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