fix(render): clip walk content to authored portal views

src/AcDream.App/Rendering/RetailPViewPassExecutor.WalkLeaf.cs

@@ -209,6 +209,7 @@ internal sealed class WalkProductionLeafRenderer : IWalkFrameLeafRenderer
     private readonly Action _drawExitSeals;
     private readonly HashSet<uint> _singleCellScratch = new();
     private readonly List<uint> _singleCellListScratch = new();
+    private readonly Dictionary<uint, int> _singleCellClipScratch = new(1);
 
     internal WalkProductionLeafRenderer(
         RetailPViewPassExecutor passes,
@@ -231,7 +232,12 @@ internal sealed class WalkProductionLeafRenderer : IWalkFrameLeafRenderer
     public void DrawTerrainSlice(int sliceIndex) =>
         _passes.DrawWalkTerrainSlice(_frame, _clipAssembly, sliceIndex);
 
-    public void DrawCellShell(uint cellId)
+    public void DrawCellShell(uint cellId, uint clipSlot)
+    {
+        _singleCellClipScratch.Clear();
+        _singleCellClipScratch.Add(cellId, checked((int)clipSlot));
+        _passes.SetCellShellClipRouting(_singleCellClipScratch);
+        try
         {
             _singleCellScratch.Clear();
             _singleCellScratch.Add(cellId);
@@ -243,6 +249,11 @@ internal sealed class WalkProductionLeafRenderer : IWalkFrameLeafRenderer
                 _passes.DrawTransparentCellShellsOrdered(_singleCellListScratch);
             }
         }
+        finally
+        {
+            _passes.SetCellShellClipRouting(null);
+        }
+    }
 
     public void ClearInteriorDepth() => _clearInteriorDepth();
 

src/AcDream.App/Rendering/RetailPViewPassExecutor.cs

@@ -240,6 +240,9 @@ internal sealed partial class RetailPViewPassExecutor :
     public void DrawOpaqueCellShells(HashSet<uint> cellIds) =>
         _envCells.Render(WbRenderPass.Opaque, cellIds);
 
+    public void SetCellShellClipRouting(IReadOnlyDictionary<uint, int>? routing) =>
+        _envCells.SetClipRouting(routing);
+
     public bool CellHasTransparentShell(uint cellId) =>
         _envCells.CellHasTransparent(cellId);
 

src/AcDream.App/Rendering/RetailPViewRenderer.cs

@@ -215,7 +215,8 @@ internal sealed class RetailPViewRenderer
             walkDriver = new Walk.WalkFrameDriver(
                 walkExecutor!.Dispatcher,
                 walkLeafRenderer,
-                _walkWorldData);
+                _walkWorldData,
+                clipFrame: clipAssembly.Frame);
 
             if (AcDream.Core.Rendering.RenderingDiagnostics.ProbeWalkRootEnabled)
             {

src/AcDream.App/Rendering/Walk/WalkFrameDriver.cs

@@ -120,7 +120,7 @@ internal interface IWalkFrameLeafRenderer
     /// second reverse loop for <c>DrawObjCellForDummies</c> @0x005a4b0d.
     /// The ordinary interior-root flood and every building look-in flood use
     /// this same two-pass discipline.</summary>
-    void DrawCellShell(uint cellId);
+    void DrawCellShell(uint cellId, uint clipSlot);
 
     /// <summary>One landscape cell's or building shell's static-owner
     /// particle submission, at its own walk turn — see
@@ -231,7 +231,9 @@ internal enum WalkFrameEventKind : byte
     TerrainSlice,
 
     /// <summary><see cref="IWalkFrameLeafRenderer.DrawCellShell"/> —
-    /// <see cref="WalkFrameEvent.CellId"/> is the cell.</summary>
+    /// <see cref="WalkFrameEvent.CellId"/> is the cell and
+    /// <see cref="WalkFrameEvent.IntArg"/> is the exact portal-view GPU clip
+    /// slot for this retail <c>DrawEnvCell</c> turn.</summary>
     CellShell,
 
     /// <summary><see cref="IWalkFrameLeafRenderer.DrawPunchFan"/> —
@@ -288,9 +290,23 @@ internal interface IWalkLookInViewSource
         int routeIndex,
         in Vector3 center,
         float radius);
+
+    /// <summary>Returns the GPU clip slots for every view slice in this
+    /// DrawObjCell turn which admits the part's retail drawing sphere. Retail
+    /// runs DrawMeshInternal once per surviving portal_view slice; a boolean
+    /// sphere gate alone is insufficient because the mesh polygons must remain
+    /// clipped to that aperture.</summary>
+    IReadOnlyList<uint> VisibleClipSlotsInLookInTurn(
+        int routeIndex,
+        in Vector3 center,
+        float radius,
+        bool testSphere);
 }
 
