fix(render): detail overlay is fogged after the combine like retail; VM1 review fixes

Opus dual-lens review of 05970306 + 388457a7 (APPROVE WITH FIXES). Four
items, all landed:

1. FOG (behavioural). Retail's D3D fixed-function fog stage runs AFTER the
   texture-stage pipeline, so the detail contribution must be fogged, not
   just the base. mesh_modern.frag already fogs the base colour
   (applyFog(rgb, vWorldPos)) before mesh_detail's replay draws over it;
   mesh_detail.frag previously emitted raw detail.rgb, understating fog by
   f*a*(fog-detail). Fix: mesh_detail.vert now outputs vWorldPos (mirroring
   mesh_modern.vert); mesh_detail.frag declares the identical SceneLighting
   UBO and applyFog function (copied verbatim, same binding/std140/math) and
   fogs detail.rgb before emitting it. This collapses algebraically to
   retail's fog-after-combine order:
     (1-a)*mix(base,fog,f) + a*mix(detail,fog,f) = mix(lerp(base,detail,a),fog,f)
   RetailDetailTextureContract gains ExpectedFogged(base,detail,opacity,fog,
   fogFactor); RetailDetailTextureContractTests pins the identity across 200
   random samples within 1e-6.

2. EnvCellRenderer.Rhi.cs's DrawEnvCell-category comment still said "apply
   the 10-50 m positive-view-depth fade" — a stale claim from before VM1
   removed the fade. Replaced with the mip-chain attenuation statement that
   mesh_detail.vert's header comment already carries.

3. Added the test the VM1 contract required but never had: TerrainAtlas
   .TryCreateDetailTexture uploads a full mip chain (MipLevelCount ==
   RhiWorldTextureArray.MipLevelsFor(w,h), GenerateMipChain called) and
   registers with the repeat/linear world sampler, not single-level or
   clamped. Drives the private method directly (reflection) against a
   synthetic PFID_A8R8G8B8 RenderSurface through a minimal in-memory
   IDatReaderWriter fake, so the lane stays hermetic (no installed DAT).

4. #226 pseudocode note: noted that retail's stage-1 OUTPUT alpha
   (MODULATE(TEXTURE, CURRENT), 0x0059c549) — the framebuffer blend weight a
   delayed-alpha subset composites with — is not modelled; acdream instead
   draws a second pass weighted by detail.a*diffuseAlpha. Identical for
   opaque subsets, a bounded difference on translucent building/EnvCell
   subsets already covered by the existing AP-34 shared-alpha-queue
   divergence row. Also qualified the tmpmaterial.Diffuse.a = 1f (0x0059cb99)
   citation to name its exact branch (burnedInStaticLights < 0 &&
   *(render_device+0x7e4) == 0); the other branch leaves diffuse FromVertex,
   but the opaque->1 / fading->opacity mapping still holds either way.

Nit also folded in: EnvCellRendererTests' new SubmitRhi instance-alpha test
is now a [Theory] over WbRenderPass.Opaque and .Transparent, pinning the
bind-before-first-draw invariant on both passes.

Regenerated mesh_detail's committed SPIR-V and the shader manifest
(tools/compile-shaders.ps1); no other shader pair changed.

Verified: dotnet build AcDream.slnx -c Release (0 warnings, 0 errors);
dotnet test on AcDream.App.Tests (Release, hermetic lanes) green, including
the shader manifest tests explicitly; AcDream.Core.Tests unaffected/green.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Rendering/RetailDetailTextureContractTests.cs

