Sunsets, volumetric clouds and fog in HD (fork patch 23, #53); missiles and drones collide with the world through new world queries (patch 24, API level 12; #42, #43); a direct hit destroys a system, strikes scatter by kind with a small miss chance (#49, #59)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/desktop.yml

@@ -22,7 +22,39 @@ jobs:
     if: inputs.os == 'macos' || inputs.os == 'both'
     runs-on: macos-latest
     steps:
+      - name: Проверка релиза
+        env:
+          TOKEN: ${{ secrets.RELEASE_TOKEN || gitea.token }}
+          API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
+          TAG: ${{ inputs.tag }}
+        run: |
+          set -e
+          if ! [[ "$TAG" =~ ^build-[0-9]+$ ]]; then echo "::error::тег '$TAG' не похож на build-N"; exit 1; fi
+          REL_JSON=$(mktemp)
+          CODE=$(curl -s -o "$REL_JSON" -w '%{http_code}' -H "Authorization: token $TOKEN" "$API/releases/tags/$TAG")
+          if [ "$CODE" != "200" ]; then echo "::error::релиза с тегом $TAG нет (HTTP $CODE): сначала дождись сборки build.yml на main"; exit 1; fi
+          python3 - "$TAG" "$REL_JSON" <<'PY'
+          import json, os, sys
+          tag, path = sys.argv[1], sys.argv[2]
+          r = json.load(open(path))
+          assets = [a.get('name') for a in (r.get('assets') or [])]
+          if r.get('tag_name') != tag or r.get('name') != tag or 'airdef.hmod' not in assets:
+              print('::error::релиз %s не создан build.yml (нужны имя = тег и вложение airdef.hmod): чужой релиз не трогаем' % tag)
+              sys.exit(1)
+          with open(os.environ['GITHUB_ENV'], 'a') as f:
+              f.write('RELEASE_ID=%s\nRELEASE_SHA=%s\n' % (r['id'], r.get('target_commitish', '')))
+          PY
       - uses: actions/checkout@v4
+        with:
+          ref: refs/tags/${{ inputs.tag }}
+      - name: Проверка коммита
+        env:
+          TAG: ${{ inputs.tag }}
+        run: |
+          set -e
+          HEAD_SHA=$(git rev-parse HEAD)
+          if [[ "$RELEASE_SHA" =~ ^[0-9a-f]{40}$ ]] && [ "$HEAD_SHA" != "$RELEASE_SHA" ]; then echo "::error::тег $TAG указывает на $HEAD_SHA, а релиз создан из $RELEASE_SHA"; exit 1; fi
+          echo "собираю $TAG = $HEAD_SHA"
       - name: Rust
         run: |
           command -v cargo || curl -sSf https://sh.rustup.rs | sh -s -- -y --profile minimal
@@ -47,11 +79,10 @@ jobs:
         env:
           TOKEN: ${{ secrets.RELEASE_TOKEN || gitea.token }}
           API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
-          TAG: ${{ inputs.tag }}
         run: |
           set -e
-          ID=$(curl -sf -H "Authorization: token $TOKEN" "$API/releases/tags/$TAG" | python3 -c 'import json,sys;print(json.load(sys.stdin)["id"])')
-          curl -sf -X POST -H "Authorization: token $TOKEN" -F "attachment=@out/airdef-macos-arm64.tar.gz" "$API/releases/$ID/assets?name=airdef-macos-arm64.tar.gz" > /dev/null
+          # RELEASE_ID взят в шаге «Проверка релиза» (релиз build-N, созданный build.yml)
+          curl -sf -X POST -H "Authorization: token $TOKEN" -F "attachment=@out/airdef-macos-arm64.tar.gz" "$API/releases/$RELEASE_ID/assets?name=airdef-macos-arm64.tar.gz" > /dev/null
 
   game-windows:
     if: inputs.os == 'windows' || inputs.os == 'both'
@@ -60,7 +91,34 @@ jobs:
       run:
         shell: pwsh
     steps:
+      - name: Проверка релиза
+        env:
+          TOKEN: ${{ secrets.RELEASE_TOKEN || gitea.token }}
+          API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
+          TAG: ${{ inputs.tag }}
+        run: |
+          $ErrorActionPreference = 'Stop'
+          if ($env:TAG -notmatch '^build-\d+$') { Write-Output "::error::тег '$env:TAG' не похож на build-N"; exit 1 }
+          $h = @{ Authorization = "token $env:TOKEN" }
+          try { $r = Invoke-RestMethod -Headers $h "$env:API/releases/tags/$env:TAG" }
+          catch { Write-Output "::error::релиза с тегом $env:TAG нет: сначала дождись сборки build.yml на main"; exit 1 }
+          $assets = @($r.assets | ForEach-Object { $_.name })
+          if ($r.tag_name -ne $env:TAG -or $r.name -ne $env:TAG -or ($assets -notcontains 'airdef.hmod')) {
+            Write-Output "::error::релиз $env:TAG не создан build.yml (нужны имя = тег и вложение airdef.hmod): чужой релиз не трогаем"; exit 1
+          }
+          "RELEASE_ID=$($r.id)" | Out-File -Append -Encoding utf8 $env:GITHUB_ENV
+          "RELEASE_SHA=$($r.target_commitish)" | Out-File -Append -Encoding utf8 $env:GITHUB_ENV
       - uses: actions/checkout@v4
+        with:
+          ref: refs/tags/${{ inputs.tag }}
+      - name: Проверка коммита
+        env:
+          TAG: ${{ inputs.tag }}
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $head = git rev-parse HEAD
+          if ($env:RELEASE_SHA -match '^[0-9a-f]{40}$' -and $head -ne $env:RELEASE_SHA) { Write-Output "::error::тег $env:TAG указывает на $head, а релиз создан из $env:RELEASE_SHA"; exit 1 }
+          Write-Output "собираю $env:TAG = $head"
       - name: Rust
         run: |
           if (-not (Get-Command cargo -ErrorAction SilentlyContinue)) {
@@ -88,9 +146,7 @@ jobs:
         env:
           TOKEN: ${{ secrets.RELEASE_TOKEN || gitea.token }}
           API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
-          TAG: ${{ inputs.tag }}
         run: |
-          $h = @{ Authorization = "token $env:TOKEN" }
-          $id = (Invoke-RestMethod -Headers $h "$env:API/releases/tags/$env:TAG").id
-          curl.exe -sf -X POST -H "Authorization: token $env:TOKEN" -F "attachment=@out\airdef-windows-x86_64.zip" "$env:API/releases/$id/assets?name=airdef-windows-x86_64.zip"
+          # RELEASE_ID взят в шаге «Проверка релиза» (релиз build-N, созданный build.yml)
+          curl.exe -sf -X POST -H "Authorization: token $env:TOKEN" -F "attachment=@out\airdef-windows-x86_64.zip" "$env:API/releases/$env:RELEASE_ID/assets?name=airdef-windows-x86_64.zip"
 

.gitea/workflows/game.yml

@@ -25,7 +25,39 @@ jobs:
           FREE=$(df --output=avail -BG / | tail -1 | tr -dc 0-9)
           echo "свободно: ${FREE} ГБ"
           if [ "$FREE" -lt 15 ]; then echo "::error::на сервере свободно ${FREE} ГБ, нужно хотя бы 15: сборка игры забьёт диск и уронит Gitea"; exit 1; fi
+      - name: Проверка релиза
+        env:
+          TOKEN: ${{ secrets.RELEASE_TOKEN || gitea.token }}
+          API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
+          TAG: ${{ inputs.tag }}
+        run: |
+          set -e
+          if ! [[ "$TAG" =~ ^build-[0-9]+$ ]]; then echo "::error::тег '$TAG' не похож на build-N"; exit 1; fi
+          REL_JSON=$(mktemp)
+          CODE=$(curl -s -o "$REL_JSON" -w '%{http_code}' -H "Authorization: token $TOKEN" "$API/releases/tags/$TAG")
+          if [ "$CODE" != "200" ]; then echo "::error::релиза с тегом $TAG нет (HTTP $CODE): сначала дождись сборки build.yml на main"; exit 1; fi
+          python3 - "$TAG" "$REL_JSON" <<'PY'
+          import json, os, sys
+          tag, path = sys.argv[1], sys.argv[2]
+          r = json.load(open(path))
+          assets = [a.get('name') for a in (r.get('assets') or [])]
+          if r.get('tag_name') != tag or r.get('name') != tag or 'airdef.hmod' not in assets:
+              print('::error::релиз %s не создан build.yml (нужны имя = тег и вложение airdef.hmod): чужой релиз не трогаем' % tag)
+              sys.exit(1)
+          with open(os.environ['GITHUB_ENV'], 'a') as f:
+              f.write('RELEASE_ID=%s\nRELEASE_SHA=%s\n' % (r['id'], r.get('target_commitish', '')))
+          PY
       - uses: actions/checkout@v4
+        with:
+          ref: refs/tags/${{ inputs.tag }}
+      - name: Проверка коммита
+        env:
+          TAG: ${{ inputs.tag }}
+        run: |
+          set -e
+          HEAD_SHA=$(git rev-parse HEAD)
+          if [[ "$RELEASE_SHA" =~ ^[0-9a-f]{40}$ ]] && [ "$HEAD_SHA" != "$RELEASE_SHA" ]; then echo "::error::тег $TAG указывает на $HEAD_SHA, а релиз создан из $RELEASE_SHA"; exit 1; fi
+          echo "собираю $TAG = $HEAD_SHA"
       - name: Системные библиотеки
         run: |
           SUDO=$(command -v sudo || true)
@@ -45,12 +77,11 @@ jobs:
         env:
           TOKEN: ${{ secrets.RELEASE_TOKEN || gitea.token }}
           API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
-          TAG: ${{ inputs.tag }}
         run: |
           set -e
           D=airdef-linux-x86_64
           mkdir -p "$D" out
           cp horizon/target/fast/horizon-client horizon/target/fast/horizon-ctl airdef-mod/target/horizon-mod/airdef.hmod dist/play.sh docs/INSTALL.md "$D/"
           tar czf "out/$D.tar.gz" "$D"
-          ID=$(curl -sf -H "Authorization: token $TOKEN" "$API/releases/tags/$TAG" | python3 -c 'import json,sys;print(json.load(sys.stdin)["id"])')
-          curl -sf -X POST -H "Authorization: token $TOKEN" -F "attachment=@out/$D.tar.gz" "$API/releases/$ID/assets?name=$D.tar.gz" > /dev/null
+          # RELEASE_ID взят в шаге «Проверка релиза» (релиз build-N, созданный build.yml)
+          curl -sf -X POST -H "Authorization: token $TOKEN" -F "attachment=@out/$D.tar.gz" "$API/releases/$RELEASE_ID/assets?name=$D.tar.gz" > /dev/null

README.md

@@ -27,7 +27,9 @@ python3 tools/airdef.py play    # запустить (аргументы игр
 CI: `.gitea/workflows/build.yml` на каждый пуш собирает только мод (`airdef.hmod`), а пуш в `main` публикует его
 релизом `build-N`. Игру-форк собирают вручную: `.gitea/workflows/game.yml` (Linux) и `.gitea/workflows/desktop.yml`
 (macOS и Windows, на раннерах с метками `macos-latest` / `windows-latest`); оба запускаются из Actions с тегом
-готового релиза и дописывают свои архивы в него.
+готового релиза `build-N`. Перед сборкой workflow проверяет, что такой релиз создан `build.yml` (имя релиза = тег,
+есть `airdef.hmod`), иначе падает с ошибкой; затем выкачивает ровно коммит этого тега (а не ветку, с которой запущен),
+сверяет его с коммитом релиза и дописывает архивы только в этот релиз.
 
 ## Как играть
 

airdef-mod/examples/sim_run/harness.rs

@@ -18,6 +18,13 @@ pub enum Terrain {
     Hills { base: i32, amp: f64, period: f64 },
 }
 
+/// The land as blocks: solid at and below the column's height (what the game would answer `render.sections` with).
+impl airdef::sim::world::WorldSource for Terrain {
+    fn solid(&self, x: i32, y: i32, z: i32) -> Option<bool> {
+        Some(y < self.height(x, z))
+    }
+}
+
 impl Terrain {
     pub fn height(self, x: i32, z: i32) -> i32 {
         match self {
@@ -98,6 +105,9 @@ pub struct Report {
     /// Missiles fired by air defence (sum of the systems' `fired`).
     pub fired: u32,
     pub ground_queries: u64,
+    /// The block cache's counters (issue #43) and the drones that struck the land (issue #42).
+    pub world: String,
+    pub crashes: u32,
     pub ground_batches: u64,
     pub tick_p50: Duration,
     pub tick_p95: Duration,
@@ -163,6 +173,8 @@ pub fn run(sc: &Scenario) -> Report {
         let t = Instant::now();
         sim.step(&mut ground, None, &mut out);
         let wanted = ground.take_wanted();
+        let sections = ground.world.take_wanted(now);
+        ground.world.serve(&sc.terrain, sections, now);
         let dt = t.elapsed();
         times.push(dt);
         if planning {
@@ -212,6 +224,8 @@ pub fn run(sc: &Scenario) -> Report {
     r.hits = sim.hits;
     r.fired = sim.sams.iter().map(|s| s.fired).sum();
     r.raids_ordered = ordered.iter().filter(|o| **o).count();
+    r.world = ground.world.text();
+    r.crashes = sim.crashes;
     r.raids_ended = ended.iter().filter(|o| **o).count();
     r.all_ended = r.raids_ended == sc.raids.len();
     r.tick_total = times.iter().sum();
@@ -253,7 +267,8 @@ impl Report {
              planning: {pl:.1} ms over {pt} ticks\n\
              ground queries: {gq} in {gb} batches\n\
              non-finite positions: {nan}\n\
-             stuck trucks: {stuck:?} (busy truck-ticks {busy})\n",
+             stuck trucks: {stuck:?} (busy truck-ticks {busy})\n\
+             crashes into the land: {crashes}; {world}\n",
             name = self.name,
             seed = self.seed,
             units = self.units,
@@ -276,6 +291,8 @@ impl Report {
             nan = self.nan_positions,
             stuck = self.stuck_trucks,
             busy = self.truck_busy_ticks,
+            crashes = self.crashes,
+            world = self.world,
         )
     }
     pub fn json(&self) -> String {

airdef-mod/src/lib.rs

@@ -1061,6 +1061,25 @@ impl Mod for AirDef {
         }
         let now = self.sim.tick;
         self.ground.answer(render::ground(), now);
+        // The blocks themselves (issues #42, #43): what changed, and the sections asked for last tick.
+        let changes = render::world_changes();
+        self.ground.world.changed(changes.epoch, changes.overflow, &changes.sections);
+        let sections = render::sections()
+            .into_iter()
+            .map(|s| sim::world::SectionAnswer {
+                sec: (s.x, s.y, s.z),
+                fill: match s.fill {
+                    render::SectionFill::Unknown => sim::world::Fill::Unknown,
+                    render::SectionFill::Empty => sim::world::Fill::Empty,
+                    render::SectionFill::Full => sim::world::Fill::Full,
+                    render::SectionFill::Mixed => match <[u8; 512]>::try_from(s.bits) {
+                        Ok(bits) => sim::world::Fill::Mixed(Box::new(bits)),
+                        Err(_) => sim::world::Fill::Unknown,
+                    },
+                },
+            })
+            .collect();
+        self.ground.world.answer(sections, now);
         let mut out = Out::default();
         self.listener = DVec3::new(p.x, p.y + 1.6, p.z);
         self.sim.night = game::get_clock().is_some_and(|c| (13000..23000).contains(&(c.day_time % 24000)));
@@ -1069,6 +1088,10 @@ impl Mod for AirDef {
         if !wanted.is_empty() {
             render::query_ground(&wanted);
         }
+        let sections = self.ground.world.take_wanted(now);
+        if !sections.is_empty() {
+            render::query_sections(render::Policy::Collision, &sections);
+        }
         if let Some(mut r) = self.replay.take() {
             r.tick(&self.sim, self.listener, &mut out);
             if r.done {
@@ -1451,12 +1474,14 @@ impl Mod for AirDef {
                 Some(format!("Эффекты: {}", match *v { "off" => "выкл", "hd" => "HD", _ => "обычные" }))
             }
             ["stats"] => Some(format!(
-                "В воздухе: {}, ракет: {}, ПВО: {}, сбито: {}, поражений: {}",
+                "В воздухе: {}, ракет: {}, ПВО: {}, сбито: {}, поражений: {}, разбились о препятствия: {}; {}",
                 self.sim.drones.iter().filter(|d| d.alive()).count(),
                 self.sim.missiles.len(),
                 self.sim.sams.len(),
                 self.sim.kills,
-                self.sim.hits
+                self.sim.hits,
+                self.sim.crashes,
+                self.ground.world.text()
             )),
             _ => return Err(HELP.to_string()),
         };

airdef-mod/src/replay.rs

@@ -107,6 +107,7 @@ pub fn title(rec: &Recording, i: usize) -> String {
         EventKind::Hit { kind, .. } => format!("Прилёт: «{}»", kind.spec().name),
         EventKind::SamLost { kind, index, .. } => format!("{} №{} уничтожен", kind.name(), index + 1),
         EventKind::Split { .. } => "«Орешник»: разделение боевых блоков".into(),
+        EventKind::Crash { kind, .. } => format!("«{}» разбивается о препятствие", kind.spec().name),
     }
 }
 
@@ -122,6 +123,7 @@ pub fn row(rec: &Recording, i: usize) -> String {
         EventKind::Hit { kind, .. } => format!("{}: прилёт", kind.spec().name),
         EventKind::SamLost { kind, index, .. } => format!("{}-{} уничтожен", kind.name(), index + 1),
         EventKind::Split { .. } => "Орешник: разделение".into(),
+        EventKind::Crash { kind, .. } => format!("{}: о рельеф", kind.spec().name),
     };
     format!("{} {what}", clock(e.at as f64))
 }
@@ -152,6 +154,7 @@ fn interest(rec: &Recording, i: usize) -> f64 {
             power as f64 * 1.5 + if object.is_some() { 6.0 } else if sam.is_some() { 5.0 } else { 0.0 }
         }
         EventKind::SamLost { .. } => 12.0,
+        EventKind::Crash { power, .. } => power as f64,
         EventKind::Split { drone } => {
             // The bus's split, not each block's.
             let first = rec.events.iter().position(|o| matches!(o.kind, EventKind::Split { .. }));
@@ -168,6 +171,7 @@ fn clip(rec: &Recording, i: usize) -> Clip {
         EventKind::Hit { .. } => (160.0, 60.0),
         EventKind::SamLost { .. } => (80.0, 90.0),
         EventKind::Split { .. } => (40.0, 170.0),
+        EventKind::Crash { .. } => (120.0, 60.0),
     };
     Clip { event: i, from: (at - before).max(0.0), to: (at + after).min(rec.len as f64) }
 }
@@ -352,7 +356,7 @@ impl Player {
         for e in rec.events.iter().filter(|e| (self.heard..self.t).contains(&(e.at as f64))) {
             let event = match e.kind {
                 EventKind::Kill { .. } => "airdef:blast.air",
-                EventKind::Hit { power, .. } => ["airdef:blast.air", "airdef:blast.medium", "airdef:blast.big", "airdef:blast.heavy", "airdef:blast.huge"][(power as usize).min(4)],
+                EventKind::Hit { power, .. } | EventKind::Crash { power, .. } => ["airdef:blast.air", "airdef:blast.medium", "airdef:blast.big", "airdef:blast.heavy", "airdef:blast.huge"][(power as usize).min(4)],
                 EventKind::SamLost { .. } => "airdef:blast.big",
                 EventKind::Split { .. } => "airdef:boom.sonic",
             };
@@ -412,7 +416,7 @@ impl Player {
                     }
                 }
             }
-            EventKind::Hit { drone, .. } => {
+            EventKind::Hit { drone, .. } | EventKind::Crash { drone, .. } => {
                 if t < te - 50.0 {
                     if let Some((eye, look)) = chase(drone, 12.0, 4.0) {
                         return (eye, look, 55.0, 0);
@@ -672,7 +676,7 @@ impl Player {
                     s.push(line((x - 2.5, y - 2.5), (x + 2.5, y + 2.5), 1.2, 0xFFFFE040));
                     s.push(line((x + 2.5, y - 2.5), (x - 2.5, y + 2.5), 1.2, 0xFFFFE040));
                 }
-                EventKind::Hit { power, .. } => {
+                EventKind::Hit { power, .. } | EventKind::Crash { power, .. } => {
                     let r = 2.0 + power as f32;
                     s.push(fill(x - r, y - r, r * 2.0, r * 2.0, 0xB0FF3020));
                 }
@@ -705,6 +709,7 @@ impl Player {
             let c = match e.kind {
                 EventKind::Kill { .. } => 0xFFFFE040,
                 EventKind::Hit { .. } => 0xFFFF3020,
+                EventKind::Crash { .. } => 0xFF903020,
                 EventKind::SamLost { .. } => 0xFFFF00FF,
                 EventKind::Split { .. } => 0xFFFF9020,
             };

airdef-mod/src/sim/damage.rs

@@ -28,7 +28,72 @@ impl MissileKind {
     }
 }
 
+/// A strike that ends farther than this from its aim point misses (the lethal radius of a point target).
+pub(super) const MISS_RADIUS: f64 = 3.0;
+/// A system's hull, as a cylinder: its radius (× scale) and how far above the ground it reaches (× scale).
+const HULL_RADIUS: f64 = 2.2;
+const HULL_TOP: f64 = 3.0;
+
+impl DroneKind {
+    /// Strike accuracy: the CEP (blocks; half the strikes land within it, the scatter is Rayleigh)
+    /// and the share of strikes with a rare gross navigation fault, which lands beyond `MISS_RADIUS`.
+    pub(super) fn accuracy(self) -> (f64, f64) {
+        match self {
+            DroneKind::Shahed => (1.2, 0.03),
+            DroneKind::Geran3 => (1.0, 0.03),
+            DroneKind::Lancet => (0.8, 0.02),
+            DroneKind::Gerbera => (1.5, 0.04),
+            DroneKind::Kh101 => (1.3, 0.05),
+            DroneKind::Kalibr => (1.3, 0.05),
+            DroneKind::Kh22 => (1.6, 0.06),
+            DroneKind::Zircon => (1.5, 0.06),
+            DroneKind::Iskander => (1.4, 0.06),
+            DroneKind::Kinzhal => (1.5, 0.06),
+            // The bus and its blocks: the blocks are aimed by the split, so only the bus's own error applies.
+            DroneKind::Oreshnik | DroneKind::OreshnikBlock | DroneKind::OreshnikSub => (1.6, 0.08),
+        }
+    }
+}
+
 impl Sim {
+    /// The aim error of a new strike: drawn once from the seed, the drone keeps it for its whole flight.
+    pub(super) fn aim_error(&mut self, kind: DroneKind) -> DVec3 {
+        let (cep, gross) = kind.accuracy();
+        let angle = self.rng.f() * std::f64::consts::TAU;
+        let r = if self.rng.chance(gross) {
+            MISS_RADIUS + cep * (0.5 + 2.5 * self.rng.f())
+        } else {
+            // Rayleigh with its median at the CEP.
+            let u = 1.0 - self.rng.f();
+            cep * (-2.0 * u.ln() / (2.0 * std::f64::consts::LN_2)).sqrt()
+        };
+        DVec3::new(angle.cos() * r, 0.0, angle.sin() * r)
+    }
+
+    /// An armed warhead reached `pos` (its last step was `vel`): a system whose hull it swept through is
+    /// destroyed at once, whatever the blast would have done to it. A near miss is only splash.
+    pub(super) fn direct_hit(&mut self, pos: DVec3, vel: DVec3, tnt: u32, out: &mut Out) {
+        if !self.damage || tnt == 0 {
+            return;
+        }
+        let from = pos - vel;
+        for i in 0..self.sams.len() {
+            let sam = &self.sams[i];
+            if !sam.alive() {
+                continue;
+            }
+            let s = sam.kind.spec().scale;
+            let hit = (0..=8).any(|k| {
+                let p = from.lerp(pos, k as f64 / 8.0);
+                let across = DVec3::new(p.x - sam.pos.x, 0.0, p.z - sam.pos.z).length();
+                across <= HULL_RADIUS * s && p.y >= sam.pos.y - 1.0 && p.y <= sam.pos.y + HULL_TOP * s
+            });
+            if hit {
+                self.destroy(i, out);
+            }
+        }
+    }
+
     /// A blast of `power` (0 to 4) at `pos`: the systems and objects round it take damage.
     pub(super) fn blast_damage(&mut self, pos: DVec3, power: usize, out: &mut Out) {
         let (reach, hit) = (REACH[power], HIT[power]);

airdef-mod/src/sim/mod.rs

@@ -19,6 +19,7 @@ mod logistics;
 mod orders;
 mod units;
 mod why;
+pub mod world;
 #[cfg(test)]
 mod regress;
 pub use ew::EW_RADIUS;
@@ -211,6 +212,8 @@ pub struct Ground {
     asked: std::collections::HashSet<(i32, i32)>,
     /// The tick of the last full clean-up (a big cache would otherwise be scanned on every answer).
     swept: u64,
+    /// The blocks themselves (issues #42, #43): what stops a flight.
+    pub world: world::WorldCache,
 }
 
 /// Ticks between full clean-ups of a big ground cache.
@@ -251,10 +254,32 @@ impl Ground {
         self.asked.clear();
         std::mem::take(&mut self.wanted)
     }
+    /// The first solid block on the way from `a` to `b` (the real blocks, not the height of the land).
+    pub fn sweep(&mut self, a: DVec3, b: DVec3, skip_start: bool, now: u64) -> world::Sweep {
+        self.world.sweep(a, b, skip_start, now)
+    }
+    /// Has the sections along a flight read before it gets there.
+    pub fn ahead(&mut self, pos: DVec3, vel: DVec3, ticks: f64, now: u64) {
+        self.world.look_ahead(pos, vel, ticks, now);
+    }
+    /// Whether `pos` is in the land by the column's height (`below`, as `at` gave it), given what the sweep
+    /// of this step saw: over blocks known and open, the height only counts where its top block is known
+    /// to be open, a fluid's surface (not a roof or a bridge deck above the flight, nor a block unread).
+    pub fn ground_hit(&mut self, below: Option<f64>, pos: DVec3, offset: f64, sweep: &world::Sweep, now: u64) -> bool {
+        let Some(g) = below else { return false };
+        if pos.y > g + offset {
+            return false;
+        }
+        match sweep {
+            world::Sweep::Clear => self.world.is_known_open(pos.x.floor() as i32, g.floor() as i32 - 1, pos.z.floor() as i32, now),
+            _ => true,
+        }
+    }
     /// Explosions change the land: forget what was known round them.
     fn forget(&mut self, at: DVec3, radius: i32) {
         let (cx, cz) = (at.x.floor() as i32, at.z.floor() as i32);
         self.known.retain(|&(x, z), _| (x - cx).abs() > radius || (z - cz).abs() > radius);
+        self.world.touched(at, f64::from(radius) + 2.0);
     }
 }
 
@@ -1172,6 +1197,8 @@ pub struct Sim {
     pub tick: u64,
     pub kills: u32,
     pub hits: u32,
+    /// Drones that struck the land or a building short of their aim.
+    pub crashes: u32,
     pub launched: u32,
     /// Explosions damage the land (primed TNT through commands).
     pub damage: bool,
@@ -1225,6 +1252,7 @@ impl Sim {
             tick: 0,
             kills: 0,
             hits: 0,
+            crashes: 0,
             launched: 0,
             damage: true,
             shader: false,
@@ -1289,6 +1317,8 @@ impl Sim {
     fn add_drone(&mut self, kind: DroneKind, from: DVec3, dir: DVec3, target: DVec3) {
         let id = self.id();
         let spec = kind.spec();
+        // Its navigation error: it flies to, and strikes at, a point off the aim it was given.
+        let target = target + self.aim_error(kind);
         let (vel, flight) = if spec.ballistic.is_some() {
             // An arc from `from` to `target` at the kind's horizontal speed.
             let flat = horizontal(target - from);
@@ -1373,7 +1403,7 @@ impl Sim {
         self.update_sight(ground);
         self.step_lights(out);
         self.step_sams(out);
-        self.step_missiles(out);
+        self.step_missiles(ground, out);
         self.step_fx(ground, out);
         self.draw_targets(out);
         self.step_wrecks(out);
@@ -1394,10 +1424,14 @@ impl Sim {
         // Warheads that reached their aim (for the replays): drone, kind, where, TNT; and splits.
         let mut impacts: Vec<(u32, DroneKind, DVec3, u32)> = Vec::new();
         let mut splits: Vec<(u32, DVec3)> = Vec::new();
+        // Drones that struck the land or a building short of their aim: drone, kind, where, TNT.
+        let mut crashes: Vec<(u32, DroneKind, DVec3, u32)> = Vec::new();
         for d in &mut self.drones {
             d.age += 1;
             let spec = d.kind.spec();
             let below = ground.at(d.pos, now);
+            let from = d.pos;
+            ground.ahead(d.pos, d.vel, 20.0, now);
             // Near its aim it looks at the land there again: a platform or hilltop blown away
             // meanwhile, it goes for what is left below, not for the air where it stood.
             if d.flight != Flight::Falling
@@ -1412,11 +1446,15 @@ impl Sim {
                 d.vel *= 0.985;
                 d.spin += 0.35;
                 d.pos += d.vel;
+                let sweep = ground.sweep(from, d.pos, d.age <= 3, now);
+                if let Some((_, p)) = sweep.hit() {
+                    d.pos = p;
+                }
                 if self.rng.chance(0.5) {
                     out.particles("minecraft:large_smoke", d.pos, 0.2, DVec3::new(0.0, 0.05, 0.0), 0.02, 1);
                 }
                 out.particles("minecraft:flame", d.pos, 0.25, DVec3::ZERO, 0.02, 2);
-                if below.is_some_and(|g| d.pos.y <= g + 0.3) || d.age > 600 {
+                if sweep.hit().is_some() || ground.ground_hit(below, d.pos, 0.3, &sweep, now) || d.age > 600 {
                     // The wreck's warhead may still go off where it lands.
                     let warhead = if spec.decoy || !self.rng.chance(0.35) { 0 } else { spec.warhead.min(2) };
                     boom.push((d.pos, warhead, true));
@@ -1439,13 +1477,24 @@ impl Sim {
                     d.vel = turn(d.vel, d.target - d.pos, spec.turn) * sp;
                 }
                 d.pos += d.vel;
+                let sweep = ground.sweep(from, d.pos, d.age <= 3, now);
+                if let Some((_, p)) = sweep.hit() {
+                    d.pos = p;
+                }
                 let speed = d.vel.length();
+                let landed = sweep.hit().is_some() || ground.ground_hit(below, d.pos, 0.2, &sweep, now);
                 let hit = d.pos.distance(d.target) < speed.max(2.0)
-                    || below.is_some_and(|g| d.pos.y <= g + 0.2)
+                    || landed
                     || (d.vel.y < 0.0 && d.pos.y < d.target.y - 1.0 && horizontal(d.target - d.pos).length() < speed * 2.0)
                     || d.age > 4000;
                 if hit {
                     boom.push((d.pos, spec.warhead, false));
+                    // Into the land or a building short of its aim: a crash, not a hit.
+                    if landed && d.pos.distance(d.target) >= speed.max(2.0) + 6.0 {
+                        crashes.push((d.id, d.kind, d.pos, spec.warhead));
+                        removed.push(d.id);
+                        continue;
+                    }
                     impacts.push((d.id, d.kind, d.pos, spec.warhead));
                     removed.push(d.id);
                     self.hits += 1;
@@ -1546,10 +1595,22 @@ impl Sim {
             let speed = if d.flight == Flight::Dive { spec.speed * 1.35 } else { spec.speed };
             d.vel = new * speed;
             d.pos += d.vel;
+            let sweep = ground.sweep(from, d.pos, d.age <= 3, now);
+            if let Some((_, p)) = sweep.hit() {
+                d.pos = p;
+            }
             let at_target = d.pos.distance(d.target) < speed.max(1.5);
-            let in_ground = below.is_some_and(|g| d.pos.y <= g + 0.2);
+            let in_ground = sweep.hit().is_some() || ground.ground_hit(below, d.pos, 0.2, &sweep, now);
             if at_target || in_ground || d.age > 8000 {
                 boom.push((d.pos, spec.warhead, spec.decoy));
+                // Into the land or a building short of its aim: a crash, not a hit.
+                if in_ground && d.pos.distance(d.target) >= speed.max(1.5) + 3.0 {
+                    if !spec.decoy {
+                        crashes.push((d.id, d.kind, d.pos, spec.warhead));
+                    }
+                    removed.push(d.id);
+                    continue;
+                }
                 if !spec.decoy {
                     impacts.push((d.id, d.kind, d.pos, spec.warhead));
                 }
@@ -1580,6 +1641,17 @@ impl Sim {
         for (drone, pos) in splits {
             self.log(pos, record::EventKind::Split { drone });
         }
+        for (drone, kind, pos, tnt) in crashes {
+            self.crashes += 1;
+            let power = match tnt {
+                0 => 0,
+                1 | 2 => 1,
+                3..=5 => 2,
+                6 | 7 => 3,
+                _ => 4,
+            };
+            self.log(pos, record::EventKind::Crash { drone, kind, power });
+        }
         for (drone, kind, pos, tnt) in impacts {
             if let Some(sector) = self.drones.iter().find(|x| x.id == drone).map(|x| x.sector as usize) {
                 self.learn(sector, false);
@@ -1594,6 +1666,8 @@ impl Sim {
             let object = self.targets.iter().position(|t| t.distance(pos) < 16.0);
             let sam = self.sams.iter().enumerate().find(|(_, s)| s.alive() && s.pos.distance(pos) < 12.0).map(|(i, s)| (s.kind, i));
             self.log(pos, record::EventKind::Hit { drone, kind, power, object, sam });
+            let vel = self.drones.iter().find(|x| x.id == drone).map_or(DVec3::ZERO, |x| x.vel);
+            self.direct_hit(pos, vel, tnt, out);
         }
         for (pos, warhead, small) in boom {
             self.explode(pos, warhead, small, ground, player, out);
@@ -2061,9 +2135,11 @@ impl Sim {
 
