fix: commit the values a transition settles within its starting frame - #10338
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ChangesCSS transition update handling
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Inline comments:
In
`@packages/react-native-reanimated/Common/cpp/reanimated/CSS/registries/CSSTransitionsRegistry.cpp`:
- Around line 237-241: Update runCSSTransition’s pendingInitialUpdates_ handling
to merge initialUpdate into the existing per-tag update object instead of
replacing it, allowing later values to override duplicate properties while
preserving distinct ones; add a regression test covering multiple runs for the
same tag before a single takeUpdatesToFlush call.
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A transition that finishes inside the frame it starts in has its interpolator retired by the very call that produces its final frame, so the flush that follows finds nothing to recompute and the value never reaches the commit batch. A pseudo selector written without a transitionDuration therefore never appears on screen. Keep that frame on the transition and hand it over from computeCurrentLoopStyle, where the flush can still commit it, letting anything still running override it. Removing a property drops it too, so an eviction is not undone.
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Several runs can land on one view before a single flush, so assigning the pending frame dropped what an earlier run had settled. Merge instead. computeCurrentLoopStyle no longer describes what it returns, now that it also hands over frames the loop has already finished with, and it consumes them rather than just computing. Renamed to takeUpdates.
MatiPl01
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August 19, 2026 14:17
pawicao
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Aug 19, 2026
A config can take a property off the loop before the next flush, through updateSettings, which retires its interpolator. The frame that property settled on was still pending, so the flush could commit a value the config had just removed. Both removal paths now go through one helper. The comment inside takeUpdates went with it; the member declaration already says why the pending frames exist.
pawicao
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Aug 20, 2026
pawicao
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Aug 20, 2026
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A CSS pseudo selector written without a
transitionDurationnever applies.The value such a transition settles on is computed once, when the run starts, and the interpolator that produced it is retired by that same call. The flush that follows finds nothing to recompute, so the value never reaches the commit batch. Longer transitions keep their interpolator and are unaffected.
The transition now holds the frames its runs settle on until the next flush and hands them over there, with anything still running overriding them.
computeCurrentLoopStylebecomestakeUpdates, since it now also returns frames the loop has finished with, and consumes them.zero-duration-before-after.mp4