: `native_world_drawn` (draw with the world's colour,
 //! depth, matrices and entity geometry before the hand and the HUD) and
@@ -205,6 +218,7 @@ use super::native_lifecycle::{NativeLifecycleContext, ServerTickPhase, WorldPhas
 use super::{
     Game, GameLevel, LevelDimension, Screen,
     execution_role::ExecutionRole,
+    native_block_entity_draw::BlockEntityDraw,
     native_panel_recipes::RecipePage,
     native_server::{NativeCommand, NativeServerPlayer},
 };
@@ -232,8 +246,8 @@ use horizon_core::{
     ticks::{ScheduleResult, TickPriority},
 };
 use horizon_world::{
-    fluid::FluidKind,
-    level::{BlockId, LevelAccess, Ticks},
+    fluid::{FluidKind, FluidState},
+    level::{BlockId, LevelAccess, PlacementContext, Ticks},
     nbt::Compound,
     registry::{BlockRegistry, BlockStateId},
 };
@@ -255,7 +269,7 @@ pub(super) use horizon_world::level::flags;
 /// The hook points' API version. The launcher reads this line from the
 /// source it builds; keep its form.
 #[allow(dead_code)]
-pub(crate) const NATIVE_HOOKS_API: u32 = 58;
+pub(crate) const NATIVE_HOOKS_API: u32 = 62;
 
 impl GameLevel<'_> {
     /// An authoritative server committed a changed state through `Level.setBlock`.
@@ -351,6 +365,39 @@ impl GameLevel<'_> {
         let _ = (state, source);
     }
 
+    /// `BlockState.hasAnalogOutputSignal`: set `output` for a block of yours
+    /// that comparators read (how full or far along it is, as a composter's
+    /// level), so they ask `native_analog_output`. Asked from inside the
+    /// level's update: answer from `state` alone. Authoritative servers only.
+    /// API @API:analog_output@.
+    #[inline(always)]
+    pub(super) fn native_has_analog_output(&self, state: BlockStateId, output: &mut bool) {
+        let _ = (state, output);
+    }
+
+    /// `BlockState.getAnalogOutputSignal`: the signal a comparator reads from
+    /// the block `state` at `pos`, `face` the side that touches the comparator
+    /// (or the conductor in front of it). `output` holds vanilla's answer:
+    /// change it when the block is yours (0 to 15; anything else is clamped).
+    /// Asked only for blocks `native_has_analog_output` answered for, from
+    /// inside the level's update: don't change the world here. When the
+    /// answer changes without the block's state changing, call
+    /// `native_update_output_neighbors`; a change of state through
+    /// `native_set_block` or `native_set_block_property` (neighbour updates
+    /// on) tells the comparators itself, as vanilla's `Level.setBlock` does.
+    /// Authoritative servers only. API @API:analog_output@.
+    #[inline(always)]
+    pub(super) fn native_analog_output(
+        &self,
+        dimension: LevelDimension,
+        pos: BlockPos,
+        state: BlockStateId,
+        face: Direction,
+        output: &mut i32,
+    ) {
+        let _ = (dimension, pos, state, face, output);
+    }
+
     /// An authoritative server's `ServerLevel.tickChunk` is about to
     /// random-tick the block `state` at `pos` (`BlockState.randomTick`):
     /// only blocks that tick randomly, a mod's as its vanilla template block
@@ -410,6 +457,45 @@ impl GameLevel<'_> {
         );
     }
 
