Support SwiftUI's spring animation

[dkwingsmt]

Use case

The spring animation is used all over iOS, and is critical to building widgets with iOS look and feel. Although Flutter currently provides spring simulators, they're not directly usable as animation curves.

Proposal

The spring animation is introduced here: https://developer.apple.com/videos/play/wwdc2023/10158/

(Github backup)

Goals:

• Various ways to construct
  • Presets: Smooth, bouncy, flattened
  • Customize with bounce and duration
  • Professional customization with mass, stiffness, and damping
• Velocity: Smoothly connect animations
• Settling time: Continue the long-tail animation beyond duration

Convert bounce and duration to detailed parameters (from the video) (Wrong formula from Apple. We've figured out the right one):

Questions:

• How extraBounce is applied
  • Done. The extraBounce is directly added to bounce.
• How settlingDuration is derived (we might not need it since our spring simulator allows a settling tolerance)

[davidhicks980]

I'm excited to see this on the radar. Assuming this would be a subclass of Curve, one thing I'm wondering is how the animation duration specified by the AnimationController would behave, considering Curves don't have access to the duration of their driving AnimationController?

animationController.animateTo(
  1,
  duration: const Duration(milliseconds: 500),
  curve: SpringCurve(bounce: 0.2, duration: 0.5), // Considering this is perceptual time, the spring wouldn't settle prior to stopping
)

Edit: I suppose the animation duration could behave as the settling time.

[jodierizky]

I've been waiting a long time for this

[HaijunWei]

I've been waiting a long time for this

[dkwingsmt]

Update: It turns out that Flutter has long supported spring simulations, but simulations are not integrated into other components well. #155575 will allow AnimationController and TransitionRoute to use simulations.

Interestingly, this PR won't help much on the fidelity of Cupertino dialog or action sheets, because the current curve is close enough. However, using the proper simulation is still useful because it allows non-zero initial velocity, such as when the animation switches half way. Although, I don't know many specific cases for this.

After #155575 there will still be some work left. One of them is some convenient APIs that constructs SpringDescription in ways that replicate the SwiftUI APIs. I've done some research, and if I remember correctly, you can simply use the numbers extracted from XCode if you just want to replicate some native behavior.

What I'm trying to say is, I'm not sure what is badly needed for this issue after #155575. So let me know if there are any specific issues that are bothering you. Thanks!