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punktfunk/crates
enricobuehlerandClaude Opus 4.8 5249d31dfa feat(host/linux): cursor-as-metadata — pointer in gamescope streams, no perf hit
gamescope draws its pointer on a hardware DRM cursor plane that never enters
the framebuffer feeding its PipeWire capture node, so captured frames arrive
cursorless. Rather than force the producer's Embedded full-frame composite,
request the pointer as PipeWire SPA_META_Cursor and composite it ourselves —
a ≤256×256 blit into the encoder-OWNED surface, never the compositor's
read-only dmabuf.

Capture (capture/linux/mod.rs, capture.rs):
- choose_cursor_mode() gates on available_cursor_modes(): Metadata > Embedded
  > Hidden (defaults Embedded on query error — never silently lose the cursor).
  Applied on both the plain and remote-desktop portal paths.
- build_cursor_meta_param() adds a SPA_PARAM_Meta pod requesting SPA_META_Cursor
  (bitmap up to 256x256) to the connect params on every path.
- CursorState parses spa_meta_cursor (id 0 = hidden; position - hotspot; bitmap
  re-read only when bitmap_offset != 0), normalizing RGBA/BGRA/ARGB/ABGR.
  Updated in .process before the corrupted/size-0 skip so cursor-only Mutter
  buffers still track movement.
- CapturedFrame gains cursor: Option<CursorOverlay> (Arc rgba + serial) riding
  the GPU (Dmabuf/Cuda) payloads; the CPU de-pad path composites inline.

GPU composite into each zero-copy backend's owned surface:
- Vulkan Video + PyroWave: folded into the shared rgb2yuv.comp CSC shader —
  cursor sampled and alpha-mixed over RGB before the YUV convert (correct
  chroma, no extra pass). binding 3 (combined image sampler) + 16B push
  constant, per-slot cursor image uploaded only on serial change. spv regenerated.
- CUDA/NVENC: real on-GPU kernel (cursor_blend.cu -> cursor_blend.ptx,
  compute_75 Turing baseline, JIT-forward) with blend_argb/blend_yuv444/
  blend_nv12 (BT.709 limited, matching the shader). Loaded via the hand-rolled
  libcuda fn-table; blended into the ring InputSurface after copy, degrading to
  no-cursor on any failure — never drops a frame.

VAAPI (AMD/Intel fallback) deferred: Vulkan Video already covers those GPUs;
blind libva struct-layout FFI shouldn't ship unverified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-15 17:19:55 +02:00
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