1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef GIF_TRANSCODER_H
18 #define GIF_TRANSCODER_H
19 
20 #include <sys/types.h>
21 
22 #include "gif_lib.h"
23 
24 // 24-bit color with alpha, stored in order: A, R, G, B.
25 // The internal GIF render buffer stores pixels using this format.
26 typedef uint32_t ColorARGB;
27 
28 // Compresses a GIF (probably animated) so it can be sent via MMS, which generally has a 1 MB limit
29 // on attachments. GIF image data is already compressed (LZW), so to achieve further reduction in
30 // file size, we reduce the image dimensions.
31 //
32 // Helpful GIF references:
33 // GIF89A spec: http://www.w3.org/Graphics/GIF/spec-gif89a.txt
34 // What's in a GIF: http://giflib.sourceforge.net/whatsinagif/index.html
35 //
36 class GifTranscoder {
37 public:
GifTranscoder()38     GifTranscoder() {}
~GifTranscoder()39     ~GifTranscoder() {}
40 
41     // Resizes a GIF's width and height to 50% of their original dimensions. The new file is
42     // written to pathOut.
43     //
44     // The image is resized using a box filter, which averages the colors in each 2x2 box of pixels
45     // in the source to generate the color of the pixel in the destination.
46     //
47     // Returns GIF_OK (1) on success, or GIF_ERROR (0) on failure.
48     int transcode(const char* pathIn, const char* pathOut);
49 
50 private:
51     // Implementation of the box filter algorithm.
52     static bool resizeBoxFilter(GifFileType* gifIn, GifFileType* gifOut);
53 
54     // Reads the raster data for the current image of the GIF.
55     static bool readImage(GifFileType* gifIn, GifByteType* rasterBits);
56 
57     // Renders the current image of the GIF into the supplied render buffer.
58     static bool renderImage(GifFileType* gifIn,
59                             GifByteType* rasterBits,
60                             int imageIndex,
61                             int transparentColorIndex,
62                             ColorARGB* renderBuffer,
63                             ColorARGB bgColor,
64                             GifImageDesc prevImageDimens,
65                             int prevImageDisposalMode);
66 
67     // Fills a rectangle in the buffer with a solid color.
68     static void fillRect(ColorARGB* renderBuffer,
69                          int imageWidth,
70                          int imageHeight,
71                          int left,
72                          int top,
73                          int width,
74                          int height,
75                          ColorARGB color);
76 
77     // Computes the color for the pixel (x,y) in the current image in the output GIF.
78     static GifByteType computeNewColorIndex(GifFileType* gifIn,
79                                             int transparentColorIndex,
80                                             ColorARGB* renderBuffer,
81                                             int x,
82                                             int y);
83 
84     // Computes the average color (by averaging the per-channel (ARGB) values).
85     static ColorARGB computeAverage(ColorARGB c1, ColorARGB c2, ColorARGB c3, ColorARGB c4);
86 
87     // Searches a color map for the color closest (Euclidean distance) to the target color.
88     static GifByteType findBestColor(ColorMapObject* colorMap, int transparentColorIndex,
89                                      ColorARGB targetColor);
90 
91     // Computes distance (squared) between 2 colors, considering each channel a separate dimension.
92     static int computeDistance(ColorARGB c1, ColorARGB c2);
93 
94     // Returns the local color map of the current image (if any), or else the global color map.
95     static ColorMapObject* getColorMap(GifFileType* gifIn);
96 
97     // Returns an indexed color from the color map.
98     static ColorARGB getColorARGB(ColorMapObject* colorMap, int transparentColorIndex,
99                                   GifByteType colorIndex);
100 
101     // Converts a 24-bit GIF color (RGB) to a 32-bit ARGB color.
102     static ColorARGB gifColorToColorARGB(const GifColorType& color);
103 };
104 
105 // Wrapper class that automatically closes the GIF files when the wrapper goes out of scope.
106 class GifFilesCloser {
107 public:
GifFilesCloser()108     GifFilesCloser() {}
109     ~GifFilesCloser();
110 
111     void setGifIn(GifFileType* gifIn);
112     void releaseGifIn();
113 
114     void setGifOut(GifFileType* gifOut);
115     void releaseGifOut();
116 
117 private:
118     GifFileType* mGifIn = NULL;
119     GifFileType* mGifOut = NULL;
120 };
121 
122 #endif // GIF_TRANSCODER_H
123