Codec.getNextFrame().image creates artifacts in semi-transparent pixels #170089
Description
Steps to reproduce
In my sample I'm setting pixel values manually, but this also happens if decoding from a PNG file.
It looks like some kind of rounding error?
Not sure what the relevant difference is between these two iPads. Could it be something to do with the "Ultra Retina XDR display" on the iPad Pro?
Expected results
Correct gradient, on iPad Air M1 MME23LL/A:
Actual results
Ugly banding, on iPad Pro M4 MVX23LL/A:
Code sample
Code sample
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
void main() async {
WidgetsFlutterBinding.ensureInitialized();
runApp(const MainApp());
}
class MainApp extends StatefulWidget {
const MainApp({super.key});
@override
State<MainApp> createState() => _MainAppState();
}
class _MainAppState extends State<MainApp> {
ui.Image? image;
@override
void initState() {
super.initState();
makeImage();
}
Future makeImage() async {
var size = 40;
var gradientWidth = 20;
var pixels = Uint8List(size * size * 4);
for (var x = 0; x < gradientWidth; x++) {
for (var y = 0; y < size; y++) {
double alpha = x / gradientWidth;
pixels[(size * y + x) * 4 + 0] = (232 * alpha).round();
pixels[(size * y + x) * 4 + 1] = (124 * alpha).round();
pixels[(size * y + x) * 4 + 2] = (42 * alpha).round();
pixels[(size * y + x) * 4 + 3] = (alpha * 255).round();
}
}
for (var x = gradientWidth; x < size; x++) {
for (var y = 0; y < size; y++) {
pixels[(size * y + x) * 4 + 0] = 232;
pixels[(size * y + x) * 4 + 1] = 124;
pixels[(size * y + x) * 4 + 2] = 42;
pixels[(size * y + x) * 4 + 3] = 255;
}
}
ui.ImmutableBuffer buffer = await ui.ImmutableBuffer.fromUint8List(pixels);
ui.ImageDescriptor descriptor = ui.ImageDescriptor.raw(buffer, width: size, height: size, pixelFormat: ui.PixelFormat.rgba8888);
ui.Codec codec = await descriptor.instantiateCodec(targetWidth: size, targetHeight: size);
ui.FrameInfo frameInfo = await codec.getNextFrame();
image = frameInfo.image;
setState((){});
}
@override
Widget build(BuildContext context) {
return MaterialApp(home:
Container(color: Color(0xffffffff), child:
Center(child:
RawImage(filterQuality: FilterQuality.none, width: 500, height: 500, fit: BoxFit.fill, image: image)
)
)
);
}
}Screenshots or Video
Logs
No response
Flutter Doctor output
Doctor output
[✓] Flutter (Channel stable, 3.32.2, on macOS 15.4 24E248 darwin-arm64, locale en-US) [375ms]
• Flutter version 3.32.2 on channel stable at /Users/weirdhat/flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 8defaa71a7 (26 hours ago), 2025-06-04 11:02:51 -0700
• Engine revision 1091508939
• Dart version 3.8.1
• DevTools version 2.45.1
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0) [1,184ms]
• Android SDK at /Users/weirdhat/Library/Android/sdk
• Platform android-35, build-tools 34.0.0
• Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
This is the JDK bundled with the latest Android Studio installation on this machine.
To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
• Java version OpenJDK Runtime Environment (build 17.0.11+0-17.0.11b1207.24-11852314)
• All Android licenses accepted.
[✓] Xcode - develop for iOS and macOS (Xcode 16.2) [776ms]
• Xcode at /Applications/Xcode.app/Contents/Developer
• Build 16C5032a
• CocoaPods version 1.16.2
[✓] Chrome - develop for the web [11ms]
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
[✓] Android Studio (version 2024.1) [11ms]
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/9212-flutter
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🔨 https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 17.0.11+0-17.0.11b1207.24-11852314)
[✓] VS Code (version 1.99.3) [10ms]
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 3.112.0
[✓] Connected device (5 available) [6.2s]
• JK iPad 2024 (wireless) (mobile) • 00008103-001659302668801E • ios • iOS 18.4 22E240
• Wendy’s iPad (mobile) • 00008132-001E30DA22B9001C • ios • iOS 18.3.2 22D82
• JACOB’s iPad (2) (wireless) (mobile) • 1b7384fb4c7a0d33045b6a8bafac34a1b0c5da58 • ios • iOS 17.2 21C62
• macOS (desktop) • macos • darwin-arm64 • macOS 15.4 24E248 darwin-arm64
• Chrome (web) • chrome • web-javascript • Google Chrome 137.0.7151.56
[✓] Network resources [644ms]
• All expected network resources are available.
• No issues found!