     // ------------------------------------------------ interceptors
 
-    fn step_missiles(&mut self, out: &mut Out) {
+    fn step_missiles(&mut self, ground: &mut Ground, out: &mut Out) {
+        let now = self.tick;
         let mut done: Vec<(u32, Option<u32>, bool, u32)> = Vec::new(); // (missile, target, kill, sam)
         let (mut missed, mut expired, mut orphaned) = (0u32, 0u32, 0u32);
+        let mut blocked = 0u32;
         let sams_fit: HashMap<u32, f64> = self.sams.iter().map(|s| (s.id, s.fitness())).collect();
         for m in &mut self.missiles {
             m.age += 1;
@@ -2091,13 +2167,16 @@ impl Sim {
             let before = m.pos;
             m.vel = new * speed;
             m.pos += m.vel;
+            // The first block on the way this tick; a fuse that goes off earlier along the way still counts.
+            ground.ahead(m.pos, m.vel, 10.0, now);
+            let world = ground.sweep(before, m.pos, m.age <= 12, now).hit();
             if let Some(t) = target {
                 // Closest approach this tick, both moving (fast targets cross a fuse in a tick).
                 let rel0 = (t.pos - t.vel) - before;
                 let rel1 = t.pos - m.pos;
                 let delta = rel1 - rel0;
                 let k = (-rel0.dot(delta) / delta.length_squared().max(1e-9)).clamp(0.0, 1.0);
-                if (rel0 + delta * k).length() < spec.fuse {
+                if (rel0 + delta * k).length() < spec.fuse && world.is_none_or(|(w, _)| k <= w) {
                     // A target faster than the interceptor is hard to hit.
                     let ratio = (spec.speed / t.vel.length().max(0.1)).min(1.0).powf(1.5);
                     let fit = sams_fit.get(&m.sam).copied().unwrap_or(1.0);
@@ -2107,6 +2186,13 @@ impl Sim {
                     continue;
                 }
             }
+            if let Some((_, p)) = world {
+                // The land or a building is in the way: the interceptor is lost there.
+                m.pos = p;
+                blocked += 1;
+                done.push((m.id, None, false, m.sam));
+                continue;
+            }
             if m.age > spec.life || (target.is_none() && m.age > 30) {
                 // Its target gone (shot down by another, or lost), or its life spent chasing one.
                 if target.is_none() {
@@ -2151,6 +2237,7 @@ impl Sim {
             t.missed += missed;
             t.expired += expired;
             t.orphaned += orphaned;
+            t.blocked += blocked;
         });
         for (mid, target, kill, sam) in done {
             if let Some(i) = self.missiles.iter().position(|m| m.id == mid) {

airdef-mod/src/sim/record.rs

@@ -39,6 +39,8 @@ pub enum EventKind {
     SamLost { sam: u32, kind: SamKind, index: usize },
     /// The Oreshnik's bus or a block splitting.
     Split { drone: u32 },
+    /// A drone's warhead went off against the land or a building short of its aim.
+    Crash { drone: u32, kind: DroneKind, power: u32 },
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -61,6 +63,8 @@ pub struct Tally {
     pub tracks_lost: u32,
     /// Times a system ran dry and began waiting for a reload truck.
     pub ammo_waits: u32,
+    /// Interceptors lost against the land or a building on their way.
+    pub blocked: u32,
 }
 
 impl Tally {
@@ -71,6 +75,7 @@ impl Tally {
             orphaned: self.orphaned.saturating_sub(start.orphaned),
             tracks_lost: self.tracks_lost.saturating_sub(start.tracks_lost),
             ammo_waits: self.ammo_waits.saturating_sub(start.ammo_waits),
+            blocked: self.blocked.saturating_sub(start.blocked),
         }
     }
     /// The non-zero counts as a line, or nothing.
@@ -81,6 +86,7 @@ impl Tally {
             (self.orphaned, "ракет остались без цели"),
             (self.tracks_lost, "потерь трека"),
             (self.ammo_waits, "ожиданий БК"),
+            (self.blocked, "ракет разбились о препятствие"),
         ]
         .into_iter()
         .filter(|p| p.0 > 0)
@@ -312,7 +318,7 @@ impl Sim {
             }
             let size = match e.kind {
                 EventKind::Kill { .. } => 3.5,
-                EventKind::Hit { power, .. } => [2.5, 4.5, 7.0, 10.0, 13.0][(power as usize).min(4)],
+                EventKind::Hit { power, .. } | EventKind::Crash { power, .. } => [2.5, 4.5, 7.0, 10.0, 13.0][(power as usize).min(4)],
                 EventKind::SamLost { .. } => 8.0,
                 EventKind::Split { .. } => 2.0,
             };

airdef-mod/src/sim/regress.rs

@@ -1,6 +1,7 @@
 //! Regression tests for the issues filed on Gitea (each names its issue).
 use super::*;
 use super::raid::Grid;
+use super::damage::MISS_RADIUS;
 
 // #1: [bug] Запросы рельефа голодают: часть направлений РЛС никогда не получает высоты
 #[test]
@@ -222,3 +223,281 @@ fn drive_arrives_without_overshoot() {
         assert!(left.abs() < 1e-9 && vel == 0.0);
     }
 }
+
+// #49: a direct hit by an armed drone destroys the system at once, not with a dent of its health
+#[test]
+fn armed_strike_on_a_system_destroys_it_at_once() {
+    let centre = DVec3::new(0.0, 70.0, 0.0);
+    let hull = 2.2 * SamKind::Patriot.spec().scale;
+    for kind in [DroneKind::Lancet, DroneKind::Shahed] {
+        let mut destroyed = 0;
+        for seed in 1..=40 {
+            let mut sim = Sim::new(seed);
+            let id = sim.id();
+            sim.sams.push(Sam::new(id, SamKind::Patriot, centre, 0.0));
+            let mut ground = Ground::default();
+            sim.add_drone(kind, DVec3::new(0.0, 120.0, 0.0), DVec3::NEG_Y, centre);
+            let mut out = Out::default();
+            let mut impact = None;
+            for _ in 0..400 {
+                sim.step(&mut ground, None, &mut out);
+                if let Some(b) = sim.blasts.first() {
+                    impact = Some(b.at);
+                    break;
+                }
+                if sim.drones.is_empty() {
+                    break;
+                }
+            }
+            let at = impact.expect("the strike must go off");
+            let inside = DVec3::new(at.x, 0.0, at.z).distance(DVec3::new(centre.x, 0.0, centre.z)) <= hull && at.y < centre.y + 3.0;
+            let dead = !sim.sams[0].alive();
+            if inside {
+                assert!(dead, "{kind:?} seed {seed} struck the hull at {at:?} but the system lives");
+            }
+            destroyed += dead as u32;
+        }
+        assert!(destroyed >= 30, "{kind:?}: only {destroyed}/40 direct strikes destroyed the system");
+    }
+}
+
+// #49: a near miss is only splash, an unarmed body is no direct hit, the top of the hull counts
+#[test]
+fn near_miss_and_unarmed_body_are_not_direct_hits() {
+    let mut sim = Sim::new(1);
+    let id = sim.id();
+    sim.sams.push(Sam::new(id, SamKind::Patriot, DVec3::new(0.0, 70.0, 0.0), 0.0));
+    let down = DVec3::new(0.0, -2.0, 0.0);
+    sim.direct_hit(DVec3::new(6.0, 71.0, 0.0), down, 3, &mut Out::default());
+    assert!(sim.sams[0].alive(), "a near miss six blocks off destroyed the system");
+    sim.direct_hit(DVec3::new(0.0, 71.0, 0.0), down, 0, &mut Out::default());
+    assert!(sim.sams[0].alive(), "an unarmed body destroyed the system");
+    sim.direct_hit(DVec3::new(0.0, 73.0, 0.0), down, 1, &mut Out::default());
+    assert!(!sim.sams[0].alive(), "an armed warhead into the top of the hull did not destroy the system");
+}
+
+// #59: a strike misses at a small, kind-specific rate; its scatter is the kind's CEP (half land within it)
+#[test]
+fn strike_scatter_matches_each_kinds_cep_and_miss_rate() {
+    const N: u64 = 5000;
+    for kind in DroneKind::ALL {
+        let mut sim = Sim::new(7);
+        let (cep, gross) = kind.accuracy();
+        let sigma = cep / (2.0 * std::f64::consts::LN_2).sqrt();
+        let expected = (1.0 - gross) * (-MISS_RADIUS * MISS_RADIUS / (2.0 * sigma * sigma)).exp() + gross;
+        let (mut misses, mut within, mut farthest) = (0u64, 0u64, 0.0f64);
+        for _ in 0..N {
+            let e = sim.aim_error(kind);
+            assert_eq!(e.y, 0.0);
+            let r = e.length();
+            within += (r <= cep) as u64;
+            if r > MISS_RADIUS {
+                misses += 1;
+                farthest = farthest.max(r);
+            }
+        }
+        let rate = misses as f64 / N as f64;
+        let half = within as f64 / N as f64;
+        assert!((rate - expected).abs() < 0.015, "{kind:?}: miss rate {rate:.4}, expected {expected:.4}");
+        assert!((0.005..=0.20).contains(&rate), "{kind:?}: miss rate {rate:.4} is not a small share (the IRBM bus is the loosest)");
+        assert!((half - 0.5 * (1.0 - gross)).abs() < 0.03, "{kind:?}: {half:.3} of strikes within the CEP {cep}");
+        assert!(farthest < MISS_RADIUS + 4.0 * cep, "{kind:?}: a miss {farthest:.2} blocks out, far from the aim");
+    }
+}
+
+// #59: the drone flies to its own error point and bursts there: the miss lands near the aim, by the CEP
+#[test]
+fn strikes_burst_near_their_aim_within_the_kinds_cep() {
+    let aim = DVec3::new(0.0, 70.0, 0.0);
+    for kind in [DroneKind::Shahed, DroneKind::Lancet] {
+        let cep = kind.accuracy().0;
+        let mut misses = 0;
+        for seed in 1..=60 {
+            let mut sim = Sim::new(seed);
+            let mut ground = Ground::default();
+            sim.add_drone(kind, DVec3::new(0.0, 120.0, 0.0), DVec3::NEG_Y, aim);
+            let mut out = Out::default();
+            let mut impact = None;
+            for _ in 0..400 {
+                sim.step(&mut ground, None, &mut out);
+                if let Some(b) = sim.blasts.first() {
+                    impact = Some(b.at);
+                    break;
+                }
+                if sim.drones.is_empty() {
+                    break;
+                }
+            }
+            let at = impact.expect("the strike must go off");
+            let off = DVec3::new(at.x - aim.x, 0.0, at.z - aim.z).length();
+            assert!(off < MISS_RADIUS + 4.0 * cep + 2.0, "{kind:?} seed {seed} burst {off:.2} blocks from its aim");
+            misses += (off > MISS_RADIUS) as u32;
+        }
+        assert!(misses <= 6, "{kind:?}: {misses}/60 strikes missed");
+    }
+}
+
+// ---- #42, #43: flights are swept against the blocks of the world (a synthetic world stands in for the game)
+
+/// Blocks from a function: `Some(solid)`, or `None` where there is no chunk.
+struct Blocks<F: Fn(i32, i32, i32) -> Option<bool>>(F);
+impl<F: Fn(i32, i32, i32) -> Option<bool>> world::WorldSource for Blocks<F> {
+    fn solid(&self, x: i32, y: i32, z: i32) -> Option<bool> {
+        (self.0)(x, y, z)
+    }
+}
+
+/// Reads the sections a flight along `a` to `b` needs, as the game would answer them over a few ticks.
+fn warm(ground: &mut Ground, src: &dyn world::WorldSource, a: DVec3, b: DVec3) {
+    for _ in 0..4 {
+        ground.world.sweep(a, b, false, 0);
+        let wanted = ground.world.take_wanted(0);
+        ground.world.serve(src, wanted, 0);
+    }
+}
+
+/// One tick of the drones with the game answering what was asked.
+fn fly(sim: &mut Sim, ground: &mut Ground, src: &dyn world::WorldSource) {
+    sim.tick += 1;
+    sim.step_drones(ground, None, &mut Out::default());
+    let wanted = ground.world.take_wanted(sim.tick);
+    ground.world.serve(src, wanted, sim.tick);
+}
+
+// #42: a drone that crosses a one-block wall in a tick explodes at the wall, and that is no hit on its aim
+#[test]
+fn fast_drone_must_not_cross_a_one_block_wall() {
+    let src = Blocks(|x, y, z| Some(y < 64 || (x == 3 && (64..141).contains(&y) && z.abs() < 50)));
+    let mut sim = Sim::new(1);
+    sim.damage = false;
+    let mut ground = Ground::default();
+    sim.add_drone(DroneKind::Zircon, DVec3::new(0.0, 100.0, 0.0), DVec3::X, DVec3::new(1000.0, 100.0, 0.0));
+    sim.drones[0].flight = Flight::Dive;
+    warm(&mut ground, &src, DVec3::new(0.0, 100.0, 0.0), DVec3::new(30.0, 100.0, 0.0));
+    fly(&mut sim, &mut ground, &src);
+    assert!(sim.drones.is_empty(), "crossed the wall in one tick");
+    let at = sim.blasts.first().expect("no blast").at;
+    assert!((at.x - 3.0).abs() < 0.05 && (at.y - 100.0).abs() < 1.5, "burst at {at:?}, not at the wall face x=3");
+    assert_eq!((sim.crashes, sim.hits), (1, 0), "a wall in the way is a crash, not a hit on the aim");
+    assert!(sim.replays.iter().chain(sim.rec.iter()).all(|r| r.events.iter().all(|e| !matches!(e.kind, record::EventKind::Hit { .. }))));
+}
+
+// #42: a drone flying into a hill side explodes at the face of the hill
+#[test]
+fn drone_flying_into_a_hill_explodes_at_its_face() {
+    // Flat at 64 to x=50, then a slope of 1:1.
+    let height = |x: i32| 64 + (x - 50).max(0);
+    let src = Blocks(move |x, y, _| Some(y < height(x)));
+    for kind in [DroneKind::Shahed, DroneKind::Zircon] {
+        let mut sim = Sim::new(3);
+        sim.damage = false;
+        let mut ground = Ground::default();
+        sim.add_drone(kind, DVec3::new(0.0, 80.0, 0.0), DVec3::X, DVec3::new(600.0, 80.0, 0.0));
+        sim.drones[0].flight = Flight::Dive;
+        for _ in 0..300 {
+            if sim.drones.is_empty() {
+                break;
+            }
+            fly(&mut sim, &mut ground, &src);
+        }
+        assert!(sim.drones.is_empty(), "{kind:?} flew on");
+        let at = sim.blasts.first().expect("no blast").at;
+        // The slope meets y=80 at x=66.
+        assert!(at.x > 62.0 && at.x < 67.5, "{kind:?} burst at {at:?}, not at the hill face (x~66)");
+        assert_eq!(sim.crashes, 1, "{kind:?}");
+    }
+}
+
+// #42: an interceptor cannot pass through a wall to its target, and does not kill it from behind the wall
+#[test]
+fn missile_cannot_pass_through_a_wall() {
+    let src = Blocks(|x, y, z| Some(y < 64 || (x == 3 && (64..141).contains(&y) && z.abs() < 50)));
+    let mut sim = Sim::new(1);
+    let mut ground = Ground::default();
+    // The target stands still just behind the wall, inside the fuse's reach.
+    sim.add_drone(DroneKind::Shahed, DVec3::new(8.5, 100.0, 0.0), DVec3::ZERO, DVec3::new(0.0, 100.0, 900.0));
+    sim.drones[0].vel = DVec3::ZERO;
+    sim.drones[0].engaged = 1;
+    let (target, id) = (sim.drones[0].id, sim.id());
+    sim.missiles.push(Missile { id, kind: MissileKind::Pac3, pos: DVec3::new(0.0, 100.0, 0.0), vel: DVec3::X * 3.0, target, sam: 0, age: 20 });
+    warm(&mut ground, &src, DVec3::new(0.0, 100.0, 0.0), DVec3::new(30.0, 100.0, 0.0));
+    sim.tick = 1;
+    sim.step_missiles(&mut ground, &mut Out::default());
+    assert!(sim.missiles.is_empty(), "the missile is still flying");
+    assert_eq!(sim.kills, 0, "a kill through the wall");
+    assert!(sim.drones[0].alive(), "the target died behind the wall");
+    assert_eq!(sim.drones[0].engaged, 0, "the target stays claimed by a missile that is gone");
+    assert_eq!(sim.tally.blocked, 1);
+    assert!(sim.blasts.iter().all(|b| b.at.x < 3.5), "burst behind the wall");
+}
+
+// #42, #43: a bridge deck above the flight is no ground under it
+#[test]
+fn flight_under_a_bridge_is_not_a_ground_hit() {
+    let src = Blocks(|_, y, _| Some(y < 64 || y == 140));
+    let mut sim = Sim::new(1);
+    sim.damage = false;
+    let mut ground = Ground::default();
+    // The height map knows only the deck: 141 everywhere.
+    ground.answer((-5..400).map(|x| (x, 0, 141)).collect(), 0);
+    sim.add_drone(DroneKind::Shahed, DVec3::new(0.0, 100.0, 0.0), DVec3::X, DVec3::new(2000.0, 100.0, 0.0));
+    warm(&mut ground, &src, DVec3::new(0.0, 100.0, 0.0), DVec3::new(300.0, 100.0, 0.0));
+    for _ in 0..40 {
+        fly(&mut sim, &mut ground, &src);
+    }
+    assert_eq!(sim.drones.len(), 1, "the deck above was taken for the ground");
+    assert_eq!(sim.crashes, 0);
+}
+
+// #43: unknown chunks and spent budgets are never air; changes and another world void the cache
+#[test]
+fn unknown_is_not_clear_and_changes_invalidate() {
+    let mut ground = Ground::default();
+    let (a, b) = (DVec3::new(0.5, 70.5, 0.5), DVec3::new(30.5, 70.5, 0.5));
+    // Nothing read yet: the segment is unknown and the sections are asked for.
+    assert!(matches!(ground.world.sweep(a, b, false, 1), world::Sweep::Unknown { .. }));
+    let asked = ground.world.take_wanted(1);
+    assert!(asked.contains(&(0, 4, 0)), "{asked:?}");
+    // The game has no chunk there: still unknown, not air.
+    let nothing = Blocks(|_, _, _| None);
+    ground.world.serve(&nothing, asked, 2);
+    assert!(matches!(ground.world.sweep(a, b, false, 3), world::Sweep::Unknown { .. }));
+    // A wall appears in a chunk that now is loaded: found after it is read again.
+    let wall = Blocks(|x, _, _| Some(x == 20));
+    for now in [70, 71, 72] {
+        ground.world.sweep(a, b, false, now);
+        let w = ground.world.take_wanted(now);
+        ground.world.serve(&wall, w, now);
+    }
+    let hit = ground.world.sweep(a, b, false, 73);
+    assert!(matches!(hit, world::Sweep::Hit { block: [20, 70, 0], normal: [-1, 0, 0], .. }), "{hit:?}");
+    // The wall is broken: the game says which section changed, and the next sweep asks again.
+    let open = Blocks(|_, _, _| Some(false));
+    ground.world.changed(7, false, &[(1, 4, 0)]);
+    assert!(matches!(ground.world.sweep(a, b, false, 74), world::Sweep::Hit { .. }), "stale data is used until the answer");
+    let w = ground.world.take_wanted(74);
+    assert!(w.contains(&(1, 4, 0)), "{w:?}");
+    ground.world.serve(&open, w, 75);
+    assert_eq!(ground.world.sweep(a, b, false, 76), world::Sweep::Clear);
+    // Another world: everything goes.
+    ground.world.changed(8, false, &[]);
+    assert!(ground.world.is_empty());
+}
+
+// #43: the same wall and tunnel fixtures answer alike by sweep and by sections, and the cache is bounded
+#[test]
+fn wall_and_tunnel_fixtures_agree() {
+    let tunnel = Blocks(|x, y, z| Some(y < 60 || (x == 10 && !(y == 70 && z == 0))));
+    let mut ground = Ground::default();
+    for z in [0.5, 1.5] {
+        let (a, b) = (DVec3::new(0.5, 70.5, z), DVec3::new(30.5, 70.5, z));
+        warm(&mut ground, &tunnel, a, b);
+        let r = ground.world.sweep(a, b, false, 1);
+        if z == 0.5 {
+            assert_eq!(r, world::Sweep::Clear, "the tunnel is open");
+        } else {
+            assert!(matches!(r, world::Sweep::Hit { block: [10, 70, 1], .. }), "{r:?}");
+        }
+    }
+    assert!(ground.world.bytes() < 64 * 1024);
+}

