rdgif.c

Jpeg source code,jpeg编码解码示范

/*
 * rdgif.c
 *
 * Copyright (C) 1991-1996, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 **************************************************************************
 * WARNING: You will need an LZW patent license from Unisys in order to   *
 * use this file legally in any commercial or shareware application.      *
 **************************************************************************
 *
 * This file contains routines to read input images in GIF format.
 *
 * These routines may need modification for non-Unix environments or
 * specialized applications.  As they stand, they assume input from
 * an ordinary stdio stream.  They further assume that reading begins
 * at the start of the file; input_init may need work if the
 * user interface has already read some data (e.g., to determine that
 * the file is indeed GIF format).
 */

/*
 * This code is loosely based on giftoppm from the PBMPLUS distribution
 * of Feb. 1991.  That file contains the following copyright notice:
 * +-------------------------------------------------------------------+
 * | Copyright 1990, David Koblas.                                     |
 * |   Permission to use, copy, modify, and distribute this software   |
 * |   and its documentation for any purpose and without fee is hereby |
 * |   granted, provided that the above copyright notice appear in all |
 * |   copies and that both that copyright notice and this permission  |
 * |   notice appear in supporting documentation.  This software is    |
 * |   provided "as is" without express or implied warranty.           |
 * +-------------------------------------------------------------------+
 *
 * We are also required to state that
 *    "The Graphics Interchange Format(c) is the Copyright property of
 *    CompuServe Incorporated. GIF(sm) is a Service Mark property of
 *    CompuServe Incorporated."
 */

#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */

#ifdef GIF_SUPPORTED


#define	MAXCOLORMAPSIZE	256	/* max # of colors in a GIF colormap */
#define NUMCOLORS	3	/* # of colors */
#define CM_RED		0	/* color component numbers */
#define CM_GREEN	1
#define CM_BLUE		2

#define	MAX_LZW_BITS	12	/* maximum LZW code size */
#define LZW_TABLE_SIZE	(1<<MAX_LZW_BITS) /* # of possible LZW symbols */

/* Macros for extracting header data --- note we assume chars may be signed */

#define LM_to_uint(a,b)		((((b)&0xFF) << 8) | ((a)&0xFF))

#define BitSet(byte, bit)	((byte) & (bit))
#define INTERLACE	0x40	/* mask for bit signifying interlaced image */
#define COLORMAPFLAG	0x80	/* mask for bit signifying colormap presence */

#define	ReadOK(file,buffer,len)	(JFREAD(file,buffer,len) == ((size_t) (len)))

/* LZW decompression tables look like this:
 *   symbol_head[K] = prefix symbol of any LZW symbol K (0..LZW_TABLE_SIZE-1)
 *   symbol_tail[K] = suffix byte   of any LZW symbol K (0..LZW_TABLE_SIZE-1)
 * Note that entries 0..end_code of the above tables are not used,
 * since those symbols represent raw bytes or special codes.
 *
 * The stack represents the not-yet-used expansion of the last LZW symbol.
 * In the worst case, a symbol could expand to as many bytes as there are
 * LZW symbols, so we allocate LZW_TABLE_SIZE bytes for the stack.
 * (This is conservative since that number includes the raw-byte symbols.)
 *
 * The tables are allocated from FAR heap space since they would use up
 * rather a lot of the near data space in a PC.
 */


/* Private version of data source object */

typedef struct {
  struct cjpeg_source_struct pub; /* public fields */

  j_compress_ptr cinfo;		/* back link saves passing separate parm */

  JSAMPARRAY colormap;		/* GIF colormap (converted to my format) */

  /* State for GetCode and LZWReadByte */
  char code_buf[256+4];		/* current input data block */
  int last_byte;		/* # of bytes in code_buf */
  int last_bit;			/* # of bits in code_buf */
  int cur_bit;			/* next bit index to read */
  boolean out_of_blocks;	/* TRUE if hit terminator data block */

  int input_code_size;		/* codesize given in GIF file */
  int clear_code,end_code;	/* values for Clear and End codes */

  int code_size;		/* current actual code size */
  int limit_code;		/* 2^code_size */
  int max_code;			/* first unused code value */
  boolean first_time;		/* flags first call to LZWReadByte */

  /* Private state for LZWReadByte */
  int oldcode;			/* previous LZW symbol */
  int firstcode;		/* first byte of oldcode's expansion */

  /* LZW symbol table and expansion stack */
  UINT16 FAR *symbol_head;	/* => table of prefix symbols */
  UINT8  FAR *symbol_tail;	/* => table of suffix bytes */
  UINT8  FAR *symbol_stack;	/* => stack for symbol expansions */
  UINT8  FAR *sp;		/* stack pointer */

