feat(render): Phase A8 — wire stencil pipeline into render frame

Replaces the pre-A8 "terrain-always + depth-clear-when-inside" pattern
with WB's stencil-aware ordering when cameraInsideCell:

  1. Upload portal triangle mesh from VisibleCellIds → LoadedCell.
  2. Draw indoor entities (EntitySet.IndoorOnly) — stencil OFF.
  3. Mark portal stencil + punch far depth (MarkAndPunch).
  4. Draw terrain — stencil-gated to portal silhouettes.
  5. Draw outdoor entities (EntitySet.OutdoorOnly) — stencil-gated.
  6. DisableStencil before particles/weather/UI.

Outdoor path unchanged (EntitySet.All, no stencil work).

Adds CellVisibility.TryGetCell(uint) for the VisibleCellIds → LoadedCell
materialization. Removes the now-redundant DepthBufferBit Clear that
was the old approximation.

Retail oracle: PView::DrawCells at
acclient_2013_pseudo_c.txt:432709 ("outside_view.view_count > 0" gate).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/CellVisibility.cs

@@ -344,6 +344,17 @@ public sealed class CellVisibility
                local.Z <= cell.LocalBoundsMax.Z + PointInCellEpsilon;
     }
 
+    /// <summary>
+    /// Looks up a loaded cell by full 32-bit cell id, or returns null if
+    /// not loaded. Used by the Phase A8 stencil pipeline to materialize
+    /// <see cref="VisibilityResult.VisibleCellIds"/> back into
+    /// <see cref="LoadedCell"/> instances for portal mesh extraction.
+    /// </summary>
+    public LoadedCell? TryGetCell(uint cellId)
+    {
+        return _cellLookup.TryGetValue(cellId, out var cell) ? cell : null;
+    }
+
     /// <summary>
     /// Brute-force scan of every loaded cell to test whether
     /// <paramref name="worldPoint"/> is inside any of them. Does not touch

src/AcDream.App/Rendering/GameWindow.cs

@@ -108,6 +108,10 @@ public sealed class GameWindow : IDisposable
     // Step 4: portal-based interior cell visibility.
     private readonly CellVisibility _cellVisibility = new();
 
+    // Phase A8: indoor-cell stencil pipeline (#78). Null until OnLoad runs
+    // (requires GL context). Never null after OnLoad completes normally.
+    private IndoorCellStencilPipeline? _indoorStencil;
+
     // Phase A.1 hotfix / Phase A.5 T10: DatCollection is NOT thread-safe.
     // DatReaderWriter's DatBinReader uses a shared buffer position internally —
     // concurrent _dats.Get<T> calls from the streaming worker thread (T11+) and
@@ -1769,6 +1773,13 @@ public sealed class GameWindow : IDisposable
         // the player.
         _particleRenderer = new ParticleRenderer(_gl, shadersDir, _textureCache, _dats);
 
+        // Phase A8 — indoor-cell visibility culling pipeline (#78).
+        // Shader files are deployed alongside the existing terrain/mesh
+        // shaders via the same .csproj content glob.
+        _indoorStencil = new IndoorCellStencilPipeline(_gl,
+            Path.Combine(shadersDir, "portal_stencil.vert"),
+            Path.Combine(shadersDir, "portal_stencil.frag"));
+
         // A.5 T22.5: apply radii from the already-resolved _resolvedQuality.
         // _resolvedQuality was set by the quality block immediately after
         // LoadAndApplyPersistedSettings() above, absorbing all env-var overrides.
@@ -7097,26 +7108,38 @@ public sealed class GameWindow : IDisposable
                 goto SkipWorldGeometry;
             }
 
-            // Phase N.5b: wrap Draw in CPU stopwatch for [TERRAIN-DIAG] rollup
+            // Phase A8 — indoor-cell visibility culling.
-            // (gated on ACDREAM_WB_DIAG=1, same env var as [WB-DIAG]). Stopwatch
+            // When the camera is inside an EnvCell, build a portal-silhouette
-            // is cheap; only the periodic Console.WriteLine is gated.
+            // stencil mask and use it to gate outdoor passes (terrain +
-            _terrainCpuStopwatch.Restart();
+            // outdoor entities) so they only write fragments inside actual
-            _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+            // portal openings. WB-style stencil port (closes #78 + cellar-
-            _terrainCpuStopwatch.Stop();
+            // stairs artifact). Retail oracle: PView::DrawCells at
-            // Multiply by 100 then divide by 100 in the diag print to keep
+            // acclient_2013_pseudo_c.txt:432709 ("outside_view.view_count > 0").
-            // 0.01 µs precision in the long-typed sample buffer. Terrain Draw
+            int portalTriCount = 0;
-            // is sub-microsecond on simple scenes; truncating to integer µs
+            if (cameraInsideCell && visibility is not null && _indoorStencil is not null)
-            // would round nearly every sample to 0.
+            {
-            _terrainCpuSamples[_terrainCpuSampleCursor] = (long)(_terrainCpuStopwatch.Elapsed.TotalMicroseconds * 100.0);
+                // Resolve VisibleCellIds → LoadedCell list via
-            _terrainCpuSampleCursor = (_terrainCpuSampleCursor + 1) % _terrainCpuSamples.Length;
+                // CellVisibility.TryGetCell (added in Task 7).
-            MaybeFlushTerrainDiag();
+                var currentBuildingCells = new List<LoadedCell>(visibility.VisibleCellIds.Count);
+                foreach (var id in visibility.VisibleCellIds)
+                {
+                    var cell = _cellVisibility.TryGetCell(id);
+                    if (cell is not null) currentBuildingCells.Add(cell);
+                }
+                portalTriCount = _indoorStencil.UploadPortalMesh(currentBuildingCells);
 