@@ -103,4 +103,46 @@ public sealed class RetailDetailTextureContractTests
         Assert.True(MathF.Abs(result.Y - detail.Y) < 1e-6f);
         Assert.True(MathF.Abs(result.Z - detail.Z) < 1e-6f);
     }
+
+    [Fact]
+    public void FogAppliedPerDrawMatchesRetailsFogAfterCombineOrder()
+    {
+        // Review fix (post-05970306): retail fogs the pixel AFTER the
+        // texture-stage combine (mix(lerp(base,detail,a), fog, f)), but
+        // acdream draws the combine as two separate passes, each fogging its
+        // own colour before the fixed-function blend recombines them
+        // (lerp(mix(base,fog,f), mix(detail,fog,f), a)). This pins that the
+        // two orders are the same pixel for arbitrary inputs — see
+        // ExpectedFogged's doc comment and mesh_detail.frag's header comment
+        // for the algebra.
+        var random = new Random(0x226226);
+        for (int i = 0; i < 200; i++)
+        {
+            var baseColour = NextColour(random);
+            var detail = new Vector4(NextColour(random), random.NextSingle());
+            float opacity = random.NextSingle();
+            var fog = NextColour(random);
+            float fogFactor = random.NextSingle();
+
+            Vector3 twoDrawOrder = RetailDetailTextureContract.ExpectedFogged(
+                baseColour, detail, opacity, fog, fogFactor);
+            Vector3 retailOrder = Vector3.Lerp(
+                RetailDetailTextureContract.Expected(baseColour, detail, opacity),
+                fog,
+                fogFactor);
+
+            Assert.True(
+                MathF.Abs(twoDrawOrder.X - retailOrder.X) < 1e-6f,
+                $"R: two-draw {twoDrawOrder.X} vs retail {retailOrder.X} (sample {i})");
+            Assert.True(
+                MathF.Abs(twoDrawOrder.Y - retailOrder.Y) < 1e-6f,
+                $"G: two-draw {twoDrawOrder.Y} vs retail {retailOrder.Y} (sample {i})");
+            Assert.True(
+                MathF.Abs(twoDrawOrder.Z - retailOrder.Z) < 1e-6f,
+                $"B: two-draw {twoDrawOrder.Z} vs retail {retailOrder.Z} (sample {i})");
+        }
+    }
+
+    private static Vector3 NextColour(Random random) =>
+        new(random.NextSingle(), random.NextSingle(), random.NextSingle());
 }

