Support disabled animations (#20354)

examples/flutter_gallery/lib/demo/material/progress_indicator_demo.dart

@@ -21,6 +21,7 @@ class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo> with Sing
     _controller = new AnimationController(
       duration: const Duration(milliseconds: 1500),
       vsync: this,
+      animationBehavior: AnimationBehavior.preserve,
     )..forward();
 
     _animation = new CurvedAnimation(

packages/flutter/lib/semantics.dart

@@ -13,5 +13,6 @@
 /// and is used by the platform-specific accessibility services.
 library semantics;
 
+export 'src/semantics/binding.dart';
 export 'src/semantics/semantics.dart';
 export 'src/semantics/semantics_service.dart';

packages/flutter/lib/src/animation/animation_controller.dart

@@ -7,6 +7,7 @@ import 'dart:ui' as ui show lerpDouble;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/physics.dart';
+import 'package:flutter/semantics.dart';
 import 'package:flutter/scheduler.dart';
 
 import 'animation.dart';
@@ -38,6 +39,30 @@ const Tolerance _kFlingTolerance = Tolerance(
   distance: 0.01,
 );
 
+/// Configures how an [AnimationController] behaves when animations are disabled.
+///
+/// When [AccessibilityFeatures.disableAnimations] is true, the device is asking
+/// flutter to reduce or disable animations as much as possible. To honor this,
+/// we reduce the duration and the corresponding number of frames for animations.
+/// This enum is used to allow certain [AnimationControllers] to opt out of this
+/// behavior.
+///
+/// For example, the [AnimationController] which controls the physics simulation
+/// for a scrollable list will have [AnimationBehavior.preserve] so that when
+/// a user attempts to scroll it does not jump to the end/beginning too quickly.
+enum AnimationBehavior {
+  /// The [AnimationController] will reduce its duration when
+  /// [AccessibilityFeatures.disableAnimations] is true.
+  normal,
+
+  /// The [AnimationController] will preserve its behavior.
+  ///
+  /// This is the default for repeating animations in order to prevent them from
+  /// flashing rapidly on the screen if the widget does not take the
+  /// [AccessibilityFeatures.disableAnimations] flag into account.
+  preserve,
+}
+
 /// A controller for an animation.
 ///
 /// This class lets you perform tasks such as:
@@ -120,6 +145,7 @@ class AnimationController extends Animation<double>
     this.debugLabel,
     this.lowerBound = 0.0,
     this.upperBound = 1.0,
+    this.animationBehavior = AnimationBehavior.normal,
     @required TickerProvider vsync,
   }) : assert(lowerBound != null),
        assert(upperBound != null),
@@ -151,6 +177,7 @@ class AnimationController extends Animation<double>
     this.duration,
     this.debugLabel,
     @required TickerProvider vsync,
+    this.animationBehavior = AnimationBehavior.preserve,
   }) : assert(value != null),
        assert(vsync != null),
        lowerBound = double.negativeInfinity,
@@ -170,6 +197,14 @@ class AnimationController extends Animation<double>
   /// identifying animation controller instances in debug output.
   final String debugLabel;
 
+  /// The behavior of the controller when [AccessibilityFeatures.disableAnimations]
+  /// is true.
+  ///
+  /// Defaults to [AnimationBehavior.normal] for the [new AnimationBehavior]
+  /// constructor, and [AnimationBehavior.preserve] for the
+  /// [new AnimationBehavior.unbounded] constructor.
+  final AnimationBehavior animationBehavior;
+
   /// Returns an [Animation<double>] for this animation controller, so that a
   /// pointer to this object can be passed around without allowing users of that
   /// pointer to mutate the [AnimationController] state.
@@ -363,7 +398,18 @@ class AnimationController extends Animation<double>
     return _animateToInternal(target, duration: duration, curve: curve);
   }
 