-internal readonly record struct WalkLookInSlice(int PlaneStart, int PlaneCount);
+internal readonly record struct WalkLookInSlice(
+    int PlaneStart,
+    int PlaneCount,
+    uint ClipSlot);
 
 internal readonly record struct WalkLookInTurn(
     uint CellId,
@@ -341,8 +357,8 @@ internal readonly struct WalkFrameEvent
     internal static WalkFrameEvent TerrainSlice(int sliceIndex) =>
         new(WalkFrameEventKind.TerrainSlice, sliceIndex, 0, 0f, null);
 
-    internal static WalkFrameEvent CellShell(uint cellId) =>
+    internal static WalkFrameEvent CellShell(uint cellId, uint clipSlot) =>
-        new(WalkFrameEventKind.CellShell, 0, cellId, 0f, null);
+        new(WalkFrameEventKind.CellShell, checked((int)clipSlot), cellId, 0f, null);
 
     internal static WalkFrameEvent PunchFan(WalkPolygon worldPolygon, int activeViewIndex) =>
         new(WalkFrameEventKind.PunchFan, activeViewIndex, 0, 0f, worldPolygon);
@@ -452,6 +468,7 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
     private readonly IWalkFrameLeafRenderer _leafRenderer;
     private readonly IWalkFrameWorldData _worldData;
     private readonly IWalkFrameDriverTrace? _trace;
+    private readonly ClipFrame? _clipFrame;
     private readonly OrderedDrawStream _stream = new();
     private readonly List<WalkFrameEvent> _events = new();
     private readonly List<int> _markPositions = new();
@@ -472,6 +489,8 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
     private readonly List<WalkLookInTurn> _lookInTurns = new();
     private readonly List<WalkLookInSlice> _lookInSlices = new();
     private readonly List<WalkPlane> _lookInPlanes = new();
+    private readonly List<uint> _visibleClipSlotScratch = new();
+    private readonly List<int> _floodViewRouteScratch = new();
     private WalkPlane _lookInCyPlane;
 
     IReadOnlyList<uint> IWalkLookInViewSource.LookInCellTurns => LookInCellTurns;
@@ -524,12 +543,14 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
         WbDrawDispatcher dispatcher,
         IWalkFrameLeafRenderer leafRenderer,
         IWalkFrameWorldData worldData,
-        IWalkFrameDriverTrace? trace = null)
+        IWalkFrameDriverTrace? trace = null,
+        ClipFrame? clipFrame = null)
     {
         _dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
         _leafRenderer = leafRenderer ?? throw new ArgumentNullException(nameof(leafRenderer));
         _worldData = worldData ?? throw new ArgumentNullException(nameof(worldData));
         _trace = trace;
+        _clipFrame = clipFrame;
         _populator = new WalkStaticStreamPopulator(dispatcher);
     }
 
@@ -621,6 +642,7 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
         _lookInTurns.Clear();
         _lookInSlices.Clear();
         _lookInPlanes.Clear();
+        _visibleClipSlotScratch.Clear();
         _lookInCyPlane = ctx.CyPlane;
         LookInCells.Clear();
         VisitedBuildings.Clear();
@@ -699,7 +721,7 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
                     _leafRenderer.DrawTerrainSlice(e.IntArg);
                     break;
                 case WalkFrameEventKind.CellShell:
-                    _leafRenderer.DrawCellShell(e.CellId);
+                    _leafRenderer.DrawCellShell(e.CellId, checked((uint)e.IntArg));
                     break;
                 case WalkFrameEventKind.PunchFan:
                     _leafRenderer.DrawPunchFan(e.Polygon!, e.IntArg);
@@ -985,12 +1007,23 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
 
