Craft better error message for OffsetLayer.toImage in the HTML renderer #49857
Description
I'm attempting to convert a Canvas widget's content to an image, using the following code. It works fine on iOS and macOS, but dies on the web.
Future<void> _capturePng() async {
RenderRepaintBoundary boundary =
globalKey.currentContext.findRenderObject();
ui.Image image = await boundary.toImage(pixelRatio: 1);
ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
Uint8List pngBytes = byteData.buffer.asUint8List();
print('PNG Image size: ${pngBytes.length}');
}VSCode console output:
════════ Exception caught by scheduler library ═════════════════════════════════
The following assertion was thrown during a scheduler callback:
Assertion failed: org-dartlang-sdk:///flutter_web_sdk/lib/_engine/engine/surface/scene_builder.dart:267:12
retainedSurface.isActive || retainedSurface.isReleased
is not true
When the exception was thrown, this was the stack
throw_ (package:dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart:196:49)
assertFailed (package:dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart:26:3)
addRetained (package:build_web_compilers/lib/_engine/engine/surface/scene_builder.dart:267:55)
[_addToSceneWithRetainedRendering]
package:flutter/…/rendering/layer.dart:439
addChildrenToScene
package:flutter/…/rendering/layer.dart:1065
...
════════════════════════════════════════════════════════════════════════════════
JS Console stacktrace
errors.dart:147 Uncaught (in promise) Error: Exception: Incorrect sequence of push/pop operations while building scene surfaces. After building the scene the persisted surface stack must contain a single element which corresponds to the scene itself (_PersistedScene). All other surfaces should have been popped off the stack. Found the following surfaces in the stack:
PersistedScene, PersistedTransform
at Object.throw_ [as throw] (errors.dart:196)
at scene_builder.dart:24
at _engine.SurfaceSceneBuilder.new.get [_persistedScene] (scene_builder.dart:31)
at _engine.SurfaceSceneBuilder.new.build (scene_builder.dart:514)
at layer$.OffsetLayer.new.buildScene (layer.dart:807)
at layer$.OffsetLayer.new.toImage (layer.dart:1240)
at toImage.next (<anonymous>)
at runBody (async_patch.dart:86)
at Object._async [as async] (async_patch.dart:125)
at layer$.OffsetLayer.new.toImage (layer.dart:1229)
at proxy_box.RenderRepaintBoundary.new.toImage (proxy_box.dart:2962)
at main._MyHomePageState.new._capturePng (main.dart:35)
at _capturePng.next (<anonymous>)
at runBody (async_patch.dart:86)
at Object._async [as async] (async_patch.dart:125)
at main._MyHomePageState.new.[_capturePng] (main.dart:32)
at _InkResponseState.new.[_handleTap] (ink_well.dart:705)
at ink_well.dart:788
at tap.TapGestureRecognizer.new.invokeCallback (recognizer.dart:182)
at tap.TapGestureRecognizer.new.handleTapUp (tap.dart:486)
at tap.TapGestureRecognizer.new.[_checkUp] (tap.dart:264)
at tap.TapGestureRecognizer.new.handlePrimaryPointer (tap.dart:199)
at tap.TapGestureRecognizer.new.handleEvent (recognizer.dart:470)
at pointer_router.PointerRouter.new.[_dispatch] (pointer_router.dart:76)
at pointer_router.dart:117
at LinkedMap.new.forEach (linked_hash_map.dart:23)
at pointer_router.PointerRouter.new.[_dispatchEventToRoutes] (pointer_router.dart:115)
at pointer_router.PointerRouter.new.route (pointer_router.dart:101)
at binding$5.WidgetsFlutterBinding.new.handleEvent (binding.dart:218)
at binding$5.WidgetsFlutterBinding.new.dispatchEvent (binding.dart:198)
at binding$5.WidgetsFlutterBinding.new.[_handlePointerEvent] (binding.dart:156)
at binding$5.WidgetsFlutterBinding.new.[_flushPointerEventQueue] (binding.dart:102)
at binding$5.WidgetsFlutterBinding.new.[_handlePointerDataPacket] (binding.dart:86)
at _engine.PointerBinding.__.[_onPointerData] (pointer_binding.dart:129)
at pointer_binding.dart:465
at pointer_binding.dart:430
at HTMLElement.<anonymous> (pointer_binding.dart:195)