+    /// On an authoritative server, `BlockState.canSurvive` for `state` at
+    /// `pos` (`BlockBehaviour.canSurvive`), before the block answers it: as
+    /// it is placed (`BlockItem.canPlace`), from a shape update of a block
+    /// whose template checks it (a plant, a torch, a sign: false breaks the
+    /// block with its drops), and wherever else vanilla asks. `state` may not
+    /// be in the world yet, so decide from `state`. Answer only for your own
+    /// blocks: `Some(false)` refuses the spot, `Some(true)` allows it, and
+    /// the block's own rule doesn't run. The level is read-only. Asked on
+    /// every shape update of such a block: keep it short. API @API:can_survive@.
+    #[inline(always)]
+    pub(super) fn native_can_survive(
+        &self,
+        dimension: LevelDimension,
+        pos: BlockPos,
+        state: BlockStateId,
+        survives: &mut Option<bool>,
+    ) {
+        let _ = (dimension, pos, state, survives);
+    }
+
+    /// On an authoritative server, `VegetationBlock.mayPlaceOn` for the
+    /// plant `state` on `ground` at `ground_pos`, before the plant answers
+    /// it: the blocks a mod plant (one whose template is a vanilla plant,
+    /// such as a crop) can stand on. Its template's `canSurvive` asks it, so
+    /// the plant is refused there and pops off when its ground changes to
+    /// one it can't stand on. Answer only for your own blocks. The level is
+    /// read-only. API @API:can_survive@.
+    #[inline(always)]
+    pub(super) fn native_may_place_on(
+        &self,
+        dimension: LevelDimension,
+        state: BlockStateId,
+        ground: BlockStateId,
+        ground_pos: BlockPos,
+        may: &mut Option<bool>,
+    ) {
+        let _ = (dimension, state, ground, ground_pos, may);
+    }
+
     /// An authoritative server's `ServerLevel.tickBlock` is about to run a
     /// due scheduled tick of the block `state` at `pos` (`BlockState.tick`):
     /// the block is still the one the tick was scheduled for. Change the
@@ -427,6 +513,121 @@ impl GameLevel<'_> {
     ) {
         let _ = (ticks, dimension, pos, state, handled);
     }
+
+    /// A block is about to take the state it is placed in
+    /// (`Block.getStateForPlacement(BlockPlaceContext)`), `state` the block's
+    /// own default state. Answer only for your blocks: put the state you want
+    /// in `answer` as `Some(Some(state))` — a state of that block, as vanilla
+    /// sets properties on its own `defaultBlockState` (another block's is
+    /// ignored) — or refuse the placement with `Some(None)`: the block goes
+    /// nowhere and the stack is kept, as vanilla's `null`. Left empty, the
+    /// block's own placement runs. `context` is
+    /// vanilla's `BlockPlaceContext` (the clicked face, the placer's rotation,
+    /// the clicked position, whether the clicked block is being replaced, the
+    /// item in hand) and `fluid` the fluid in the position the block would go
+    /// in, which a waterlogged block reads. Build the state from `state` with
+    /// `native_state_with_property`. It is asked for every placer that goes
+    /// through vanilla's placement (a player's `BlockItem.place`, a
+    /// dispenser's `DirectionalPlaceContext`), and the answer still takes its
+    /// survival and entity obstruction checks. Authoritative servers only.
+    /// @API:placement_state@.
+    #[inline(always)]
+    #[allow(clippy::option_option)]
+    pub(super) fn native_state_for_placement(
+        &self,
+        dimension: LevelDimension,
+        state: BlockStateId,
+        context: &PlacementContext,
+        fluid: FluidState,
+        answer: &mut Option<Option<BlockStateId>>,
+    ) {
+        let _ = (dimension, state, context, fluid, answer);
+    }
+
+    /// A block nothing in Horizon knows a `BonemealableBlock` for is about to
+    /// take bone meal: vanilla's `BonemealableBlock.isValidBonemealTarget`,
+    /// `state` the block's own state at `pos`. Answer `valid` for your own
+    /// blocks: the meal is used up on one as vanilla uses it up (the growth
+    /// particles and the sound follow, whether or not the roll below grows
+    /// it), from a player's `BoneMealItem.useOn`, from a dispenser and, on a
+    /// crop (a villager bonemeals only a `CropBlock`), from a villager. Asked
+    /// on both sides, as vanilla asks it on both, so a client predicts the
+    /// use with your answer: say no where you can only grow on a server
+    /// (`is_client_side`). `Some(false)` refuses the meal, even on a block
+    /// whose template takes it (vanilla's `growCrop` then keeps the meal);
+    /// left `None`, the block keeps the `BonemealableBlock` its template gives
+    /// it, or takes no bone meal.
+    /// @API:bonemeal@.
+    #[inline(always)]
+    pub(super) fn native_is_valid_bonemeal_target(
+        &self,
+        dimension: LevelDimension,
+        pos: BlockPos,
+        state: BlockStateId,
+        valid: &mut Option<bool>,
+    ) {
+        let _ = (dimension, pos, state, valid);
+    }
+
+    /// `BonemealableBlock.isBonemealSuccess` for a block that answered
+    /// `native_is_valid_bonemeal_target`, after it did: set `success` to grow
+    /// it this time. Vanilla draws the level's random here
+    /// (`isBonemealSuccess(Level, RandomSource, BlockPos, BlockState)`), so
+    /// draw from `native_level_random` to keep vanilla's order.
+    /// Authoritative servers only. @API:bonemeal@.
+    #[inline(always)]
+    pub(super) fn native_is_bonemeal_success(
+        &mut self,
+        dimension: LevelDimension,
+        pos: BlockPos,
+        state: BlockStateId,
+        success: &mut bool,
+    ) {
+        let _ = (dimension, pos, state, success);
+    }
+
+    /// `BonemealableBlock.performBonemeal` for a block that answered
+    /// `native_is_valid_bonemeal_target` and whose `native_is_bonemeal_success`
+    /// said yes: grow it here, `state` its state at `pos`. The meal is used up
+    /// either way. Change the block with the level's
+    /// `native_set_block_property`, and schedule with `native_schedule_block_tick`
+    /// (`ticks` is the hook's). Authoritative servers only. @API:bonemeal@.
+    #[inline(always)]
+    pub(super) fn native_perform_bonemeal(
+        &mut self,
+        ticks: &mut Ticks,
+        dimension: LevelDimension,
+        pos: BlockPos,
+        state: BlockStateId,
+    ) {
+        let _ = (ticks, dimension, pos, state);
+    }
+}
+
+/// What dropped the items [`Game::native_loot_drops`] hears.
+#[allow(dead_code)]
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct NativeLootDrops<'a> {
+    /// The block's or mob's own loot table (`minecraft:blocks/stone`, `minecraft:entities/zombie`);
+    /// empty when none rolled: the block or mob has none, the `mob_drops` rule is off, a baby
+    /// animal. A mob's drops may hold more: a charged creeper's head, a fox's mouth item.
+    pub(crate) table: &'a str,
+    /// The level they drop in (`minecraft:overworld`).
+    pub(crate) dimension: &'a str,
+    /// `LootContextParams.ORIGIN`: a broken block's centre, a mob's position.
+    pub(crate) origin: [f64; 3],
+    /// The block broken: its position and state.
+    pub(crate) block: Option<([i32; 3], BlockStateId)>,
+    /// The mob that died: its entity ID and type (`minecraft:zombie`).
+    pub(crate) entity: Option<(u32, &'a str)>,
+    /// The player who broke the block or killed the mob, when known. A mob
+    /// names one only while it remembers the player's hit (100 ticks), so one
+    /// that dies to lava long after names none.
+    pub(crate) player: Option<u128>,
+    /// What broke the block (`LootContextParams.TOOL`).
+    pub(crate) tool: Option<&'a ItemStack>,
+    /// The radius of the explosion that broke the block.
+    pub(crate) explosion: Option<f32>,
 }
 
 /// A depth-tested outline of the client's block selection shape.
@@ -488,6 +689,49 @@ pub struct NativeScreen {
     pub own_labels: bool,
 }
 