     private void EmitFloodTurns(WalkDrawStage stage, IReadOnlyList<uint> cells)
     {
+        _floodViewRouteScratch.Clear();
+        for (int i = 0; i < cells.Count; i++)
+            _floodViewRouteScratch.Add(-1);
+
         // PView::DrawCells @0x005A4840, loop 2 (005A4A00–005A4ADE):
-        // cell_draw_list[count - 1] down to zero, DrawEnvCell only.
+        // cell_draw_list[count - 1] down to zero. DrawEnvCell loops the
+        // cell's live portal_view slices, so capture those slices here and
+        // replay the shell once per exact GPU clip slot.
         for (int i = cells.Count - 1; i >= 0; i--)
         {
+            int viewRouteIndex = CaptureCellViewRoute(cells[i]);
+            _floodViewRouteScratch[i] = viewRouteIndex;
+            IReadOnlyList<uint> clipSlots = VisibleClipSlotsInLookInTurn(
+                viewRouteIndex, default, 0f, testSphere: false);
             MarkIfGrown();
-            _events.Add(WalkFrameEvent.CellShell(cells[i]));
+            for (int slotIndex = 0; slotIndex < clipSlots.Count; slotIndex++)
+                _events.Add(WalkFrameEvent.CellShell(cells[i], clipSlots[slotIndex]));
         }
 
         // Loop 3 (005A4ADE–005A4B2D): restart at count - 1 and draw each
@@ -998,23 +1031,31 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
         // static records and its dynamic/particle tail stay at that exact
         // retail turn.
         for (int i = cells.Count - 1; i >= 0; i--)
-            EmitCellContentsTurn(stage, cells[i]);
+            EmitCellContentsTurn(stage, cells[i], _floodViewRouteScratch[i]);
     }
 
-    private void EmitCellContentsTurn(WalkDrawStage stage, uint cellId)
+    private int CaptureCellViewRoute(uint cellId)
     {
+        int viewRouteIndex = _cellViewRouteIndex++;
+        CaptureCellViews(cellId);
+        return viewRouteIndex;
+    }
+
+    private void EmitCellContentsTurn(
+        WalkDrawStage stage,
+        uint cellId,
+        int viewRouteIndex)
+    {
+        // The shell loop captured the exact live portal_view for this cell.
+        // Static and dynamic object lists reuse that same route: retail's
+        // DrawEnvCell and DrawObjCell consume the same PortalList.
         WalkFrameStaticRecords records = _worldData.GetCellStatics(cellId);
         _populator.PopulateCell(
             _stream, stage, cellId, records.Records, records.TupleLandblockId,
-            _cameraWorldPosition, _viewProjection);
+            _cameraWorldPosition, _viewProjection,
+            this, viewRouteIndex);
         MarkIfGrown();
 
-        // PView::DrawObjCellForDummies draws this cell's live objects at the
-        // same turn as its statics. Capture the currently installed portal
-        // views before the walk pops them, then apply retail's per-GfxObj
-        // drawing-sphere viewcone check in the walk classifier.
-        int viewRouteIndex = _cellViewRouteIndex++;
-        CaptureCellViews(cellId);
         if (stage == WalkDrawStage.LookInStatic)
         {
             LookInCellTurns.Add(cellId);
@@ -1062,8 +1103,9 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
                 _lookInPlanes.Add(
                     portalView.View.Vertices[poly.VertexIndex + edge].Plane);
             }
+            uint clipSlot = AppendClipSlot(portalView, poly);
             _lookInSlices.Add(new WalkLookInSlice(
-                planeStart, poly.VertexCount));
+                planeStart, poly.VertexCount, clipSlot));
         }
         _lookInTurns.Add(new WalkLookInTurn(
             cellId, sliceStart, _lookInSlices.Count - sliceStart));
@@ -1095,6 +1137,100 @@ internal sealed class WalkFrameDriver : IWalkEventSink, IWalkLookInViewSource
         return false;
     }
 