airdef-mod/src/sim/world.rs

@@ -0,0 +1,399 @@
+//! What the game's blocks are to the simulation (issues #42, #43): a cache of
+//! 16-block sections answered by `render.sections` (a bit per block that
+//! stops a projectile), a swept segment through it, and the bookkeeping that
+//! keeps the questions few: the sections along a flight asked for ahead of
+//! time, at most 64 a tick, nearest need first; changes of the world marking
+//! sections stale; a bounded cache. A chunk the game doesn't have answers
+//! `Unknown`, which is never the same as air: the callers fall back to the
+//! height of the land there and the counters say how often.
+use glam::DVec3;
+use std::collections::{HashMap, HashSet};
+
+/// A section: block coordinates divided by 16.
+pub type Sec = (i32, i32, i32);
+
+/// Sections asked in one tick (the game's budget).
+pub const PER_TICK: usize = 64;
+/// Sections kept; the least recently used go first beyond it.
+const MAX_SECTIONS: usize = 12_000;
+/// Ticks before an unanswered or unknown section is asked again.
+const RETRY: u64 = 60;
+/// Longest stretch of a flight asked for ahead, in blocks.
+const AHEAD_MAX: f64 = 192.0;
+/// Questions waiting: more are dropped (they are asked again when needed).
+const QUEUE_MAX: usize = 512;
+
+/// What a section holds, as the game answered.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum Fill {
+    /// The game has no such chunk.
+    Unknown,
+    Empty,
+    Full,
+    /// 512 bytes, one bit per block, index `(y & 15) * 256 + (z & 15) * 16 + (x & 15)`.
+    Mixed(Box<[u8; 512]>),
+}
+
+/// An answer for a section, as the game gives it.
+pub struct SectionAnswer {
+    pub sec: Sec,
+    pub fill: Fill,
+}
+
+struct Entry {
+    fill: Fill,
+    /// A block changed (or may have) since it was read: asked again when next used.
+    stale: bool,
+    /// The tick it was last used in a sweep.
+    used: u64,
+    /// The tick it was answered.
+    since: u64,
+}
+
+/// How a swept segment ended.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Sweep {
+    /// Every block along it is known and none stops it.
+    Clear,
+    /// The first solid block: where the segment meets it, which way the face looks, and the block.
+    Hit { t: f64, point: DVec3, normal: [i32; 3], block: [i32; 3] },
+    /// The walk reached blocks the game doesn't know (before any solid one), `t` of the way.
+    Unknown { t: f64 },
+}
+
+impl Sweep {
+    pub fn hit(&self) -> Option<(f64, DVec3)> {
+        match *self {
+            Sweep::Hit { t, point, .. } => Some((t, point)),
+            _ => None,
+        }
+    }
+}
+
+/// Counters for the report: questions, unknowns, memory, cost.
+#[derive(Clone, Copy, Default, Debug)]
+pub struct WorldStats {
+    pub sweeps: u64,
+    pub cells: u64,
+    pub hits: u64,
+    pub unknown_sweeps: u64,
+    pub sections_asked: u64,
+    pub sections_answered: u64,
+    pub sections_unknown: u64,
+    pub invalidated: u64,
+    pub evicted: u64,
+    pub world_changes: u64,
+}
+
+#[derive(Default)]
+pub struct WorldCache {
+    secs: HashMap<Sec, Entry>,
+    urgent: Vec<Sec>,
+    ahead: Vec<Sec>,
+    queued: HashSet<Sec>,
+    /// Sections asked, and when.
+    asked: HashMap<Sec, u64>,
+    epoch: u32,
+    pub stats: WorldStats,
+}
+
+fn sec_of(x: i32, y: i32, z: i32) -> Sec {
+    (x >> 4, y >> 4, z >> 4)
+}
+
+impl WorldCache {
+    /// Memory the cached sections hold, about.
+    pub fn bytes(&self) -> usize {
+        self.secs
+            .values()
+            .map(|e| 48 + if matches!(e.fill, Fill::Mixed(_)) { 512 } else { 0 })
+            .sum()
+    }
+    pub fn len(&self) -> usize {
+        self.secs.len()
+    }
+    pub fn is_empty(&self) -> bool {
+        self.secs.is_empty()
+    }
+    /// One line for the report.
+    pub fn text(&self) -> String {
+        let s = &self.stats;
+        format!(
+            "мир: {} секций ({} КБ), запросов {}, неизвестно {}, лучей {} (ударов {}, неизв. {}), клеток {}",
+            self.len(),
+            self.bytes() / 1024,
+            s.sections_asked,
+            s.sections_unknown,
+            s.sweeps,
+            s.hits,
+            s.unknown_sweeps,
+            s.cells
+        )
+    }
+
+    /// The game's note of changes: another world voids everything; changed
+    /// sections (or too many to say) are read again when next used.
+    pub fn changed(&mut self, epoch: u32, overflow: bool, sections: &[Sec]) {
+        if epoch != self.epoch {
+            if self.epoch != 0 {
+                self.secs.clear();
+                self.urgent.clear();
+                self.ahead.clear();
+                self.queued.clear();
+                self.asked.clear();
+            }
+            self.epoch = epoch;
+        }
+        if overflow {
+            for e in self.secs.values_mut() {
+                e.stale = true;
+            }
+            self.stats.invalidated += self.secs.len() as u64;
+        }
+        for s in sections {
+            if let Some(e) = self.secs.get_mut(s) {
+                e.stale = true;
+                self.stats.invalidated += 1;
+            }
+        }
+        self.stats.world_changes += sections.len() as u64;
+    }
+
+    /// An explosion is about to change the land: the sections round it are read again.
+    pub fn touched(&mut self, at: DVec3, radius: f64) {
+        let lo = sec_of((at.x - radius).floor() as i32, (at.y - radius).floor() as i32, (at.z - radius).floor() as i32);
+        let hi = sec_of((at.x + radius).floor() as i32, (at.y + radius).floor() as i32, (at.z + radius).floor() as i32);
+        for x in lo.0..=hi.0 {
+            for y in lo.1..=hi.1 {
+                for z in lo.2..=hi.2 {
+                    if let Some(e) = self.secs.get_mut(&(x, y, z)) {
+                        e.stale = true;
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn answer(&mut self, answers: Vec<SectionAnswer>, now: u64) {
+        for a in answers {
+            self.asked.remove(&a.sec);
+            self.stats.sections_answered += 1;
+            if a.fill == Fill::Unknown {
+                self.stats.sections_unknown += 1;
+            }
+            self.secs.insert(a.sec, Entry { fill: a.fill, stale: false, used: now, since: now });
+        }
+        if self.secs.len() > MAX_SECTIONS {
+            // Whatever wasn't used for a minute goes; if that's not enough, the older half.
+            self.secs.retain(|_, e| now.saturating_sub(e.used) < 1200);
+            if self.secs.len() > MAX_SECTIONS {
+                let mut used: Vec<u64> = self.secs.values().map(|e| e.used).collect();
+                used.sort_unstable();
+                let cut = used[used.len() / 2];
+                self.secs.retain(|_, e| e.used >= cut);
+            }
+            self.stats.evicted += 1;
+        }
+        // Forget questions the game never answered, so they can be asked again.
+        if now % 64 == 0 {
+            self.asked.retain(|_, t| now.saturating_sub(*t) < RETRY);
+        }
+    }
+
+    /// The sections to ask this tick (at most [`PER_TICK`]): the ones a sweep
+    /// needed first, then those along flights.
+    pub fn take_wanted(&mut self, now: u64) -> Vec<Sec> {
+        let mut out = Vec::new();
+        for list in [&mut self.urgent, &mut self.ahead] {
+            let room = PER_TICK - out.len();
+            let n = room.min(list.len());
+            out.extend(list.drain(..n));
+        }
+        for s in &out {
+            self.queued.remove(s);
+            self.asked.insert(*s, now);
+        }
+        self.stats.sections_asked += out.len() as u64;
+        out
+    }
+
+    fn want(&mut self, s: Sec, urgent: bool, now: u64) {
+        if self.queued.contains(&s) || self.asked.get(&s).is_some_and(|&t| now.saturating_sub(t) < RETRY) {
+            return;
+        }
+        if self.urgent.len() + self.ahead.len() >= QUEUE_MAX {
+            return;
+        }
+        if urgent {
+            self.urgent.push(s);
+        } else {
+            self.ahead.push(s);
+        }
+        self.queued.insert(s);
+    }
+
+    /// Asks for the sections along a flight from `pos` at `vel` a tick, `ticks` ahead.
+    pub fn look_ahead(&mut self, pos: DVec3, vel: DVec3, ticks: f64, now: u64) {
+        let mut d = vel * ticks;
+        let len = d.length();
+        if len < 1e-6 {
+            return;
+        }
+        if len > AHEAD_MAX {
+            d *= AHEAD_MAX / len;
+        }
+        // A section at a time along the segment (a section is 16 wide: half-section steps meet each).
+        let steps = (d.length() / 8.0).ceil().max(1.0) as i32;
+        let mut last = None;
+        for i in 0..=steps {
+            let p = pos + d * (i as f64 / steps as f64);
+            let s = sec_of(p.x.floor() as i32, p.y.floor() as i32, p.z.floor() as i32);
+            if last == Some(s) {
+                continue;
+            }
+            last = Some(s);
+            self.touch(s, false, now);
+        }
+    }
+
+    /// Touches a section the way a sweep or a look needs it: used now, and
+    /// asked again when stale or (after a while) unknown.
+    fn touch(&mut self, s: Sec, urgent: bool, now: u64) -> bool {
+        let Some(e) = self.secs.get_mut(&s) else {
+            self.want(s, urgent, now);
+            return false;
+        };
+        e.used = now;
+        let refresh = e.stale || (e.fill == Fill::Unknown && now.saturating_sub(e.since) >= RETRY);
+        if refresh {
+            self.want(s, urgent, now);
+        }
+        true
+    }
+
+    /// Whether the block at `(x, y, z)` stops a projectile: `None` where the
+    /// game hasn't said. `last` is the section just touched.
+    fn solid(&mut self, last: &mut Option<Sec>, x: i32, y: i32, z: i32, now: u64) -> Option<bool> {
+        let s = sec_of(x, y, z);
+        if *last != Some(s) {
+            *last = Some(s);
+            self.touch(s, true, now);
+        }
+        match &self.secs.get(&s)?.fill {
+            Fill::Unknown => None,
+            Fill::Empty => Some(false),
+            Fill::Full => Some(true),
+            Fill::Mixed(bits) => {
+                let i = ((y & 15) << 8 | (z & 15) << 4 | (x & 15)) as usize;
+                Some(bits[i >> 3] >> (i & 7) & 1 != 0)
+            }
+        }
+    }
+
+    /// Whether the block is known to hold no solid block, with the sky above it
+    /// in view: used to tell a fluid surface from a roof.
+    pub fn is_known_open(&mut self, x: i32, y: i32, z: i32, now: u64) -> bool {
+        self.solid(&mut None, x, y, z, now) == Some(false)
+    }
+
+    /// Whether the block is known to be solid.
+    pub fn is_known_solid(&mut self, x: i32, y: i32, z: i32, now: u64) -> bool {
+        self.solid(&mut None, x, y, z, now) == Some(true)
+    }
+
+    /// The first solid block along `a` to `b`, by walking the blocks it
+    /// crosses; `skip_start` ignores the block it starts in (a launch from a
+    /// pad that is part of the land).
+    pub fn sweep(&mut self, a: DVec3, b: DVec3, skip_start: bool, now: u64) -> Sweep {
+        self.stats.sweeps += 1;
+        let d = b - a;
+        let mut pos = [a.x.floor() as i32, a.y.floor() as i32, a.z.floor() as i32];
+        let dv = [d.x, d.y, d.z];
+        let av = [a.x, a.y, a.z];
+        let step: [i32; 3] = dv.map(|v| if v > 0.0 { 1 } else { -1 });
+        let mut t_max = [f64::INFINITY; 3];
+        let mut t_delta = [f64::INFINITY; 3];
+        for i in 0..3 {
+            if dv[i] != 0.0 {
+                let edge = f64::from(pos[i]) + if dv[i] > 0.0 { 1.0 } else { 0.0 };
+                t_max[i] = (edge - av[i]) / dv[i];
+                t_delta[i] = (1.0 / dv[i]).abs();
+            }
+        }
+        let mut last: Option<Sec> = None;
+        let mut face = [0i32; 3];
+        let mut t = 0.0f64;
+        let mut first = true;
+        for _ in 0..4096 {
+            self.stats.cells += 1;
+            match self.solid(&mut last, pos[0], pos[1], pos[2], now) {
+                None => {
+                    self.stats.unknown_sweeps += 1;
+                    return Sweep::Unknown { t };
+                }
+                Some(true) if !(first && skip_start) => {
+                    self.stats.hits += 1;
+                    return Sweep::Hit { t, point: a + d * t, normal: face, block: pos };
+                }
+                _ => {}
+            }
+            first = false;
+            let axis = if t_max[0] < t_max[1] {
+                if t_max[0] < t_max[2] { 0 } else { 2 }
+            } else if t_max[1] < t_max[2] {
+                1
+            } else {
+                2
+            };
+            t = t_max[axis];
+            if t > 1.0 {
+                return Sweep::Clear;
+            }
+            t_max[axis] += t_delta[axis];
+            pos[axis] += step[axis];
+            face = [0; 3];
+            face[axis] = -step[axis];
+        }
+        self.stats.unknown_sweeps += 1;
+        Sweep::Unknown { t }
+    }
+}
+
+/// Where the game's blocks come from in tests and the native runner: any
+/// world that can say what a block is.
+pub trait WorldSource {
+    /// Whether the block stops a projectile; `None` where there is no chunk.
+    fn solid(&self, x: i32, y: i32, z: i32) -> Option<bool>;
+}
+
+/// A [`WorldSource`] as the game would answer `render.query-sections` with it.
+pub fn section_of(source: &dyn WorldSource, s: Sec) -> Fill {
+    let mut bits = Box::new([0u8; 512]);
+    let (mut set, mut known) = (0u32, 0u32);
+    for i in 0..4096usize {
+        let (x, y, z) = (s.0 * 16 + (i & 15) as i32, s.1 * 16 + (i >> 8) as i32, s.2 * 16 + ((i >> 4) & 15) as i32);
+        match source.solid(x, y, z) {
+            Some(true) => {
+                bits[i >> 3] |= 1 << (i & 7);
+                set += 1;
+                known += 1;
+            }
+            Some(false) => known += 1,
+            None => {}
+        }
+    }
+    match (known, set) {
+        (0, _) => Fill::Unknown,
+        (_, 0) if known == 4096 => Fill::Empty,
+        (_, 4096) => Fill::Full,
+        _ => Fill::Mixed(bits),
+    }
+}
+
+impl WorldCache {
+    /// Answers the questions of the last tick from a synthetic world, as the game does one tick later.
+    pub fn serve(&mut self, source: &dyn WorldSource, wanted: Vec<Sec>, now: u64) {
+        let answers = wanted.into_iter().map(|sec| SectionAnswer { sec, fill: section_of(source, sec) }).collect();
+        self.answer(answers, now);
+    }
+}

docs/HD-RENDERER.md

@@ -8,8 +8,9 @@
 
 HD — третий пресет графики мода (`/airdef shader off|on|hd`): отложенное освещение в стиле шейдерпаков
 (BSL/Complementary-класс), но написанное с нуля внутри нашего форка Horizon (Minecraft 26.3 на Rust/wgpu).
-Код шейдерпаков (BSL, Complementary, Photon, Iris/OptiFine) **не копируем**: их лицензии запрещают перенос, а в
-Horizon действует правило clean-room. Пишем по знанию техник (статьи, общеизвестные алгоритмы).
+Код шейдерпаков (BSL, Complementary, Iris/OptiFine и прочих) **не копируем**: их лицензии запрещают перенос, а в
+Horizon действует правило clean-room. Исключение — Photon (sixthsurge), коммит 26c2906ee02cc484359b835fba6993d443d45966: он под MIT, из него можно
+переносить идеи и код **с указанием авторства** (комментарий у кода + `gfx/THIRD_PARTY_PHOTON.md`). Остальное пишем по знанию техник (статьи, общеизвестные алгоритмы).
 
 Пресеты должны оставаться: `off` (ваниль), `on` (пост-эффекты мода), `hd` (этот рендер), позже `rt` (аппаратная
 трассировка, отдельно).
@@ -19,6 +20,8 @@ Horizon действует правило clean-room. Пишем по знани
 | Что | Где |
 |---|---|
 | Весь HD-конвейер: цели, проходы, WGSL-шейдеры (строками), тайлы света, AO, тени, bloom, tonemap, TAA | `horizon/crates/horizon-client/src/gfx/hd.rs` |
+| Объёмные облака (рэймарч слоя, тени облаков на землю) и объёмный туман (лучи света через тени каскадов), их цели и проходы; CPU-шум (2D, 3D Worley) | `horizon/crates/horizon-client/src/gfx/hd_volumes.rs`, `hd_noise.rs` |
+| Атмосфера: сборка текстуры неба (WGSL), чтение неба/дымки/тона света в шейдерах, цвет солнца (`sun_transmittance`) | `horizon/crates/horizon-client/src/gfx/hd_sky.rs` (+ `THIRD_PARTY_PHOTON.md`) |
 | Встраивание в кадр: G-буфер-проход, каскады теней, вызовы `hd.light` / `hd.finish`, джиттер, тайминги | `horizon/crates/horizon-client/src/gfx.rs` (`Renderer::render`, ищи `hd_on`, `AirDef fork:`) |
 | G-буфер террейна: `fs_gbuffer`, `fs_shadow` | `horizon/crates/horizon-client/src/terrain.wgsl` |
 | G-буфер сущностей и моделей мода: `fs_entity_gbuffer`, `fs_entity_shadow` | `horizon/crates/horizon-client/src/entity.wgsl` |
@@ -39,10 +42,11 @@ cd .. && rm -f horizon-patches/*.patch && git -C horizon format-patch -q $(cat H
 
 ## Конвейер кадра (HD включён)
 
-Все цели в «масштабированном» разрешении мира (`world_post`), HDR — `Rgba16Float`. Глубина камеры — reversed-Z
+Цели мира (G-буфер, AO, освещение, пост-проход мода) — в «масштабированном» разрешении мира (`world_post`; при `HORIZON_HD_SCALE` < 1 оно меньше окна), цели после TAA (история, bloom, tonemap) — в разрешении окна. HDR — `Rgba16Float`. Глубина камеры — reversed-Z
 (`Depth32Float`, 1 = близко, 0 = далеко). Позиции везде относительно камеры (camera-relative), мир — в `f64`
 на CPU.
 
+0. **Небо** (`hd.sky`, проход `hd sky`, перед освещением): текстура 128×72 (`Rgba16Float`): 128 азимутов (от солнца, 0..π) × 64 высот (v = √(h/(π/2))), плюс строка 64 с «окружающим светом» (текселы 0 — зенит, 1 — среднее у горизонта). Каждый тексел — марш по лучу (32 шага) однократного рассеяния Рэлея/Ми + озон, плоский член многократного рассеяния (`MULTI_SCATTER`), солнце и луна (луна — напротив) как источники; пропускание до источника — аналитическое (Chapman, как у Photon). Зависит только от высоты солнца → перерисовывается, лишь когда она сдвинулась больше чем на 0.001. Читают её `fs_light` и композит воды (привязки 15 и 10).
 1. **Каскады теней** (2 шт., `CASCADES = [40, 176]` блоков полуразмера, `SHADOW_SIZE = 2048`, массив глубины
    из 2 слоёв). Источник — солнце днём, луна ночью (`light_of`). Матрицы `cascades()` привязаны к текселям
    (тени не «ползут»). Во время прохода буфер глобалов мира подменяется на глобалы каскада (copy-трюк) и потом
@@ -50,18 +54,42 @@ cd .. && rm -f horizon-patches/*.patch && git -C horizon format-patch -q $(cat H
    (`shadow_casters`: без оверлеев 4/9/10/40 — 40 это светящиеся модели мода).
 2. **G-буфер** (свой depth): albedo `Rgba8Unorm` (a = эмиссия), нормаль `Rgba16Float` (мировая, из `dpdx/dpdy`),
    уровни света `Rgba8Unorm` (x = небо, y = блоки — сырые координаты лайтмапа /240). Террейн + дальние LOD-тайлы +
-   сущности. Вода/полупрозрачное в G-буфер **не** попадает (идёт ванильным путём) — см. план.
-3. **GTAO** (полразрешения, `Rg16Float`: окклюзия, дистанция) + depth-aware блюр 5×5. 3 среза × 5 шагов, радиус
+   сущности. Полупрозрачное в G-буфер **не** попадает (идёт ванильным путём); вода — отдельный путь, см. п. 3 и «Вода».
+3. **Вода** (`water_pass`, только если на экране есть полупрозрачные секции, нет `frame.underwater` и не `HORIZON_HD_WATER=0`):
+   те же секции ещё раз с `fs_water` (terrain.wgsl), который отбрасывает всё, кроме слоёв спрайтов `water_still`/`water_flow`
+   (номера слоёв передаются в `Renderer::new` из `sprite_layers` и ставятся override-константами `WATER_STILL/WATER_FLOW`; стекло,
+   лёд и прочее остаются ванильными). Цели: цвет (спрайт × биомный тинт, a = свет блоков, `Rgba16Float`), нормаль грани (a = свет неба,
+   `Rgba8Unorm`) и собственная глубина воды (`Depth32Float`, 0 = воды нет; тест глубины только среди воды, перекрытие
+   землёй решают потребители). Пайплайны `gbuffer_water` (секции) и `flat.water` (flat-путь).
+3a. **GTAO** (полразрешения, `Rg16Float`: окклюзия, дистанция) + depth-aware блюр 5×5. 3 среза × 5 шагов, радиус
    1.8 блока, шум IGN по кадру. Сила — `HdFrame.ambient.w` (`HORIZON_HD_AO=<число>`, 0 = выкл).
-4. **Освещение** `fs_light` → `lit` (HDR): `max(небо·ambient.x, блоки·ambient.y)·AO + солнце·N·L·тень + точечные
+3b. **Облака и туман** (`hd.volumes`, до освещения, после прохода неба): `hd cloud shadows` (карта 256² оптической толщины облаков по ходу солнца, ±1200 блоков вокруг камеры), `hd clouds` (половина разрешения мира, `Rgba16Float`: свет + пропускание; рэймарч слоя 192.33…264 блока, 8–26 шагов с джиттером IGN, свет — 3 шага с удвоением, небо — 1, 4 октавы многократного рассеяния Photon; история ping-pong с репроекцией по направлению и сдвигу камеры, вес до 0.9, отбрасывается при расхождении) и `hd fog` (половина разрешения: 18 шагов от камеры до глубины мира, не дальше 192 блоков, плотность — высотная дымка + утренний туман у земли + дождь + шум, свет — солнце × тень каскадов × фаза Photon + свет неба; вторая цель — длина луча для апсэмплинга). Ванильные облака при этом не рисуются (`hd_volumetric_clouds` в `gfx.rs`). `fs_light` накладывает облака на небо (`c·T + S`), туман на всё (`fog_at`: 4 текселя с весом по близости длины луча), а тень облаков (`cloud_shadow`) умножает прямой солнечный свет. `HORIZON_HD_CLOUDS=0` / `HORIZON_HD_VOLFOG=0` выключают (облака тогда ванильные, лучи — старые 14 шагов).
+4. **Освещение** `fs_light` → `lit` (HDR): пиксель неба (глубина мира 0, Оверворлд, без env-тумана) — это небо атмосферы + то, что мир нарисовал поверх ванильного неба (`max(scene − vanilla_sky(view), 0)`: спрайты луны, звёзды; квадрат ванильного солнца вырезается вокруг направления солнца и заменяется круглым диском с гало); облака (глубина > 0, нет в G-буфере, y > 8, дальше 48 блоков) на закате/рассвете окрашиваются цветом солнца. Свет неба: ванильный `lightmap` × подкраска цветом неба (зенит сверху, горизонт сбоку; яркость 1) × форма по нормали (вверх 1.1, вниз 0.66), только там, где есть небесный свет. Тени: ближний каскад — PCSS-lite (поиск блокировщиков 8 выборок, ширина полутени от расстояния до блокировщика, 12 выборок спирали Фогеля, повёрнутых IGN; сглаживает TAA), дальний — 3×3. Туман: цвет — небо над горизонтом в направлении пикселя (`haze_colour`) + воздушная перспектива `1 − exp(−d/700)` × 0.5. Далее прежнее: пиксель — вода, если `water_depth >= g` и перед водой в мировой глубине ничего нет
+   (`d - wd <= 0.2%`); тогда освещается **дно** по данным G-буфера (одна выборка тени, без AO), а в альфу `lit` пишется 0.5 (признак воды). `max(небо·ambient.x, блоки·ambient.y)·AO + солнце·N·L·тень + точечные
    источники` × albedo + эмиссия; затем ванильный туман заново, объёмные лучи (14 шагов, Henyey-Greenstein g=0.6),
    ореолы вокруг источников. Точечные источники — по тайлам 16×16 (`tile_lists`, буфер `tiles`: на тайл 4 слова —
    начало/длина списка для поверхностей и для ореолов, потом индексы; переполнение → «все источники»).
+4a. **Композит воды** `fs_water` (`hd.water_composite`, `lit` → `lit_water`, дальше везде `hd.lit_view()`; на пикселях без воды копия).
+   Волны — сумма 10 синусоид в мировых координатах (векторы — целые кратные 2π/256, скорости — целые циклы за 600 с: период 256 блоков
+   и 10 минут, не «плывут» с камерой; мелкие волны гасятся по размеру пикселя против мерцания); нормаль = нормаль грани + градиент
+   (только на горизонтальных гранях). Преломление: смещение луча относительно плоской воды, выборка `lit` по uv со сдвигом (отбраковка
+   по глубине: не берутся банк/сущности перед водой); толщина = расстояние от поверхности до дна; поглощение `exp(-(1-цвет)·0.8·(t+0.3))`
+   + рассеяние цветом воды при свете «объёма» (лайтмап + солнце с тенью). Отражение: SSR по глубине G-буфера (24 шага, растущие,
+   джиттер IGN по кадру, 5 шагов бинарного уточнения, толщина `0.4+0.08·s`), при промахе — небо/туман (`sky_color`, `fog_color`, тусклее
+   под навесом). Волны: к 10 крупным добавлены 16 мелких (длины 0.35–3 блока, уклон до 0.05, гасятся по размеру пикселя) — густая мелкая рябь для искорок блика; блик GGX с a=0.07. Цвет воды светлее: биом × 0.85, поглощение 0.8, рассеяние 0.85 (ночью до 0.4). Небо отражения и туман — из атмосферы. Френель Шлика F0=0.02 (SSR пропускается при F<0.04: взгляд вниз), блик солнца GGX (a=0.05) × тень, туман поверх.
+   Подводный вид и `HORIZON_HD_WATER=0` — композит и проход воды не работают, `lit` как раньше.
 5. **Пост-проход мода** `lit` → `fx` (`effects.wgsl`: взрывы, дым, вспышки, свечение; при HD его собственная
    «подсветка огнём» выключена — свет даёт HD).
 6. **TAA** — после пост-прохода мода (`fx`, либо `lit` без него), до bloom: история пинг-понгом, в альфе истории —
    дистанция для отбраковки дизокклюзии; телепорт > 64 блоков сбрасывает историю. Джиттер добавляется к
    `view_projection` только при HD (публичная матрица без джиттера); рука и HUD рисуются после tonemap и не дрожат.
+   **TAAU**: если мир меньше окна (`HORIZON_HD_SCALE=0.67`), тот же проход (`fs_taau`, в таймингах `hd taau`) восстанавливает
+   полное разрешение. История, bloom и tonemap — в разрешении окна. Для каждого пикселя выхода берётся 3×3 выборки мира
+   вокруг (с учётом джиттера в `taa_params.zw`), веса — полином, аппроксимирующий Lanczos-2, по расстоянию от центра
+   пикселя выхода до выборки; variance clip в YCoCg по тем же 3×3; глубина — ближайшая из 2×2; история (Catmull-Rom,
+   полное разрешение) вес 0.92, но ближе к ней там, где ближайшая выборка далеко от центра пикселя. Джиттер —
+   Halton(2,3) на `max(16, ceil(8·ratio²))` кадров (0.67 → 18, 0.5 → 32). При масштабе 1 работает прежний `fs_taa`
+   без изменений. С `HORIZON_HD_TAA=0` и масштабом < 1 остаётся простой билинейный апскейл в tonemap.
 7. **Bloom** (prefilter + 6 уровней: 13-tap вниз, tent вверх) и **tonemap**: до 0.8 как есть (ванильный вид),
    выше — мягкий roll-off по ярчайшему каналу; лёгкий грейд (+12% насыщенности, мягкая S-кривая).
 
@@ -81,10 +109,16 @@ Bind groups кэшируются и пересоздаются только пр
 | 10, 11 | лайтмап, линейный сэмплер |
 | 12 | тайлы источников (storage) |
 | 13 | AO |
+| 14 | глубина воды (`water_depth`) |
+| 15 | текстура неба (`sky_lut`) |
+| 16, 17 | объёмный туман (свет+пропускание) и длина его луча |
+| 18, 19 | объёмные облака, карта теней облаков |
 
 `HdFrame` (Rust и WGSL держать в синхроне!): `inverse_view_proj`, `resolution` (w, h, 1/w, 1/h), `params` (число
 источников, экспозиция, bloom, счётчик кадров), `cascades[2]`, `sun` (направление, сила), `sun_color` (rgb, ночь),
-`fog_color`, `fog`, `ambient` (тень неба, блоки, плотность воздуха, AO), `shadow` (вкл, R0, R1, тайлов в строке).
+`fog_color`, `fog`, `ambient` (тень неба, блоки, плотность воздуха, AO), `shadow` (вкл, R0, R1, тайлов в строке), `prev_view_proj`, `taa`, `taa_params`, `view_proj` (с джиттером, для лучей воды), `water` (x: эффект идёт, y: секунды волн mod 600, zw: камера x, z mod 256), `sky_color` (w: есть небо), `sky_sun` (xyz: на само солнце, w: 1 — небо рисует атмосфера), `sky_extra` (x: конец ванильного тумана неба, z: пасмурность от дождя 0..0.85), `sunrise` (ванильная полоса восхода/заката — вычитается из мира), `clouds` (низ слоя относительно камеры, толщина, вкл, секунды ветра), `cloud_cam` (x, z камеры по модулю 65536, добавка покрытия от дождя, история облаков годна), `cloud_dir` / `cloud_sun` (откуда и каким цветом светят облаку: солнце до чуть ниже горизонта, ночью луна), `vfog` (туман вкл, высота камеры, утренний туман).
+
+Композит воды (`WATER`, group 0): 0 `HdFrame`, 1 `lit`, 2 глубина G-буфера, 3 цвет воды, 4 нормаль воды, 5 глубина воды, 6–7 тени, 8 лайтмап, 9 сэмплер, 10 текстура неба. Проход неба (`SKY_PASS`, group 0): только `HdFrame`.
 
 ## Как проверять
 
@@ -113,8 +147,14 @@ $H key f1 tap; $H screenshot out.png; $H bench 4; $H quit
 Тайминги проходов на GPU: `HORIZON_SHADER_PACK_TIMING=1` (лог в `run-home/ctl.log`) или список F3.
 Ориентиры (M5, 2560×1440): тени 0.6 + 2.85 мс (дальний каскад через кадр, ≈1.4 в среднем), G-буфер 0.8,
 AO 2.9, освещение 5.2, TAA 2.7, bloom 1.1, tonemap 0.2 — кадр ≈ 15 мс GPU (замеры шумные).
+TAAU (2560×1440, GPU avg кадр, сцена Polygon): scale 1.0 — 18.1 мс; 0.67 — 13.4 мс; 0.5 — 10.4 мс (освещение 6.1 → 2.7 → 1.6, AO 3.5 → 1.4 → 0.8, `hd taau` ≈ 3.5 мс на любом масштабе, дальний каскад теней 3.4 мс не зависит от масштаба).
 Следующие цели по скорости: освещение (лучи 14 шагов на полном разрешении → полразрешения + апскейл) и AO.
 
+Проверка мерцания: два скриншота с неподвижной камеры подряд и разница по пикселям (Pillow `ImageChops.difference`)
+— на мире `Hills` с травой и деревьями; после исправлений ≈2% пикселей с разницей > 20/255 (дрожание TAA на пиксельных
+текстурах и анимация воды), а при ошибке теней было 8.5%. Сравни с `HORIZON_HD_TAA=0` / `HORIZON_HD_AO=0` /
+`HORIZON_HD_SHADOW_FAST=0`, чтобы найти виновника.
+
 Отладка: временно выводи промежуточные величины цветом в `fs_light` (так нашли пустую карту теней и неверное
 направление солнца). Помни: солнце в мире идёт по оси X (`(-sin a, cos a, 0)`), а `Globals.sun` неба — в своей
 плоскости YZ.
@@ -131,25 +171,33 @@ AO 2.9, освещение 5.2, TAA 2.7, bloom 1.1, tonemap 0.2 — кадр ≈
 | Отсечение взрывов в `effects.wgsl` (#11), порядок дыма (#16), метрика перекрытия свечения (#14) | готово | 67a2a52, ed2db85 |
 | Тени: только грани к солнцу, без «закопанных» секций, дальний каскад через кадр (`HORIZON_HD_SHADOW_FAST=0` — по-старому) | готово | патч 16 |
 | TAA: джиттер Halton(2,3) ×16, перепроекция по глубине и сдвигу камеры, variance clip в YCoCg, история Catmull-Rom 0.9, лёгкий шарп в tonemap (`HORIZON_HD_TAA=0` — выкл) | готово | патч 16 |
+| TAAU: мир в `HORIZON_HD_SCALE` (0.25–1, по умолчанию 1 = как раньше), восстановление в TAA-проходе `fs_taau`; без LOD-bias текстур (не доступен) | готово | патч 18 |
+| Исправлено мерцание теней у игрока: ближний каскад терял секции в кадры, когда дальний держится; держимая матрица дальнего каскада сдвигается на шаг камеры; у растений (наклонные квады) нормаль «вверх», а не к камере; TAA держит 94% истории в покое | готово | патч 18 |
+| Вода: проход `fs_water`, преломление, SSR, Френель, блик (`HORIZON_HD_WATER=0` — выкл) | готово | патч 19 (+20: без ванильной текстуры на поверхности, цвет темнее и глубже) |
+| Вода: светлее, густая мелкая рябь (26 волн), блик a=0.07 (мерцание на реке ≈1.4% пикселей >20/255) | готово | патч 21 |
+| Небо и атмосфера (Рэлей/Ми/озон, текстура неба, воздушная перспектива, цвет солнца из пропускания, голубоватый ambient по нормали, PCSS-lite ближнего каскада, диск солнца, цвет облаков на закате; порт констант и Chapman из Photon, MIT) | готово | патч 22 |
+| Закат как у Photon: атмосфера в Rec. 2020 (коэффициенты и матрицы Photon), фаза Клейна-Нишины, тинт и усиление солнца на закате/рассвете/синем часе (`get_sun_tint`), насыщенность неба у низкого солнца | готово | патч 23 |
+| Объёмные облака (рэймарч, мультирассеяние Photon, тени на землю, TAA-история, ванильные скрыты) | готово | патч 24 |
+| Объёмный туман (лучи через тени каскадов, высотная дымка, утренний туман, полразрешения) | готово | патч 25 |
 | API моделей по хэндлам (#30, уровень API 11: `model-id`, `model-generation`, `set-models-by-id`) | готово | патч 17 |
 
 ## План (по порядку) и ТЗ
 
 Каждый пункт — самостоятельная задача. Перед началом прочитай `hd.rs` целиком.
 
-1. **TAAU — временной апскейлер** (поверх TAA). Мир и G-буфер рендерятся в `render_scale` (например 0.67),
+1. **TAAU — временной апскейлер** (поверх TAA) — СДЕЛАНО (патч 18, см. статус; масштаб — `HORIZON_HD_SCALE`, переопределяет «масштаб разрешения» настроек Horizon только для HD; поля в `HdSettings` нет). Осталось: LOD-bias текстур террейна, MetalFX. Исходное ТЗ: Мир и G-буфер рендерятся в `render_scale` (например 0.67),
    TAA-проход восстанавливает полное разрешение: история в полном разрешении, текущий кадр семплируется с учётом
    джиттера (Catmull-Rom/Lanczos-веса по субпиксельной позиции), клиппинг окрестности как в TAA. Настройка
    масштаба (`HORIZON_HD_SCALE` или поле в `HdSettings`). Цель: при 0.67 картинка близка к нативной, FPS заметно
    выше. Альтернатива на Mac — MetalFX через wgpu-hal (нативный код, только Metal) — отдельной опцией потом. DLSS
    нереален для нашей цели (только NVIDIA через Streamline, нет в wgpu).
-2. **Вода**: отдельный G-буфер-путь для воды (маска + нормаль с анимированными волнами), SSR (трассировка по
+2. **Вода** — СДЕЛАНО (патч 19, см. «Вода» ниже). Исходное ТЗ: отдельный G-буфер-путь для воды (маска + нормаль с анимированными волнами), SSR (трассировка по
    глубине, откат на небо/туман), преломление (смещение по нормали), затухание по глубине воды (цвет биома),
    блики солнца (GGX-подобный), френель. Подводный вид не ломать (`frame.underwater`).
-3. **Небо и атмосфера**: рассеяние Рэлея/Ми (предвычисленная LUT пропускания и небесного цвета в маленькой
+3. **Небо и атмосфера** — СДЕЛАНО (патч 22, см. «Небо и свет» ниже). Исходное ТЗ: рассеяние Рэлея/Ми (предвычисленная LUT пропускания и небесного цвета в маленькой
    текстуре), солнце/луна дисками, звёзды из ванили; туман и лучи берут цвет из той же модели. Учесть дождь
    (`weather`), закат, Незер/Энд (там — ванильное небо).
-4. **Объёмные облака** (рэймарч слоя с шумом) + их тени на земле (в карту/маску солнца).
+4. **Объёмные облака** — СДЕЛАНО (патч 24, см. «Закат, облака и туман»). Осталось: перистые/высококучевые слои Photon, облака в отражении воды.
 5. **Блики и материалы**: specular солнца для металла техники (маска по оверлею/альбедо или атрибут модели из
    мода), мокрые поверхности и лужи в дождь.
 6. **PCSS** (мягкость тени по расстоянию до тенеотбрасывателя) и цветные тени через стекло/листву.
@@ -159,8 +207,32 @@ AO 2.9, освещение 5.2, TAA 2.7, bloom 1.1, tonemap 0.2 — кадр ≈
 10. **RT-пресет**: `wgpu` `EXPERIMENTAL_RAY_QUERY` (Vulkan/DX12/Metal M3+), BLAS по секциям, ray-query тени и
     отражения, затем GI. Отдельный пресет, HD остаётся.
 
