Implement Image.clone for CanvasKit

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

@@ -41,10 +41,16 @@ class CkAnimatedImage implements ui.Image {
 
   // Use a box because `SkImage` may be deleted either due to this object
   // being garbage-collected, or by an explicit call to [delete].
-  late final SkiaObjectBox box;
+  late final RefCountedSkiaObjectBox box;
 
-  CkAnimatedImage(this._skAnimatedImage) {
-    box = SkiaObjectBox(this, _skAnimatedImage as SkDeletable);
+  CkAnimatedImage(SkAnimatedImage skAnimatedImage) : this._(skAnimatedImage, null);
+
+  CkAnimatedImage._(this._skAnimatedImage, RefCountedSkiaObjectBox? boxToClone) {
+    if (boxToClone != null) {
+      box = boxToClone.clone(this);
+    } else {
+      box = RefCountedSkiaObjectBox(this, _skAnimatedImage as SkDeletable);
+    }
   }
 
   @override
@@ -53,13 +59,17 @@ class CkAnimatedImage implements ui.Image {
   }
 
   @override
-  ui.Image clone() => this;
+  ui.Image clone() => CkAnimatedImage._(_skAnimatedImage, box);
 
   @override
-  bool isCloneOf(ui.Image other) => other == this;
+  bool isCloneOf(ui.Image other) {
+    return other is CkAnimatedImage
+        && other._skAnimatedImage == _skAnimatedImage;
+  }
 
   @override
-  List<StackTrace>? debugGetOpenHandleStackTraces() => null;
+  List<StackTrace>? debugGetOpenHandleStackTraces() => box.debugGetStackTraces();
+
   int get frameCount => _skAnimatedImage.getFrameCount();
 
   /// Decodes the next frame and returns the frame duration.
@@ -114,10 +124,16 @@ class CkImage implements ui.Image {
 
   // Use a box because `SkImage` may be deleted either due to this object
   // being garbage-collected, or by an explicit call to [delete].
-  late final SkiaObjectBox box;
+  late final RefCountedSkiaObjectBox box;
 
-  CkImage(this.skImage) {
-    box = SkiaObjectBox(this, skImage as SkDeletable);
+  CkImage(SkImage skImage) : this._(skImage, null);
+
+  CkImage._(this.skImage, RefCountedSkiaObjectBox? boxToClone) {
+    if (boxToClone != null) {
+      box = boxToClone.clone(this);
+    } else {
+      box = RefCountedSkiaObjectBox(this, skImage as SkDeletable);
+    }
   }
 
   @override
@@ -126,13 +142,16 @@ class CkImage implements ui.Image {
   }
 
   @override
-  ui.Image clone() => this;
+  ui.Image clone() => CkImage._(skImage, box);
 
   @override
-  bool isCloneOf(ui.Image other) => other == this;
+  bool isCloneOf(ui.Image other) {
+    return other is CkImage
+        && other.skImage == skImage;
+  }
 
   @override
-  List<StackTrace>? debugGetOpenHandleStackTraces() => null;
+  List<StackTrace>? debugGetOpenHandleStackTraces() => box.debugGetStackTraces();
 
   @override
   int get width => skImage.width();

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

@@ -282,6 +282,72 @@ class SkiaObjectBox {
   }
 }
 
+/// Uses reference counting to manage the lifecycle of a Skia object owned by a
+/// wrapper object.
+///
+/// When the wrapper is garbage collected, decrements the refcount (only in
+/// browsers that support weak references).
+///
+/// The [delete] method can be used to eagerly decrement the refcount before the
+/// wrapper is garbage collected.
+///
+/// The [delete] method may be called any number of times. The box
+/// will only delete the object once.
+class RefCountedSkiaObjectBox extends SkiaObjectBox {
+  RefCountedSkiaObjectBox(Object wrapper, SkDeletable skObject)
+      : this._(wrapper, skObject, <RefCountedSkiaObjectBox>{});
+
+  RefCountedSkiaObjectBox._(Object wrapper, SkDeletable skObject, this._refs)
+      : super(wrapper, skObject) {
+    _refs.add(this);
+    if (assertionsEnabled) {
+      _debugStackTrace = StackTrace.current;
+    }
+  }
+
+  /// Reference handles to the same underlying [skObject].
+  final Set<RefCountedSkiaObjectBox> _refs;
+
+  late final StackTrace? _debugStackTrace;
+  /// If asserts are enabled, the [StackTrace]s representing when a reference
+  /// was created.
+  List<StackTrace>? debugGetStackTraces() {
+    if (assertionsEnabled) {
+      return _refs
+          .map<StackTrace>((RefCountedSkiaObjectBox box) => box._debugStackTrace!)
+          .toList();
+    }
+    return null;
+  }
+
+  RefCountedSkiaObjectBox clone(Object wrapper) {
+    assert(!_isDeleted, 'Cannot clone from a deleted handle.');
+    assert(_refs.isNotEmpty);
+    return RefCountedSkiaObjectBox._(wrapper, skObject, _refs);
+  }
+
+  /// Removes the reference count for the [skObject].
+  ///
+  /// Does nothing if the object has already been deleted.
+  ///
+  /// If this causes the reference count to drop to zero, deletes the
+  /// [skObject].
+  @override
+  void delete() {
+    if (_isDeleted) {
+      assert(!_refs.contains(this));
+      return;
+    }
+    final bool removed = _refs.remove(this);
+    assert(removed);
+    _isDeleted = true;
+    if (_refs.isEmpty) {
+      _skObjectDeleteQueue.add(skObject);
+      _skObjectCollector ??= _scheduleSkObjectCollection();
+    }
+  }
+}
+
 /// Singleton that manages the lifecycles of [SkiaObject] instances.
 class SkiaObjects {
   @visibleForTesting

