[web] Don't close image source too early (#57200)

A `CkImage` instance holds a reference to `ImageSource?`. When that `CkImage` gets cloned, the `ImageSource` instance becomes shared between the original `CkImage` and its new clone. Then when one of the `CkImage`s gets disposed of, it closes the shared `ImageSource` leaving other live `CkImage`s holding on to a closed `ImageSource`.

The quick solution to this is to have a ref count on the `ImageSource` to count how many `CkImage`s are referencing it. The `ImageSource` will only be closed if its ref count reaches 0.

Fixes flutter/flutter#160199
Fixes flutter/flutter#158093

Author: mdebbar

lib/web_ui/lib/src/engine/canvaskit/image.dart

@@ -7,6 +7,7 @@ import 'dart:js_interop';
 import 'dart:math' as math;
 import 'dart:typed_data';
 
+import 'package:meta/meta.dart';
 import 'package:ui/src/engine.dart';
 import 'package:ui/ui.dart' as ui;
 import 'package:ui/ui_web/src/ui_web.dart' as ui_web;
@@ -403,11 +404,13 @@ class CkImage implements ui.Image, StackTraceDebugger {
   CkImage(SkImage skImage, {this.imageSource}) {
     box = CountedRef<CkImage, SkImage>(skImage, this, 'SkImage');
     _init();
+    imageSource?.refCount++;
   }
 
   CkImage.cloneOf(this.box, {this.imageSource}) {
     _init();
     box.ref(this);
+    imageSource?.refCount++;
   }
 
   void _init() {
@@ -454,6 +457,8 @@ class CkImage implements ui.Image, StackTraceDebugger {
     ui.Image.onDispose?.call(this);
     _disposed = true;
     box.unref(this);
+
+    imageSource?.refCount--;
     imageSource?.close();
   }
 
@@ -645,7 +650,26 @@ sealed class ImageSource {
   DomCanvasImageSource get canvasImageSource;
   int get width;
   int get height;
-  void close();
+
+  /// The number of references to this image source.
+  ///
+  /// Calling [close] is a no-op if [refCount] is greater than 0.
+  ///
+  /// Only when [refCount] is 0 will the [close] method actually close the
+  /// image source.
+  int refCount = 0;
+
+  @visibleForTesting
+  bool debugIsClosed = false;
+
+  void close() {
+    if (refCount == 0) {
+      _doClose();
+      debugIsClosed = true;
+    }
+  }
+
+  void _doClose();
 }
 
 class VideoFrameImageSource extends ImageSource {
@@ -654,7 +678,7 @@ class VideoFrameImageSource extends ImageSource {
   final VideoFrame videoFrame;
 
   @override
-  void close() {
+  void _doClose() {
     // Do nothing. Skia will close the VideoFrame when the SkImage is disposed.
   }
 
@@ -674,7 +698,7 @@ class ImageElementImageSource extends ImageSource {
   final DomHTMLImageElement imageElement;
 
   @override
-  void close() {
+  void _doClose() {
     // There's no way to immediately close the <img> element. Just let the
     // browser garbage collect it.
   }
@@ -695,7 +719,7 @@ class ImageBitmapImageSource extends ImageSource {
   final DomImageBitmap imageBitmap;
 
   @override
-  void close() {
+  void _doClose() {
     imageBitmap.close();
   }
 

lib/web_ui/lib/src/engine/dom.dart

@@ -169,6 +169,12 @@ extension DomWindowExtension on DomWindow {
   /// The Trusted Types API (when available).
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/Trusted_Types_API
   external DomTrustedTypePolicyFactory? get trustedTypes;
+
+  @JS('createImageBitmap')
+  external JSPromise<JSAny?> _createImageBitmap(DomImageData source);
+  Future<DomImageBitmap> createImageBitmap(DomImageData source) {
+    return js_util.promiseToFuture<DomImageBitmap>(_createImageBitmap(source));
+  }
 }
 
 typedef DomRequestAnimationFrameCallback = void Function(JSNumber highResTime);

lib/web_ui/test/canvaskit/image_test.dart

@@ -7,12 +7,11 @@ import 'dart:typed_data';
 
 import 'package:test/bootstrap/browser.dart';
 import 'package:test/test.dart';
-import 'package:ui/src/engine/canvaskit/image.dart';
-import 'package:ui/src/engine/image_decoder.dart';
-import 'package:ui/src/engine/util.dart';
+import 'package:ui/src/engine.dart';
 import 'package:ui/ui.dart' as ui;
 
 import 'common.dart';
+import 'test_data.dart';
 
 void main() {
   internalBootstrapBrowserTest(() => testMain);
@@ -131,6 +130,31 @@ void testMain() {
 
     expect(activeImages.length, 0);
   });
+
+  test('CkImage does not close image source too early', () async {
+    final ImageSource imageSource = ImageBitmapImageSource(
+      await domWindow.createImageBitmap(createBlankDomImageData(4, 4)),
+    );
+
+    final SkImage skImage1 = canvasKit.MakeAnimatedImageFromEncoded(k4x4PngImage)!.makeImageAtCurrentFrame();
+    final CkImage image1 = CkImage(skImage1, imageSource: imageSource);
+
+    final SkImage skImage2 = canvasKit.MakeAnimatedImageFromEncoded(k4x4PngImage)!.makeImageAtCurrentFrame();
+    final CkImage image2 = CkImage(skImage2, imageSource: imageSource);
+
+    final CkImage image3 = image1.clone();
+
+    expect(imageSource.debugIsClosed, isFalse);
+
+    image1.dispose();
+    expect(imageSource.debugIsClosed, isFalse);
+
+    image2.dispose();
+    expect(imageSource.debugIsClosed, isFalse);
+
+    image3.dispose();
+    expect(imageSource.debugIsClosed, isTrue);
+  });
 }
 
 Future<ui.Image> _createImage() => _createPicture().toImage(10, 10);