todo: added todos for new blocks

Pure-air chunks (above terrain) and chunks where every face culls
produce a zero-length mesh from ChunkMesher.Build(). Previously
InstallResult still allocated a real ChunkRenderer (VBO + VAO) and
registered a zero-vertex draw call. With RenderDistanceVertical=2 and
a player at surface Y, the topmost vertical layer is typically all
pure air -- roughly H*H = ~289 wasted renderers per spawn.

The chunk still gets added to _ready so SpawnReady, dirty-marking and
unload bookkeeping continue to work; DrawAll's iteration over the
renderer dictionary naturally skips entries that don't exist.

Assets/shaders/chunk.frag

@@ -1,13 +1,20 @@
 #version 330 core
 in vec2 vUv;
 in float vShade;
+in float vWorldY;
 
 out vec4 FragColor;
 
 uniform sampler2D atlas;
+uniform float u_caveDarkStartY;
+uniform float u_caveDarkEndY;
+uniform float u_caveMinBrightness;
 
 void main()
 {
     vec4 texel = texture(atlas, vUv);
-    FragColor = vec4(texel.rgb * vShade, 1.0);
+    float t = clamp((u_caveDarkStartY - vWorldY) /
+                    (u_caveDarkStartY - u_caveDarkEndY), 0.0, 1.0);
+    float brightness = mix(1.0, u_caveMinBrightness, t);
+    FragColor = vec4(texel.rgb * vShade * brightness, 1.0);
 }

Assets/shaders/chunk.vert

@@ -5,6 +5,7 @@ layout(location = 2) in float aShade;
 
 out vec2 vUv;
 out float vShade;
+out float vWorldY;
 
 uniform mat4 model;
 uniform mat4 view;
@@ -14,6 +15,8 @@ void main()
 {
     vUv = aUv;
     vShade = aShade;
-    // Vector-on-left convention; matrices are uploaded with transpose=true.
+    // World-space position uses row-vector convention (matches gl_Position below).
-    gl_Position = vec4(aPos, 1.0) * model * view * projection;
+    vec4 worldPos = vec4(aPos, 1.0) * model;
+    vWorldY = worldPos.y;
+    gl_Position = worldPos * view * projection;
 }

Core/Configuration.cs

@@ -10,6 +10,11 @@ public sealed class Configuration
     public int MaxMeshUploadsPerFrame { get; set; } = 4;
     public int WorkerThreadCount { get; set; } = Math.Max(1, Environment.ProcessorCount / 2);
 
+    // Multiplier applied to (dy)^2 in chunk-load priority. >1 prioritizes
+    // chunks at the player's Y over equally-distant chunks above/below, so the
+    // visible surface fills in before far-underground / overhead chunks.
+    public int VerticalPriorityWeight { get; set; } = 4;
+
     public float MoveSpeed { get; set; } = 8f;
     public float MouseSensitivity { get; set; } = 0.15f;
     public float Fov { get; set; } = 60f;
@@ -18,4 +23,18 @@ public sealed class Configuration
     public int WindowHeight { get; set; } = 720;
 
     public int? Seed { get; set; } = null;
+
+    // -- Cave generation tuning --
+    public float CaveNoiseFrequency           { get; set; } = 0.03f;
+    public float CaveNoiseThreshold           { get; set; } = -0.3f;
+    public int   WormCellSize                 { get; set; } = 64;
+    public int   WormSpawnProbabilityPermille { get; set; } = 300;
+    public int   WormMaxLength                { get; set; } = 80;
+    public float WormMinRadius                { get; set; } = 1.5f;
+    public float WormMaxRadius                { get; set; } = 3.5f;
+
+    // -- Cave lighting (fog-distance darkness) --
+    public float CaveDarkStartY    { get; set; } = 72f;   // WorldConstants.SeaLevel + 8
+    public float CaveDarkEndY      { get; set; } = 32f;   // WorldConstants.SeaLevel - 32
+    public float CaveMinBrightness { get; set; } = 0.15f;
 }

Core/Game.cs

@@ -55,7 +55,7 @@ public sealed class Game : GameWindow
         this._world = new World.World(this._registry, this._modStore);
 
         int seed = this._cfg.Seed ?? new Random().Next();
-        this._generator = new WorldGenerator(seed, this._registry);
+        this._generator = new WorldGenerator(seed, this._registry, this._cfg);
 
         // Spawn at terrain surface above (0, 0).
         int surfaceY = this._generator.SurfaceHeightAt(0, 0);
@@ -116,6 +116,9 @@ public sealed class Game : GameWindow
         this._shader.SetMatrix4("view", this._player.Camera.GetViewMatrix());
         this._shader.SetMatrix4("projection", this._player.Camera.GetProjectionMatrix());
         this._shader.SetInt("atlas", 0);
+        this._shader.SetFloat("u_caveDarkStartY",    this._cfg.CaveDarkStartY);
+        this._shader.SetFloat("u_caveDarkEndY",      this._cfg.CaveDarkEndY);
+        this._shader.SetFloat("u_caveMinBrightness", this._cfg.CaveMinBrightness);
         this._texture.Use(TextureUnit.Texture0);
 
         this._streamer.DrawAll((pos, renderer) =>

Rendering/Shader.cs

@@ -36,6 +36,9 @@ public sealed class Shader : IDisposable
     public void SetInt(string name, int value) =>
         GL.Uniform1(this.Location(name), value);
 
