Push PopupMenu's animation code into its build function and use transitions.

Also add intervals and curves to AnimationPerformance, which affect all
variables used by the performance.

packages/flutter/lib/animation/animated_value.dart

@@ -15,15 +15,15 @@ abstract class AnimatedVariable {
   String toString();
 }
 
-abstract class CurvedVariable implements AnimatedVariable {
-  CurvedVariable({this.interval, this.reverseInterval, this.curve, this.reverseCurve});
+class AnimationTiming {
+  AnimationTiming({this.interval, this.reverseInterval, this.curve, this.reverseCurve});
 
   Interval interval;
   Interval reverseInterval;
   Curve curve;
   Curve reverseCurve;
 
-  double _transform(double t, Direction direction) {
+  double transform(double t, Direction direction) {
     Interval interval = _getInterval(direction);
     if (interval != null)
       t = interval.transform(t);
@@ -48,7 +48,7 @@ abstract class CurvedVariable implements AnimatedVariable {
   }
 }
 
-class AnimatedValue<T extends dynamic> extends CurvedVariable {
+class AnimatedValue<T extends dynamic> extends AnimationTiming implements AnimatedVariable {
   AnimatedValue(this.begin, { this.end, Interval interval, Curve curve, Curve reverseCurve })
     : super(interval: interval, curve: curve, reverseCurve: reverseCurve) {
     value = begin;
@@ -62,7 +62,7 @@ class AnimatedValue<T extends dynamic> extends CurvedVariable {
 
   void setProgress(double t, Direction direction) {
     if (end != null) {
-      t = _transform(t, direction);
+      t = transform(t, direction);
       value = (t == 1.0) ? end : lerp(t);
     }
   }
@@ -70,14 +70,14 @@ class AnimatedValue<T extends dynamic> extends CurvedVariable {
   String toString() => 'AnimatedValue(begin=$begin, end=$end, value=$value)';
 }
 
-class AnimatedList extends CurvedVariable {
+class AnimatedList extends AnimationTiming implements AnimatedVariable {
   List<AnimatedVariable> variables;
 
   AnimatedList(this.variables, { Interval interval, Curve curve, Curve reverseCurve })
     : super(interval: interval, curve: curve, reverseCurve: reverseCurve);
 
   void setProgress(double t, Direction direction) {
-    double adjustedTime = _transform(t, direction);
+    double adjustedTime = transform(t, direction);
     for (AnimatedVariable variable in variables)
       variable.setProgress(adjustedTime, direction);
   }

packages/flutter/lib/animation/animation_performance.dart

@@ -46,6 +46,8 @@ class AnimationPerformance {
   Direction _curveDirection;
   Direction get curveDirection => _curveDirection;
 
+  AnimationTiming timing;
+
   // If non-null, animate with this force instead of a tween animation.
   Force attachedForce;
 
@@ -67,6 +69,10 @@ class AnimationPerformance {
     _checkStatusChanged();
   }
 
+  double get curvedProgress {
+    return timing != null ? timing.transform(progress, curveDirection) : progress;
+  }
+
   bool get isDismissed => status == AnimationStatus.dismissed;
   bool get isCompleted => status == AnimationStatus.completed;
   bool get isAnimating => timeline.isAnimating;
@@ -82,7 +88,7 @@ class AnimationPerformance {
   }
 
   void updateVariable(AnimatedVariable variable) {
-    variable.setProgress(progress, curveDirection);
+    variable.setProgress(curvedProgress, curveDirection);
   }
 
   Future play([Direction direction = Direction.forward]) {
@@ -165,7 +171,7 @@ class AnimationPerformance {
   void _tick(double t) {
     _updateCurveDirection();
     if (variable != null)
-      variable.setProgress(t, curveDirection);
+      variable.setProgress(curvedProgress, curveDirection);
     _notifyListeners();
     _checkStatusChanged();
   }

packages/flutter/lib/widgets/popup_menu.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:math' as math;
+import 'dart:async';
 import 'dart:sky' as sky;
 
 import 'package:sky/animation/animated_value.dart';
@@ -10,11 +10,11 @@ import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/theme/colors.dart';
 import 'package:sky/theme/shadows.dart';
-import 'package:sky/widgets/animated_component.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/popup_menu_item.dart';
 import 'package:sky/widgets/scrollable.dart';
+import 'package:sky/widgets/transitions.dart';
 
 export 'package:sky/animation/animation_performance.dart' show AnimationStatus;
 
