fix(ui): memoise the a11y tree so the paint loop stops re-laying out every frame - #152
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…every frame Since #149 the app runs on go-widgets/window, whose accessibility bridge pulls Scene.A11yElements() on every paint frame, and run.go drives a 60 Hz repaint. Each pull rebuilt the whole accessibility tree, and building it runs a full layout pass — text measurement for every card included. At 60 fps that is a complete feed re-layout 60 times a second on the render thread, pinning a core and freezing the UI even while the app is idle (the spinning process's goroutine dump showed paintFrame -> A11yElements -> A11yTree -> layout -> wrapMeasured with no aggregation in flight). Cache the built tree against the scene's damage sequence (rev): a pull with no intervening state change returns the cached slice, and any change bumps rev and forces a rebuild on the next pull, so the tree a screen reader sees never goes stale. Measured on the ui benchmark scene: a cached pull is 1.0 ns/op with 0 allocs versus 9085 ns/op / 192 allocs to rebuild — and a real feed measures far more text per rebuild than this two-card scene. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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The freeze
Since #149 the reader runs on
go-widgets/window, whose accessibility bridge pullsScene.A11yElements()on every paint frame, andrun.godrives an unconditional 60 Hz repaint ticker. Each pull rebuilt the entire accessibility tree, and building it runs a fullScene.layout()pass — text measurement (wrapMeasured) for every card.At 60 fps that is a complete feed re-layout 60×/sec on the render thread → one core pinned at 100 %+ → the UI freezes even while idle. A goroutine dump of the spinning process showed the hot loop:
with no aggregation goroutines in flight — i.e. the spin was the idle a11y pull, not a hung fetch.
The fix
Memoise the built tree against the scene's damage sequence (
rev): a pull with no intervening change returns the cached slice; any state change bumpsrevand forces a rebuild on the next pull, so a screen reader never sees a stale tree.Measured
uibenchmark scene:~8,700× per pull — and a real feed measures far more text per rebuild than this two-card scene.
uiretained (TestA11yTreeCachesUntilAChangecovers hit + invalidation; benchmarks exercise both paths)gofmtclean, full build green🤖 Generated with Claude Code