Save a bitmap copy when advancing to dependent GIF and WebP animation frames

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 338 matching lines @@
 {
     // Initialize the frame rect in our buffer.
     ImageFrame* const buffer = &m_frameBufferCache[frameIndex];
 
     size_t requiredPreviousFrameIndex = buffer->requiredPreviousFrameIndex();
     if (requiredPreviousFrameIndex == kNotFound) {
         // This frame doesn't rely on any previous data.
         if (!buffer->setSizeAndColorProfile(size().width(), size().height(), ImageFrame::ICCProfile()))
             return setFailed();
     } else {
-        const ImageFrame* prevBuffer = &m_frameBufferCache[requiredPreviousFrameIndex];
+        ImageFrame* prevBuffer = &m_frameBufferCache[requiredPreviousFrameIndex];
         ASSERT(prevBuffer->getStatus() == ImageFrame::FrameComplete);
 
-        // Preserve the last frame as the starting state for this frame.
-        if (!buffer->copyBitmapData(*prevBuffer))
-            return setFailed();
+        // We try to reuse |prevBuffer| as starting state and avoid copy.

[Peter Kasting, 2016/08/26 19:04:04]

See comments in WebP decoder, they also apply to this file

[aleksandar.stojiljkovic, 2016/08/26 21:53:51]

Done.

+        // For DisposeOverwritePrevious, the next frame will also use
+        // |prevBuffer| as its starting state, so we can't take over its image
+        // data using takeBitmapDataIfWritable.  Copy the data instead.
+        if (buffer->getDisposalMethod() == ImageFrame::DisposeOverwritePrevious || !buffer->takeBitmapDataIfWritable(prevBuffer)) {
+            if (!buffer->copyBitmapData(*prevBuffer))
+                return setFailed();
+        }
 
         if (prevBuffer->getDisposalMethod() == ImageFrame::DisposeOverwriteBgcolor) {
             // We want to clear the previous frame to transparent, without
             // affecting pixels in the image outside of the frame.
             const IntRect& prevRect = prevBuffer->originalFrameRect();
             ASSERT(!prevRect.contains(IntRect(IntPoint(), size())));
             buffer->zeroFillFrameRect(prevRect);
         }
     }
 
@@ skipping 42 matching lines @@
         m_purgeAggressively = true;
         return;
     }
 
     const uint64_t totalMemoryUsage = frameMemoryUsage * index;
     if (totalMemoryUsage > m_maxDecodedBytes) {
         m_purgeAggressively = true;
     }
 }
 } // namespace blink