Animated WebP: Optimize decoding in case of seeking

Source/core/platform/image-decoders/ImageDecoderTest.cpp

Index: Source/core/platform/image-decoders/ImageDecoderTest.cpp
diff --git a/Source/core/platform/image-decoders/ImageDecoderTest.cpp b/Source/core/platform/image-decoders/ImageDecoderTest.cpp
index 65dfe4d76f810462e5ab3899fdfb28820ce4b7fc..7f6e81d587a44dae9fbf93d7a958c7fbff93da88 100644
--- a/Source/core/platform/image-decoders/ImageDecoderTest.cpp
+++ b/Source/core/platform/image-decoders/ImageDecoderTest.cpp
@@ -54,10 +54,10 @@ public:
         return m_frameBufferCache;
     }
 
-    void resetRequiredPreviousFrames()
+    void resetRequiredPreviousFrames(bool knownOpaque = false)
     {
         for (size_t i = 0; i < m_frameBufferCache.size(); ++i)
-            m_frameBufferCache[i].setRequiredPreviousFrameIndex(findRequiredPreviousFrame(i));
+            m_frameBufferCache[i].setRequiredPreviousFrameIndex(findRequiredPreviousFrame(i, knownOpaque));
     }
 
     void initFrames(size_t numFrames, unsigned width = 100, unsigned height = 100)
@@ -140,6 +140,40 @@ TEST(ImageDecoderTest, requiredPreviousFrameIndexForFrame1)
     EXPECT_EQ(notFound, decoderFrameBufferCache[1].requiredPreviousFrameIndex());
 }
 
+// A full frame with 'blending method == BlendOverwrite' doesn't depend on any prior frames.
+TEST(ImageDecoderTest, requiredPreviousFrameIndexFullFrameBlendOverwrite)
+{
+    OwnPtr<TestImageDecoder> decoder(adoptPtr(new TestImageDecoder()));
+    decoder->initFrames(2);
+    Vector<ImageFrame, 1>& decoderFrameBufferCache = decoder->frameBufferCache();
+
+    decoderFrameBufferCache[0].setOriginalFrameRect(IntRect(25, 25, 50, 50));
+    decoderFrameBufferCache[1].setBlendingMethod(ImageFrame::BlendOverwrite);
+
+    for (int disposeMethod = ImageFrame::DisposeNotSpecified; disposeMethod <= ImageFrame::DisposeOverwritePrevious; ++disposeMethod) {
+        decoderFrameBufferCache[0].setDisposalMethod(static_cast<ImageFrame::FrameDisposalMethod>(disposeMethod));
+        decoder->resetRequiredPreviousFrames();
+        EXPECT_EQ(notFound, decoderFrameBufferCache[1].requiredPreviousFrameIndex());
+    }
+}
+
+// A full frame that is known to be opaque doesn't depend on any prior frames.
+TEST(ImageDecoderTest, requiredPreviousFrameIndexFullFrameOpaque)
+{
+    OwnPtr<TestImageDecoder> decoder(adoptPtr(new TestImageDecoder()));
+    decoder->initFrames(2);
+    Vector<ImageFrame, 1>& decoderFrameBufferCache = decoder->frameBufferCache();
+
+    decoderFrameBufferCache[0].setOriginalFrameRect(IntRect(25, 25, 50, 50));
+    decoderFrameBufferCache[1].setBlendingMethod(ImageFrame::BlendOverwrite);
+
+    for (int disposeMethod = ImageFrame::DisposeNotSpecified; disposeMethod <= ImageFrame::DisposeOverwritePrevious; ++disposeMethod) {
+        decoderFrameBufferCache[0].setDisposalMethod(static_cast<ImageFrame::FrameDisposalMethod>(disposeMethod));
+        decoder->resetRequiredPreviousFrames(true); // Opaque.
+        EXPECT_EQ(notFound, decoderFrameBufferCache[1].requiredPreviousFrameIndex());
+    }
+}
+
 TEST(ImageDecoderTest, clearCacheExceptFrameDoNothing)
 {
     OwnPtr<TestImageDecoder> decoder(adoptPtr(new TestImageDecoder()));