春先 Harusaki

A super simple SpringSimulation API for Flutter, providing conventional defaults.

Usage

import 'package:harusaki/harusaki.dart';

final controller = AnimationController(/* ... */)

/// 1) just animate with the simulation...

controller.animateWith(
  Harusaki.spring(
    Harusaki.normal.
    from: 0.0,
    to: 1.0,
  ),
);

/// 2) or grab a velocity value to animate with:

onDragEnd: (details) {

  // assumes we're dragging something the size of the screen in a vertical direction
  final velocity = details.primaryVelocity / MediaQuery.of(context).size.height;

  controller.animateWith(
    Harusaki.spring(
      Harusaki.normal,
      from: controller.value,
      to: 1.0,
      velocity: velocity,
    )
  );
}

API

Harusaki SpringSimulation & SpringDescriptions

We use the same defaults as react-spring, so you have the following spring simulations to choose from

• SpringDescription Harusaki.normal([double velocity = 0]) ("default" in react-spring)
• SpringDescription Harusaki.gentle([double velocity = 0])
• SpringDescription Harusaki.wobbly([double velocity = 0])
• SpringDescription Harusaki.stiff([double velocity = 0])
• SpringDescription Harusaki.slow([double velocity = 0])
• SpringDescription Harusaki.molasses([double velocity = 0])

and you can create a conventional simulation with

• SpringSimulation Harusaki.spring(double stiffness, double damping, [double velocity])

and get the default tolerance with

• Tolerance Harusaki.tolerance

HarusakiAnimationController

HarusakiAnimationController implements AnimationController with some specific changes. First, it replaces all of the normal linear interpolations with spring-based simulations given a description. Since it conforms to AnimationController, it can be passed to any widgets that expect one. Then when those widgets call .forward or .reverse or .fling, it'll use the spring description you've provided to animate the value, rather than the default linear interpolation.

HarusakiAnimationController also removes the famously annoying clamp behavior of an AnimationController than ensures that its value never goes above the upperBound or below the lowerBound. This allows the .value property to be in an unbounded range (though usually not that much higher than upperBound).

It also stubs out .duration and .reverseDuration, so make sure nothing really depends on that. TBD: duration estimation.

final controller = Harusaki.controller(Harusaki.normal, vsync: this);

// OR

final controller = HarusakiAnimationController(
  description: Harusaki.normal,
  vsync: this,
);

// all of the expected values are supported as well.

Related

See an example of harusaki in action by checking out the holy_sheet package example, which uses Harusaki to create a fabulously springing sheet/panel widget.

Inspo

harusaki is inspired by lukepighetti/sprung and react-spring/react-spring.

The haru packagename was already taken, so we'll go with "the beginning of spring" as a motif ¯\_(ツ)_/¯

Notes

As far as I can tell, stiffness and tension are the same concept and damping and friction are the same concept.