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

third_party/WebKit/Source/platform/image-decoders/webp/WEBPImageDecoder.cpp

 /*
  * Copyright (C) 2010 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:
  *
  * 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
@@ skipping 234 matching lines @@
     if (buffer.getStatus() != ImageFrame::FrameEmpty) // Already initialized.
         return true;
 
     const size_t requiredPreviousFrameIndex = buffer.requiredPreviousFrameIndex();
     if (requiredPreviousFrameIndex == kNotFound) {
         // This frame doesn't rely on any previous data.
         if (!buffer.setSizeAndColorProfile(size().width(), size().height(), colorProfile()))
             return setFailed();
         m_frameBackgroundHasAlpha = !buffer.originalFrameRect().contains(IntRect(IntPoint(), size()));
     } 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))
+        // Preserve the last frame as the starting state for this frame. We try
+        // to reuse |prevBuffer| as starting state to avoid copying.
+        // For BlendAtopPreviousFrame, both frames are required, so we can't
+        // take over its image data using takeBitmapDataIfWritable.
+        if ((buffer.getAlphaBlendSource() == ImageFrame::BlendAtopPreviousFrame || !buffer.takeBitmapDataIfWritable(&prevBuffer)) && !buffer.copyBitmapData(prevBuffer))

[Ken Russell (switch to Gerrit), 2016/09/29 00:40:04]

Same comment.

             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);

[Ken Russell (switch to Gerrit), 2016/09/29 00:40:04]

Same comment.

         }
 
         m_frameBackgroundHasAlpha = prevBuffer.hasAlpha() || (prevBuffer.getDisposalMethod() == ImageFrame::DisposeOverwriteBgcolor);
     }
 
     buffer.setStatus(ImageFrame::FramePartial);
     // The buffer is transparent outside the decoded area while the image is loading.
     // The correct value of 'hasAlpha' for the frame will be set when it is fully decoded.
     buffer.setHasAlpha(true);
     return true;
@@ skipping 221 matching lines @@
             return false;
         }
         // FALLTHROUGH
     default:
         clear();
         return setFailed();
     }
 }
 
 } // namespace blink