GIF Animations "clear from cache related glitch" fix

third_party/WebKit/Source/platform/image-decoders/gif/GIFImageDecoder.cpp

 /*
  * Copyright (C) 2006 Apple Computer, 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 209 matching lines @@
 
 size_t GIFImageDecoder::clearCacheExceptFrame(size_t clearExceptFrame)
 {
     // We need to preserve frames such that:
     //  1. We don't clear |clearExceptFrame|;
     //  2. We don't clear any frame from which a future initFrameBuffer() call
     //     will copy bitmap data.
     // All other frames can be cleared.
     while ((clearExceptFrame < m_frameBufferCache.size()) && (m_frameBufferCache[clearExceptFrame].status() == ImageFrame::FrameEmpty))
         clearExceptFrame = m_frameBufferCache[clearExceptFrame].requiredPreviousFrameIndex();
+    if ((clearExceptFrame >= m_frameBufferCache.size()) || (m_frameBufferCache.size() == 1)
+        || (m_frameBufferCache[clearExceptFrame].disposalMethod() != ImageFrame::DisposeOverwritePrevious))
+        return ImageDecoder::clearCacheExceptFrame(clearExceptFrame);
+    // For case with DisposeOverwritePrevious, enumerate through required to
+    // find the one that is complete.
+    size_t frame2 = m_frameBufferCache[clearExceptFrame].requiredPreviousFrameIndex();
+    while ((frame2 < m_frameBufferCache.size()) && (m_frameBufferCache[frame2].status() == ImageFrame::FrameEmpty))
+        frame2 = m_frameBufferCache[frame2].requiredPreviousFrameIndex();
+    return clearCacheExceptTwoFrames(clearExceptFrame, frame2);
+}
 
-    return ImageDecoder::clearCacheExceptFrame(clearExceptFrame);
+
+size_t GIFImageDecoder::clearCacheExceptTwoFrames(size_t dontClearFrame1, size_t dontClearFrame2)
+{
+    size_t frameBytesCleared = 0;
+    for (size_t i = 0; i < m_frameBufferCache.size(); ++i) {
+        if (m_frameBufferCache[i].status() != ImageFrame::FrameEmpty && i != dontClearFrame1 && i != dontClearFrame2) {
+            frameBytesCleared += frameBytesAtIndex(i);
+            clearFrameBuffer(i);
+        }
+    }
+    return frameBytesCleared;
 }
 
 void GIFImageDecoder::clearFrameBuffer(size_t frameIndex)
 {
     if (m_reader && m_frameBufferCache[frameIndex].status() == ImageFrame::FramePartial) {
         // Reset the state of the partial frame in the reader so that the frame
         // can be decoded again when requested.
         m_reader->clearDecodeState(frameIndex);
     }
     ImageDecoder::clearFrameBuffer(frameIndex);
@@ skipping 93 matching lines @@
 
     // Update our status to be partially complete.
     buffer->setStatus(ImageFrame::FramePartial);
 
     // Reset the alpha pixel tracker for this frame.
     m_currentBufferSawAlpha = false;
     return true;
 }
 
 } // namespace blink