  /* State for interlaced image processing */
  boolean is_interlaced;	/* TRUE if have interlaced image */
  jvirt_sarray_ptr interlaced_image; /* full image in interlaced order */
  JDIMENSION cur_row_number;	/* need to know actual row number */
  JDIMENSION pass2_offset;	/* # of pixel rows in pass 1 */
  JDIMENSION pass3_offset;	/* # of pixel rows in passes 1&2 */
  JDIMENSION pass4_offset;	/* # of pixel rows in passes 1,2,3 */
} gif_source_struct;

typedef gif_source_struct * gif_source_ptr;


/* Forward declarations */
METHODDEF(JDIMENSION) get_pixel_rows
	JPP((j_compress_ptr cinfo, cjpeg_source_ptr sinfo));
METHODDEF(JDIMENSION) load_interlaced_image
	JPP((j_compress_ptr cinfo, cjpeg_source_ptr sinfo));
METHODDEF(JDIMENSION) get_interlaced_row
	JPP((j_compress_ptr cinfo, cjpeg_source_ptr sinfo));


LOCAL(int)
ReadByte (gif_source_ptr sinfo)
/* Read next byte from GIF file */
{
  register FILE * infile = sinfo->pub.input_file;
  int c;

  if ((c = getc(infile)) == EOF)
    ERREXIT(sinfo->cinfo, JERR_INPUT_EOF);
  return c;
}


LOCAL(int)
GetDataBlock (gif_source_ptr sinfo, char *buf)
/* Read a GIF data block, which has a leading count byte */
/* A zero-length block marks the end of a data block sequence */
{
  int count;

  count = ReadByte(sinfo);
  if (count > 0) {
    if (! ReadOK(sinfo->pub.input_file, buf, count))
      ERREXIT(sinfo->cinfo, JERR_INPUT_EOF);
  }
  return count;
}


LOCAL(void)
SkipDataBlocks (gif_source_ptr sinfo)
/* Skip a series of data blocks, until a block terminator is found */
{
  char buf[256];

  while (GetDataBlock(sinfo, buf) > 0)
    /* skip */;
}


LOCAL(void)
ReInitLZW (gif_source_ptr sinfo)
/* (Re)initialize LZW state; shared code for startup and Clear processing */
{
  sinfo->code_size = sinfo->input_code_size + 1;
  sinfo->limit_code = sinfo->clear_code << 1;	/* 2^code_size */
  sinfo->max_code = sinfo->clear_code + 2;	/* first unused code value */
  sinfo->sp = sinfo->symbol_stack;		/* init stack to empty */
}


LOCAL(void)
InitLZWCode (gif_source_ptr sinfo)
/* Initialize for a series of LZWReadByte (and hence GetCode) calls */
{
  /* GetCode initialization */
  sinfo->last_byte = 2;		/* make safe to "recopy last two bytes" */
  sinfo->last_bit = 0;		/* nothing in the buffer */
  sinfo->cur_bit = 0;		/* force buffer load on first call */
  sinfo->out_of_blocks = FALSE;

  /* LZWReadByte initialization: */
  /* compute special code values (note that these do not change later) */
  sinfo->clear_code = 1 << sinfo->input_code_size;
  sinfo->end_code = sinfo->clear_code + 1;
  sinfo->first_time = TRUE;
  ReInitLZW(sinfo);
}


LOCAL(int)
GetCode (gif_source_ptr sinfo)
/* Fetch the next code_size bits from the GIF data */
/* We assume code_size is less than 16 */
{
  register INT32 accum;
  int offs, ret, count;

  while ( (sinfo->cur_bit + sinfo->code_size) > sinfo->last_bit) {
    /* Time to reload the buffer */
    if (sinfo->out_of_blocks) {
      WARNMS(sinfo->cinfo, JWRN_GIF_NOMOREDATA);
      return sinfo->end_code;	/* fake something useful */
    }
    /* preserve last two bytes of what we have -- assume code_size <= 16 */
    sinfo->code_buf[0] = sinfo->code_buf[sinfo->last_byte-2];
    sinfo->code_buf[1] = sinfo->code_buf[sinfo->last_byte-1];
    /* Load more bytes; set flag if we reach the terminator block */
    if ((count = GetDataBlock(sinfo, &sinfo->code_buf[2])) == 0) {
      sinfo->out_of_blocks = TRUE;
      WARNMS(sinfo->cinfo, JWRN_GIF_NOMOREDATA);
      return sinfo->end_code;	/* fake something useful */
    }
    /* Reset counters */
    sinfo->cur_bit = (sinfo->cur_bit - sinfo->last_bit) + 16;
    sinfo->last_byte = 2 + count;
    sinfo->last_bit = sinfo->last_byte * 8;
  }

