Allow config to defer animation start time in FrameAnimationDriver (#56929)#56929
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Summary: Pull Request resolved: react#56929 ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
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May 27, 2026
Summary: Pull Request resolved: react#56929 ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
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May 27, 2026
Summary: Pull Request resolved: react#56929 ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
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May 27, 2026
Summary: Pull Request resolved: react#56929 ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
added a commit
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that referenced
this pull request
May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
added a commit
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that referenced
this pull request
May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
added a commit
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
added a commit
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that referenced
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
zeyap
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May 29, 2026
Summary: ## Changelog: [Internal] [Fixed] - Defer animation start time in FrameAnimationDriver **Problem**: In complex apps, if animation is started in commit phase (the case if animation starts in useLayoutEffect, or from ViewTransition event handlers), it'll skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. - Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
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Summary: **Problem**: In complex apps, view transition animations skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
…eact#56929) Summary: ## Changelog: [Internal] - Allow config to defer animation start time in FrameAnimationDriver **Problem**: In complex apps, view transition animations skip initial frames — the user sees the animation snap to an intermediate position. This happens because `FrameAnimationDriver` anchors its start time on the first `runAnimationStep` call, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causing `frameIndex` to jump ahead. **Why**: `startFrameTimeMs_` is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later — `timeDeltaMs` jumps and the animation skips to a mid-point. Every major framework solves this: Flutter uses lazy start (`_startTime ??= timeStamp` on first actual tick), Android native uses `CALLBACK_COMMIT` to adjust post-traversal, and CSS View Transitions spec defers start until post-composite. **Fix**: On the very first `update()` call, output the starting value (frame 0) and reset `startFrameTimeMs_ = -1`. This causes the base class to re-anchor on the next `runAnimationStep`, so elapsed time is measured from the first frame that has actually been rendered — not from when `startAnimatingNode` was dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change. Differential Revision: D106007152
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Summary:
Changelog:
[Internal] - Allow config to defer animation start time in FrameAnimationDriver
Problem: In complex apps, view transition animations skip initial frames — the user sees the animation snap to an intermediate position. This happens because
FrameAnimationDriveranchors its start time on the firstrunAnimationStepcall, but the UI thread may be busy with layout/mount work for several frames before the view actually composites. The elapsed wall-clock time advances, causingframeIndexto jump ahead.Why:
startFrameTimeMs_is set to the Choreographer frame time on the first tick. If the UI thread is blocked processing a heavy tree (many views mounting), subsequent ticks arrive much later —timeDeltaMsjumps and the animation skips to a mid-point. Every major framework solves this: Flutter uses lazy start (_startTime ??= timeStampon first actual tick), Android native usesCALLBACK_COMMITto adjust post-traversal, and CSS View Transitions spec defers start until post-composite.Fix: On the very first
update()call, output the starting value (frame 0) and resetstartFrameTimeMs_ = -1. This causes the base class to re-anchor on the nextrunAnimationStep, so elapsed time is measured from the first frame that has actually been rendered — not from whenstartAnimatingNodewas dispatched. The flag disables itself after one use, so all subsequent frames use pure elapsed-time with no behavioral change.Differential Revision: D106007152