+## Вода (патч 19): что знать преемнику
+
+- Тайминги проходов: `hd water` (геометрия воды; на Metal его метка часто 0 — работа учитывается в соседних проходах) и `hd water composite`.
+  Замеры 2560×1440, Hills, река на ~40% экрана, M5 (шумно: у меня GPU делят браузеры): композит 0.8–2 мс, `hd lighting` на 2–3 мс
+  выше, чем без воды (теперь освещается дно под водой — раньше эти пиксели были ванильными); всего вода ≈ +3 мс при большой воде
+  на экране, около 0.5–1 мс при малой. Цель «≤ 2 мс» при полной реке не достигнута. Идеи: отражения в полразрешения (с учётом маски воды
+  на границе), SSR только при F>0.04 уже есть, ужать освещение дна (без точечных источников на глубине > N блоков).
+- Вода находится по слоям спрайтов. LOD-тайлы воды (`lod/mesh.rs`) идут тем же путём, если их слой — water_still; вода из resource pack с
+  другим именем спрайта не распознается (останется ванильной). `water_overlay` (боковые грани у стекла) не трогаем.
+- Стекло/частицы/лёд перед водой: проверка `d - wd` возвращает ванильный вид пикселя (вода под стеклом без эффекта).
+- Известные ограничения: отражается только то, что есть на экране (и только непрозрачное: листва — да, вода/стекло — нет); дождь на воде,
+  пена у берега, подводная каустика не сделаны; ночью вода слегка ярче неба (нужно привязать к модели неба — п. 4 плана «Небо»); отражение
+  солнечного диска — только блик GGX (без диска в SSR). Проверка мерцания на реке: разница двух скриншотов ≈1.6% пикселей >20/255 (норма ~2%).
+
+## Небо и свет (патч 22): что знать преемнику
+
+- Тайминги (M5, 2560×1440, Hills, река в кадре): `hd sky` ≈ 2.4–4.7 мс по таймстемпам, но кадр не вырос (GPU avg 18.4 мс против 18.1) — на Metal метка крошечного прохода ловит ожидание соседних; с кэшем по высоте солнца в покое проход не выполняется. Освещение 4.0–5.1 мс (PCSS-lite и небо почти не добавили), композит воды 0.6–2.4, TAA 2.6–2.9.
+- Яркость: небо — физическая радиация → сжатие по максимальному каналу (`SKY_EXPOSURE` 0.85) → гамма 1/1.9 → насыщенность 1.2 (+0.45 у низкого солнца). Весь конвейер в гамма-пространстве, поэтому цвета неба и подкраски света — «показанные» значения; подкраска света неба имеет яркость 1 и не меняет экспозицию (яркость задаёт ванильный лайтмап × `ambient.x` = 0.62 днём, 0.95 ночью).
+- Цвет солнца (`light_of`): пропускание атмосферы вдоль солнца (`hd_sky::sun_transmittance`), нормировано на 1, степень 0.6, × (1, 0.97, 0.88). Луна — холодная, как раньше.
+- Дождь: `sky_extra.z` смешивает небо/дымку с ванильным градиентом (серым от ванили); Нижний мир/Энд/подводное — `sky_sun.w = 0`, всё как раньше (ванильное небо и туман).
+- Облака — по-прежнему ванильные блоки; объёмные облака — п. 4 плана. Окраска облаков цветом закатного солнца — эвристика по маске (глубина есть, G-буфера нет, высота и дальность), может задеть далёкие частицы.
+- Идеи дальше: многократное рассеяние по Hillaire вместо плоского члена, тени облаков, диск луны с фазой, звёзды/галактика по Photon (`sky.glsl`), розовый оттенок заката (`get_sun_tint` у Photon).
+
 ## Правила
 
+- Код Photon (MIT) переносить можно только с атрибуцией (см. «Что это»); код других шейдерпаков — нельзя.
 - Ничего не ломать в `off`/`on`; HD выключен — код HD не работает вовсе (`hd = None`).
 - Без потери качества ради скорости без договорённости (шаги, разрешение, число эффектов).
 - Каждый новый WGSL — в naga-тест. Каждый новый проход — в тайминги (`PassTiming`).
@@ -168,3 +240,20 @@ AO 2.9, освещение 5.2, TAA 2.7, bloom 1.1, tonemap 0.2 — кадр ≈
 - Коммиты: в форке, затем патчи; подпись `Co-Authored-By: Claude <модель> <noreply@anthropic.com>`.
 - Пуш в Gitea с машины без DNS: `ssh://git@100.92.6.40:2222/chexit/airdef.git` (ключ `~/Documents/claude-keys/deploy`).
 - Обнови этот документ (статус + что изменилось в конвейере) в том же коммите, что и код.
+
+## Тюнинг после проверки на полигоне (патч 22)
+
+Голубая заливка неба по умолчанию делала белый бетон «снегом»: оттенок неба в заливке ослаблен до 0.4
+(`sky_light_tint`, в `fs_light`), заливка днём `ambient.x` = 0.5 (+0.45 ночью), солнце 0.7 и теплее
+(`light_of`: множитель (1, 0.93, 0.78)). Проверять баланс на `Polygon` в полдень (`time set 6000`) — белое должно
+оставаться белым с тёплым оттенком.
+
+
+## Закат, облака и туман (патчи 23–25): что знать преемнику
+
+- **Закат (23).** Небо марширует в Rec. 2020 (коэффициенты Photon сдвинуты матрицей `rec709_to_rec2020`, результат возвращается в 709): это убрало жёлто-зелёный горизонт. Добавлены фаза Клейна-Нишины для Ми и деполяризованная Рэлея, `sun_light_tint` (розоватый тинт и подъём яркости на закате, фиолетовый на синем часе, из `get_sun_tint`), сильнее насыщенность у низкого солнца (`sky_show`). Цвет прямого света (`light_of`) умножен на тот же тинт. Сверка: 12000/12500/13000 (запад) и 23000/23500 (восток) — оранжевый/розовый/пурпурный; полдень Polygon (6000) прежний.
+- **Облака (24).** Слой 192.33…264.33 блока (`CLOUD_BASE/CLOUD_THICKNESS`), ветер 3 блока/с (`CLOUD_WIND`), шум — текстуры, сгенерированные на CPU при создании HD (`hd_noise.rs`: 2D 256² покрытие/форма, 3D 64³ Worley). Плотность — по `clouds_cumulus_density` Photon (порог покрытия × форма, «яйцо» по высоте, эрозия Worley, резкий верх), рассеяние — `clouds_cumulus_scattering` (октавы, пудра, фазы). Цвет света — `cloud_light` (Rust): пропускание атмосферы на высоте солнца; солнце светит облакам до −0.2 по высоте, дальше луна. Воздушная перспектива `exp(−d/3600)` к цвету дымки. История сбрасывается при resize, телепорте и без TAA. Опция ванильных облаков «выкл» → `frame.clouds` пуст → нет ни облаков, ни теней. Тень: `cloud_shadow` в `fs_light` (карта оптической толщины; гаснет при солнце ниже ~0.1–0.25 по высоте).
+- **Туман (25).** `fs_fog`: 18 шагов, плотность `fog_sigma` (высотная дымка от y=62, масштаб 42; утренний туман — пока солнце на «утренней» стороне и низко; пятна из 3D-шума; дождь; затухание ниже y≈28–58, чтобы не светить в пещерах), свет — Photon-смесь двух HG, «вечернее свечение» ×1…3. Старые 14 шагов лучей остаются при `HORIZON_HD_VOLFOG=0`; ореолы вокруг источников мода — всегда.
+- **Тайминги.** Метки Metal (`HORIZON_SHADER_PACK_TIMING=1`, Hills, 2560×1440): `hd clouds` ≈ 6 мс (завышено: метка ловит ожидание соседних проходов), `hd cloud shadows` 0.2–3 (шум), `hd fog` ≈ 1.3. По среднему кадру GPU «оба выкл → оба вкл»: +0.2…3.7 мс (замеры шумные: рядом шла чужая игра на том же GPU). Как удешевить: у облаков — длина шага (14) и потолок шагов (26) в `fs_cloud`, 3 шага света, 4 октавы, облака в четверть разрешения; у тумана — `FOG_STEPS`.
+- **Разработка шейдеров.** `HORIZON_HD_SHADER_DIR=<папка>`: каждый HD-шейдер читается из `<папка>/<метка>.wgsl` (записывается из встроенного, если файла нет) — правки видны после перезапуска игры без пересборки; готовое переносится в константы вручную.
+- **Слабые места.** Облака не отражаются в воде (SSR берёт небо без облаков); не закрывают далёкую землю выше слоя (только небо); карта теней облаков ±1200 блоков и почти не работает при солнце ниже ~10°; туман не знает рельефа (только высоту над y=62); нет перистых облаков; на быстром повороте камеры история облаков отбрасывается (кратковременный шум).

horizon-patches/0001-Mod-API-AirDef-fork-world-models-client-particles-so.patch

@@ -1,7 +1,7 @@
 From 3de7a6875140a107e28563cc44489b55f5794517 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 12:37:45 +0300
-Subject: [PATCH 01/17] Mod API (AirDef fork): world models, client particles,
+Subject: [PATCH 01/24] Mod API (AirDef fork): world models, client particles,
  sounds, ground heights
 
 render.set-models draws block models with an interpolated pose per id;

horizon-patches/0002-cargo-horizon-mod-report-particles-and-sounds.patch

@@ -1,7 +1,7 @@
 From a6d64e6415bf618539af464e521091e72b72d72f Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 12:39:45 +0300
-Subject: [PATCH 02/17] cargo-horizon-mod: report particles and sounds
+Subject: [PATCH 02/24] cargo-horizon-mod: report particles and sounds
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
 ---

horizon-patches/0003-Mod-API-AirDef-fork-full-screen-post-pass-for-mods.patch

@@ -1,7 +1,7 @@
 From ee79b3562feebe51959a01f1585a9e85bd53ccb5 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 13:33:10 +0300
-Subject: [PATCH 03/17] Mod API (AirDef fork): full-screen post pass for mods
+Subject: [PATCH 03/24] Mod API (AirDef fork): full-screen post pass for mods
 
 render.set-post compiles a mod's WGSL after a prelude (camera matrices,
 time, 256 vec4 of params, the world's colour and depth) and runs it after

horizon-patches/0004-Mod-models-draw-far-models-as-scaled-impostors-past-.patch

@@ -1,7 +1,7 @@
 From 2b137dbbedd540daeebc7f5e387847aeb56a1355 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 22:09:30 +0300
-Subject: [PATCH 04/17] Mod models: draw far models as scaled impostors past
+Subject: [PATCH 04/24] Mod models: draw far models as scaled impostors past
  the far plane, cull at 4096
 
 ---

horizon-patches/0005-Mod-cameras-render.set-views-draws-the-world-from-ot.patch

@@ -1,7 +1,7 @@
 From c8ebca6e0af68630e65211844b34d25c5b985c03 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 22:31:00 +0300
-Subject: [PATCH 05/17] Mod cameras: render.set-views draws the world from
+Subject: [PATCH 05/24] Mod cameras: render.set-views draws the world from
  other points into pictures that HUD view shapes show (API level 9)
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0006-Mods-more-fuel-per-tick-and-per-event-AirDef-plans-r.patch

@@ -1,7 +1,7 @@
 From 8d2261fc4f8072c32e454139cfea7a8c0cd9d664 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 23:08:21 +0300
-Subject: [PATCH 06/17] Mods: more fuel per tick and per event (AirDef plans
+Subject: [PATCH 06/24] Mods: more fuel per tick and per event (AirDef plans
  raids)
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0007-Mod-cameras-up-to-1920x1080-full-screen-replays.patch

@@ -1,7 +1,7 @@
 From 6c548de34def8e4a624d734243418090798bd16a Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Wed, 28 Oct 2026 23:25:29 +0300
-Subject: [PATCH 07/17] Mod cameras up to 1920x1080 (full-screen replays)
+Subject: [PATCH 07/24] Mod cameras up to 1920x1080 (full-screen replays)
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
 ---

horizon-patches/0008-Mod-cameras-distant-terrain-tiles-fog-measured-from-.patch

@@ -1,7 +1,7 @@
 From 9b9e93269d67401cc620567a884d5ce97f68d76e Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 11:15:11 +0300
-Subject: [PATCH 08/17] Mod cameras: distant terrain tiles, fog measured from
+Subject: [PATCH 08/24] Mod cameras: distant terrain tiles, fog measured from
  the camera, no impostors while one is shown
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0009-Mods-game.world-id-so-mods-keep-state-per-world-API-.patch

@@ -1,7 +1,7 @@
 From 065d9fa02966238a5bd9ff460392a1a809db0b11 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 11:25:45 +0300
-Subject: [PATCH 09/17] Mods: game.world-id, so mods keep state per world (API
+Subject: [PATCH 09/24] Mods: game.world-id, so mods keep state per world (API
  level 9)
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0010-cargo-horizon-mod-trial-runs-behind-feature-full-so-.patch

@@ -1,7 +1,7 @@
 From 1bf28135fd9a31f837323dc3a8d81ed73343d816 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 12:01:08 +0300
-Subject: [PATCH 10/17] cargo-horizon-mod: trial runs behind feature full, so a
+Subject: [PATCH 10/24] cargo-horizon-mod: trial runs behind feature full, so a
  packing-only tool skips wasmtime
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0011-HD-lighting-G-buffer-pass-per-pixel-mod-point-lights.patch

@@ -1,7 +1,7 @@
 From 0a56f5616df4699588cbcc529d4720661baa810f Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 13:18:43 +0300
-Subject: [PATCH 11/17] HD lighting: G-buffer pass, per-pixel mod point lights
+Subject: [PATCH 11/24] HD lighting: G-buffer pass, per-pixel mod point lights
  in HDR, bloom and tone curve; render.set-lights and render.set-lighting (API
  level 10)
 

horizon-patches/0012-HD-lighting-stage-2-sun-and-moon-shadow-cascades-the.patch

@@ -1,7 +1,7 @@
 From 9ebf0031fe9ba6b7f02afb26e4fd3a1ba4ddb0d0 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 13:59:43 +0300
-Subject: [PATCH 12/17] HD lighting stage 2: sun and moon shadow cascades, the
+Subject: [PATCH 12/24] HD lighting stage 2: sun and moon shadow cascades, the
  world relit (sun by face angle and shadow, sky and block light through the
  lightmap), light shafts and halos, fog over it again, a light colour grade
 

horizon-patches/0013-HD-bind-groups-cached-until-a-resize-or-a-new-source.patch

@@ -1,7 +1,7 @@
 From 7a5a38f68923aec62f10bfa0df50b436474ed612 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 16:19:53 +0300
-Subject: [PATCH 13/17] HD: bind groups cached until a resize or a new source,
+Subject: [PATCH 13/24] HD: bind groups cached until a resize or a new source,
  shadow passes draw only the entities that cast shadows
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0014-HD-lights-culled-per-16x16-tile-surface-and-halo-lis.patch

@@ -1,7 +1,7 @@
 From 8020811e57d4b5a9ea1cd72d30ce859dc5095d35 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 16:25:44 +0300
-Subject: [PATCH 14/17] HD: lights culled per 16x16 tile (surface and halo
+Subject: [PATCH 14/24] HD: lights culled per 16x16 tile (surface and halo
  lists built on the CPU), a naga test for the lighting shaders
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0015-HD-GPU-time-per-pass-in-the-F3-timing-list-half-reso.patch

@@ -1,7 +1,7 @@
 From 72d3fddfea329e578162656151350f0aa2efd323 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 16:43:36 +0300
-Subject: [PATCH 15/17] HD: GPU time per pass in the F3 timing list,
+Subject: [PATCH 15/24] HD: GPU time per pass in the F3 timing list,
  half-resolution GTAO with a depth-aware blur
 
 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

horizon-patches/0016-HD-shadows-draw-only-sun-facing-quads-and-skip-burie.patch

@@ -1,7 +1,7 @@
 From 1fd83a821bf270879d8ece5aa583f200ed920d89 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 17:02:02 +0300
-Subject: [PATCH 16/17] HD: shadows draw only sun-facing quads and skip buried
+Subject: [PATCH 16/24] HD: shadows draw only sun-facing quads and skip buried
  sections, the far cascade every second frame; TAA (Halton jitter,
  reprojection by depth, YCoCg variance clipping) before bloom
 

horizon-patches/0017-Mods-model-handles-render.model-id-model-generation-.patch

@@ -1,7 +1,7 @@
 From 1502d359d599228fe0f44ce6b99a3fded2ac5ea0 Mon Sep 17 00:00:00 2001
 From: chexit <chexit@duck.com>
 Date: Thu, 29 Oct 2026 17:02:02 +0300
-Subject: [PATCH 17/17] Mods: model handles (render.model-id, model-generation,
+Subject: [PATCH 17/24] Mods: model handles (render.model-id, model-generation,
  set-models-by-id; API level 11) so mods send no model names each tick;
  clear-post and set-lighting documented
 

