Merge pull request #1162 from ludovic111/feat/dynamic-lights

🤖 Agent: merged after integration wave 1 on the desktop (main e730dc14 + #1108 #1114 #1131 #1157 #1158 #1162 = ae482a72): fmt, clippy -D warnings, workspace tests (one port-race flake in horizon-server panel, passes on rerun), release build, tools/parity.py --changed origin/main 299/302 then the 3 rerun: save_roundtrip pass, world_reopen pass x2 (one early-count flake), dedicated_server = known flake also failing on main (fixed by #1183/#1184).

crates/horizon-client/src/dynamic_light.rs

@@ -0,0 +1,133 @@
+//! Horizon Extras' dynamic lights (docs/extras.md): a torch, lantern or other light source held by
+//! a player or mob, dropped as an item, or an entity on fire lights the blocks and entities
+//! around it. Not in vanilla; off by default.
+//!
+//! Client-only and at render time: the light engine, chunk meshes and saves never see it. Each
+//! frame the game picks the [`MAX`] sources nearest the camera; terrain.wgsl and entity.wgsl
+//! raise a vertex's block light to `level - distance` (one level per block, as block light falls
+//! off) when that is brighter. Off, the list is empty and the shaders skip the loop.
+use crate::blocks::BlockFacts;
+use glam::DVec3;
+use horizon_world::registry::BlockRegistry;
+use std::collections::HashMap;
+
+/// Lights the shaders read: `Globals.dynamic_lights` in gfx.rs, terrain.wgsl and entity.wgsl.
+pub const MAX: usize = 16;
+/// What an entity on fire gives off, as a lit campfire or fire block does.
+pub const BURNING: u8 = 15;
+/// Sources farther than this from the camera light nothing it can see well.
+const REACH: f64 = 96.0;
+
+/// How brightly each item glows when held or dropped.
+#[derive(Debug, Default)]
+pub struct Luminance(HashMap<String, u8>);
+
+impl Luminance {
+    /// A block item glows like its block's default state (`getLightEmission`): torches 14,
+    /// lanterns and glowstone 15, a lit redstone torch 7; a furnace's item, unlit, not at all.
+    pub fn new(facts: &BlockFacts, registry: &BlockRegistry) -> Self {
+        let mut map = HashMap::new();
+        for (id, state) in facts.states.iter().enumerate() {
+            if state.emission == 0 || *state.item != *state.name {
+                continue;
+            }
+            if registry.default_state(&state.name).map(|d| d.0 as usize) == Some(id) {
+                map.insert(state.item.to_string(), state.emission);
+            }
+        }
+        // A bucket of lava glows as lava does.
+        map.insert("minecraft:lava_bucket".into(), 15);
+        Self(map)
+    }
+
+    pub fn of(&self, item: &str) -> u8 {
+        self.0.get(item).copied().unwrap_or(0)
+    }
+
+    #[cfg(test)]
+    fn from_pairs(pairs: &[(&str, u8)]) -> Self {
+        Self(pairs.iter().map(|(k, v)| (k.to_string(), *v)).collect())
+    }
+}
+
+/// One light this frame: where it is (world space) and its level, 1 to 15.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Source {
+    pub at: DVec3,
+    pub level: u8,
+}
+
+/// The [`MAX`] sources nearest `camera` within reach, as the shaders read them: camera-relative
+/// position and level. Overwrites `out`.
+pub fn select(sources: &[Source], camera: DVec3, out: &mut Vec<[f32; 4]>) {
+    out.clear();
+    let key = |s: &Source| s.at.distance_squared(camera);
+    let mut near: Vec<&Source> = sources
+        .iter()
+        .filter(|s| s.level > 0 && key(s) <= REACH * REACH)
+        .collect();
+    near.sort_by(|a, b| key(a).total_cmp(&key(b)));
+    out.extend(near.into_iter().take(MAX).map(|s| {
+        let p = (s.at - camera).as_vec3();
+        [p.x, p.y, p.z, f32::from(s.level.min(15))]
+    }));
+}
+
+/// The block light a vertex at `pos` (camera-relative) gets from `lights`, 0 to 15: the WGSL
+/// `dynamic_block_light` in Rust, for tests.
+pub fn level_at(pos: [f32; 3], lights: &[[f32; 4]]) -> f32 {
+    lights.iter().fold(0.0f32, |level, l| {
+        let d =
+            ((pos[0] - l[0]).powi(2) + (pos[1] - l[1]).powi(2) + (pos[2] - l[2]).powi(2)).sqrt();
+        level.max(l[3] - d)
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn nearest_sources_win() {
+        let camera = DVec3::new(100.0, 64.0, 100.0);
+        let mut sources: Vec<Source> = (0..40)
+            .map(|i| Source {
+                at: camera + DVec3::new(f64::from(i), 0.0, 0.0),
+                level: 14,
+            })
+            .collect();
+        sources.push(Source {
+            at: camera + DVec3::new(0.5, 0.0, 0.0),
+            level: 0,
+        });
+        sources.push(Source {
+            at: camera + DVec3::new(0.0, 0.0, 200.0),
+            level: 15,
+        });
+        let mut out = Vec::new();
+        select(&sources, camera, &mut out);
+        assert_eq!(out.len(), MAX);
+        assert_eq!(out[0], [0.0, 0.0, 0.0, 14.0]);
+        assert_eq!(out[MAX - 1][0], (MAX - 1) as f32);
+        select(&[], camera, &mut out);
+        assert!(out.is_empty());
+    }
+
+    #[test]
+    fn light_falls_off_a_level_per_block() {
+        let torch = [[0.0, 0.0, 0.0, 14.0]];
+        assert_eq!(level_at([0.0, 0.0, 0.0], &torch), 14.0);
+        assert_eq!(level_at([3.0, 4.0, 0.0], &torch), 9.0);
+        assert_eq!(level_at([20.0, 0.0, 0.0], &torch), 0.0);
+        let two = [[0.0, 0.0, 0.0, 14.0], [10.0, 0.0, 0.0, 15.0]];
+        assert_eq!(level_at([8.0, 0.0, 0.0], &two), 13.0);
+        assert_eq!(level_at([0.0; 3], &[]), 0.0);
+    }
+
+    #[test]
+    fn item_luminance() {
+        let l = Luminance::from_pairs(&[("minecraft:torch", 14)]);
+        assert_eq!(l.of("minecraft:torch"), 14);
+        assert_eq!(l.of("minecraft:stone"), 0);
+    }
+}