+    public IReadOnlyList<uint> VisibleClipSlotsInLookInTurn(
+        int routeIndex,
+        in Vector3 center,
+        float radius,
+        bool testSphere)
+    {
+        _visibleClipSlotScratch.Clear();
+        if ((uint)routeIndex >= (uint)_lookInTurns.Count)
+            return _visibleClipSlotScratch;
+
+        WalkLookInTurn turn = _lookInTurns[routeIndex];
+        for (int sliceOffset = 0; sliceOffset < turn.SliceCount; sliceOffset++)
+        {
+            WalkLookInSlice slice = _lookInSlices[turn.SliceStart + sliceOffset];
+            if (!testSphere
+                || WalkVisibilityMath.ViewconeCheck(
+                    center,
+                    radius,
+                    _lookInCyPlane,
+                    CollectionsMarshal.AsSpan(_lookInPlanes).Slice(
+                        slice.PlaneStart,
+                        slice.PlaneCount)) != WalkBoundingType.Outside)
+            {
+                _visibleClipSlotScratch.Add(slice.ClipSlot);
+            }
+        }
+        return _visibleClipSlotScratch;
+    }
+
+    /// <summary>Converts one retail pixel-space portal_view polygon into the
+    /// clip-space half-planes consumed by mesh_modern.vert. copy_view already
+    /// deduplicates and removes collinear vertices, so 3..8 points map
+    /// directly. The rare >8-edge case uses its convex AABB as a conservative
+    /// four-plane gate rather than falling back to slot 0 (which would erase
+    /// the aperture entirely).</summary>
+    private uint AppendClipSlot(WalkPortalView portalView, WalkViewPoly poly)
+    {
+        if (_clipFrame is null)
+            return 0;
+
+        IRetailFrameWalkContext ctx = (IRetailFrameWalkContext)RequireOpenFrame();
+        int count = poly.VertexCount;
+        if (count < 3)
+            return 0;
+
+        Span<Vector2> ndc = stackalloc Vector2[Math.Min(count, WalkCopyView.MaxVertices)];
+        float minX = float.MaxValue, minY = float.MaxValue;
+        float maxX = float.MinValue, maxY = float.MinValue;
+        for (int i = 0; i < ndc.Length; i++)
+        {
+            Vector2 px = portalView.View.Vertices[poly.VertexIndex + i].Point;
+            Vector2 point = new(
+                px.X / ctx.ViewportWidth * 2f - 1f,
+                1f - px.Y / ctx.ViewportHeight * 2f);
+            ndc[i] = point;
+            minX = MathF.Min(minX, point.X);
+            minY = MathF.Min(minY, point.Y);
+            maxX = MathF.Max(maxX, point.X);
+            maxY = MathF.Max(maxY, point.Y);
+        }
+
+        if (ndc.Length > ClipFrame.MaxPlanes)
+        {
+            Span<Vector4> aabbPlanes = stackalloc Vector4[4]
+            {
+                new(1f, 0f, 0f, -minX),
+                new(-1f, 0f, 0f, maxX),
+                new(0f, 1f, 0f, -minY),
+                new(0f, -1f, 0f, maxY),
+            };
+            return checked((uint)_clipFrame.AppendSlot(aabbPlanes));
+        }
+
+        float area2 = 0f;
+        for (int i = 0; i < ndc.Length; i++)
+            area2 += ndc[i].X * ndc[(i + 1) % ndc.Length].Y
+                - ndc[(i + 1) % ndc.Length].X * ndc[i].Y;
+        bool ccw = area2 >= 0f;
+        Span<Vector4> planes = stackalloc Vector4[ClipFrame.MaxPlanes];
+        for (int i = 0; i < ndc.Length; i++)
+        {
+            int current = ccw ? i : ndc.Length - 1 - i;
+            int next = ccw
+                ? (i + 1) % ndc.Length
+                : (ndc.Length - 2 - i + ndc.Length) % ndc.Length;
+            Vector2 p = ndc[current];
+            Vector2 q = ndc[next];
+            Vector2 dir = q - p;
+            Vector2 normal = Vector2.Normalize(new Vector2(-dir.Y, dir.X));
+            planes[i] = new Vector4(normal.X, normal.Y, 0f, -Vector2.Dot(normal, p));
+        }
+        return checked((uint)_clipFrame.AppendSlot(planes[..ndc.Length]));
+    }
+
     /// <summary>Campaign FW3.4a: the collect-time analogue of the old
     /// immediate driver's <c>FlushIfNonEmpty</c> — records a
     /// <see cref="WalkFrameEventKind.StreamMark"/> at the stream's current

src/AcDream.App/Rendering/Walk/WalkStaticStreamPopulator.cs

@@ -64,14 +64,17 @@ internal sealed class WalkStaticStreamPopulator
         ReadOnlySpan<RenderProjectionRecord> records,
         uint tupleLandblockId,
         Vector3 cameraWorldPosition,
-        Matrix4x4 viewProjection)
+        Matrix4x4 viewProjection,
+        IWalkLookInViewSource? views = null,
+        int viewRouteIndex = -1)
     {
         ArgumentNullException.ThrowIfNull(stream);
         for (int i = 0; i < records.Length; i++)
         {
             ClassifyAndAppend(
                 stream, stage, cellId, in records[i], tupleLandblockId,
-                cameraWorldPosition, viewProjection);
+                cameraWorldPosition, viewProjection,
+                liveDynamic: false, views, viewRouteIndex);
         }
     }
 

src/AcDream.App/Rendering/Wb/WbDrawDispatcher.WalkClassify.cs

@@ -274,23 +274,15 @@ public sealed partial class WbDrawDispatcher
                     Matrix4x4 model = restPose * entity.RootWorld;
                     int selectionPartIndex = unchecked((partIndex << 16) | (setupPartIndex & 0xFFFF));
 
