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/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkCodec.h"
#include "SkColorTable.h"
#include "SkImageInfo.h"
#include "SkSwizzler.h"
#include "gif_lib.h"
/*
*
* This class implements the decoding for gif images
*
*/
class SkGifCodec : public SkCodec {
public:
/*
* Checks the start of the stream to see if the image is a gif
*/
static bool IsGif(SkStream*);
/*
* Assumes IsGif was called and returned true
* Creates a gif decoder
* Reads enough of the stream to determine the image format
*/
static SkCodec* NewFromStream(SkStream*);
protected:
/*
* Read enough of the stream to initialize the SkGifCodec.
* Returns a bool representing success or failure.
*
* @param codecOut
* If it returned true, and codecOut was not nullptr,
* codecOut will be set to a new SkGifCodec.
*
* @param gifOut
* If it returned true, and codecOut was nullptr,
* gifOut must be non-nullptr and gifOut will be set to a new
* GifFileType pointer.
*
* @param stream
* Deleted on failure.
* codecOut will take ownership of it in the case where we created a codec.
* Ownership is unchanged when we returned a gifOut.
*
*/
static bool ReadHeader(SkStream* stream, SkCodec** codecOut,
GifFileType** gifOut);
/*
* Performs the full gif decode
*/
Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&,
SkPMColor*, int*, int*) override;
SkEncodedFormat onGetEncodedFormat() const override {
return kGIF_SkEncodedFormat;
}
bool onRewind() override;
uint32_t onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const override;
int onOutputScanline(int inputScanline) const override;
private:
/*
* A gif can contain multiple image frames. We will only decode the first
* frame. This function reads up to the first image frame, processing
* transparency and/or animation information that comes before the image
* data.
*
* @param gif Pointer to the library type that manages the gif decode
* @param transIndex This call will set the transparent index based on the
* extension data.
*/
static Result ReadUpToFirstImage(GifFileType* gif, uint32_t* transIndex);
/*
* A gif may contain many image frames, all of different sizes.
* This function checks if the gif dimensions are valid, based on the frame
* dimensions, and corrects the gif dimensions if necessary.
*
* @param gif Pointer to the library type that manages the gif decode
* @param size Size of the image that we will decode.
* Will be set by this function if the return value is true.
* @param frameRect Contains the dimenions and offset of the first image frame.
* Will be set by this function if the return value is true.
*
* @return true on success, false otherwise
*/
static bool GetDimensions(GifFileType* gif, SkISize* size, SkIRect* frameRect);
/*
* Initializes the color table that we will use for decoding.
*
* @param dstInfo Contains the requested dst color type.
* @param inputColorPtr Copies the encoded color table to the client's
* input color table if the client requests kIndex8.
* @param inputColorCount If the client requests kIndex8, sets
* inputColorCount to 256. Since gifs always
* contain 8-bit indices, we need a 256 entry color
* table to ensure that indexing is always in
* bounds.
*/
void initializeColorTable(const SkImageInfo& dstInfo, SkPMColor* colorPtr,
int* inputColorCount);
/*
* Checks for invalid inputs and calls setFrameDimensions(), and
* initializeColorTable() in the proper sequence.
*/
Result prepareToDecode(const SkImageInfo& dstInfo, SkPMColor* inputColorPtr,
int* inputColorCount, const Options& opts);
/*
* Initializes the swizzler.
*
* @param dstInfo Output image information. Dimensions may have been
* adjusted if the image frame size does not match the size
* indicated in the header.
* @param options Informs the swizzler if destination memory is zero initialized.
* Contains subset information.
*/
Result initializeSwizzler(const SkImageInfo& dstInfo,
const Options& options);
SkSampler* getSampler(bool createIfNecessary) override {
SkASSERT(fSwizzler);
return fSwizzler;
}
/*
* @return true if the read is successful and false if the read fails.
*/
bool readRow();
Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& opts,
SkPMColor inputColorPtr[], int* inputColorCount) override;
int onGetScanlines(void* dst, int count, size_t rowBytes) override;
bool onSkipScanlines(int count) override;
/*
* For a scanline decode of "count" lines, this function indicates how
* many of the "count" lines should be skipped until we reach the top of
* the image frame and how many of the "count" lines are actually inside
* the image frame.
*
* @param count The number of scanlines requested.
* @param rowsBeforeFrame Output variable. The number of lines before
* we reach the top of the image frame.
* @param rowsInFrame Output variable. The number of lines to decode
* inside the image frame.
*/
void handleScanlineFrame(int count, int* rowsBeforeFrame, int* rowsInFrame);
SkScanlineOrder onGetScanlineOrder() const override;
/*
* This function cleans up the gif object after the decode completes
* It is used in a SkAutoTCallIProc template
*/
static void CloseGif(GifFileType* gif);
/*
* Frees any extension data used in the decode
* Used in a SkAutoTCallVProc
*/
static void FreeExtension(SavedImage* image);
/*
* Creates an instance of the decoder
* Called only by NewFromStream
*
* @param srcInfo contains the source width and height
* @param stream the stream of image data
* @param gif pointer to library type that manages gif decode
* takes ownership
* @param transIndex The transparent index. An invalid value
* indicates that there is no transparent index.
*/
SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream, GifFileType* gif, uint32_t transIndex,
const SkIRect& frameRect, bool frameIsSubset);
SkAutoTCallVProc<GifFileType, CloseGif> fGif; // owned
SkAutoTDeleteArray<uint8_t> fSrcBuffer;
const SkIRect fFrameRect;
const uint32_t fTransIndex;
uint32_t fFillIndex;
const bool fFrameIsSubset;
SkAutoTDelete<SkSwizzler> fSwizzler;
SkAutoTUnref<SkColorTable> fColorTable;
typedef SkCodec INHERITED;
};
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