+    public void SetFloat(string name, float value) =>
+        GL.Uniform1(this.Location(name), value);
+
     private int Location(string name)
     {
         if (this._uniforms.TryGetValue(name, out int location)) return location;

VoxelEngine.Tests/BlockRegistryTests.cs

@@ -71,4 +71,36 @@ public class BlockRegistryTests
         Assert.Equal("Snow Block", registry.Get(5).Name);
         Assert.Equal("Water", registry.Get(6).Name);
     }
+
+    [Fact]
+    public void Registry_ResolvesOreBlocks_ByStableIds()
+    {
+        var registry = new BlockRegistry();
+
+        Assert.Equal("Coal Ore",    registry.Get(7).Name);
+        Assert.Equal("Iron Ore",    registry.Get(8).Name);
+        Assert.Equal("Gold Ore",    registry.Get(9).Name);
+        Assert.Equal("Diamond Ore", registry.Get(10).Name);
+    }
+
+    [Fact]
+    public void Ores_AreOpaqueAndSolid()
+    {
+        var registry = new BlockRegistry();
+        foreach (ushort id in new ushort[] { 7, 8, 9, 10 })
+        {
+            Assert.True(registry.Get(id).IsOpaque, $"ore id {id} should be opaque");
+            Assert.True(registry.Get(id).IsSolid,  $"ore id {id} should be solid");
+        }
+    }
+
+    [Fact]
+    public void NamedOreAccessors_MatchIds()
+    {
+        var registry = new BlockRegistry();
+        Assert.Equal((ushort)7,  registry.CoalOre.Id);
+        Assert.Equal((ushort)8,  registry.IronOre.Id);
+        Assert.Equal((ushort)9,  registry.GoldOre.Id);
+        Assert.Equal((ushort)10, registry.DiamondOre.Id);
+    }
 }

VoxelEngine.Tests/ConfigurationTests.cs

@@ -54,4 +54,24 @@ public class ConfigurationTests
         Assert.Equal(800,  c2.WindowWidth);
         Assert.Equal(600,  c2.WindowHeight);
     }
+
+    [Fact]
+    public void Defaults_HaveCaveTuningConstants()
+    {
+        var c = new Configuration();
+
+        // Algorithm
+        Assert.Equal(0.03f, c.CaveNoiseFrequency);
+        Assert.Equal(-0.3f, c.CaveNoiseThreshold);
+        Assert.Equal(64,    c.WormCellSize);
+        Assert.Equal(300,   c.WormSpawnProbabilityPermille);
+        Assert.Equal(80,    c.WormMaxLength);
+        Assert.Equal(1.5f,  c.WormMinRadius);
+        Assert.Equal(3.5f,  c.WormMaxRadius);
+
+        // Lighting (fog)
+        Assert.Equal(72f,   c.CaveDarkStartY);    // SeaLevel (64) + 8
+        Assert.Equal(32f,   c.CaveDarkEndY);      // SeaLevel (64) - 32
+        Assert.Equal(0.15f, c.CaveMinBrightness);
+    }
 }

VoxelEngine.Tests/Streaming/ChunkStreamerTests.cs

@@ -35,6 +35,13 @@ internal sealed class FakeMesher : IChunkMesher
         => new float[6]; // one vertex worth
 }
 
