[bartlomiejbloniarz]

Summary:
Stacked on #59585, which is stacked on #59584. Review the last two commits: the change and its tests.

With the shared animation backend, the backend's commit hook writes C++ Animated's latest values into every React commit made while it animates. C++ Animated without the backend does not do this. It writes non-layout props straight to the views, keeps them over React's mounts with AnimatedMountingOverrideDelegate, and commits the final values when an animation finishes.

This PR adds a way to experiment with the second approach on the backend. It adds commitDirectProps to AnimationFrontend and the enableCxxAnimatedDirectPathInBackend flag. With the flag, C++ Animated registers with commitDirectProps = false and behaves as it does without the backend:

• The commit hook does not write its direct values into React commits. Layout updates are unchanged.
• AnimatedMountingOverrideDelegate keeps the values of connected props nodes over React mounts.
• The last update of an animation is recorded apart, and the end-of-animation commit writes it.
• One end-of-animation commit per surface is scheduled at a time.

Without the flag, C++ Animated registers with commitDirectProps = true and the end-of-animation commit is unchanged. Turning commitDirectProps off without the flag asserts.

Changelog:

[INTERNAL] [ADDED] - Add enableCxxAnimatedDirectPathInBackend to keep C++ Animated's direct updates out of React commits with the shared animation backend

Test Plan:
Unit tests. AnimatedPropsRegistryTest, AnimationBackendFrontendTest and NativeAnimatedFrontendTests cover which values the commit hook writes, when final values are written, taken and restored, that older recorded values do not overwrite a final value, and one end-of-animation commit per surface. The tests for final values and for one commit per surface fail without the code they cover.

Fantom.

• yarn fantom packages/react-native/Libraries/Animated/__tests__/AnimatedBackend-itest.js runs with the flag on and off and passes.
• yarn fantom packages/react-native/Libraries/Animated/__tests__/AnimatedBackendDirectUpdates-itest.js checks that a React commit of an animated view keeps its animated value mounted, with the flag on and off. It fails without the mount override delegate.
• yarn fantom packages/react-native/Libraries/Animated/__tests__/Animated-itest.js passes. I also ran it locally with the backend and the flag forced on. Fantom allows at most 12 flag combinations per file, so that run is not encoded in the file.

Devices. RNTester on an Android emulator and an iOS simulator, with the backend and C++ Animated on, once with the flag on and once with it off. I tracked a square frame by frame in screen recordings:

Check	Android, flag on	Android, flag off	iOS, flag on	iOS, flag off
React re-renders the view every 50 ms during a looping native animation	No backward jumps	No backward jumps	No backward jumps	No backward jumps
The animation finishes, then React keeps re-rendering	Keeps the final values	Keeps the final values	Keeps the final values	Keeps the final values
setValue(0), then React keeps re-rendering	Stays reset	Stays reset	Stays reset	Stays reset

Differential Revision: D128154682

Pulled By: bartlomiejbloniarz

[meta-codesync]

@bartlomiejbloniarz has imported this pull request. If you are a Meta employee, you can view this in D128154682.

[meta-codesync]

@bartlomiejbloniarz has exported this pull request. If you are a Meta employee, you can view the originating Diff in D128154682.

[github-actions]

Visual regression

1 visual difference(s) at 3ee655b649ba. Visual differences need maintainer approval. Review the report, then apply visual-change-approved.

ios touchable/feedback-events/pressed: Changed, 1620 px (0.285%)

Expected and Captured

Expected	Captured