crates/horizon-client/src/entity.wgsl

@@ -14,11 +14,13 @@ struct Globals {
     // Atlas rects (u0, v0, width, height) of end_sky.png and end_portal.png.
     end_portal_sprites: array<vec4<f32>, 2>,
     // x: vanilla's GameTime ((game time % 24000 + partial tick) / 24000)
-    // y: Nether cardinal lighting.
+    // y: Nether cardinal lighting, z: how many dynamic_lights are set.
     time: vec4<f32>,
     crumbling_sprite: vec4<f32>,
     // Selection outline parameters (read by terrain.wgsl).
     outline_params: vec4<f32>,
+    // Horizon Extras' dynamic lights: camera-relative position and level (dynamic_light.rs).
+    dynamic_lights: array<vec4<f32>, 16>,
 }
 @group(0) @binding(0) var<uniform> globals: Globals;
 @group(0) @binding(1) var atlas: texture_2d<f32>;
@@ -58,13 +60,25 @@ fn overlay_texel(overlay: u32) -> vec4<f32> {
     if overlay >= 16u && overlay < 32u { return vec4(1.0, 1.0, 1.0, WHITE_OVERLAY_ALPHA[overlay - 16u]); }
     return vec4(1.0);
 }
+// Horizon Extras' dynamic lights (dynamic_light.rs): the block light, in the vertex's units
+// (16 per level), a vertex at camera-relative `pos` gets from the frame's light sources, one
+// level less per block. time.z of them are set: none when the extra is off, so no loop runs.
+fn dynamic_block_light(pos: vec3<f32>) -> f32 {
+    let count = min(u32(globals.time.z), 16u);
+    var level = 0.0;
+    for (var i = 0u; i < count; i++) {
+        let l = globals.dynamic_lights[i];
+        level = max(level, l.w - distance(pos, l.xyz));
+    }
+    return level * 16.0;
+}
 fn entity_vertex(position: vec3<f32>, uv: vec2<f32>,
     overlay: u32, color: vec4<f32>, light: vec4<u32>, normal: vec4<f32>) -> Out {
     var out: Out;
     out.clip = globals.view_proj * vec4(position, 1.0);
     out.proj = vec4(out.clip.xy * 0.5 + out.clip.w * 0.5, out.clip.zw);
     out.uv = uv;
-    let l = vec2(f32(light.y), f32(light.x));
+    let l = vec2(max(f32(light.y), dynamic_block_light(position)), f32(light.x));
     let lm = textureSampleLevel(lightmap, lightmap_sampler,
         clamp(l / 256.0 + 0.5 / 16.0, vec2(0.5 / 16.0), vec2(15.5 / 16.0)), 0.0);
     // Celestial bodies, clouds, beacon beams, End portals and breaking cracks are unlit.

