gtween_poc.dart

/// Example usage
///
/// One shot:
// GTweener.fade(from: .9, to: 1, child: const FlutterLogo()),
///
/// Or use a key for future control
// final _tweenKey = GlobalKey<GTweenerState>();
// ...
// return GTweener.fade(key: _tweenKey, child: const FlutterLogo()),
// ...
// onPressed: () => _tweenKey.currentState!.anim.reverse(from: 1);

class TweenExamples extends StatelessWidget {
  final _tweenKey = GlobalKey<GTweenerState>();
  AnimationController get _tween => _tweenKey.currentState!.anim;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          GTweener.fade(key: _tweenKey, child: const FlutterLogo()),
          TextButton(
            onPressed: () => _tween.forward(from: 0),
            child: const Text('Run Again'),
          )
        ],
      ),
    );
  }
}

class GTweener<T> extends StatefulWidget {
  static const _defaultDuration = Duration(milliseconds: 300);
  const GTweener(
    this.builder, {
    required this.child,
    this.duration = _defaultDuration,
    this.autoPlay = true,
    this.from,
    required this.to,
    Key? key,
  }) : super(key: key);
  final Widget Function(BuildContext context, Widget child, AnimationController anim) builder;
  final Widget child;
  final Duration duration;
  final bool autoPlay;
  final T? from;
  final T? to;

  @override
  State<GTweener> createState() => GTweenerState();

  static Widget _fadeBuilder(BuildContext context, Widget child, AnimationController anim) => FadeTransition(
        opacity: anim,
        child: child,
      );
  static GTweener<double> fade({
    required Widget child,
    Duration duration = _defaultDuration,
    bool autoPlay = true,
    double? from,
    double? to,
    Key? key,
  }) {
    return GTweener(
      _fadeBuilder,
      key: key,
      child: child,
      duration: duration,
      autoPlay: autoPlay,
      // TODO: handle from / to somehow, need to figure out how we want to map the controller upper and lower bounds
      from: from,
      to: to,
    );
  }
}

class GTweenerState extends State<GTweener> with SingleTickerProviderStateMixin {
  late final AnimationController anim = AnimationController(
    vsync: this,
    duration: widget.duration,
  );

  @override
  void initState() {
    super.initState();
    if (widget.autoPlay) anim.forward();
  }

  @override
  Widget build(BuildContext context) => widget.builder(context, widget.child, anim);
}

/*
// Alternate API style:
GFade.tween(to: 1, key: gTween, child: FlutterLogo()),

// Some extension ideas:
FlutterLogo().gFade(to: 1),
FlutterLogo().gMultiTweener([
   GTweener.fade(to: 1),
   GTweener.scale(to: 1)
]),

/*
GTweener API Spec TODO,
config:
// autoPlay
// duration
* delay
* reflect
* ease
* timeScale

events
* onChange
* onComplete
* onInit
*/
 */