feat: derive atlas tile size from loaded texture dimensions

Core/Game.cs

@@ -44,7 +44,7 @@ public sealed class Game : GameWindow
             this._world.SetChunk(new Vector3i(x, 0, z), this.BuildChunk());
         }
 
-        ChunkMesher mesher = new();
+        ChunkMesher mesher = new(this._texture.Width, this._texture.Height);
         foreach ((Vector3i pos, Chunk chunk) in this._world)
         {
             Vector3i origin = pos *  Chunk.Size;

Rendering/Texture.cs

@@ -7,6 +7,9 @@ public sealed class Texture : IDisposable
 {
     private readonly int _handle;
 
+    public int Width { get; }
+    public int Height { get; }
+
     public Texture(string path)
     {
         this._handle = GL.GenTexture();
@@ -15,6 +18,8 @@ public sealed class Texture : IDisposable
         StbImage.stbi_set_flip_vertically_on_load(1);
         using FileStream stream = File.OpenRead(path);
         ImageResult image = ImageResult.FromStream(stream, ColorComponents.RedGreenBlueAlpha);
+        this.Width = image.Width;
+        this.Height = image.Height;
 
         GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba,
             image.Width, image.Height, 0, PixelFormat.Rgba, PixelType.UnsignedByte, image.Data);

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");
+        }
+    }
 }

World/Chunk/ChunkMesher.cs

@@ -5,9 +5,15 @@ namespace VoxelEngine.World.Chunk;
 public sealed class ChunkMesher : IChunkMesher
 {
     private const int TileSizePixels = 32;  // each tile is 32x32 pixels
-    private const int AtlasSizePixels = 64; // atlas is 64x64 pixels (2x2 grid)
 
-    private const float TileSize = (float)TileSizePixels / AtlasSizePixels; // normalized tile size
+    private readonly float _tileU; // normalized tile width
+    private readonly float _tileV; // normalized tile height
+
+    public ChunkMesher(int atlasWidthPixels, int atlasHeightPixels)
+    {
+        this._tileU = (float)ChunkMesher.TileSizePixels / atlasWidthPixels;
+        this._tileV = (float)ChunkMesher.TileSizePixels / atlasHeightPixels;
+    }
 
     // Per-face geometry: base corner + two in-plane edge vectors (u, v) with
     // cross(u, v) == outward normal, guaranteeing CCW winding from outside.
@@ -72,18 +78,18 @@ public sealed class ChunkMesher : IChunkMesher
                         : (neighborOpaqueOutside?.Invoke(nx, ny, nz) ?? false);
                 if (neighborOpaque) continue;
 
-                ChunkMesher.AddFace(verts, x, y, z, face, block.GetTextureTile(face.Kind));
+                this.AddFace(verts, x, y, z, face, block.GetTextureTile(face.Kind));
             }
         }
 
         return verts.ToArray();
     }
 
-    private static void AddFace(List<float> verts, int x, int y, int z, Face face, TileCoord tile)
+    private void AddFace(List<float> verts, int x, int y, int z, Face face, TileCoord tile)
     {
-        float uBase = tile.X * ChunkMesher.TileSize;
+        float uBase = tile.X * this._tileU;
         // Image is flipped on load, so offset from the top to keep tile (0,0) = top-left.
-        float vBase = 1f - (tile.Y + 1) * ChunkMesher.TileSize;
+        float vBase = 1f - (tile.Y + 1) * this._tileV;
 
         foreach (int corner in ChunkMesher.Triangle)
         {
@@ -93,8 +99,8 @@ public sealed class ChunkMesher : IChunkMesher
             float py = y + face.Base.y + face.U.y * cu + face.V.y * cv;
             float pz = z + face.Base.z + face.U.z * cu + face.V.z * cv;
 
-            float u = uBase + cu * ChunkMesher.TileSize;
+            float u = uBase + cu * this._tileU;
-            float v = vBase + cv * ChunkMesher.TileSize;
+            float v = vBase + cv * this._tileV;
 
             verts.Add(px); verts.Add(py); verts.Add(pz);
             verts.Add(u); verts.Add(v);