tests/AcDream.App.Tests/Rendering/TerrainAtlasDetailTextureTests.cs

@@ -0,0 +1,173 @@
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Reflection;
+using AcDream.App.Rendering;
+using AcDream.App.Rendering.Gpu;
+using AcDream.App.Rendering.Wb;
+using AcDream.App.Tests.Rendering.Gpu;
+using AcDream.Content;
+using DatReaderWriter;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Enums;
+using DatReaderWriter.Lib.IO;
+using DatReaderWriter.Types;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+/// <summary>
+/// Campaign VM VM1 review fix: pins the two facts the #226 note relies on
+/// for retail's mip-driven attenuation to actually be true — <c>TerrainAtlas
+/// .TryCreateDetailTexture</c> (~TerrainAtlas.cs:488-556) must upload a FULL
+/// mip chain, and it must be sampled with the repeat/linear world sampler,
+/// or the "attenuation is the sampler's linear mip chain" claim in
+/// mesh_detail.vert's header comment and the VM1 commit is unverified.
+/// Drives the private method directly (reflection, same pattern as
+/// EnvCellRendererTests' private-method tests) against a synthetic
+/// PFID_A8R8G8B8 RenderSurface, so no installed DAT is required — this lane
+/// stays hermetic.
+/// </summary>
+public sealed class TerrainAtlasDetailTextureTests
+{
+    private const uint SurfaceTextureId = 0x05001787u;
+    private const uint RenderSurfaceId = 0x06006D58u;
+
+    [Fact]
+    public void DetailTexture_UploadsFullMipChainAndUsesRepeatLinearSampler()
+    {
+        const int width = 4;
+        const int height = 4;
+
+        using var device = new RecordingGpuDevice();
+        device.Clear();
+
+        var dats = new FakeDetailTextureDats();
+        dats.Register(new SurfaceTexture
+        {
+            Textures = new List<QualifiedDataId<RenderSurface>> { RenderSurfaceId },
+        }, SurfaceTextureId);
+        dats.Register(new RenderSurface
+        {
+            Width = width,
+            Height = height,
+            Format = PixelFormat.PFID_A8R8G8B8,
+            SourceData = new byte[width * height * 4],
+        }, RenderSurfaceId);
+
+        var terrain = new TMTerrainDesc
+        {
+            TerrainTex = new TerrainTex
+            {
+                DetailTextureId = SurfaceTextureId,
+                DetailTexTiling = 4u,
+            },
+        };
+
+        IGpuSampler sampler = device.CreateSampler(GpuSamplerDescription.WorldRepeat);
+
+        MethodInfo method = typeof(TerrainAtlas).GetMethod(
+            "TryCreateDetailTexture",
+            BindingFlags.NonPublic | BindingFlags.Static)!;
+        object? result = method.Invoke(
+            null,
+            new object[] { device, dats, sampler, terrain, "building" });
+
+        Assert.NotNull(result);
+
+        // Full mip chain: TerrainAtlas.cs sizes MipLevelCount from
+        // RhiWorldTextureArray.MipLevelsFor(decoded.Width, decoded.Height) and
+        // then calls GenerateMipChain() — not a single-level upload.
+        RecordingGpuTexture texture = Assert.Single(device.CreatedTextures);
+        Assert.Equal(width, texture.Width);
+        Assert.Equal(height, texture.Height);
+        int expectedMipLevels = RhiWorldTextureArray.MipLevelsFor(width, height);
+        Assert.True(expectedMipLevels > 1, "the test fixture must exercise a real mip chain, not a 1x1 edge case");
+        Assert.Equal(expectedMipLevels, texture.MipLevelCount);
+        Assert.True(texture.MipChainGenerated);
+
+        // Repeat/linear sampler: the exact sampler GpuBindingModel world
+        // draws use, not WorldClamp (the alpha atlas' sampler) or any
+        // point-filtered UI sampler.
+        GpuRecordedTextureRegistration registration = Assert.Single(
+            device.Calls.OfType<GpuRecordedTextureRegistration>());
+        Assert.Equal(GpuSamplerDescription.WorldRepeat, registration.Sampler);
+        Assert.Equal(GpuFilter.Linear, registration.Sampler.MinFilter);
+        Assert.Equal(GpuFilter.Linear, registration.Sampler.MagFilter);
+        Assert.Equal(GpuMipFilter.Linear, registration.Sampler.MipFilter);
+        Assert.Equal(GpuAddressMode.Repeat, registration.Sampler.AddressU);
+        Assert.Equal(GpuAddressMode.Repeat, registration.Sampler.AddressV);
+    }
+
+    /// <summary>
+    /// Minimal synthetic <see cref="IDatReaderWriter"/> — same shape as the
+    /// NoopDatReaderWriter pattern already used for hermetic tests
+    /// (LiveEntityNetworkOnPositionCollapseMatrixTests), except <c>Get</c>
+    /// resolves from an explicit id-&gt;object map instead of always missing.
+    /// Every other member is unreachable by TryCreateDetailTexture and throws
+    /// if that assumption ever changes.
+    /// </summary>
+    private sealed class FakeDetailTextureDats : IDatReaderWriter
+    {
+        private readonly Dictionary<uint, IDBObj> _objects = new();
+
+        public void Register<T>(T obj, uint id) where T : IDBObj => _objects[id] = obj;
+
+        public string SourceDirectory => string.Empty;
+        public IDatDatabase Portal => throw new NotSupportedException();
+        public IDatDatabase Cell => throw new NotSupportedException();
+        public ReadOnlyDictionary<uint, IDatDatabase> CellRegions { get; } =
+            new(new Dictionary<uint, IDatDatabase>());
+        public IDatDatabase HighRes => throw new NotSupportedException();
+        public IDatDatabase Language => throw new NotSupportedException();
+        public IDatDatabase Local => throw new NotSupportedException();
+        public ReadOnlyDictionary<uint, uint> RegionFileMap { get; } =
+            new(new Dictionary<uint, uint>());
+        public int PortalIteration => 0;
+        public int CellIteration => 0;
+        public int HighResIteration => 0;
+        public int LanguageIteration => 0;
+
+        public bool TryGetFileBytes(
+            uint regionId,
+            uint fileId,
+            ref byte[] bytes,
+            out int bytesRead)
+        {
+            bytesRead = 0;
+            return false;
+        }
+
+        public IEnumerable<uint> GetAllIdsOfType<T>() where T : IDBObj =>
+            Array.Empty<uint>();
+
+        public IEnumerable<IDatReaderWriter.IdResolution> ResolveId(uint id) =>
+            Array.Empty<IDatReaderWriter.IdResolution>();
+
+        public bool TrySave<T>(T obj, int iteration = 0) where T : IDBObj =>
+            throw new NotSupportedException();
+
+        public bool TrySave<T>(uint regionId, T obj, int iteration = 0) where T : IDBObj =>
+            throw new NotSupportedException();
+
+        [return: MaybeNull]
+        public T Get<T>(uint fileId) where T : IDBObj =>
+            _objects.TryGetValue(fileId, out IDBObj? obj) && obj is T typed ? typed : default;
+
+        public bool TryGet<T>(uint fileId, [MaybeNullWhen(false)] out T value) where T : IDBObj
+        {
+            if (_objects.TryGetValue(fileId, out IDBObj? obj) && obj is T typed)
+            {
+                value = typed;
+                return true;
+            }
+            value = default;
+            return false;
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+}

