Make Switch a standalone class with a custom RenderObject

This changes Switch from being a subclass of the Toggleable widget to
being a standalone Component with a custom RenderObject. This is to
enable adding Switch-specific radial reaction animations in a
subsequent patch. The CustomPaint logic that Toggleable was using does
not provide a nice way for a class and its subclass to both participate
in deciding to repaint.

packages/flutter/example/widgets/big_switch.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/switch.dart';
+import 'package:sky/theme/colors.dart';
+import 'package:vector_math/vector_math.dart';
+
+class BigSwitchApp extends App {
+  bool _value = false;
+
+  void _handleOnChanged(bool value) {
+    setState(() {
+      _value = value;
+    });
+  }
+
+  Widget build() {
+    Matrix4 scale = new Matrix4.identity();
+    scale.scale(5.0, 5.0);
+    return new Container(
+        child: new Switch(value: _value, onChanged: _handleOnChanged),
+        padding: new EdgeDims.all(5.0),
+        transform: scale,
+        decoration: new BoxDecoration(
+          backgroundColor: Teal[600]
+        )
+    );
+  }
+}
+
+void main() {
+  runApp(new BigSwitchApp());
+}

packages/flutter/lib/widgets/basic.dart

@@ -24,6 +24,7 @@ export 'package:sky/rendering/flex.dart' show FlexDirection, FlexJustifyContent,
 export 'package:sky/rendering/object.dart' show Point, Offset, Size, Rect, Color, Paint, Path;
 export 'package:sky/widgets/widget.dart' show Key, GlobalKey, Widget, Component, StatefulComponent, App, runApp, Listener, ParentDataNode;
 
+typedef void ValueChanged(bool);
 
 // PAINTING NODES
 

packages/flutter/lib/widgets/switch.dart

@@ -4,14 +4,18 @@
 
 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/painting/shadows.dart';
 import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/object.dart';
 import 'package:sky/theme/shadows.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/theme.dart';
-import 'package:sky/widgets/toggleable.dart';
+import 'package:sky/widgets/widget.dart';
 
-export 'package:sky/widgets/toggleable.dart' show ValueChanged;
+export 'package:sky/widgets/basic.dart' show ValueChanged;
 
 const sky.Color _kThumbOffColor = const sky.Color(0xFFFAFAFA);
 const sky.Color _kTrackOffColor = const sky.Color(0x42000000);
@@ -20,52 +24,136 @@ const double _kThumbRadius = 10.0;
 const double _kSwitchHeight = _kThumbRadius * 2.0;
 const double _kTrackHeight = 14.0;
 const double _kTrackRadius = _kTrackHeight / 2.0;
-const double _kTrackWidth = _kSwitchWidth - (_kThumbRadius - _kTrackRadius) * 2.0;
+const double _kTrackWidth =
+    _kSwitchWidth - (_kThumbRadius - _kTrackRadius) * 2.0;
+const Duration _kCheckDuration = const Duration(milliseconds: 200);
+const Size _kSwitchSize = const Size(_kSwitchWidth + 2.0, _kSwitchHeight + 2.0);
 
-class Switch extends Toggleable {
-  // TODO(jackson): Hit-test the switch so that it can respond to both taps and swipe gestures
+class Switch extends Component {
+  Switch({Key key, this.value, this.onChanged}) : super(key: key);
 
-  Switch({
-    Key key,
-    bool value,
-    ValueChanged onChanged
-  }) : super(key: key, value: value, onChanged: onChanged);
+  final bool value;
+  final ValueChanged onChanged;
 
-  Size get size => const Size(_kSwitchWidth + 2.0, _kSwitchHeight + 2.0);
+  Widget build() {
+    return new _SwitchWrapper(
+        value: value,
+        onChanged: onChanged,
+        thumbColor: Theme.of(this).accentColor);
+  }
+}
+
+// This wrapper class exists only because Switch needs to be a Component in
+// order to get an accent color from a Theme but Components do not know how to
+// host RenderObjects.
+class _SwitchWrapper extends LeafRenderObjectWrapper {
+  _SwitchWrapper({Key key, this.value, this.onChanged, this.thumbColor})
+      : super(key: key);
+
+  final bool value;
+  final ValueChanged onChanged;
+  final Color thumbColor;
+
+  _RenderSwitch get root => super.root;
+  _RenderSwitch createNode() => new _RenderSwitch(
+      value: value, thumbColor: thumbColor, onChanged: onChanged);
+
+  void syncRenderObject(_SwitchWrapper old) {
+    super.syncRenderObject(old);
+    root.value = value;
+    root.onChanged = onChanged;
+    root.thumbColor = thumbColor;
+  }
+}
+
+class _RenderSwitch extends RenderConstrainedBox {
+  _RenderSwitch(
+      {bool value, Color thumbColor: _kThumbOffColor, ValueChanged onChanged})
+      : _value = value,
+        _thumbColor = thumbColor,
+        _onChanged = onChanged,
+        super(additionalConstraints: new BoxConstraints.tight(_kSwitchSize)) {
+    _performance = new AnimationPerformance()
+      ..variable = _position
+      ..duration = _kCheckDuration
+      ..progress = _value ? 1.0 : 0.0
+      ..addListener(markNeedsPaint);
+  }
+
+  void handleEvent(sky.Event event, BoxHitTestEntry entry) {
+    if (event is sky.GestureEvent &&
+        event.type == 'gesturetap') _onChanged(!_value);
+  }
+
+  bool _value;
+  bool get value => _value;
 
