feat: derive atlas tile size from loaded texture dimensions

VoxelEngine.Tests/ChunkMesherTests.cs

@@ -16,7 +16,7 @@ public class ChunkMesherTests
     [Fact]
     public void EmptyChunk_ProducesNoFaces()
     {
-        var mesh = new ChunkMesher().Build(new Chunk(), new BlockRegistry());
+        var mesh = new ChunkMesher(128, 128).Build(new Chunk(), new BlockRegistry());
         Assert.Empty(mesh);
     }
 
@@ -26,7 +26,7 @@ public class ChunkMesherTests
         var chunk = new Chunk();
         chunk[8, 8, 8] = 1; // stone
 
-        var mesh = new ChunkMesher().Build(chunk, new BlockRegistry());
+        var mesh = new ChunkMesher(128, 128).Build(chunk, new BlockRegistry());
 
         Assert.Equal(6, FaceCount(mesh));
     }
@@ -40,7 +40,7 @@ public class ChunkMesherTests
         for (int z = 0; z < Chunk.Size; z++)
             chunk[x, y, z] = 1; // stone
 
-        var mesh = new ChunkMesher().Build(chunk, new BlockRegistry());
+        var mesh = new ChunkMesher(128, 128).Build(chunk, new BlockRegistry());
 
         // 6 sides * 16 * 16 visible faces
         Assert.Equal(6 * Chunk.Size * Chunk.Size, FaceCount(mesh));
@@ -52,10 +52,32 @@ public class ChunkMesherTests
         var chunk = new Chunk();
         chunk[0, 0, 0] = 1; // corner block: all 6 neighbors are air/out-of-bounds -> 6 faces
 
-        var mesh = new ChunkMesher().Build(chunk, new BlockRegistry());
+        var mesh = new ChunkMesher(128, 128).Build(chunk, new BlockRegistry());
 
         // Pins the layout: 6 faces * 6 vertices/face * 6 floats/vertex.
         Assert.Equal(6 * VerticesPerFace * FloatsPerVertex, mesh.Length);
         Assert.Equal(0, mesh.Length % FloatsPerVertex);
     }
+
+    [Fact]
+    public void Mesher_UsesAtlasDimensions_ForTileSize()
+    {
+        var chunk = new Chunk();
+        chunk[0, 0, 0] = 1; // stone, tile (1,0)
+
+        // 128px atlas, 32px tiles => 4x4 grid, normalized tile size 0.25.
+        var mesh = new ChunkMesher(128, 128).Build(chunk, new BlockRegistry());
+
+        // Gather all U coords (offset 3) and V coords (offset 4); each must be a
+        // multiple of 0.25 within [0,1].
+        for (int i = 0; i < mesh.Length; i += 6)
+        {
+            float u = mesh[i + 3];
+            float v = mesh[i + 4];
+            Assert.InRange(u, 0f, 1f);
+            Assert.InRange(v, 0f, 1f);
+            Assert.True(System.Math.Abs(u * 4f - System.MathF.Round(u * 4f)) < 1e-4f, $"u={u} not on 0.25 grid");
+            Assert.True(System.Math.Abs(v * 4f - System.MathF.Round(v * 4f)) < 1e-4f, $"v={v} not on 0.25 grid");
+        }
+    }
 }