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

@@ -116,8 +116,11 @@ public class EnvCellRendererTests
     /// pass, mesh_modern's shell pipeline and (when enabled) mesh_detail's
     /// replay alike.
     /// </summary>
-    [Fact]
-    public void SubmitRhi_BindsConstantOneInstanceAlphaBeforeAnyDrawInThePass()
+    [Theory]
+    [InlineData(WbRenderPass.Opaque)]
+    [InlineData(WbRenderPass.Transparent)]
+    public void SubmitRhi_BindsConstantOneInstanceAlphaBeforeAnyDrawInThePass(
+        WbRenderPass renderPass)
     {
         const int instanceCount = 5;
 
@@ -144,7 +147,13 @@ public class EnvCellRendererTests
         // Seed one real draw command, exactly what
         // RenderModernMDIInternal would have built from a live landblock,
         // so the test can assert an actual ordering against a real draw
-        // rather than a vacuous "no draw happened" pass.
+        // rather than a vacuous "no draw happened" pass. Same command for
+        // both passes: with _buildingDetailEnabled left at its default
+        // (false), the Transparent branch's own detail-interleave logic
+        // (SubmitRhi's "detailEnabled" block) never fires, so it draws
+        // through the identical MultiDrawIndexedIndirect call the Opaque
+        // pass does — only the pipeline rebound inside the per-range loop
+        // differs, which is not what this test is pinning.
         Type rendererType = typeof(EnvCellRenderer);
         FieldInfo commandsField = rendererType.GetField(
             "_commands", BindingFlags.NonPublic | BindingFlags.Instance)!;
@@ -184,7 +193,7 @@ public class EnvCellRendererTests
             "SubmitRhi", BindingFlags.NonPublic | BindingFlags.Instance)!;
         submitRhi.Invoke(
             renderer,
-            new object[] { allInstances, WbRenderPass.Opaque, 1, instanceCount });
+            new object[] { allInstances, renderPass, 1, instanceCount });
 
         IReadOnlyList<GpuRecordedCall> calls = device.Calls;
         int alphaBindIndex = -1;