-                    if (!PartVisibleInLookInTurn(
+                    IReadOnlyList<uint>? partClipSlots = ResolvePartClipSlots(
-                            lookInViews,
+                        lookInViews, lookInRouteIndex, partData, model);
-                            lookInRouteIndex,
+                    if (partClipSlots is { Count: 0 })
-                            lookInCellId,
-                            in entity,
-                            selectionPartIndex,
-                            (uint)gfxObjId,
-                            partData,
-                            model))
-                    {
                         continue;
-                    }
 
                     EmitClassifiedBatches(
                         partData, model, in entity, meshRef, paletteIdentity,
                         entityHasCutoutSubset, slot, lights, indoor, selectionLighting,
-                        detailCategory, opacity, batches);
+                        detailCategory, opacity, partClipSlots, batches);
                     selectionParts.Add(new WalkClassifiedSelectionPart(
                         entity.ServerGuid, entity.LocalEntityId, selectionPartIndex,
                         (uint)gfxObjId, model));
@@ -308,22 +300,14 @@ public sealed partial class WbDrawDispatcher
                     continue;
 
                 Matrix4x4 model = meshRef.PartTransform * entity.RootWorld;
-                if (!PartVisibleInLookInTurn(
+                IReadOnlyList<uint>? partClipSlots = ResolvePartClipSlots(
-                        lookInViews,
+                    lookInViews, lookInRouteIndex, renderData, model);
-                        lookInRouteIndex,
+                if (partClipSlots is { Count: 0 })
-                        lookInCellId,
-                        in entity,
-                        partIndex,
-                        (uint)meshRef.GfxObjId,
-                        renderData,
-                        model))
-                {
                     continue;
-                }
                 EmitClassifiedBatches(
                     renderData, model, in entity, meshRef, paletteIdentity,
                     entityHasCutoutSubsetOverride: null, slot, lights, indoor,
-                    selectionLighting, detailCategory, opacity, batches);
+                    selectionLighting, detailCategory, opacity, partClipSlots, batches);
                 selectionParts.Add(new WalkClassifiedSelectionPart(
                     entity.ServerGuid, entity.LocalEntityId, partIndex,
                     (uint)meshRef.GfxObjId, model));
@@ -379,28 +363,29 @@ public sealed partial class WbDrawDispatcher
         lights = InstanceLightSet.From(selected);
     }
 
-    private static bool PartVisibleInLookInTurn(
+    private static IReadOnlyList<uint>? ResolvePartClipSlots(
         IWalkLookInViewSource? lookInViews,
         int routeIndex,
-        uint cellId,
-        in RenderInstanceCandidate entity,
-        int partIndex,
-        uint gfxObjId,
         ObjectRenderData renderData,
         Matrix4x4 localToWorld)
     {
         if (lookInViews is null)
-            return true;
+            return null;
         if (renderData.SelectionSphere is not { Radius: > 0f } sphere)
-            return true;
+        {
-
+            return lookInViews.VisibleClipSlotsInLookInTurn(
-        return LookInDrawingSphereVisible(
-            lookInViews,
                 routeIndex,
-            sphere,
+                Vector3.Zero,
-            localToWorld,
+                radius: 0f,
-            out _,
+                testSphere: false);
-            out _);
+        }
+
+        TransformDrawingSphere(sphere, localToWorld, out Vector3 center, out float radius);
+        return lookInViews.VisibleClipSlotsInLookInTurn(
+            routeIndex,
+            in center,
+            radius,
+            testSphere: true);
     }
 
     internal static bool LookInDrawingSphereVisible(
@@ -414,6 +399,19 @@ public sealed partial class WbDrawDispatcher
         ArgumentNullException.ThrowIfNull(lookInViews);
         ArgumentNullException.ThrowIfNull(sphere);
 
