tween_benchmark.dart

class Benchmark extends StatefulWidget {
  const Benchmark({Key? key}) : super(key: key);
  @override
  _BenchmarkState createState() => _BenchmarkState();
}

class _BenchmarkState extends State<Benchmark> {
  double _tweenSliderValue = .2;
  bool _enableRendering = false;
  bool _useGTween = false;

  int get _tweenCount => 10 + (_tweenSliderValue * 5000).round();
  @override
  Widget build(BuildContext context) {
    final rnd = Random(0);
    return Center(
      child: SizedBox(
        width: 400,
        height: 400,
        child: Stack(children: [
          ...List.generate(_tweenCount, (index) {
            return Positioned(
              top: 20.0 + rnd.nextInt(300),
              left: 20.0 + rnd.nextInt(300),
              child: Opacity(
                opacity: _enableRendering ? 1 : 0,
                child: buildLogo(),
              ),
            );
          }),
          Column(
            children: [
              CheckboxListTile(
                title: Text('Show Tweens'),
                value: _enableRendering,
                onChanged: _handleShowTweensToggled,
              ),
              CheckboxListTile(
                title: Text('use gtween'),
                value: _useGTween,
                onChanged: _handleUseGTweenToggled,
              ),
              Row(
                children: [
                  Expanded(child: Slider(value: _tweenSliderValue, onChanged: _handleSliderChanged)),
                  Text('$_tweenCount'),
                ],
              ),
            ],
          )
        ]),
      ),
    );
  }

  StatefulWidget _buildLogo() => !_useGTween
      ? _FadeInOut()
      : const FlutterLogo().gTweener.fade().withInit(
            (controller) => controller.animation.repeat(reverse: true),
          );

  void _handleSliderChanged(v) => setState(() => _tweenSliderValue = v);
  void _handleShowTweensToggled(_) => setState(() => _enableRendering = !_enableRendering);
  void _handleUseGTweenToggled(_) => setState(() => _useGTween = !_useGTween);
}



/// ///////////////////////////////////
/// Vanilla Flutter Version
class _FadeInOut extends StatefulWidget {
  @override
  __FadeInOutState createState() => __FadeInOutState();
}

class __FadeInOutState extends State<_FadeInOut> with SingleTickerProviderStateMixin {
  late final _anim = AnimationController(vsync: this, duration: .3.seconds)..repeat(reverse: true);

  @override
  void dispose() {
    _anim.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) => FadeTransition(opacity: _anim, child: const FlutterLogo());
}