+// Mesher that returns an empty mesh, simulating a pure-air chunk.
+internal sealed class EmptyMesher : IChunkMesher
+{
+    public float[] Build(VoxelChunk chunk, BlockRegistry registry, Func<int, int, int, bool>? neighborOpaqueOutside = null)
+        => Array.Empty<float>();
+}
+
 public class ChunkStreamerTests
 {
     private static (ChunkStreamer streamer, World.World world, List<FakeRenderer> created) CreateStreamer(Configuration cfg)
@@ -351,4 +358,65 @@ public class ChunkStreamerTests
         streamer.Tick(new Vector3i(0, 0, 0));
         Assert.Equal(1, generateCalls);
     }
+
+    [Fact]
+    public void InstallResult_EmptyMesh_SkipsRendererCreationButMarksReady()
+    {
+        var cfg = new Configuration
+        {
+            RenderDistanceHorizontal = 0,
+            RenderDistanceVertical = 0,
+            MaxGenerateJobsInFlight = 100,
+            MaxMeshUploadsPerFrame = 100,
+        };
+        var registry = new BlockRegistry();
+        var store = new InMemoryChunkModificationStore();
+        var world = new World.World(registry, store);
+        var mesher = new EmptyMesher();
+        var executor = new SynchronousJobExecutor();
+        int rendererFactoryCalls = 0;
+        Func<float[], IChunkRenderer> factory = m =>
+        {
+            rendererFactoryCalls++;
+            return new FakeRenderer(m);
+        };
+        Func<Vector3i, VoxelChunk> generate = _ => new VoxelChunk();
+
+        var streamer = new ChunkStreamer(cfg, world, generate, mesher, registry, executor, factory);
+        var pos = new Vector3i(0, 0, 0);
+        streamer.Tick(pos);
+
+        Assert.True(streamer.IsReady(pos));
+        Assert.Equal(0, rendererFactoryCalls);
+        Assert.Equal(0, streamer.RendererCount);
+    }
+
+    [Fact]
+    public void Tick_VerticalPriorityWeight_PrefersHorizontalAtSameDistance()
+    {
+        var cfg = new Configuration
+        {
+            RenderDistanceHorizontal = 1,
+            RenderDistanceVertical = 1,
+            MaxGenerateJobsInFlight = 100,
+            MaxMeshUploadsPerFrame = 5,  // player's chunk + 4 horizontal cardinals
+            VerticalPriorityWeight = 4,
+        };
+        var (streamer, world, _) = CreateStreamer(cfg);
+
+        // Player chunk at Y=2 so vertical neighbors Y=1 and Y=3 are valid.
+        var playerPos = new Vector3i(0, 2, 0);
+        streamer.Tick(playerPos);
+
+        // Drain budget = 5 = priority 0 (player) + 4 priority-1 (horizontal
+        // cardinals). With VerticalPriorityWeight=4, vertical cardinals
+        // (Y=1, Y=3) have priority 4 — they should NOT be among the first 5.
+        Assert.NotNull(world.GetChunk(playerPos));
+        Assert.NotNull(world.GetChunk(new Vector3i( 1, 2,  0)));
+        Assert.NotNull(world.GetChunk(new Vector3i(-1, 2,  0)));
+        Assert.NotNull(world.GetChunk(new Vector3i( 0, 2,  1)));
+        Assert.NotNull(world.GetChunk(new Vector3i( 0, 2, -1)));
+        Assert.Null(world.GetChunk(new Vector3i(0, 3, 0)));
+        Assert.Null(world.GetChunk(new Vector3i(0, 1, 0)));
+    }
 }

VoxelEngine.Tests/Streaming/StreamingIntegrationTests.cs

@@ -18,7 +18,7 @@ public class StreamingIntegrationTests
         var registry = new BlockRegistry();
         var store = new InMemoryChunkModificationStore();
         var world = new World.World(registry, store);
-        var gen = new WorldGenerator(seed: 1337, blocks: registry);
+        var gen = new WorldGenerator(seed: 1337, blocks: registry, cfg: new Configuration());
         var mesher = new ChunkMesher(atlasWidthPixels: 128, atlasHeightPixels: 32);
         var executor = new SynchronousJobExecutor();
         Func<float[], IChunkRenderer> factory = m => new FakeRenderer(m);