crates/horizon-client/src/extras.rs

@@ -69,6 +69,8 @@ impl Corner {
 #[derive(Clone, Debug, PartialEq)]
 pub struct Extras {
     pub fullbright: bool,
+    /// Held, dropped and burning light sources light their surroundings (`dynamic_light`).
+    pub dynamic_lights: bool,
     pub zoom: bool,
     /// A vanilla key name (`key.keyboard.z`).
     pub zoom_key: String,
@@ -110,6 +112,7 @@ impl Default for Extras {
     fn default() -> Self {
         Self {
             fullbright: false,
+            dynamic_lights: false,
             zoom: false,
             zoom_key: "key.keyboard.z".into(),
             zoom_level: 4,
@@ -158,6 +161,7 @@ impl Extras {
             };
             match key.trim() {
                 "fullbright" => e.fullbright = flag(e.fullbright),
+                "dynamicLights" => e.dynamic_lights = flag(e.dynamic_lights),
                 "zoom" => e.zoom = flag(e.zoom),
                 "zoomKey" if value.starts_with("key.") => e.zoom_key = value.to_owned(),
                 "zoomLevel" => {
@@ -201,8 +205,9 @@ impl Extras {
     }
     pub fn serialize(&self) -> String {
         format!(
-            "fullbright:{}\nzoom:{}\nzoomKey:{}\nzoomLevel:{}\nzoomSmooth:{}\nzoomSensitivity:{}\nfps:{}\nfpsCorner:{}\nfpsLows:{}\nkeystrokes:{}\nkeystrokesCorner:{}\nkeystrokesCps:{}\nminimap:{}\nminimapCorner:{}\nminimapSize:{}\nminimapShape:{}\nminimapZoom:{}\nminimapRotate:{}\nautoReconnect:{}\nmouseTweaks:{}\nmouseTweaksWheel:{}\nsort:{}\nsortKey:{}\n",
+            "fullbright:{}\ndynamicLights:{}\nzoom:{}\nzoomKey:{}\nzoomLevel:{}\nzoomSmooth:{}\nzoomSensitivity:{}\nfps:{}\nfpsCorner:{}\nfpsLows:{}\nkeystrokes:{}\nkeystrokesCorner:{}\nkeystrokesCps:{}\nminimap:{}\nminimapCorner:{}\nminimapSize:{}\nminimapShape:{}\nminimapZoom:{}\nminimapRotate:{}\nautoReconnect:{}\nmouseTweaks:{}\nmouseTweaksWheel:{}\nsort:{}\nsortKey:{}\n",
             bool_text(self.fullbright),
+            bool_text(self.dynamic_lights),
             bool_text(self.zoom),
             self.zoom_key,
             self.zoom_level,
@@ -423,6 +428,7 @@ impl Cps {
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Item {
     Fullbright,
+    DynamicLights,
     Zoom,
     ZoomKey,
     ZoomLevel,
@@ -452,6 +458,7 @@ pub fn rows() -> Vec<Result<Item, &'static str>> {
     vec![
         Err("Lighting"),
         Ok(Fullbright),
+        Ok(DynamicLights),
         Err("Zoom"),
         Ok(Zoom),
         Ok(ZoomKey),
@@ -501,6 +508,7 @@ impl Item {
     pub fn caption(self) -> &'static str {
         match self {
             Item::Fullbright => "Fullbright",
+            Item::DynamicLights => "Dynamic lights",
             Item::Zoom => "Zoom",
             Item::ZoomKey => "Zoom key",
             Item::ZoomLevel => "Starting zoom",
@@ -533,7 +541,8 @@ impl Item {
             KeystrokesCorner | KeystrokesCps => Keystrokes,
             MouseTweaksWheel => MouseTweaks,
             SortKey => Sort,
