gifimagedecoder.h

linux下开源浏览器WebKit的源码,市面上的很多商用浏览器都是移植自WebKit

/*
 * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
 * Copyright (C) 2008, 2009 Google, 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
 *    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 "ImageDecoder.h"

namespace WebCore {

    class GIFImageDecoderPrivate;

    // This class decodes the GIF image format.
    class GIFImageDecoder : public ImageDecoder {
    public:
        GIFImageDecoder();
        ~GIFImageDecoder();

        virtual String filenameExtension() const { return "gif"; }

        // Take the data and store it.
        virtual void setData(SharedBuffer* data, bool allDataReceived);

        // Whether or not the size information has been decoded yet.
        virtual bool isSizeAvailable() const;

        // The total number of frames for the image.  Will scan the image data for the answer
        // (without necessarily decoding all of the individual frames).
        virtual int frameCount();

        // The number of repetitions to perform for an animation loop.
        virtual int repetitionCount() const;

        virtual RGBA32Buffer* frameBufferAtIndex(size_t index);

        virtual void clearFrameBufferCache(size_t clearBeforeFrame);

        virtual unsigned frameDurationAtIndex(size_t index) { return 0; }

        enum GIFQuery { GIFFullQuery, GIFSizeQuery, GIFFrameCountQuery };

        void decode(GIFQuery, unsigned haltAtFrame) const;

        // Callbacks from the GIF reader.
        bool sizeNowAvailable(unsigned width, unsigned height);
        void decodingHalted(unsigned bytesLeft);
        void haveDecodedRow(unsigned frameIndex, unsigned char* rowBuffer, unsigned char* rowEnd, unsigned rowNumber, 
                            unsigned repeatCount, bool writeTransparentPixels);
        void frameComplete(unsigned frameIndex, unsigned frameDuration, RGBA32Buffer::FrameDisposalMethod disposalMethod);
        void gifComplete();

    private:
        // 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);

        // A helper for initFrameBuffer(), this sets the size of the buffer, and
        // fills it with transparent pixels.
        bool prepEmptyFrameBuffer(RGBA32Buffer*) const;

        bool m_frameCountValid;
        bool m_currentBufferSawAlpha;
        mutable int m_repetitionCount;
        mutable GIFImageDecoderPrivate* m_reader;
    };

} // namespace WebCore

#endif