VoxelEngine.Tests/WorldGen/CaveCarverTests.cs

@@ -0,0 +1,186 @@
+using OpenTK.Mathematics;
+using VoxelEngine.Core;
+using VoxelEngine.World.Blocks;
+using VoxelEngine.World.Chunk;
+using VoxelEngine.World.WorldGen;
+using Xunit;
+
+namespace VoxelEngine.Tests.WorldGen;
+
+public class CaveCarverTests
+{
+    private static readonly BlockRegistry Blocks = new();
+    private static readonly Configuration Cfg = new();
+
+    private static Chunk MakeStoneChunk()
+    {
+        Chunk c = new();
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+            c[x, y, z] = Blocks.Stone.Id;
+        return c;
+    }
+
+    [Fact]
+    public void Carve_IsNoOpOnAirChunk()
+    {
+        var carver = new CaveCarver(seed: 42, Blocks, Cfg);
+        Chunk c = new(); // all-air by default
+
+        carver.Carve(c, new Vector3i(0, 4, 0));
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(Blocks.Air.Id, c[x, y, z]);
+    }
+
+    [Fact]
+    public void NoiseCaves_OnlyConvertsSolidToAir_NeverWaterNeverOtherBlocks()
+    {
+        var carver = new CaveCarver(seed: 42, Blocks, Cfg);
+        Chunk c = MakeStoneChunk();
+
+        // Plant some water and air voxels we expect untouched.
+        c[1, 1, 1] = Blocks.Water.Id;
+        c[2, 2, 2] = Blocks.Air.Id;
+
+        carver.CarveNoiseCaves(c, new Vector3i(0, 4, 0));
+
+        Assert.Equal(Blocks.Water.Id, c[1, 1, 1]); // water survived
+        Assert.Equal(Blocks.Air.Id,   c[2, 2, 2]); // air survived
+
+        // Spot-check that everywhere else is either Stone or Air (no other blocks).
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+        {
+            ushort id = c[x, y, z];
+            Assert.True(
+                id == Blocks.Stone.Id || id == Blocks.Air.Id || id == Blocks.Water.Id,
+                $"unexpected block id {id} at ({x},{y},{z})");
+        }
+    }
+
+    [Fact]
+    public void NoiseCaves_IsDeterministic_ForSameSeedAndChunkPos()
+    {
+        var carver1 = new CaveCarver(seed: 1234, Blocks, Cfg);
+        var carver2 = new CaveCarver(seed: 1234, Blocks, Cfg);
+        Chunk a = MakeStoneChunk();
+        Chunk b = MakeStoneChunk();
+
+        carver1.CarveNoiseCaves(a, new Vector3i(2, 4, 3));
+        carver2.CarveNoiseCaves(b, new Vector3i(2, 4, 3));
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(a[x, y, z], b[x, y, z]);
+    }
+
+    [Fact]
+    public void NoiseCaves_RespectsBedrockFloor_DoesNotCarveBelowY1()
+    {
+        // ChunkPos.Y = 0 means worldY ranges 0..15. We require Y=0 stays solid.
+        var carver = new CaveCarver(seed: 42, Blocks, Cfg);
+        Chunk c = MakeStoneChunk();
+
+        carver.CarveNoiseCaves(c, new Vector3i(0, 0, 0));
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(Blocks.Stone.Id, c[x, 0, z]); // worldY = 0 is bedrock
+    }
+
+    [Fact]
+    public void NoiseCaves_SeamContinuity_AdjacentChunksAgreeAtBoundary()
+    {
+        var carver = new CaveCarver(seed: 7, Blocks, Cfg);
+        Chunk c1 = MakeStoneChunk();
+        Chunk c2 = MakeStoneChunk();
+
+        carver.CarveNoiseCaves(c1, new Vector3i(0, 4, 0));
+        carver.CarveNoiseCaves(c2, new Vector3i(1, 4, 0));
+
+        int airAtSeamC1 = 0, airAtSeamC2 = 0;
+        for (int y = 1; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+        {
+            if (c1[15, y, z] == Blocks.Air.Id) airAtSeamC1++;
+            if (c2[0,  y, z] == Blocks.Air.Id) airAtSeamC2++;
+        }
+        // Sanity: noise threshold = -0.3 yields some carved cells in each.
+        Assert.True(airAtSeamC1 > 0, "c1 seam column had no air — carve too sparse?");
+        Assert.True(airAtSeamC2 > 0, "c2 seam column had no air — carve too sparse?");
+    }
+
+    [Fact]
+    public void WormCaves_IsDeterministic_ForSameSeedAndChunkPos()
+    {
+        var c1 = new CaveCarver(seed: 999, Blocks, Cfg);
+        var c2 = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk a = MakeStoneChunk();
+        Chunk b = MakeStoneChunk();
+
+        c1.CarveWormCaves(a, new Vector3i(0, 4, 0));
+        c2.CarveWormCaves(b, new Vector3i(0, 4, 0));
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(a[x, y, z], b[x, y, z]);
+    }
+
+    [Fact]
+    public void WormCaves_OnlyConvertsSolidToAir_NeverWater()
+    {
+        var carver = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk c = MakeStoneChunk();
+        // Set every voxel along a diagonal to water — must survive.
+        for (int i = 0; i < Chunk.Size; i++)
+            c[i, i, i] = Blocks.Water.Id;
+
+        carver.CarveWormCaves(c, new Vector3i(0, 4, 0));
+
+        for (int i = 0; i < Chunk.Size; i++)
+            Assert.Equal(Blocks.Water.Id, c[i, i, i]);
+    }
+
+    [Fact]
+    public void WormCaves_RespectsBedrockFloor()
+    {
+        var carver = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk c = MakeStoneChunk();
+
+        carver.CarveWormCaves(c, new Vector3i(0, 0, 0)); // worldY = 0..15
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(Blocks.Stone.Id, c[x, 0, z]); // bedrock untouched
+    }
+
+    [Fact]
+    public void WormCaves_SeamContinuity_VoxelAtSharedWorldCoord_IsSame()
+    {
+        var carver = new CaveCarver(seed: 999, Blocks, Cfg);
+        Chunk c1 = MakeStoneChunk();
+        Chunk c2 = MakeStoneChunk();
+
+        carver.CarveWormCaves(c1, new Vector3i(0, 4, 0));
+        carver.CarveWormCaves(c2, new Vector3i(1, 4, 0));
+
+        int airC1Seam = 0, airC2Seam = 0;
+        for (int y = 1; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+        {
+            if (c1[15, y, z] == Blocks.Air.Id) airC1Seam++;
+            if (c2[0,  y, z] == Blocks.Air.Id) airC2Seam++;
+        }
+        bool bothEmpty = airC1Seam == 0 && airC2Seam == 0;
+        bool bothCarved = airC1Seam > 0 && airC2Seam > 0;
+        Assert.True(bothEmpty || bothCarved,
+            $"seam mismatch: c1={airC1Seam}, c2={airC2Seam}");
+    }
+}