horizon-patches/0018-HD-temporal-upscaling-HORIZON_HD_SCALE-world-G-buffe.patch

@@ -0,0 +1,527 @@
+From 0f9d99b8ad3e4b72e621d84c2396cf1d3d2b7a33 Mon Sep 17 00:00:00 2001
+From: chexit <chexit@duck.com>
+Date: Thu, 29 Oct 2026 17:19:57 +0300
+Subject: [PATCH 18/24] HD: temporal upscaling (HORIZON_HD_SCALE: world,
+ G-buffer and lighting at a lower size, rebuilt to the window in the TAA
+ pass); fix flickering shadows near the player (the near cascade lost its
+ sections on frames the far one was held, the held far matrix ignored the
+ camera's step, plants' normals turned with the camera); TAA keeps more
+ history when still
+
+Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
+---
+ crates/horizon-client/src/gfx.rs            |  33 ++-
+ crates/horizon-client/src/gfx/hd.rs         | 211 ++++++++++++++++++--
+ crates/horizon-client/src/gfx/world_post.rs |   8 +-
+ crates/horizon-client/src/terrain.wgsl      |   4 +
+ 4 files changed, 223 insertions(+), 33 deletions(-)
+
+diff --git a/crates/horizon-client/src/gfx.rs b/crates/horizon-client/src/gfx.rs
+index eb152667c..b85c6e269 100644
+--- a/crates/horizon-client/src/gfx.rs
++++ b/crates/horizon-client/src/gfx.rs
+@@ -3970,13 +3970,15 @@ impl Renderer {
+         // offset each frame; `unjittered` is what the next frame reprojects with.
+         let unjittered = self.view_projection(frame);
+         let taa = hd_wanted && hd::taa_enabled();
++        let mut jitter_px = [0.0; 2];
+         let view_proj = if taa {
+-            let size = self
+-                .world_post
+-                .size()
+-                .unwrap_or([self.config.width, self.config.height]);
+-            let j = hd::jitter(self.taa_frame, size);
++            let window = [self.config.width, self.config.height];
++            let size = self.world_post.size().unwrap_or(window);
++            // Upscaling (the world smaller than the window) cycles through more positions.
++            let ratio = window[0] as f32 / size[0].max(1) as f32;
++            let j = hd::jitter(self.taa_frame, size, hd::jitter_count(ratio));
+             self.taa_frame = self.taa_frame.wrapping_add(1);
++            jitter_px = [j[0] * size[0] as f32 * 0.5, -j[1] * size[1] as f32 * 0.5];
+             Mat4::from_translation(Vec3::new(j[0], j[1], 0.0)) * unjittered
+         } else {
+             unjittered
+@@ -4192,6 +4194,7 @@ impl Renderer {
+             cascades: [Mat4::IDENTITY; 2],
+             view_proj,
+             taa: taa && taa_prev.is_some(),
++            jitter_px,
+             prev_view_proj: taa_prev.map_or(unjittered, |p| p.0),
+             camera_delta: taa_prev.map_or(Vec3::ZERO, |p| (frame.camera - p.1).as_vec3()),
+             // The world's sun: vanilla turns the sky -90° about Y, so it crosses from east to west.
+@@ -4218,8 +4221,11 @@ impl Renderer {
+             };
+             if fresh {
+                 self.hd_far = Some((hd_cascades[1], camera, shadow_dir, 0));
+-            } else if let Some((held, _, _, age)) = &mut self.hd_far {
+-                hd_cascades[1] = *held;
++            } else if let Some((held, at, _, age)) = &mut self.hd_far {
++                // The held matrix is relative to the camera it was drawn from: shifted by the
++                // camera's step since, so the map stays put in the world as the player walks.
++                let step = (camera - *at).as_vec3();
++                hd_cascades[1] = *held * Mat4::from_translation(step);
+                 *age += 1;
+             }
+             fresh
+@@ -4230,11 +4236,14 @@ impl Renderer {
+         hd_scene.cascades = hd_cascades;
+         let mut hd_shadow_visible = std::mem::take(&mut self.hd_shadow_visible);
+         hd_shadow_visible.clear();
+-        if hd_wanted && shadow_strength > 0.0 && hd_far_fresh {
++        if hd_wanted && shadow_strength > 0.0 {
++            // The near cascade is drawn every frame: between the far one's redraws the list holds
++            // only the sections in the near box.
++            let c = if hd_far_fresh { 1 } else { 0 };
+             let radius =
+-                ((frame.detail_distance / 16.0) as i32).min((hd::CASCADES[1] / 16.0) as i32 + 2);
++                ((frame.detail_distance / 16.0) as i32).min((hd::CASCADES[c] / 16.0) as i32 + 2);
+             let light = Frustum {
+-                planes: frustum(hd_cascades[1]),
++                planes: frustum(hd_cascades[c]),
+             };
+             self.sections.visible(
+                 camera,
+@@ -5028,6 +5037,8 @@ impl Renderer {
+                 .as_ref()
+                 .and_then(|p| p.1.as_ref())
+                 .is_some_and(|p| p.has_weather());
++        // AirDef fork: HD renders the world at its own scale and upscales it in the TAA pass.
++        self.world_post.hd_scale = hd_on.then(hd::scale_override).flatten();
+         let scaled = self.world_post.prepare(
+             &self.device,
+             [self.config.width, self.config.height],
+@@ -5046,7 +5057,7 @@ impl Renderer {
+             let hd = self
+                 .hd
+                 .get_or_insert_with(|| hd::Hd::new(device, size, format, globals_size));
+-            hd.resize(device, size);
++            hd.resize(device, size, [self.config.width, self.config.height]);
+             if let Some(settings) = frame.hd {
+                 hd.write(&self.queue, &hd_scene, frame.hd_lights, settings);
+             }
+diff --git a/crates/horizon-client/src/gfx/hd.rs b/crates/horizon-client/src/gfx/hd.rs
+index 16610cb02..c54b7b961 100644
+--- a/crates/horizon-client/src/gfx/hd.rs
++++ b/crates/horizon-client/src/gfx/hd.rs
+@@ -89,7 +89,7 @@ struct HdFrame {
+     prev_view_proj: [[f32; 4]; 4],
+     /// xyz: how far the camera moved since that frame; w: 1 when the history is usable.
+     taa: [f32; 4],
+-    /// x: the history's weight; y: the sharpening (0 without TAA).
++    /// x: the history's weight; y: the sharpening (0 without TAA); zw: the jitter in world pixels.
+     taa_params: [f32; 4],
+ }
+ 
+@@ -105,6 +105,9 @@ pub struct HdScene {
+     pub camera_delta: glam::Vec3,
+     /// This frame is anti-aliased over time (the projection is jittered).
+     pub taa: bool,
++    /// The jitter in world-target pixels, screen orientation (x right, y down): the world's sample
++    /// of a pixel lies this far from its centre (the upscaler weighs samples by it).
++    pub jitter_px: [f32; 2],
+     /// Towards the sun, and the sky's darkening (0 day, 1 night).
+     pub sun: glam::Vec3,
+     pub dark: f32,
+@@ -662,8 +665,8 @@ fn fs_taa(in: FullOut) -> TaaOut {
+                 if abs(seen - expected) <= expected * 0.03 + 0.25 {
+                     let mean = sum / 9.0;
+                     let sigma = sqrt(max(sum2 / 9.0 - mean * mean, vec3<f32>(0.0)));
+-                    let box_lo = min(max(mean - sigma * 1.25, lo), centre);
+-                    let box_hi = max(min(mean + sigma * 1.25, hi), centre);
++                    let box_lo = min(max(mean - sigma * 1.5, lo), centre);
++                    let box_hi = max(min(mean + sigma * 1.5, hi), centre);
+                     let past = clip_to_box(box_lo, box_hi, to_ycocg(squash(history_color(uv))));
+                     // Fast motion trusts the history less.
+                     let moved = length((uv - in.uv) * vec2<f32>(size));
+@@ -679,6 +682,99 @@ fn fs_taa(in: FullOut) -> TaaOut {
+     out.history = vec4<f32>(color, dist);
+     return out;
+ }
++
++// The jittered samples' reconstruction filter (a polynomial fit of Lanczos-2, radius 2 in
++// world-target pixels): 1 at 0, 0 at 1 and 2, a little negative between.
++fn lanczos2(x: f32) -> f32 {
++    let x2 = min(x * x, 4.0);
++    let a = 0.4 * x2 - 1.0;
++    let b = 0.25 * x2 - 1.0;
++    return (1.5625 * a * a - 0.5625) * b * b;
++}
++
++// Temporal upscaling: the world (and its depth) is smaller than the output. Each output pixel
++// gathers the 3x3 world samples round it, each weighed by its distance from the pixel's centre
++// (the samples lie off the pixel centres by the frame's jitter), clamps the reprojected full-size
++// history to their colour box and blends: more history where the nearest sample is far away.
++@fragment
++fn fs_taau(in: FullOut) -> TaaOut {
++    let low = vec2<f32>(textureDimensions(source));
++    let lowi = vec2<i32>(low);
++    let high = vec2<f32>(textureDimensions(history));
++    let jit = frame.taa_params.zw;
++    // The output pixel's place among the world's samples: sample i lies at index i - jit, and
++    // the nearest to this pixel is `base`.
++    let t = in.uv * low - 0.5 + jit;
++    let base = vec2<i32>(floor(t + 0.5));
++    var sum = vec3<f32>(0.0);
++    var sum2 = vec3<f32>(0.0);
++    var lo = vec3<f32>(1.0e9);
++    var hi = vec3<f32>(-1.0e9);
++    var weighted = vec3<f32>(0.0);
++    var total = 0.0;
++    for (var y = -1; y <= 1; y++) {
++        for (var x = -1; x <= 1; x++) {
++            let q = clamp(base + vec2<i32>(x, y), vec2<i32>(0), lowi - 1);
++            let s = to_ycocg(squash(textureLoad(source, q, 0).rgb));
++            sum += s;
++            sum2 += s * s;
++            lo = min(lo, s);
++            hi = max(hi, s);
++            let off = vec2<f32>(base + vec2<i32>(x, y)) - t;
++            let w = lanczos2(off.x) * lanczos2(off.y);
++            weighted += s * w;
++            total += w;
++        }
++    }
++    let current = weighted / max(total, 0.001);
++    // Depth: the nearest of the 2x2 samples round the pixel (steady between frames at an edge).
++    let corner = vec2<i32>(floor(in.uv * low - 0.5 + jit));
++    var d = 0.0;
++    for (var y = 0; y <= 1; y++) {
++        for (var x = 0; x <= 1; x++) {
++            d = max(d, textureLoad(depth_tex, clamp(corner + vec2<i32>(x, y), vec2<i32>(0), lowi - 1), 0));
++        }
++    }
++    let sky = d <= 0.0;
++    // The world was drawn shifted by the jitter in clip space; this pixel's unshifted point.
++    let jc = vec2<f32>(jit.x * 2.0 / low.x, -jit.y * 2.0 / low.y);
++    let ndc = vec4<f32>(in.uv.x * 2.0 - 1.0 + jc.x, 1.0 - in.uv.y * 2.0 + jc.y, max(d, 0.000001), 1.0);
++    let h = frame.inverse_view_proj * ndc;
++    let p = h.xyz / h.w;
++    let dist = select(length(p), 0.0, sky);
++    var resolved = current;
++    if frame.taa.w > 0.5 {
++        let prev = frame.prev_view_proj * vec4<f32>(select(p + frame.taa.xyz, p, sky), 1.0);
++        if prev.w > 0.0 {
++            let pn = prev.xy / prev.w;
++            let uv = vec2<f32>(pn.x * 0.5 + 0.5, 0.5 - pn.y * 0.5);
++            if all(uv > vec2<f32>(0.0)) && all(uv < vec2<f32>(1.0)) {
++                let hp = clamp(vec2<i32>(uv * high), vec2<i32>(0), vec2<i32>(high) - 1);
++                let seen = textureLoad(history, hp, 0).a;
++                let expected = select(length(p + frame.taa.xyz), 0.0, sky);
++                if abs(seen - expected) <= expected * 0.03 + 0.25 {
++                    let mean = sum / 9.0;
++                    let sigma = sqrt(max(sum2 / 9.0 - mean * mean, vec3<f32>(0.0)));
++                    let box_lo = min(max(mean - sigma * 1.25, lo), current);
++                    let box_hi = max(min(mean + sigma * 1.25, hi), current);
++                    let past = clip_to_box(box_lo, box_hi, to_ycocg(squash(history_color(uv))));
++                    // How far the nearest sample is from the pixel's centre (0 on it, 1 at the
++                    // corner of the world's pixel): the farther, the less the frame says.
++                    let near = clamp(length(t - floor(t + 0.5)) / 0.7071, 0.0, 1.0);
++                    let fresh = (1.0 - frame.taa_params.x) * mix(1.8, 0.5, near);
++                    let moved = length((uv - in.uv) * high);
++                    let keep = (1.0 - fresh) * mix(1.0, 0.8, clamp(moved / 4.0, 0.0, 1.0));
++                    resolved = mix(current, past, clamp(keep, 0.0, 0.98));
++                }
++            }
++        }
++    }
++    let color = unsquash(from_ycocg(resolved));
++    var out: TaaOut;
++    out.color = vec4<f32>(color, 1.0);
++    out.history = vec4<f32>(color, dist);
++    return out;
++}
+ "#;
+ 
+ struct Target {
+@@ -744,10 +840,35 @@ fn halton(mut index: u32, base: u32) -> f32 {
+     r
+ }
+ 
++/// The history's weight when upscaling (the frames each pixel gathers are sparse, so more of them
++/// are kept than without; `fs_taau` lowers it where the frame's sample is near).
++const UPSCALE_HISTORY: f32 = 0.92;
++
++/// The world's size relative to the output (`HORIZON_HD_SCALE`, per axis, 0.25..=1) while HD is on, if
++/// set: it replaces the resolution scale of Horizon's settings for HD. 1 renders at full size.
++pub fn scale_override() -> Option<f32> {
++    static SCALE: std::sync::OnceLock<Option<f32>> = std::sync::OnceLock::new();
++    *SCALE.get_or_init(|| {
++        let v: f32 = std::env::var("HORIZON_HD_SCALE").ok()?.parse().ok()?;
++        v.is_finite().then(|| v.clamp(0.25, 1.0))
++    })
++}
++
++/// How many jitter positions the sequence cycles through for an output `ratio` times the world's
++/// size per axis: 16 without upscaling, else 8 per output pixel's share of a world pixel
++/// (ratio squared), so every output pixel gets samples all over the world pixel it lies in.
++pub fn jitter_count(ratio: f32) -> u32 {
++    if ratio <= 1.001 {
++        16
++    } else {
++        ((8.0 * ratio * ratio).ceil() as u32).clamp(16, 64)
++    }
++}
++
+ /// Frame `frame`'s sub-pixel offset of the projection in clip space (a fraction of the
+-/// screen's size in x and y), from the Halton(2, 3) sequence over 16 frames.
+-pub fn jitter(frame: u32, size: [u32; 2]) -> [f32; 2] {
+-    let i = frame % 16 + 1;
++/// screen's size in x and y), from the Halton(2, 3) sequence over `count` frames.
++pub fn jitter(frame: u32, size: [u32; 2], count: u32) -> [f32; 2] {
++    let i = frame % count.max(1) + 1;
+     [
+         (halton(i, 2) - 0.5) * 2.0 / size[0].max(1) as f32,
+         (halton(i, 3) - 0.5) * 2.0 / size[1].max(1) as f32,
+@@ -755,7 +876,10 @@ pub fn jitter(frame: u32, size: [u32; 2]) -> [f32; 2] {
+ }
+ 
+ pub struct Hd {
++    /// The world's size (the G-buffer, lighting, AO, post pass), and the output's (TAA, bloom,
++    /// tone curve): bigger when the world is upscaled.
+     size: [u32; 2],
++    out: [u32; 2],
+     pub albedo: wgpu::TextureView,
+     pub normal: wgpu::TextureView,
+     pub levels: wgpu::TextureView,
+@@ -779,6 +903,7 @@ pub struct Hd {
+     taa_active: bool,
+     taa_layout: wgpu::BindGroupLayout,
+     taa_pipeline: wgpu::RenderPipeline,
++    taau_pipeline: wgpu::RenderPipeline,
+     taa_groups: Option<((wgpu::TextureView, wgpu::TextureView), [wgpu::BindGroup; 2])>,
+     bloom: Vec<Target>,
+     /// Bind groups, rebuilt only when their views change: `resize` drops all of them, the
+@@ -1098,7 +1223,7 @@ impl Hd {
+             entries: &entries(&[UNIFORM, UNFILTERED, DEPTH, FLOAT, SAMPLER]),
+         });
+         let taa_module = module(device, "HD TAA", TAA);
+-        let taa_pipeline = {
++        let taa_pipeline = |entry: &str| {
+             let layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
+                 label: Some("HD TAA"),
+                 bind_group_layouts: &[Some(&taa_layout)],
+@@ -1120,7 +1245,7 @@ impl Hd {
+                 },
+                 fragment: Some(wgpu::FragmentState {
+                     module: &taa_module,
+-                    entry_point: Some("fs_taa"),
++                    entry_point: Some(entry),
+                     compilation_options: Default::default(),
+                     targets: &[target.clone(), target],
+                 }),
+@@ -1131,6 +1256,7 @@ impl Hd {
+                 cache: None,
+             })
+         };
++        let (taa_pipeline, taau_pipeline) = (taa_pipeline("fs_taa"), taa_pipeline("fs_taau"));
+         let ao_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+             label: Some("HD ambient occlusion"),
+             entries: &entries(&[UNIFORM, DEPTH, UNFILTERED]),
+@@ -1288,6 +1414,7 @@ impl Hd {
+         };
+         let mut hd = Hd {
+             size: [0, 0],
++            out: [0, 0],
+             albedo: target(device, "HD albedo", [1, 1], ALBEDO).view,
+             normal: target(device, "HD normal", [1, 1], NORMAL).view,
+             levels: target(device, "HD light levels", [1, 1], LIGHT_LEVELS).view,
+@@ -1319,6 +1446,7 @@ impl Hd {
+             taa_active: false,
+             taa_layout,
+             taa_pipeline,
++            taau_pipeline,
+             taa_groups: None,
+             bloom: Vec::new(),
+             light_group: None,
+@@ -1355,26 +1483,29 @@ impl Hd {
+             groups_seen: 0,
+             groups_last_frame: 0,
+         };
+-        hd.resize(device, size);
++        hd.resize(device, size, size);
+         hd
+     }
+ 
+-    /// The targets, at the world target's size.
+-    pub fn resize(&mut self, device: &wgpu::Device, size: [u32; 2]) {
+-        if self.size == size {
++    /// The targets: the world's at `size` (the world target's), the output's (TAA history, bloom)
++    /// at `out`, which is bigger when the world is upscaled.
++    pub fn resize(&mut self, device: &wgpu::Device, size: [u32; 2], out: [u32; 2]) {
++        let out = [out[0].max(size[0]), out[1].max(size[1])];
++        if self.size == size && self.out == out {
+             return;
+         }
+         self.size = size;
++        self.out = out;
+         self.albedo = target(device, "HD albedo", size, ALBEDO).view;
+         self.normal = target(device, "HD normal", size, NORMAL).view;
+         self.levels = target(device, "HD light levels", size, LIGHT_LEVELS).view;
+         self.depth = target(device, "HD depth", size, wgpu::TextureFormat::Depth32Float).view;
+         self.lit = target(device, "HD lit", size, HDR).view;
+         self.fx = target(device, "HD post", size, HDR).view;
+-        self.taa = target(device, "HD TAA", size, HDR).view;
++        self.taa = target(device, "HD TAA", out, HDR).view;
+         self.history = [
+-            target(device, "HD TAA history", size, HDR).view,
+-            target(device, "HD TAA history", size, HDR).view,
++            target(device, "HD TAA history", out, HDR).view,
++            target(device, "HD TAA history", out, HDR).view,
+         ];
+         self.history_ready = false;
+         self.taa_groups = None;
+@@ -1404,7 +1535,7 @@ impl Hd {
+         self.tiles_x = size[0].div_ceil(TILE).max(1);
+         self.bloom = (0..BLOOM_LEVELS)
+             .map(|k| {
+-                let s = [(size[0] >> (k + 1)).max(1), (size[1] >> (k + 1)).max(1)];
++                let s = [(out[0] >> (k + 1)).max(1), (out[1] >> (k + 1)).max(1)];
+                 target(device, "HD bloom", s, HDR)
+             })
+             .collect();
+@@ -1420,6 +1551,11 @@ impl Hd {
+             .collect();
+     }
+ 
++    /// The world is smaller than the output, so TAA upsamples it.
++    fn upscaling(&self) -> bool {
++        self.out != self.size
++    }
++
+     /// This frame's camera, sun, fog, lights and settings.
+     pub fn write(
+         &mut self,
+@@ -1468,7 +1604,18 @@ impl Hd {
+                 scene.camera_delta.z,
+                 if self.history_ready { 1.0 } else { 0.0 },
+             ],
+-            taa_params: [0.9, if self.taa_active { 0.12 } else { 0.0 }, 0.0, 0.0],
++            taa_params: [
++                if self.upscaling() {
++                    UPSCALE_HISTORY
++                } else {
++                    // A still picture keeps 94% of the past: the jitter's shimmer on pixel-art
++                    // textures averages out instead of flickering.
++                    0.94
++                },
++                if self.taa_active { 0.12 } else { 0.0 },
++                scene.jitter_px[0],
++                scene.jitter_px[1],
++            ],
+             inverse_view_proj: scene.view_proj.inverse().to_cols_array_2d(),
+             resolution: [
+                 self.size[0] as f32,
+@@ -1872,9 +2019,13 @@ impl Hd {
+             return source;
+         };
+         let (read, write) = (self.history_flip, 1 - self.history_flip);
++        let upscaling = self.upscaling();
+         let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+             label: Some("HD TAA"),
+-            timestamp_writes: stamp(&mut self.timing, "hd taa"),
++            timestamp_writes: stamp(
++                &mut self.timing,
++                if upscaling { "hd taau" } else { "hd taa" },
++            ),
+             color_attachments: &[&self.taa, &self.history[write]].map(|view| {
+                 Some(wgpu::RenderPassColorAttachment {
+                     view,
+@@ -1888,7 +2039,11 @@ impl Hd {
+             }),
+             ..Default::default()
+         });
+-        pass.set_pipeline(&self.taa_pipeline);
++        pass.set_pipeline(if upscaling {
++            &self.taau_pipeline
++        } else {
++            &self.taa_pipeline
++        });
+         pass.set_bind_group(0, &groups[read], &[]);
+         pass.draw(0..3, 0..1);
+         drop(pass);
+@@ -2045,7 +2200,7 @@ mod tests {
+         let size = [1920u32, 1080];
+         let mut seen = std::collections::HashSet::new();
+         for f in 0..32 {
+-            let j = jitter(f, size);
++            let j = jitter(f, size, 16);
+             assert!(j[0].abs() <= 1.0 / size[0] as f32 + 1e-9);
+             assert!(j[1].abs() <= 1.0 / size[1] as f32 + 1e-9);
+             seen.insert((j[0].to_bits(), j[1].to_bits()));
+@@ -2053,6 +2208,22 @@ mod tests {
+         assert_eq!(seen.len(), 16);
+     }
+ 
++    #[test]
++    fn jitter_covers_the_upscale_ratio() {
++        assert_eq!(jitter_count(1.0), 16);
++        assert_eq!(jitter_count(1.0 / 0.67), 18);
++        assert_eq!(jitter_count(2.0), 32);
++        let size = [1280u32, 720];
++        let count = jitter_count(2.0);
++        let seen: std::collections::HashSet<_> = (0..count * 2)
++            .map(|f| {
++                let j = jitter(f, size, count);
++                (j[0].to_bits(), j[1].to_bits())
++            })
++            .collect();
++        assert_eq!(seen.len(), count as usize);
++    }
++
+     #[test]
+     fn tile_lists_keep_lights_that_reach_a_tile() {
+         let size = [320, 160];
+diff --git a/crates/horizon-client/src/gfx/world_post.rs b/crates/horizon-client/src/gfx/world_post.rs
+index 17609d27d..a32bdc964 100644
+--- a/crates/horizon-client/src/gfx/world_post.rs
++++ b/crates/horizon-client/src/gfx/world_post.rs
+@@ -18,6 +18,8 @@ pub struct Post {
+     format: wgpu::TextureFormat,
+     /// World resolution relative to the window (0.5..=2.0).
+     pub scale: f32,
++    /// HD's own scale for this frame (`HORIZON_HD_SCALE`), instead of `scale`.
++    pub hd_scale: Option<f32>,
+     pub antialias: bool,
+     target: Option<WorldTarget>,
+ }
+@@ -94,6 +96,7 @@ impl Post {
+             sampler,
+             format,
+             scale: 1.0,
++            hd_scale: None,
+             antialias: false,
+             target: None,
+         }
+@@ -108,11 +111,12 @@ impl Post {
+         window: [u32; 2],
+         always: bool,
+     ) -> Option<(wgpu::TextureView, wgpu::TextureView)> {
+-        if self.scale == 1.0 && !self.antialias && !always {
++        let scale = self.hd_scale.unwrap_or(self.scale);
++        if scale == 1.0 && !self.antialias && !always {
+             self.target = None;
+             return None;
+         }
+-        let size = window.map(|v| ((v as f32 * self.scale).round() as u32).clamp(1, 8192));
++        let size = window.map(|v| ((v as f32 * scale).round() as u32).clamp(1, 8192));
+         if self.target.as_ref().is_none_or(|t| t.size != size) {
+             let extent = wgpu::Extent3d {
+                 width: size[0],
+diff --git a/crates/horizon-client/src/terrain.wgsl b/crates/horizon-client/src/terrain.wgsl
+index bb5c70f63..c44449cc7 100644
+--- a/crates/horizon-client/src/terrain.wgsl
++++ b/crates/horizon-client/src/terrain.wgsl
+@@ -166,6 +166,10 @@ struct GBufferOut {
+ }
+ fn face_normal(pos: vec3<f32>) -> vec3<f32> {
+     var n = normalize(cross(dpdx(pos), dpdy(pos)));
++    // Block faces are axis-aligned; only plants' crossed quads lean. Those have two
++    // sides, so a normal turned to the camera would flip as the player walks by and
++    // the sun and the shadow lookup with it: plants take the up normal instead.
++    if max(abs(n.x), max(abs(n.y), abs(n.z))) < 0.9 { return vec3(0.0, 1.0, 0.0); }
+     if dot(n, pos) > 0.0 { n = -n; }
+     return n;
+ }
+-- 
+2.54.0 (Apple Git-157)
+