-  TickerFuture _animateToInternal(double target, { Duration duration, Curve curve = Curves.linear }) {
+  TickerFuture _animateToInternal(double target, { Duration duration, Curve curve = Curves.linear, AnimationBehavior animationBehavior }) {
+    final AnimationBehavior behavior = animationBehavior ?? this.animationBehavior;
+    double scale = 1.0;
+    if (SemanticsBinding.instance.disableAnimations) {
+      switch (behavior) {
+        case AnimationBehavior.normal:
+          scale = 0.05;
+          break;
+        case AnimationBehavior.preserve:
+          break;
+      }
+    }
     Duration simulationDuration = duration;
     if (simulationDuration == null) {
       assert(() {
@@ -398,7 +444,7 @@ class AnimationController extends Animation<double>
     }
     assert(simulationDuration > Duration.zero);
     assert(!isAnimating);
-    return _startSimulation(new _InterpolationSimulation(_value, target, simulationDuration, curve));
+    return _startSimulation(new _InterpolationSimulation(_value, target, simulationDuration, curve, scale));
   }
 
   /// Starts running this animation in the forward direction, and
@@ -441,11 +487,22 @@ class AnimationController extends Animation<double>
   /// The most recently returned [TickerFuture], if any, is marked as having been
   /// canceled, meaning the future never completes and its [TickerFuture.orCancel]
   /// derivative future completes with a [TickerCanceled] error.
-  TickerFuture fling({ double velocity = 1.0 }) {
+  TickerFuture fling({ double velocity = 1.0, AnimationBehavior animationBehavior}) {
     _direction = velocity < 0.0 ? _AnimationDirection.reverse : _AnimationDirection.forward;
     final double target = velocity < 0.0 ? lowerBound - _kFlingTolerance.distance
                                          : upperBound + _kFlingTolerance.distance;
-    final Simulation simulation = new SpringSimulation(_kFlingSpringDescription, value, target, velocity)
+    double scale = 1.0;
+    final AnimationBehavior behavior = animationBehavior ?? this.animationBehavior;
+    if (SemanticsBinding.instance.disableAnimations) {
+      switch (behavior) {
+        case AnimationBehavior.normal:
+          scale = 200.0;
+          break;
+        case AnimationBehavior.preserve:
+          break;
+      }
+    }
+    final Simulation simulation = new SpringSimulation(_kFlingSpringDescription, value, target, velocity * scale)
       ..tolerance = _kFlingTolerance;
     return animateWith(simulation);
   }
@@ -558,11 +615,11 @@ class AnimationController extends Animation<double>
 }
 
 class _InterpolationSimulation extends Simulation {
-  _InterpolationSimulation(this._begin, this._end, Duration duration, this._curve)
+  _InterpolationSimulation(this._begin, this._end, Duration duration, this._curve, double scale)
     : assert(_begin != null),
       assert(_end != null),
       assert(duration != null && duration.inMicroseconds > 0),
-      _durationInSeconds = duration.inMicroseconds / Duration.microsecondsPerSecond;
+      _durationInSeconds = (duration.inMicroseconds * scale) / Duration.microsecondsPerSecond;
 
   final double _durationInSeconds;
   final double _begin;

packages/flutter/lib/src/material/refresh_indicator.dart

@@ -153,7 +153,6 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
   @override
   void initState() {
     super.initState();
-
     _positionController = new AnimationController(vsync: this);
     _positionFactor = new Tween<double>(
       begin: 0.0,

packages/flutter/lib/src/material/reorderable_list.dart

@@ -154,6 +154,7 @@ class _ReorderableListContent extends StatefulWidget {
 }
 
 class _ReorderableListContentState extends State<_ReorderableListContent> with TickerProviderStateMixin {
+
   // The extent along the [widget.scrollDirection] axis to allow a child to
   // drop into when the user reorders list children.
   //
@@ -280,6 +281,7 @@ class _ReorderableListContentState extends State<_ReorderableListContent> with T
       viewport.getOffsetToReveal(contextObject, 1.0).offset + margin,
     );
     final bool onScreen = scrollOffset <= topOffset && scrollOffset >= bottomOffset;
+
     // If the context is off screen, then we request a scroll to make it visible.
     if (!onScreen) {
       _scrolling = true;

packages/flutter/lib/src/rendering/binding.dart

@@ -21,7 +21,7 @@ import 'view.dart';
 export 'package:flutter/gestures.dart' show HitTestResult;
 