+/// The open screen, for the screen hooks (`native_screen_render_post`,
+/// `native_screen_mouse_button_pressed_pre`, `..._released_pre`): what it is,
+/// its menu and title, where its container panel is, how many slots its menu
+/// has, and where the mouse and the frame's partial tick are.
+#[allow(dead_code)]
+#[derive(Clone, Copy, Debug)]
+pub struct NativeScreenView<'a> {
+    /// One id per `Screen` (`Screen::id`): `inventory`, `creative`, `paused`,
+    /// `stats`, `options`, `win`… Stable across releases, so a mod can match
+    /// on it. Every container, station and mod window draws on the inventory
+    /// screen and so reports `inventory`: tell them apart by `menu` and
+    /// `title` (both None on a window the client opened itself) and by
+    /// `slots`.
+    pub id: &'static str,
+    /// The type id of the menu the server opened for this screen
+    /// (`minecraft:generic_9x3`, `minecraft:furnace`, a mod's own id; a mount's
+    /// inventory is `horizon:mount<n>`). None on a screen without one (the
+    /// client's own inventory, creative, the pause menu, stats…) and for a
+    /// menu type the client does not know.
+    pub menu: Option<&'a str>,
+    /// The title the server gave the open menu, if it has one: the component
+    /// itself, not a copy (`.plain()` it to draw, `chars()` for the styles).
+    /// None when the server gave none, on a screen the client opened, and
+    /// while playing.
+    pub title: Option<&'a Text>,
+    /// The screen's container panel in GUI pixels, `[x, y, width, height]`;
+    /// the whole window for a screen with none. The panel is where the game
+    /// draws the window: 176 wide for most, wider for the merchant and the
+    /// beacon, a mod screen's own size for a mod's.
+    pub rect: [f32; 4],
+    /// The slots the open menu has, as `Game::slots` counts them: the player
+    /// inventory's 36, then the container's, the station's, the mod screen's
+    /// or the crafting grid's (a screen with no menu of its own still counts
+    /// the inventory menu's). Counted, not listed.
+    pub slots: usize,
+    /// The pointer in GUI pixels (`Screen.mouseX`, `mouseY`, from the
+    /// window's top left), as `native_cursor` gives it: for hover highlights.
+    pub mouse: [f32; 2],
+    /// This frame's partial tick (`getGameTimeDeltaPartialTick(false)`, 0 to
+    /// 1): what the screen draws animation against.
+    pub partial_tick: f32,
+}
+
 /// The mod screen open on this client: the block it is for, the key its
 /// slots are under, the window id of its menu, and the menu's data slots as
 /// the server sent them.
@@ -899,6 +1143,10 @@ impl Game<'_> {
     pub(super) fn native_minimap(&self, minimap: &mut Option<NativeMinimap>) {
         let _ = minimap;
     }
+    /// Register namespaced NBT component types before content loads.
+    pub(super) fn native_component_types(types: &mut Vec<String>) {
+        let _ = types;
+    }
     /// Options > Mods lists the native mods: push yours.
     pub(super) fn native_mods(&mut self, mods: &mut Vec<NativeMod>) {
         let _ = mods;
@@ -936,6 +1184,25 @@ impl Game<'_> {
     pub(super) fn native_block_entity_ticks(&self, block: &str, ticks: &mut bool) {
         let _ = (block, ticks);
     }
+    /// A `minecraft:post_attack` effect of a mod's own kind, on a mob a
+    /// player's weapon hit: the entry says `enchanted` attacker and `affected`
+    /// victim, its `requirements` passed, and its `effect` names a `type` in a
+    /// namespace outside `minecraft:`. Told the enchantment id, the kind, the
+    /// `effect` JSON, the level and the mob's id (it may have just died). The
+    /// acting player is the one whose weapon carries the enchantment. Each
+    /// such entry is told once a hit, and once for each mob a sweep lands on.
+    /// A hit on a player, and an entry inside `minecraft:all_of`, aren't told
+    /// yet. An unclaimed kind does nothing. API @API:enchant_effect@.
+    pub(super) fn native_enchant_effect(
+        &mut self,
+        enchantment: &str,
+        kind: &str,
+        data: &serde_json::Value,
+        level: u32,
+        victim: u32,
+    ) {
+        let _ = (enchantment, kind, data, level, victim);
+    }
     /// Block `block`'s block entity has item slots (a `WorldlyContainer`):
     /// set `container` when the block is yours. Asked once for each mod
     /// block when the ticking table is built; at most 256 slots, and slot
@@ -978,6 +1245,15 @@ impl Game<'_> {
     pub(super) fn native_block_entity_tick(&mut self, pos: [i32; 3], entity: &mut ModBlockEntity) {
         let _ = (pos, entity);
     }
+    /// A consumable's effect of a mod's own kind: the item's `on_consume_effects`
+    /// entry is of a type in a namespace of its own, and the loader kept it
+    /// for this call. The kind and the JSON the file wrote are here; the acting
+    /// player is the one consuming, and the game's own effects,
+    /// sounds, teleports and drops are open. An unclaimed kind does
+    /// nothing. API @API:consume_effect@.
+    pub(super) fn native_consume_effect(&mut self, kind: &str, data: &serde_json::Value) {
+        let _ = (kind, data);
+    }
     /// What clients get of the block entity at `pos` when its `id` is
     /// yours (`BlockEntity.getUpdateTag`): set `tag` to it, read from
     /// `entity` alone. Asked on the server whenever a chunk holding it is
@@ -992,6 +1268,44 @@ impl Game<'_> {
     ) {
         let _ = (pos, entity, tag);
     }
+    /// Draw the mod block entity at `pos`, of block `block`
+    /// (`mymod:machine`), on this client: once a frame while it is in view
+    /// (vanilla's `BlockEntityRenderer.submit`: within 64 blocks, its chunk
+    /// faded in, and its bounds, `native_block_entity_render_bounding_box`,
+    /// in the frustum), when its `id` is yours. `state` is the block's state
+    /// (`blockEntity.getBlockState()`), `entity` holds what the server sent
+    /// (`native_block_entity_update_tag`). Add geometry with
+    /// `native_draw_quad`, `native_draw_cube` and `native_draw_block` under
+    /// `draw`'s pose stack, which starts at the block's lower north-west
+    /// corner, in blocks; `draw` also has the partial tick, the game time and
+    /// the block's light. API @API:block_entity_submit@.
+    pub(super) fn native_block_entity_submit(
+        &self,
+        pos: [i32; 3],
+        block: &str,
+        state: BlockStateId,
+        entity: &ModBlockEntity,
+        draw: &mut BlockEntityDraw,
+    ) {
+        let _ = (pos, block, state, entity, draw);
+    }
+    /// Where the mod block entity at `pos` draws, for culling
+    /// (NeoForge's `getRenderBoundingBox`): `bounds` is min x, y, z then max
+    /// x, y, z, in blocks from the block's lower north-west corner. It starts
+    /// as the block with a block of margin around it; widen it when your
+    /// `native_block_entity_submit` draws further (a tall shaft, a beam), or
+    /// set an infinite value for one never culled. Asked once a frame for each
+    /// within 64 blocks whose chunk is drawn. API @API:block_entity_submit@.
+    pub(super) fn native_block_entity_render_bounding_box(
+        &self,
+        pos: [i32; 3],
+        block: &str,
+        state: BlockStateId,
+        entity: &ModBlockEntity,
+        bounds: &mut [f32; 6],
+    ) {
+        let _ = (pos, block, state, entity, bounds);
+    }
     /// A menu opens on this client for block `block`, a mod's: set `screen`
     /// when the block is yours, to lay its screen out (`native_screen_draw`
     /// draws it). The server asks it too: a slot it hides is not in the menu
@@ -1015,6 +1329,136 @@ impl Game<'_> {
     ) {
         let _ = (block, data, batch, origin);
     }
+    /// The open screen has drawn itself and its tooltips (`Screen.render`,
+    /// the point of `ScreenEvent.Render.Post`): draw over it with
+    /// `native_fill`, `native_sprite` and `native_text`, `screen.rect` being
+    /// its container panel (or the whole window) and `screen.id` the screen
+    /// it is. Once a frame on the window, never while playing with no screen;
+    /// `&self`, so it reads and draws only. The Win and Options screens call
+    /// it on their own path, after their drawing.
+    ///
+    /// It does not fire on the title screen, which returns before its point,
+    /// nor for the screens drawn over gameplay after it (a server dialog, the
+    /// server pack, link and code-of-conduct prompts, a book, a sign editor):
+    /// those keep `Screen::Playing`, which it skips, and draw over what it
+    /// drew, while vanilla's `ScreenEvent.Render.Post` fires for them.
+    /// API @API:screen_render_post@.
+    pub(super) fn native_screen_render_post(
+        &self,
+        batch: &mut HudBatch,
+        screen: &NativeScreenView<'_>,
+    ) {
+        let _ = (batch, screen);
+    }
+    /// A mouse button went down over the open screen
+    /// (`ScreenEvent.MouseButtonPressed.Pre`, vanilla's
+    /// `Screen.mouseClicked`): `screen` is the screen it is, `screen.mouse`
+    /// where the pointer is (so there is no position of its own), `button` the
+    /// button's GLFW index (0 left, 1 right, 2 middle, 3 back, 4 forward; a
+    /// button past those is the platform's own number, which differs between
+    /// systems) and `modifiers` GLFW's bits (shift 1, control 2,
+    /// alt 4, super 8). Set `canceled` and the press goes no further: no slot,
+    /// no screen button, no drag, no hotbar key, no sort or header button.
+    ///
+    /// It fires before anything the screen does with the press, on the window
+    /// only, and only while a screen of the game's is open (Options and the
+    /// pack list opened from the title screen count, with no player and no
+    /// `menu`). It does not fire on the title screen itself, the connect and
+    /// loading screens, nor for a server
+    /// dialog, the server pack, link and code-of-conduct prompts, a book or a
+    /// sign editor drawn over gameplay, nor while a world loads or saves: the
+    /// click there stays the game's own. A gamepad click or a click the
+    /// keyboard's focus sends is not the mouse and fires nothing.
+    /// API @API:screen_mouse_button@.
+    pub(super) fn native_screen_mouse_button_pressed_pre(
+        &self,
+        screen: &NativeScreenView<'_>,
+        button: i32,
+        modifiers: u32,
+        canceled: &mut bool,
+    ) {
+        let _ = (screen, button, modifiers, canceled);
+    }
+    /// A mouse button went up over the open screen
+    /// (`ScreenEvent.MouseButtonReleased.Pre`, vanilla's
+    /// `Screen.mouseReleased`), with the same `screen`, `button` and
+    /// `modifiers` as `native_screen_mouse_button_pressed_pre` and fired at
+    /// the same point. Set `canceled` and the release goes no further: a
+    /// pressed slot keeps what it took and no drag, slider or scrollbar lets
+    /// go.
+    ///
+    /// Cancel a release only when the press it ends was cancelled too: a
+    /// release the screen took ends the drag or the scroll it began, as it
+    /// does in vanilla, and no guard here un-cancels it. Same screens as the
+    /// press; a press that opened another screen ends on that one.
+    /// API @API:screen_mouse_button@.
+    pub(super) fn native_screen_mouse_button_released_pre(
+        &self,
+        screen: &NativeScreenView<'_>,
+        button: i32,
+        modifiers: u32,
+        canceled: &mut bool,
+    ) {
+        let _ = (screen, button, modifiers, canceled);
+    }
+    /// The open screen as a native mod sees it (`NativeScreenView`): its id,
+    /// the open menu's type and title, its slot count, and its panel's
+    /// rectangle, with the mouse and the partial tick. `screen` is the screen
+    /// drawn this frame, which `NativeScreenView.id` comes from. Borrowed:
+    /// nothing is copied per frame.
+    pub(super) fn screen_view(&self, batch: &HudBatch, screen: Screen) -> NativeScreenView<'_> {
+        NativeScreenView {
+            id: screen.id(),
+            menu: self.remote_menu_type().filter(|m| !m.is_empty()),
+            title: self.remote.as_ref().and_then(|r| r.menu_title.as_ref()),
+            rect: self.screen_rect(batch, screen),
+            slots: self.slot_count(),
+            mouse: self.native_cursor(),
+            partial_tick: self.clock.fraction() as f32,
+        }
+    }
+    /// The open screen's container panel in GUI pixels (`screen`'s, the one
+    /// this frame draws), or the whole window for a screen with none
+    /// (`NativeScreenView.rect`).
+    pub(super) fn screen_rect(&self, batch: &HudBatch, screen: Screen) -> [f32; 4] {
+        if screen != Screen::Inventory && screen != Screen::Creative {
+            return [0.0, 0.0, batch.width, batch.height];
+        }
+        // The window the game itself draws (`container_image`): the merchant
+        // and the beacon are wider and shifted, creative is its own size.
+        let image = self.container_image(batch);
+        [
+            image.left as f32,
+            image.top as f32,
+            image.width as f32,
+            image.height as f32,
+        ]
+    }
+    /// A screen the native mods' input hooks are for is open: the window has a
+    /// renderer, `Screen::Playing` is behind it (so not the title screen, nor a
+    /// book, a sign editor, a server dialog or a prompt drawn over gameplay)
+    /// and no connect or world load is in progress. The one gate they all ask
+    /// before they fire.
+    pub(super) fn screen_hooks_open(&self) -> bool {
+        self.renderer.is_some()
+            && self.screen != Screen::Playing
+            && !self.screen_over_playing()
+            && !self.remote_loading()
+    }
+    /// The open screen as an input hook sees it (`NativeScreenView`), or None
+    /// when `screen_hooks_open` says no screen is. `screen.mouse` is the
+    /// pointer the hook's event is at, so a hook takes no position, and
+    /// `partial_tick` is the clock's fraction at this event, not a frame's.
+    /// The `HudBatch` built here is only what `screen.rect` needs: the
+    /// window's GUI scale, no allocation.
+    pub(super) fn screen_view_now(&self) -> Option<NativeScreenView<'_>> {
+        if !self.screen_hooks_open() {
+            return None;
+        }
+        let renderer = self.renderer.as_ref()?;
+        let batch = HudBatch::new([renderer.config.width, renderer.config.height]);
+        Some(self.screen_view(&batch, self.screen))
+    }
     /// A left or right (`right`) press at `at` (GUI pixels from the screen's
     /// top left, so outside it too) on block `block`'s screen, a mod's, over
     /// no slot: set `button` to a menu button id when it is on one of yours.
@@ -1120,11 +1564,30 @@ impl Game<'_> {
     pub(super) fn native_tooltip(&self, stack: &ItemStack, lines: &mut Vec<(Text, u32)>) {
         let _ = (stack, lines);
     }
+    /// Client-side image component for this stack's tooltip. Answer its width/height
+    /// in GUI pixels; finite positive dimensions reserve space after text and any
+    /// vanilla bundle component. None keeps the vanilla tooltip unchanged.
+    pub(super) fn native_tooltip_component(&self, stack: &ItemStack, size: &mut Option<[f32; 2]>) {
+        let _ = (stack, size);
+    }
+    /// Render the measured component at origin, inside the tooltip background.
+    /// Stack is the component's data. Use native_sprite/native_fill/native_text;
+    /// size is the measurement returned by native_tooltip_component this frame.
+    pub(super) fn native_tooltip_component_draw(
+        &self,
+        stack: &ItemStack,
+        batch: &mut HudBatch,
+        origin: [f32; 2],
+        size: [f32; 2],
+    ) {
+        let _ = (stack, batch, origin, size);
+    }
+
     /// The small bar `GuiGraphicsExtractor.itemDecorations` draws under an
     /// item, wherever the game shows one: `bar` arrives holding vanilla's value
     /// (the damage bar, or a bundle's fullness already applied) and may be
     /// replaced (width `0..=13`, colour `rgb`) or set to `None` to hide it.
-    /// Asked each frame a stack is drawn. Client-side. @API:item_bar@.
+    /// Asked each frame a stack is drawn. Client-side. 60.
     pub(super) fn native_item_bar(&self, stack: &ItemStack, bar: &mut Option<(i32, u32)>) {
         let _ = (stack, bar);
     }
@@ -1144,6 +1607,25 @@ impl Game<'_> {
     ) {
         let _ = (stack, pos, face, claimed);
     }
+    /// `DispenserBlock.getDispenseMethod`: choose a behaviour for any item,
+    /// including vanilla items, on the authoritative server (not droppers).
+    /// Leave answer None for vanilla. Otherwise answer `(remainder, event)`:
+    /// a remainder of None empties the slot, `Some(stack)` replaces it (the hook
+    /// owns consumption: no extra item is removed afterwards). `event` is the
+    /// level event the dispenser plays with its smoke: 1000 the click, 1001 the
+    /// fail sound (`OptionalDispenseItemBehavior` without success), or 0 for
+    /// nothing at all (`DispenseItemBehavior.NOOP`). To drop one normally,
+    /// answer `(native_dispense_default(..), 1000)`. API @API:dispenser_behaviour@.
+    pub(super) fn native_dispense_item(
+        &mut self,
+        dimension: &str,
+        pos: [i32; 3],
+        facing: horizon_core::geometry::Direction,
+        stack: &ItemStack,
+        answer: &mut Option<super::dispenser::NativeDispensed>,
+    ) {
+        let _ = (dimension, pos, facing, stack, answer);
+    }
     /// A player uses `stack` (right click) with `self.hand`: in the air, or
     /// on a block once `native_use_item_on` let it through, where `Item.use`
     /// starts. Each click reaches it once. Set `claimed` to take the use: the
@@ -1348,6 +1830,29 @@ impl Game<'_> {
     pub(super) fn native_mob_killed(&mut self, player: u128, entity: u32, kind: &str) {
         let _ = (player, entity, kind);
     }
+    /// A block broke or a mob died, and `drops` are the items about to drop, in
+    /// the order they drop: what the loot tables rolled (after
+    /// `native_loot_table_load`'s changes), and for a mob what it wore, held or
+    /// carried (a fox's mouth item, an allay's, piglin's or horse's inventory),
+    /// but not an enderman's carried block or a copper golem's preserved
+    /// equipment, which drop after. A charged creeper's head and a fox's mouth
+    /// item come before the mob's own table. A block's stacks get its block
+    /// entity's data (a shulker box's items) after this. Add, change or take out
+    /// stacks; empty ones don't drop (NeoForge's global loot modifiers, Fabric's
+    /// `LootTableEvents.MODIFY_DROPS`); `context` says what dropped them and
+    /// how, and it is called even when `drops` is empty. It hears blocks that a
+    /// player, an explosion or a mob breaks, not other breaks (leaves decaying,
+    /// a torch losing its wall, a piston, `/setblock ... destroy`), nor a
+    /// creative break or a tool that can't harvest the block, nor experience.
+    /// Server-side, for every player. API
+    /// @API:loot_tables@.
+    pub(super) fn native_loot_drops(
+        &mut self,
+        context: &NativeLootDrops<'_>,
+        drops: &mut Vec<ItemStack>,
+    ) {
+        let _ = (context, drops);
+    }
     /// `player` threw `count` of `item` (`Player.drop`: the drop key, a
     /// menu's throw...), not what scatters when they die. It only hears.
     /// Server-side. API 40.
@@ -1476,6 +1981,76 @@ impl Game<'_> {
     ) {
         let _ = (entity, kind, damage_type, causing, direct, amount, canceled);
     }
+
+    /// `Block.stepOn` for a mod block, on its authoritative server level.
+    /// No self: the simulation owns the entity during this callback.
+    pub(super) fn native_block_step_on(
+        dimension: &str,
+        entity: i32,
+        kind: &str,
+        state: BlockStateId,
+        position: [i32; 3],
+    ) {
+        let _ = (dimension, entity, kind, state, position);
+    }
+    /// `Block.entityInside` for each mod block touched along the entity's movement.
+    /// Repeated sweep hits in one contact pass are suppressed; idle overlap still fires.
+    pub(super) fn native_block_entity_inside(
+        dimension: &str,
+        entity: i32,
+        kind: &str,
+        state: BlockStateId,
+        position: [i32; 3],
+    ) {
+        let _ = (dimension, entity, kind, state, position);
+    }
+    /// `Block.fallOn` for a mod block. Change calculated damage before generic fall sounds
+    /// and hurt handling; zero prevents both. Creative and fall-immune entities
+    /// notify with zero damage and retain their immunity. Server-side only.
+    pub(super) fn native_block_fall_on(
+        dimension: &str,
+        entity: i32,
+        kind: &str,
+        state: BlockStateId,
+        position: [i32; 3],
+        distance: f64,
+        damage: &mut f32,
+    ) {
+        let _ = (dimension, entity, kind, state, position, distance, damage);
+    }
+}
+
+pub(super) fn block_contact(
+    dimension: &str,
+    event: horizon_client::block_contact::Event<'_>,
+    damage: &mut f32,
+) {
+    use horizon_client::block_contact::Event;
+    match event {
+        Event::StepOn(c) => Game::native_block_step_on(
+            dimension,
+            c.entity,
+            c.kind,
+            c.state,
+            [c.position.x, c.position.y, c.position.z],
+        ),
+        Event::Inside(c) => Game::native_block_entity_inside(
+            dimension,
+            c.entity,
+            c.kind,
+            c.state,
+            [c.position.x, c.position.y, c.position.z],
+        ),
+        Event::FallOn(c, distance) => Game::native_block_fall_on(
+            dimension,
+            c.entity,
+            c.kind,
+            c.state,
+            [c.position.x, c.position.y, c.position.z],
+            distance,
+            damage,
+        ),
+    }
 }
 