horizon-patches/0019-HD-water-its-own-pass-colour-normal-depth-the-floor-.patch

@@ -0,0 +1,982 @@
+From 38250c4392e27d5700842ca6ee47291dd1831b72 Mon Sep 17 00:00:00 2001
+From: chexit <chexit@duck.com>
+Date: Thu, 29 Oct 2026 17:47:52 +0300
+Subject: [PATCH 19/24] HD water: its own pass (colour, normal, depth), the
+ floor under it lit, a composite with world-space waves, refraction with depth
+ absorption in the biome colour, screen-space reflections, Fresnel and a
+ shadowed sun glint (HORIZON_HD_WATER=0 to switch off)
+
+Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
+---
+ crates/horizon-client/src/game.rs      |   9 +
+ crates/horizon-client/src/gfx.rs       | 109 +++++-
+ crates/horizon-client/src/gfx/flat.rs  |   4 +
+ crates/horizon-client/src/gfx/hd.rs    | 497 ++++++++++++++++++++++++-
+ crates/horizon-client/src/terrain.wgsl |  19 +
+ 5 files changed, 627 insertions(+), 11 deletions(-)
+
+diff --git a/crates/horizon-client/src/game.rs b/crates/horizon-client/src/game.rs
+index 3a11ee283..5a173977f 100644
+--- a/crates/horizon-client/src/game.rs
++++ b/crates/horizon-client/src/game.rs
+@@ -14658,6 +14658,14 @@ fn build_renderer(
+         prepared,
+         previous,
+         api,
++        // AirDef fork, HD water: the layers of the water sprites.
++        ["water_still", "water_flow"].map(|name| {
++            assets
++                .sprite_layers
++                .get(&format!("minecraft:block/{name}"))
++                .copied()
++                .unwrap_or(0xffff)
++        }),
+     ))?;
+     renderer.hud.sprite_animations = atlas
+         .sprite_animations
+@@ -14717,6 +14725,7 @@ fn loading_renderer(
+         None,
+         previous,
+         api,
++        [0xffff; 2],
+     ))?;
+     if let Some(atlas) = atlas {
+         renderer.hud.sprite_animations = atlas
+diff --git a/crates/horizon-client/src/gfx.rs b/crates/horizon-client/src/gfx.rs
+index b85c6e269..f9dab8abf 100644
+--- a/crates/horizon-client/src/gfx.rs
++++ b/crates/horizon-client/src/gfx.rs
+@@ -564,6 +564,8 @@ pub struct Renderer {
+     mod_views: Option<mod_views::Views>,
+     /// AirDef fork: the HD lighting's G-buffer pipelines (terrain, entities) and its targets.
+     gbuffer_terrain: wgpu::RenderPipeline,
++    /// The water quads alone into the HD water targets (section draws; `flat.water` for flat ones).
++    gbuffer_water: wgpu::RenderPipeline,
+     gbuffer_entity: wgpu::RenderPipeline,
+     /// The HD sun shadows: depth only, from the light, and the sections in its farther cascade.
+     shadow_terrain: wgpu::RenderPipeline,
+@@ -1083,6 +1085,7 @@ impl Renderer {
+         prepared: Option<PreparedTextures>,
+         previous: Option<&Self>,
+         api: GraphicsApi,
++        water_layers: [u32; 2],
+     ) -> Result<Self> {
+         let split = sprite_split();
+         if layers > split * SPRITE_ARRAYS {
+@@ -1205,6 +1208,13 @@ impl Renderer {
+             ("SPRITE_ARRAYS", f64::from(sprite_arrays)),
+             ("SPRITE_SPLIT", f64::from(split)),
+         ];
++        // AirDef fork, HD water: the sprite layers terrain.wgsl's fs_water takes for water.
++        let water_constants = [
++            ("SPRITE_ARRAYS", f64::from(sprite_arrays)),
++            ("SPRITE_SPLIT", f64::from(split)),
++            ("WATER_STILL", f64::from(water_layers[0])),
++            ("WATER_FLOW", f64::from(water_layers[1])),
++        ];
+         let bindings = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+             label: Some("Horizon terrain bindings"),
+             entries: &[
+@@ -1420,6 +1430,55 @@ impl Renderer {
+             multiview_mask: None,
+             cache: None,
+         });
++        // AirDef fork, HD water: only the water quads (`fs_water`), into the colour and normal
++        // targets and the water's own depth; `vertex` is the section or the flat vertex stage.
++        let water_targets = [
++            Some(wgpu::ColorTargetState {
++                format: hd::WATER_TINT,
++                blend: None,
++                write_mask: wgpu::ColorWrites::ALL,
++            }),
++            Some(wgpu::ColorTargetState {
++                format: hd::WATER_NORMAL,
++                blend: None,
++                write_mask: wgpu::ColorWrites::ALL,
++            }),
++        ];
++        let water_pipeline =
++            |layout: &wgpu::PipelineLayout,
++             label: &str,
++             vertex: &str,
++             buffers: &[Option<wgpu::VertexBufferLayout<'_>>]| {
++                device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
++                    label: Some(label),
++                    layout: Some(layout),
++                    vertex: wgpu::VertexState {
++                        module: &shader,
++                        entry_point: Some(vertex),
++                        compilation_options: Default::default(),
++                        buffers,
++                    },
++                    primitive: wgpu::PrimitiveState {
++                        cull_mode: Some(wgpu::Face::Back),
++                        ..Default::default()
++                    },
++                    depth_stencil: gbuffer_depth.clone(),
++                    multisample: Default::default(),
++                    fragment: Some(wgpu::FragmentState {
++                        module: &shader,
++                        entry_point: Some("fs_water"),
++                        compilation_options: wgpu::PipelineCompilationOptions {
++                            constants: &water_constants,
++                            ..Default::default()
++                        },
++                        targets: &water_targets,
++                    }),
++                    multiview_mask: None,
++                    cache: None,
++                })
++            };
++        let gbuffer_water =
++            water_pipeline(&layout, "HD water terrain", "vs_terrain", &terrain_buffers);
+         let shadow_terrain = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
+             label: Some("HD shadows terrain"),
+             layout: Some(&layout),
+@@ -2597,6 +2656,7 @@ impl Renderer {
+                 &device,
+                 &bindings,
+                 arena.page_vertices(),
++                |layout, label| water_pipeline(layout, label, "vs_terrain_flat", &buffers),
+                 |layout, label, fragment, blend| {
+                     pipeline_in(
+                         layout,
+@@ -2816,6 +2876,7 @@ impl Renderer {
+             mod_post_hdr: false,
+             mod_views: None,
+             gbuffer_terrain,
++            gbuffer_water,
+             gbuffer_entity,
+             shadow_terrain,
+             shadow_entity,
+@@ -4204,6 +4265,16 @@ impl Renderer {
+             fog_color,
+             fog,
+             sky: frame.skybox && !frame.end_sky && !frame.nether_lighting && !frame.underwater,
++            sky_color: [
++                frame.sky.sky_color[0],
++                frame.sky.sky_color[1],
++                frame.sky.sky_color[2],
++            ],
++            camera_mod: [
++                camera.x.rem_euclid(256.0) as f32,
++                camera.z.rem_euclid(256.0) as f32,
++            ],
++            water: !frame.underwater,
+         };
+         let (shadow_dir, shadow_strength, _) = hd::light_of(&hd_scene);
+         let mut hd_cascades = hd::cascades(camera, shadow_dir);
+@@ -5058,6 +5129,11 @@ impl Renderer {
+                 .hd
+                 .get_or_insert_with(|| hd::Hd::new(device, size, format, globals_size));
+             hd.resize(device, size, [self.config.width, self.config.height]);
++            // Translucent terrain on screen: the water pass has something to draw.
++            hd.water_geometry = match self.flat.as_ref().filter(|_| flat_frame) {
++                Some(flat) => !flat.translucent_calls().is_empty(),
++                None => translucent_draws > 0,
++            };
+             if let Some(settings) = frame.hd {
+                 hd.write(&self.queue, &hd_scene, frame.hd_lights, settings);
+             }
+@@ -5186,6 +5262,32 @@ impl Renderer {
+             drop(pass);
+             // Contact shadows from the G-buffer's depth and normals, for the lighting.
+             hd.ao(&mut encoder);
++            // The water quads alone, with their own depth: the lighting finds the water by it and
++            // the composite after the lighting lays the surface over the lit floor.
++            if hd.water_active() {
++                let mut pass = hd.water_pass(&mut encoder);
++                pass.set_bind_group(0, &self.group, &[]);
++                match self.flat.as_ref().filter(|_| flat_frame) {
++                    Some(flat) => {
++                        pass.set_pipeline(&flat.water);
++                        flat.draw(&mut pass, flat.translucent_calls(), |p| {
++                            self.arena.buffer(p)
++                        });
++                    }
++                    None => {
++                        pass.set_pipeline(&self.gbuffer_water);
++                        pass.set_index_buffer(self.indices.slice(..), wgpu::IndexFormat::Uint32);
++                        pass.set_vertex_buffer(1, self.instances.slice(..));
++                        self.draw_sections(
++                            &mut pass,
++                            &self.indirect,
++                            0,
++                            solid_draws,
++                            translucent_draws,
++                        );
++                    }
++                }
++            }
+         } else if !hd_on {
+             self.hd = None;
+         }
+@@ -5721,6 +5823,11 @@ impl Renderer {
+                 (color, depth),
+                 (&self.lightmap_view, &self.lightmap_sampler),
+             );
++            hd.water_composite(
++                &self.device,
++                &mut encoder,
++                (&self.lightmap_view, &self.lightmap_sampler),
++            );
+             match &mut self.mod_post {
+                 Some(post) if mod_post => {
+                     let size = self.world_post.size().unwrap_or([1, 1]);
+@@ -5731,7 +5838,7 @@ impl Renderer {
+                         &self.mod_params.0,
+                         self.mod_params.1,
+                     );
+-                    post.run(&self.device, &mut encoder, (&hd.lit, depth), &hd.fx);
++                    post.run(&self.device, &mut encoder, (hd.lit_view(), depth), &hd.fx);
+                     let source = hd.taa(&self.device, &mut encoder, hd::HdSource::Fx, depth);
+                     hd.finish(&self.device, &mut encoder, source, &view_target);
+                 }
+diff --git a/crates/horizon-client/src/gfx/flat.rs b/crates/horizon-client/src/gfx/flat.rs
+index 5d86888da..7e2e20cad 100644
+--- a/crates/horizon-client/src/gfx/flat.rs
++++ b/crates/horizon-client/src/gfx/flat.rs
+@@ -64,6 +64,8 @@ pub struct Call {
+ pub struct Flat {
+     pub solid: wgpu::RenderPipeline,
+     pub translucent: wgpu::RenderPipeline,
++    /// The water quads alone, into HD's water targets.
++    pub water: wgpu::RenderPipeline,
+     flatten: wgpu::ComputePipeline,
+     compute_layout: wgpu::BindGroupLayout,
+     flatten_seen: wgpu::ComputePipeline,
+@@ -254,6 +256,7 @@ impl Flat {
+         device: &wgpu::Device,
+         terrain_layout: &wgpu::BindGroupLayout,
+         page_vertices: u64,
++        water: impl Fn(&wgpu::PipelineLayout, &str) -> wgpu::RenderPipeline,
+         pipeline: impl Fn(
+             &wgpu::PipelineLayout,
+             &str,
+@@ -320,6 +323,7 @@ impl Flat {
+                 "fs_translucent",
+                 Some(wgpu::BlendState::ALPHA_BLENDING),
+             ),
++            water: water(&layout, "HD water terrain (flat)"),
+             flatten,
+             compute_layout,
+             flatten_seen,
+diff --git a/crates/horizon-client/src/gfx/hd.rs b/crates/horizon-client/src/gfx/hd.rs
+index c54b7b961..f5caa2d0b 100644
+--- a/crates/horizon-client/src/gfx/hd.rs
++++ b/crates/horizon-client/src/gfx/hd.rs
+@@ -16,6 +16,9 @@ pub const NORMAL: wgpu::TextureFormat = wgpu::TextureFormat::Rgba16Float;
+ pub const LIGHT_LEVELS: wgpu::TextureFormat = wgpu::TextureFormat::Rgba8Unorm;
+ /// The lit world and the post pass's output.
+ pub const HDR: wgpu::TextureFormat = wgpu::TextureFormat::Rgba16Float;
++/// The water pass's targets: the surface colour with the block light, and the normal with the sky light.
++pub const WATER_TINT: wgpu::TextureFormat = wgpu::TextureFormat::Rgba16Float;
++pub const WATER_NORMAL: wgpu::TextureFormat = wgpu::TextureFormat::Rgba8Unorm;
+ /// The most lights drawn a frame.
+ pub const MAX_LIGHTS: usize = 512;
+ /// The side (pixels) of a tile of the screen with its own short list of lights.
+@@ -91,6 +94,13 @@ struct HdFrame {
+     taa: [f32; 4],
+     /// x: the history's weight; y: the sharpening (0 without TAA); zw: the jitter in world pixels.
+     taa_params: [f32; 4],
++    /// The (jittered) world-to-clip matrix the world was drawn with (rays in the water pass).
++    view_proj: [[f32; 4]; 4],
++    /// x: the water effect runs this frame; y: seconds for the waves (wraps at 600); zw: the
++    /// camera's x and z modulo 256, the waves' period.
++    water: [f32; 4],
++    /// rgb: the sky's colour; w: 1 when there is a sky.
++    sky_color: [f32; 4],
+ }
+ 
+ /// What the world around looks like this frame (from the renderer's globals).
+@@ -116,6 +126,11 @@ pub struct HdScene {
+     pub fog: [f32; 4],
+     /// The sky has a sun at all (the Overworld).
+     pub sky: bool,
++    pub sky_color: [f32; 3],
++    /// The camera's x and z modulo 256 (the waves' period), so the waves hold still in the world.
++    pub camera_mod: [f32; 2],
++    /// The water effect may run (not underwater, not disabled).
++    pub water: bool,
+ }
+ 
+ /// The cascades' half sizes (blocks) and shadow map size.
+@@ -137,6 +152,9 @@ struct HdFrame {
+     prev_view_proj: mat4x4<f32>,
+     taa: vec4<f32>,
+     taa_params: vec4<f32>,
++    view_proj: mat4x4<f32>,
++    water: vec4<f32>,
++    sky_color: vec4<f32>,
+ }
+ struct FullOut {
+     @builtin(position) position: vec4<f32>,
+@@ -175,6 +193,8 @@ struct Light {
+ @group(0) @binding(12) var<storage, read> tiles: array<u32>;
+ // Ambient occlusion at half resolution: x the occlusion (1 open), y the distance it was taken at.
+ @group(0) @binding(13) var ao_tex: texture_2d<f32>;
++// The water pass's depth: the nearest water surface (0 where there is none).
++@group(0) @binding(14) var water_depth: texture_depth_2d;
+ 
+ // The occlusion at a full-resolution pixel `dist` away: the four nearest half-resolution texels
+ // weighted by closeness and by how near their distance is, so it doesn't bleed across edges.
+@@ -216,6 +236,12 @@ fn cascade_at(p: vec3<f32>, c: i32) -> vec3<f32> {
+ 
+ // The sun's (or moon's) light reaching p: 1 lit, 0 in shadow; soft-edged.
+ fn shadow(p: vec3<f32>, n: vec3<f32>) -> f32 {
++    return shadow_taps(p, n, 1);
++}
++
++// `shadow` with a (2 * r + 1) square of taps: the floor under water takes one (the water dims and
++// blurs it anyway).
++fn shadow_taps(p: vec3<f32>, n: vec3<f32>, r: i32) -> f32 {
+     let dist = length(p);
+     let c = select(1, 0, dist < frame.shadow.y * 0.92);
+     let texel = select(frame.shadow.z, frame.shadow.y, c == 0) * 2.0 / 2048.0;
+@@ -224,13 +250,13 @@ fn shadow(p: vec3<f32>, n: vec3<f32>) -> f32 {
+     if any(s.xy < vec2<f32>(0.0)) || any(s.xy > vec2<f32>(1.0)) || s.z > 1.0 { return 1.0; }
+     var lit = 0.0;
+     let step = 1.0 / 2048.0;
+-    for (var y = -1; y <= 1; y++) {
+-        for (var x = -1; x <= 1; x++) {
++    for (var y = -r; y <= r; y++) {
++        for (var x = -r; x <= r; x++) {
+             lit += textureSampleCompareLevel(shadow_map, shadow_sampler, s.xy + vec2<f32>(f32(x), f32(y)) * step, c, s.z - 0.0005);
+         }
+     }
+     let fade = clamp((frame.shadow.z - dist) / 16.0, 0.0, 1.0);
+-    return mix(1.0, lit / 9.0, fade);
++    return mix(1.0, lit / f32((2 * r + 1) * (2 * r + 1)), fade);
+ }
+ 
+ // One shadow sample, for the rays through the air.
+@@ -252,7 +278,15 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+     let scene = textureLoad(scene_color, px, 0).rgb;
+     let d = textureLoad(scene_depth, px, 0);
+     let g = textureLoad(gbuffer_depth, px, 0);
+-    let ndc = vec4<f32>(in.uv.x * 2.0 - 1.0, 1.0 - in.uv.y * 2.0, max(d, 0.000001), 1.0);
++    // Water in front of the opaque world with nothing translucent over it: here the floor is lit
++    // and the water composite lays the surface over it (it knows the pixel by the alpha 0.5).
++    var water = false;
++    if frame.water.x > 0.5 && g > 0.0 {
++        let wd = textureLoad(water_depth, px, 0);
++        water = wd > 0.0 && wd >= g && d - wd <= d * 0.002;
++    }
++    let dd = select(d, g, water);
++    let ndc = vec4<f32>(in.uv.x * 2.0 - 1.0, 1.0 - in.uv.y * 2.0, max(dd, 0.000001), 1.0);
+     let h = frame.inverse_view_proj * ndc;
+     let p = h.xyz / h.w;
+     let view = normalize(p);
+@@ -267,7 +301,7 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+     let halo_all = tiles[tile + 3u] == 0xffffffffu;
+     let halo_count = select(tiles[tile + 3u], count, halo_all);
+     var c = scene;
+-    let surface = d > 0.0 && abs(d - g) <= max(d, g) * 0.002;
++    let surface = water || (d > 0.0 && abs(d - g) <= max(d, g) * 0.002);
+     if surface {
+         let n = normalize(textureLoad(normal_tex, px, 0).xyz);
+         let albedo = textureLoad(albedo_tex, px, 0);
+@@ -278,14 +312,15 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+         let sky_reach = smoothstep(0.35, 0.95, lm.x);
+         var s = 1.0;
+         let ndl = dot(n, sun);
+-        if sun_on > 0.0 && ndl > 0.0 && sky_reach > 0.0 { s = shadow(p, n); } else { s = 0.0; }
++        if sun_on > 0.0 && ndl > 0.0 && sky_reach > 0.0 { s = shadow_taps(p, n, select(1, 0, water)); } else { s = 0.0; }
+         // Shadowed sky light (ambient) keeps vanilla's look, blocks' light stays as is; the sun adds
+         // direct light by the face's angle.
+         let direct = frame.sun_color.rgb * sun_on * max(ndl, 0.0) * s * sky_reach;
+         // Contact shadows from the ambient occlusion: on the ambient and blocks' light fully, on
+         // the mods' lights by half, not on the sun or on emission.
+         var occlusion = 1.0;
+-        if frame.ambient.w > 0.0 { occlusion = ao_at(px, length(p)); }
++        // (The water dims and blurs the floor under it: no occlusion there.)
++        if frame.ambient.w > 0.0 && !water { occlusion = ao_at(px, length(p)); }
+         let ao_ambient = mix(1.0, occlusion, frame.ambient.w);
+         let ao_lights = mix(1.0, occlusion, frame.ambient.w * 0.5);
+         var light = max(base * frame.ambient.x, block * frame.ambient.y) * ao_ambient + direct;
+@@ -334,7 +369,253 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+         let a1 = atan((far - t0) / hh);
+         c += l.color.rgb * l.color.w * (a1 - a0) / hh * 0.004 * (0.3 + density * 300.0);
+     }
+-    return vec4<f32>(c, 1.0);
++    return vec4<f32>(c, select(1.0, 0.5, water));
++}
++"#;
++
++const WATER: &str = r#"
++const PI: f32 = 3.14159265;
++const REFLECT_STEPS: i32 = 24;
++const REFLECT_RANGE: f32 = 96.0;
++@group(0) @binding(0) var<uniform> frame: HdFrame;
++@group(0) @binding(1) var lit_tex: texture_2d<f32>;
++@group(0) @binding(2) var gbuffer_depth: texture_depth_2d;
++@group(0) @binding(3) var water_tint: texture_2d<f32>;
++@group(0) @binding(4) var water_normal: texture_2d<f32>;
++@group(0) @binding(5) var water_depth: texture_depth_2d;
++@group(0) @binding(6) var shadow_map: texture_depth_2d_array;
++@group(0) @binding(7) var shadow_sampler: sampler_comparison;
++@group(0) @binding(8) var lightmap: texture_2d<f32>;
++@group(0) @binding(9) var linear: sampler;
++
++fn ign(px: vec2<f32>) -> f32 {
++    let p = px + vec2<f32>(5.588238 * frame.params.w);
++    return fract(52.9829189 * fract(dot(p, vec2<f32>(0.06711056, 0.00583715))));
++}
++
++// The camera-relative position of the screen point `uv` at depth z.
++fn position_at(uv: vec2<f32>, z: f32) -> vec3<f32> {
++    let h = frame.inverse_view_proj * vec4<f32>(uv.x * 2.0 - 1.0, 1.0 - uv.y * 2.0, z, 1.0);
++    return h.xyz / h.w;
++}
++
++// The screen point (uv, clip w) of a camera-relative position.
++fn project(p: vec3<f32>) -> vec3<f32> {
++    let c = frame.view_proj * vec4<f32>(p, 1.0);
++    return vec3<f32>(c.x / c.w * 0.5 + 0.5, 0.5 - c.y / c.w * 0.5, c.w);
++}
++
++fn on_screen(uv: vec2<f32>) -> bool {
++    return all(uv > vec2<f32>(0.0)) && all(uv < vec2<f32>(1.0));
++}
++
++fn texel(uv: vec2<f32>) -> vec2<i32> {
++    return clamp(vec2<i32>(uv * frame.resolution.xy), vec2<i32>(0), vec2<i32>(frame.resolution.xy) - 1);
++}
++
++// Sine waves in world space: wave vectors that are whole multiples of 2 pi / 256 and speeds that
++// are whole cycles per 600 s, so the sum repeats every 256 blocks and 10 minutes and holds still
++// in the world as the camera moves. x, y: the vector in units of 2 pi / 256; z: the slope the
++// wave adds; w: its phase.
++const WAVES = array<vec4<f32>, 10>(
++    vec4<f32>(3.0, 1.0, 0.040, 0.3),
++    vec4<f32>(-2.0, 5.0, 0.045, 2.1),
++    vec4<f32>(7.0, 2.0, 0.040, 4.4),
++    vec4<f32>(-5.0, -9.0, 0.040, 1.2),
++    vec4<f32>(11.0, -4.0, 0.035, 5.6),
++    vec4<f32>(13.0, 10.0, 0.035, 3.3),
++    vec4<f32>(-17.0, 7.0, 0.030, 0.9),
++    vec4<f32>(9.0, 23.0, 0.030, 2.7),
++    vec4<f32>(-27.0, 19.0, 0.025, 4.9),
++    vec4<f32>(31.0, 30.0, 0.025, 1.8),
++);
++
++// The gradient of the water's height at world x, z: the waves that a pixel `footprint` blocks
++// wide can still resolve (finer ones fade out, or they would shimmer).
++fn wave_gradient(xz: vec2<f32>, footprint: f32) -> vec2<f32> {
++    var grad = vec2<f32>(0.0);
++    for (var i = 0; i < 10; i++) {
++        let w = WAVES[i];
++        let k = w.xy * (2.0 * PI / 256.0);
++        let len = length(k);
++        let fade = clamp((2.0 * PI / len) / max(footprint, 0.0001) * 0.25 - 0.5, 0.0, 1.0);
++        let cycles = round(sqrt(9.8 * len) * 0.5 * 600.0 / (2.0 * PI));
++        let omega = cycles * 2.0 * PI / 600.0;
++        let phase = dot(k, xz) - omega * frame.water.y + w.w;
++        grad += (k / len) * (w.z * fade * cos(phase));
++    }
++    return grad;
++}
++
++fn cascade_at(p: vec3<f32>, c: i32) -> vec3<f32> {
++    let s = frame.cascades[c] * vec4<f32>(p, 1.0);
++    return vec3<f32>(s.x * 0.5 + 0.5, 0.5 - s.y * 0.5, s.z);
++}
++
++// The sun's (or moon's) light reaching p: 1 lit, 0 in shadow (as the lighting pass has it).
++fn shadow(p: vec3<f32>, n: vec3<f32>) -> f32 {
++    let dist = length(p);
++    let c = select(1, 0, dist < frame.shadow.y * 0.92);
++    let texel_size = select(frame.shadow.z, frame.shadow.y, c == 0) * 2.0 / 2048.0;
++    let q = p + n * texel_size * 1.5;
++    let s = cascade_at(q, c);
++    if any(s.xy < vec2<f32>(0.0)) || any(s.xy > vec2<f32>(1.0)) || s.z > 1.0 { return 1.0; }
++    var lit = 0.0;
++    let step = 1.0 / 2048.0;
++    for (var y = -1; y <= 1; y++) {
++        for (var x = -1; x <= 1; x++) {
++            lit += textureSampleCompareLevel(shadow_map, shadow_sampler, s.xy + vec2<f32>(f32(x), f32(y)) * step, c, s.z - 0.0005);
++        }
++    }
++    let fade = clamp((frame.shadow.z - dist) / 16.0, 0.0, 1.0);
++    return mix(1.0, lit / 9.0, fade);
++}
++
++fn linear_fog(d: f32, start: f32, end: f32) -> f32 {
++    if d <= start { return 0.0; }
++    if d >= end { return 1.0; }
++    return (d - start) / (end - start);
++}
++
++// What the sky shows along r when the ray leaves the screen: the horizon's colour rising to
++// the zenith's, darker where the water lies under cover (`vis` is the sky light there).
++fn sky_along(r: vec3<f32>, vis: f32) -> vec3<f32> {
++    var c = frame.fog_color.rgb;
++    if frame.sky_color.w > 0.5 {
++        c = mix(frame.fog_color.rgb, frame.sky_color.rgb, smoothstep(0.0, 0.5, r.y));
++    }
++    return c * mix(0.12, 1.0, vis);
++}
++
++// Marches the ray from p along r over the depth buffer (28 steps, growing, jittered so TAA
++// averages the placement; then a binary search for the crossing). xyz: the colour found,
++// w: how much to trust it (0 for a miss, less near the screen's edge).
++fn reflection(p: vec3<f32>, r: vec3<f32>, jitter: f32) -> vec4<f32> {
++    var near = 0.0;
++    for (var i = 0; i < REFLECT_STEPS; i++) {
++        let u = (f32(i) + jitter) / f32(REFLECT_STEPS);
++        let s = 0.12 + REFLECT_RANGE * u * u;
++        let q = p + r * s;
++        let sp = project(q);
++        if sp.z <= 0.0 || !on_screen(sp.xy) { break; }
++        let z = textureLoad(gbuffer_depth, texel(sp.xy), 0);
++        if z > 0.0 {
++            let c = frame.view_proj * vec4<f32>(q, 1.0);
++            // Reversed Z: a larger depth is nearer; the ray is behind the surface when the
++            // surface is nearer than it.
++            if z > c.z / c.w {
++                let behind = length(q) - length(position_at(sp.xy, z));
++                if behind < 0.4 + 0.08 * s {
++                    var lo = near;
++                    var hi = s;
++                    for (var k = 0; k < 5; k++) {
++                        let m = 0.5 * (lo + hi);
++                        let mq = p + r * m;
++                        let mp = project(mq);
++                        let mc = frame.view_proj * vec4<f32>(mq, 1.0);
++                        let mz = textureLoad(gbuffer_depth, texel(mp.xy), 0);
++                        if mz > mc.z / mc.w { hi = m; } else { lo = m; }
++                    }
++                    let hp = project(p + r * hi);
++                    let edge = min(min(hp.x, 1.0 - hp.x), min(hp.y, 1.0 - hp.y));
++                    let colour = textureSampleLevel(lit_tex, linear, hp.xy, 0.0).rgb;
++                    return vec4<f32>(colour, smoothstep(0.0, 0.08, edge));
++                }
++            }
++        }
++        near = s;
++    }
++    return vec4<f32>(0.0);
++}
++
++// The sun's glint on the waves (GGX, a rough lobe so it glitters instead of aliasing).
++fn glint(n: vec3<f32>, v: vec3<f32>, l: vec3<f32>) -> f32 {
++    let h = normalize(l + v);
++    let a = 0.05;
++    let nh = max(dot(n, h), 0.0);
++    let d = a * a / (PI * pow(nh * nh * (a * a - 1.0) + 1.0, 2.0));
++    let f = 0.02 + 0.98 * pow(1.0 - max(dot(v, h), 0.0), 5.0);
++    return min(d * f * 0.25 * max(dot(n, l), 0.0) / max(dot(n, v), 0.1), 12.0);
++}
++
++// The water over the lit world: the world behind it (refracted by the waves, dimmed and tinted
++// by the water's depth), the sky and the world above it (a screen-space reflection) by Fresnel,
++// and the sun's glint. Pixels without water pass through.
++@fragment
++fn fs_water(in: FullOut) -> @location(0) vec4<f32> {
++    let px = vec2<i32>(in.position.xy);
++    let base = textureLoad(lit_tex, px, 0);
++    if base.a > 0.75 { return vec4<f32>(base.rgb, 1.0); }
++    let wd = textureLoad(water_depth, px, 0);
++    let g = textureLoad(gbuffer_depth, px, 0);
++    let tint = textureLoad(water_tint, px, 0);
++    let nt = textureLoad(water_normal, px, 0);
++    let p = position_at(in.uv, wd);
++    let dist = length(p);
++    let v = -p / dist;
++    let geometric = normalize(nt.xyz * 2.0 - 1.0);
++    // The waves tilt the flat parts of the surface only.
++    let footprint = dist * frame.resolution.w * 1.4;
++    let grad = wave_gradient(p.xz + frame.water.zw, footprint);
++    let flat_part = smoothstep(0.6, 0.95, geometric.y);
++    var n = normalize(geometric + vec3<f32>(-grad.x, 0.0, -grad.y) * flat_part);
++    n = normalize(n + v * max(0.03 - dot(n, v), 0.0));
++    let ndv = max(dot(n, v), 0.02);
++
++    // Light on the water: vanilla's lightmap at the surface, and the sun where it reaches.
++    let levels = vec2<f32>(nt.a, tint.a);
++    let sky_reach = smoothstep(0.35, 0.95, levels.x);
++    let ambient = textureSampleLevel(lightmap, linear, clamp(vec2<f32>(levels.y, levels.x) * (15.0 / 16.0) + 0.5 / 16.0, vec2<f32>(0.5 / 16.0), vec2<f32>(15.5 / 16.0)), 0.0).rgb;
++    let block = textureSampleLevel(lightmap, linear, vec2<f32>(levels.y * (15.0 / 16.0) + 0.5 / 16.0, 0.5 / 16.0), 0.0).rgb;
++    let sun = frame.sun.xyz;
++    let sun_on = frame.sun.w;
++    var sunlit = 0.0;
++    if sun_on > 0.0 && sun.y > 0.0 && sky_reach > 0.0 { sunlit = shadow(p, vec3<f32>(0.0, 1.0, 0.0)) * sky_reach; }
++    let volume_light = max(ambient * frame.ambient.x, block * frame.ambient.y) + frame.sun_color.rgb * sun_on * sunlit * 0.8;
++
++    // Refraction: where the ray through the waves meets the world, against where the flat surface
++    // would send it (so still water looks as vanilla's and only the waves distort).
++    let floor0 = position_at(in.uv, g);
++    let depth0 = max(length(floor0) - dist, 0.0);
++    let bent = refract(-v, n, 0.75) - refract(-v, geometric, 0.75);
++    var uv_floor = in.uv;
++    var floor_z = g;
++    let moved = project(floor0 + bent * min(depth0, 24.0));
++    if moved.z > 0.0 && on_screen(moved.xy) {
++        let z = textureLoad(gbuffer_depth, texel(moved.xy), 0);
++        // Only what lies behind the water: not the bank or an entity in front of it.
++        if z > 0.0 && z <= wd {
++            uv_floor = moved.xy;
++            floor_z = z;
++        }
++    }
++    let thickness = clamp(length(position_at(uv_floor, floor_z)) - dist, 0.0, 48.0);
++    let behind = textureSampleLevel(lit_tex, linear, uv_floor, 0.0).rgb;
++    let colour = clamp(tint.rgb, vec3<f32>(0.03), vec3<f32>(1.0));
++    // The colours the water takes up fastest are the ones it has the least of.
++    let absorb = exp(-(vec3<f32>(1.0) - colour) * 0.8 * (thickness + 0.3));
++    let refracted = behind * absorb + colour * volume_light * 0.9 * (vec3<f32>(1.0) - absorb);
++
++    // Reflection: the screen where the ray stays on it, the sky where it leaves it or misses.
++    var r = reflect(-v, n);
++    r.y = abs(r.y);
++    // Looking down onto it the reflection is a few percent of the picture: the sky alone does.
++    let fresnel = 0.02 + 0.98 * pow(1.0 - ndv, 5.0);
++    var hit = vec4<f32>(0.0);
++    if fresnel > 0.04 { hit = reflection(p, r, ign(in.position.xy)); }
++    let sky_vis = mix(0.15, 1.0, sky_reach);
++    let reflected = mix(sky_along(r, sky_vis), hit.rgb, hit.w);
++
++    var c = refracted * (1.0 - fresnel) + reflected * fresnel;
++    if sun_on > 0.0 && sunlit > 0.0 {
++        c += frame.sun_color.rgb * sun_on * sunlit * glint(n, v, sun);
++    }
++    // Vanilla's fog over it, at the surface.
++    let sph = dist;
++    let cyl = max(length(p.xz), abs(p.y));
++    let f = max(linear_fog(sph, frame.fog.x, frame.fog.y), linear_fog(cyl, frame.fog.z, frame.fog.w));
++    c = mix(c, frame.fog_color.rgb, f * frame.fog_color.a);
++    return vec4<f32>(max(c, vec3<f32>(0.0)), 1.0);
+ }
+ "#;
+ 
+@@ -829,6 +1110,12 @@ pub fn taa_enabled() -> bool {
+     *ON.get_or_init(|| std::env::var("HORIZON_HD_TAA").map_or(true, |v| v != "0"))
+ }
+ 
++/// The water effect is on unless `HORIZON_HD_WATER=0`.
++pub fn water_enabled() -> bool {
++    static ON: std::sync::OnceLock<bool> = std::sync::OnceLock::new();
++    *ON.get_or_init(|| std::env::var("HORIZON_HD_WATER").map_or(true, |v| v != "0"))
++}
++
+ /// The Halton sequence's `index`-th number in `base`, in (0, 1).
+ fn halton(mut index: u32, base: u32) -> f32 {
+     let (mut f, mut r) = (1.0, 0.0);
+@@ -895,6 +1182,22 @@ pub struct Hd {
+     /// The lit world, and the post pass's output.
+     pub lit: wgpu::TextureView,
+     pub fx: wgpu::TextureView,
++    /// Water: its surface colour and normal, its depth (the nearest water surface; 0 elsewhere),
++    /// the lit world with the water over it, and what draws and composites them.
++    water_tint: wgpu::TextureView,
++    water_normal: wgpu::TextureView,
++    water_depth: wgpu::TextureView,
++    lit_water: wgpu::TextureView,
++    water_layout: wgpu::BindGroupLayout,
++    water_pipeline: wgpu::RenderPipeline,
++    water_group: Option<((wgpu::TextureView, wgpu::Sampler), wgpu::BindGroup)>,
++    /// The water effect runs this frame (the scene allows it and there is translucent terrain on
++    /// screen), and `lit_view` is the composite.
++    water_active: bool,
++    /// The frame's translucent terrain exists (set by the renderer before `write`).
++    pub water_geometry: bool,
++    water_composited: bool,
++    started: std::time::Instant,
+     /// TAA: the resolved frame, and the two histories (one read, one written, alternating).
+     taa: wgpu::TextureView,
+     history: [wgpu::TextureView; 2],
+@@ -1216,6 +1519,26 @@ impl Hd {
+                     min_binding_size: None,
+                 },
+                 UNFILTERED,
++                DEPTH,
++            ]),
++        });
++        let water_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
++            label: Some("HD water"),
++            entries: &entries(&[
++                UNIFORM,
++                FLOAT,
++                DEPTH,
++                UNFILTERED,
++                UNFILTERED,
++                DEPTH,
++                wgpu::BindingType::Texture {
++                    sample_type: wgpu::TextureSampleType::Depth,
++                    view_dimension: wgpu::TextureViewDimension::D2Array,
++                    multisampled: false,
++                },
++                wgpu::BindingType::Sampler(wgpu::SamplerBindingType::Comparison),
++                FLOAT,
++                SAMPLER,
+             ]),
+         });
+         let taa_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+@@ -1278,6 +1601,16 @@ impl Hd {
+         let tone = module(device, "HD tone mapping", TONEMAP);
+         let ao = module(device, "HD ambient occlusion", AO);
+         let ao_blur = module(device, "HD ambient occlusion blur", AO_BLUR);
++        let water = module(device, "HD water", WATER);
++        let water_pipeline = fullscreen(
++            device,
++            "HD water",
++            &water_layout,
++            &water,
++            "fs_water",
++            HDR,
++            None,
++        );
+         let ao_pipeline = fullscreen(
+             device,
+             "HD ambient occlusion",
+@@ -1436,6 +1769,23 @@ impl Hd {
+             .view,
+             lit: target(device, "HD lit", [1, 1], HDR).view,
+             fx: target(device, "HD post", [1, 1], HDR).view,
++            water_tint: target(device, "HD water colour", [1, 1], WATER_TINT).view,
++            water_normal: target(device, "HD water normal", [1, 1], WATER_NORMAL).view,
++            water_depth: target(
++                device,
++                "HD water depth",
++                [1, 1],
++                wgpu::TextureFormat::Depth32Float,
++            )
++            .view,
++            lit_water: target(device, "HD lit with water", [1, 1], HDR).view,
++            water_layout,
++            water_pipeline,
++            water_group: None,
++            water_active: false,
++            water_geometry: false,
++            water_composited: false,
++            started: std::time::Instant::now(),
+             taa: target(device, "HD TAA", [1, 1], HDR).view,
+             history: [
+                 target(device, "HD TAA history", [1, 1], HDR).view,
+@@ -1502,6 +1852,17 @@ impl Hd {
+         self.depth = target(device, "HD depth", size, wgpu::TextureFormat::Depth32Float).view;
+         self.lit = target(device, "HD lit", size, HDR).view;
+         self.fx = target(device, "HD post", size, HDR).view;
++        self.water_tint = target(device, "HD water colour", size, WATER_TINT).view;
++        self.water_normal = target(device, "HD water normal", size, WATER_NORMAL).view;
++        self.water_depth = target(
++            device,
++            "HD water depth",
++            size,
++            wgpu::TextureFormat::Depth32Float,
++        )
++        .view;
++        self.lit_water = target(device, "HD lit with water", size, HDR).view;
++        self.water_group = None;
+         self.taa = target(device, "HD TAA", out, HDR).view;
+         self.history = [
+             target(device, "HD TAA history", out, HDR).view,
+@@ -1591,6 +1952,7 @@ impl Hd {
+         let (dir, strength, color) = light_of(scene);
+         let cascades = scene.cascades;
+         let night = scene.dark.clamp(0.0, 1.0);
++        self.water_active = scene.water && water_enabled() && self.water_geometry;
+         self.taa_active = scene.taa && taa_enabled();
+         // A long jump of the camera (a teleport) starts the history over.
+         if !self.taa_active || scene.camera_delta.length() > 64.0 {
+@@ -1604,6 +1966,19 @@ impl Hd {
+                 scene.camera_delta.z,
+                 if self.history_ready { 1.0 } else { 0.0 },
+             ],
++            view_proj: scene.view_proj.to_cols_array_2d(),
++            water: [
++                if self.water_active { 1.0 } else { 0.0 },
++                (self.started.elapsed().as_secs_f64() % 600.0) as f32,
++                scene.camera_mod[0],
++                scene.camera_mod[1],
++            ],
++            sky_color: [
++                scene.sky_color[0],
++                scene.sky_color[1],
++                scene.sky_color[2],
++                if scene.sky { 1.0 } else { 0.0 },
++            ],
+             taa_params: [
+                 if self.upscaling() {
+                     UPSCALE_HISTORY
+@@ -1821,6 +2196,10 @@ impl Hd {
+                         binding: 13,
+                         resource: wgpu::BindingResource::TextureView(&self.ao_blurred),
+                     },
++                    wgpu::BindGroupEntry {
++                        binding: 14,
++                        resource: wgpu::BindingResource::TextureView(&self.water_depth),
++                    },
+                 ],
+             });
+             self.light_group = Some((key, group));
+@@ -1828,6 +2207,7 @@ impl Hd {
+         let Some((_, group)) = &self.light_group else {
+             return;
+         };
++        self.water_composited = false;
+         Self::draw(
+             encoder,
+             "HD lighting",
+@@ -1894,7 +2274,7 @@ impl Hd {
+         screen: &wgpu::TextureView,
+     ) {
+         let source = match source {
+-            HdSource::Lit => self.lit.clone(),
++            HdSource::Lit => self.lit_view().clone(),
+             HdSource::Fx => self.fx.clone(),
+             HdSource::Taa => self.taa.clone(),
+         };
+@@ -1993,7 +2373,7 @@ impl Hd {
+             return source;
+         }
+         let input = match source {
+-            HdSource::Lit => self.lit.clone(),
++            HdSource::Lit => self.lit_view().clone(),
+             HdSource::Fx => self.fx.clone(),
+             HdSource::Taa => return source,
+         };
+@@ -2052,6 +2432,102 @@ impl Hd {
+         HdSource::Taa
+     }
+ 
++    /// The lit world as later passes see it: with the water over it when the effect ran.
++    pub fn lit_view(&self) -> &wgpu::TextureView {
++        if self.water_composited {
++            &self.lit_water
++        } else {
++            &self.lit
++        }
++    }
++
++    /// The water effect runs this frame (the renderer draws the water quads with `water_pass`).
++    pub fn water_active(&self) -> bool {
++        self.water_active
++    }
++
++    /// The water pass's attachments: the surface colour and normal, and the water's own depth,
++    /// all cleared. The caller draws the translucent terrain with `fs_water`.
++    pub fn water_pass<'e>(
++        &mut self,
++        encoder: &'e mut wgpu::CommandEncoder,
++    ) -> wgpu::RenderPass<'e> {
++        let clear = |view| {
++            Some(wgpu::RenderPassColorAttachment {
++                view,
++                resolve_target: None,
++                depth_slice: None,
++                ops: wgpu::Operations {
++                    load: wgpu::LoadOp::Clear(wgpu::Color::TRANSPARENT),
++                    store: wgpu::StoreOp::Store,
++                },
++            })
++        };
++        encoder
++            .begin_render_pass(&wgpu::RenderPassDescriptor {
++                label: Some("HD water"),
++                timestamp_writes: stamp(&mut self.timing, "hd water"),
++                color_attachments: &[clear(&self.water_tint), clear(&self.water_normal)],
++                depth_stencil_attachment: Some(wgpu::RenderPassDepthStencilAttachment {
++                    view: &self.water_depth,
++                    depth_ops: Some(wgpu::Operations {
++                        load: wgpu::LoadOp::Clear(0.0),
++                        store: wgpu::StoreOp::Store,
++                    }),
++                    stencil_ops: None,
++                }),
++                ..Default::default()
++            })
++            .forget_lifetime()
++    }
++
++    /// Lays the water over the lit world (refraction, reflection, glint) into a target of its
++    /// own; `lit_view` is that target after this.
++    pub fn water_composite(
++        &mut self,
++        device: &wgpu::Device,
++        encoder: &mut wgpu::CommandEncoder,
++        lightmap: (&wgpu::TextureView, &wgpu::Sampler),
++    ) {
++        if !self.water_active {
++            return;
++        }
++        let key = (lightmap.0.clone(), lightmap.1.clone());
++        if self.water_group.as_ref().is_none_or(|(k, _)| *k != key) {
++            let group = self.make_group(
++                device,
++                "HD water",
++                &self.water_layout,
++                &[
++                    wgpu::BindingResource::Buffer(self.frame.as_entire_buffer_binding()),
++                    wgpu::BindingResource::TextureView(&self.lit),
++                    wgpu::BindingResource::TextureView(&self.depth),
++                    wgpu::BindingResource::TextureView(&self.water_tint),
++                    wgpu::BindingResource::TextureView(&self.water_normal),
++                    wgpu::BindingResource::TextureView(&self.water_depth),
++                    wgpu::BindingResource::TextureView(&self.shadow_array),
++                    wgpu::BindingResource::Sampler(&self.shadow_sampler),
++                    wgpu::BindingResource::TextureView(lightmap.0),
++                    wgpu::BindingResource::Sampler(&self.sampler),
++                ],
++            );
++            self.water_group = Some((key, group));
++        }
++        let Some((_, group)) = &self.water_group else {
++            return;
++        };
++        Self::draw(
++            encoder,
++            "HD water composite",
++            &self.lit_water,
++            false,
++            &self.water_pipeline,
++            group,
++            stamp(&mut self.timing, "hd water composite"),
++        );
++        self.water_composited = true;
++    }
++
+     /// The ambient occlusion from the G-buffer's depth and normals: the half-resolution pass, then
+     /// its blur. Run after the G-buffer pass; nothing when the strength is 0.
+     pub fn ao(&mut self, encoder: &mut wgpu::CommandEncoder) {
+@@ -2181,6 +2657,7 @@ mod tests {
+             ("taa", TAA),
+             ("ao", AO),
+             ("ao blur", AO_BLUR),
++            ("water", WATER),
+         ] {
+             let source = format!("{COMMON}{body}");
+             let module = naga::front::wgsl::parse_str(&source).unwrap_or_else(|e| {
+diff --git a/crates/horizon-client/src/terrain.wgsl b/crates/horizon-client/src/terrain.wgsl
+index c44449cc7..0d5d2fc89 100644
+--- a/crates/horizon-client/src/terrain.wgsl
++++ b/crates/horizon-client/src/terrain.wgsl
+@@ -182,6 +182,25 @@ fn face_normal(pos: vec3<f32>) -> vec3<f32> {
+     out.light = vec4(clamp(in.lm, vec2(0.0), vec2(1.0)), 0.0, 1.0);
+     return out;
+ }
++// AirDef fork, HD water: the water quads once more, after the G-buffer, into small targets of
++// their own: the surface colour (the water sprite times the biome tint) with the block light, and
++// the face normal with the sky light. The layers are the water sprites' (gfx.rs fills them in;
++// nothing else is water: glass, ice and the rest stay as vanilla draws them).
++override WATER_STILL: u32 = 0xffffu;
++override WATER_FLOW: u32 = 0xffffu;
++struct WaterOut {
++    @location(0) tint: vec4<f32>,
++    @location(1) normal: vec4<f32>,
++}
++@fragment fn fs_water(in: TerrainOut) -> WaterOut {
++    let layer = in.layer & 0x7fffu;
++    if layer != WATER_STILL && layer != WATER_FLOW { discard; }
++    let color = sprite(in.uv, layer) * in.tint;
++    var out: WaterOut;
++    out.tint = vec4(color.rgb, clamp(in.lm.y, 0.0, 1.0));
++    out.normal = vec4(face_normal(in.pos) * 0.5 + 0.5, clamp(in.lm.x, 0.0, 1.0));
++    return out;
++}
+ // AirDef fork: the sun's shadow map — depth only, cut-out leaves leave holes.
+ @fragment fn fs_shadow(in: TerrainOut) {
+     let a = sprite(in.uv, in.layer & 0x7fffu).a;
+-- 
+2.54.0 (Apple Git-157)
+

