Pillow/libImaging/Gif.h

/*
 * The Python Imaging Library.
 * $Id$
 *
 * Declarations for a fast, suspendable GIF decoder.
 *
 * Copyright (c) Fredrik Lundh 1995-96.
 */


/* Max size for a LZW code word. */

#define	GIFBITS	    12

#define	GIFTABLE    (1<<GIFBITS)
#define	GIFBUFFER   (1<<GIFBITS)


typedef struct {

    /* CONFIGURATION */

    /* Initial number of bits. The caller should clear all fields in
       this structure and set this field before calling the decoder
       the first time. */
    int bits;

    /* If set, this is an interlaced image.  Process it the following way:
     * 1st pass: start at top line, lines are 8 pixels high, step 8 pixels
     * 2nd pass: start at line 4, lines are 4 pixels high, step 8 pixels
     * 3rd pass: start at line 2, lines are 2 pixels high, step 4 pixels
     * 4th pass: start at line 1, lines are 1 pixels high, step 2 pixels
     */
    int interlace;

    /* PRIVATE CONTEXT (set by decoder) */

    /* Interlace parameters */
    int step, repeat;

    /* Input bit buffer */
    INT32 bitbuffer;
    int bitcount;
    int blocksize;

    /* Code buffer */
    int codesize;
    int codemask;

    /* Constant symbol codes */
    int clear, end;

    /* Symbol history */
    int lastcode;
    unsigned char lastdata;

    /* History buffer */
    int bufferindex;
    unsigned char buffer[GIFTABLE];

    /* Symbol table */
    unsigned INT16 link[GIFTABLE];
    unsigned char data[GIFTABLE];
    int next;

} GIFDECODERSTATE;

typedef struct GIFENCODERBLOCK_T
{
    struct GIFENCODERBLOCK_T *next;
    int size;
    UINT8 data[255];
} GIFENCODERBLOCK;

typedef struct {

    /* CONFIGURATION */

    /* Initial number of bits. The caller should clear all fields in
       this structure and set this field before calling the encoder
       the first time. */
    int bits;

    /* NOTE: the expanding encoder ignores this field */

    /* If set, write an interlaced image (see above) */
    int interlace;

    /* PRIVATE CONTEXT (set by encoder) */

    /* Interlace parameters */
    int step, repeat;

    /* Output bit buffer */
    INT32 bitbuffer;
    int bitcount;

    /* Output buffer list (linked list) */
    GIFENCODERBLOCK* block; /* current block */
    GIFENCODERBLOCK* flush; /* output queue */
    GIFENCODERBLOCK* free; /* if not null, use this */

    /* Fields used for run-length encoding */
    int first; /* true if we haven't read the first pixel */
    int last; /* last byte value seen */
    int count; /* how many bytes with that value we've seen */
    int lastcode;

} GIFENCODERSTATE;