 /// The glue between the render tree and the Flutter engine.
-abstract class RendererBinding extends BindingBase with ServicesBinding, SchedulerBinding, HitTestable {
+abstract class RendererBinding extends BindingBase with ServicesBinding, SchedulerBinding, SemanticsBinding, HitTestable {
   // This class is intended to be used as a mixin, and should not be
   // extended directly.
   factory RendererBinding._() => null;
@@ -153,12 +153,6 @@ abstract class RendererBinding extends BindingBase with ServicesBinding, Schedul
   @protected
   void handleTextScaleFactorChanged() { }
 
-  /// Called when the platform accessibility features change.
-  ///
-  /// See [Window.onAccessibilityFeaturesChanged].
-  @protected
-  void handleAccessibilityFeaturesChanged() {}
-
   /// Returns a [ViewConfiguration] configured for the [RenderView] based on the
   /// current environment.
   ///
@@ -341,7 +335,7 @@ void debugDumpSemanticsTree(DebugSemanticsDumpOrder childOrder) {
 /// that layer's binding.
 ///
 /// See also [BindingBase].
-class RenderingFlutterBinding extends BindingBase with GestureBinding, ServicesBinding, SchedulerBinding, RendererBinding {
+class RenderingFlutterBinding extends BindingBase with GestureBinding, ServicesBinding, SchedulerBinding, SemanticsBinding, RendererBinding {
   /// Creates a binding for the rendering layer.
   ///
   /// The `root` render box is attached directly to the [renderView] and is

packages/flutter/lib/src/scheduler/ticker.dart

@@ -225,7 +225,6 @@ class Ticker {
     _animationId = null;
 
     _startTime ??= timeStamp;
-
     _onTick(timeStamp - _startTime);
 
     // The onTick callback may have scheduled another tick already, for

packages/flutter/lib/src/semantics/binding.dart

+// Copyright 2018 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:ui' as ui show AccessibilityFeatures, window;
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+
+/// The glue between the semantics layer and the Flutter engine.
+// TODO(jonahwilliams): move the remaining semantic related bindings here.
+class SemanticsBinding extends BindingBase with ServicesBinding {
+  // This class is intended to be used as a mixin, and should not be
+  // extended directly.
+  factory SemanticsBinding._() => null;
+
+  /// The current [SemanticsBinding], if one has been created.
+  static SemanticsBinding get instance => _instance;
+  static SemanticsBinding _instance;
+
+  @override
+  void initInstances() {
+    super.initInstances();
+    _instance = this;
+    _accessibilityFeatures = ui.window.accessibilityFeatures;
+  }
+
+  /// Called when the platform accessibility features change.
+  ///
+  /// See [Window.onAccessibilityFeaturesChanged].
+  @protected
+  void handleAccessibilityFeaturesChanged() {
+    _accessibilityFeatures = ui.window.accessibilityFeatures;
+  }
+
+  /// The currently active set of [AccessibilityFeatures].
+  ///
+  /// This is initialized the first time [runApp] is called and updated whenever
+  /// a flag is changed.
+  ///
+  /// To listen to changes to accessibility features, create a
+  /// [WidgetsBindingObserver] and listen to [didChangeAccessibilityFeatures].
+  ui.AccessibilityFeatures get accessibilityFeatures => _accessibilityFeatures;
+  ui.AccessibilityFeatures _accessibilityFeatures;
+
+  /// Whether the device is requesting that animations be disabled.
+  bool get disableAnimations => accessibilityFeatures.disableAnimations;
+}
\ No newline at end of file

packages/flutter/lib/src/widgets/binding.dart

@@ -917,7 +917,7 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
 
 /// A concrete binding for applications based on the Widgets framework.
 /// This is the glue that binds the framework to the Flutter engine.
-class WidgetsFlutterBinding extends BindingBase with GestureBinding, ServicesBinding, SchedulerBinding, PaintingBinding, RendererBinding, WidgetsBinding {
+class WidgetsFlutterBinding extends BindingBase with GestureBinding, ServicesBinding, SchedulerBinding, PaintingBinding, SemanticsBinding, RendererBinding, WidgetsBinding {
 