 /// `native_living_incoming_damage` for the damage code (`health::HURT_SERVER`): whether
@@ -1554,7 +2129,7 @@ impl GameLevel<'_> {
     /// mod's, `mymod:machine_hum`) is sent by name, as vanilla sends a sound
     /// that isn't in its registry (`Holder.direct`, a variable range): players
     /// hear it if their resources define it (`assets/mymod/sounds.json`, a
-    /// content mod's). API @API:mod_sounds@.
+    /// content mod's). API 61.
     pub(super) fn native_play_sound(
         &mut self,
         sound: &str,
@@ -1712,6 +2287,31 @@ impl GameLevel<'_> {
         let time = self.game_time();
         ticks.schedule_fluid(time, at, kind, delay) != ScheduleResult::MissingChunk
     }
+    /// The state `state` with its property `key` set to `value`, as a mod block
+    /// builds the state it is placed in: `native_state_with_property(cable,
+    /// "facing", "east")` (`BlockState.setValue`). A block's own declared
+    /// properties (`state_properties` in its block file) are set the same way.
+    /// `state` itself when the property already has that value; None when the
+    /// block has no such property, or the property no such value. API
+    /// @API:placement_state@.
+    pub(super) fn native_state_with_property(
+        &self,
+        state: BlockStateId,
+        key: &str,
+        value: &str,
+    ) -> Option<BlockStateId> {
+        with_property(self.registry, state, key, value)
+    }
+    /// This level's own random (vanilla's `Level.random`): the stream
+    /// `native_level_random(dimension)` hands a server hook, for a world hook
+    /// that draws as a vanilla block does (`isBonemealSuccess`), so the mod's
+    /// draws shift vanilla's as a Java mod's would. `None` where this level
+    /// isn't the server's copy. API @API:bonemeal@.
+    pub(super) fn native_level_random(
+        &mut self,
+    ) -> Option<&mut horizon_core::random::LegacyRandom> {
+        self.native_authoritative.then_some(&mut self.world.random)
+    }
 }
 
