Reland VelocityTracker update (again) (#138843)

This updates the implementation to use the stopwatch from the Clock object and piping it through to the TestWidgetsFlutterBinding so it will be kept in sync with FakeAsync.

Relands https://github.com/flutter/flutter/pull/137381 which attempted to reland #132291
Fixes https://github.com/flutter/flutter/issues/97761

The original change was reverted due to flakiness it introduced in tests that use fling gestures.
* https://github.com/flutter/flutter/issues/135728

It was reverted again due to a change in the leak tracking tests that broke it.

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

@@ -366,7 +366,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
 
     if (resamplingEnabled) {
       _resampler.addOrDispatch(event);
-      _resampler.sample(samplingOffset, _samplingClock);
+      _resampler.sample(samplingOffset, samplingClock);
       return;
     }
 
@@ -505,16 +505,10 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     _hitTests.clear();
   }
 
-  /// Overrides the sampling clock for debugging and testing.
-  ///
-  /// This value is ignored in non-debug builds.
-  @protected
-  SamplingClock? get debugSamplingClock => null;
-
   void _handleSampleTimeChanged() {
     if (!locked) {
       if (resamplingEnabled) {
-        _resampler.sample(samplingOffset, _samplingClock);
+        _resampler.sample(samplingOffset, samplingClock);
       }
       else {
         _resampler.stop();
@@ -522,7 +516,18 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     }
   }
 
-  SamplingClock get _samplingClock {
+  /// Overrides the [samplingClock] for debugging and testing.
+  ///
+  /// This value is ignored in non-debug builds.
+  @protected
+  SamplingClock? get debugSamplingClock => null;
+
+  /// Provides access to the current [DateTime] and `StopWatch` objects for
+  /// sampling.
+  ///
+  /// Overridden by [debugSamplingClock] for debug builds and testing. Using
+  /// this object under test will maintain synchronization with [FakeAsync].
+  SamplingClock get samplingClock {
     SamplingClock value = SamplingClock();
     assert(() {
       final SamplingClock? debugValue = debugSamplingClock;

packages/flutter/lib/src/gestures/velocity_tracker.dart

@@ -5,6 +5,7 @@
 
 import 'package:flutter/foundation.dart';
 
+import 'binding.dart';
 import 'events.dart';
 import 'lsq_solver.dart';
 
@@ -149,12 +150,21 @@ class VelocityTracker {
   /// The kind of pointer this tracker is for.
   final PointerDeviceKind kind;
 
+  // Time difference since the last sample was added
+  Stopwatch get _sinceLastSample {
+    _stopwatch ??= GestureBinding.instance.samplingClock.stopwatch();
+    return _stopwatch!;
+  }
+  Stopwatch? _stopwatch;
+
   // Circular buffer; current sample at _index.
   final List<_PointAtTime?> _samples = List<_PointAtTime?>.filled(_historySize, null);
   int _index = 0;
 
   /// Adds a position as the given time to the tracker.
   void addPosition(Duration time, Offset position) {
+    _sinceLastSample.start();
+    _sinceLastSample.reset();
     _index += 1;
     if (_index == _historySize) {
       _index = 0;
@@ -169,6 +179,16 @@ class VelocityTracker {
   ///
   /// Returns null if there is no data on which to base an estimate.
   VelocityEstimate? getVelocityEstimate() {
+    // Has user recently moved since last sample?
+    if (_sinceLastSample.elapsedMilliseconds > VelocityTracker._assumePointerMoveStoppedMilliseconds) {
+      return const VelocityEstimate(
+        pixelsPerSecond: Offset.zero,
+        confidence: 1.0,
+        duration: Duration.zero,
+        offset: Offset.zero,
+      );
+    }
+
     final List<double> x = <double>[];
     final List<double> y = <double>[];
     final List<double> w = <double>[];
@@ -195,7 +215,7 @@ class VelocityTracker {
       final double age = (newestSample.time - sample.time).inMicroseconds.toDouble() / 1000;
       final double delta = (sample.time - previousSample.time).inMicroseconds.abs().toDouble() / 1000;
       previousSample = sample;
-      if (age > _horizonMilliseconds || delta > _assumePointerMoveStoppedMilliseconds) {
+      if (age > _horizonMilliseconds || delta > VelocityTracker._assumePointerMoveStoppedMilliseconds) {
         break;
       }
 
@@ -288,6 +308,8 @@ class IOSScrollViewFlingVelocityTracker extends VelocityTracker {
 
   @override
   void addPosition(Duration time, Offset position) {
+    _sinceLastSample.start();
+    _sinceLastSample.reset();
     assert(() {
       final _PointAtTime? previousPoint = _touchSamples[_index];
       if (previousPoint == null || previousPoint.time <= time) {
@@ -326,6 +348,16 @@ class IOSScrollViewFlingVelocityTracker extends VelocityTracker {
 