-            Fullbright | Zoom | Minimap | Fps | Keystrokes | MouseTweaks | Sort | AutoReconnect => {
+            Fullbright | DynamicLights | Zoom | Minimap | Fps | Keystrokes | MouseTweaks | Sort
+            | AutoReconnect => {
                 return None;
             }
         })
@@ -542,6 +551,9 @@ impl Item {
     pub fn description(self) -> &'static str {
         match self {
             Item::Fullbright => "Show blocks and entities at full light, even in dark areas.",
+            Item::DynamicLights => {
+                "Torches and other light sources held, dropped or on fire light the blocks around them."
+            }
             Item::Zoom => "Hold the zoom key to zoom; the wheel changes it while held.",
             Item::ZoomKey => "Click, then press a key. Escape unbinds it.",
             Item::ZoomLevel => "The zoom the key starts at.",
@@ -581,7 +593,7 @@ impl Item {
         use crate::graphics_style::Cost;
         match self {
             Item::Fullbright | Item::Zoom | Item::Fps | Item::Keystrokes => Some(Cost::None),
-            Item::Minimap => Some(Cost::Low),
+            Item::Minimap | Item::DynamicLights => Some(Cost::Low),
             Item::AutoReconnect | Item::MouseTweaks | Item::Sort => Some(Cost::None),
             _ => None,
         }
@@ -590,6 +602,7 @@ impl Item {
     pub fn switch(self, e: &Extras) -> Option<bool> {
         Some(match self {
             Item::Fullbright => e.fullbright,
+            Item::DynamicLights => e.dynamic_lights,
             Item::Zoom => e.zoom,
             Item::ZoomSmooth => e.zoom_smooth,
             Item::ZoomSensitivity => e.zoom_sensitivity,
@@ -632,6 +645,7 @@ impl Item {
     pub fn cycle(self, e: &mut Extras, back: bool) {
         match self {
             Item::Fullbright => e.fullbright = !e.fullbright,
+            Item::DynamicLights => e.dynamic_lights = !e.dynamic_lights,
             Item::Zoom => e.zoom = !e.zoom,
             Item::ZoomSmooth => e.zoom_smooth = !e.zoom_smooth,
             Item::ZoomSensitivity => e.zoom_sensitivity = !e.zoom_sensitivity,
@@ -677,7 +691,7 @@ mod tests {
     #[test]
     fn everything_is_off_by_default_and_round_trips() {
         let d = Extras::default();
-        assert!(!d.fullbright);
+        assert!(!d.fullbright && !d.dynamic_lights);
         assert!(!d.zoom && !d.fps && !d.keystrokes && !d.minimap && !d.auto_reconnect);
         assert!(!d.mouse_tweaks && !d.sort);
         assert_eq!(Extras::parse(""), d);
@@ -685,6 +699,9 @@ mod tests {
         let mut e = d.clone();
         Item::Fullbright.cycle(&mut e, false);
         assert_eq!(Item::Fullbright.switch(&e), Some(true));
+        Item::DynamicLights.cycle(&mut e, false);
+        assert_eq!(Item::DynamicLights.switch(&e), Some(true));
+        assert_eq!(Extras::parse(&e.serialize()), e);
         e.zoom = true;
         e.zoom_key = "key.keyboard.c".into();
         e.zoom_level = 6;

