Use transitions for Dismissable.

Simplifies the code a bit.

packages/flutter/lib/animation/animation_performance.dart

@@ -137,11 +137,11 @@ class AnimationPerformance {
   }
 
   Future _animateTo(double target) {
-    double remainingDistance = (target - timeline.value).abs();
+    Duration remainingDuration = duration * (target - timeline.value).abs();
     timeline.stop();
-    if (remainingDistance == 0.0)
+    if (remainingDuration == Duration.ZERO)
       return new Future.value();
-    return timeline.animateTo(target, duration: duration * remainingDistance);
+    return timeline.animateTo(target, duration: remainingDuration);
   }
 
   void _tick(double t) {

packages/flutter/lib/widgets/dismissable.dart

@@ -7,14 +7,14 @@ import 'dart:sky' as sky;
 import 'package:sky/animation/animated_value.dart';
 import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/animation/curves.dart';
-import 'package:sky/widgets/animated_component.dart';
 import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/transitions.dart';
 import 'package:sky/widgets/widget.dart';
 import 'package:vector_math/vector_math.dart';
 
 const Duration _kCardDismissFadeout = const Duration(milliseconds: 200);
 const Duration _kCardDismissResize = const Duration(milliseconds: 300);
-const double _kCardDismissResizeDelay = 0.4;
+final Interval _kCardDismissResizeInterval = new Interval(0.4, 1.0);
 const double _kMinFlingVelocity = 700.0;
 const double _kMinFlingVelocityDelta = 400.0;
 const double _kFlingVelocityScale = 1.0 / 300.0;
@@ -23,7 +23,7 @@ const double _kDismissCardThreshold = 0.6;
 typedef void ResizedCallback();
 typedef void DismissedCallback();
 
-class Dismissable extends AnimatedComponent {
+class Dismissable extends StatefulComponent {
 
   Dismissable({
     Key key,
@@ -37,8 +37,6 @@ class Dismissable extends AnimatedComponent {
   ResizedCallback onResized;
   DismissedCallback onDismissed;
 
-  AnimatedValue<Point> _position;
-  AnimatedValue<double> _opacity;
   AnimationPerformance _fadePerformance;
   AnimationPerformance _resizePerformance;
 
@@ -47,29 +45,23 @@ class Dismissable extends AnimatedComponent {
   bool _dragUnderway = false;
 
   void initState() {
-    _position = new AnimatedValue<Point>(Point.origin);
-    _opacity = new AnimatedValue<double>(1.0, end: 0.0);
-    _fadePerformance = new AnimationPerformance()
-      ..duration = _kCardDismissFadeout
-      ..variable = new AnimatedList([_position, _opacity])
-      ..addListener(_handleFadeProgressChanged);
+    _fadePerformance = new AnimationPerformance(duration: _kCardDismissFadeout);
   }
 
-  void _handleFadeProgressChanged() {
-    setState(() {
-      if (_fadePerformance.isCompleted && !_dragUnderway)
+  void _handleFadeCompleted() {
+    if (!_dragUnderway)
       _startResizePerformance();
-    });
   }
 
   void syncFields(Dismissable source) {
     child = source.child;
     onResized = source.onResized;
     onDismissed = source.onDismissed;
-    super.syncFields(source);
   }
 
   Point get _activeCardDragEndPoint {
+    if (!_isActive)
+      return Point.origin;
     assert(_size != null);
     return new Point(_dragX.sign * _size.width * _kDismissCardThreshold, 0.0);
   }
@@ -91,38 +83,27 @@ class Dismissable extends AnimatedComponent {
   void _startResizePerformance() {
     assert(_size != null);
     assert(_fadePerformance != null);
+    assert(_fadePerformance.isCompleted);
     assert(_resizePerformance == null);
 
-    // TODO(hansmuller): _fadePerformance is completed; stop shouldn't be needed.
-    _fadePerformance.stop();
-
-    AnimatedValue<double> dismissHeight = new AnimatedValue<double>(_size.height,
-      end: 0.0,
-      curve: ease,
-      interval: new Interval(_kCardDismissResizeDelay, 1.0)
-    );
+    setState(() {
       _resizePerformance = new AnimationPerformance()
-      ..variable = dismissHeight
         ..duration = _kCardDismissResize
-      ..addListener(_handleResizeProgressChanged)
-      ..play();
+        ..addListener(_handleResizeProgressChanged);
+    });
   }
 
   void _handleResizeProgressChanged() {
-    setState(() {
     if (_resizePerformance.isCompleted)
       _maybeCallOnDismissed();
     else
       _maybeCallOnResized();
-    });
   }
 
   void _handlePointerDown(sky.PointerEvent event) {
-    setState(() {
     _dragUnderway = true;
     _dragX = 0.0;
     _fadePerformance.progress = 0.0;
-    });
   }
 
   void _handlePointerMove(sky.PointerEvent event) {
@@ -131,26 +112,21 @@ class Dismissable extends AnimatedComponent {
 
     double oldDragX = _dragX;
     _dragX += event.dx;
-    setState(() {
-      if (!_fadePerformance.isAnimating) {
     if (oldDragX.sign != _dragX.sign)
-          _position.end = _activeCardDragEndPoint;
+      setState(() {}); // Rebuild to update the new drag endpoint.
+    if (!_fadePerformance.isAnimating)
       _fadePerformance.progress = _dragX.abs() / (_size.width * _kDismissCardThreshold);
   }
-    });
-  }
 
   void _handlePointerUpOrCancel(_) {
     if (!_isActive)
       return;
 
