Decode GIF image frames on demand.

Source/core/platform/graphics/ImageSource.h

 /*
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2007-2008 Torch Mobile, Inc.
  *
  * 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 63 matching lines @@
 
     enum GammaAndColorProfileOption {
         GammaAndColorProfileApplied,
         GammaAndColorProfileIgnored
     };
 
     ImageSource(AlphaOption alphaOption = AlphaPremultiplied, GammaAndColorProfileOption gammaAndColorProfileOption = GammaAndColorProfileApplied);
     ~ImageSource();
 
     // Tells the ImageSource that the Image no longer cares about decoded frame
-    // data -- at all (if |destroyAll| is true), or before frame
-    // |clearBeforeFrame| (if |destroyAll| is false).  The ImageSource should
+    // data -- at all (if |destroyAll| is true), or except frame
+    // |clearExceptFrame| (if |destroyAll| is false). The ImageSource should
     // delete cached decoded data for these frames where possible to keep memory
     // usage low.  When |destroyAll| is true, the ImageSource should also reset
     // any local state so that decoding can begin again.
     //
     // Implementations that delete less than what's specified above waste

[Peter Kasting, 2013/05/24 03:15:22]

Nit: Change "waste" to "may waste", since ultimately we're going to want to
preserve more frames than are requested here, at least for GIF.

[Xianzhu, 2013/05/28 22:54:21]

Done.

     // memory.  Implementations that delete more may burn CPU re-decoding frames
     // that could otherwise have been cached, or encounter errors if they're
     // asked to decode frames they can't decode due to the loss of previous
     // decoded frames.
     //
-    // Callers should not call clear(false, n) and subsequently call
-    // createFrameAtIndex(m) with m < n, unless they first call clear(true).
-    // This ensures that stateful ImageSources/decoders will work properly.
-    //
     // The |data| and |allDataReceived| parameters should be supplied by callers
     // who set |destroyAll| to true if they wish to be able to continue using
     // the ImageSource.  This way implementations which choose to destroy their
     // decoders in some cases can reconstruct them correctly.
-    void clear(bool destroyAll,
-               size_t clearBeforeFrame = 0,
-               SharedBuffer* data = NULL,
-               bool allDataReceived = false);
+    void clear(bool destroyAll, size_t clearExceptFrame = 0, SharedBuffer* data = 0, bool allDataReceived = false);
 
     bool initialized() const;
 
     void setData(SharedBuffer* data, bool allDataReceived);
     String filenameExtension() const;
 
     bool isSizeAvailable();
     IntSize size(RespectImageOrientationEnum = DoNotRespectImageOrientation) const;
     IntSize frameSizeAtIndex(size_t, RespectImageOrientationEnum = DoNotRespectImageOrientation) const;
 
@@ skipping 31 matching lines @@
     AlphaOption m_alphaOption;
     GammaAndColorProfileOption m_gammaAndColorProfileOption;
 #if ENABLE(IMAGE_DECODER_DOWN_SAMPLING)
     static unsigned s_maxPixelsPerDecodedImage;
 #endif
 };
 
 }
 
 #endif