Decode GIF image frames on demand.

Source/core/platform/image-decoders/gif/GIFImageDecoder.h

 /*
  * 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
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef GIFImageDecoder_h
 #define GIFImageDecoder_h
 
 #include "core/platform/image-decoders/ImageDecoder.h"
-#include <wtf/OwnPtr.h>
+#include "wtf/BitVector.h"
+#include "wtf/NotFound.h"
+#include "wtf/OwnPtr.h"
 
 class GIFImageReader;
 
 namespace WebCore {
 
     // This class decodes the GIF image format.
     class GIFImageDecoder : public ImageDecoder {
     public:
         GIFImageDecoder(ImageSource::AlphaOption, ImageSource::GammaAndColorProfileOption);
         virtual ~GIFImageDecoder();
 
-        enum GIFQuery { GIFFullQuery, GIFSizeQuery, GIFFrameCountQuery };
+        enum GIFParseQuery { GIFSizeQuery, GIFFrameCountQuery };
 
         // ImageDecoder
         virtual String filenameExtension() const { return "gif"; }
         virtual void setData(SharedBuffer* data, bool allDataReceived);
         virtual bool isSizeAvailable();
         virtual bool setSize(unsigned width, unsigned height);
         virtual size_t frameCount();
         virtual int repetitionCount() const;
         virtual ImageFrame* frameBufferAtIndex(size_t index);
         virtual bool frameIsCompleteAtIndex(size_t) const;
         virtual float frameDurationAtIndex(size_t) const;
         // CAUTION: setFailed() deletes |m_reader|.  Be careful to avoid
         // accessing deleted memory, especially when calling this from inside
         // GIFImageReader!
         virtual bool setFailed();
         virtual void clearFrameBufferCache(size_t clearBeforeFrame);
 
         // Callbacks from the GIF reader.
-        bool haveDecodedRow(unsigned frameIndex, const Vector<unsigned char>& rowBuffer, size_t width, size_t rowNumber, unsigned repeatCount, bool writeTransparentPixels);
-        bool frameComplete(unsigned frameIndex, unsigned frameDuration, ImageFrame::FrameDisposalMethod disposalMethod);
+        bool haveDecodedRow(size_t frameIndex, const Vector<unsigned char>& rowBuffer, size_t width, size_t rowNumber, unsigned repeatCount, bool writeTransparentPixels);
+        bool frameComplete(size_t frameIndex, unsigned frameDuration, ImageFrame::FrameDisposalMethod);
         void gifComplete();

[Alpha Left Google, 2013/05/18 00:39:35]

I suggest removing this method. This used to mean that the entire GIF image is
decoded until the end without error. This change allows GIF frames to be decoded
out of order and this method doesn't apply.

[Xianzhu, 2013/05/20 04:30:59]

Done.

 
     private:
-        // If the query is GIFFullQuery, decodes the image up to (but not
-        // including) |haltAtFrame|.  Otherwise, decodes as much as is needed to
-        // answer the query, ignoring bitmap data.  If decoding fails but there
-        // is no more data coming, sets the "decode failure" flag.
-        void decode(unsigned haltAtFrame, GIFQuery);
+        // Parses as much as is needed to answer the query, ignoring bitmap
+        // data. If parsing fails but there is no more data coming, sets the

[Alpha Left Google, 2013/05/18 00:39:35]

If parsing fails we report an error anyway, regardless of whether there's new
incoming data.

[Xianzhu, 2013/05/20 04:30:59]

Done.

+        // "decode failure" flag.
+        void parse(GIFParseQuery);
+
+        // Decodes bitmap data of the frame. Depending on the disposal method
+        // of prior frames, also decodes all required prior frames. If decoding
+        // fails but there is no more data coming, sets the "decode failure"
+        // flag.
+        void decode(size_t frameIndex);
+
+        // Gets all frames that need to be decoded for decoding the given frame,
+        // not including completed frames.
+        void getFramesToDecode(size_t frameIndex, BitVector* frames);
+
+        // Gets the previous required frame for decoding the given frame.
+        // Returns notFound if there is no previous required frame.
+        size_t getPreviousRequiredFrame(size_t frameIndex);
 
         // Called to initialize the frame buffer with the given index, based on
         // the previous frame's disposal method. Returns true on success. On
         // failure, this will mark the image as failed.
-        bool initFrameBuffer(unsigned frameIndex);
+        bool initFrameBuffer(size_t frameIndex);
 
         bool m_currentBufferSawAlpha;
         mutable int m_repetitionCount;
         OwnPtr<GIFImageReader> m_reader;
     };
 
 } // namespace WebCore
 
 #endif