VoxelEngine.Tests/WorldGen/WorldGeneratorTests.cs

@@ -1,4 +1,5 @@
 using OpenTK.Mathematics;
+using VoxelEngine.Core;
 using VoxelEngine.World.Blocks;
 using VoxelEngine.World.Chunk;
 using VoxelEngine.World.WorldGen;
@@ -58,8 +59,8 @@ public class WorldGeneratorTests
     [Fact]
     public void Generate_IsDeterministic()
     {
-        var gen1 = new WorldGenerator(99, Blocks);
+        var gen1 = new WorldGenerator(99, Blocks, new Configuration());
-        var gen2 = new WorldGenerator(99, Blocks);
+        var gen2 = new WorldGenerator(99, Blocks, new Configuration());
         Chunk a = gen1.Generate(new Vector3i(0, 4, 0));
         Chunk b = gen2.Generate(new Vector3i(0, 4, 0));
         for (int x = 0; x < Chunk.Size; x++)
@@ -67,4 +68,32 @@ public class WorldGeneratorTests
         for (int z = 0; z < Chunk.Size; z++)
             Assert.Equal(a[x, y, z], b[x, y, z]);
     }
+
+    [Fact]
+    public void Generate_AppliesCaves_ProducesAirVoxelsBelowSurface()
+    {
+        var gen = new WorldGenerator(seed: 12345, Blocks, new Configuration());
+        // A chunk well below typical surface height — guaranteed mostly stone before carving.
+        Chunk c = gen.Generate(new Vector3i(0, 1, 0)); // worldY = 16..31
+
+        int airCount = 0;
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int y = 0; y < Chunk.Size; y++)
+        for (int z = 0; z < Chunk.Size; z++)
+            if (c[x, y, z] == Blocks.Air.Id) airCount++;
+
+        Assert.True(airCount > 0,
+            "Deep chunk had zero air voxels after generation — caves not running?");
+    }
+
+    [Fact]
+    public void Generate_PreservesBedrockFloor_Y0_IsStone()
+    {
+        var gen = new WorldGenerator(seed: 12345, Blocks, new Configuration());
+        Chunk c = gen.Generate(new Vector3i(0, 0, 0)); // worldY = 0..15
+
+        for (int x = 0; x < Chunk.Size; x++)
+        for (int z = 0; z < Chunk.Size; z++)
+            Assert.Equal(Blocks.Stone.Id, c[x, 0, z]);
+    }
 }

VoxelEngine.Tests/WorldGen/WormHashTests.cs

@@ -0,0 +1,40 @@
+using VoxelEngine.World.WorldGen;
+using Xunit;
+
+namespace VoxelEngine.Tests.WorldGen;
+
+public class WormHashTests
+{
+    [Fact]
+    public void Hash_IsDeterministic_ForSameInputs()
+    {
+        uint a = WormHash.Hash(3, -2, 7, seed: 1337);
+        uint b = WormHash.Hash(3, -2, 7, seed: 1337);
+        Assert.Equal(a, b);
+    }
+
+    [Fact]
+    public void Hash_DiffersForDifferentCells()
+    {
+        uint a = WormHash.Hash(3, -2, 7, seed: 1337);
+        uint b = WormHash.Hash(3, -2, 8, seed: 1337);
+        Assert.NotEqual(a, b);
+    }
+
+    [Fact]
+    public void Hash_DiffersForDifferentSeeds()
+    {
+        uint a = WormHash.Hash(3, -2, 7, seed: 1337);
+        uint b = WormHash.Hash(3, -2, 7, seed: 9999);
+        Assert.NotEqual(a, b);
+    }
+
+    [Fact]
+    public void Hash_HandlesNegativeCoords()
+    {
+        // Just shouldn't throw and shouldn't collide trivially with the positive case.
+        uint a = WormHash.Hash(-1, -1, -1, seed: 1);
+        uint b = WormHash.Hash(1, 1, 1, seed: 1);
+        Assert.NotEqual(a, b);
+    }
+}

VoxelEngine.csproj

@@ -22,4 +22,8 @@
         </None>
     </ItemGroup>
 
+    <ItemGroup>
+        <InternalsVisibleTo Include="VoxelEngine.Tests" />
+    </ItemGroup>
+
 </Project>

World/Blocks/BlockClasses/CoalOreBlock.cs

@@ -0,0 +1,10 @@
+namespace VoxelEngine.World.Blocks;
+
+public sealed class CoalOreBlock : IBlock
+{
+    public ushort Id => 7;
+    public string Name => "Coal Ore";
+    public bool IsOpaque => true;
+    public bool IsSolid => true;
+    public TileCoord GetTextureTile(BlockFace face) => new(0, 0); // TODO: Add Texture
+}

World/Blocks/BlockClasses/DiamondOreBlock.cs

@@ -0,0 +1,10 @@
+namespace VoxelEngine.World.Blocks;
+
+public sealed class DiamondOreBlock : IBlock
+{
+    public ushort Id => 10;
+    public string Name => "Diamond Ore";
+    public bool IsOpaque => true;
+    public bool IsSolid => true;
+    public TileCoord GetTextureTile(BlockFace face) => new(0, 0); // TODO: Add Texture
+}