@@ -29,7 +29,7 @@ const double _kMenuVerticalPadding = 8.0;
 
 typedef void PopupMenuStatusChangedCallback(AnimationStatus status);
 
-class PopupMenu extends AnimatedComponent {
+class PopupMenu extends StatefulComponent {
 
   PopupMenu({
     Key key,
@@ -46,63 +46,42 @@ class PopupMenu extends AnimatedComponent {
   int level;
   Navigator navigator;
 
-  AnimatedValue<double> _opacity;
-  AnimatedValue<double> _width;
-  AnimatedValue<double> _height;
-  List<AnimatedValue<double>> _itemOpacities;
   AnimationPerformance _performance;
 
   void initState() {
     _performance = new AnimationPerformance()
-      ..duration = _kMenuDuration
-      ..addStatusListener(_onStatusChanged);
-    _updateAnimationVariables();
-    watch(_performance);
+      ..duration = _kMenuDuration;
+    _performance.timing = new AnimationTiming()
+      ..reverseInterval = new Interval(0.0, _kMenuCloseIntervalEnd);
     _updateBoxPainter();
+
     if (showing)
       _open();
   }
 
   void syncFields(PopupMenu source) {
-    if (showing != source.showing) {
-      showing = source.showing;
-      if (showing)
+    if (!showing && source.showing)
       _open();
-      else
-        _close();
-    }
+    showing = source.showing;
     onStatusChanged = source.onStatusChanged;
     if (level != source.level) {
       level = source.level;
       _updateBoxPainter();
     }
-    if (items.length != source.items.length)
-      _updateAnimationVariables();
     items = source.items;
     navigator = source.navigator;
-    super.syncFields(source);
   }
 
-  void _updateAnimationVariables() {
-    double unit = 1.0 / (items.length + 1.5); // 1.0 for the width and 0.5 for the last item's fade.
-    _opacity = new AnimatedValue<double>(0.0, end: 1.0);
-    _width = new AnimatedValue<double>(0.0, end: 1.0, interval: new Interval(0.0, unit));
-    _height = new AnimatedValue<double>(0.0, end: 1.0, interval: new Interval(0.0, unit * items.length));
-    _itemOpacities = new List<AnimatedValue<double>>();
-    for (int i = 0; i < items.length; ++i) {
-      double start = (i + 1) * unit;
-      double end = (start + 1.5 * unit).clamp(0.0, 1.0);
-      _itemOpacities.add(new AnimatedValue<double>(
-          0.0, end: 1.0, interval: new Interval(start, end)));
+  void _open() {
+    if (navigator != null) {
+      scheduleMicrotask(() {
+        navigator.pushState(this, (_) => _close());
+      });
     }
-    List<AnimatedVariable> variables = new List<AnimatedVariable>()
-      ..add(_opacity)
-      ..add(_width)
-      ..add(_height)
-      ..addAll(_itemOpacities);
-    AnimatedList list = new AnimatedList(variables)
-      ..reverseInterval = new Interval(0.0, _kMenuCloseIntervalEnd);
-    _performance.variable = list;
+  }
+
+  void _close() {
+    _performance.reverse();
   }
 
   void _updateBoxPainter() {
@@ -112,44 +91,49 @@ class PopupMenu extends AnimatedComponent {
       boxShadow: shadows[level]));
   }
 
-  void _onStatusChanged(AnimationStatus status) {
-    if (status == AnimationStatus.dismissed &&
-        navigator != null &&
+  void _onDismissed() {
+    if (navigator != null &&
         navigator.currentRoute is RouteState &&
         (navigator.currentRoute as RouteState).owner == this) // TODO(ianh): remove cast once analyzer is cleverer
       navigator.pop();
     if (onStatusChanged != null)
-      onStatusChanged(status);
-  }
-
-
-  void _open() {
-    _performance.play();
-    if (navigator != null)
-      navigator.pushState(this, (_) => _close());
-  }
-
-  void _close() {
-    _performance.reverse();
+      onStatusChanged(AnimationStatus.dismissed);
   }
 
   BoxPainter _painter;
 