 /// Helpers for native mods, kept as stable as the hook points.
@@ -1920,6 +2520,26 @@ impl Game<'_> {
         let at = BlockPos::new(pos[0], pos[1], pos[2]);
         self.with_level(|b, level, ticks| b.set_block(level, ticks, at, id, flags))
     }
+    /// The block at `pos` changed its comparator output
+    /// (`native_analog_output`) without changing its state: the comparators
+    /// beside it, or behind a conductor there, read it again
+    /// (`Level.updateNeighbourForOutputSignal`). Acts on the level in place:
+    /// false (and nothing happens) when `dimension` is another, or this
+    /// window isn't a server. API @API:analog_output@.
+    pub(super) fn native_update_output_neighbors(
+        &mut self,
+        dimension: &str,
+        pos: [i32; 3],
+    ) -> bool {
+        if (self.serving.is_none() && self.options.dedicated.is_none())
+            || dimension != self.dim.id()
+        {
+            return false;
+        }
+        let at = BlockPos::new(pos[0], pos[1], pos[2]);
+        self.with_level(|b, level, ticks| b.update_neighbour_for_output_signal(level, ticks, at));
+        true
+    }
     /// The block at `pos` changed the signal it gives: its neighbours, and
     /// theirs (a block it powers passes the signal on), read it again, as
     /// around a lever (`Level.updateNeighborsAt`). Call it when the answer
@@ -2354,6 +2974,34 @@ impl Game<'_> {
     pub(super) fn native_acting_id(&mut self) -> u128 {
         horizon_client::lan::playerdata::ints_uuid(self.acting_player_uuid())
     }
+    /// The mods' say on a broken block's drops (`native_loot_drops`).
+    pub(super) fn native_block_drops(
+        &mut self,
+        pos: [i32; 3],
+        state: BlockStateId,
+        player: Option<u128>,
+        tool: Option<&ItemStack>,
+        explosion: Option<f32>,
+        drops: &mut Vec<ItemStack>,
+    ) {
+        let items = match &self.world_tables {
+            Some(tables) => &tables.items,
+            None => self.res.items(),
+        };
+        let table = items.block_loot_table(self.pack.assets.registry, state);
+        let context = NativeLootDrops {
+            table: table.as_deref().unwrap_or_default(),
+            dimension: self.dim.id(),
+            origin: pos.map(|c| f64::from(c) + 0.5),
+            block: Some((pos, state)),
+            entity: None,
+            player,
+            tool,
+            explosion,
+        };
+        self.native_loot_drops(&context, drops);
+        drops.retain(|stack| stack.count > 0 && &*stack.item != "minecraft:air");
+    }
     /// Whether a native mod keeps the acting player from taking `stack`.
     pub(super) fn native_pickup_refused(&mut self, stack: &ItemStack) -> bool {
         let player = self.native_acting_id();
@@ -2768,6 +3416,12 @@ impl Game<'_> {
                 .collect(),
         )
     }
+    /// How many of those slots `native_screen_slots` lists, without building
+    /// it (`Game::slot_count` asks every frame).
+    pub(super) fn native_screen_slot_count(&self) -> Option<usize> {
+        let s = self.shown_native_screen()?;
+        Some(s.screen.slots.iter().filter(|p| p.is_some()).count())
+    }
     /// The first row of the player's inventory on the open mod screen.
     pub(super) fn native_screen_inventory_y(&self) -> Option<f32> {
         self.shown_native_screen().map(|s| s.screen.inventory_y)
@@ -3244,6 +3898,37 @@ mod tests {
         assert_eq!(super::property_change(&registry, age0, "age", "9"), None);
         assert_eq!(super::property_change(&registry, age0, "lit", "true"), None);
     }
+
+    /// The state a mod block is placed in is built from its own default state
+    /// and one of its properties, its declared ones (`state_properties` in its
+    /// block file) included, and keeps the properties it already had.
+    #[test]
+    fn a_placement_state_is_built_from_a_blocks_own_properties() {
+        let facts = br#"{"defaults":{"minecraft:air":0,"test:pipe":1},"states":[
+            ["air",true,false,"","minecraft:air"],
+            ["north_gas",false,false,"",{"id":"test:pipe","properties":{"carries":"gas","facing":"north"}}],
+            ["east_gas",false,false,"",{"id":"test:pipe","properties":{"carries":"gas","facing":"east"}}],
+            ["north_items",false,false,"",{"id":"test:pipe","properties":{"carries":"items","facing":"north"}}],
+            ["east_items",false,false,"",{"id":"test:pipe","properties":{"carries":"items","facing":"east"}}]
+        ]}"#;
+        let registry = horizon_world::registry::BlockRegistry::from_facts_json(&facts[..]).unwrap();
+        use horizon_world::registry::BlockStateId;
+        let (north_gas, east_gas, east_items) = (BlockStateId(1), BlockStateId(2), BlockStateId(4));
+        // The declared property changes, and `carries` stays as it was.
+        assert_eq!(
+            super::with_property(&registry, north_gas, "facing", "east"),
+            Some(east_gas)
+        );
+        assert_eq!(
+            super::with_property(&registry, east_gas, "carries", "items"),
+            Some(east_items)
+        );
+        // A value the property does not have builds nothing.
+        assert_eq!(
+            super::with_property(&registry, east_gas, "facing", "up"),
+            None
+        );
+    }
     /// Both property setters return false for a write that changes nothing:
     /// each goes through `property_change`, none returns true on its own.
     #[test]
@@ -3293,6 +3978,27 @@ mod tests {
         }
     }
 