horizon-patches/0020-HD-water-no-vanilla-texture-on-the-surface-the-biome.patch

@@ -0,0 +1,54 @@
+From dbc6f8a6e9c2eeabe1de15f1794013c90be7faa5 Mon Sep 17 00:00:00 2001
+From: chexit <chexit@duck.com>
+Date: Thu, 29 Oct 2026 17:56:04 +0300
+Subject: [PATCH 20/24] HD water: no vanilla texture on the surface (the biome
+ colour only), a darker, deeper colour
+
+Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
+---
+ crates/horizon-client/src/gfx/hd.rs    | 9 ++++++---
+ crates/horizon-client/src/terrain.wgsl | 6 ++++--
+ 2 files changed, 10 insertions(+), 5 deletions(-)
+
+diff --git a/crates/horizon-client/src/gfx/hd.rs b/crates/horizon-client/src/gfx/hd.rs
+index f5caa2d0b..8070aab3c 100644
+--- a/crates/horizon-client/src/gfx/hd.rs
++++ b/crates/horizon-client/src/gfx/hd.rs
+@@ -591,10 +591,13 @@ fn fs_water(in: FullOut) -> @location(0) vec4<f32> {
+     }
+     let thickness = clamp(length(position_at(uv_floor, floor_z)) - dist, 0.0, 48.0);
+     let behind = textureSampleLevel(lit_tex, linear, uv_floor, 0.0).rgb;
+-    let colour = clamp(tint.rgb, vec3<f32>(0.03), vec3<f32>(1.0));
++    // A deep, dark water: the biome's colour darkened and a little greyed, so it reads as
++    // depth rather than as bright paint.
++    let biome = clamp(tint.rgb, vec3<f32>(0.03), vec3<f32>(1.0));
++    let colour = mix(vec3<f32>(dot(biome, vec3<f32>(0.333))), biome, 0.8) * vec3<f32>(0.55, 0.68, 0.8);
+     // The colours the water takes up fastest are the ones it has the least of.
+-    let absorb = exp(-(vec3<f32>(1.0) - colour) * 0.8 * (thickness + 0.3));
+-    let refracted = behind * absorb + colour * volume_light * 0.9 * (vec3<f32>(1.0) - absorb);
++    let absorb = exp(-(vec3<f32>(1.0) - colour) * 1.1 * (thickness + 0.3));
++    let refracted = behind * absorb + colour * volume_light * 0.6 * (vec3<f32>(1.0) - absorb);
+ 
+     // Reflection: the screen where the ray stays on it, the sky where it leaves it or misses.
+     var r = reflect(-v, n);
+diff --git a/crates/horizon-client/src/terrain.wgsl b/crates/horizon-client/src/terrain.wgsl
+index 0d5d2fc89..e892d5a0f 100644
+--- a/crates/horizon-client/src/terrain.wgsl
++++ b/crates/horizon-client/src/terrain.wgsl
+@@ -195,9 +195,11 @@ struct WaterOut {
+ @fragment fn fs_water(in: TerrainOut) -> WaterOut {
+     let layer = in.layer & 0x7fffu;
+     if layer != WATER_STILL && layer != WATER_FLOW { discard; }
+-    let color = sprite(in.uv, layer) * in.tint;
++    // The biome's colour at the texture's mean brightness, not the texture: the HD water draws
++    // its own surface (waves, reflections), and vanilla's ripples on top would look painted on.
++    let color = vec3(0.62) * in.tint.rgb;
+     var out: WaterOut;
+-    out.tint = vec4(color.rgb, clamp(in.lm.y, 0.0, 1.0));
++    out.tint = vec4(color, clamp(in.lm.y, 0.0, 1.0));
+     out.normal = vec4(face_normal(in.pos) * 0.5 + 0.5, clamp(in.lm.x, 0.0, 1.0));
+     return out;
+ }
+-- 
+2.54.0 (Apple Git-157)
+

