Fix gif frame reuse

lib/ui/painting/multi_frame_codec.cc

@@ -115,9 +115,6 @@ sk_sp<DlImage> MultiFrameCodec::State::GetNextFrameImage(
           << "Frame " << nextFrameIndex_ << " depends on frame "
           << requiredFrameIndex
           << " and no required frames are cached. Using blank slate instead.";
-    } else if (lastRequiredFrameIndex_ != requiredFrameIndex) {
-      FML_DLOG(INFO) << "Required frame " << requiredFrameIndex
-                     << " is not cached. Using blank slate instead.";
     } else {
       // Copy the previous frame's output buffer into the current frame as the
       // starting point.
@@ -138,7 +135,8 @@ sk_sp<DlImage> MultiFrameCodec::State::GetNextFrameImage(
   }
 
   // Hold onto this if we need it to decode future frames.
-  if (frameInfo.disposal_method == SkCodecAnimation::DisposalMethod::kKeep) {
+  if (frameInfo.disposal_method == SkCodecAnimation::DisposalMethod::kKeep ||
+      lastRequiredFrame_) {
     lastRequiredFrame_ = std::make_unique<SkBitmap>(bitmap);
     lastRequiredFrameIndex_ = nextFrameIndex_;
   }
@@ -161,9 +159,9 @@ sk_sp<DlImage> MultiFrameCodec::State::GetNextFrameImage(
   gpu_disable_sync_switch->Execute(
       fml::SyncSwitch::Handlers()
           .SetIfTrue([&skImage, &bitmap] {
-            // Defer decoding until time of draw later on the raster thread. Can
-            // happen when GL operations are currently forbidden such as in the
-            // background on iOS.
+            // Defer decoding until time of draw later on the raster thread.
+            // Can happen when GL operations are currently forbidden such as
+            // in the background on iOS.
             skImage = SkImage::MakeFromBitmap(bitmap);
           })
           .SetIfFalse([&skImage, &resourceContext, &bitmap] {
@@ -257,8 +255,8 @@ Dart_Handle MultiFrameCodec::getNextFrame(Dart_Handle callback_handle) {
       }));
 
   return Dart_Null();
-  // The static leak checker gets confused by the control flow, unique pointers
-  // and closures in this function.
+  // The static leak checker gets confused by the control flow, unique
+  // pointers and closures in this function.
   // NOLINTNEXTLINE(clang-analyzer-cplusplus.NewDeleteLeaks)
 }
 

testing/dart/codec_test.dart

@@ -126,6 +126,57 @@ void main() {
       expect(e.toString(), contains('Decoded image has been disposed'));
     }
   });
+
+  test('Animated gif can reuse across multiple frames', () async {
+    // Regression test for b/271947267 and https://github.com/flutter/flutter/issues/122134
+
+    final Uint8List data = File(
+      path.join('flutter', 'lib', 'ui', 'fixtures', 'four_frame_with_reuse.gif'),
+    ).readAsBytesSync();
+    final ui.Codec codec = await ui.instantiateImageCodec(data);
+
+    // Capture the final frame of animation. If we have not composited
+    // correctly, it will be clipped strangely.
+    late ui.FrameInfo frameInfo;
+    for (int i = 0; i < 4; i++) {
+      frameInfo = await codec.getNextFrame();
+    }
+
+    final ui.Image image = frameInfo.image;
+    final ByteData imageData = (await image.toByteData(format: ui.ImageByteFormat.png))!;
+
+    final Uint8List goldenData = File(
+      path.join('flutter', 'lib', 'ui', 'fixtures', 'four_frame_with_reuse_end.png'),
+    ).readAsBytesSync();
+
+    expect(imageData.buffer.asUint8List(), goldenData);
+  });
+
+  test('Animated webp can reuse across multiple frames', () async {
+    // Regression test for https://github.com/flutter/flutter/issues/61150#issuecomment-679055858
+
+    final Uint8List data = File(
+      path.join('flutter', 'lib', 'ui', 'fixtures', 'heart.webp'),
+    ).readAsBytesSync();
+    final ui.Codec codec = await ui.instantiateImageCodec(data);
+
+    // Capture the final frame of animation. If we have not composited
+    // correctly, the hearts will be incorrectly repeated in the image.
+    late ui.FrameInfo frameInfo;
+    for (int i = 0; i < 69; i++) {
+      frameInfo  = await codec.getNextFrame();
+    }
+
+    final ui.Image image = frameInfo.image;
+    final ByteData imageData = (await image.toByteData(format: ui.ImageByteFormat.png))!;
+
+    final Uint8List goldenData = File(
+      path.join('flutter', 'lib', 'ui', 'fixtures', 'heart_end.png'),
+    ).readAsBytesSync();
+
+    expect(imageData.buffer.asUint8List(), goldenData);
+
+  });
 }
 
 /// Returns a File handle to a file in the skia/resources directory.