Move animationgenerator.dart to sky/framework/animation/generator.dart

sky/examples/fn/widgets/animationgenerator.dart

-part of widgets;
-
-class FrameGenerator {
-
-  Function onDone;
-  StreamController _controller;
-
-  Stream<double> get onTick => _controller.stream;
-
-  int _animationId = 0;
-  bool _cancelled = false;
-
-  FrameGenerator({this.onDone}) {
-    _controller = new StreamController(
-      sync: true,
-      onListen: _scheduleTick,
-      onCancel: cancel);
-  }
-
-  void cancel() {
-    if (_cancelled) {
-      return;
-    }
-    if (_animationId != 0) {
-      sky.window.cancelAnimationFrame(_animationId);
-    }
-    _animationId = 0;
-    _cancelled = true;
-    if (onDone != null) {
-      onDone();
-    }
-  }
-
-  void _scheduleTick() {
-    assert(_animationId == 0);
-    _animationId = sky.window.requestAnimationFrame(_tick);
-  }
-
-  void _tick(double timeStamp) {
-    _animationId = 0;
-    _controller.add(timeStamp);
-    if (!_cancelled) {
-      _scheduleTick();
-    }
-  }
-}
-
-class AnimationGenerator extends FrameGenerator {
-
-  Stream<double> get onTick => _stream;
-  final double duration;
-  final double begin;
-  final double end;
-  final Curve curve;
-  Stream<double> _stream;
-  bool _done = false;
-
-  AnimationGenerator(this.duration, {
-    this.begin: 0.0,
-    this.end: 1.0,
-    this.curve: linear,
-    Function onDone
-  }):super(onDone: onDone) {
-    double startTime = 0.0;
-    double targetTime = 0.0;
-    _stream = super.onTick.map((timeStamp) {
-      if (startTime == 0.0) {
-        startTime = timeStamp;
-        targetTime = startTime + duration;
-      }
-      return math.min((timeStamp - startTime) / duration, 1.0);
-    })
-    .takeWhile(_checkForCompletion)
-    .map((t) =>  begin + (end - begin) * curve.transform(t));
-  }
-
-  bool _checkForCompletion(double t) {
-    if (_done)
-      return false;
-    _done = t >= 1;
-    return true;
-  }
-}