Fix lavapipe empty-fill snapshots (WG barrier early-return) - #107
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Paid org GPU runners are unavailable after the move to koubaa; use free ubuntu-24.04 with the existing lavapipe setup script. Co-authored-by: Cursor <cursoragent@cursor.com>
Early `return` before GroupMemoryBarrierWithGroupSync in backdrop_dyn (and sibling shaders) prevented the hillis-steele backdrop prefix scan from completing on lavapipe, leaving interior tiles with backdrop=0 so coarse skipped solid fills. Gate work on failed==0 and only return after barrier-heavy sections (or when the exit is workgroup-uniform). Co-authored-by: Mohamed Koubaa <koubaa@users.noreply.github.com>
Lavapipe reports mean ≈ 0.0101 against Metal-era references under the shared 0.0095 budget; raise this scene only to 0.011. Co-authored-by: Mohamed Koubaa <koubaa@users.noreply.github.com>
Co-authored-by: Mohamed Koubaa <koubaa@users.noreply.github.com>
This reverts commit 09252bd.
This reverts commit fa372ca.
Hardware SampleLevel bilinear differs by ±1–2 between Metal and lavapipe; luminance-mask scenes amplify that past the 0.0095 FLIP budget. Snapshots still reflect Vello's explicit 4-tap path — restore that for image atlas reads (atlas remains CPU-premultiplied). Co-authored-by: Mohamed Koubaa <koubaa@users.noreply.github.com>
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Summary
Pixel snapshot tests failed on Linux lavapipe with large empty interiors (FLIP means often 0.3–0.9) while the same scenes passed on macOS Metal. Two separate issues were fixed; FLIP thresholds were not relaxed.
Fix 1 — empty fills (barrier early-return)
In
backdrop_dyn.slang, an earlyreturnwhenbump.failed != 0ran before the hillis-steeleGroupMemoryBarrierWithGroupSyncscan.On lavapipe this prevented the backdrop prefix from completing → interior tiles kept
backdrop=0→coarseskipped solid fills → large empty regions.Same anti-pattern fixed in
tile_alloc.slang,binning.slang, andcoarse.slang.Fix 2 —
image_luminance_mask(±1–2 RGB / FLIP 0.0101)Not an AA threshold issue to paper over. Diff vs Metal-era LFS references:
SampleLevelbilinear, which diverges between Metal and lavapipe; luminance-mask amplifies that past 0.0095Fix: restore Load-based nearest / 4-tap bilinear in
fine.slang(atlas still CPU-premultiplied). Lavapipeimage_luminance_maskmean 0.0101 → 0.00817. Other image scenes also improved (image_sampling~0.004 → ~0.0004).Verification (lavapipe)
snapshot_test_scenes(incl.image_luminance_mask@ 0.0095)Test plan