fix: complete retail parity stability pass

tests/AcDream.Content.Tests/MeshExtractorSolidFaceExtractionTests.cs

@@ -11,6 +11,7 @@ using DatReaderWriter.Enums;
 using DatReaderWriter.Lib.IO;
 using DatReaderWriter.Types;
 using Microsoft.Extensions.Logging.Abstractions;
+using RetailCullMode = DatReaderWriter.Enums.CullMode;
 
 namespace AcDream.Content.Tests;
 
@@ -180,6 +181,61 @@ public sealed class MeshExtractorSolidFaceExtractionTests
         Assert.Equal(4 * 4 * 4, Assert.Single(group.Value).TextureData.Length);
     }
 
+    [Fact]
+    public void PrepareCellStructMeshData_LandblockSide_PreservesRetailTriangleFanWinding()
+    {
+        var dats = new FakeMeshExtractorDats();
+        dats.Register(SolidSurfaceId, new Surface
+        {
+            Type = SurfaceType.Base1Solid,
+            ColorValue = new ColorARGB { Alpha = 255, Red = 64, Green = 96, Blue = 128 },
+        });
+        var extractor = new MeshExtractor(dats, NullLogger.Instance, sideStagedSink: null);
+
+        ObjectMeshData mesh = Assert.IsType<ObjectMeshData>(
+            extractor.PrepareCellStructMeshData(
+                id: 1,
+                BuildQuadCellStruct(RetailCullMode.Landblock),
+                surfaceOverrides: [1],
+                Matrix4x4.Identity,
+                CancellationToken.None));
+
+        TextureBatchData batch = Assert.Single(Assert.Single(mesh.TextureBatches).Value);
+        Assert.Equal(RetailCullMode.Landblock, batch.CullMode);
+        Assert.Equal([0, 1, 2, 0, 2, 3], batch.Indices);
+        Assert.Equal(4, mesh.Vertices.Length);
+        Assert.All(mesh.Vertices, vertex => Assert.Equal(Vector3.UnitZ, vertex.Normal));
+    }
+
+    [Fact]
+    public void PrepareCellStructMeshData_NoneSide_ExpandsReversedFaceExactlyLikeRetailConstructMesh()
+    {
+        var dats = new FakeMeshExtractorDats();
+        dats.Register(SolidSurfaceId, new Surface
+        {
+            Type = SurfaceType.Base1Solid,
+            ColorValue = new ColorARGB { Alpha = 255, Red = 64, Green = 96, Blue = 128 },
+        });
+        var extractor = new MeshExtractor(dats, NullLogger.Instance, sideStagedSink: null);
+
+        ObjectMeshData mesh = Assert.IsType<ObjectMeshData>(
+            extractor.PrepareCellStructMeshData(
+                id: 1,
+                BuildQuadCellStruct(RetailCullMode.None),
+                surfaceOverrides: [1],
+                Matrix4x4.Identity,
+                CancellationToken.None));
+
+        TextureBatchData batch = Assert.Single(Assert.Single(mesh.TextureBatches).Value);
+        Assert.Equal(RetailCullMode.None, batch.CullMode);
+        Assert.Equal(
+            [0, 1, 2, 0, 2, 3, 6, 5, 4, 7, 6, 4],
+            batch.Indices);
+        Assert.Equal(8, mesh.Vertices.Length);
+        Assert.All(mesh.Vertices.Take(4), vertex => Assert.Equal(Vector3.UnitZ, vertex.Normal));
+        Assert.All(mesh.Vertices.Skip(4), vertex => Assert.Equal(-Vector3.UnitZ, vertex.Normal));
+    }
+
     private static void RegisterTexturedQuad(
         FakeMeshExtractorDats dats,
         SurfaceType surfaceType,
@@ -207,6 +263,30 @@ public sealed class MeshExtractorSolidFaceExtractionTests
         });
     }
 
+    private static CellStruct BuildQuadCellStruct(RetailCullMode sidesType) => new()
+    {
+        VertexArray = new VertexArray
+        {
+            Vertices = new Dictionary<ushort, SWVertex>
+            {
+                [0] = new() { Origin = new Vector3(0, 0, 0), Normal = Vector3.UnitZ },
+                [1] = new() { Origin = new Vector3(1, 0, 0), Normal = Vector3.UnitZ },
+                [2] = new() { Origin = new Vector3(1, 1, 0), Normal = Vector3.UnitZ },
+                [3] = new() { Origin = new Vector3(0, 1, 0), Normal = Vector3.UnitZ },
+            },
+        },
+        Polygons = new Dictionary<ushort, Polygon>
+        {
+            [0] = new()
+            {
+                SidesType = sidesType,
+                PosSurface = 0,
+                NegSurface = -1,
+                VertexIds = [0, 1, 2, 3],
+            },
+        },
+    };
+
     /// <summary>One quad (4 verts), single polygon, PosSurface referencing <paramref name="surfaceId"/>.</summary>
     private static GfxObj BuildQuadGfxObj(uint surfaceId, bool noPos)
     {