   /// Returns an instance of the [WidgetsBinding], creating and
   /// initializing it if necessary. If one is created, it will be a

packages/flutter/test/animation/animation_controller_test.dart

@@ -578,4 +578,84 @@ void main() {
     expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
     statusLog.clear();
   });
+
+  group('AnimationBehavior', () {
+    test('Default values for constructor', () {
+      final AnimationController controller = new AnimationController(vsync: const TestVSync());
+      expect(controller.animationBehavior, AnimationBehavior.normal);
+
+      final AnimationController repeating = new AnimationController.unbounded(vsync: const TestVSync());
+      expect(repeating.animationBehavior, AnimationBehavior.preserve);
+    });
+
+    testWidgets('AnimationBehavior.preserve runs at normal speed when animatingTo', (WidgetTester tester) async {
+      tester.binding.disableAnimations = true;
+      final AnimationController controller = new AnimationController(
+        vsync: const TestVSync(),
+        animationBehavior: AnimationBehavior.preserve,
+      );
+
+      expect(controller.value, 0.0);
+      expect(controller.status, AnimationStatus.dismissed);
+
+      controller.animateTo(1.0, duration: const Duration(milliseconds: 100));
+      tick(const Duration(milliseconds: 0));
+      tick(const Duration(milliseconds: 50));
+
+      expect(controller.value, 0.5);
+      expect(controller.status, AnimationStatus.forward);
+
+      tick(const Duration(milliseconds: 0));
+      tick(const Duration(milliseconds: 150));
+
+      expect(controller.value, 1.0);
+      expect(controller.status, AnimationStatus.completed);
+      tester.binding.disableAnimations = false;
+    });
+
+    testWidgets('AnimationBehavior.normal runs at 20x speed when animatingTo', (WidgetTester tester) async {
+      tester.binding.disableAnimations = true;
+      final AnimationController controller = new AnimationController(
+        vsync: const TestVSync(),
+        animationBehavior: AnimationBehavior.normal,
+      );
+
+      expect(controller.value, 0.0);
+      expect(controller.status, AnimationStatus.dismissed);
+
+      controller.animateTo(1.0, duration: const Duration(milliseconds: 100));
+      tick(const Duration(milliseconds: 0));
+      tick(const Duration(microseconds: 2500));
+
+      expect(controller.value, 0.5);
+      expect(controller.status, AnimationStatus.forward);
+
+      tick(const Duration(milliseconds: 0));
+      tick(const Duration(milliseconds: 5, microseconds: 1000));
+
+      expect(controller.value, 1.0);
+      expect(controller.status, AnimationStatus.completed);
+
+      tester.binding.disableAnimations = false;
+    });
+
+    testWidgets('AnimationBehavior.normal runs "faster" whan AnimationBehavior.preserve', (WidgetTester tester) async {
+      tester.binding.disableAnimations = true;
+      final AnimationController controller = new AnimationController(
+        vsync: const TestVSync(),
+      );
+      final AnimationController fastController = new AnimationController(
+        vsync: const TestVSync(),
+      );
+
+      controller.fling(velocity: 1.0, animationBehavior: AnimationBehavior.preserve);
+      fastController.fling(velocity: 1.0, animationBehavior: AnimationBehavior.normal);
+      tick(const Duration(milliseconds: 0));
+      tick(const Duration(milliseconds: 50));
+
+      // We don't assert a specific faction that normal animation.
+      expect(controller.value < fastController.value, true);
+      tester.binding.disableAnimations = false;
+    });
+  });
 }