+        TransformDrawingSphere(sphere, localToWorld, out center, out radius);
+        return lookInViews.SphereVisibleInLookInTurn(
+            routeIndex,
+            in center,
+            radius);
+    }
+
+    private static void TransformDrawingSphere(
+        DatReaderWriter.Types.Sphere sphere,
+        Matrix4x4 localToWorld,
+        out Vector3 center,
+        out float radius)
+    {
         center = Vector3.Transform(sphere.Origin, localToWorld);
         float scaleX = new Vector3(
             localToWorld.M11,
@@ -429,10 +427,6 @@ public sealed partial class WbDrawDispatcher
             localToWorld.M33).Length();
         radius = sphere.Radius
             * MathF.Max(scaleX, MathF.Max(scaleY, scaleZ));
-        return lookInViews.SphereVisibleInLookInTurn(
-            routeIndex,
-            in center,
-            radius);
     }
 
     /// <summary>
@@ -454,6 +448,7 @@ public sealed partial class WbDrawDispatcher
         Vector2 selectionLighting,
         uint detailCategory,
         float opacity,
+        IReadOnlyList<uint>? clipSlots,
         List<WalkClassifiedBatch> sink)
     {
         bool entityHasCutoutSubset = entityHasCutoutSubsetOverride ?? renderData.HasCutoutSubset;
@@ -466,10 +461,23 @@ public sealed partial class WbDrawDispatcher
             if (!survives)
                 continue;
 
+            if (clipSlots is null)
+            {
                 sink.Add(new WalkClassifiedBatch(
                     key, model, slot, lights, indoor ? 1u : 0u, Alpha: opacity,
                     selectionLighting, detailCategory, IsOpaque: IsOpaque(key.Translucency),
                     LocalSortCenter: renderData.SortCenter));
+                continue;
+            }
+
+            for (int clipIndex = 0; clipIndex < clipSlots.Count; clipIndex++)
+            {
+                sink.Add(new WalkClassifiedBatch(
+                    key, model, clipSlots[clipIndex], lights, indoor ? 1u : 0u,
+                    Alpha: opacity, selectionLighting, detailCategory,
+                    IsOpaque: IsOpaque(key.Translucency),
+                    LocalSortCenter: renderData.SortCenter));
+            }
         }
     }
 

tests/AcDream.App.Tests/Rendering/Walk/WalkFrameDriverTests.cs

@@ -43,12 +43,17 @@ public sealed class WalkFrameDriverTests
     private sealed class RecordingLeafRenderer(List<string> log) : IWalkFrameLeafRenderer
     {
         public readonly List<WalkPolygon> Punches = new();
+        public readonly List<(uint CellId, uint ClipSlot)> Shells = new();
 
         public void DrawSky() => log.Add("SKY");
 
         public void DrawTerrainSlice(int sliceIndex) => log.Add($"TERRAIN:{sliceIndex}");
 
-        public void DrawCellShell(uint cellId) => log.Add($"SHELL:{cellId:x8}");
+        public void DrawCellShell(uint cellId, uint clipSlot)
+        {
+            Shells.Add((cellId, clipSlot));
+            log.Add($"SHELL:{cellId:x8}");
+        }
 
         public void ClearInteriorDepth() => log.Add("CLEAR");
 
@@ -427,7 +432,9 @@ public sealed class WalkFrameDriverTests
 
         var leaf = new RecordingLeafRenderer(log);
         var trace = new RecordingTrace(log);
-        var driver = new WalkFrameDriver(fx.Dispatcher, leaf, worldData, trace);
+        using ClipFrame clipFrame = ClipFrame.NoClip();
+        var driver = new WalkFrameDriver(
+            fx.Dispatcher, leaf, worldData, trace, clipFrame);
         var walk = new RetailFrameWalk();
 
         var activeView = new WalkPortalView();
@@ -456,6 +463,13 @@ public sealed class WalkFrameDriverTests
 
         Assert.Equal([0x104u], driver.LookInCellTurns);
         Assert.Equal([0x104u], driver.LookInCells);
+        Assert.Collection(
+            leaf.Shells,
+            shell =>
+            {
+                Assert.Equal(0x104u, shell.CellId);
+                Assert.NotEqual(0u, shell.ClipSlot);
+            });
         WalkPortalView capturedView = ctx.Cells[0x104].PortalViews[0];
         WalkViewPoly capturedPoly = Assert.Single(capturedView.View.Polys);
         Vector2 capturedCenter = Vector2.Zero;
@@ -470,6 +484,10 @@ public sealed class WalkFrameDriverTests
             0, in insideCone, 0.1f));
         Assert.False(driver.SphereVisibleInLookInTurn(
             0, new Vector3(10_000f, 0f, 10f), 0.1f));
+        uint clipSlot = Assert.Single(driver.VisibleClipSlotsInLookInTurn(
+            0, in insideCone, 0.1f, testSphere: true));
+        Assert.NotEqual(0u, clipSlot);
+        Assert.Equal(2, clipFrame.SlotCount);
 
