Decode GIF image frames on demand.

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

Index: Source/core/platform/image-decoders/gif/GIFImageDecoder.h
diff --git a/Source/core/platform/image-decoders/gif/GIFImageDecoder.h b/Source/core/platform/image-decoders/gif/GIFImageDecoder.h
index b05f2a177f47ff3b91de6830e77d54bb26fb957d..f0a9ef37c00e5480b458e6a7a7b1cdcf029e5478 100644
--- a/Source/core/platform/image-decoders/gif/GIFImageDecoder.h
+++ b/Source/core/platform/image-decoders/gif/GIFImageDecoder.h
@@ -27,7 +27,9 @@
 #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;
 
@@ -39,7 +41,7 @@ namespace WebCore {
         GIFImageDecoder(ImageSource::AlphaOption, ImageSource::GammaAndColorProfileOption);
         virtual ~GIFImageDecoder();
 
-        enum GIFQuery { GIFFullQuery, GIFSizeQuery, GIFFrameCountQuery };
+        enum GIFParseQuery { GIFSizeQuery, GIFFrameCountQuery };
 
         // ImageDecoder
         virtual String filenameExtension() const { return "gif"; }
@@ -58,21 +60,34 @@ namespace WebCore {
         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;