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 #ifndef _GIF_H_
   6 #define _GIF_H_
   7
   8 #define MAX_LZW_BITS          12
   9 #define MAX_BITS            4097 /* 2^MAX_LZW_BITS+1 */
  10 #define MAX_COLORS           256
  11 #define MAX_HOLD_SIZE        256
  12
  13 enum { GIF_TRAILER                     = 0x3B }; //';'
  14 enum { GIF_IMAGE_SEPARATOR             = 0x2C }; //','
  15 enum { GIF_EXTENSION_INTRODUCER        = 0x21 }; //'!'
  16 enum { GIF_GRAPHIC_CONTROL_LABEL       = 0xF9 };
  17 enum { GIF_COMMENT_LABEL               = 0xFE };
  18 enum { GIF_PLAIN_TEXT_LABEL            = 0x01 };
  19 enum { GIF_APPLICATION_EXTENSION_LABEL = 0xFF };
  20
  21 /* gif2.h
  22    The interface for the GIF87/89a decoder.
  23 */
  24 // List of possible parsing states
  25 typedef enum {
  26     gif_type,
  27     gif_global_header,
  28     gif_global_colormap,
  29     gif_image_start,
  30     gif_image_header,
  31     gif_image_colormap,
  32     gif_image_body,
  33     gif_lzw_start,
  34     gif_lzw,
  35     gif_sub_block,
  36     gif_extension,
  37     gif_control_extension,
  38     gif_consume_block,
  39     gif_skip_block,
  40     gif_done,
  41     gif_error,
  42     gif_comment_extension,
  43     gif_application_extension,
  44     gif_netscape_extension_block,
  45     gif_consume_netscape_extension,
  46     gif_consume_comment
  47 } gstate;
  48
  49 /* A GIF decoder's state */
  50 typedef struct gif_struct {
  51     /* Parsing state machine */
  52     gstate state;                   /* Curent decoder master state */
  53     uint32_t bytes_to_consume;      /* Number of bytes to accumulate */
  54     uint32_t bytes_in_hold;         /* bytes accumulated so far*/
  55
  56     /* LZW decoder state machine */
  57     uint8_t *stackp;              /* Current stack pointer */
  58     int datasize;
  59     int codesize;
  60     int codemask;
  61     int avail;                  /* Index of next available slot in dictionary */
  62     int oldcode;
  63     uint8_t firstchar;
  64     int count;                  /* Remaining # bytes in sub-block */
  65     int bits;                   /* Number of unread bits in "datum" */
  66     int32_t datum;              /* 32-bit input buffer */
  67
  68     /* Output state machine */
  69     int ipass;                  /* Interlace pass; Ranges 1-4 if interlaced. */
  70     unsigned rows_remaining;        /* Rows remaining to be output */
  71     unsigned irow;                  /* Current output row, starting at zero */
  72     uint8_t *rowp;                 /* Current output pointer */
  73
  74     /* Parameters for image frame currently being decoded*/
  75     unsigned x_offset, y_offset;    /* With respect to "screen" origin */
  76     unsigned height, width;
  77     int tpixel;                 /* Index of transparent pixel */
  78     int32_t disposal_method;    /* Restore to background, leave in place, etc.*/
  79     uint32_t *local_colormap;   /* Per-image colormap */
  80     int local_colormap_size;    /* Size of local colormap array. */
  81     uint32_t delay_time;        /* Display time, in milliseconds,
  82                                    for this image in a multi-image GIF */
  83
  84     /* Global (multi-image) state */
  85     int version;                /* Either 89 for GIF89 or 87 for GIF87 */
  86     unsigned screen_width;       /* Logical screen width & height */
  87     unsigned screen_height;
  88     uint32_t global_colormap_depth;  /* Depth of global colormap array. */
  89     int images_decoded;         /* Counts images for multi-part GIFs */
  90     int loop_count;             /* Netscape specific extension block to control
  91                                    the number of animation loops a GIF renders. */
  92
  93     bool progressive_display;    /* If TRUE, do Haeberli interlace hack */
  94     bool interlaced;             /* TRUE, if scanlines arrive interlaced order */
  95     bool is_transparent;         /* TRUE, if tpixel is valid */
  96
  97     uint16_t  prefix[MAX_BITS];          /* LZW decoding tables */
  98     uint8_t   hold[MAX_HOLD_SIZE];       /* Accumulation buffer */
  99     uint32_t  global_colormap[MAX_COLORS];   /* Default colormap if local not supplied */
 100     uint8_t   suffix[MAX_BITS];          /* LZW decoding tables */
 101     uint8_t   stack[MAX_BITS];           /* Base of LZW decoder stack */
 102
 103 } gif_struct;
 104
 105 #endif
 106