-            // Conditional depth clear: when camera is inside a building, clear
+                if (AcDream.Core.Rendering.RenderingDiagnostics.ProbeVisibilityEnabled)
-            // depth (not color) so interior geometry writes fresh Z values on top
+                {
-            // of the terrain color buffer. Exit portals show outdoor terrain color
+                    Console.WriteLine(
-            // because we kept the color buffer. Matching ACME GameScene.cs pattern.
+                        $"[vis] cameraInside=true cells={visibility.VisibleCellIds.Count} " +
-            if (cameraInsideCell)
+                        $"exitPortalVisible={visibility.HasExitPortalVisible} " +
-                _gl!.Clear(ClearBufferMask.DepthBufferBit);
+                        $"portalTris={portalTriCount / 3}");
+                }
+            }
+            else if (AcDream.Core.Rendering.RenderingDiagnostics.ProbeVisibilityEnabled)
+            {
+                Console.WriteLine("[vis] cameraInside=false");
+            }
 
             // L-fix1 (2026-04-28): pass the set of animated-entity ids so
             // the renderer keeps remote players / NPCs / monsters
@@ -7134,11 +7157,65 @@ public sealed class GameWindow : IDisposable
                     animatedIds.Add(k);
             }
 
-            // N.5: WbDrawDispatcher is always non-null (modern path mandatory).
+            if (cameraInsideCell && portalTriCount > 0)
-            _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+            {
-                neverCullLandblockId: playerLb,
+                // WB Step 3: draw indoor entities first, stencil OFF.
-                visibleCellIds: visibility?.VisibleCellIds,
+                // Indoor entities (cell mesh + cell statics) ALWAYS draw
-                animatedEntityIds: animatedIds);
+                // inside the camera-building, regardless of portal coverage.
+                _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+                    neverCullLandblockId: playerLb,
+                    visibleCellIds: visibility!.VisibleCellIds,
+                    animatedEntityIds: animatedIds,
+                    set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.IndoorOnly);
+
+                // WB Steps 1+2: mark stencil + punch far depth in portal regions.
+                _indoorStencil!.MarkAndPunch(camera.View * camera.Projection);
+
+                // WB Step 4a: terrain, stencil-gated to portal silhouettes.
+                _indoorStencil!.EnableOutdoorPass();
+                // Phase N.5b: wrap Draw in CPU stopwatch for [TERRAIN-DIAG] rollup
+                // (gated on ACDREAM_WB_DIAG=1, same env var as [WB-DIAG]). Stopwatch
+                // is cheap; only the periodic Console.WriteLine is gated.
+                _terrainCpuStopwatch.Restart();
+                _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+                _terrainCpuStopwatch.Stop();
+                _terrainCpuSamples[_terrainCpuSampleCursor] =
+                    (long)(_terrainCpuStopwatch.Elapsed.TotalMicroseconds * 100.0);
+                _terrainCpuSampleCursor = (_terrainCpuSampleCursor + 1) % _terrainCpuSamples.Length;
+                MaybeFlushTerrainDiag();
+
+                // WB Step 4b: outdoor entities, still stencil-gated.
+                _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+                    neverCullLandblockId: playerLb,
+                    visibleCellIds: visibility.VisibleCellIds,
+                    animatedEntityIds: animatedIds,
+                    set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.OutdoorOnly);
+
+                _indoorStencil!.DisableStencil();
+            }
+            else
+            {
+                // Outdoor (or indoor with no exit portals): pre-A8 path.
+                // Phase N.5b: wrap Draw in CPU stopwatch for [TERRAIN-DIAG] rollup.
+                _terrainCpuStopwatch.Restart();
+                _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+                _terrainCpuStopwatch.Stop();
+                // Multiply by 100 then divide by 100 in the diag print to keep
+                // 0.01 µs precision in the long-typed sample buffer. Terrain Draw
+                // is sub-microsecond on simple scenes; truncating to integer µs
+                // would round nearly every sample to 0.
+                _terrainCpuSamples[_terrainCpuSampleCursor] =
+                    (long)(_terrainCpuStopwatch.Elapsed.TotalMicroseconds * 100.0);
+                _terrainCpuSampleCursor = (_terrainCpuSampleCursor + 1) % _terrainCpuSamples.Length;
+                MaybeFlushTerrainDiag();
+
+                // N.5: WbDrawDispatcher is always non-null (modern path mandatory).
+                _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+                    neverCullLandblockId: playerLb,
+                    visibleCellIds: visibility?.VisibleCellIds,
+                    animatedEntityIds: animatedIds,
+                    set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.All);
+            }
 
             // Phase G.1 / E.3: draw all live particles after opaque
             // scene geometry so alpha blending composites correctly.
@@ -10494,6 +10571,8 @@ public sealed class GameWindow : IDisposable
         _liveSession = null;
         _audioEngine?.Dispose();  // Phase E.2: stop all voices, close AL context
         _wbDrawDispatcher?.Dispose();
+        _indoorStencil?.Dispose();
+        _indoorStencil = null;
         _skyRenderer?.Dispose();      // depends on sampler cache; dispose first
         _samplerCache?.Dispose();
         _textureCache?.Dispose();