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How to write a render speed test for Flutter

There are many ways to write a render speed test for Flutter. In this article, we give one example that uses the [Flutter driver][flutter_driver], the [dev/benchmarks/macrobenchmarks][macrobenchmarks] app, and the [dev/devicelab][devicelab] to automatically collect metrics for every future Flutter commit and send them to [flutter/cocoon][cocoon].

The instructions below are for contributors who want to expose a Flutter SDK (framework or engine) performance issue, or write pull requests to fix such issues. If one only needs to test the performance of a particular Flutter app, please reference

• https://flutter.dev/docs/cookbook/testing/integration/introduction.
• https://flutter.dev/docs/perf/rendering

Since Flutter Web and Flutter Desktop are still in their early stages, the content here is only well tested and supported on mobile platforms (Android/iOS). We'll come up with docs on how to write performance tests for W

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import 'package:flutter/material.dart';

void main() {
  runApp(IssueDemoApp());
}

class IssueDemoApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(

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https://dart-review.googlesource.com/c/sdk/+/127920
https://dart-review.googlesource.com/c/sdk/+/128200
https://dart-review.googlesource.com/c/sdk/+/127921
https://github.com/flutter/engine/pull/14323
https://github.com/flutter/engine/pull/14521
https://github.com/flutter/engine/pull/14319
https://github.com/flutter/flutter/pull/47742

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import 'package:flutter/material.dart';

final imageUrl =
    'https://cdn.vox-cdn.com/thumbor/yacVJaRnOvWiuIO3L6pe5Tmlv68=/0x26:640x453/920x613/filters:focal(0x26:640x453):format(webp)/cdn.vox-cdn.com/assets/1275052/kitten_field_jump.jpeg';

class CostlyToRasterize extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    const color = Color(0xff00ff);
    return Stack(

liyuqian

diff --git a/lib/ui/window/pointer_data_packet.cc b/lib/ui/window/pointer_data_packet.cc
index bd2abd6f1..61f68c561 100644
--- a/lib/ui/window/pointer_data_packet.cc
+++ b/lib/ui/window/pointer_data_packet.cc
@@ -20,8 +20,9 @@ void PointerDataPacket::SetPointerData(size_t i, const PointerData& data) {
   memcpy(&data_[i * sizeof(PointerData)], &data, sizeof(PointerData));
 }
 
-void PointerDataPacket::GetPointerData(size_t i, PointerData* data) const {
-  memcpy(data, &data_[i * sizeof(PointerData)], sizeof(PointerData));

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import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(

liyuqian

import random

def sample():
  phase = random.random()
  if phase < 3/8.0:
    return random.random(), random.random()
  elif phase < 6/8.0:
    return random.random() + 1, random.random() + 1
  elif phase < 7/8.0:
    return random.random() + 1, random.random()

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import 'dart:math';
import 'dart:io';

import 'package:console/console.dart';

void main() {
  Console.init();
  double a = _askInputAndClearConsole('A, please tell me your value: ');
  double b = _askInputAndClearConsole('B, please tell me your cost: ');
  if (a < b) {

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import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override

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/// Run this with `flutter run --profile` and check its tracing in the observatory.
///
/// You should see janky animations of the CircularProgressIndicator caused by
/// expensiveFunction which has nothing to do with the Flutter framework.
import 'package:flutter/material.dart';
import 'dart:developer';

void expensiveFunction() {
  // It will be very hard to tell why it's so janky without the following Timeline tracing
  // (if the expensiveFunction has a much more innocent name, and is burried beneath hundreds