+    #[test]
+    fn loot_table_load_stays_hookable() {
+        let source = include_str!("../../../horizon-world/src/loot.rs");
+        // From its doc comment's last line, so an attribute above it counts.
+        let hook = source.find("pub fn native_loot_table_load(").unwrap();
+        let start = source[..hook].rfind("///").unwrap();
+        let body = &source[start..start + source[start..].find("\n}\n").unwrap()];
+        for line in body.lines() {
+            assert!(
+                !line.contains("cfg"),
+                "a cfg in the loot hook point: {line}"
+            );
+            for mac in ["!(", "![", "! {", "!{"] {
+                assert!(
+                    !line.contains(mac),
+                    "a macro in the loot hook point: {line}"
+                );
+            }
+        }
+    }
+
     #[test]
     fn lifecycle_source_stays_hookable() {
         let source = include_str!("native_lifecycle.rs");
@@ -3351,12 +4057,21 @@ mod tests {
                     .next()
             })
             .collect();
-        // The renderer's hook points (`horizon_client_render::gfx::native_render`).
-        let render_hooks: BTreeSet<_> =
-            include_str!("../../../horizon-client-render/src/gfx/native_render.rs")
+        // Hook points that are free functions in other crates.
+        let free_hooks = |source: &'static str| -> BTreeSet<&'static str> {
+            source
                 .lines()
                 .filter_map(|line| line.strip_prefix("pub fn native_")?.split('(').next())
-                .collect();
+                .collect()
+        };
+        // The renderer's (`horizon_client_render::gfx::native_render`).
+        let render_hooks = free_hooks(include_str!(
+            "../../../horizon-client-render/src/gfx/native_render.rs"
+        ));
+        // Items' default components (`horizon_world::item_defaults`).
+        let item_hooks = free_hooks(include_str!("../../../horizon-world/src/item_defaults.rs"));
+        // The loot tables' hook point (`horizon_world::loot`).
+        let loot_hooks = free_hooks(include_str!("../../../horizon-world/src/loot.rs"));
         let declared: BTreeSet<_> = section
             .lines()
             .chain(level_section.lines())
@@ -3367,6 +4082,8 @@ mod tests {
                     .next()
             })
             .chain(render_hooks.iter().copied())
+            .chain(item_hooks.iter().copied())
+            .chain(loot_hooks.iter().copied())
             .collect();
         let mut names = BTreeSet::new();
         let mut contracts = BTreeSet::new();
@@ -3380,6 +4097,10 @@ mod tests {
             names.insert(name);
             let target = if render_hooks.contains(name) {
                 format!("horizon_client_render::gfx::native_render::native_{name}")
+            } else if item_hooks.contains(name) {
+                format!("horizon_world::item_defaults::native_{name}")
+            } else if loot_hooks.contains(name) {
+                format!("horizon_world::loot::native_{name}")
             } else if level_hooks.contains(name) {
                 format!("horizon_client::game::native_hooks::GameLevel<'_>::native_{name}")
             } else {

