av

/// Just a container for parameters 
/// allowing to draw a circle on a [Canvas] later
class CircleParameters {
  double radius;
  Offset offset;

  CircleParameters({@required this.radius, @required this.offset});
}

/// Renders certain amount of circles on a [Canvas],

av

class FadingCircle extends Particle with Fading {
  final double radius;
  final Color color;

  FadingCircle({
    this.radius = 10,
    this.color = Colors.white,
  });

  @override

av

/// A function which returns [Particle] when called
typedef ParticleProvider = Particle Function(int i);

/// A [CompositeParticle] which allows to use [ParticleProvider] 
/// generator functions as source for children particles
/// 
/// ```dart
/// // 10 plain fading circles
/// ParticleGenerator(10, (i) => FadingCircle());
/// 

av

// In OutlineButton.build > Particles > Aligned
// ...
child: Burst(
  children: List<Particle>.generate(
    20,
    (i) => ScalingParticle(
      child: FadingCircle(radius: Randoms.rnd.nextDouble() * 8 + 2),
      from: .2,
      to: 1.5,
    ),

av

// in Burst constructor, children.map(...)
// ...
(particle) => CurvedParticle(
  curve: Interval(
    // Interval would start at random point from 0 to 0.5
    // and finish at random point between 0.6 and 1.0
    Randoms.rnd.nextDouble() * .5,
    Randoms.rnd.nextDouble() * .4 + .6,
  ),
  child: MovingParticle(

av

class CurvedParticle extends Particle with NestedParticle, Curved {
  Curve curve;
  Particle child;

  CurvedParticle({
    @required this.curve,
    @required this.child,
  });
}

av

class CurvedParticle extends Particle with NestedParticle, Curved {
  Curve curve;
  Particle child;

  CurvedParticle({
    @required this.curve,
    @required this.child,
  });
}

av

mixin Curved on Updatable {
  Curve curve;

  @override
  void update(Animation animation) {
    super.update(
      CurveTween(curve: curve).animate(animation),
    );
  }
}

av

class Particles extends StatefulWidget {
  final Duration duration;
  final Particle particle;
  final ParticlesWidgetBuilder builder;
  
  // New property you defined to make animation
  // easing configurable from outside
  final Curve curve;

  const Particles({

av

// In OutlineButton.build > Particles > Aligned > FadingCircle
// ...
radius: Randoms.rnd.nextDouble() * 10
// ...