   @override
   VelocityEstimate getVelocityEstimate() {
+    // Has user recently moved since last sample?
+    if (_sinceLastSample.elapsedMilliseconds > VelocityTracker._assumePointerMoveStoppedMilliseconds) {
+      return const VelocityEstimate(
+        pixelsPerSecond: Offset.zero,
+        confidence: 1.0,
+        duration: Duration.zero,
+        offset: Offset.zero,
+      );
+    }
+
     // The velocity estimated using this expression is an approximation of the
     // scroll velocity of an iOS scroll view at the moment the user touch was
     // released, not the final velocity of the iOS pan gesture recognizer
@@ -387,6 +419,16 @@ class MacOSScrollViewFlingVelocityTracker extends IOSScrollViewFlingVelocityTrac
 
   @override
   VelocityEstimate getVelocityEstimate() {
+    // Has user recently moved since last sample?
+    if (_sinceLastSample.elapsedMilliseconds > VelocityTracker._assumePointerMoveStoppedMilliseconds) {
+      return const VelocityEstimate(
+        pixelsPerSecond: Offset.zero,
+        confidence: 1.0,
+        duration: Duration.zero,
+        offset: Offset.zero,
+      );
+    }
+
     // The velocity estimated using this expression is an approximation of the
     // scroll velocity of a macOS scroll view at the moment the user touch was
     // released.

packages/flutter/test/gestures/gesture_binding_resample_event_on_widget_test.dart

@@ -4,35 +4,17 @@
 
 import 'dart:ui' as ui;
 
-import 'package:clock/clock.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
 
-class TestResampleEventFlutterBinding extends AutomatedTestWidgetsFlutterBinding {
-  @override
-  SamplingClock? get debugSamplingClock => TestSamplingClock(this.clock);
-}
-
-class TestSamplingClock implements SamplingClock {
-  TestSamplingClock(this._clock);
-
-  @override
-  DateTime now() => _clock.now();
-
-  @override
-  Stopwatch stopwatch() => _clock.stopwatch();
-
-  final Clock _clock;
-}
-
 void main() {
-  final TestWidgetsFlutterBinding binding = TestResampleEventFlutterBinding();
   testWidgetsWithLeakTracking('PointerEvent resampling on a widget', (WidgetTester tester) async {
-    assert(WidgetsBinding.instance == binding);
-    Duration currentTestFrameTime() => Duration(milliseconds: binding.clock.now().millisecondsSinceEpoch);
+    Duration currentTestFrameTime() => Duration(
+      milliseconds: TestWidgetsFlutterBinding.instance.clock.now().millisecondsSinceEpoch,
+    );
     void requestFrame() => SchedulerBinding.instance.scheduleFrameCallback((_) {});
     final Duration epoch = currentTestFrameTime();
     final ui.PointerDataPacket packet = ui.PointerDataPacket(

packages/flutter/test/gestures/gesture_tester.dart

@@ -4,7 +4,7 @@
 
 import 'package:fake_async/fake_async.dart';
 import 'package:flutter/gestures.dart';
-import 'package:flutter_test/flutter_test.dart';
+import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
 import 'package:meta/meta.dart';
 
 class GestureTester {
@@ -26,7 +26,7 @@ typedef GestureTest = void Function(GestureTester tester);
 
 @isTest
 void testGesture(String description, GestureTest callback) {
-  test(description, () {
+  testWidgetsWithLeakTracking(description, (_) async {
     FakeAsync().run((FakeAsync async) {
       callback(GestureTester._(async));
     });

packages/flutter/test/gestures/velocity_tracker_test.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/gestures.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
+
 import 'velocity_tracker_data.dart';
 
 bool _withinTolerance(double actual, double expected) {
@@ -34,7 +36,7 @@ void main() {
     Offset(-71.51939428321249, 3716.7385187526947),
   ];
 
-  test('Velocity tracker gives expected results', () {
+  testWidgetsWithLeakTracking('Velocity tracker gives expected results', (WidgetTester tester) async {
     final VelocityTracker tracker = VelocityTracker.withKind(PointerDeviceKind.touch);
     int i = 0;
     for (final PointerEvent event in velocityEventData) {
@@ -48,7 +50,7 @@ void main() {
     }
   });
 
-  test('Velocity control test', () {
+  testWidgetsWithLeakTracking('Velocity control test', (WidgetTester tester) async {
     const Velocity velocity1 = Velocity(pixelsPerSecond: Offset(7.0, 0.0));
     const Velocity velocity2 = Velocity(pixelsPerSecond: Offset(12.0, 0.0));
     expect(velocity1, equals(const Velocity(pixelsPerSecond: Offset(7.0, 0.0))));
@@ -60,7 +62,7 @@ void main() {
     expect(velocity1, hasOneLineDescription);
   });
 
-  test('Interrupted velocity estimation', () {
+  testWidgetsWithLeakTracking('Interrupted velocity estimation', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/pull/7510
     final VelocityTracker tracker = VelocityTracker.withKind(PointerDeviceKind.touch);
     for (final PointerEvent event in interruptedVelocityEventData) {
@@ -73,12 +75,12 @@ void main() {
     }
   });
 
-  test('No data velocity estimation', () {
+  testWidgetsWithLeakTracking('No data velocity estimation', (WidgetTester tester) async {
     final VelocityTracker tracker = VelocityTracker.withKind(PointerDeviceKind.touch);
     expect(tracker.getVelocity(), Velocity.zero);
   });
 