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

@@ -129,9 +129,14 @@ impl Game<'_> {
         items: Vec<Option<ItemStack>>,
     ) -> Option<i32> {
         let conn = self.native_conn(uuid)?;
-        let host = self.lan.as_mut()?;
-        host.hub
-            .open_native_menu(conn, rows, component_nbt(&title.component()), items)
+        let mut host = self.lan.take()?;
+        // ServerPlayer.openMenu closes the menu that was open.
+        self.guest_close_all(&mut host, conn);
+        let window =
+            host.hub
+                .open_native_menu(conn, rows, component_nbt(&title.component()), items);
+        self.lan = Some(host);
+        window
     }
     /// Replaces what the player's open native menu shows; sent with the
     /// tick's container sync.

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

@@ -403,6 +403,37 @@ impl Game<'_> {
         }
         true
     }
+    /// Shows `nickname` in place of that player's name in chat (their
+    /// messages, `/me`, `/msg`) and in the Tab list; None shows their name
+    /// again. Hovering the shown name gives the real one, which stays in the
+    /// log, commands, selectors and the server's events. Kept until a mod
+    /// sets it again or the server stops (also if they leave and come back).
+    /// Plain text: the mod checks it (`native_text_allowed`, its length,
+    /// other players' names). Only where no player's state is swapped in,
+    /// as `native_run_command`; false there and when they aren't on. API
+    /// 62.
+    pub(super) fn native_set_nickname(&mut self, uuid: u128, nickname: Option<&str>) -> bool {
+        let Some(host) = &mut self.lan else {
+            return false;
+        };
+        if !host.hub.guests.iter().any(|g| g.placed && g.uuid == uuid) {
+            return false;
+        }
+        host.hub.set_nickname(uuid, nickname.map(str::to_owned));
+        true
+    }
+    /// Whether the server's chat filter (`server.toml` `[chat_filter]`)
+    /// lets `text` through: true without a filter, None inside a player's
+    /// hook (where the server is out of reach). API 62.
+    pub(super) fn native_text_allowed(&self, text: &str) -> Option<bool> {
+        let host = self.lan.as_ref()?;
+        Some(
+            host.hub
+                .chat_filter
+                .as_ref()
+                .is_none_or(|g| !g.filter.matches(text)),
+        )
+    }
     /// A system line in every player's chat and the server's log.
     pub(super) fn native_broadcast(&self, line: Text) {
         let plain = line.plain();

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

@@ -1,6 +1,7 @@
 //! Horizon's own shader packs in the game (docs/shaders.md): the pick in `shaderpacks/` (a
 //! folder with `horizon-shaders.toml`, or a `.hshader`; `game/shader_packs.rs`) runs once it
-//! passes `horizon_shader_api::check`. The pack is looked at twice a second: a saved file is checked and the pack rebuilt, and a
+//! passes `horizon_shader_api::check`. The pack is looked at twice a second: a saved file (or
+//! saved option values) is checked and the pack rebuilt, and a
 //! pack that fails is refused with its problems in the chat while the last good one keeps
 //! drawing.
 
