phase(N.5b) Task 1: TerrainAtlas bindless extension

Add optional BindlessSupport ctor parameter + GetBindlessHandles()
method that returns (terrainHandle, alphaHandle) ulongs with both
textures made resident. Two-phase Dispose mirroring TextureCache
(MakeNonResident before DeleteTexture per ARB_bindless_texture spec).

Existing callers pass `Build(gl, dats)` unchanged; bindless = null
default keeps them working until T6/T8 wires the renderer.

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

src/AcDream.App/Rendering/TerrainAtlas.cs

@@ -53,14 +53,45 @@ public sealed unsafe class TerrainAtlas : IDisposable
     /// <summary>RCode for each RoadMap, parallel to <see cref="RoadAlphaLayers"/>.</summary>
     public IReadOnlyList<uint> RoadAlphaRCodes { get; }
 
+    private readonly Wb.BindlessSupport? _bindless;
+
+    // Cached bindless handles. Generated lazily on first GetBindlessHandles() call;
+    // reused for the lifetime of the atlas.
+    private ulong _terrainHandle;
+    private ulong _alphaHandle;
+    private bool  _handlesGenerated;
+
+    /// <summary>
+    /// Get 64-bit bindless handles for the terrain + alpha texture arrays.
+    /// Throws <see cref="InvalidOperationException"/> if the atlas was constructed
+    /// without a <see cref="Wb.BindlessSupport"/> instance. Handles are generated
+    /// lazily on first call and cached for the atlas's lifetime; both textures
+    /// are made resident.
+    /// </summary>
+    public (ulong terrain, ulong alpha) GetBindlessHandles()
+    {
+        if (_bindless is null)
+            throw new InvalidOperationException(
+                "TerrainAtlas was constructed without BindlessSupport; cannot return bindless handles.");
+        if (!_handlesGenerated)
+        {
+            _terrainHandle = _bindless.GetResidentHandle(GlTexture);
+            _alphaHandle   = _bindless.GetResidentHandle(GlAlphaTexture);
+            _handlesGenerated = true;
+        }
+        return (_terrainHandle, _alphaHandle);
+    }
+
     private TerrainAtlas(
         GL gl,
+        Wb.BindlessSupport? bindless,
         uint glTexture, IReadOnlyDictionary<uint, uint> map, int layerCount,
         uint glAlphaTexture, int alphaLayerCount,
         IReadOnlyList<byte> cornerLayers, IReadOnlyList<byte> sideLayers, IReadOnlyList<byte> roadLayers,
         IReadOnlyList<uint> cornerTCodes, IReadOnlyList<uint> sideTCodes, IReadOnlyList<uint> roadRCodes)
     {
         _gl = gl;
+        _bindless = bindless;
         GlTexture = glTexture;
         TerrainTypeToLayer = map;
         LayerCount = layerCount;
@@ -79,7 +110,7 @@ public sealed unsafe class TerrainAtlas : IDisposable
     /// for the mapping from TerrainTextureType to SurfaceTexture id, decoding each
     /// to RGBA8, and uploading as layers in a single GL_TEXTURE_2D_ARRAY.
     /// </summary>
-    public static TerrainAtlas Build(GL gl, DatCollection dats)
+    public static TerrainAtlas Build(GL gl, DatCollection dats, Wb.BindlessSupport? bindless = null)
     {
         var region = dats.Get<Region>(0x13000000u)
             ?? throw new InvalidOperationException("Region dat id 0x13000000 missing");
@@ -89,7 +120,7 @@ public sealed unsafe class TerrainAtlas : IDisposable
         if (terrainDesc is null || terrainDesc.Count == 0)
         {
             Console.WriteLine("WARN: TerrainDesc missing, using single white fallback layer");
-            return BuildFallback(gl);
+            return BuildFallback(gl, bindless);
         }
 
         // ---- Terrain atlas (unchanged Phase 2b logic) ----
@@ -167,6 +198,7 @@ public sealed unsafe class TerrainAtlas : IDisposable
 
         return new TerrainAtlas(
             gl,
+            bindless,
             tex, map, layerCount,
             alphaBuild.gl, alphaBuild.layerCount,
             alphaBuild.corner, alphaBuild.side, alphaBuild.road,
@@ -350,7 +382,7 @@ public sealed unsafe class TerrainAtlas : IDisposable
         return dst;
     }
 
-    private static TerrainAtlas BuildFallback(GL gl)
+    private static TerrainAtlas BuildFallback(GL gl, Wb.BindlessSupport? bindless = null)
     {
         uint tex = gl.GenTexture();
         gl.BindTexture(TextureTarget.Texture2DArray, tex);
@@ -372,6 +404,7 @@ public sealed unsafe class TerrainAtlas : IDisposable
 
         return new TerrainAtlas(
             gl,
+            bindless,
             tex, new Dictionary<uint, uint> { [0] = 0u }, 1,
             alphaTex, 1,
             Array.Empty<byte>(), Array.Empty<byte>(), Array.Empty<byte>(),
@@ -380,6 +413,16 @@ public sealed unsafe class TerrainAtlas : IDisposable
 
     public void Dispose()
     {
+        // Phase 1: release bindless residency BEFORE deleting textures.
+        // ARB_bindless_texture requires this ordering; interleaving is UB.
+        if (_handlesGenerated && _bindless is not null)
+        {
+            _bindless.MakeNonResident(_terrainHandle);
+            _bindless.MakeNonResident(_alphaHandle);
+            _handlesGenerated = false;
+        }
+
+        // Phase 2: delete the underlying GL textures.
         _gl.DeleteTexture(GlTexture);
         _gl.DeleteTexture(GlAlphaTexture);
     }