1 /* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* This Source Code Form is subject to the terms of the Mozilla Public
3  * License, v. 2.0. If a copy of the MPL was not distributed with this
4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
5 
6 #ifndef mozilla_image_decoders_GIF2_H
7 #define mozilla_image_decoders_GIF2_H
8 
9 #define MAX_LZW_BITS 12
10 #define MAX_BITS 4097  // 2^MAX_LZW_BITS+1
11 #define MAX_COLORS 256
12 #define MIN_HOLD_SIZE 256
13 
14 enum { GIF_TRAILER = 0x3B };               // ';'
15 enum { GIF_IMAGE_SEPARATOR = 0x2C };       // ','
16 enum { GIF_EXTENSION_INTRODUCER = 0x21 };  // '!'
17 enum { GIF_GRAPHIC_CONTROL_LABEL = 0xF9 };
18 enum { GIF_APPLICATION_EXTENSION_LABEL = 0xFF };
19 
20 // A GIF decoder's state
21 typedef struct gif_struct {
22   // LZW decoder state machine
23   uint8_t* stackp;  // Current stack pointer
24   int datasize;
25   int codesize;
26   int codemask;
27   int avail;  // Index of next available slot in dictionary
28   int oldcode;
29   uint8_t firstchar;
30   int bits;       // Number of unread bits in "datum"
31   int32_t datum;  // 32-bit input buffer
32 
33   // Output state machine
34   int64_t pixels_remaining;  // Pixels remaining to be output.
35 
36   // Parameters for image frame currently being decoded
37   int tpixel;                // Index of transparent pixel
38   int32_t disposal_method;   // Restore to background, leave in place, etc.
39   uint32_t* local_colormap;  // Per-image colormap
40   uint32_t local_colormap_buffer_size;  // Size of the buffer containing the
41                                         // local colormap.
42   int local_colormap_size;              // Size of local colormap array.
43   uint32_t delay_time;                  // Display time, in milliseconds,
44                                         // for this image in a multi-image GIF
45 
46   // Global (multi-image) state
47   int version;           // Either 89 for GIF89 or 87 for GIF87
48   int32_t screen_width;  // Logical screen width & height
49   int32_t screen_height;
50   uint8_t global_colormap_depth;   // Depth of global colormap array
51   uint16_t global_colormap_count;  // Number of colors in global colormap
52   int images_decoded;              // Counts images for multi-part GIFs
53   int loop_count;  // Netscape specific extension block to control
54                    // the number of animation loops a GIF
55                    // renders.
56 
57   bool is_transparent;  // TRUE, if tpixel is valid
58 
59   uint16_t prefix[MAX_BITS];             // LZW decoding tables
60   uint32_t global_colormap[MAX_COLORS];  // Default colormap if local not
61                                          //   supplied
62   uint8_t suffix[MAX_BITS];              // LZW decoding tables
63   uint8_t stack[MAX_BITS];               // Base of LZW decoder stack
64 
65 } gif_struct;
66 
67 #endif  // mozilla_image_decoders_GIF2_H
68