   Widget build() {
-    int i = 0;
-    List<Widget> children = new List.from(items.map((Widget item) {
-      return new Opacity(opacity: _itemOpacities[i++].value, child: item);
-    }));
+    double unit = 1.0 / (items.length + 1.5); // 1.0 for the width and 0.5 for the last item's fade.
+    List<Widget> children = [];
+    for (int i = 0; i < items.length; ++i) {
+      double start = (i + 1) * unit;
+      double end = (start + 1.5 * unit).clamp(0.0, 1.0);
+      children.add(new FadeTransition(
+        direction: showing ? Direction.forward : Direction.reverse,
+        performance: _performance,
+        opacity: new AnimatedValue<double>(0.0, end: 1.0, interval: new Interval(start, end)),
+        child: items[i]));
+    }
 
-    return new Opacity(
-      opacity: math.min(1.0, _opacity.value * 3.0),
+    final width = new AnimatedValue<double>(0.0, end: 1.0, interval: new Interval(0.0, unit));
+    final height = new AnimatedValue<double>(0.0, end: 1.0, interval: new Interval(0.0, unit * items.length));
+    return new FadeTransition(
+      direction: showing ? Direction.forward : Direction.reverse,
+      performance: _performance,
+      onDismissed: _onDismissed,
+      opacity: new AnimatedValue<double>(0.0, end: 1.0, interval: new Interval(0.0, 1.0 / 3.0)),
       child: new Container(
         margin: new EdgeDims.all(_kMenuMargin),
-        child: new CustomPaint(
+        child: new BuilderTransition(
+          direction: showing ? Direction.forward : Direction.reverse,
+          performance: _performance,
+          variables: [width, height],
+          builder: () {
+            return new CustomPaint(
               callback: (sky.Canvas canvas, Size size) {
-            double width = _width.value * size.width;
-            double height = _height.value * size.height;
-            _painter.paint(canvas, new Rect.fromLTWH(size.width - width, 0.0, width, height));
+                double widthValue = width.value * size.width;
+                double heightValue = height.value * size.height;
+                _painter.paint(canvas, new Rect.fromLTWH(size.width - widthValue, 0.0, widthValue, heightValue));
               },
               child: new ConstrainedBox(
                 constraints: new BoxConstraints(
@@ -169,6 +153,8 @@ class PopupMenu extends AnimatedComponent {
                   )
                 )
               )
+            );
+          }
         )
       )
     );

packages/flutter/lib/widgets/transitions.dart

@@ -92,9 +92,9 @@ class SlideTransition extends TransitionBase {
 
   AnimatedValue<Point> position;
 
-  void syncFields(SlideTransition updated) {
-    position = updated.position;
-    super.syncFields(updated);
+  void syncFields(SlideTransition source) {
+    position = source.position;
+    super.syncFields(source);
   }
 
   Widget build() {
@@ -125,9 +125,9 @@ class FadeTransition extends TransitionBase {
 
   AnimatedValue<double> opacity;
 
-  void syncFields(FadeTransition updated) {
-    opacity = updated.opacity;
-    super.syncFields(updated);
+  void syncFields(FadeTransition source) {
+    opacity = source.opacity;
+    super.syncFields(source);
   }
 
   Widget build() {
@@ -156,9 +156,9 @@ class ColorTransition extends TransitionBase {
 
   AnimatedColorValue color;
 
-  void syncFields(ColorTransition updated) {
-    color = updated.color;
-    super.syncFields(updated);
+  void syncFields(ColorTransition source) {
+    color = source.color;
+    super.syncFields(source);
   }
 
   Widget build() {
@@ -192,10 +192,10 @@ class SquashTransition extends TransitionBase {
   AnimatedValue<double> width;
   AnimatedValue<double> height;
 
-  void syncFields(SquashTransition updated) {
-    width = updated.width;
-    height = updated.height;
-    super.syncFields(updated);
+  void syncFields(SquashTransition source) {
+    width = source.width;
+    height = source.height;
+    super.syncFields(source);
   }
 
   Widget build() {
@@ -206,3 +206,40 @@ class SquashTransition extends TransitionBase {
     return new SizedBox(width: _maybe(width), height: _maybe(height), child: child);
   }
 }
+
+typedef Widget BuilderFunction();
+
+class BuilderTransition extends TransitionBase {
+  BuilderTransition({
+    Key key,
+    this.variables,
+    this.builder,
+    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);
+
+  List<AnimatedValue> variables;
+  BuilderFunction builder;
+
+  void syncFields(BuilderTransition source) {
+    variables = source.variables;
+    builder = source.builder;
+    super.syncFields(source);
+  }
+
+  Widget build() {
+    for (int i = 0; i < variables.length; ++i)
+      performance.updateVariable(variables[i]);
+    return builder();
+  }
+}