World/Blocks/BlockClasses/GoldOreBlock.cs

@@ -0,0 +1,10 @@
+namespace VoxelEngine.World.Blocks;
+
+public sealed class GoldOreBlock : IBlock
+{
+    public ushort Id => 9;
+    public string Name => "Gold Ore";
+    public bool IsOpaque => true;
+    public bool IsSolid => true;
+    public TileCoord GetTextureTile(BlockFace face) => new(0, 0); // TODO: Add Texture
+}

World/Blocks/BlockClasses/IronOreBlock.cs

@@ -0,0 +1,10 @@
+namespace VoxelEngine.World.Blocks;
+
+public sealed class IronOreBlock : IBlock
+{
+    public ushort Id => 8;
+    public string Name => "Iron Ore";
+    public bool IsOpaque => true;
+    public bool IsSolid => true;
+    public TileCoord GetTextureTile(BlockFace face) => new(0, 0); // TODO: Add Texture
+}

World/Blocks/BlockRegistry.cs

@@ -11,12 +11,18 @@ public sealed class BlockRegistry
     public SandBlock       Sand       { get; } = new();
     public SnowBlock       Snow       { get; } = new();
     public WaterBlock      Water      { get; } = new();
+    public CoalOreBlock    CoalOre    { get; } = new();
+    public IronOreBlock    IronOre    { get; } = new();
+    public GoldOreBlock    GoldOre    { get; } = new();
+    public DiamondOreBlock DiamondOre { get; } = new();
 
     public BlockRegistry()
     {
-        // Index by id. Order does not matter; slot = block.Id.
         IBlock[] blocks = new IBlock[]
-            { this.Air, this.Stone, this.Dirt, this.Grass, this.Sand, this.Snow, this.Water };
+        {
+            this.Air, this.Stone, this.Dirt, this.Grass, this.Sand, this.Snow, this.Water,
+            this.CoalOre, this.IronOre, this.GoldOre, this.DiamondOre,
+        };
         this._byId = new IBlock[blocks.Length];
         foreach (IBlock block in blocks)
         {

World/Streaming/ChunkStreamer.cs

@@ -122,9 +122,12 @@ public sealed class ChunkStreamer : IDisposable
             if (this._failed.Contains(pos)) continue;
             if (this._tracked.Add(pos))
             {
-                int priority = (pos.X - p.X) * (pos.X - p.X)
+                int dx = pos.X - p.X;
-                             + (pos.Y - p.Y) * (pos.Y - p.Y)
+                int dy = pos.Y - p.Y;
-                             + (pos.Z - p.Z) * (pos.Z - p.Z);
+                int dz = pos.Z - p.Z;
+                int priority = dx * dx
+                             + dz * dz
+                             + dy * dy * this._cfg.VerticalPriorityWeight;
                 this._pendingLoad.Enqueue(pos, priority);
             }
         }
@@ -207,8 +210,15 @@ public sealed class ChunkStreamer : IDisposable
         if (this._renderers.TryGetValue(result.Pos, out IChunkRenderer? old))
         {
             old.Dispose();
+            this._renderers.Remove(result.Pos);
         }
+        // Skip renderer allocation for empty meshes (pure-air chunks above
+        // terrain, or chunks whose every face culls). The chunk still counts
+        // as ready — DrawAll's iteration over _renderers naturally no-ops.
+        if (result.Mesh.Length > 0)
+        {
             this._renderers[result.Pos] = this._rendererFactory(result.Mesh);
+        }
         this._ready.Add(result.Pos);
         this._dirty.Remove(result.Pos);
 