-    setState(() {
     _dragUnderway = false;
     if (_fadePerformance.isCompleted)
       _startResizePerformance();
     else if (!_fadePerformance.isAnimating)
       _fadePerformance.reverse();
-    });
   }
 
   bool _isHorizontalFlingGesture(sky.GestureEvent event) {
@@ -166,24 +142,31 @@ class Dismissable extends AnimatedComponent {
     if (_isHorizontalFlingGesture(event)) {
       _dragUnderway = false;
       _dragX = event.velocityX.sign;
-      _position.end = _activeCardDragEndPoint;
       _fadePerformance.fling(Direction.forward, velocity: event.velocityX.abs() * _kFlingVelocityScale);
     }
   }
 
   void _handleSizeChanged(Size newSize) {
+    setState(() {
       _size = new Size.copy(newSize);
-    _position.end = _activeCardDragEndPoint;
+    });
   }
 
   Widget build() {
     if (_resizePerformance != null) {
-      AnimatedValue<double> height = _resizePerformance.variable;
-      return new Container(height: height.value);
+      AnimatedValue<double> dismissHeight = new AnimatedValue<double>(
+        _size.height,
+        end: 0.0,
+        curve: ease,
+        interval: _kCardDismissResizeInterval
+      );
+
+      return new SquashTransition(
+        performance: _resizePerformance,
+        direction: Direction.forward,
+        height: dismissHeight);
     }
 
-    Matrix4 transform = new Matrix4.identity();
-    transform.translate(_position.value.x, _position.value.y);
     return new Listener(
       onPointerDown: _handlePointerDown,
       onPointerMove: _handlePointerMove,
@@ -192,10 +175,13 @@ class Dismissable extends AnimatedComponent {
       onGestureFlingStart: _handleFlingStart,
       child: new SizeObserver(
         callback: _handleSizeChanged,
-        child: new Opacity(
-          opacity: _opacity.value,
-          child: new Transform(
-            transform: transform,
+        child: new SlideIn(
+          performance: _fadePerformance,
+          position: new AnimatedValue<Point>(Point.origin, end: _activeCardDragEndPoint),
+          child: new FadeIn(
+            performance: _fadePerformance,
+            onCompleted: _handleFadeCompleted,
+            opacity: new AnimatedValue<double>(1.0, end: 0.0),
             child: child
           )
         )

packages/flutter/lib/widgets/transitions.dart

@@ -8,6 +8,8 @@ import 'package:sky/animation/animated_value.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:vector_math/vector_math.dart';
 
+dynamic _maybe(AnimatedValue x) => x != null ? x.value : null;
+
 abstract class TransitionBase extends AnimatedComponent {
   TransitionBase({
     Key key,
@@ -68,6 +70,7 @@ abstract class TransitionBase extends AnimatedComponent {
   Widget build();
 }
 
+// TODO(mpcomplete): rename SlideTransition
 class SlideIn extends TransitionBase {
   // TODO(mpcomplete): this constructor is mostly boilerplate, passing values
   // to super. Is there a simpler way?
@@ -103,6 +106,7 @@ class SlideIn extends TransitionBase {
   }
 }
 
+// TODO(mpcomplete): rename FadeTransition
 class FadeIn extends TransitionBase {
   FadeIn({
     Key key,
@@ -167,3 +171,40 @@ class ColorTransition extends TransitionBase {
     );
   }
 }
+
+class SquashTransition extends TransitionBase {
+  SquashTransition({
+    Key key,
+    this.width,
+    this.height,
+    Duration duration,
+    AnimationPerformance performance,
+    Direction direction,
+    Function onDismissed,
+    Function onCompleted,
+    Widget child
+  }) : super(key: key,
+             duration: duration,
+             performance: performance,
+             direction: direction,
+             onDismissed: onDismissed,
+             onCompleted: onCompleted,
+             child: child);
+
+  AnimatedValue<double> width;
+  AnimatedValue<double> height;
+
+  void syncFields(SquashTransition updated) {
+    width = updated.width;
+    height = updated.height;
+    super.syncFields(updated);
+  }
+
+  Widget build() {
+    if (width != null)
+      width.setProgress(performance.progress);
+    if (height != null)
+      height.setProgress(performance.progress);
+    return new SizedBox(width: _maybe(width), height: _maybe(height), child: child);
+  }
+}