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Update VelocityTracker (4) (#139166)
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This updates the implementation to use the stopwatch from the Clock object and pipes it through to the TestWidgetsFlutterBinding so it will be kept in sync with FakeAsync.

Relands flutter/flutter#138843 attempted to reland flutter/flutter#137381 which attempted to reland #132291
Fixes flutter/flutter#97761

1. The original change was reverted due to flakiness it introduced in tests that use fling gestures.
  * Using a mocked clock through the test binding fixes this now
2. It was reverted a second time because a change at tip of tree broke it, exposing memory leaks, but it was not rebased before landing. 
  * These leaks are now fixed
3. It was reverted a third time, because we were so excellently quick to revert those other times, that we did not notice the broken benchmark that only runs in postsubmit.
  * The benchmark is now fixed
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@Piinks
Piinks authored Nov 29, 2023
1 parent 133711b commit 8ba459c
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Showing 9 changed files with 178 additions and 65 deletions.
52 changes: 29 additions & 23 deletions dev/benchmarks/microbenchmarks/lib/gestures/velocity_tracker_bench.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
// found in the LICENSE file.

import 'package:flutter/gestures.dart';
import 'package:flutter_test/flutter_test.dart';

import '../common.dart';
import 'data/velocity_tracker_data.dart';
Expand All @@ -16,38 +17,43 @@ class TrackerBenchmark {
final String name;
}

void main() {
Future<void> main() async {
assert(false, "Don't run benchmarks in debug mode! Use 'flutter run --release'.");
final BenchmarkResultPrinter printer = BenchmarkResultPrinter();
final List<TrackerBenchmark> benchmarks = <TrackerBenchmark>[
TrackerBenchmark(name: 'velocity_tracker_iteration', tracker: VelocityTracker.withKind(PointerDeviceKind.touch)),
TrackerBenchmark(name: 'velocity_tracker_iteration_ios_fling', tracker: IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch)),
TrackerBenchmark(name: 'velocity_tracker_iteration',
tracker: VelocityTracker.withKind(PointerDeviceKind.touch)),
TrackerBenchmark(name: 'velocity_tracker_iteration_ios_fling',
tracker: IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch)),
];
final Stopwatch watch = Stopwatch();

for (final TrackerBenchmark benchmark in benchmarks) {
print('${benchmark.name} benchmark...');
final VelocityTracker tracker = benchmark.tracker;
watch.reset();
watch.start();
for (int i = 0; i < _kNumIters; i += 1) {
for (final PointerEvent event in velocityEventData) {
if (event is PointerDownEvent || event is PointerMoveEvent) {
tracker.addPosition(event.timeStamp, event.position);
}
if (event is PointerUpEvent) {
tracker.getVelocity();
await benchmarkWidgets((WidgetTester tester) async {
for (final TrackerBenchmark benchmark in benchmarks) {
print('${benchmark.name} benchmark...');
final VelocityTracker tracker = benchmark.tracker;
watch.reset();
watch.start();
for (int i = 0; i < _kNumIters; i += 1) {
for (final PointerEvent event in velocityEventData) {
if (event is PointerDownEvent || event is PointerMoveEvent) {
tracker.addPosition(event.timeStamp, event.position);
}
if (event is PointerUpEvent) {
tracker.getVelocity();
}
}
}
watch.stop();

printer.addResult(
description: 'Velocity tracker: ${tracker.runtimeType}',
value: watch.elapsedMicroseconds / _kNumIters,
unit: 'µs per iteration',
name: benchmark.name,
);
}
watch.stop();
printer.addResult(
description: 'Velocity tracker: ${tracker.runtimeType}',
value: watch.elapsedMicroseconds / _kNumIters,
unit: 'µs per iteration',
name: benchmark.name,
);
}
});

printer.printToStdout();
}
23 changes: 14 additions & 9 deletions packages/flutter/lib/src/gestures/binding.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -373,7 +373,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H

if (resamplingEnabled) {
_resampler.addOrDispatch(event);
_resampler.sample(samplingOffset, _samplingClock);
_resampler.sample(samplingOffset, samplingClock);
return;
}

Expand Down Expand Up @@ -512,24 +512,29 @@ 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();
}
}
}

SamplingClock get _samplingClock {
/// Overrides the sampling clock 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;
Expand Down
42 changes: 42 additions & 0 deletions packages/flutter/lib/src/gestures/velocity_tracker.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@

import 'package:flutter/foundation.dart';

import 'binding.dart';
import 'events.dart';
import 'lsq_solver.dart';

Expand Down Expand Up @@ -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;
Expand All @@ -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 > _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>[];
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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.
Expand Down
10 changes: 10 additions & 0 deletions packages/flutter/test/gestures/double_tap_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ void main() {

setUp(() {
tap = DoubleTapGestureRecognizer();
addTearDown(tap.dispose);

doubleTapRecognized = false;
tap.onDoubleTap = () {
Expand Down Expand Up @@ -156,6 +157,7 @@ void main() {
final DoubleTapGestureRecognizer tapSecondary = DoubleTapGestureRecognizer(
allowedButtonsFilter: (int buttons) => buttons == kSecondaryButton,
);
addTearDown(tapSecondary.dispose);
tapSecondary.onDoubleTap = () {
doubleTapRecognized = true;
};
Expand Down Expand Up @@ -545,6 +547,7 @@ void main() {
final DoubleTapGestureRecognizer tapPrimary = DoubleTapGestureRecognizer(
allowedButtonsFilter: (int buttons) => buttons == kPrimaryButton,
);
addTearDown(tapPrimary.dispose);
tapPrimary.onDoubleTap = () {
doubleTapRecognized = true;
};
Expand Down Expand Up @@ -647,14 +650,17 @@ void main() {
..onTapDown = (TapDownDetails details) {
recognized.add('tapPrimary');
};
addTearDown(tapPrimary.dispose);
tapSecondary = TapGestureRecognizer()
..onSecondaryTapDown = (TapDownDetails details) {
recognized.add('tapSecondary');
};
addTearDown(tapSecondary.dispose);
doubleTap = DoubleTapGestureRecognizer()
..onDoubleTap = () {
recognized.add('doubleTap');
};
addTearDown(doubleTap.dispose);
});

tearDown(() {
Expand Down Expand Up @@ -692,6 +698,7 @@ void main() {
..onDoubleTap = () {
recognized.add('primary');
};
addTearDown(doubleTap.dispose);

// Down/up pair 7: normal tap sequence close to pair 6
const PointerDownEvent down7 = PointerDownEvent(
Expand Down Expand Up @@ -730,6 +737,7 @@ void main() {
..onDoubleTap = () {
recognized.add('primary');
};
addTearDown(doubleTap.dispose);

// Down/up pair 7: normal tap sequence close to pair 6
const PointerDownEvent down7 = PointerDownEvent(
Expand Down Expand Up @@ -765,8 +773,10 @@ void main() {
int tapCount = 0;
final DoubleTapGestureRecognizer doubleTap = DoubleTapGestureRecognizer()
..onDoubleTap = () {};
addTearDown(doubleTap.dispose);
final TapGestureRecognizer tap = TapGestureRecognizer()
..onTap = () => tapCount++;
addTearDown(tap.dispose);

// Open a arena with 2 members and holding.
doubleTap.addPointer(down1);
Expand Down
24 changes: 3 additions & 21 deletions packages/flutter/test/gestures/gesture_binding_resample_event_on_widget_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -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(
Expand Down
4 changes: 2 additions & 2 deletions packages/flutter/test/gestures/gesture_tester.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand All @@ -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));
});
Expand Down
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