World/WorldGen/CaveCarver.cs

@@ -0,0 +1,178 @@
+using OpenTK.Mathematics;
+using VoxelEngine.Core;
+using VoxelEngine.World.Blocks;
+using VoxelChunk = VoxelEngine.World.Chunk.Chunk;
+
+namespace VoxelEngine.World.WorldGen;
+
+// Carves caves into an already-terrain-filled chunk. Stateless after
+// construction; the carve methods are pure functions of (chunk, chunkPos).
+// Safe to share across worker threads.
+public sealed class CaveCarver
+{
+    private readonly int _seed;
+    private readonly BlockRegistry _blocks;
+    private readonly Configuration _cfg;
+    private readonly FastNoiseLite _caveNoise;
+    private readonly FastNoiseLite _wormDirNoise;
+
+    public CaveCarver(int seed, BlockRegistry blocks, Configuration cfg)
+    {
+        this._seed = seed;
+        this._blocks = blocks;
+        this._cfg = cfg;
+
+        this._caveNoise = new FastNoiseLite(seed + 100);
+        this._caveNoise.SetNoiseType(FastNoiseLite.NoiseType.OpenSimplex2);
+        this._caveNoise.SetFrequency(cfg.CaveNoiseFrequency);
+
+        this._wormDirNoise = new FastNoiseLite(seed + 200);
+        this._wormDirNoise.SetNoiseType(FastNoiseLite.NoiseType.OpenSimplex2);
+        this._wormDirNoise.SetFrequency(0.05f);
+    }
+
+    public void Carve(VoxelChunk chunk, Vector3i chunkPos)
+    {
+        this.CarveNoiseCaves(chunk, chunkPos);
+        this.CarveWormCaves(chunk, chunkPos);
+    }
+
+    // Per-voxel 3D simplex threshold. Public for direct testability,
+    // matching the pattern of WorldGenerator.BlockAt.
+    public void CarveNoiseCaves(VoxelChunk chunk, Vector3i chunkPos)
+    {
+        int baseX = chunkPos.X * VoxelChunk.Size;
+        int baseY = chunkPos.Y * VoxelChunk.Size;
+        int baseZ = chunkPos.Z * VoxelChunk.Size;
+
+        for (int x = 0; x < VoxelChunk.Size; x++)
+        for (int y = 0; y < VoxelChunk.Size; y++)
+        for (int z = 0; z < VoxelChunk.Size; z++)
+        {
+            int worldY = baseY + y;
+            if (worldY <= 0) continue;
+
+            ushort id = chunk[x, y, z];
+            if (id == this._blocks.Air.Id) continue;
+            if (id == this._blocks.Water.Id) continue;
+
+            float density = this._caveNoise.GetNoise(baseX + x, worldY, baseZ + z);
+            if (density < this._cfg.CaveNoiseThreshold)
+            {
+                chunk[x, y, z] = this._blocks.Air.Id;
+            }
+        }
+    }
+
+    public void CarveWormCaves(VoxelChunk chunk, Vector3i chunkPos)
+    {
+        int cellSize = this._cfg.WormCellSize;
+        int radius = (int)Math.Ceiling((double)this._cfg.WormMaxLength / cellSize) + 1;
+
+        int chunkBaseX = chunkPos.X * VoxelChunk.Size;
+        int chunkBaseY = chunkPos.Y * VoxelChunk.Size;
+        int chunkBaseZ = chunkPos.Z * VoxelChunk.Size;
+
+        int chunkCellX = CaveCarver.FloorDiv(chunkBaseX, cellSize);
+        int chunkCellY = CaveCarver.FloorDiv(chunkBaseY, cellSize);
+        int chunkCellZ = CaveCarver.FloorDiv(chunkBaseZ, cellSize);
+
+        for (int cdx = -radius; cdx <= radius; cdx++)
+        for (int cdy = -radius; cdy <= radius; cdy++)
+        for (int cdz = -radius; cdz <= radius; cdz++)
+        {
+            int cellX = chunkCellX + cdx;
+            int cellY = chunkCellY + cdy;
+            int cellZ = chunkCellZ + cdz;
+
+            uint h = WormHash.Hash(cellX, cellY, cellZ, this._seed);
+            if ((h % 1000) >= (uint)this._cfg.WormSpawnProbabilityPermille) continue;
+
+            // Hash bit layout: [ox:6][oy:6][oz:6][theta:8][phi:6] = 32 bits
+            float ox = (h         & 0x3F) / 64f * cellSize;
+            float oy = ((h >> 6)  & 0x3F) / 64f * cellSize;
+            float oz = ((h >> 12) & 0x3F) / 64f * cellSize;
+            Vector3 pos = new(cellX * cellSize + ox,
+                              cellY * cellSize + oy,
+                              cellZ * cellSize + oz);
+
+            float theta = ((h >> 18) & 0xFF) / 255f * MathF.Tau;
+            float phi   = (((h >> 26) & 0x3F) / 63f * 2f - 1f) * 0.3f * MathF.PI;
+            Vector3 dir = new(
+                MathF.Cos(theta) * MathF.Cos(phi),
+                MathF.Sin(phi),
+                MathF.Sin(theta) * MathF.Cos(phi));
+            dir = Vector3.Normalize(dir);
+
+            this.TraceAndCarveWorm(chunk, chunkPos, pos, dir);
+        }
+    }
+
+    private void TraceAndCarveWorm(VoxelChunk chunk, Vector3i chunkPos,
+                                   Vector3 startPos, Vector3 startDir)
+    {
+        int maxLen = this._cfg.WormMaxLength;
+        float minR = this._cfg.WormMinRadius;
+        float maxR = this._cfg.WormMaxRadius;
+
+        Vector3 pos = startPos;
+        Vector3 dir = startDir;
+
+        for (int step = 0; step < maxLen; step++)
+        {
+            float t = step / (float)maxLen;
+            float bulgeT = 0.5f + 0.5f * MathF.Sin(t * MathF.Tau * 3f);
+            float r = minR + (maxR - minR) * bulgeT;
+
+            this.CarveSphere(chunk, chunkPos, pos, r);
+
+            float px = this._wormDirNoise.GetNoise(pos.X,        pos.Y, pos.Z);
+            float py = this._wormDirNoise.GetNoise(pos.X + 100f, pos.Y, pos.Z);
+            float pz = this._wormDirNoise.GetNoise(pos.X,        pos.Y, pos.Z + 100f);
+            Vector3 perturbation = new(px, py, pz);
+            dir = Vector3.Normalize(dir + perturbation * 0.3f);
+
+            dir = new Vector3(dir.X, dir.Y * 0.7f, dir.Z);
+            dir = Vector3.Normalize(dir);
+
+            pos += dir;
+        }
+    }
+
+    private void CarveSphere(VoxelChunk chunk, Vector3i chunkPos, Vector3 center, float r)
+    {
+        int baseX = chunkPos.X * VoxelChunk.Size;
+        int baseY = chunkPos.Y * VoxelChunk.Size;
+        int baseZ = chunkPos.Z * VoxelChunk.Size;
+
+        int xMin = Math.Max(0, (int)MathF.Floor(center.X - r) - baseX);
+        int xMax = Math.Min(VoxelChunk.Size - 1, (int)MathF.Ceiling(center.X + r) - baseX);
+        int yMin = Math.Max(0, (int)MathF.Floor(center.Y - r) - baseY);
+        int yMax = Math.Min(VoxelChunk.Size - 1, (int)MathF.Ceiling(center.Y + r) - baseY);
+        int zMin = Math.Max(0, (int)MathF.Floor(center.Z - r) - baseZ);
+        int zMax = Math.Min(VoxelChunk.Size - 1, (int)MathF.Ceiling(center.Z + r) - baseZ);
+
+        float r2 = r * r;
+
+        for (int x = xMin; x <= xMax; x++)
+        for (int y = yMin; y <= yMax; y++)
+        for (int z = zMin; z <= zMax; z++)
+        {
+            int worldY = baseY + y;
+            if (worldY <= 0) continue;
+
+            float vx = baseX + x + 0.5f;
+            float vy = baseY + y + 0.5f;
+            float vz = baseZ + z + 0.5f;
+            float dx = vx - center.X, dy = vy - center.Y, dz = vz - center.Z;
+            if (dx * dx + dy * dy + dz * dz > r2) continue;
+
+            ushort id = chunk[x, y, z];
+            if (id == this._blocks.Air.Id) continue;
+            if (id == this._blocks.Water.Id) continue;
+            chunk[x, y, z] = this._blocks.Air.Id;
+        }
+    }
+
+    private static int FloorDiv(int a, int b) => a >= 0 ? a / b : -(((-a) + b - 1) / b);
+}

