Initial commit of Effen reactive framework experiment for Sky

sky/examples/fn/widgets/drawer.dart

Index: sky/examples/fn/widgets/drawer.dart
diff --git a/sky/examples/fn/widgets/drawer.dart b/sky/examples/fn/widgets/drawer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..ee0c58b38d015b09320b056ca926ce20f747b187
--- /dev/null
+++ b/sky/examples/fn/widgets/drawer.dart
@@ -0,0 +1,199 @@
+part of widgets;
+
+const double _kWidth = 256.0;
+const double _kMinFlingVelocity = 0.4;
+const double _kMinAnimationDurationMS = 246.0;
+const double _kMaxAnimationDurationMS = 600.0;
+const Cubic _kAnimationCurve = easeOut;
+
+class DrawerAnimation {
+
+  Stream<double> get onPositionChanged => _controller.stream;
+
+  StreamController _controller;
+  AnimationGenerator _animation;
+  double _position;
+  bool get _isAnimating => _animation != null;
+  bool get _isMostlyClosed => _position <= -_kWidth / 2;
+
+  DrawerAnimation() {
+    _controller = new StreamController(sync: true);
+    _setPosition(-_kWidth);
+  }
+
+  void toggle(_) => _isMostlyClosed ? _open() : _close();
+
+  void handleMaskTap(_) => _close();
+
+  void handlePointerDown(_) => _cancelAnimation();
+
+  void handlePointerMove(sky.PointerEvent event) {
+    assert(_animation == null);
+    _setPosition(_position + event.dx);
+  }
+
+  void handlePointerUp(_) {
+    if (!_isAnimating)
+      _settle();
+  }
+
+  void handlePointerCancel(_) {
+    if (!_isAnimating)
+      _settle();
+  }
+
+  void _open() => _animateToPosition(0.0);
+
+  void _close() => _animateToPosition(-_kWidth);
+
+  void _settle() => _isMostlyClosed ? _close() : _open();
+
+  void _setPosition(double value) {
+    _position = math.min(0.0, math.max(value, -_kWidth));
+    _controller.add(_position);
+  }
+
+  void _cancelAnimation() {
+    if (_animation != null) {
+      _animation.cancel();
+      _animation = null;
+    }
+  }
+
+  void _animate(double duration, double begin, double end, Curve curve) {
+    _cancelAnimation();
+
+    _animation = new AnimationGenerator(duration, begin: begin, end: end,
+        curve: curve);
+
+    _animation.onTick.listen(_setPosition, onDone: () {
+      _animation = null;
+    });
+  }
+
+  void _animateToPosition(double targetPosition) {
+    double distance = (targetPosition - _position).abs();
+    double duration = math.max(
+        _kMinAnimationDurationMS,
+        _kMaxAnimationDurationMS * distance / _kWidth);
+
+    _animate(duration, _position, targetPosition, _kAnimationCurve);
+  }
+
+  void handleFlingStart(event) {
+    double direction = event.velocityX.sign;
+    double velocityX = event.velocityX.abs() / 1000;
+    if (velocityX < _kMinFlingVelocity)
+      return;
+
+    double targetPosition = direction < 0.0 ? -_kWidth : 0.0;
+    double distance = (targetPosition - _position).abs();
+    double duration = distance / velocityX;
+
+    _animate(duration, _position, targetPosition, linear);
+  }
+}
+
+class Drawer extends Component {
+
+  static Style _style = new Style('''
+    position: absolute;
+    z-index: 2;
+    top: 0;
+    left: 0;
+    bottom: 0;
+    right: 0;
+    box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);'''
+  );
+
+  static Style _maskStyle = new Style('''
+    background-color: black;
+    will-change: opacity;
+    position: absolute;
+    top: 0;
+    left: 0;
+    bottom: 0;
+    right: 0;'''
+  );
+
+  static Style _contentStyle = new Style('''
+    background-color: #FAFAFA;
+    will-change: transform;
+    position: absolute;
+    width: 256px;
+    top: 0;
+    left: 0;
+    bottom: 0;'''
+  );
+
+  Stream<double> onPositionChanged;
+  sky.EventListener handleMaskFling;
+  sky.EventListener handleMaskTap;
+  sky.EventListener handlePointerCancel;
+  sky.EventListener handlePointerDown;
+  sky.EventListener handlePointerMove;
+  sky.EventListener handlePointerUp;
+  List<Node> children;
+
+  Drawer({
+    Object key,
+    this.onPositionChanged,
+    this.handleMaskFling,
+    this.handleMaskTap,
+    this.handlePointerCancel,
+    this.handlePointerDown,
+    this.handlePointerMove,
+    this.handlePointerUp,
+    this.children
+  }) : super(key: key);
+
+  double _position = -_kWidth;
+
+  bool _listening = false;
+
+  void _ensureListening() {
+    if (_listening)
+      return;
+
+    _listening = true;
+    onPositionChanged.listen((position) {
+      setState(() {
+        _position = position;
+      });
+    });
+  }
+
+  Node render() {
+    _ensureListening();
+
+    bool isClosed = _position <= -_kWidth;
+    String inlineStyle = 'display: ${isClosed ? 'none' : ''}';
+    String maskInlineStyle = 'opacity: ${(_position / _kWidth + 1) * 0.25}';
+    String contentInlineStyle = 'transform: translateX(${_position}px)';
+
+    return new Container(
+      style: _style,
+      inlineStyle: inlineStyle,
+      onPointerDown: handlePointerDown,
+      onPointerMove: handlePointerMove,
+      onPointerUp: handlePointerUp,
+      onPointerCancel: handlePointerCancel,
+
+      children: [
+        new Container(
+          key: 'Mask',
+          style: _maskStyle,
+          inlineStyle: maskInlineStyle,
+          onGestureTap: handleMaskTap,
+          onFlingStart: handleMaskFling
+        ),
+        new Container(
+          key: 'Content',
+          style: _contentStyle,
+          inlineStyle: contentInlineStyle,
+          children: children
+        )
+      ]
+    );
+  }
+}