VG-Lite scene rejection diagnostics

2026-09-23 UTC, apply/vglite-composition, base 221fa17a462a5396b1e0a39cb9d9b1c69a6e33e2. Source/host follow-up to a coordinator-reported board session with renderer selection but only Pixman replays. This checkpoint itself performs no board action.

Deterministic source finding

Pinned wlroots 0.20.2 types/scene/surface.c:290–318 assigns ordinary Wayland surfaces WLR_COLOR_TRANSFER_FUNCTION_GAMMA22 plus sRGB primaries, even without client color-management requests. types/scene/wlr_scene.c:1529–1556 passes both into the renderer. The current experimental renderer rejects every nonzero transfer function and every nonnull primaries pointer, so every such textured scene is ineligible regardless of target format. This source finding explains one guaranteed rejection; it does not establish the full runtime reason chain.

The initial scene background at types/scene/wlr_scene.c:2574–2578 is black with alpha one, with its clip restricted to uncovered damaged areas. It passes the alpha check. A completely occluded background can have an empty clip. Texture clipping and incomplete redraw remain separate guards. No guard is loosened in this checkpoint, including the default color metadata guard.

Fixed diagnostic schema

At debug logging level, each replay emits VG-Lite decision v=1 with: result, reason, zero-based op (-1 for a pass/target condition), ops, target, dmabuf, numeric format, modifier, planes, stride, offset, and vg_status (SDK status when the first rejection is an SDK call, zero otherwise).

A rejected operation also emits VG-Lite operation v=1, reporting rect alpha, blend and clip rectangle count, or texture alpha/opacity, blend, filter, transform, transfer, presence of primaries, luminance, encoding/range, source and destination boxes, and clip rectangle count. The first rejecting condition wins, except a disabled GPU or absent exact trial flag takes precedence. No device fd, process address, client identity or pixel content is logged.

result=attempt reason=eligible is emitted only after operation/coverage, dma-buf and CPU target-layout checks, immediately before cache handoff and vg_lite_init. It proves reaching the submission path, not a successful GPU operation. result=gpu follows successful completion/cleanup; result=failed records a discarded/quarantined GPU pass. result=pixman records the decision to replay, before Pixman submission; it does not itself claim that fallback submission succeeded. Existing completion and full-pass messages remain available for comparison with previous captures.

Host proof

WLROOTS_SOURCE=/nix/store/r2zcb3d3dgmz09qjaqsy945inal2h41r-source \
VGLITE_SOURCE=/tmp/k230-sdk-vglite-src/buildroot-overlay/package/vg_lite \
  tools/test-vglite-renderer.sh
nix build .#shell-compositor-vglite --no-link --print-out-paths

The sanitizer-backed production-renderer suite passes. Added behavior tests reproduce rejection of the actual scene-default GAMMA22/sRGB tuple, assert the fixed target/operation fields and zero GPU attempts, and distinguish an opaque full clear from alpha-clear and invalid-stride rejection. Injected init/map/ clear errors assert both stage and original numeric SDK status; subsequent cleanup success cannot erase the first error. Existing Pixman pixel comparisons and completion-quarantine tests still pass.

Physical gate: the reserved operator repeats the existing bounded root scene harness with this rebuilt diagnostic Sway, captures its debug journal including decision and operation records, and verifies normal-shell restoration. Interpret attempt, completed GPU frame and actual visible correctness as separate evidence. An eligibility change for scene-default color metadata requires its own narrowly justified behavior/pixel test and board comparison; this checkpoint does not approve arbitrary color-transform bypass.

Cross-build passed with wrapper /nix/store/zdqgq0c3ajqsyjazg6c94bcvb20w6kvj-sway-1.12 and actual unwrapped diagnostic executable /nix/store/a78y0w6zaiyy86dhixgvdfalcj8b5bsc-sway-unwrapped-riscv64-unknown-linux-gnu-1.12/bin/sway. The operator command, after importing that closure, is:

python3 tools/vglite-root-scene-trial.py --seconds 20 \
  --compositor /nix/store/a78y0w6zaiyy86dhixgvdfalcj8b5bsc-sway-unwrapped-riscv64-unknown-linux-gnu-1.12/bin/sway \
  -- <trusted-self-terminating-probe> <probe-arguments>