Reimplemented StretchingOverscrollIndicator with Simulation ported from Android 12.

[MTtankkeo]

Fixed an issue #169659

This PR improves the StretchingOverscrollIndicator to better match native Android behavior.

• Previously, the stretch effect worked well only for slow dragging, and during fast flings it was absent or felt clipped.
• Implemented a Simulation-based animation that responds naturally to both slow drags and high-velocity flings.
• The result closely resembles the native Android overscroll behavior while maintaining Flutter's performance characteristics.

This change ensures that momentum-based gestures produce a more natural and intuitive overscroll experience, especially for users accustomed to native Android scroll views.

Fling

3.mp4

Pull And Reduce

Also, a very similar animation is implemented when pulling as well.

3.mp4

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request is a great improvement to the StretchingOverscrollIndicator, replacing the previous animation logic with a more physically realistic SpringSimulation. This results in a much more natural feel, especially for high-velocity flings, aligning it better with native Android behavior. The code is well-structured, and the addition of a regression test is appreciated.

I've found a critical issue related to animation controller lifecycle management that could lead to race conditions. I've also identified a couple of medium-severity issues related to code clarity and maintainability. Addressing these will make the implementation more robust and easier to understand.

Overall, this is a high-quality contribution.

[dkwingsmt]

Thank you for this amazing change! My first round of review focuses on the constants for the spring simulation.

[Piinks]

Checking in here: there are many failing tests behind the Google testing check here. I am working through them to validate the changes are expected, for example screenshot tests that captured the overscroll state.

[Piinks]

@MTtankkeo can you make this update in behavior opt-in? I have determined we won't be able to land this based on some of the failures coming from other dependencies that will have to update first once it gets to stable - https://pub.dev/packages/data_table_2 being one of them.

[MTtankkeo]

@MTtankkeo can you make this update in behavior opt-in? I have determined we won't be able to land this based on some of the failures coming from other dependencies that will have to update first once it gets to stable - https://pub.dev/packages/data_table_2 being one of them.

@Piinks How should I implement the opt-in behavior? Personally, I can’t think of a good approach right now. Could you provide an example?

[victorsanni]

Failing tests in data_table_2:

• test 1
• test 2
• test 3

EDIT: I think these are all the failing tests

[Piinks]

One thing we could do is update data table to soften the affected tests, and roll the updated package into google, and then land this change. It looks like it's been 7 months since the package's last update.

[Piinks]

@MTtankkeo which do you prefer, updating the package and then returning here, or introducing an opt in?

[MTtankkeo]

@MTtankkeo which do you prefer, updating the package and then returning here, or introducing an opt in?

@Piinks Sounds good, I’ll look into fixing the failing tests in the data_table_2 package and open a PR soon.

[victorsanni]

data_table_2 tests have been resolved, the only Google testing failures now are from image diffs.

[victorsanni]

Looked through the screenshot tests, they all look intended with this PR.