Scrollable TabBar Version 1 - support for flinging

sky/sdk/lib/widgets/tabs.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 'package:sky/animation/generators.dart';
+import 'package:sky/animation/mechanics.dart';
 import 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:vector_math/vector_math.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/icon.dart';
 import 'package:sky/widgets/ink_well.dart';
 import 'package:sky/widgets/scrollable.dart';
 import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/widget.dart';
 
 typedef void SelectedIndexChanged(int selectedIndex);
 typedef void LayoutChanged(Size size, List<double> widths);
 
 // See https://www.google.com/design/spec/components/tabs.html#tabs-specs
 const double _kTabHeight = 46.0;
 const double _kTextAndIconTabHeight = 72.0;
 const double _kTabIndicatorHeight = 2.0;
 const double _kMinTabWidth = 72.0;
 const double _kMaxTabWidth = 264.0;
 const double _kRelativeMaxTabWidth = 56.0;
 const EdgeDims _kTabLabelPadding = const EdgeDims.symmetric(horizontal: 12.0);
 const TextStyle _kTabTextStyle = const TextStyle(textAlign: TextAlign.center);
 const int _kTabIconSize = 24;
+const double _kTabBarScrollFriction = 0.005;
 
 class TabBarParentData extends BoxParentData with
     ContainerParentDataMixin<RenderBox> { }
 
 class RenderTabBar extends RenderBox with
     ContainerRenderObjectMixin<RenderBox, TabBarParentData>,
     RenderBoxContainerDefaultsMixin<RenderBox, TabBarParentData> {
 
   RenderTabBar(this.onLayoutChanged);
 
@@ skipping 293 matching lines @@
     Container centeredLabel = new Container(
       child: new Center(child: highlightedLabel),
       constraints: new BoxConstraints(minWidth: _kMinTabWidth),
       padding: _kTabLabelPadding
     );
 
     return new InkWell(child: centeredLabel);
   }
 }
 
+class TabBarScrollBehavior extends ScrollBehavior {
+  TabBarScrollBehavior({ this.maxScrollOffset: 0.0 });
+
+  double maxScrollOffset;
+
+  Simulation release(Particle particle) {
+    if (particle.velocity == 0.0 || particle.position < 0.0 || particle.position >= maxScrollOffset)
+      return null;
+
+    System system = new ParticleInBoxWithFriction(
+      particle: particle,
+      friction: _kTabBarScrollFriction,
+      box: new ClosedBox(min: 0.0, max: maxScrollOffset));
+    return new Simulation(system, terminationCondition: () => particle.position == 0.0);
+  }
+
+  double applyCurve(double scrollOffset, double scrollDelta) {
+    return (scrollOffset + scrollDelta).clamp(0.0, maxScrollOffset);
+  }
+}
+
 class TabBar extends Scrollable {
   TabBar({
     String key,
     this.labels,
     this.selectedIndex: 0,
     this.onChanged,
     this.scrollable: false
   }) : super(key: key, direction: ScrollDirection.horizontal);
 
   Iterable<TabLabel> labels;
   int selectedIndex;
   SelectedIndexChanged onChanged;
   bool scrollable;
 
   void syncFields(TabBar source) {
     super.syncFields(source);
     labels = source.labels;
     selectedIndex = source.selectedIndex;
     onChanged = source.onChanged;
     scrollable = source.scrollable;
     if (!scrollable)
       scrollTo(0.0);
   }
 
-  ScrollBehavior createScrollBehavior() => new BoundedScrollBehavior();
-  BoundedScrollBehavior get scrollBehavior => super.scrollBehavior;
+  ScrollBehavior createScrollBehavior() => new TabBarScrollBehavior();
+  TabBarScrollBehavior get scrollBehavior => super.scrollBehavior;
 
   void _handleTap(int tabIndex) {
     if (tabIndex != selectedIndex && onChanged != null)
       onChanged(tabIndex);
   }
 
   Widget _toTab(TabLabel label, int tabIndex) {
     Tab tab = new Tab(
       label: label,
       selected: tabIndex == selectedIndex,
       key: label.text == null ? label.icon : label.text
     );
     return new Listener(
       child: tab,
       onGestureTap: (_) => _handleTap(tabIndex)
     );
   }
 
   Size _tabBarSize;
   List<double> _tabWidths;
 
   void _layoutChanged(Size tabBarSize, List<double> tabWidths) {
     setState(() {
       _tabBarSize = tabBarSize;
       _tabWidths = tabWidths;
-      scrollBehavior.maxOffset =
+      scrollBehavior.maxScrollOffset =
         _tabWidths.reduce((sum, width) => sum + width) - _tabBarSize.width;
     });
   }
 
   Widget buildContent() {
     assert(labels != null && labels.isNotEmpty);
     List<Widget> tabs = <Widget>[];
     bool textAndIcons = false;
     int tabIndex = 0;
     for (TabLabel label in labels) {
@@ skipping 61 matching lines @@
       selectedIndex: selectedIndex,
       scrollable: scrollable
     );
 
     Widget content = views[selectedIndex].buildContent();
     return new Flex([tabBar, new Flexible(child: content)],
       direction: FlexDirection.vertical
     );
   }
 }