The Flutter 3.22.5 update included significant changes to the underlying graphics engine (Skia) and Impeller, which, while improving things in the long run, can introduce performance regressions (jank, lag, dropped frames) in some apps. Based on community reports and research, here are the most likely causes and their solutions.
1. The Skia Graphics Engine Update (Primary Suspect)
This is the most common culprit discussed in the community. Flutter 3.22.5 shipped with a major update to the Skia graphics library. While this brings many benefits, it can sometimes introduce rendering bottlenecks or compatibility issues on certain devices or GPUs.
Solution.Enable an experimental Skia configuration flag. This can often force a more optimized rendering path.
Navigate to your Android manifest file:
`android/app/src/main/AndroidManifest.xml`
Add the following meta-data tag inside the `<application>` tag:
“`xml
<application …>
…
<!– Add this line to enable experimental Skia rendering –>
<meta-data
android:name=”flutter_enable_skia”
android:value=”true” />
…
</application>
“`
Note: This flag is experimental, but it has resolved jank issues for many developers. Test your app thoroughly after applying it.
2. Impeller-Specific Changes
Impeller, Flutter’s new rendering runtime, is being actively developed. With each Flutter version, its behavior can change. If your app has Impeller enabled (it’s the default on new iOS projects and can be enabled on Android), it might be the source of the lag.
Diagnostic Step: Toggle Impeller
To Disable Impeller (for testing): Add a flag to disable it. If the lag disappears, you’ve identified the cause.
On Android: Add the following to the same `AndroidManifest.xml` file:
“`xml
<meta-data
android:name=”flutter_impeller”
android:value=”false” />
“`
On iOS: Open `ios/Runner/Info.plist` and add:
“`xml
<key>FLTEnableImpeller</key>
<false/>
“`
If disabling Impeller fixes the lag: Report the issue to the Flutter team with a detailed reproduction case. In the meantime, you can keep it disabled, but note that Impeller is the future of Flutter rendering.
If the lag persists with Impeller off: The issue is likely elsewhere (like the Skia update mentioned above).
3. Shader Compilation Jitter
This is a classic cause of lag in Flutter, especially the first time a new animation or complex screen is displayed. The upgrade might have invalidated old shader caches.
Solution: Leverage Shader Warm-up
1. Profile Mode: Run your app in profile mode (`flutter run –profile`) and navigate through every screen and animation. This pre-compiles the shaders.
2. Shader Cache: Ensure you are not deleting the `shader_cache` folder between builds. Flutter uses this to persist compiled shaders for faster subsequent launches.
4. Third-Party Package Incompatibility
A package you depend on might not be fully optimized or compatible with the latest engine changes in Flutter 3.22.5.
Solution: Investigate Your Packages
1. Update: Run `flutter pub outdated` and then `flutter pub upgrade` to ensure all your packages are at their latest compatible versions.
2. Isolate the Culprit: If the lag started after the upgrade, try temporarily removing or commenting out features that rely on specific packages (especially those related to UI, graphics, or animations) to see if the performance improves.
3. Check Issues:Visit the GitHub repository for your key packages to see if other users are reporting similar performance regressions.
5. General Performance Profiling (Crucial Step)
To find the exact cause, you must use Flutter’s DevTools.
1. Run in Profile Mode: Always profile performance in profile mode, as debug mode is not representative of real-world performance.
“`bash
flutter run –profile
“`
2. Open DevTools: Start the DevTools suite (`flutter devtools`) and connect to your running app.
3. Use the Performance Tab:
Frame Time Chart: Look for frames that exceed the 16ms budget (for 60fps) or 8ms budget (for 120fps). These are the laggy frames.
CPU Profiler: Record a CPU profile while performing the laggy action. It will show you exactly which Dart methods are taking too long. Look for expensive `build()` methods or custom painting operations.
GPU View: If using Impeller, the GPU view can show if the bottleneck is in the rendering pipeline itself.
Action Plan: Step-by-Step
1. First, try the Skia flag. It’s a simple change that has worked for many. Clean and rebuild your app (`flutter clean && flutter run`).
2. If that doesn’t work, profile with DevTools. This is the most important step. Identify if the lag is coming from the UI thread (Dart code) or the raster thread (graphics).
3. Based on the profiling results:
* If the UI thread is slow, optimize your Dart code. Look for expensive widgets, unnecessary rebuilds, and move heavy work to isolates.
* If the Raster thread is slow, the issue is likely with Skia/Impeller or complex rendering layers. Proceed to step 4.
4. Toggle Impeller to see if it resolves the raster thread issue.
5. Check your packages for known issues and updates.
By systematically working through these points, you should be able to identify and resolve the performance regression introduced by the Flutter 3.22.5 upgrade.
