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 
14 struct GifFileType;
15 struct SavedImage;
16 
17 /*
18  *
19  * This class implements the decoding for gif images
20  *
21  */
22 class SkGifCodec : public SkCodec {
23 public:
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 
33 protected:
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 
onGetEncodedFormat()63     SkEncodedFormat onGetEncodedFormat() const override {
64         return kGIF_SkEncodedFormat;
65     }
66 
67     bool onRewind() override;
68 
69     uint64_t onGetFillValue(const SkImageInfo&) const override;
70 
71     int onOutputScanline(int inputScanline) const override;
72 
73 private:
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 
getSampler(bool createIfNecessary)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 info contains properties of the encoded data
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(int width, int height, const SkEncodedInfo& info, SkStream* stream,
193             GifFileType* gif, uint32_t transIndex, 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