  /* Form up next 24 bits in accum */
  offs = sinfo->cur_bit >> 3;	/* byte containing cur_bit */
#ifdef CHAR_IS_UNSIGNED
  accum = sinfo->code_buf[offs+2];
  accum <<= 8;
  accum |= sinfo->code_buf[offs+1];
  accum <<= 8;
  accum |= sinfo->code_buf[offs];
#else
  accum = sinfo->code_buf[offs+2] & 0xFF;
  accum <<= 8;
  accum |= sinfo->code_buf[offs+1] & 0xFF;
  accum <<= 8;
  accum |= sinfo->code_buf[offs] & 0xFF;
#endif

  /* Right-align cur_bit in accum, then mask off desired number of bits */
  accum >>= (sinfo->cur_bit & 7);
  ret = ((int) accum) & ((1 << sinfo->code_size) - 1);
  
  sinfo->cur_bit += sinfo->code_size;
  return ret;
}


LOCAL(int)
LZWReadByte (gif_source_ptr sinfo)
/* Read an LZW-compressed byte */
{
  register int code;		/* current working code */
  int incode;			/* saves actual input code */

  /* First time, just eat the expected Clear code(s) and return next code, */
  /* which is expected to be a raw byte. */
  if (sinfo->first_time) {
    sinfo->first_time = FALSE;
    code = sinfo->clear_code;	/* enables sharing code with Clear case */
  } else {

    /* If any codes are stacked from a previously read symbol, return them */
    if (sinfo->sp > sinfo->symbol_stack)
      return (int) *(-- sinfo->sp);

    /* Time to read a new symbol */
    code = GetCode(sinfo);

  }

  if (code == sinfo->clear_code) {
    /* Reinit state, swallow any extra Clear codes, and */
    /* return next code, which is expected to be a raw byte. */
    ReInitLZW(sinfo);
    do {
      code = GetCode(sinfo);
    } while (code == sinfo->clear_code);
    if (code > sinfo->clear_code) { /* make sure it is a raw byte */
      WARNMS(sinfo->cinfo, JWRN_GIF_BADDATA);
      code = 0;			/* use something valid */
    }
    /* make firstcode, oldcode valid! */
    sinfo->firstcode = sinfo->oldcode = code;
    return code;
  }

  if (code == sinfo->end_code) {
    /* Skip the rest of the image, unless GetCode already read terminator */
    if (! sinfo->out_of_blocks) {
      SkipDataBlocks(sinfo);
      sinfo->out_of_blocks = TRUE;
    }
    /* Complain that there's not enough data */
    WARNMS(sinfo->cinfo, JWRN_GIF_ENDCODE);
    /* Pad data with 0's */
    return 0;			/* fake something usable */
  }

  /* Got normal raw byte or LZW symbol */
  incode = code;		/* save for a moment */
  
  if (code >= sinfo->max_code) { /* special case for not-yet-defined symbol */
    /* code == max_code is OK; anything bigger is bad data */
    if (code > sinfo->max_code) {
      WARNMS(sinfo->cinfo, JWRN_GIF_BADDATA);
      incode = 0;		/* prevent creation of loops in symbol table */
    }
    /* this symbol will be defined as oldcode/firstcode */
    *(sinfo->sp++) = (UINT8) sinfo->firstcode;
    code = sinfo->oldcode;
  }

  /* If it's a symbol, expand it into the stack */
  while (code >= sinfo->clear_code) {
    *(sinfo->sp++) = sinfo->symbol_tail[code]; /* tail is a byte value */
    code = sinfo->symbol_head[code]; /* head is another LZW symbol */
  }
  /* At this point code just represents a raw byte */
  sinfo->firstcode = code;	/* save for possible future use */

  /* If there's room in table, */
  if ((code = sinfo->max_code) < LZW_TABLE_SIZE) {
    /* Define a new symbol = prev sym + head of this sym's expansion */
    sinfo->symbol_head[code] = sinfo->oldcode;
    sinfo->symbol_tail[code] = (UINT8) sinfo->firstcode;
    sinfo->max_code++;
    /* Is it time to increase code_size? */
    if ((sinfo->max_code >= sinfo->limit_code) &&
	(sinfo->code_size < MAX_LZW_BITS)) {