World/WorldGen/WorldGenerator.cs

@@ -1,4 +1,5 @@
 using OpenTK.Mathematics;
+using VoxelEngine.Core;
 using VoxelEngine.World.Blocks;
 using VoxelChunk = VoxelEngine.World.Chunk.Chunk;
 
@@ -12,8 +13,9 @@ public sealed class WorldGenerator
     private readonly BlockRegistry _blocks;
     private readonly BiomeMap _biomeMap;
     private readonly TerrainSampler _terrain;
+    private readonly CaveCarver _caves;
 
-    public WorldGenerator(int seed, BlockRegistry blocks)
+    public WorldGenerator(int seed, BlockRegistry blocks, Configuration cfg)
     {
         this._blocks = blocks;
         NoiseSource noise = new(seed);
@@ -21,6 +23,7 @@ public sealed class WorldGenerator
         BiomeRegistry biomes = new(seed, blocks);
         this._biomeMap = new BiomeMap(noise, cells, biomes);
         this._terrain = new TerrainSampler(noise, this._biomeMap);
+        this._caves = new CaveCarver(seed, blocks, cfg);
     }
 
     public int SurfaceHeightAt(int worldX, int worldZ) => this._terrain.HeightAt(worldX, worldZ);
@@ -46,10 +49,11 @@ public sealed class WorldGenerator
                 chunk[x, y, z] = WorldGenerator.BlockAt(worldY, height, biome, this._blocks);
             }
         }
+
+        this._caves.Carve(chunk, chunkPos);
         return chunk;
     }
 
-    // Pure column fill rule, extracted for testability.
     public static ushort BlockAt(int worldY, int surfaceHeight, IBiome biome, BlockRegistry blocks)
     {
         if (worldY > surfaceHeight)

World/WorldGen/WormHash.cs

@@ -0,0 +1,21 @@
+namespace VoxelEngine.World.WorldGen;
+
+// Deterministic 32-bit mixing hash for worm-cell coordinates.
+// Cell coords can be negative; cast through unchecked to preserve bit pattern.
+internal static class WormHash
+{
+    public static uint Hash(int cellX, int cellY, int cellZ, int seed)
+    {
+        unchecked
+        {
+            uint h = (uint)seed;
+            h ^= (uint)cellX * 73856093u;
+            h ^= (uint)cellY * 19349663u;
+            h ^= (uint)cellZ * 83492791u;
+            h ^= h >> 13;
+            h *= 0x5bd1e995u;
+            h ^= h >> 15;
+            return h;
+        }
+    }
+}