-  void customPaintCallback(sky.Canvas canvas, Size size) {
+  void set value(bool value) {
+    if (value == _value) return;
+    _value = value;
+    // TODO(abarth): Setting the curve on the position means there's a
+    // discontinuity when we reverse the timeline.
+    if (value) {
+      _position.curve = easeIn;
+      _performance.play();
+    } else {
+      _position.curve = easeOut;
+      _performance.reverse();
+    }
+  }
+
+  Color _thumbColor;
+  Color get thumbColor  => _thumbColor;
+
+  void set thumbColor(Color value) {
+    if (value == _thumbColor) return;
+    _thumbColor = value;
+    markNeedsPaint();
+  }
+
+  ValueChanged _onChanged;
+  ValueChanged get onChanged => _onChanged;
+
+  void set onChanged(ValueChanged onChanged) {
+    _onChanged = onChanged;
+  }
+
+  final AnimatedValue<double> _position =
+      new AnimatedValue<double>(0.0, end: 1.0);
+
+  AnimationPerformance _performance;
+
+  void paint(PaintingCanvas canvas, Offset offset) {
     sky.Color thumbColor = _kThumbOffColor;
     sky.Color trackColor = _kTrackOffColor;
-    if (value) {
-      thumbColor = Theme.of(this).accentColor;
-      trackColor = new sky.Color(thumbColor.value & 0x80FFFFFF);
+    if (_value) {
+      thumbColor = _thumbColor;
+      trackColor = new sky.Color(_thumbColor.value & 0x80FFFFFF);
     }
 
     // Draw the track rrect
     sky.Paint paint = new sky.Paint()..color = trackColor;
     paint.setStyle(sky.PaintingStyle.fill);
-    sky.Rect rect = new sky.Rect.fromLTRB(
-      0.0,
-      _kSwitchHeight / 2.0 - _kTrackHeight / 2.0,
-      _kTrackWidth,
-      _kSwitchHeight / 2.0 + _kTrackHeight / 2.0
-    );
-    sky.RRect rrect = new sky.RRect()..setRectXY(rect, _kTrackRadius, _kTrackRadius);
+    sky.Rect rect = new sky.Rect.fromLTWH(offset.dx,
+        offset.dy + _kSwitchHeight / 2.0 - _kTrackHeight / 2.0, _kTrackWidth,
+        _kTrackHeight);
+    sky.RRect rrect = new sky.RRect()
+      ..setRectXY(rect, _kTrackRadius, _kTrackRadius);
     canvas.drawRRect(rrect, paint);
 
     // Draw the raised thumb with a shadow
     paint.color = thumbColor;
     var builder = new ShadowDrawLooperBuilder();
-    for (BoxShadow boxShadow in shadows[1])
-      builder.addShadow(boxShadow.offset, boxShadow.color, boxShadow.blur);
+    for (BoxShadow boxShadow in shadows[1]) builder.addShadow(
+        boxShadow.offset, boxShadow.color, boxShadow.blur);
     paint.setDrawLooper(builder.build());
 
     // The thumb contracts slightly during the animation
-    double inset = 2.0 - (position.value - 0.5).abs() * 2.0;
-    Point thumbPos = new Point(
-      _kTrackRadius + position.value * (_kTrackWidth - _kTrackRadius * 2),
-      _kSwitchHeight / 2.0
-    );
+    double inset = 2.0 - (_position.value - 0.5).abs() * 2.0;
+    Point thumbPos = new Point(offset.dx +
+            _kTrackRadius +
+            _position.value * (_kTrackWidth - _kTrackRadius * 2),
+        offset.dy + _kSwitchHeight / 2.0);
     canvas.drawCircle(thumbPos, _kThumbRadius - inset, paint);
   }
 }

packages/flutter/lib/widgets/toggleable.dart

@@ -10,7 +10,7 @@ import 'package:sky/animation/curves.dart';
 import 'package:sky/widgets/animated_component.dart';
 import 'package:sky/widgets/basic.dart';
 
-typedef void ValueChanged(bool value);
+export 'package:sky/widgets/basic.dart' show ValueChanged;
 
 const Duration _kCheckDuration = const Duration(milliseconds: 200);