GeometryBufferArena class Geometry

Packs immutable mesh uploads into shared GPU buffers.

Pass one arena to many MeshGeometry objects to avoid one GPU allocation per mesh. Uploads are bump-allocated into fixed-size blocks, filling the first block with room, while uploads larger than blockSizeInBytes receive a dedicated block. Geometry buffer views retain their blocks, so the arena itself need not outlive the meshes.

The arena never reclaims space. An allocation stays reserved for as long as the arena is alive, whether or not the geometry that used it still exists, so an arena only ever grows. Use it for geometry loaded or generated in batches with a lifetime the arena can share (a level, a screen), and drop the arena with them. Geometry rebuilt every frame belongs in GeometryStorage.updatable, which reuses its buffers in place; an updatable geometry cannot use an arena.