packages/flutter/test/foundation/service_extensions_test.dart

@@ -20,6 +20,7 @@ class TestServiceExtensionsBinding extends BindingBase
        GestureBinding,
        SchedulerBinding,
        PaintingBinding,
+       SemanticsBinding,
        RendererBinding,
        WidgetsBinding {
 

packages/flutter/test/rendering/rendering_tester.dart

@@ -11,7 +11,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart' show EnginePhase;
 export 'package:flutter_test/flutter_test.dart' show EnginePhase;
 
-class TestRenderingFlutterBinding extends BindingBase with ServicesBinding, GestureBinding, SchedulerBinding, PaintingBinding, RendererBinding {
+class TestRenderingFlutterBinding extends BindingBase with ServicesBinding, GestureBinding, SchedulerBinding, PaintingBinding, SemanticsBinding, RendererBinding {
   EnginePhase phase = EnginePhase.composite;
 
   @override

packages/flutter/test/scheduler/ticker_test.dart

@@ -83,6 +83,38 @@ void main() {
     expect(ticker.toString(debugIncludeStack: true), contains('testFunction'));
   });
 
+  testWidgets('Ticker can be sped up with time dilation', (WidgetTester tester) async {
+    timeDilation = 0.5; // Move twice as fast.
+    Duration lastDuration;
+    void handleTick(Duration duration) {
+      lastDuration = duration;
+    }
+
+    final Ticker ticker = new Ticker(handleTick);
+    ticker.start();
+    await tester.pump(const Duration(milliseconds: 10));
+    await tester.pump(const Duration(milliseconds: 10));
+    expect(lastDuration, const Duration(milliseconds: 20));
+
+    ticker.dispose();
+  });
+
+  testWidgets('Ticker can be slowed down with time dilation', (WidgetTester tester) async {
+    timeDilation = 2.0; // Move half as fast.
+    Duration lastDuration;
+    void handleTick(Duration duration) {
+      lastDuration = duration;
+    }
+
+    final Ticker ticker = new Ticker(handleTick);
+    ticker.start();
+    await tester.pump(const Duration(milliseconds: 10));
+    await tester.pump(const Duration(milliseconds: 10));
+    expect(lastDuration, const Duration(milliseconds: 5));
+
+    ticker.dispose();
+  });
+
   testWidgets('Ticker stops ticking when application is paused', (WidgetTester tester) async {
     int tickCount = 0;
     void handleTick(Duration duration) {

packages/flutter_driver/lib/src/extension/extension.dart

@@ -36,7 +36,7 @@ const String _extensionMethod = 'ext.flutter.$_extensionMethodName';
 /// eventually completes to a string response.
 typedef Future<String> DataHandler(String message);
 
-class _DriverBinding extends BindingBase with ServicesBinding, SchedulerBinding, GestureBinding, PaintingBinding, RendererBinding, WidgetsBinding {
+class _DriverBinding extends BindingBase with ServicesBinding, SchedulerBinding, GestureBinding, PaintingBinding, SemanticsBinding, RendererBinding, WidgetsBinding {
   _DriverBinding(this._handler, this._silenceErrors);
 
   final DataHandler _handler;

packages/flutter_test/lib/src/binding.dart

@@ -86,6 +86,7 @@ const Size _kDefaultTestViewportSize = Size(800.0, 600.0);
 abstract class TestWidgetsFlutterBinding extends BindingBase
   with SchedulerBinding,
        GestureBinding,
+       SemanticsBinding,
        RendererBinding,
        ServicesBinding,
        PaintingBinding,
@@ -127,6 +128,9 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   @protected
   bool get checkIntrinsicSizes => false;
 
+  @override
+  bool disableAnimations = false;
+
   /// Creates and initializes the binding. This function is
   /// idempotent; calling it a second time will just return the
   /// previously-created instance.