         // The punch polygon reached the leaf renderer in WORLD space: the
         // building-local Quad(-2f) vertex (-0.5,-0.5,-2) translates by

tests/AcDream.App.Tests/Rendering/Walk/WalkProductionWorldConformanceTests.cs

@@ -48,7 +48,13 @@ public sealed class WalkProductionWorldConformanceTests
     private sealed class Recorder : IWalkEventSink
     {
         public readonly List<WalkEvent> Events = new();
-        public void Emit(in WalkEvent walkEvent) => Events.Add(walkEvent);
+        public Action<WalkEvent>? OnEmit { get; init; }
+
+        public void Emit(in WalkEvent walkEvent)
+        {
+            Events.Add(walkEvent);
+            OnEmit?.Invoke(walkEvent);
+        }
     }
 
     private static DatCollection OpenDats()
@@ -227,6 +233,93 @@ public sealed class WalkProductionWorldConformanceTests
             $"production walk diverged from the FW1 test adapter ({fixture})\nEXPECTED: {expected}\nACTUAL:   {actual}");
     }
 
+    [Theory]
+    [InlineData(0xF4180100u, 36.166267f, 79.828407f)]
+    [InlineData(0xF4180101u, 36.391270f, 72.167931f)]
+    public void Cathedral_transition_keeps_south_hall_draws_inside_the_authored_aperture(
+        uint cameraCellId,
+        float x,
+        float y)
+    {
+        // Owner's exact 2026-08-31 repro: the remote player and special NPC
+        // are parented in 0xF4180112, behind opaque cathedral walls. Retail
+        // hides them on BOTH sides of the 0x100 <-> 0x101 transition. The walk
+        // legitimately reaches 0x112 through one authored building aperture;
+        // the regression was submitting each admitted mesh with slot 0, so the
+        // whole player/NPC escaped that aperture. Preserve the installed-DAT
+        // fact this fix depends on: every admitted route is a real, bounded
+        // portal polygon, never a pass-all zero-plane route.
+        var pose = new WalkOraclePose(
+            cameraCellId,
+            new Vector3(x, y, 169.804993f),
+            Q0: -0.004591f,
+            Q1: 0f,
+            Q2: 0f,
+            Q3: 0.999989f);
+        using DatCollection dats = OpenDats();
+        using var adapter = new DatCollectionAdapter(dats);
+        (WalkLandscapeAssembler assembler, Dictionary<uint, WalkCell> cells,
+            Dictionary<WalkBuilding, WalkWorldDatAdapter.BuildingEntry> buildings) =
+            BuildProductionWorld(adapter, pose.CellId, pose.Origin);
+        var ctx = new WalkTraceReplayContext(pose, cells) { Buildings = buildings };
+        WalkCell camera = Assert.Contains(cameraCellId, cells);
+        var remotePlayer = new Vector3(36.299465f, 18.594580f, 169.804993f);
+        var southHallAdmission = new List<string>();
+        var recorder = new Recorder
+        {
+            OnEmit = e =>
+            {
+                if (e.Kind != WalkEventKind.DrawCells
+                    || !e.Cells.Contains(0xF4180112u))
+                {
+                    return;
+                }
+
+                WalkPortalView views = cells[0xF4180112u].TopView;
+                for (int viewIndex = 0; viewIndex < views.ViewCount; viewIndex++)
+                {
+                    WalkViewPoly poly = views.View.Polys[viewIndex];
+                    var planes = new WalkPlane[poly.VertexCount];
+                    for (int edge = 0; edge < poly.VertexCount; edge++)
+                    {
+                        planes[edge] = views.View.Vertices[
+                            poly.VertexIndex + edge].Plane;
+                    }
+
+                    WalkBoundingType verdict = WalkVisibilityMath.ViewconeCheck(
+                        remotePlayer,
+                        radius: 1.5f,
+                        ctx.CyPlane,
+                        planes);
+                    float minDistance = planes
+                        .Select(plane => Vector3.Dot(plane.Normal, remotePlayer) + plane.D)
+                        .Append(Vector3.Dot(ctx.CyPlane.Normal, remotePlayer) + ctx.CyPlane.D)
+                        .Min();
+                    southHallAdmission.Add(
+                        $"view={viewIndex} planes={poly.VertexCount} verdict={verdict} min={minDistance:F4}");
+                }
+            },
+        };
+
+        new RetailFrameWalk().WalkFrame(
+            cameraCellId,
+            camera,
+            assembler.Landscape,
+            ctx,
+            recorder);
+
+        WalkEvent[] drawCells = recorder.Events
+            .Where(static e => e.Kind == WalkEventKind.DrawCells)
+            .ToArray();
+        Assert.NotEmpty(drawCells);
+        Assert.Contains(cameraCellId, drawCells[0].Cells);
+        Assert.NotEmpty(southHallAdmission);
+        Assert.Contains(
+            southHallAdmission,
+            static verdict => verdict.Contains("verdict=PartiallyInside")
+                && !verdict.Contains("planes=0"));
+    }
+
     [Fact]
     public void Foundry_entry_reproduces_every_frame_before_the_f67_order_segment()
     {