-  test('FreeScrollStartVelocityTracker.getVelocity throws when no points', () {
+  testWidgetsWithLeakTracking('FreeScrollStartVelocityTracker.getVelocity throws when no points', (WidgetTester tester) async {
     final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
     AssertionError? exception;
     try {
@@ -90,7 +92,7 @@ void main() {
     expect(exception?.toString(), contains('at least 1 point'));
   });
 
-  test('FreeScrollStartVelocityTracker.getVelocity throws when the new point precedes the previous point', () {
+  testWidgetsWithLeakTracking('FreeScrollStartVelocityTracker.getVelocity throws when the new point precedes the previous point', (WidgetTester tester) async {
     final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
     AssertionError? exception;
 
@@ -105,7 +107,7 @@ void main() {
     expect(exception?.toString(), contains('has a smaller timestamp'));
   });
 
-  test('Estimate does not throw when there are more than 1 point', () {
+  testWidgetsWithLeakTracking('Estimate does not throw when there are more than 1 point', (WidgetTester tester) async {
     final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
     Offset position = Offset.zero;
     Duration time = Duration.zero;
@@ -127,7 +129,7 @@ void main() {
     }
   });
 
-  test('Makes consistent velocity estimates with consistent velocity', () {
+  testWidgetsWithLeakTracking('Makes consistent velocity estimates with consistent velocity', (WidgetTester tester) async {
     final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
     Offset position = Offset.zero;
     Duration time = Duration.zero;
@@ -144,4 +146,55 @@ void main() {
       }
     }
   });
+
+  testWidgetsWithLeakTracking('Assume zero velocity when there are no recent samples - base VelocityTracker', (WidgetTester tester) async {
+    final VelocityTracker tracker = VelocityTracker.withKind(PointerDeviceKind.touch);
+    Offset position = Offset.zero;
+    Duration time = Duration.zero;
+    const Offset positionDelta = Offset(0, -1);
+    const Duration durationDelta = Duration(seconds: 1);
+
+    for (int i = 0; i < 10; i+=1) {
+      position += positionDelta;
+      time += durationDelta;
+      tracker.addPosition(time, position);
+    }
+    await tester.pumpAndSettle();
+
+    expect(tracker.getVelocity().pixelsPerSecond, Offset.zero);
+  });
+
+  testWidgetsWithLeakTracking('Assume zero velocity when there are no recent samples - IOS', (WidgetTester tester) async {
+    final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
+    Offset position = Offset.zero;
+    Duration time = Duration.zero;
+    const Offset positionDelta = Offset(0, -1);
+    const Duration durationDelta = Duration(seconds: 1);
+
+    for (int i = 0; i < 10; i+=1) {
+      position += positionDelta;
+      time += durationDelta;
+      tracker.addPosition(time, position);
+    }
+    await tester.pumpAndSettle();
+
+    expect(tracker.getVelocity().pixelsPerSecond, Offset.zero);
+  });
+
+  testWidgetsWithLeakTracking('Assume zero velocity when there are no recent samples - MacOS', (WidgetTester tester) async {
+    final MacOSScrollViewFlingVelocityTracker tracker = MacOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
+    Offset position = Offset.zero;
+    Duration time = Duration.zero;
+    const Offset positionDelta = Offset(0, -1);
+    const Duration durationDelta = Duration(seconds: 1);
+
+    for (int i = 0; i < 10; i+=1) {
+      position += positionDelta;
+      time += durationDelta;
+      tracker.addPosition(time, position);
+    }
+    await tester.pumpAndSettle();
+
+    expect(tracker.getVelocity().pixelsPerSecond, Offset.zero);
+  });
 }

packages/flutter/test/rendering/editable_gesture_test.dart

@@ -8,9 +8,10 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  setUp(() => _GestureBindingSpy());
+  final TestWidgetsFlutterBinding binding = _GestureBindingSpy();
 
-  test('attach and detach correctly handle gesture', () {
+  testWidgets('attach and detach correctly handle gesture', (_) async {
+    assert(WidgetsBinding.instance == binding);
     final TextSelectionDelegate delegate = FakeEditableTextState();
     final RenderEditable editable = RenderEditable(
       backgroundCursorColor: Colors.grey,

packages/flutter_test/lib/src/binding.dart

@@ -425,6 +425,9 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   /// actual current wall-clock time.
   Clock get clock;
 
+  @override
+  SamplingClock? get debugSamplingClock => _TestSamplingClock(clock);
+
   /// Triggers a frame sequence (build/layout/paint/etc),
   /// then flushes microtasks.
   ///
@@ -2149,6 +2152,18 @@ class TestViewConfiguration extends ViewConfiguration {
   String toString() => 'TestViewConfiguration';
 }
 
+class _TestSamplingClock implements SamplingClock {
+  _TestSamplingClock(this._clock);
+
+  @override
+  DateTime now() => _clock.now();
+
+  @override
+  Stopwatch stopwatch() => _clock.stopwatch();
+
+  final Clock _clock;
+}
+
 const int _kPointerDecay = -2;
 
 class _LiveTestPointerRecord {