SkGifCodec.h revision ad8bcfeac4a684a64db3a7447aeea5bc35155f16 
1/*
2 * Copyright 2015 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#include "SkCodec.h"
9#include "SkColorSpace.h"
10#include "SkColorTable.h"
11#include "SkImageInfo.h"
12#include "SkSwizzler.h"
13
14struct GifFileType;
15struct SavedImage;
16
17/*
18 *
19 * This class implements the decoding for gif images
20 *
21 */
22class SkGifCodec : public SkCodec {
23public:
24    static bool IsGif(const void*, size_t);
25
26    /*
27     * Assumes IsGif was called and returned true
28     * Creates a gif decoder
29     * Reads enough of the stream to determine the image format
30     */
31    static SkCodec* NewFromStream(SkStream*);
32
33protected:
34
35    /*
36     * Read enough of the stream to initialize the SkGifCodec.
37     * Returns a bool representing success or failure.
38     *
39     * @param codecOut
40     * If it returned true, and codecOut was not nullptr,
41     * codecOut will be set to a new SkGifCodec.
42     *
43     * @param gifOut
44     * If it returned true, and codecOut was nullptr,
45     * gifOut must be non-nullptr and gifOut will be set to a new
46     * GifFileType pointer.
47     *
48     * @param stream
49     * Deleted on failure.
50     * codecOut will take ownership of it in the case where we created a codec.
51     * Ownership is unchanged when we returned a gifOut.
52     *
53     */
54    static bool ReadHeader(SkStream* stream, SkCodec** codecOut,
55            GifFileType** gifOut);
56
57    /*
58     * Performs the full gif decode
59     */
60    Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&,
61            SkPMColor*, int*, int*) override;
62
63    SkEncodedFormat onGetEncodedFormat() const override {
64        return kGIF_SkEncodedFormat;
65    }
66
67    bool onRewind() override;
68
69    uint32_t onGetFillValue(SkColorType) const override;
70
71    int onOutputScanline(int inputScanline) const override;
72
73private:
74
75    /*
76     * A gif can contain multiple image frames.  We will only decode the first
77     * frame.  This function reads up to the first image frame, processing
78     * transparency and/or animation information that comes before the image
79     * data.
80     *
81     * @param gif        Pointer to the library type that manages the gif decode
82     * @param transIndex This call will set the transparent index based on the
83     *                   extension data.
84     */
85     static Result ReadUpToFirstImage(GifFileType* gif, uint32_t* transIndex);
86
87     /*
88      * A gif may contain many image frames, all of different sizes.
89      * This function checks if the gif dimensions are valid, based on the frame
90      * dimensions, and corrects the gif dimensions if necessary.
91      *
92      * @param gif       Pointer to the library type that manages the gif decode
93      * @param size      Size of the image that we will decode.
94      *                  Will be set by this function if the return value is true.
95      * @param frameRect Contains the dimenions and offset of the first image frame.
96      *                  Will be set by this function if the return value is true.
97      *
98      * @return true on success, false otherwise
99      */
100     static bool GetDimensions(GifFileType* gif, SkISize* size, SkIRect* frameRect);
101
102    /*
103     * Initializes the color table that we will use for decoding.
104     *
105     * @param dstInfo         Contains the requested dst color type.
106     * @param inputColorPtr   Copies the encoded color table to the client's
107     *                        input color table if the client requests kIndex8.
108     * @param inputColorCount If the client requests kIndex8, sets
109     *                        inputColorCount to 256.  Since gifs always
110     *                        contain 8-bit indices, we need a 256 entry color
111     *                        table to ensure that indexing is always in
112     *                        bounds.
113     */
114    void initializeColorTable(const SkImageInfo& dstInfo, SkPMColor* colorPtr,
115            int* inputColorCount);
116
117   /*
118    * Checks for invalid inputs and calls setFrameDimensions(), and
119    * initializeColorTable() in the proper sequence.
120    */
121    Result prepareToDecode(const SkImageInfo& dstInfo, SkPMColor* inputColorPtr,
122            int* inputColorCount, const Options& opts);
123
124    /*
125     * Initializes the swizzler.
126     *
127     * @param dstInfo  Output image information.  Dimensions may have been
128     *                 adjusted if the image frame size does not match the size
129     *                 indicated in the header.
130     * @param options  Informs the swizzler if destination memory is zero initialized.
131     *                 Contains subset information.
132     */
133    void initializeSwizzler(const SkImageInfo& dstInfo,
134            const Options& options);
135
136    SkSampler* getSampler(bool createIfNecessary) override {
137        SkASSERT(fSwizzler);
138        return fSwizzler;
139    }
140
141    /*
142     * @return true if the read is successful and false if the read fails.
143     */
144    bool readRow();
145
146    Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& opts,
147                   SkPMColor inputColorPtr[], int* inputColorCount) override;
148
149    int onGetScanlines(void* dst, int count, size_t rowBytes) override;
150
151    bool onSkipScanlines(int count) override;
152
153    /*
154     * For a scanline decode of "count" lines, this function indicates how
155     * many of the "count" lines should be skipped until we reach the top of
156     * the image frame and how many of the "count" lines are actually inside
157     * the image frame.
158     *
159     * @param count           The number of scanlines requested.
160     * @param rowsBeforeFrame Output variable.  The number of lines before
161     *                        we reach the top of the image frame.
162     * @param rowsInFrame     Output variable.  The number of lines to decode
163     *                        inside the image frame.
164     */
165    void handleScanlineFrame(int count, int* rowsBeforeFrame, int* rowsInFrame);
166
167    SkScanlineOrder onGetScanlineOrder() const override;
168
169    /*
170     * This function cleans up the gif object after the decode completes
171     * It is used in a SkAutoTCallIProc template
172     */
173    static void CloseGif(GifFileType* gif);
174
175    /*
176     * Frees any extension data used in the decode
177     * Used in a SkAutoTCallVProc
178     */
179    static void FreeExtension(SavedImage* image);
180
181    /*
182     * Creates an instance of the decoder
183     * Called only by NewFromStream
184     *
185     * @param srcInfo contains the source width and height
186     * @param stream the stream of image data
187     * @param gif pointer to library type that manages gif decode
188     *            takes ownership
189     * @param transIndex  The transparent index.  An invalid value
190     *            indicates that there is no transparent index.
191     */
192    SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream, GifFileType* gif, uint32_t transIndex,
193            const SkIRect& frameRect, bool frameIsSubset);
194
195    SkAutoTCallVProc<GifFileType, CloseGif> fGif; // owned
196    SkAutoTDeleteArray<uint8_t>             fSrcBuffer;
197    const SkIRect                           fFrameRect;
198    const uint32_t                          fTransIndex;
199    uint32_t                                fFillIndex;
200    const bool                              fFrameIsSubset;
201    SkAutoTDelete<SkSwizzler>               fSwizzler;
202    SkAutoTUnref<SkColorTable>              fColorTable;
203
204    typedef SkCodec INHERITED;
205};
206