crates/horizon-client/src/game.rs

@@ -38,6 +38,7 @@ mod deflect;
 mod dispense_fixture;
 mod dispenser;
 mod dragon;
+mod dynamic_lights;
 mod enchant_effects;
 mod end;
 mod entity_culling;
@@ -1184,6 +1185,10 @@ struct Game<'a> {
     renderer: Option<Renderer>,
     /// CPU geometry storage retained across frames, including empty/title frames.
     entity_vertices: Vec<Vertex>,
+    /// Horizon Extras' dynamic lights this frame (`dynamic_lights.rs`), and how brightly each
+    /// item glows (built the first time the extra is on).
+    dynamic_lights: Vec<[f32; 4]>,
+    luminance: Option<horizon_client::dynamic_light::Luminance>,
     /// Name tags drawn over everything (`RenderPipelines.TEXT_SEE_THROUGH`).
     see_through_vertices: Vec<Vertex>,
     started: Instant,
@@ -9665,6 +9670,11 @@ impl Game<'_> {
             .then(|| self.border_draw(camera.to_array(), alpha as f32))
             .flatten();
         let see_through = std::mem::take(&mut self.see_through_vertices);
+        if title {
+            self.dynamic_lights.clear();
+        } else {
+            self.gather_dynamic_lights(camera, alpha);
+        }
         let frame = Frame {
             shader: self.shader_inputs(camera, alpha as f32),
             nether_lighting: self.dim == Dim::Nether,
@@ -9722,6 +9732,7 @@ impl Game<'_> {
                 color: sky.cloud_color,
             }),
             entities: &entities,
+            dynamic_lights: &self.dynamic_lights,
             additive: &additive,
             see_through: &see_through,
             celestial: if self.settings.horizon.sky || title {
@@ -11312,6 +11323,8 @@ impl<'a> Game<'a> {
             window: None,
             renderer: None,
             entity_vertices: Vec::new(),
+            dynamic_lights: Vec::new(),
+            luminance: None,
             see_through_vertices: Vec::new(),
             health_hud: hud_layout::HealthHud::default(),
             started: now,
@@ -12185,6 +12198,7 @@ fn loading_frame(hud: &HudBatch) -> Frame<'_> {
         hud,
         nether_lighting: false,
         entities: &[],
+        dynamic_lights: &[],
         clouds: None,
         additive: &[],
         see_through: &[],

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

@@ -0,0 +1,67 @@
+//! Horizon Extras' dynamic lights (`horizon_client::dynamic_light`): the light sources near the
+//! camera this frame. Nothing is gathered while the extra is off.
+use super::{Game, shield};
+use glam::DVec3;
+use horizon_client::dynamic_light::{self, BURNING, Luminance, Source};
+
+impl Game<'_> {
+    /// Fills `dynamic_lights` for the frame: the player's and mobs' held items and fire, and
+    /// glowing dropped items, the nearest [`dynamic_light::MAX`] of them.
+    pub(super) fn gather_dynamic_lights(&mut self, camera: DVec3, alpha: f64) {
+        let mut out = std::mem::take(&mut self.dynamic_lights);
+        out.clear();
+        if !self.settings.extras.dynamic_lights {
+            self.dynamic_lights = out;
+            return;
+        }
+        if self.luminance.is_none() {
+            self.luminance = Some(Luminance::new(self.res.facts(), self.pack.assets.registry));
+        }
+        let lum = self.luminance.as_ref().expect("built above");
+        let held = |item: Option<&str>| item.map_or(0, |i| lum.of(i));
+        let mut sources = Vec::new();
+        if let Some(p) = &self.player
+            && !p.spectator
+        {
+            let feet = self
+                .previous_position
+                .lerp(p.position, self.clock.camera_fraction());
+            let level = held(self.stack_in(self.selected).map(|s| &*s.item))
+                .max(held(self.stack_in(shield::OFFHAND_SLOT).map(|s| &*s.item)))
+                .max(if p.fire_ticks > 0 { BURNING } else { 0 });
+            // About where the hands are.
+            sources.push(Source {
+                at: DVec3::new(feet.x, feet.y + 1.2, feet.z),
+                level,
+            });
+        }
+        for m in self.mobs.iter().filter(|m| !m.removed) {
+            let level = held(m.extra.main_hand.as_deref())
+                .max(held(m.extra.off_hand.as_deref()))
+                .max(if m.fire_ticks > 0 { BURNING } else { 0 });
+            if level == 0 {
+                continue;
+            }
+            let at = m.previous.lerp(m.position, alpha);
+            sources.push(Source {
+                at: DVec3::new(at.x, at.y + f64::from(m.height()) * 0.6, at.z),
+                level,
+            });
+        }
+        for item in &self.dropped {
+            let level = lum
+                .of(&item.stack.item)
+                .max(if item.fire_ticks > 0 { BURNING } else { 0 });
+            if level == 0 {
+                continue;
+            }
+            let at = item.previous.lerp(item.position, alpha);
+            sources.push(Source {
+                at: DVec3::new(at.x, at.y + 0.25, at.z),
+                level,
+            });
+        }
+        dynamic_light::select(&sources, camera, &mut out);
+        self.dynamic_lights = out;
+    }
+}

