Introduce a Mesa pipe_resource-style PipeResource that owns a GL buffer's bytes
and its backend GPU resource, abstracting WHERE the authoritative bytes live:
- Shadow mode (non-persistent buffers): a CPU Vector; the backend keeps its own
GPU copy in sync via BufferBackendOps, exactly as before.
- Persistent mode (coherent GL_MAP_PERSISTENT maps): the backend's host-visible,
COHERENT, persistently-mapped GPU memory is the single source of truth. The app
writes into it directly, every reader resolves against it, and NO per-write
backend transfer happens. The CPU shadow is released.
BufferObject no longer owns a raw shadow Vector; it holds a PipeResource and
exposes one accessor, MappedData(), that all readers go through. Every buffer-data
consumer (UBO payload, PBO texture upload, indirect draws, resident/streamed
uploads, both backends) was migrated from GetDataReadOnly()->data() to
MappedData(), so a persistent buffer's readers see GPU memory - not a stale
shadow. That stale-shadow inconsistency is what corrupted rendering (wrong UBOs ->
misplaced/"lost" vertices) in the first zero-copy attempt (625c8a6, reverted in
896cafc); routing every consumer through one accessor makes it structurally
impossible.
Backends provide the map via BufferBackendOps::AcquirePersistentMap:
- DirectVulkan: a HOST_VISIBLE|HOST_COHERENT (required, not just requested),
persistently mapped resident VkBuffer carrying every usage, seeded from the
shadow, never recreated; AcquireResidentSlice binds it directly.
- DirectGLES: EXT_buffer_storage immutable persistent+coherent glMapBufferRange,
falling back to the shadow when the extension is absent.
Fixes the ~7GB GpuMemory OOM + 100%-CPU/ANR running modern Blaze3D Minecraft on
both Magma and Espryt (per-draw whole-buffer re-upload of the coherent persistent
ring buffer), without the coherency/stale-read hazards of the reverted attempt.
BufferTest: zero-copy stress guard (15,360 draws -> 0 per-draw transfers, and every
reader resolves to GPU memory) + a shadow-fallback test. Host suite: 203/203 pass.
Device verification pending.
swung0x48