feat: add streaming primitives (IChunkRenderer, IJobExecutor, NeighborSnapshots, ChunkJob)

World/Streaming/ChunkJob.cs

@@ -0,0 +1,21 @@
+using OpenTK.Mathematics;
+using VoxelEngine.World.Chunk;
+
+namespace VoxelEngine.World.Streaming;
+
+// Job dispatched to an IJobExecutor. For a fresh load, ExistingChunk is null
+// and the worker generates + applies diff + meshes. For a remesh-only job,
+// ExistingChunk holds the chunk and the worker only meshes (no generation).
+internal sealed record ChunkJob(
+    Vector3i Pos,
+    Chunk.Chunk? ExistingChunk,
+    NeighborSnapshots Neighbors,
+    IReadOnlyDictionary<int, ushort>? Diff);
+
+// Posted by the worker back to the main thread via a ConcurrentQueue.
+internal sealed record ChunkJobResult(
+    Vector3i Pos,
+    Chunk.Chunk? Chunk,
+    float[]? Mesh,
+    Exception? Error,
+    bool IsRemeshOnly);

World/Streaming/IChunkRenderer.cs

@@ -0,0 +1,6 @@
+namespace VoxelEngine.World.Streaming;
+
+public interface IChunkRenderer : IDisposable
+{
+    void Draw();
+}

World/Streaming/IJobExecutor.cs

@@ -0,0 +1,15 @@
+namespace VoxelEngine.World.Streaming;
+
+public interface IJobExecutor
+{
+    void Submit(Action work);
+}
+
+public sealed class ThreadPoolJobExecutor : IJobExecutor
+{
+    // Fire-and-forget: the Task is intentionally discarded. The caller's `work`
+    // delegate MUST catch its own exceptions and report them via a dedicated
+    // channel (e.g. ChunkJobResult.Error in the streaming pipeline). Unhandled
+    // exceptions here are silently lost.
+    public void Submit(Action work) => _ = Task.Run(work);
+}

World/Streaming/NeighborSnapshots.cs

@@ -0,0 +1,52 @@
+using VoxelEngine.World.Chunk;
+
+namespace VoxelEngine.World.Streaming;
+
+// Snapshots of the six cardinal neighbor chunks' block arrays, taken on the
+// main thread at job-dispatch time. Each slot is null if that neighbor is not
+// currently loaded. The ChunkMesher reads only these arrays from a worker
+// thread — never the live World.
+public sealed class NeighborSnapshots
+{
+    public ushort[]? NegX { get; }
+    public ushort[]? PosX { get; }
+    public ushort[]? NegY { get; }
+    public ushort[]? PosY { get; }
+    public ushort[]? NegZ { get; }
+    public ushort[]? PosZ { get; }
+
+    // Snapshots take ownership of the arrays passed in. Callers must hand
+    // in fresh copies (not live references into a chunk's _ids buffer) —
+    // the snapshot does NOT copy defensively. This is enforced at the
+    // single call-site in ChunkStreamer.SnapshotNeighbors which allocates
+    // fresh arrays. The arrays must not be mutated after construction.
+    public NeighborSnapshots(
+        ushort[]? negX, ushort[]? posX,
+        ushort[]? negY, ushort[]? posY,
+        ushort[]? negZ, ushort[]? posZ)
+    {
+        this.NegX = negX; this.PosX = posX;
+        this.NegY = negY; this.PosY = posY;
+        this.NegZ = negZ; this.PosZ = posZ;
+    }
+
+    // Returns true if the out-of-chunk position (nx, ny, nz) — exactly one of
+    // which is out of [0, Chunk.Chunk.Size) — is occupied by an opaque block
+    // in the snapshot. Returns false if the relevant neighbor is null.
+    public bool IsOpaqueOutside(int nx, int ny, int nz, Func<ushort, bool> isOpaque)
+    {
+        ushort[]? n;
+        int lx = nx, ly = ny, lz = nz;
+        if (nx < 0)                     { n = this.NegX; lx = Chunk.Chunk.Size - 1; }
+        else if (nx >= Chunk.Chunk.Size)      { n = this.PosX; lx = 0; }
+        else if (ny < 0)                { n = this.NegY; ly = Chunk.Chunk.Size - 1; }
+        else if (ny >= Chunk.Chunk.Size)      { n = this.PosY; ly = 0; }
+        else if (nz < 0)                { n = this.NegZ; lz = Chunk.Chunk.Size - 1; }
+        else if (nz >= Chunk.Chunk.Size)      { n = this.PosZ; lz = 0; }
+        else return false; // not actually outside — shouldn't happen, mesher guards
+
+        if (n == null) return false;
+        int index = (lx * Chunk.Chunk.Size + ly) * Chunk.Chunk.Size + lz;
+        return isOpaque(n[index]);
+    }
+}