Make the popup menu width animation work

sky/sdk/lib/widgets/popup_menu.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 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/painting/box_painter.dart';
 import 'package:sky/theme/colors.dart';
@@ skipping 29 matching lines @@
     this.items,
     this.level
   }) : super(key: key);
 
   bool showing;
   PopupMenuStatusChangedCallback onStatusChanged;
   List<PopupMenuItem> items;
   int level;
 
   AnimatedType<double> _opacity;
+  AnimatedType<double> _width;
   AnimatedType<double> _height;
-  AnimatedType<double> _width;
   List<AnimatedType<double>> _itemOpacities;
   AnimationPerformance _performance;
 
   void initState() {
     _performance = new AnimationPerformance()
       ..addListener(_checkForStateChanged);
     _updateAnimationVariables();
     watch(_performance);
     _updateBoxPainter();
     if (showing)
@@ skipping 13 matching lines @@
       level = source.level;
       _updateBoxPainter();
     }
     if (items.length != source.items.length)
       _updateAnimationVariables();
     items = source.items;
     super.syncFields(source);
   }
 
   void _updateAnimationVariables() {
+    double unit = 1.0 / (items.length + 1);
     _opacity = new AnimatedType<double>(0.0, end: 1.0);
-    _width = new AnimatedType<double>(0.5, end: 1.0, interval: new Interval(0.0, 0.5));
-    _height = new AnimatedType<double>(0.0, end: 1.0, interval: new Interval(0.0, 0.33));
+    _width = new AnimatedType<double>(0.0, end: 1.0, interval: new Interval(0.0, unit));
+    _height = new AnimatedType<double>(0.0, end: 1.0, interval: new Interval(0.0, 0.5));
     _itemOpacities = new List<AnimatedType<double>>();
-    double unit = 1.0 / items.length;
     for (int i = 0; i < items.length; ++i) {
-      double start = i * unit;
+      double start = (i + 1) * unit;
       double end = (start + 1.5 * unit).clamp(0.0, 1.0);
       _itemOpacities.add(new AnimatedType<double>(
           0.0, end: 1.0, interval: new Interval(start, end)));
     }
     List<AnimatedVariable> variables = new List<AnimatedVariable>()
       ..add(_opacity)
       ..add(_width)
       ..add(_height)
       ..addAll(_itemOpacities);
     _performance.variable = new AnimatedList(variables);
@@ skipping 37 matching lines @@
     }));
 
     return new Opacity(
       opacity: math.min(1.0, _opacity.value * 3.0),
       child: new Container(
         margin: new EdgeDims.all(_kMenuMargin),
         child: 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.fromLTRB(size.width - width, 0.0, width, height));
+            _painter.paint(canvas, new Rect.fromLTWH(size.width - width, 0.0, width, height));
           },
           child: new ConstrainedBox(
             constraints: new BoxConstraints(
               minWidth: _kMenuMinWidth,
               maxWidth: _kMenuMaxWidth
             ),
             child: new ShrinkWrapWidth(
               stepWidth: _kMenuWidthStep,
               child: new ScrollableViewport(
                 child: new Container(
                   padding: const EdgeDims.symmetric(
                     horizontal: _kMenuHorizontalPadding,
                     vertical: _kMenuVerticalPadding
                   ),
                   child: new Block(children)
                 )
               )
             )
           )
         )
       )
     );
   }
 
 }