Fix regressions with Drawer animations that I introduced.

sky/sdk/lib/widgets/drawer.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:sky' as sky;
 
 import '../animation/animation_performance.dart';
 import '../animation/curves.dart';
 import '../theme/shadows.dart';
 import 'animated_component.dart';
 import 'basic.dart';
 import 'theme.dart';
 
 // TODO(eseidel): Draw width should vary based on device size:
 // http://www.google.com/design/spec/layout/structure.html#structure-side-nav
 
 // Mobile:
 // Width = Screen width − 56 dp
 // Maximum width: 320dp
 // Maximum width applies only when using a left nav. When using a right nav,
 // the panel can cover the full width of the screen.
 
 // Desktop/Tablet:
 // Maximum width for a left nav is 400dp.
 // The right nav can vary depending on content.
 
 const double _kWidth = 304.0;
 const double _kMinFlingVelocity = 0.4;
 const int _kBaseSettleDurationMS = 246;
-const Curve _kAnimationCurve = parabolicRise;
+// TODO(mpcomplete): The curve must be linear if we want the drawer to track
+// the user's finger. Odeon remedies this by attaching spring forces to the
+// initial timeline when animating (so it doesn't look linear).
+const Curve _kAnimationCurve = linear;
 
 typedef void DrawerStatusChangeHandler (bool showing);
 
 class DrawerController {
   DrawerController(this.onStatusChange) {
     performance = new AnimationPerformance()
       ..duration = new Duration(milliseconds: _kBaseSettleDurationMS)
       ..variable = position;
     performance.timeline.onValueChanged.listen(_checkValue);
   }
@@ skipping 23 matching lines @@
 
   void handleMaskTap(_) => close();
 
   // TODO(mpcomplete): Figure out how to generalize these handlers on a
   // "PannableThingy" interface.
   void handlePointerDown(_) => performance.stop();
 
   void handlePointerMove(sky.PointerEvent event) {
     if (performance.isAnimating)
       return;
     performance.progress += event.dx / _kWidth;

[Matt Perry, 2015/07/06 20:30:28]

This part is why we need a linear curve. We're updating the performance's
timeline. With a nonlinear curve, the position change would not be 1-1 with the
drag event.

   }
 
   void handlePointerUp(_) {
     if (!performance.isAnimating)
       _settle();
   }
 
   void handlePointerCancel(_) {
     if (!performance.isAnimating)
       _settle();
@@ skipping 25 matching lines @@
     level = source.level;
     controller = source.controller;
     super.syncFields(source);
   }
 
   // TODO(mpcomplete): the animation system should handle building, maybe? Or
   // at least setting the transform. Figure out how this could work for things
   // like fades, slides, rotates, pinch, etc.
   Widget build() {
     // TODO(mpcomplete): animate as a fade-in.
-    double scaler = controller.performance.progress + 1.0;
+    double scaler = controller.performance.progress;
     Color maskColor = new Color.fromARGB((0x7F * scaler).floor(), 0, 0, 0);
 
     var mask = new Listener(
       child: new Container(decoration: new BoxDecoration(backgroundColor: maskColor)),
       onGestureTap: controller.handleMaskTap
     );
 
     Widget content = controller.position.build(
       new Container(
         decoration: new BoxDecoration(
           backgroundColor: Theme.of(this).canvasColor,
           boxShadow: shadows[level]),
         width: _kWidth,
         child: new Block(children)
       ));
 
     return new Listener(
       child: new Stack([ mask, content ]),
       onPointerDown: controller.handlePointerDown,
       onPointerMove: controller.handlePointerMove,
       onPointerUp: controller.handlePointerUp,
       onPointerCancel: controller.handlePointerCancel,
       onGestureFlingStart: controller.handleFlingStart
     );
   }
 
 }