New Atlas + Texture Pipeline

World/Blocks/AirBlock.cs

@@ -6,5 +6,5 @@ public sealed class AirBlock : IBlock
     public string Name => "Air";
     public bool IsOpaque => false;
     public bool IsSolid => false;
-    public int GetTextureIndex(BlockFace face) => 0;
+    public TileCoord GetTextureTile(BlockFace face) => new(0, 0);
 }

World/Blocks/DirtBlock.cs

@@ -6,5 +6,5 @@ public sealed class DirtBlock : IBlock
     public string Name => "Dirt";
     public bool IsOpaque => true;
     public bool IsSolid => true;
-    public int GetTextureIndex(BlockFace face) => 1;
+    public TileCoord GetTextureTile(BlockFace face) => new(0, 0);
 }

World/Blocks/GrassBlock.cs

@@ -7,10 +7,10 @@ public sealed class GrassBlock : IBlock
     public bool IsOpaque => true;
     public bool IsSolid => true;
 
-    public int GetTextureIndex(BlockFace face) => face switch
+    public TileCoord GetTextureTile(BlockFace face) => face switch
     {
-        BlockFace.Top => 0,    // grass top
-        BlockFace.Bottom => 1, // dirt
-        _ => 3                 // grass side
+        BlockFace.Top => new(0, 1),    // grass top
+        BlockFace.Bottom => new(0, 0), // dirt
+        _ => new(1, 1)                 // grass side
     };
 }

World/Blocks/IBlock.cs

@@ -11,8 +11,8 @@ public interface IBlock
     // Reserved for future collision (not used in the baseline).
     bool IsSolid { get; }
 
-    // Atlas tile index for the given face.
-    int GetTextureIndex(BlockFace face);
+    // Atlas tile coordinate for the given face.
+    TileCoord GetTextureTile(BlockFace face);
 
     // Interaction hooks — capability present now, system built post-baseline.
     void OnInteract() { }

World/Blocks/StoneBlock.cs

@@ -6,5 +6,5 @@ public sealed class StoneBlock : IBlock
     public string Name => "Stone";
     public bool IsOpaque => true;
     public bool IsSolid => true;
-    public int GetTextureIndex(BlockFace face) => 2;
+    public TileCoord GetTextureTile(BlockFace face) => new(1, 0);
 }