crates/horizon-client/src/gfx.rs

@@ -107,13 +107,16 @@ struct Globals {
     fog_ends: [f32; 4],
     /// Atlas rects (u0, v0, width, height) of end_sky.png and end_portal.png.
     end_portal_sprites: [[f32; 4]; 2],
-    /// x: vanilla's `GameTime` uniform; y: nether cardinal lighting, zw unused.
+    /// x: vanilla's `GameTime` uniform; y: nether cardinal lighting; z: how many
+    /// `dynamic_lights` are set; w unused.
     time: [f32; 4],
     /// Atlas rect of a destroy stage (entity.wgsl takes only its size: every stage's is the same,
     /// and each crack carries its own stage's origin).
     crumbling_sprite: [f32; 4],
     /// Framebuffer size, selection stroke width, perspective layering scale.
     outline_params: [f32; 4],
+    /// Horizon Extras' dynamic lights: camera-relative position and level (`dynamic_light`).
+    dynamic_lights: [[f32; 4]; crate::dynamic_light::MAX],
 }
 pub type SectionKey = (i32, i32, i32);
 struct SectionGpu {
@@ -186,6 +189,8 @@ pub struct Frame<'a> {
     pub nether_lighting: bool,
     /// Camera-relative entity geometry textured from the shared atlas.
     pub entities: &'a [Vertex],
+    /// Horizon Extras' dynamic lights, nearest first (`dynamic_light::select`); empty when off.
+    pub dynamic_lights: &'a [[f32; 4]],
     /// Cloud mesh inputs; geometry and GPU storage are retained by the renderer.
     pub clouds: Option<crate::clouds::Input<'a>>,
     /// Additive translucent geometry after the entities (lightning, dragon rays).
@@ -2908,10 +2913,17 @@ impl Renderer {
             time: [
                 frame.shader_game_time,
                 f32::from(frame.nether_lighting),
-                0.0,
+                frame.dynamic_lights.len().min(crate::dynamic_light::MAX) as f32,
                 0.0,
             ],
             outline_params: outline_params(self.config.width, self.config.height),
+            dynamic_lights: {
+                let mut lights = [[0.0; 4]; crate::dynamic_light::MAX];
+                for (to, from) in lights.iter_mut().zip(frame.dynamic_lights) {
+                    *to = *from;
+                }
+                lights
+            },
         };
         self.uploads
             .buffer(&mut encoder, &self.globals, 0, bytemuck::bytes_of(&globals));

crates/horizon-client/src/lib.rs

@@ -51,6 +51,7 @@ pub mod datapack;
 pub mod debug_chart;
 pub mod debug_keys;
 pub mod debug_overlay;
+pub mod dynamic_light;
 pub mod effects;
 pub mod enchant;
 pub mod end_crystal;

