Replaces the T7-temporary default! MeshData placeholder. Streamer
now takes Func<uint, LoadedLandblock?, LandblockMeshData?> at
construction; the worker calls it after _loadLandblock succeeds and
passes the pre-built mesh into LandblockStreamResult.Loaded.
GameWindow's buildMeshOrNull factory takes the already-loaded
LoadedLandblock (lb.Heightmap is the LandBlock dat object), so no
additional dat read is needed — _heightTable and _blendCtx are
read-only after init, _surfaceCache is ConcurrentDictionary (T9).
Zero dat lock needed inside the mesh-build closure.
StreamingController._applyTerrain delegate signature widened to
Action<LoadedLandblock, LandblockMeshData> so the pre-built mesh
flows render-thread-side via the Loaded result. ApplyLoadedTerrainLocked
now accepts meshData and calls _terrain.AddLandblock directly, skipping
the per-frame LandblockMesh.Build that previously ran on the render
thread (~5ms per LB at radius=12 first traversal).
StreamingControllerTests updated: all four applyTerrain lambdas
adapted to the two-arg Action signature.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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