Animated WebP: Optimize decoding in case of seeking

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 36 matching lines @@
     }
 
     virtual String filenameExtension() const OVERRIDE { return ""; }
     virtual ImageFrame* frameBufferAtIndex(size_t) OVERRIDE { return 0; }
 
     Vector<ImageFrame, 1>& frameBufferCache()
     {
         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)
     {
         setSize(width, height);
         m_frameBufferCache.resize(numFrames);
         for (size_t i = 0; i < numFrames; ++i)
             m_frameBufferCache[i].setOriginalFrameRect(IntRect(0, 0, width, height));
     }
 };
@@ skipping 62 matching lines @@
     decoderFrameBufferCache[0].setOriginalFrameRect(IntRect(50, 50, 50, 50));
 
     decoderFrameBufferCache[0].setDisposalMethod(ImageFrame::DisposeOverwritePrevious);
     decoder->resetRequiredPreviousFrames();
     EXPECT_EQ(notFound, decoderFrameBufferCache[1].requiredPreviousFrameIndex());
     decoderFrameBufferCache[0].setDisposalMethod(ImageFrame::DisposeOverwriteBgcolor);
     decoder->resetRequiredPreviousFrames();
     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()));
     decoder->clearCacheExceptFrame(0);
 
     // This should not crash.
     decoder->initFrames(20);
     decoder->clearCacheExceptFrame(notFound);
 }
 
@@ skipping 26 matching lines @@
     decoder->resetRequiredPreviousFrames();
     decoder->clearCacheExceptFrame(5);
     for (size_t i = 0; i < numFrames; ++i) {
         SCOPED_TRACE(testing::Message() << i);
         if (i == 5)
             EXPECT_EQ(ImageFrame::FrameComplete, decoderFrameBufferCache[i].status());
         else
             EXPECT_EQ(ImageFrame::FrameEmpty, decoderFrameBufferCache[i].status());
     }
 }