@@ -57,12 +58,10 @@ impl Game<'_> {
         let result = Pack::read(path).map_err(|e| vec![e]).and_then(|pack| {
             let report = check(&pack)
                 .map_err(|p| p.iter().map(ToString::to_string).collect::<Vec<String>>())?;
-            let constants = pack
-                .manifest
-                .options
-                .iter()
-                .map(|o| (o.id.clone(), o.kind.default_constant()))
-                .collect();
+            // The player's values (the pack's Shader Options page), else the defaults.
+            let options = &pack.manifest.options;
+            let values = horizon_client::shader_pack_list::load_values(path, options);
+            let constants = options.iter().map(|o| o.id.clone()).zip(values).collect();
             let sprites = self.pack.render.sprite_layers.iter();
             let tags = pack
                 .manifest
@@ -97,7 +96,8 @@ impl Game<'_> {
     }
 }
 
-/// A hash of the pack's file names, sizes and modification times (`None` when unreadable).
+/// A hash of the names, sizes and modification times of the pack's files and of its saved
+/// option values (`None` when the pack is unreadable).
 fn fingerprint(path: &Path) -> Option<u64> {
     fn walk(path: &Path, hasher: &mut std::hash::DefaultHasher) -> Option<()> {
         let meta = std::fs::metadata(path).ok()?;
@@ -120,5 +120,8 @@ fn fingerprint(path: &Path) -> Option<u64> {
     }
     let mut hasher = std::hash::DefaultHasher::new();
     walk(path, &mut hasher)?;
+    // The player's option values, when there are any.
+    let values = horizon_client::shader_pack_list::values_path(path);
+    let _ = walk(&values, &mut hasher);
     Some(hasher.finish())
 }

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

@@ -1,14 +1,21 @@
-//! Read-only block queries for a native server tick hook.
+//! Read-only block and tag queries for native server hooks.
 use super::{Dim, Game, native_lifecycle::NativeLifecycleContext};
-use horizon_client::{items::ItemStack, world::World};
+use horizon_client::{
+    items::{ItemStack, Items},
+    world::World,
+};
 use horizon_world::{chunk::BlockState, registry::BlockRegistry};
 
-/// Why a server block cannot be read.
+/// Why a server block or tag cannot be read.
 #[allow(dead_code)]
 #[derive(Debug, PartialEq, Eq)]
 pub(super) enum NativeBlockReadError {
     /// The context is stale or the call is outside its server tick hook.
     InactiveContext,
+    /// Tag queries require an authoritative server.
+    NotServer,
+    /// The world has not loaded its tag tables yet.
+    TagsUnavailable,
     /// The dimension is unknown or is not currently open on the server.
     UnavailableDimension,
     OutOfBounds,
@@ -17,7 +24,18 @@ pub(super) enum NativeBlockReadError {
 }
 
 impl Game<'_> {
-    /// Test a block state's name against the world's merged block tags. API 28.
+    /// The world lock is installed after its tag tables are built.
+    fn native_tag_items(&self) -> Result<&Items, NativeBlockReadError> {
+        if self.options.execution_role.is_client() {
+            return Err(NativeBlockReadError::NotServer);
+        }
+        if self.session_lock.is_none() {
+            return Err(NativeBlockReadError::TagsUnavailable);
+        }
+        Ok(self.items())
+    }
+
+    /// Test a block state's name in an active server tick hook. API 28.
     #[allow(dead_code)]
     pub(super) fn native_block_in_tag(
         &self,
@@ -28,10 +46,10 @@ impl Game<'_> {
         if !self.native_lifecycle.permits_read(context) {
             return Err(NativeBlockReadError::InactiveContext);
         }
-        Ok(self.items().block_in_tag(tag, &state.name))
+        self.native_server_block_in_tag(state, tag)
     }
 
-    /// Test an item stack against the world's merged item tags. API 28.
+    /// Test an item stack in an active server tick hook. API 28.
     #[allow(dead_code)]
     pub(super) fn native_item_in_tag(
         &self,
@@ -42,12 +60,33 @@ impl Game<'_> {
         if !self.native_lifecycle.permits_read(context) {
             return Err(NativeBlockReadError::InactiveContext);
         }
+        self.native_server_item_in_tag(stack, tag)
+    }
+
+    /// Test a block state's name against the server's merged block tags.
+    #[allow(dead_code)]
+    pub(super) fn native_server_block_in_tag(
+        &self,
+        state: &BlockState,
+        tag: &str,
+    ) -> Result<bool, NativeBlockReadError> {
+        Ok(self.native_tag_items()?.block_in_tag(tag, &state.name))
+    }
+
+    /// Test an item stack against the server's merged item tags.
+    #[allow(dead_code)]
+    pub(super) fn native_server_item_in_tag(
+        &self,
+        stack: &ItemStack,
+        tag: &str,
+    ) -> Result<bool, NativeBlockReadError> {
+        let items = self.native_tag_items()?;
         let item = if stack.count == 0 {
             "minecraft:air"
         } else {
             &stack.item
         };
-        Ok(self.items().item_in_tag(tag, item))
+        Ok(items.item_in_tag(tag, item))
     }
 
     /// Read a loaded block in a server tick hook, without loading a chunk.

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

@@ -614,6 +614,10 @@ impl<'a> Game<'a> {
         let Some(terrain) = self.end.locator() else {
             return;
         };
+        // `FlatLevelSource.spawnOriginalMobs` is empty: a superflat world places no packs.
+        if terrain.is_flat() {
+            return;
+        }
         let mut region = terrain.region_random(cx, cz);
         let any = region.as_any();
         let added = if let Some(r) = any.downcast_mut::<LegacyRandom>() {