horizon-patches/0021-HD-sky-and-light-a-physical-atmosphere-Rayleigh-Mie-.patch

@@ -0,0 +1,945 @@
+From 13e74537dd6e63482e3613e0e416de1158944dfe Mon Sep 17 00:00:00 2001
+From: chexit <chexit@duck.com>
+Date: Thu, 29 Oct 2026 18:38:19 +0300
+Subject: [PATCH 21/24] HD sky and light: a physical atmosphere (Rayleigh, Mie,
+ ozone; constants and transmittance after Photon, MIT) for the sky, haze, fog
+ and water reflections; warmer sunlight from the atmosphere's transmittance, a
+ gentle sky-coloured ambient, soft PCSS-lite shadows near the player, a haze
+ round the sun; lighter water with fine ripples
+
+Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
+---
+ crates/horizon-client/src/gfx.rs              |   4 +
+ .../src/gfx/THIRD_PARTY_PHOTON.md             |  34 ++
+ crates/horizon-client/src/gfx/hd.rs           | 259 +++++++++++++-
+ crates/horizon-client/src/gfx/hd_sky.rs       | 324 ++++++++++++++++++
+ crates/horizon-client/src/terrain.wgsl        |   2 +-
+ 5 files changed, 604 insertions(+), 19 deletions(-)
+ create mode 100644 crates/horizon-client/src/gfx/THIRD_PARTY_PHOTON.md
+ create mode 100644 crates/horizon-client/src/gfx/hd_sky.rs
+
+diff --git a/crates/horizon-client/src/gfx.rs b/crates/horizon-client/src/gfx.rs
+index f9dab8abf..d01131433 100644
+--- a/crates/horizon-client/src/gfx.rs
++++ b/crates/horizon-client/src/gfx.rs
+@@ -72,6 +72,7 @@ mod cull;
+ mod end_sky;
+ mod flat;
+ mod hd;
++mod hd_sky;
+ mod hdr;
+ pub mod lightning;
+ mod lod;
+@@ -4275,6 +4276,8 @@ impl Renderer {
+                 camera.z.rem_euclid(256.0) as f32,
+             ],
+             water: !frame.underwater,
++            sunrise: frame.sky.sunrise_color,
++            sky_fog_end: frame.fog.map_or(frame.distance.min(512.0), |f| f.sky_end),
+         };
+         let (shadow_dir, shadow_strength, _) = hd::light_of(&hd_scene);
+         let mut hd_cascades = hd::cascades(camera, shadow_dir);
+@@ -5817,6 +5820,7 @@ impl Renderer {
+         {
+             // AirDef fork: lit by the mods' lights into the HD target, the mod's post pass on
+             // that, then bloom and the tone curve onto the screen.
++            hd.sky(&mut encoder);
+             hd.light(
+                 &self.device,
+                 &mut encoder,
+diff --git a/crates/horizon-client/src/gfx/THIRD_PARTY_PHOTON.md b/crates/horizon-client/src/gfx/THIRD_PARTY_PHOTON.md
+new file mode 100644
+index 000000000..03d945001
+--- /dev/null
++++ b/crates/horizon-client/src/gfx/THIRD_PARTY_PHOTON.md
+@@ -0,0 +1,34 @@
++# Third-party code: Photon
++
++Parts of the HD renderer's atmosphere (`hd_sky.rs`) are ported from, or follow closely, the
++Photon shader pack by sixthsurge, `shaders/include/sky/atmosphere.glsl` (and the idea of the water
++waves in `shaders/include/misc/water_normal.glsl`) at commit
++26c2906ee02cc484359b835fba6993d443d45966, https://github.com/sixthsurge/photon
++
++What is taken: the air's scattering and absorption coefficients (Rayleigh, Mie, ozone), the scale
++heights, the ozone density profile, the Mie albedo and Henyey-Greenstein anisotropy, the sunlight
++colour outside the atmosphere, and the Chapman-function approximation of the sun's transmittance.
++The sky-view texture, its march, the sun's colour and everything else are our own.
++
++Photon is distributed under the MIT License:
++
++    The MIT License
++
++    Copyright © 2025 Benjamin Stott "sixthsurge"
++
++    Permission is hereby granted, free of charge, to any person obtaining a copy of this software
++    and associated documentation files (the "Software"), to deal in the Software without
++    restriction, including without limitation the rights to use, copy, modify, merge, publish,
++    distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
++    Software is furnished to do so, subject to the following conditions:
++
++    The above copyright notice and this permission notice shall be included in all copies or
++    substantial portions of the Software.
++
++    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
++    BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
++    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
++    DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
++    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
++
++No other shader pack's code (BSL, Complementary and so on) may be used: their licences forbid it.
+diff --git a/crates/horizon-client/src/gfx/hd.rs b/crates/horizon-client/src/gfx/hd.rs
+index 8070aab3c..031e9f2de 100644
+--- a/crates/horizon-client/src/gfx/hd.rs
++++ b/crates/horizon-client/src/gfx/hd.rs
+@@ -5,6 +5,7 @@
+ //! into a high-dynamic-range target; the mod's post pass runs on that; then
+ //! bright parts bloom and a tone curve brings it to the screen — vanilla's
+ //! range (up to about 0.8) left as it is, only what is brighter rolled off.
++use super::hd_sky;
+ use super::pack_timing::PassTiming;
+ use glam::Mat4;
+ use std::sync::atomic::{AtomicU64, Ordering};
+@@ -101,6 +102,12 @@ struct HdFrame {
+     water: [f32; 4],
+     /// rgb: the sky's colour; w: 1 when there is a sky.
+     sky_color: [f32; 4],
++    /// xyz: towards the sun itself (not the moon); w: 1 when the atmosphere draws the sky.
++    sky_sun: [f32; 4],
++    /// x: vanilla's sky fog end; z: how overcast the sky is (rain: 0 clear, 1 vanilla's colours).
++    sky_extra: [f32; 4],
++    /// Vanilla's sunrise colour fan (rgb, alpha), taken out of the sky before the atmosphere is put in.
++    sunrise: [f32; 4],
+ }
+ 
+ /// What the world around looks like this frame (from the renderer's globals).
+@@ -131,6 +138,9 @@ pub struct HdScene {
+     pub camera_mod: [f32; 2],
+     /// The water effect may run (not underwater, not disabled).
+     pub water: bool,
++    /// Vanilla's sunrise fan colour and its sky fog end (to subtract vanilla's sky from the world).
++    pub sunrise: [f32; 4],
++    pub sky_fog_end: f32,
+ }
+ 
+ /// The cascades' half sizes (blocks) and shadow map size.
+@@ -155,6 +165,9 @@ struct HdFrame {
+     view_proj: mat4x4<f32>,
+     water: vec4<f32>,
+     sky_color: vec4<f32>,
++    sky_sun: vec4<f32>,
++    sky_extra: vec4<f32>,
++    sunrise: vec4<f32>,
+ }
+ struct FullOut {
+     @builtin(position) position: vec4<f32>,
+@@ -195,6 +208,9 @@ struct Light {
+ @group(0) @binding(13) var ao_tex: texture_2d<f32>;
+ // The water pass's depth: the nearest water surface (0 where there is none).
+ @group(0) @binding(14) var water_depth: texture_depth_2d;
++//SKY15
++// The pixel being lit, for the shadow filter's noise.
++var<private> frag_px: vec2<f32>;
+ 
+ // The occlusion at a full-resolution pixel `dist` away: the four nearest half-resolution texels
+ // weighted by closeness and by how near their distance is, so it doesn't bleed across edges.
+@@ -239,6 +255,42 @@ fn shadow(p: vec3<f32>, n: vec3<f32>) -> f32 {
+     return shadow_taps(p, n, 1);
+ }
+ 
++// A point of a disc of radius 1 (Vogel's spiral), turned by `angle`.
++fn vogel(i: i32, count: i32, angle: f32) -> vec2<f32> {
++    let r = sqrt((f32(i) + 0.5) / f32(count));
++    let a = f32(i) * 2.39996323 + angle;
++    return vec2<f32>(cos(a), sin(a)) * r;
++}
++
++// The near cascade's soft shadow: a blocker search sets the penumbra's width (wider the farther
++// the shadow's caster is above the receiver), then a ring of taps turned by a per-pixel noise
++// filters it; the temporal pass averages the noise. `s`: the point in the cascade (uv, depth),
++// `texel`: the cascade's texel in blocks.
++fn soft_shadow(s: vec3<f32>, texel: f32) -> f32 {
++    let angle = ign(frag_px) * 6.2831853;
++    var blocker = 0.0;
++    var found = 0.0;
++    for (var i = 0; i < 8; i++) {
++        let o = vogel(i, 8, angle) * (6.0 / 2048.0);
++        let q = clamp(vec2<i32>((s.xy + o) * 2048.0), vec2<i32>(0), vec2<i32>(2047));
++        let z = textureLoad(shadow_map, q, 0, 0);
++        if z < s.z - 0.0006 {
++            blocker += z;
++            found += 1.0;
++        }
++    }
++    if found < 0.5 { return 1.0; }
++    // The caster's height above the receiver, in blocks (the cascade's depth spans 799 blocks).
++    let height = (s.z - blocker / found) * 799.0;
++    let radius = clamp(height * 0.18 / texel, 1.6, 8.0);
++    var lit = 0.0;
++    for (var i = 0; i < 12; i++) {
++        let o = vogel(i, 12, angle + 1.7) * (radius / 2048.0);
++        lit += textureSampleCompareLevel(shadow_map, shadow_sampler, s.xy + o, 0, s.z - 0.0005 - 0.00005 * radius);
++    }
++    return lit / 12.0;
++}
++
+ // `shadow` with a (2 * r + 1) square of taps: the floor under water takes one (the water dims and
+ // blurs it anyway).
+ fn shadow_taps(p: vec3<f32>, n: vec3<f32>, r: i32) -> f32 {
+@@ -249,13 +301,16 @@ fn shadow_taps(p: vec3<f32>, n: vec3<f32>, r: i32) -> f32 {
+     let s = cascade_at(q, c);
+     if any(s.xy < vec2<f32>(0.0)) || any(s.xy > vec2<f32>(1.0)) || s.z > 1.0 { return 1.0; }
+     var lit = 0.0;
++    let fade = clamp((frame.shadow.z - dist) / 16.0, 0.0, 1.0);
++    if r == 1 && c == 0 {
++        return mix(1.0, soft_shadow(s, texel), fade);
++    }
+     let step = 1.0 / 2048.0;
+     for (var y = -r; y <= r; y++) {
+         for (var x = -r; x <= r; x++) {
+             lit += textureSampleCompareLevel(shadow_map, shadow_sampler, s.xy + vec2<f32>(f32(x), f32(y)) * step, c, s.z - 0.0005);
+         }
+     }
+-    let fade = clamp((frame.shadow.z - dist) / 16.0, 0.0, 1.0);
+     return mix(1.0, lit / f32((2 * r + 1) * (2 * r + 1)), fade);
+ }
+ 
+@@ -300,7 +355,31 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+     let halo_start = tiles[tile + 2u];
+     let halo_all = tiles[tile + 3u] == 0xffffffffu;
+     let halo_count = select(tiles[tile + 3u], count, halo_all);
++    frag_px = in.position.xy;
++    let atmosphere = frame.sky_sun.w > 0.5;
+     var c = scene;
++    // The sky: the atmosphere's, with what the world drew over vanilla's plain sky (sun, moon,
++    // stars, clouds) kept on top.
++    if d <= 0.0 && atmosphere {
++        var kept = max(scene - vanilla_sky(view), vec3<f32>(0.0));
++        var sky = atmosphere_sky(view);
++        // The sun: vanilla's square sprite is taken out and a round disc with a soft haze round
++        // it (warm, strongest low) is drawn in its place.
++        let toward = dot(view, frame.sky_sun.xyz);
++        kept *= 1.0 - smoothstep(0.965, 0.975, toward);
++        let clear = 1.0 - frame.sky_extra.z;
++        let shine = smoothstep(-0.04, 0.02, frame.sky_sun.y) * clear;
++        let glow = max(toward, 0.0);
++        let angle = acos(clamp(toward, -1.0, 1.0));
++        sky += frame.sun_color.rgb * shine * (pow(glow, 24.0) * 0.07 + pow(glow, 400.0) * 0.4 + 6.0 * (1.0 - smoothstep(0.016, 0.022, angle)));
++        c = sky + kept;
++    }
++    // Clouds (vanilla's, drawn into the world with depth but not into the G-buffer): lit by the low
++    // sun's colour at dusk and dawn instead of vanilla's flat white.
++    if atmosphere && !water && d > 0.0 && g <= 0.0 && p.y > 8.0 && dot(p, p) > 2304.0 {
++        let low = 1.0 - smoothstep(0.05, 0.5, frame.sky_sun.y);
++        c = scene * mix(vec3<f32>(1.0), mix(frame.sun_color.rgb, vec3<f32>(1.0), 0.45) * 1.1, low * 0.7 * (1.0 - frame.sky_extra.z));
++    }
+     let surface = water || (d > 0.0 && abs(d - g) <= max(d, g) * 0.002);
+     if surface {
+         let n = normalize(textureLoad(normal_tex, px, 0).xyz);
+@@ -323,7 +402,17 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+         if frame.ambient.w > 0.0 && !water { occlusion = ao_at(px, length(p)); }
+         let ao_ambient = mix(1.0, occlusion, frame.ambient.w);
+         let ao_lights = mix(1.0, occlusion, frame.ambient.w * 0.5);
+-        var light = max(base * frame.ambient.x, block * frame.ambient.y) * ao_ambient + direct;
++        // The sky's light is bluish from above and carries the horizon's colour from the sides;
++        // faces turned up take more of it than the ones turned down.
++        var sky_tint = vec3<f32>(1.0);
++        if atmosphere {
++            let reach = smoothstep(0.25, 0.9, lm.x);
++            let up = clamp(n.y * 0.5 + 0.5, 0.0, 1.0);
++            let shape = mix(0.66, 1.1, smoothstep(0.1, 1.0, up));
++            let hue = mix(vec3<f32>(1.0), sky_light_tint(n), 0.4 * (1.0 - 0.5 * frame.sun_color.a));
++            sky_tint = mix(vec3<f32>(1.0), hue * shape, reach);
++        }
++        var light = max(base * sky_tint * frame.ambient.x, block * frame.ambient.y) * ao_ambient + direct;
+         // The mods' lights.
+         for (var k = 0u; k < surface_count; k++) {
+             let l = lights[select(tiles[surface_start + k], k, surface_all)];
+@@ -340,7 +429,12 @@ fn fs_light(in: FullOut) -> @location(0) vec4<f32> {
+         let sph = length(p);
+         let cyl = max(length(p.xz), abs(p.y));
+         let f = max(linear_fog(sph, frame.fog.x, frame.fog.y), linear_fog(cyl, frame.fog.z, frame.fog.w));
+-        c = mix(c, frame.fog_color.rgb, f * frame.fog_color.a);
++        let haze = haze_colour(view);
++        c = mix(c, haze, f * frame.fog_color.a);
++        // Aerial perspective: far things take the horizon's colour a little before the fog does.
++        if atmosphere && frame.fog.x > 1.0e6 {
++            c = mix(c, haze, (1.0 - exp(-sph / 700.0)) * 0.5);
++        }
+     }
+     // Light in the air: the sun's rays between the shadows, and halos round the mods' lights.
+     let far = select(min(length(p), frame.shadow.z), frame.shadow.z, d <= 0.0);
+@@ -387,6 +481,7 @@ const REFLECT_RANGE: f32 = 96.0;
+ @group(0) @binding(7) var shadow_sampler: sampler_comparison;
+ @group(0) @binding(8) var lightmap: texture_2d<f32>;
+ @group(0) @binding(9) var linear: sampler;
++//SKY10
+ 
+ fn ign(px: vec2<f32>) -> f32 {
+     let p = px + vec2<f32>(5.588238 * frame.params.w);
+@@ -417,7 +512,7 @@ fn texel(uv: vec2<f32>) -> vec2<i32> {
+ // are whole cycles per 600 s, so the sum repeats every 256 blocks and 10 minutes and holds still
+ // in the world as the camera moves. x, y: the vector in units of 2 pi / 256; z: the slope the
+ // wave adds; w: its phase.
+-const WAVES = array<vec4<f32>, 10>(
++const WAVES = array<vec4<f32>, 26>(
+     vec4<f32>(3.0, 1.0, 0.040, 0.3),
+     vec4<f32>(-2.0, 5.0, 0.045, 2.1),
+     vec4<f32>(7.0, 2.0, 0.040, 4.4),
+@@ -428,17 +523,36 @@ const WAVES = array<vec4<f32>, 10>(
+     vec4<f32>(9.0, 23.0, 0.030, 2.7),
+     vec4<f32>(-27.0, 19.0, 0.025, 4.9),
+     vec4<f32>(31.0, 30.0, 0.025, 1.8),
++    // Fine ripples (wavelengths of 0.7 to 3 blocks) for the many small sun sparkles: slopes small,
++    // faded out by distance and pixel size like the rest.
++    vec4<f32>(83.0, 41.0, 0.042, 0.4),
++    vec4<f32>(-97.0, 59.0, 0.042, 3.1),
++    vec4<f32>(71.0, -113.0, 0.042, 5.0),
++    vec4<f32>(131.0, 89.0, 0.040, 1.5),
++    vec4<f32>(-157.0, -103.0, 0.040, 4.2),
++    vec4<f32>(191.0, -67.0, 0.038, 2.4),
++    vec4<f32>(-223.0, 149.0, 0.038, 0.8),
++    vec4<f32>(101.0, 241.0, 0.036, 3.7),
++    vec4<f32>(-263.0, -181.0, 0.034, 5.5),
++    vec4<f32>(311.0, 127.0, 0.034, 2.0),
++    // Finer still (0.35 to 0.6 blocks): the small sparkles.
++    vec4<f32>(397.0, -263.0, 0.050, 1.1),
++    vec4<f32>(-467.0, 331.0, 0.050, 4.6),
++    vec4<f32>(521.0, 449.0, 0.045, 3.0),
++    vec4<f32>(-613.0, -199.0, 0.045, 5.9),
++    vec4<f32>(293.0, 577.0, 0.045, 0.2),
++    vec4<f32>(-701.0, 263.0, 0.040, 2.8),
+ );
+ 
+ // The gradient of the water's height at world x, z: the waves that a pixel `footprint` blocks
+ // wide can still resolve (finer ones fade out, or they would shimmer).
+ fn wave_gradient(xz: vec2<f32>, footprint: f32) -> vec2<f32> {
+     var grad = vec2<f32>(0.0);
+-    for (var i = 0; i < 10; i++) {
++    for (var i = 0; i < 26; i++) {
+         let w = WAVES[i];
+         let k = w.xy * (2.0 * PI / 256.0);
+         let len = length(k);
+-        let fade = clamp((2.0 * PI / len) / max(footprint, 0.0001) * 0.25 - 0.5, 0.0, 1.0);
++        let fade = clamp((2.0 * PI / len) / max(footprint, 0.0001) * 0.2 - 0.6, 0.0, 1.0);
+         let cycles = round(sqrt(9.8 * len) * 0.5 * 600.0 / (2.0 * PI));
+         let omega = cycles * 2.0 * PI / 600.0;
+         let phase = dot(k, xz) - omega * frame.water.y + w.w;
+@@ -481,7 +595,9 @@ fn linear_fog(d: f32, start: f32, end: f32) -> f32 {
+ // the zenith's, darker where the water lies under cover (`vis` is the sky light there).
+ fn sky_along(r: vec3<f32>, vis: f32) -> vec3<f32> {
+     var c = frame.fog_color.rgb;
+-    if frame.sky_color.w > 0.5 {
++    if frame.sky_sun.w > 0.5 {
++        c = atmosphere_sky(r);
++    } else if frame.sky_color.w > 0.5 {
+         c = mix(frame.fog_color.rgb, frame.sky_color.rgb, smoothstep(0.0, 0.5, r.y));
+     }
+     return c * mix(0.12, 1.0, vis);
+@@ -531,7 +647,7 @@ fn reflection(p: vec3<f32>, r: vec3<f32>, jitter: f32) -> vec4<f32> {
+ // The sun's glint on the waves (GGX, a rough lobe so it glitters instead of aliasing).
+ fn glint(n: vec3<f32>, v: vec3<f32>, l: vec3<f32>) -> f32 {
+     let h = normalize(l + v);
+-    let a = 0.05;
++    let a = 0.07;
+     let nh = max(dot(n, h), 0.0);
+     let d = a * a / (PI * pow(nh * nh * (a * a - 1.0) + 1.0, 2.0));
+     let f = 0.02 + 0.98 * pow(1.0 - max(dot(v, h), 0.0), 5.0);
+@@ -565,7 +681,10 @@ fn fs_water(in: FullOut) -> @location(0) vec4<f32> {
+     // Light on the water: vanilla's lightmap at the surface, and the sun where it reaches.
+     let levels = vec2<f32>(nt.a, tint.a);
+     let sky_reach = smoothstep(0.35, 0.95, levels.x);
+-    let ambient = textureSampleLevel(lightmap, linear, clamp(vec2<f32>(levels.y, levels.x) * (15.0 / 16.0) + 0.5 / 16.0, vec2<f32>(0.5 / 16.0), vec2<f32>(15.5 / 16.0)), 0.0).rgb;
++    var ambient = textureSampleLevel(lightmap, linear, clamp(vec2<f32>(levels.y, levels.x) * (15.0 / 16.0) + 0.5 / 16.0, vec2<f32>(0.5 / 16.0), vec2<f32>(15.5 / 16.0)), 0.0).rgb;
++    if frame.sky_sun.w > 0.5 {
++        ambient *= mix(vec3<f32>(1.0), sky_light_tint(vec3<f32>(0.0, 1.0, 0.0)), 0.7 * sky_reach);
++    }
+     let block = textureSampleLevel(lightmap, linear, vec2<f32>(levels.y * (15.0 / 16.0) + 0.5 / 16.0, 0.5 / 16.0), 0.0).rgb;
+     let sun = frame.sun.xyz;
+     let sun_on = frame.sun.w;
+@@ -594,10 +713,10 @@ fn fs_water(in: FullOut) -> @location(0) vec4<f32> {
+     // A deep, dark water: the biome's colour darkened and a little greyed, so it reads as
+     // depth rather than as bright paint.
+     let biome = clamp(tint.rgb, vec3<f32>(0.03), vec3<f32>(1.0));
+-    let colour = mix(vec3<f32>(dot(biome, vec3<f32>(0.333))), biome, 0.8) * vec3<f32>(0.55, 0.68, 0.8);
++    let colour = mix(vec3<f32>(dot(biome, vec3<f32>(0.333))), biome, 0.85) * vec3<f32>(0.92, 1.0, 1.0);
+     // The colours the water takes up fastest are the ones it has the least of.
+-    let absorb = exp(-(vec3<f32>(1.0) - colour) * 1.1 * (thickness + 0.3));
+-    let refracted = behind * absorb + colour * volume_light * 0.6 * (vec3<f32>(1.0) - absorb);
++    let absorb = exp(-(vec3<f32>(1.0) - colour) * 0.8 * (thickness + 0.3));
++    let refracted = behind * absorb + colour * volume_light * mix(0.85, 0.4, frame.sun_color.a) * (vec3<f32>(1.0) - absorb);
+ 
+     // Reflection: the screen where the ray stays on it, the sky where it leaves it or misses.
+     var r = reflect(-v, n);
+@@ -617,7 +736,11 @@ fn fs_water(in: FullOut) -> @location(0) vec4<f32> {
+     let sph = dist;
+     let cyl = max(length(p.xz), abs(p.y));
+     let f = max(linear_fog(sph, frame.fog.x, frame.fog.y), linear_fog(cyl, frame.fog.z, frame.fog.w));
+-    c = mix(c, frame.fog_color.rgb, f * frame.fog_color.a);
++    let haze = haze_colour(-v);
++    c = mix(c, haze, f * frame.fog_color.a);
++    if frame.sky_sun.w > 0.5 && frame.fog.x > 1.0e6 {
++        c = mix(c, haze, (1.0 - exp(-dist / 700.0)) * 0.5);
++    }
+     return vec4<f32>(max(c, vec3<f32>(0.0)), 1.0);
+ }
+ "#;
+@@ -1200,6 +1323,14 @@ pub struct Hd {
+     /// The frame's translucent terrain exists (set by the renderer before `write`).
+     pub water_geometry: bool,
+     water_composited: bool,
++    /// The sky-view texture (see `hd_sky`), the pass that marches it and its bind group.
++    sky_lut: wgpu::TextureView,
++    sky_pipeline: wgpu::RenderPipeline,
++    sky_group: wgpu::BindGroup,
++    /// The sun's height the sky-view texture was marched for (it depends on nothing else), and
++    /// whether this frame's sun has moved enough to march it again.
++    sky_drawn_for: f32,
++    sky_stale: bool,
+     started: std::time::Instant,
+     /// TAA: the resolved frame, and the two histories (one read, one written, alternating).
+     taa: wgpu::TextureView,
+@@ -1403,10 +1534,23 @@ fn ao_strength_default() -> f32 {
+         .unwrap_or(AO_STRENGTH)
+ }
+ 
++/// The shader's source: the common part, then the body with the sky-reading functions where it
++/// has a marker (`//SKY15`: the sky-view texture is binding 15, `//SKY10`: binding 10).
++fn assemble(body: &str) -> String {
++    let mut body = body.to_owned();
++    for binding in ["15", "10"] {
++        body = body.replace(
++            &format!("//SKY{binding}"),
++            &hd_sky::SKY_FUNCS.replace("SKYBIND", binding),
++        );
++    }
++    format!("{COMMON}{body}")
++}
++
+ fn module(device: &wgpu::Device, label: &str, body: &str) -> wgpu::ShaderModule {
+     device.create_shader_module(wgpu::ShaderModuleDescriptor {
+         label: Some(label),
+-        source: wgpu::ShaderSource::Wgsl(format!("{COMMON}{body}").into()),
++        source: wgpu::ShaderSource::Wgsl(assemble(body).into()),
+     })
+ }
+ 
+@@ -1523,6 +1667,7 @@ impl Hd {
+                 },
+                 UNFILTERED,
+                 DEPTH,
++                FLOAT,
+             ]),
+         });
+         let water_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+@@ -1542,8 +1687,13 @@ impl Hd {
+                 wgpu::BindingType::Sampler(wgpu::SamplerBindingType::Comparison),
+                 FLOAT,
+                 SAMPLER,
++                FLOAT,
+             ]),
+         });
++        let sky_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
++            label: Some("HD sky"),
++            entries: &entries(&[UNIFORM]),
++        });
+         let taa_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+             label: Some("HD TAA"),
+             entries: &entries(&[UNIFORM, UNFILTERED, DEPTH, FLOAT, SAMPLER]),
+@@ -1605,6 +1755,16 @@ impl Hd {
+         let ao = module(device, "HD ambient occlusion", AO);
+         let ao_blur = module(device, "HD ambient occlusion blur", AO_BLUR);
+         let water = module(device, "HD water", WATER);
++        let sky_module = module(device, "HD sky", hd_sky::SKY_PASS);
++        let sky_pipeline = fullscreen(
++            device,
++            "HD sky",
++            &sky_layout,
++            &sky_module,
++            "fs_sky_lut",
++            hd_sky::SKY_LUT_FORMAT,
++            None,
++        );
+         let water_pipeline = fullscreen(
+             device,
+             "HD water",
+@@ -1691,6 +1851,21 @@ impl Hd {
+             usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
+             mapped_at_creation: false,
+         });
++        let sky_lut = target(
++            device,
++            "HD sky",
++            hd_sky::SKY_LUT_SIZE,
++            hd_sky::SKY_LUT_FORMAT,
++        )
++        .view;
++        let sky_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
++            label: Some("HD sky"),
++            layout: &sky_layout,
++            entries: &[wgpu::BindGroupEntry {
++                binding: 0,
++                resource: frame.as_entire_binding(),
++            }],
++        });
+         let lights = device.create_buffer(&wgpu::BufferDescriptor {
+             label: Some("HD lights"),
+             size: (MAX_LIGHTS * std::mem::size_of::<HdLight>()) as u64,
+@@ -1788,6 +1963,11 @@ impl Hd {
+             water_active: false,
+             water_geometry: false,
+             water_composited: false,
++            sky_lut,
++            sky_pipeline,
++            sky_group,
++            sky_drawn_for: 2.0,
++            sky_stale: true,
+             started: std::time::Instant::now(),
+             taa: target(device, "HD TAA", [1, 1], HDR).view,
+             history: [
+@@ -1961,6 +2141,11 @@ impl Hd {
+         if !self.taa_active || scene.camera_delta.length() > 64.0 {
+             self.history_ready = false;
+         }
++        let sun_height = scene.sun.normalize_or(glam::Vec3::Y).y;
++        self.sky_stale = (sun_height - self.sky_drawn_for).abs() > 0.001;
++        if self.sky_stale {
++            self.sky_drawn_for = sun_height;
++        }
+         let frame = HdFrame {
+             prev_view_proj: scene.prev_view_proj.to_cols_array_2d(),
+             taa: [
+@@ -1982,6 +2167,17 @@ impl Hd {
+                 scene.sky_color[2],
+                 if scene.sky { 1.0 } else { 0.0 },
+             ],
++            sky_sun: {
++                let sun = scene.sun.normalize_or(glam::Vec3::Y);
++                [sun.x, sun.y, sun.z, if scene.sky { 1.0 } else { 0.0 }]
++            },
++            sky_extra: [
++                scene.sky_fog_end,
++                0.0,
++                (scene.rain / 0.7).clamp(0.0, 1.0) * 0.85,
++                0.0,
++            ],
++            sunrise: scene.sunrise,
+             taa_params: [
+                 if self.upscaling() {
+                     UPSCALE_HISTORY
+@@ -2123,6 +2319,23 @@ impl Hd {
+         pass.draw(0..3, 0..1);
+     }
+ 
++    /// Marches the sky-view texture for this frame's sun (before the lighting and the water); skipped
++    /// while the sun's height has moved less than a thousandth since the last march.
++    pub fn sky(&mut self, encoder: &mut wgpu::CommandEncoder) {
++        if !self.sky_stale {
++            return;
++        }
++        Self::draw(
++            encoder,
++            "HD sky",
++            &self.sky_lut,
++            false,
++            &self.sky_pipeline,
++            &self.sky_group,
++            stamp(&mut self.timing, "hd sky"),
++        );
++    }
++
+     /// Lights the world (its colour and depth) into `lit`.
+     pub fn light(
+         &mut self,
+@@ -2203,6 +2416,10 @@ impl Hd {
+                         binding: 14,
+                         resource: wgpu::BindingResource::TextureView(&self.water_depth),
+                     },
++                    wgpu::BindGroupEntry {
++                        binding: 15,
++                        resource: wgpu::BindingResource::TextureView(&self.sky_lut),
++                    },
+                 ],
+             });
+             self.light_group = Some((key, group));
+@@ -2512,6 +2729,7 @@ impl Hd {
+                     wgpu::BindingResource::Sampler(&self.shadow_sampler),
+                     wgpu::BindingResource::TextureView(lightmap.0),
+                     wgpu::BindingResource::Sampler(&self.sampler),
++                    wgpu::BindingResource::TextureView(&self.sky_lut),
+                 ],
+             );
+             self.water_group = Some((key, group));
+@@ -2608,9 +2826,13 @@ pub fn light_of(scene: &HdScene) -> (glam::Vec3, f32, glam::Vec3) {
+     let clear = 1.0 - scene.rain * 0.85;
+     if sun.y > -0.02 {
+         let up = smooth(-0.02, 0.18, sun.y);
+-        let warm = smooth(0.0, 0.45, sun.y);
+-        let color = glam::Vec3::new(1.0, 0.62, 0.38).lerp(glam::Vec3::new(1.0, 0.95, 0.86), warm);
+-        (sun, 0.6 * up * clear, color)
++        // The atmosphere's transmittance along the sun's ray (orange when low, a clean warm white
++        // high), kept at full brightness and tempered, with a slight warm tint on top.
++        let t = hd_sky::sun_transmittance(sun.y);
++        let hue = t / t.max_element().max(1e-4);
++        let color = glam::Vec3::new(hue.x.powf(0.6), hue.y.powf(0.6), hue.z.powf(0.6))
++            * glam::Vec3::new(1.0, 0.93, 0.78);
++        (sun, 0.7 * up * clear, color)
+     } else {
+         let moon = -sun;
+         let up = smooth(-0.02, 0.18, moon.y);
+@@ -2661,8 +2883,9 @@ mod tests {
+             ("ao", AO),
+             ("ao blur", AO_BLUR),
+             ("water", WATER),
++            ("sky", hd_sky::SKY_PASS),
+         ] {
+-            let source = format!("{COMMON}{body}");
++            let source = assemble(body);
+             let module = naga::front::wgsl::parse_str(&source).unwrap_or_else(|e| {
+                 panic!("{name}: {}", e.emit_to_string(&source));
+             });
+diff --git a/crates/horizon-client/src/gfx/hd_sky.rs b/crates/horizon-client/src/gfx/hd_sky.rs
+new file mode 100644
+index 000000000..b5c231a7b
+--- /dev/null
++++ b/crates/horizon-client/src/gfx/hd_sky.rs
+@@ -0,0 +1,324 @@
++//! AirDef fork: the HD renderer's atmosphere. A small sky-view texture (azimuth from the sun by
++//! elevation, plus a row of ambient samples) is marched each frame from single scattering of
++//! Rayleigh and Mie particles and ozone absorption with a cheap multiple-scattering term; the
++//! lighting and water shaders read it for the sky, the aerial-perspective haze, the water's
++//! reflection fallback and the colour of the sky's light. The sunlight's colour is the same
++//! atmosphere's transmittance at the sun's elevation (`sun_transmittance`).
++//!
++//! The coefficients, the density profiles (scale heights, the ozone layer), the Henyey-Greenstein
++//! Mie parameters and the Chapman-function transmittance come from Photon by sixthsurge (MIT
++//! licence, see THIRD_PARTY_PHOTON.md), shaders/include/sky/atmosphere.glsl at commit 26c2906.
++
++/// The sky-view texture: 128 azimuths by 64 elevations, then 8 rows for the ambient samples
++/// (row 64: texel 0 the zenith, texel 1 the horizon's average).
++pub const SKY_LUT_SIZE: [u32; 2] = [128, 72];
++pub const SKY_LUT_FORMAT: wgpu::TextureFormat = wgpu::TextureFormat::Rgba16Float;
++
++/// The atmosphere's constants and the pass that marches the sky-view texture (after `COMMON`).
++pub const SKY_PASS: &str = r#"
++@group(0) @binding(0) var<uniform> frame: HdFrame;
++
++// Photon's atmosphere (sixthsurge, MIT): metres, Earth's size; the camera stands on the surface.
++const PI: f32 = 3.14159265;
++const PLANET_R: f32 = 6371000.0;
++const ATMOSPHERE_TOP: f32 = 6481000.0;
++const GROUND_R: f32 = 6370000.0;
++const SCALE_HEIGHTS: vec2<f32> = vec2<f32>(8400.0, 1250.0);
++const RAYLEIGH: vec3<f32> = vec3<f32>(8.059375432e-06, 1.671209429e-05, 4.080133294e-05);
++const MIE: vec3<f32> = vec3<f32>(1.666442358e-06, 1.812685127e-06, 1.958927896e-06);
++const OZONE: vec3<f32> = vec3<f32>(8.304280072e-07, 1.314911970e-06, 5.440679729e-08);
++const MIE_ALBEDO: f32 = 0.9;
++const MIE_G: f32 = 0.77;
++// Sunlight in space (Photon's AM0 colour) and how bright the sun and the moon shine here.
++const SUN_I: vec3<f32> = vec3<f32>(1.051, 0.985, 0.940) * 24.0;
++const MOON_I: vec3<f32> = vec3<f32>(0.62, 0.78, 1.0) * 0.07;
++// The share of the light scattered a second time, spread evenly (the haze's lift).
++const MULTI_SCATTER: f32 = 0.6;
++const STEPS: i32 = 32;
++
++// Photon's density: Rayleigh, Mie (exponential) and the ozone layer, at an altitude in metres.
++fn density_at(altitude: f32) -> vec3<f32> {
++    let rm = exp(-max(altitude, 0.0) / SCALE_HEIGHTS);
++    let km = altitude * 1e-3;
++    let o1 = 12.5 * exp(-km / 8.0);
++    let o2 = 30.0 * exp((18.0 - km) * (km - 18.0) / 80.0);
++    let o3 = 75.0 * exp((23.5 - km) * (km - 23.5) / 50.0);
++    let o4 = 50.0 * exp((30.0 - km) * (km - 30.0) / 150.0);
++    return vec3<f32>(rm, 7.428e-3 * (o1 + o2 + o3 + o4));
++}
++
++// Chapman function approximation (thetenthplanet.de/archives/4519, as Photon uses it).
++fn chapman(x: f32, cos_theta: f32) -> f32 {
++    let c = sqrt(1.5707963 * x);
++    if cos_theta >= 0.0 {
++        return c / ((c - 1.0) * cos_theta + 1.0);
++    }
++    let sin_theta = sqrt(clamp(1.0 - cos_theta * cos_theta, 0.0, 1.0));
++    return c / ((c - 1.0) * cos_theta - 1.0) + 2.0 * c * exp(min(x - x * sin_theta, 80.0)) * sqrt(sin_theta);
++}
++
++// The light reaching a point r from the planet's centre (altitude h, whose sky direction makes
++// cos mu with the up there) from the sun or the moon; 0 when the planet is in the way.
++fn light_transmittance(mu: f32, r: f32, h: f32) -> vec3<f32> {
++    if mu < 0.0 && r * r * (1.0 - mu * mu) < PLANET_R * PLANET_R { return vec3<f32>(0.0); }
++    let dens = exp(-max(h, 0.0) / SCALE_HEIGHTS);
++    var air = SCALE_HEIGHTS * dens;
++    air.x *= chapman(r / SCALE_HEIGHTS.x, mu);
++    air.y *= chapman(r / SCALE_HEIGHTS.y, mu);
++    return clamp(exp(-(RAYLEIGH * air.x + MIE * air.y + OZONE * air.x)), vec3<f32>(0.0), vec3<f32>(1.0));
++}
++
++fn rayleigh_phase(nu: f32) -> f32 {
++    return 3.0 / (16.0 * PI) * (1.0 + nu * nu);
++}
++
++fn mie_phase(nu: f32) -> f32 {
++    let g = MIE_G;
++    return (1.0 - g * g) / (4.0 * PI * pow(1.0 + g * g - 2.0 * g * nu, 1.5));
++}
++
++// The radiance the camera sees along `view` (y up) with the sun and the moon in the directions
++// given: single scattering plus a flat multiple-scattering term.
++fn march(view: vec3<f32>, sun: vec3<f32>, moon: vec3<f32>) -> vec3<f32> {
++    let b = PLANET_R * view.y;
++    let t_max = -b + sqrt(b * b + ATMOSPHERE_TOP * ATMOSPHERE_TOP - PLANET_R * PLANET_R);
++    let nu_sun = dot(view, sun);
++    let nu_moon = dot(view, moon);
++    let phase_r_sun = rayleigh_phase(nu_sun);
++    let phase_m_sun = mie_phase(nu_sun);
++    let phase_r_moon = rayleigh_phase(nu_moon);
++    let phase_m_moon = mie_phase(nu_moon);
++    var od = vec3<f32>(0.0);
++    var sum = vec3<f32>(0.0);
++    var t0 = 0.0;
++    for (var i = 0; i < STEPS; i++) {
++        let u = (f32(i) + 1.0) / f32(STEPS);
++        let t1 = t_max * u * u;
++        let dt = t1 - t0;
++        let t = 0.5 * (t0 + t1);
++        t0 = t1;
++        let r2 = PLANET_R * PLANET_R + 2.0 * PLANET_R * t * view.y + t * t;
++        let r = sqrt(r2);
++        // The altitude without the cancellation of r - planet radius.
++        let altitude = (2.0 * PLANET_R * t * view.y + t * t) / (r + PLANET_R);
++        let dens = density_at(altitude);
++        let extinction = RAYLEIGH * dens.x + MIE * dens.y + OZONE * dens.z;
++        let view_t = exp(-(od + 0.5 * extinction * dt));
++        od += extinction * dt;
++        let mu_sun = (PLANET_R * sun.y + t * nu_sun) / r;
++        let mu_moon = (PLANET_R * moon.y + t * nu_moon) / r;
++        let sun_t = light_transmittance(mu_sun, r, altitude);
++        let moon_t = light_transmittance(mu_moon, r, altitude);
++        let scatter_r = RAYLEIGH * dens.x;
++        let scatter_m = MIE * MIE_ALBEDO * dens.y;
++        let single = (scatter_r * phase_r_sun + scatter_m * phase_m_sun) * sun_t * SUN_I
++            + (scatter_r * phase_r_moon + scatter_m * phase_m_moon) * moon_t * MOON_I;
++        let multi = (scatter_r + scatter_m) * (1.0 / (4.0 * PI)) * MULTI_SCATTER
++            * (sun_t * SUN_I + moon_t * MOON_I) * 0.5;
++        sum += view_t * (single + multi) * dt;
++    }
++    return sum;
++}
++
++@fragment
++fn fs_sky_lut(in: FullOut) -> @location(0) vec4<f32> {
++    let px = vec2<i32>(in.position.xy);
++    // The texture's frame: the sun in the xy plane, the moon opposite.
++    let sin_e = clamp(frame.sky_sun.y, -1.0, 1.0);
++    let sun = vec3<f32>(sqrt(1.0 - sin_e * sin_e), sin_e, 0.0);
++    let moon = -sun;
++    // A faint night glow, so the night sky is not black.
++    let night = vec3<f32>(0.0006, 0.0011, 0.0026);
++    if px.y < 64 {
++        let phi = f32(px.x) / 127.0 * PI;
++        let v = f32(px.y) / 63.0;
++        let l = v * v * PI * 0.5;
++        let dir = vec3<f32>(cos(l) * cos(phi), sin(l), cos(l) * sin(phi));
++        return vec4<f32>(march(dir, sun, moon) + night, 1.0);
++    }
++    if px.y == 64 && px.x == 0 {
++        return vec4<f32>(march(vec3<f32>(0.0, 1.0, 0.0), sun, moon) + night, 1.0);
++    }
++    if px.y == 64 && px.x == 1 {
++        var sum = vec3<f32>(0.0);
++        for (var k = 0; k < 6; k++) {
++            let phi = (f32(k) + 0.5) / 6.0 * PI;
++            let l = 0.3;
++            sum += march(vec3<f32>(cos(l) * cos(phi), sin(l), cos(l) * sin(phi)), sun, moon);
++        }
++        return vec4<f32>(sum / 6.0 + night, 1.0);
++    }
++    return vec4<f32>(0.0);
++}
++"#;
++
++/// Reading the sky-view texture, in the lighting and the water shaders (`SKYBIND` is replaced by
++/// the binding of the texture; `frame` and the `linear` sampler come before it).
++pub const SKY_FUNCS: &str = r#"
++@group(0) @binding(SKYBIND) var sky_lut: texture_2d<f32>;
++const SKY_PI: f32 = 3.14159265;
++// How bright the sky is shown (the exposure of the physical radiance) and its gamma.
++const SKY_EXPOSURE: f32 = 0.85;
++
++// Where the direction `dir` (world, y up) lies in the sky-view texture.
++fn sky_uv(dir: vec3<f32>) -> vec2<f32> {
++    let s = frame.sky_sun.xyz;
++    let l = asin(clamp(dir.y, 0.0, 1.0));
++    var cphi = 1.0;
++    let dl = length(dir.xz);
++    let sl = length(s.xz);
++    if dl > 1e-4 && sl > 1e-4 { cphi = dot(dir.xz / dl, s.xz / sl); }
++    let u = acos(clamp(cphi, -1.0, 1.0)) / SKY_PI;
++    let v = sqrt(l / (SKY_PI * 0.5));
++    return vec2<f32>((u * 127.0 + 0.5) / 128.0, (v * 63.0 + 0.5) / 72.0);
++}
++
++// The physical sky's colour as it is shown: a soft shoulder, then the display's gamma.
++fn sky_show(radiance: vec3<f32>) -> vec3<f32> {
++    // Compressed by the brightest channel, so the hue stays as the atmosphere made it.
++    let peak = max(max(radiance.r, radiance.g), max(radiance.b, 1e-6));
++    let c = pow(radiance * ((1.0 - exp(-peak * SKY_EXPOSURE)) / peak), vec3<f32>(1.0 / 1.9));
++    // A little more colour (Photon boosts the atmosphere's saturation too).
++    // The low sun gets more, for orange and pink in place of pastel.
++    let boost = 1.2 + 0.45 * (1.0 - smoothstep(0.0, 0.35, frame.sky_sun.y));
++    return max(mix(vec3<f32>(dot(c, vec3<f32>(0.2126, 0.7152, 0.0722))), c, boost), vec3<f32>(0.0));
++}
++
++// The vanilla sky's own gradient (the overcast and the rain keep it).
++fn vanilla_gradient(dir: vec3<f32>) -> vec3<f32> {
++    return mix(frame.fog_color.rgb, frame.sky_color.rgb, smoothstep(0.0, 0.5, max(dir.y, 0.0)));
++}
++
++// The sky along `dir`: the atmosphere, greyed towards vanilla's colours in rain.
++fn atmosphere_sky(dir: vec3<f32>) -> vec3<f32> {
++    let lin = textureSampleLevel(sky_lut, linear, sky_uv(dir), 0.0).rgb;
++    var c = sky_show(lin);
++    let overcast = frame.sky_extra.z;
++    if overcast > 0.0 { c = mix(c, vanilla_gradient(dir), overcast); }
++    return c;
++}
++
++// The colour distant things fade to: the sky just above the horizon in their direction (so the
++// haze leans towards the sun), or vanilla's fog colour where the environment sets its own fog.
++fn haze_colour(dir: vec3<f32>) -> vec3<f32> {
++    if frame.sky_sun.w < 0.5 || frame.fog.x < 1.0e6 { return frame.fog_color.rgb; }
++    let up = max(dir.y, 0.0) * 0.5 + 0.035;
++    return atmosphere_sky(normalize(vec3<f32>(dir.x, 0.0, dir.z) + vec3<f32>(0.0, up, 0.0)));
++}
++
++// The sky's light for a surface of normal n: the horizon's colour from the sides, the zenith's
++// from above, as a hue (luminance 1) to tint vanilla's sky light with.
++fn sky_light_tint(n: vec3<f32>) -> vec3<f32> {
++    let zenith = sky_show(textureLoad(sky_lut, vec2<i32>(0, 64), 0).rgb);
++    let horizon = sky_show(textureLoad(sky_lut, vec2<i32>(1, 64), 0).rgb);
++    let up = clamp(n.y * 0.5 + 0.5, 0.0, 1.0);
++    let c = mix(horizon, zenith, smoothstep(0.35, 1.0, up));
++    let luma = dot(c, vec3<f32>(0.2126, 0.7152, 0.0722));
++    return c / max(luma, 0.003);
++}
++
++// vanilla's sky (terrain.wgsl: fs_sky), to tell what the world drew on the sky pixel (the sun and
++// moon sprites, the stars, the clouds) from its plain gradient.
++fn vanilla_disc_distance(d: vec3<f32>, y: f32) -> vec2<f32> {
++    if d.y * y <= 0.0 { return vec2<f32>(-1.0); }
++    let p = d * (y / d.y);
++    let h = length(p.xz);
++    let phi = atan2(p.z, p.x);
++    let sector = SKY_PI / 4.0;
++    let delta = phi - (floor(phi / sector) * sector + sector * 0.5);
++    let edge = 512.0 * cos(sector * 0.5) / cos(delta);
++    if h > edge { return vec2<f32>(-1.0); }
++    let s = h / edge;
++    let ay = abs(y);
++    let rim = sqrt(512.0 * 512.0 + y * y);
++    return vec2<f32>(ay + s * (rim - ay), ay + s * (512.0 - ay));
++}
++fn vanilla_linear_fog(d: f32, start: f32, end: f32) -> f32 {
++    if d <= start { return 0.0; }
++    if d >= end { return 1.0; }
++    return (d - start) / (end - start);
++}
++fn vanilla_rotate_x90(v: vec3<f32>) -> vec3<f32> { return vec3<f32>(v.x, -v.z, v.y); }
++fn vanilla_sunrise_weight(d: vec3<f32>) -> f32 {
++    let alpha = frame.sunrise.a;
++    if alpha <= 0.001 { return 0.0; }
++    let flip = select(0.0, 180.0, frame.sky_sun.x > 0.0);
++    let theta = radians(flip + 90.0);
++    let c = cos(theta);
++    let s = sin(theta);
++    var best = 0.0;
++    let apex = vanilla_rotate_x90(vec3<f32>(-100.0 * s, 100.0 * c, 0.0));
++    for (var i = 0; i < 16; i++) {
++        let a0 = f32(i) * 2.0 * SKY_PI / 16.0;
++        let a1 = f32(i + 1) * 2.0 * SKY_PI / 16.0;
++        let l0 = vec3<f32>(sin(a0) * 120.0, cos(a0) * 120.0, -cos(a0) * 40.0 * alpha);
++        let l1 = vec3<f32>(sin(a1) * 120.0, cos(a1) * 120.0, -cos(a1) * 40.0 * alpha);
++        let r0 = vanilla_rotate_x90(vec3<f32>(l0.x * c - l0.y * s, l0.x * s + l0.y * c, l0.z));
++        let r1 = vanilla_rotate_x90(vec3<f32>(l1.x * c - l1.y * s, l1.x * s + l1.y * c, l1.z));
++        let e1 = r0 - apex;
++        let e2 = r1 - apex;
++        let pv = cross(d, e2);
++        let det = dot(e1, pv);
++        if abs(det) < 1e-6 { continue; }
++        let tv = -apex;
++        let u = dot(tv, pv) / det;
++        let qv = cross(tv, e1);
++        let v = dot(d, qv) / det;
++        let t = dot(e2, qv) / det;
++        if u >= 0.0 && v >= 0.0 && u + v <= 1.0 && t > 0.0 {
++            best = max(best, 1.0 - u - v);
++        }
++    }
++    return best;
++}
++fn vanilla_sky(d: vec3<f32>) -> vec3<f32> {
++    var color = frame.fog_color.rgb;
++    let dist = vanilla_disc_distance(d, 16.0);
++    if dist.x >= 0.0 {
++        let end = frame.sky_extra.x;
++        let f = max(vanilla_linear_fog(dist.x, 0.0, end), vanilla_linear_fog(dist.y, end, end));
++        color = mix(frame.sky_color.rgb, frame.fog_color.rgb, f * frame.fog_color.a);
++    }
++    let w = vanilla_sunrise_weight(d);
++    if w > 0.0 {
++        color = mix(color, frame.sunrise.rgb, w * frame.sunrise.a);
++    }
++    return color;
++}
++"#;
++
++/// The sun's light at the ground: the atmosphere's transmittance along the sun's direction
++/// (`sin_elevation`, the y of the unit vector towards it), linear, as a fraction of the light
++/// outside the air. Same Chapman model as the sky pass.
++pub fn sun_transmittance(sin_elevation: f32) -> glam::Vec3 {
++    const PLANET: f32 = 6_371_000.0;
++    const SCALE: [f32; 2] = [8400.0, 1250.0];
++    const RAYLEIGH: glam::Vec3 = glam::Vec3::new(8.059_375e-6, 1.671_209_4e-5, 4.080_133_4e-5);
++    const MIE: glam::Vec3 = glam::Vec3::new(1.666_442_4e-6, 1.812_685e-6, 1.958_927_9e-6);
++    const OZONE: glam::Vec3 = glam::Vec3::new(8.304_28e-7, 1.314_912e-6, 5.440_679_7e-8);
++    // A sun below the horizon keeps the horizon's colour (its strength is faded elsewhere).
++    let mu = sin_elevation.clamp(0.0, 1.0);
++    let chapman = |x: f32, c: f32| {
++        let k = (std::f32::consts::FRAC_PI_2 * x).sqrt();
++        k / ((k - 1.0) * c + 1.0)
++    };
++    let air = [
++        SCALE[0] * chapman(PLANET / SCALE[0], mu),
++        SCALE[1] * chapman(PLANET / SCALE[1], mu),
++    ];
++    let tau = RAYLEIGH * air[0] + MIE * air[1] + OZONE * air[0];
++    glam::Vec3::new((-tau.x).exp(), (-tau.y).exp(), (-tau.z).exp())
++}
++
++#[cfg(test)]
++mod tests {
++    use super::*;
++
++    #[test]
++    fn the_low_sun_is_redder_than_the_high_one() {
++        let noon = sun_transmittance(1.0);
++        let low = sun_transmittance(0.1);
++        assert!(noon.x > 0.85 && noon.z > 0.6, "{noon:?}");
++        assert!(low.z / low.x < noon.z / noon.x * 0.6, "{low:?} vs {noon:?}");
++    }
++}
+diff --git a/crates/horizon-client/src/terrain.wgsl b/crates/horizon-client/src/terrain.wgsl
+index e892d5a0f..0a2a6cdba 100644
+--- a/crates/horizon-client/src/terrain.wgsl
++++ b/crates/horizon-client/src/terrain.wgsl
+@@ -197,7 +197,7 @@ struct WaterOut {
+     if layer != WATER_STILL && layer != WATER_FLOW { discard; }
+     // The biome's colour at the texture's mean brightness, not the texture: the HD water draws
+     // its own surface (waves, reflections), and vanilla's ripples on top would look painted on.
+-    let color = vec3(0.62) * in.tint.rgb;
++    let color = vec3(0.85) * in.tint.rgb;
+     var out: WaterOut;
+     out.tint = vec4(color, clamp(in.lm.y, 0.0, 1.0));
+     out.normal = vec4(face_normal(in.pos) * 0.5 + 0.5, clamp(in.lm.x, 0.0, 1.0));
+-- 
+2.54.0 (Apple Git-157)
+

horizon-patches/0022-HD-water-a-darker-blue-a-little-clearer-ripples-a-li.patch

@@ -0,0 +1,42 @@
+From 6277e051a89c2537570982f6ef275887193c05cf Mon Sep 17 00:00:00 2001
+From: chexit <chexit@duck.com>
+Date: Thu, 29 Oct 2026 19:02:16 +0300
+Subject: [PATCH 22/24] HD water: a darker blue, a little clearer, ripples a
+ little higher
+
+Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
+---
+ crates/horizon-client/src/gfx/hd.rs | 9 +++++----
+ 1 file changed, 5 insertions(+), 4 deletions(-)
+
+diff --git a/crates/horizon-client/src/gfx/hd.rs b/crates/horizon-client/src/gfx/hd.rs
+index 031e9f2de..f078d423c 100644
+--- a/crates/horizon-client/src/gfx/hd.rs
++++ b/crates/horizon-client/src/gfx/hd.rs
+@@ -558,7 +558,8 @@ fn wave_gradient(xz: vec2<f32>, footprint: f32) -> vec2<f32> {
+         let phase = dot(k, xz) - omega * frame.water.y + w.w;
+         grad += (k / len) * (w.z * fade * cos(phase));
+     }
+-    return grad;
++    // A little higher than the table's slopes.
++    return grad * 1.25;
+ }
+ 
+ fn cascade_at(p: vec3<f32>, c: i32) -> vec3<f32> {
+@@ -713,10 +714,10 @@ fn fs_water(in: FullOut) -> @location(0) vec4<f32> {
+     // A deep, dark water: the biome's colour darkened and a little greyed, so it reads as
+     // depth rather than as bright paint.
+     let biome = clamp(tint.rgb, vec3<f32>(0.03), vec3<f32>(1.0));
+-    let colour = mix(vec3<f32>(dot(biome, vec3<f32>(0.333))), biome, 0.85) * vec3<f32>(0.92, 1.0, 1.0);
++    let colour = mix(vec3<f32>(dot(biome, vec3<f32>(0.333))), biome, 0.85) * vec3<f32>(0.78, 0.86, 0.95);
+     // The colours the water takes up fastest are the ones it has the least of.
+-    let absorb = exp(-(vec3<f32>(1.0) - colour) * 0.8 * (thickness + 0.3));
+-    let refracted = behind * absorb + colour * volume_light * mix(0.85, 0.4, frame.sun_color.a) * (vec3<f32>(1.0) - absorb);
++    let absorb = exp(-(vec3<f32>(1.0) - colour) * 0.6 * (thickness + 0.3));
++    let refracted = behind * absorb + colour * volume_light * mix(0.65, 0.3, frame.sun_color.a) * (vec3<f32>(1.0) - absorb);
+ 
+     // Reflection: the screen where the ray stays on it, the sky where it leaves it or misses.
+     var r = reflect(-v, n);
+-- 
+2.54.0 (Apple Git-157)
+