tests/AcDream.App.Tests/Rendering/Walk/WalkStaticStreamPopulatorTests.cs

@@ -45,6 +45,22 @@ public sealed class WalkStaticStreamPopulatorTests
             Calls.Add((serverGuid, localEntityId, partIndex, gfxObjId, partWorld));
     }
 
+    private sealed class FixedWalkViews(params uint[] slots) : IWalkLookInViewSource
+    {
+        public IReadOnlyList<uint> LookInCellTurns { get; } = [0x8C040112u];
+
+        public bool SphereVisibleInLookInTurn(
+            int routeIndex,
+            in Vector3 center,
+            float radius) => slots.Length != 0;
+
+        public IReadOnlyList<uint> VisibleClipSlotsInLookInTurn(
+            int routeIndex,
+            in Vector3 center,
+            float radius,
+            bool testSphere) => slots;
+    }
+
     // ── Synthetic RenderProjectionRecord construction ──────────────────────
 
     private static RenderProjectionRecord MakeRecord(
@@ -212,6 +228,35 @@ public sealed class WalkStaticStreamPopulatorTests
         Assert.Equal((uint)leavesGfxObj, selectionParts[1].GfxObjId);
     }
 
+    [Fact]
+    public void ClassifyEntityForWalk_EmitsOneGpuClippedInstancePerPortalViewSlice()
+    {
+        using var fx = new DispatcherFixture();
+        const ulong gfxObj = 0x0100_0013UL;
+        InjectRenderData(fx.Manager, gfxObj, MakeFlatMesh(
+            MakeBatch(0x08000013u, TranslucencyKind.Opaque, 0, 0, 3, 1)));
+        RenderProjectionRecord record = MakeRecord(
+            201, 0, Vector3.Zero,
+            [new MeshRef((uint)gfxObj, Matrix4x4.Identity)],
+            parentCellId: 0x8C040112u);
+        var batches = new List<WbDrawDispatcher.WalkClassifiedBatch>();
+        var selectionParts = new List<WbDrawDispatcher.WalkClassifiedSelectionPart>();
+        var views = new FixedWalkViews(7u, 9u);
+
+        fx.Dispatcher.ClassifyEntityForWalk(
+            in record,
+            0x8C04u,
+            batches,
+            selectionParts,
+            liveDynamic: true,
+            views,
+            lookInRouteIndex: 0,
+            lookInCellId: 0x8C040112u);
+
+        Assert.Equal([7u, 9u], batches.Select(static batch => batch.ClipSlot));
+        Assert.Single(selectionParts);
+    }
+
     // ── Deliverable 2: WalkStaticStreamPopulator routing ───────────────────
 
     [Fact]

tests/AcDream.App.Tests/Rendering/Wb/WbDrawDispatcherLookInConeTests.cs

@@ -56,5 +56,17 @@ public sealed class WbDrawDispatcherLookInConeTests
             Radius = radius;
             return true;
         }
+
+        public IReadOnlyList<uint> VisibleClipSlotsInLookInTurn(
+            int routeIndex,
+            in Vector3 center,
+            float radius,
+            bool testSphere)
+        {
+            RouteIndex = routeIndex;
+            Center = center;
+            Radius = radius;
+            return [7u];
+        }
     }
 }