lib/web_ui/test/canvaskit/image_test.dart

@@ -38,6 +38,21 @@ void testMain() {
       expect(image.box.isDeleted, true);
     });
 
+    test('CkAnimatedImage can be cloned and explicitly disposed of', () {
+      final SkAnimatedImage skAnimatedImage = canvasKit.MakeAnimatedImageFromEncoded(kTransparentImage);
+      final CkAnimatedImage image = CkAnimatedImage(skAnimatedImage);
+      final CkAnimatedImage imageClone = image.clone();
+
+      expect(image.isCloneOf(imageClone), true);
+      expect(image.box.isDeleted, false);
+      image.dispose();
+      expect(image.box.isDeleted, true);
+      expect(imageClone.box.isDeleted, false);
+      imageClone.dispose();
+      expect(image.box.isDeleted, true);
+      expect(imageClone.box.isDeleted, true);
+    });
+
     test('CkImage toString', () {
       final SkImage skImage = canvasKit.MakeAnimatedImageFromEncoded(kTransparentImage).getCurrentFrame();
       final CkImage image = CkImage(skImage);
@@ -54,6 +69,21 @@ void testMain() {
       image.dispose();
       expect(image.box.isDeleted, true);
     });
+
+    test('CkImage can be explicitly disposed of', () {
+      final SkImage skImage = canvasKit.MakeAnimatedImageFromEncoded(kTransparentImage).getCurrentFrame();
+      final CkImage image = CkImage(skImage);
+      final CkImage imageClone = image.clone();
+
+      expect(image.isCloneOf(imageClone), true);
+      expect(image.box.isDeleted, false);
+      image.dispose();
+      expect(image.box.isDeleted, true);
+      expect(imageClone.box.isDeleted, false);
+      imageClone.dispose();
+      expect(image.box.isDeleted, true);
+      expect(imageClone.box.isDeleted, true);
+    });
   // TODO: https://github.com/flutter/flutter/issues/60040
   }, skip: isIosSafari);
 }

lib/web_ui/test/canvaskit/skia_objects_cache_test.dart

@@ -12,6 +12,7 @@ import 'package:ui/ui.dart' as ui;
 import 'package:ui/src/engine.dart';
 
 import 'common.dart';
+import '../matchers.dart';
 
 void main() {
   internalBootstrapBrowserTest(() => testMain);
@@ -153,6 +154,36 @@ void _tests() {
       expect(SkiaObjects.oneShotCache.debugContains(object2), isFalse);
     });
   });
+
+  group(RefCountedSkiaObjectBox, () {
+    test('Records stack traces and respects refcounts', () {
+      final TestSkiaObject skObject = TestSkiaObject();
+      final Object wrapper = Object();
+      final RefCountedSkiaObjectBox box = RefCountedSkiaObjectBox(wrapper, skObject);
+
+      expect(box.debugGetStackTraces().length, 1);
+
+      final RefCountedSkiaObjectBox clone = box.clone(wrapper);
+      expect(clone, isNot(same(box)));
+      expect(clone.debugGetStackTraces().length, 2);
+      expect(box.debugGetStackTraces().length, 2);
+
+      box.delete();
+
+      expect(() => box.clone(wrapper), throwsAssertionError);
+
+      expect(skObject.deleteCount, 0);
+      expect(clone.debugGetStackTraces().length, 1);
+      expect(box.debugGetStackTraces().length, 1);
+
+      clone.delete();
+      expect(() => clone.clone(wrapper), throwsAssertionError);
+
+      expect(skObject.deleteCount, 1);
+      expect(clone.debugGetStackTraces().length, 0);
+      expect(box.debugGetStackTraces().length, 0);
+    });
+  });
 }
 
 class TestOneShotSkiaObject extends OneShotSkiaObject<SkPaint> {
@@ -167,7 +198,7 @@ class TestOneShotSkiaObject extends OneShotSkiaObject<SkPaint> {
   }
 }
 
-class TestSkiaObject extends ManagedSkiaObject<SkPaint> {
+class TestSkiaObject extends ManagedSkiaObject<SkPaint> implements SkDeletable {
   int createDefaultCount = 0;
   int resurrectCount = 0;
   int deleteCount = 0;