Sibling FloatingActionButtons nested under a Wrap slow to repaint on the Web

[yjbanov]

Sample app that reproduces the issue: https://gist.github.com/clocksmith/240a6bbe1a0f72847ee4139fe493a712.

This is reproducible on the HTML backend. We should also check CanvasKit, just in case.

Hat tip to @clocksmith for narrowing it down to a reproducible app.

[yjbanov]

This has improved slightly after the static content scrolling optimization (https://github.com/flutter/engine/pull/17621). As the action buttons scroll out of the view we now prune the invisible paint ops. However, it does not fix the case when all the fabs are visible at once. We need a different strategy for that. I won't be able to come back to this very soon, so I'm unassigning for now.

[TahaTesser]

Canvaskit test looks fine

Dom

Canvaskit

code sample

```dart import 'package:flutter/material.dart'; void main() { runApp(MyApp()); } class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', home: _MyHomePage(), ); } } class _MyHomePage extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( body: _SlidingBackdrop(), ); } } class _SlidingBackdrop extends StatefulWidget { @override _SlidingBackdropState createState() => _SlidingBackdropState(); } class _SlidingBackdropState extends State<_SlidingBackdrop> with SingleTickerProviderStateMixin { AnimationController _controller; Widget _content; @override void initState() { super.initState(); _controller = AnimationController( duration: Duration(seconds: 5), vsync: this, ); _content = _ExpensiveWidget(); } @override Widget build(BuildContext context) { return LayoutBuilder(builder: (context, constraints) { return SizedBox.expand( child: Stack( children: [ RaisedButton( child: Text('top'), onPressed: () { print('onTap'); if (_controller.isCompleted) { _controller.reverse(); } else if (_controller.isDismissed) { _controller.forward(); } }, ), PositionedTransition( rect: RelativeRectTween( begin: const RelativeRect.fromLTRB(0, 100, 0, 0), end: RelativeRect.fromLTRB( 0, constraints.biggest.height - 100, 0, 0), ).animate(CurvedAnimation( parent: _controller, curve: Curves.easeInOut)), child: _content, ), ], ), ); }); } } class _ExpensiveWidget extends StatelessWidget { static List _colors = [ Colors.redAccent, Colors.orangeAccent, Colors.yellowAccent, Colors.greenAccent, Colors.blueAccent, Colors.purpleAccent, ]; static const _fabCount = 200; @override Widget build(BuildContext context) { return Container( color: Colors.black12, child: Wrap( children: [ for (int i = 0; i < _fabCount; i++) FloatingActionButton( child: Icon(Icons.add), onPressed: () {}, backgroundColor: _colors[i % _colors.length], ) ], ), ); } } ```

flutter doctor -v

```bash [✓] Flutter (Channel master, 1.24.0-8.0.pre.194, on Mac OS X 10.15.7 19H15 darwin-x64, locale en-GB) • Flutter version 1.24.0-8.0.pre.194 at /Users/tahatesser/Code/flutter_master • Framework revision 018467cdb1 (4 hours ago), 2020-11-11 02:04:03 -0500 • Engine revision 81f219c59c • Dart version 2.12.0 (build 2.12.0-31.0.dev) [✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2) • Android SDK at /Users/tahatesser/Code/sdk • Platform android-30, build-tools 30.0.2 • ANDROID_HOME = /Users/tahatesser/Code/sdk • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495) • All Android licenses accepted. [✓] Xcode - develop for iOS and macOS (Xcode 12.2) • Xcode at /Volumes/SanDisk/Xcode-beta.app/Contents/Developer • Xcode 12.2, Build version 12B5044c • CocoaPods version 1.10.0 [✓] Chrome - develop for the web • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome [✓] Android Studio (version 4.1) • Android Studio at /Applications/Android Studio.app/Contents • Flutter plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495) [✓] VS Code (version 1.51.0) • VS Code at /Applications/Visual Studio Code.app/Contents • Flutter extension version 3.16.0 [✓] Connected device (4 available) • Taha’s iPad (mobile) • 00008020-000255113EE8402E • ios • iOS 14.2 • macOS (desktop) • macos • darwin-x64 • Mac OS X 10.15.7 19H15 darwin-x64 • Web Server (web) • web-server • web-javascript • Flutter Tools • Chrome (web) • chrome • web-javascript • Google Chrome 86.0.4240.193 • No issues found! ```

[darshankawar]

Verified this using latest versions and observed the using html renderer, the issue persists, wherein the rendering is slow and FABs are nots repainted properly, as compared to canvaskit.

1. html:

https://github.com/flutter/flutter/assets/67046386/48e69399-8c1e-4ae8-a01b-f990040f3788

2. canvaskit:

https://github.com/flutter/flutter/assets/67046386/46730ed9-9650-445d-b73b-cdb6c1c8b358

stable, master flutter doctor -v

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[!] Xcode - develop for iOS and macOS (Xcode 12.3) • Xcode at /Applications/Xcode.app/Contents/Developer ! Flutter recommends a minimum Xcode version of 13. Download the latest version or update via the Mac App Store. • CocoaPods version 1.11.2 [✓] Chrome - develop for the web • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome [✓] VS Code (version 1.62.0) • VS Code at /Applications/Visual Studio Code.app/Contents • Flutter extension version 3.21.0 [✓] Connected device (5 available) • SM G975F (mobile) • RZ8M802WY0X • android-arm64 • Android 11 (API 30) • Darshan's iphone (mobile) • 21150b119064aecc249dfcfe05e259197461ce23 • ios • iOS 14.4.1 18D61 • iPhone 12 Pro Max (mobile) • A5473606-0213-4FD8-BA16-553433949729 • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-3 (simulator) • macOS (desktop) • macos • darwin-x64 • Mac OS X 10.15.4 19E2269 darwin-x64 • Chrome (web) • chrome • web-javascript • Google Chrome 98.0.4758.80 [✓] HTTP Host Availability • All required HTTP hosts are available ! Doctor found issues in 1 category. ```