Re-implement stretch overscroll behavior as a custom shader #82906
Description
Update August 2023:
- The current implementation of StretchingOverscrollIndicator uses a transform animation. This is not precisely accurate to the native implementation, which uses a shader:
- https://cs.android.com/android/platform/superproject/main/+/main:frameworks/native/libs/renderengine/skia/filters/StretchShaderFactory.cpp?q=overscroll%20stretch&ss=android&start=1
- Implementing this shader in Flutter for better fidelity is currently blocked on [Impeller] Allow creation of ImageFilter objects from fragment shaders. #132099
- Since useMaterial3 is now true by default, the StretchingOverscrollIndicator is now enabled on Android by default
Internal: b/195519748
Use case
Staring from Android 12 the default visual overscroll behavior will be Stretch instead of the glow effect.
More about this change: https://developer.android.com/about/versions/12/overscroll
Proposal
The default GlowingOverscrollIndicator shouldn't be applied when targeting Android 12
A new StretchOverscrollIndicator should be created and used when targeeting Android 12 + (some additional data about the dragging and flinging values should be provided to the ScrollView builder, see the EdgeEffect Api)