[mboetger]

Deprecates the synchronous FlutterRenderer.getBitmap() and FlutterJNI.getBitmap() APIs in the Android embedder, which block the Android UI thread waiting on Rasterizer::Screenshot across the platform/raster threads, and introduces an asynchronous replacement: FlutterRenderer.getBitmapAsync(...).

Summary of Changes

1. Framework (flutter/screenshot):
   • Adds SystemChannels.screenshot (MethodChannel('flutter/screenshot', StandardMethodCodec())) in packages/flutter/lib/src/services/system_channels.dart.
   • Registers _handleScreenshotMethodCall in RendererBinding.initInstances() (packages/flutter/lib/src/rendering/binding.dart) to handle Screenshot.captureView(int viewId):
     • Locates the RenderView matching viewId and reads its composited OffsetLayer.
     • Rasterizes the layer tree via OffsetLayer.toImage(Offset.zero & targetView.size, pixelRatio: targetView.configuration.devicePixelRatio) and encodes raw RGBA pixels (ui.ImageByteFormat.rawRgba), returning {'width': int, 'height': int, 'bytes': Uint8List} without blocking the Android UI thread.
2. Android Embedder (ScreenshotChannel & FlutterRenderer):
   • Adds ScreenshotChannel (io.flutter.embedding.engine.systemchannels.ScreenshotChannel) and wires it in FlutterEngine.
   • Adds @Deprecated annotations and migration Javadocs to FlutterRenderer.getBitmap() and FlutterJNI.getBitmap().
   • Adds FlutterRenderer.getBitmapAsync(@NonNull Consumer<Bitmap> callback) and FlutterRenderer.getBitmapAsync(long viewId, @NonNull Consumer<Bitmap> callback).
3. Tests:
   • Adds framework unit tests in packages/flutter/test/rendering/screenshot_channel_test.dart.
   • Adds Android Robolectric unit tests in ScreenshotChannelTest.java and FlutterRendererTest.java.

Fixes #195720
Related RFC: flutter/rfc#41

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant in-code documentation (doc comments with ///).
• If this PR introduces a new feature or capability, I created and linked a website documentation issue or PR in flutter/website (or verified none is needed).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

[gemini-code-assist]

Code Review

This pull request introduces an asynchronous screenshot mechanism via a new ScreenshotChannel (flutter/screenshot), deprecating the existing synchronous getBitmap APIs in FlutterJNI and FlutterRenderer. On the Android side, FlutterRenderer now supports getBitmapAsync to request view captures. On the Dart side, RendererBinding handles these requests by converting the root OffsetLayer to an image and returning its raw RGBA bytes. Feedback on these changes suggests specifying the device pixel ratio in toImage to maintain high-DPI image quality, catching OutOfMemoryError during bitmap creation to prevent crashes, and restricting the visibility of the channel field in ScreenshotChannel to private to improve encapsulation.

[gemini-code-assist]

The current implementation of rootLayer.toImage(bounds) does not specify a pixelRatio, which defaults to 1.0. This will cause screenshots to be captured at logical pixel resolution rather than the device's physical pixel resolution. On high-DPI devices (e.g., with a device pixel ratio of 2.0 or 3.0), this results in a significant loss of image quality and resolution compared to the original synchronous getBitmap() API. Specifying pixelRatio: targetView.flutterView.devicePixelRatio ensures the captured image matches the physical screen resolution.

    final ui.Image image = await rootLayer.toImage(bounds, pixelRatio: targetView.flutterView.devicePixelRatio);

[gemini-code-assist]

Creating a large Bitmap via Bitmap.createBitmap can throw an OutOfMemoryError if the device is low on memory or the screenshot dimensions are extremely large. Since OutOfMemoryError is an Error (not a RuntimeException), it will bypass the current catch (RuntimeException e) block and crash the application. Catching OutOfMemoryError alongside RuntimeException allows the application to fail gracefully and return null to the callback.

Suggested change

	} catch (RuntimeException e) {
	} catch (OutOfMemoryError | RuntimeException e) {

[gemini-code-assist]

The channel field is not accessed outside of the ScreenshotChannel class. To improve encapsulation and adhere to standard Java best practices, it should be declared as private instead of public.

Suggested change

	@NonNull public final MethodChannel channel;
	@NonNull private final MethodChannel channel;

References

1. Fields should be declared with the most restrictive access level possible to enforce encapsulation.

[flutter-dashboard]

This pull request has been changed to a draft. The currently pending flutter-gold status will not be able to resolve until a new commit is pushed or the change is marked ready for review again.

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Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.