119 lines
6.5 KiB
Markdown
119 lines
6.5 KiB
Markdown
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# occ-export flake: SwiftShader congestion → GAL recovery cascade (fixed by GL-stack swap)
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Status 2026-07-16: fully root-caused with page-level canvas/context telemetry +
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temp C++ instrumentation in a local docker rig. **Final remedy: CI Chromium
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now runs WebGL on ANGLE → Mesa llvmpipe instead of SwiftShader**
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(`tests/playwright.config.ts`, `CHROMIUM_CI_ARGS`) — the same software-GL
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stack the Firefox projects use, where none of this ever happened. Four small
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product fixes found along the way were kept (below); everything else was
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deliberately **not** hardened — the trigger cannot occur outside congested
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SwiftShader.
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## Symptom
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`chromium/occ-export-{dialog,done}.png` bistable on CI only: the board behind
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the modal STEP-export dialog flips between runs (~1.2% changedRatio both
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directions). Firefox (llvmpipe) never affected.
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## The causal chain (every step observed in the rig)
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1. **Transient SwiftShader failure at the first post-board-load draw**
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(~10-15% of instances at `REPEAT=40-80 WORKERS=4`): `DoRePaint threw:
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Requested render buffer size is not supported`, plus LRU context evictions
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the moment a 3rd context appears (21/80 runs; the usual victim is a leaked
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hidden 881×159 startup GAL canvas, so the `CONTEXT_LOST_WEBGL` line alone
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was harmless). No flag stops it — `--max-active-webgl-contexts=64`,
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`--force-gpu-mem-available-mb=4096`, `--disable-low-end-device-mode`,
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`--disable-gpu-driver-bug-workarounds` all verified present and useless.
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2. **`recoverFromGalError` attempt 1** (`common/draw_panel_gal.cpp:205`)
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destroys + recreates the WebGL GAL (board canvas `glcanvas-2` →
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`glcanvas-3`).
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3. **Attempt 1 then always failed** on stale cross-context GL state:
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- static `g_fontTexture` bound on the new context → `INVALID_OPERATION:
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bindTexture: object does not belong to this context` → `checkGlError`
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throw (**fixed — kept**: per-instance `m_fontTexture`,
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`common/gal/webgl/webgl_gal.{cpp,h}`);
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- sticky GL error flags left by the old GAL's teardown (its `LockCtx`
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targets a lost context, so the deletes land on the current one) →
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the fresh GAL's first `checkGlError` ("generating vertices buffer:
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invalid enum") misattributed the leftover and threw (**fixed — kept**:
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drain `glGetError()` before first-frame `init()` in
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`WEBGL_GAL::BeginDrawing`). With both fixes, reinit-on-WebGL succeeds
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(validated: 0 Cairo fallbacks / 60 after, vs 100% of recoveries before).
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4. **Attempt 2 = silent permanent Cairo fallback** (`GAL_FALLBACK ==
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GAL_TYPE_CAIRO` on emscripten, dialog suppressed). Cairo renders the board
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through the wx software path — shots LOOK painted but are a different
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engine → subtle whole-board diffs vs the WebGL baseline. **This engine
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flip IS the original "~1.2% changedRatio both directions" flake.**
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`FULLSCREEN_QUAD` (singleton VAOs) is the same static-GL-state disease and
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produced `bindVertexArray: object does not belong` + one wasm abort in
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rare runs — NOT fixed (unreachable once recovery never triggers; noted
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here in case in-app recovery robustness is ever wanted).
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5. **wx paint-flag races turned it into a stuck-blank board** (both
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**fixed — kept**, `wxwidgets/src/wasm/window.cpp`):
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- `Invalidate` early-out skipped the upward walk while the sweep can
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strand a window "flags set, ancestors clear" → every later `Refresh()`
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swallowed. Fix: always propagate to the top.
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- `PaintSelf`/`PaintChildren` cleared the dirty flags AFTER dispatching
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paint, so an `Invalidate` issued reentrantly from inside a paint handler
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(canvas recreated mid-frame, board-load refresh mid-sweep) was clobbered
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with nothing re-issuing it. Fix: `DoPaint` snapshots + clears both flags
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BEFORE dispatching. (Pre-fix rigs showed stuck half-painted toolbars —
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this is a real production-reachable bug, not a CI artifact.)
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One rare mode ("grid-mode": board data loaded, UI painted, canvas alive,
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items never drawn, zoom-to-fit doesn't help; VIEW had all 464 items and
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the same Clear/DisplayBoard ordering as healthy runs) was still being
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diagnosed when the GL-stack swap made it — and everything above —
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unobservable: **80/80 runs clean on llvmpipe**, all dialog shots pixel-
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identical (single 55.65% ratio value across all 80; SwiftShader scattered
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over 55.5–56.8%).
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## The fix that ships
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`CHROMIUM_CI_ARGS` = `--use-gl=angle --use-angle=gl --ignore-gpu-blocklist`
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(CI-gated). Requirements, all already present on CI: an X display
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(`xvfb-run -a` wraps the whole e2e step) and Mesa (installed by
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`playwright install --with-deps`). `--ignore-gpu-blocklist` is mandatory —
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llvmpipe is on Chromium's software-GL blocklist and WebGL silently reports
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unavailable without it (the exact analog of the Firefox projects'
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`webgl.force-enabled`). Headless works; headed is NOT needed.
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Renderer-string ground truth (Chrome falls back silently — always verify):
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`gl.getExtension('WEBGL_debug_renderer_info')` must report
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`ANGLE (Mesa, llvmpipe …)`, not SwiftShader.
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Consequence: chromium renders shift slightly → the chromium baseline set
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must be re-promoted once from the first green CI run
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(`cd tests && npm run screenshots:promote -- --run <id>`).
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## Test-side hardening (kept, independent)
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Popup menu items register in the element registry progressively while the
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menu paints; a coarse ">3 menuitems" gate + single-shot `clickMenuItem` races
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(4–8/20 under contention, pre-existing). Rule (tests/TESTING.md): wait for the
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specific item via `waitForRenderedByLabel(page, label, { elementType:
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'menuitem' })` before every `clickMenuItem`. Applied to `occ-export`,
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`occ-export-models`, `3d-viewer-models`, `load-pcb`; `pl_editor` already did
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this; `clickMenuItemByText` waits internally.
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## Open leads (not blocking)
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- The leaked hidden 881×159 startup GAL canvas: destroying it would free a
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context + memory.
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- If in-app GL-error recovery ever matters on real GPUs: fix the
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`FULLSCREEN_QUAD` singleton VAOs (per-instance like the font texture) and
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audit remaining cross-context statics.
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## Repro rig (for revalidation)
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Docker `mcr.microsoft.com/playwright:v1.57.0-jammy`, worktree bind-mount,
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container-local node_modules volume, `CI=1`, `xvfb-run -a npx playwright test
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--project=kicad-chromium --repeat-each=N --workers=4` with a temp spec that
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loads `pic_programmer`, screenshots board-load / settled / export-dialog /
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post-poke, and logs the WebGL renderer string + canvas/context telemetry per
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instance. Canaries: `CONTEXT_LOST_WEBGL`, `does not belong to this context`,
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board-strip pixel ratio of the shots.
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