From 142b40d515cf1ba309ce01d3c1b12719a4a2a85d Mon Sep 17 00:00:00 2001
From: Yegor <yjbanov@google.com>
Date: Wed, 19 May 2021 20:53:26 -0700
Subject: [PATCH] recall the last frame in the animated image after
 resurrection

---
 .../lib/src/engine/canvaskit/image.dart       | 22 +++++++++++++--
 lib/web_ui/test/canvaskit/image_test.dart     | 28 +++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/lib/web_ui/lib/src/engine/canvaskit/image.dart b/lib/web_ui/lib/src/engine/canvaskit/image.dart
index 0306ce8d7bafd..94a9034228bf3 100644
--- a/lib/web_ui/lib/src/engine/canvaskit/image.dart
+++ b/lib/web_ui/lib/src/engine/canvaskit/image.dart
@@ -101,6 +101,11 @@ class CkAnimatedImage extends ManagedSkiaObject<SkAnimatedImage>
 
   final String src;
   final Uint8List _bytes;
+  int _frameCount = 0;
+  int _repetitionCount = -1;
+
+  /// The index to the next frame to be decoded.
+  int _nextFrameIndex = 0;
 
   @override
   SkAnimatedImage createDefault() {
@@ -112,12 +117,24 @@ class CkAnimatedImage extends ManagedSkiaObject<SkAnimatedImage>
         'Image source: $src',
       );
     }
+
+    _frameCount = animatedImage.getFrameCount();
+    _repetitionCount = animatedImage.getRepetitionCount();
+
+    // If the object has been deleted then resurrected, it may already have
+    // iterated over some frames. We need to skip over them.
+    for (int i = 0; i < _nextFrameIndex; i++) {
+      animatedImage.decodeNextFrame();
+    }
     return animatedImage;
   }
 
   @override
   SkAnimatedImage resurrect() => createDefault();
 
+  @override
+  bool get isResurrectionExpensive => true;
+
   @override
   void delete() {
     rawSkiaObject?.delete();
@@ -144,13 +161,13 @@ class CkAnimatedImage extends ManagedSkiaObject<SkAnimatedImage>
   @override
   int get frameCount {
     assert(_debugCheckIsNotDisposed());
-    return skiaObject.getFrameCount();
+    return _frameCount;
   }
 
   @override
   int get repetitionCount {
     assert(_debugCheckIsNotDisposed());
-    return skiaObject.getRepetitionCount();
+    return _repetitionCount;
   }
 
   @override
@@ -159,6 +176,7 @@ class CkAnimatedImage extends ManagedSkiaObject<SkAnimatedImage>
     final int durationMillis = skiaObject.decodeNextFrame();
     final Duration duration = Duration(milliseconds: durationMillis);
     final CkImage image = CkImage(skiaObject.getCurrentFrame());
+    _nextFrameIndex = (_nextFrameIndex + 1) % _frameCount;
     return Future<ui.FrameInfo>.value(AnimatedImageFrameInfo(duration, image));
   }
 }
diff --git a/lib/web_ui/test/canvaskit/image_test.dart b/lib/web_ui/test/canvaskit/image_test.dart
index 0d1e255079403..4b99a8deeb41b 100644
--- a/lib/web_ui/test/canvaskit/image_test.dart
+++ b/lib/web_ui/test/canvaskit/image_test.dart
@@ -43,6 +43,34 @@ void testMain() {
       testCollector.collectNow();
     });
 
+    test('CkAnimatedImage remembers last animation position after resurrection', () async {
+      browserSupportsFinalizationRegistry = false;
+
+      Future<void> expectFrameData(ui.FrameInfo frame, List<int> data) async {
+        final ByteData frameData = await frame.image.toByteData();
+        expect(frameData.buffer.asUint8List(), Uint8List.fromList(data));
+      }
+
+      final CkAnimatedImage image = CkAnimatedImage.decodeFromBytes(kAnimatedGif, 'test');
+      expect(image.frameCount, 3);
+      expect(image.repetitionCount, -1);
+
+      final ui.FrameInfo frame1 = await image.getNextFrame();
+      expectFrameData(frame1, <int>[0, 255, 0, 255]);
+      final ui.FrameInfo frame2 = await image.getNextFrame();
+      expectFrameData(frame2, <int>[0, 0, 255, 255]);
+
+      // Pretend that the image is temporarily deleted.
+      image.delete();
+      image.didDelete();
+
+      // Check that we got the 3rd frame after resurrection.
+      final ui.FrameInfo frame3 = await image.getNextFrame();
+      expectFrameData(frame3, <int>[255, 0, 0, 255]);
+
+      testCollector.collectNow();
+    });
+
     test('CkImage toString', () {
       final SkImage skImage =
           canvasKit.MakeAnimatedImageFromEncoded(kTransparentImage)