Reproduce confetti animation bug: non-deterministic particles#68
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jappeace merged 2 commits intojappeace:masterfrom Apr 19, 2026
Merged
Reproduce confetti animation bug: non-deterministic particles#68jappeace merged 2 commits intojappeace:masterfrom
jappeace merged 2 commits intojappeace:masterfrom
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Add integration tests that render the confetti widget tree through hatter's rendering engine and verify animation behaviour. The reproducer test "confetti uses newStdGen" demonstrates the bug: confettiOverlay uses newStdGen on every call, producing different particle positions each render. The diff engine sees changed widgets, re-registers tweens and restarts animation from scratch. AppState already has stConfettiSeed for deterministic particles but confettiOverlay ignores it. Five passing tests confirm the animation system itself works: - Tweens register on first render - Tweens register on Stack 1->2 child transition - Particles start at origin (0,0) - Particles have non-zero target positions - Fade end-state has alpha 0 Prompt: investigate why the animation for confetti doesn't work, make a reproducer first Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
confettiOverlay was calling newStdGen on every render, producing different random particle positions each time. Hatter's diff engine saw the changed widgets, re-registered tweens, and restarted the animation from scratch on every re-render. Now confettiOverlay takes a StdGen parameter. enterPRView passes stConfettiSeed from AppState, which was already created for this purpose but never used. The determinism test now passes. Prompt: okay go do that then Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
confettiOverlayusesnewStdGeninstead ofstConfettiSeed, making particles non-deterministic across re-rendersTest results
confettiOverlayis not deterministic across callsRoot cause
confettiOverlay(Views.hs:231) callsnewStdGenon every invocation.AppStatealready hasstConfettiSeed :: StdGen(AppState.hs:37) intended for deterministic particles, butconfettiOverlayignores it.Test plan
cabal buildpassesconfettiOverlayacceptStdGenparameter, passstConfettiSeed🤖 Generated with Claude Code