image/decoders/GIF2.h

   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_COMMENT_LABEL               = 0xFE };
  19 enum { GIF_PLAIN_TEXT_LABEL            = 0x01 };
  20 enum { GIF_APPLICATION_EXTENSION_LABEL = 0xFF };
  21
  22 // gif2.h
  23 // The interface for the GIF87/89a decoder.
  24
  25 // List of possible parsing states
  26 typedef enum {
  27     gif_type,
  28     gif_global_header,
  29     gif_global_colormap,
  30     gif_image_start,
  31     gif_image_header,
  32     gif_image_header_continue,
  33     gif_image_colormap,
  34     gif_lzw_start,
  35     gif_lzw,
  36     gif_sub_block,
  37     gif_extension,
  38     gif_control_extension,
  39     gif_consume_block,
  40     gif_skip_block,
  41     gif_done,
  42     gif_error,
  43     gif_comment_extension,
  44     gif_application_extension,
  45     gif_netscape_extension_block,
  46     gif_consume_netscape_extension,
  47     gif_consume_comment
  48 } gstate;
  49
  50 // A GIF decoder's state
  51 typedef struct gif_struct {
  52     // Parsing state machine
  53     gstate state;               // Current decoder master state
  54     uint32_t bytes_to_consume;  // Number of bytes to accumulate
  55     uint32_t bytes_in_hold;     // bytes accumulated so far
  56
  57     // LZW decoder state machine
  58     uint8_t* stackp;            // Current stack pointer
  59     int datasize;
  60     int codesize;
  61     int codemask;
  62     int avail;                  // Index of next available slot in dictionary
  63     int oldcode;
  64     uint8_t firstchar;
  65     int count;                  // Remaining # bytes in sub-block
  66     int bits;                   // Number of unread bits in "datum"
  67     int32_t datum;              // 32-bit input buffer
  68
  69     // Output state machine
  70     int ipass;                  // Interlace pass; Ranges 1-4 if interlaced.
  71     unsigned rows_remaining;    // Rows remaining to be output
  72     unsigned irow;              // Current output row, starting at zero
  73     uint8_t* rowp;              // Current output pointer
  74
  75     // Parameters for image frame currently being decoded
  76     unsigned x_offset, y_offset; // With respect to "screen" origin
  77     unsigned height, width;
  78     int tpixel;                 // Index of transparent pixel
  79     int32_t disposal_method;    // Restore to background, leave in place, etc.
  80     uint32_t* local_colormap;   // Per-image colormap
  81     int local_colormap_size;    // Size of local colormap array.
  82     uint32_t delay_time;        // Display time, in milliseconds,
  83                                 // for this image in a multi-image GIF
  84
  85     // Global (multi-image) state
  86     int version;                // Either 89 for GIF89 or 87 for GIF87
  87     unsigned screen_width;      // Logical screen width & height
  88     unsigned screen_height;
  89     uint32_t global_colormap_depth; // Depth of global colormap array
  90     int images_decoded;         // Counts images for multi-part GIFs
  91     int loop_count;             // Netscape specific extension block to control
  92                                 // the number of animation loops a GIF
  93                                 // renders.
  94
  95     bool progressive_display;   // If TRUE, do Haeberli interlace hack
  96     bool interlaced;            // TRUE, if scanlines arrive interlaced order
  97     bool is_transparent;        // TRUE, if tpixel is valid
  98
  99     uint16_t  prefix[MAX_BITS];            // LZW decoding tables
 100     uint8_t*  hold;                        // Accumulation buffer
 101     uint32_t  global_colormap[MAX_COLORS]; // Default colormap if local not
 102                                            //   supplied
 103     uint8_t   suffix[MAX_BITS];            // LZW decoding tables
 104     uint8_t   stack[MAX_BITS];             // Base of LZW decoder stack
 105
 106 } gif_struct;
 107
 108 #endif // mozilla_image_decoders_GIF2_H