crates/horizon-client/src/terrain.wgsl

@@ -16,11 +16,14 @@ struct Globals {
     fog_ends: vec4<f32>,
     // Atlas rects (u0, v0, width, height) of end_sky.png and end_portal.png.
     end_portal_sprites: array<vec4<f32>, 2>,
-    // x: vanilla's GameTime ((game time % 24000 + partial tick) / 24000)
+    // x: vanilla's GameTime ((game time % 24000 + partial tick) / 24000), z: how many
+    // dynamic_lights are set
     time: vec4<f32>,
     // Atlas rect of the current destroy stage (read by entity.wgsl).
     crumbling_sprite: vec4<f32>,
     outline_params: vec4<f32>,
+    // Horizon Extras' dynamic lights: camera-relative position and level (dynamic_light.rs).
+    dynamic_lights: array<vec4<f32>, 16>,
 }
 @group(0) @binding(0) var<uniform> globals: Globals;
 @group(0) @binding(1) var sprites: texture_2d_array<f32>;
@@ -67,6 +70,18 @@ struct TerrainOut {
     @location(3) spherical: f32,
     @location(4) cylindrical: f32,
 }
+// Horizon Extras' dynamic lights (dynamic_light.rs): the block light, in the vertex's units
+// (16 per level), a vertex at camera-relative `pos` gets from the frame's light sources, one
+// level less per block. time.z of them are set: none when the extra is off, so no loop runs.
+fn dynamic_block_light(pos: vec3<f32>) -> f32 {
+    let count = min(u32(globals.time.z), 16u);
+    var level = 0.0;
+    for (var i = 0u; i < count; i++) {
+        let l = globals.dynamic_lights[i];
+        level = max(level, l.w - distance(pos, l.xyz));
+    }
+    return level * 16.0;
+}
 fn sample_lightmap(sky: f32, block: f32) -> vec4<f32> {
     let uv = vec2(block, sky) * 16.0;
     return textureSampleLevel(lightmap, lightmap_sampler,
@@ -105,7 +120,8 @@ fn terrain_vertex(position: vec3<f32>, uv: vec2<f32>, layer: u32, color: vec4<f3
     out.clip = globals.view_proj * vec4(pos, 1.0);
     out.uv = uv;
     out.layer = layer;
-    out.color = color * sample_lightmap(f32(light.x) / 16.0, f32(light.y) / 16.0);
+    let block = max(f32(light.y), dynamic_block_light(pos));
+    out.color = color * sample_lightmap(f32(light.x) / 16.0, block / 16.0);
     out.spherical = length(pos);
     out.cylindrical = max(length(pos.xz), abs(pos.y));
     return out;

docs/extras.md

@@ -1,6 +1,6 @@
 # Horizon extras
 
-Optional conveniences built into the client: fullbright, zoom, a minimap, an FPS counter, a
+Optional conveniences built into the client: fullbright, dynamic lights, zoom, a minimap, an FPS counter, a
 keystroke overlay, auto-reconnect, Mouse Tweaks-style inventory controls and
 inventory sorting. **Every one is off by default**: a fresh
 install looks and behaves exactly like vanilla 26.3, and turning an extra off
@@ -12,6 +12,7 @@ again restores vanilla's behaviour completely.
 |---|---|
 | Settings, parsing and saving | `crates/horizon-client/src/extras.rs` |
 | Zoom curve, FPS and click counters | `extras.rs` (pure logic, unit tested) |
+| Dynamic lights: item glow, nearest sources | `crates/horizon-client/src/dynamic_light.rs` (unit tested), `game/dynamic_lights.rs`, `terrain.wgsl` and `entity.wgsl` (`dynamic_block_light`) |
 | HUD drawing (FPS, keystrokes, minimap frame) | `crates/horizon-client/src/extras_hud.rs` |
 | Minimap colours, tiles and image | `crates/horizon-client/src/minimap.rs` |
 | Reconnect policy and backoff | `crates/horizon-client/src/reconnect.rs` |
@@ -45,6 +46,21 @@ Horizon category in Controls, and adding one would put a non-vanilla mapping int
 - Turning it off restores the normal lightmap using the current brightness,
   time of day and effects. The brightness slider keeps its normal range.
 
+### Dynamic lights (`dynamicLights`, default off)
+- A light source held by a player or mob (main or off hand), dropped as an item, or an entity on
+  fire lights the blocks, entities and hand around it, as LambDynamicLights and OptiFine do. Not
+  in vanilla; the idea is ported, not a mod's code (issue #814).
+- An item glows like its block's default state (`getLightEmission`): torches 14, lanterns,
+  glowstone, sea lanterns and jack o'lanterns 15, soul torches 10, a redstone torch 7; a lava bucket
+  15. An entity on fire gives 15.
+- Client-only, at render time: the light engine, meshes, saves and other players never see it.
+  Each frame the game picks the 16 sources nearest the camera (within 96 blocks,
+  `dynamic_light::select`); terrain.wgsl and entity.wgsl raise each vertex's block light to the
+  source's level minus its distance in blocks when that is brighter, then light it through the
+  lightmap as usual. The light doesn't stop at walls.
+- Off: nothing is gathered and the shaders' loop runs zero times (the count is 0), so it costs
+  nothing measurable (numbers in the pull request, #814).
+
 ### Zoom (`zoom`, default off)
 - Hold the zoom key (default **Z**, unused by every vanilla 26.3 key mapping; C
   is `key.saveToolbarActivator`) to zoom. The key does nothing while zoom is off.