File: gifread.c

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gif2png 0.6-1
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/* +-------------------------------------------------------------------+ */
/* | Copyright 1990 - 1994, David Koblas. (koblas@netcom.com)          | */
/* |   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.           | */
/* +-------------------------------------------------------------------+ */

/*
 * this was heavily munged to accomodate the gif2png conversion program.
 * since this file was taken from the Mosaic 2.5 source distribution, it is
 * not certain that the file may be used this way. I have repeatedly mailed
 * NCSA about this, but have not received a reply yet.
 *
 * Alexander Lehmann <alex@hal.rhein-main.de>
 *
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "gif2png.h"

#define TRUE    1
#define FALSE   0

#define CM_RED          0
#define CM_GREEN        1
#define CM_BLUE         2

#define MAX_LWZ_BITS            12

#define INTERLACE               0x40
#define GLOBALCOLORMAP  0x80
#define LOCALCOLORMAP   0x80
#define BitSet(byte, bit)       (((byte) & (bit)) == (bit))

#define ReadOK(file,buffer,len) (fread(buffer, len, 1, file) != 0)

#define LM_to_uint(a,b)                 (((b)<<8)|(a))

struct gif_scr GifScreen;

struct {
  int   transparent;
  int   delayTime;
  int   inputFlag;
  int   disposal;
} Gif89;

extern int c_437_l1[];

static int ReadColorMap(FILE *fd, int number, GifColor buffer[MAXCMSIZE]);
static int DoExtension(FILE *fd, int label);
static int GetDataBlock(FILE *fd, unsigned char  *buf);
static int ReadImage(FILE *fd, int x_off, int y_off, int len, int height, int cmapSize, GifColor cmap[MAXCMSIZE], int interlace);

int imagecount;
int recover_message; /* ==TRUE message already printed */

/* check if recover option is active, if not, print warning */

int check_recover(int some_data)
{
  if(recover)
    return imagecount;
  if(!recover_message && (imagecount>0 || some_data)) {
    fprintf(stderr, "image reading error, use option -r to recover ");
    if(imagecount>0)
      fprintf(stderr, "%d complete image%s ", imagecount,
              (imagecount>1?"s":""));
    if(imagecount>0 && some_data)
      fprintf(stderr, "and ");
    if(some_data)
      fprintf(stderr, "partial data of a broken image");
    fprintf(stderr, "\n");
    recover_message=TRUE;
  }
  return -1;
}

int
ReadGIF(FILE *fd)
{
  unsigned char buf[16];
  unsigned char c;
  GifColor      localColorMap[MAXCMSIZE];
  int           useGlobalColormap;
  int           bitPixel;
  char          version[4];
  int i;
  int w, h, x_off, y_off;

  imagecount=0;
  recover_message=FALSE;

  /*
   * Initialize GIF89 extensions
   */
  Gif89.transparent = -1;
  Gif89.delayTime = -1;
  Gif89.inputFlag = -1;
  Gif89.disposal = 0;

  if (! ReadOK(fd,buf,6)) {
    fprintf(stderr, "error reading magic number\n");
    return(-1);
  }

  if (strncmp((char *)buf,"GIF",3) != 0) {
    fprintf(stderr, "not a GIF file\n");
    return(-1);
  }

  strncpy(version, (char *)buf + 3, 3);
  version[3] = '\0';

  if ((strcmp(version, "87a") != 0) && (strcmp(version, "89a") != 0)) {
    fprintf(stderr, "bad version number, not '87a' or '89a', trying anyway\n");
  }

  if (! ReadOK(fd,buf,7)) {
    fprintf(stderr, "failed to read screen descriptor\n");
    return(-1);
  }

  GifScreen.Width           = LM_to_uint(buf[0],buf[1]);
  GifScreen.Height          = LM_to_uint(buf[2],buf[3]);
  GifScreen.BitPixel        = 2<<(buf[4]&0x07);
  GifScreen.ColorResolution = (((buf[4]&0x70)>>3)+1);
  GifScreen.ColorMap_present = BitSet(buf[4], GLOBALCOLORMAP);

  if (GifScreen.ColorMap_present) {     /* Global Colormap */

    if (ReadColorMap(fd,GifScreen.BitPixel,GifScreen.ColorMap)) {
      fprintf(stderr, "error reading global colormap\n");
      return(-1);
    }
  } else {
    /* the GIF spec says that if neither global nor local
     * color maps are present, the decoder should use a system
     * default map, which should have black and white as the
     * first two colors. So we use black, white, red, green, blue,
     * yellow, purble and cyan in decreasing intensity.
     * I don't think missing color tables are a common case,
     * at least it's not handled by most GIF readers.
     */

    static int colors[]={0, 7, 1, 2, 4, 3, 5, 6};

    for(i=0 ; i<MAXCMSIZE-8 ; i++) {
      GifScreen.ColorMap[i].red   = (colors[i&7]&1) ? ((255-i)&0xf8) : 0;
      GifScreen.ColorMap[i].green = (colors[i&7]&2) ? ((255-i)&0xf8) : 0;
      GifScreen.ColorMap[i].blue  = (colors[i&7]&4) ? ((255-i)&0xf8) : 0;
    }
    for(i=MAXCMSIZE-8 ; i<MAXCMSIZE; i++) {
      GifScreen.ColorMap[i].red   = (colors[i&7]&1) ? 4 : 0;
      GifScreen.ColorMap[i].green = (colors[i&7]&2) ? 4 : 0;
      GifScreen.ColorMap[i].blue  = (colors[i&7]&4) ? 4 : 0;
    }
  }

  if(GifScreen.ColorMap_present) {
    GifScreen.Background       = buf[5];
  } else {
    GifScreen.Background       = -1; /* background unspecified */
  }

  GifScreen.AspectRatio     = buf[6];

  while (1) {
    if (! ReadOK(fd,&c,1)) {
      fprintf(stderr, "EOF / read error on image data\n");
      return check_recover(FALSE);
    }

    if (c == GIFterminator) {           /* GIF terminator */
      fprintf(stderr, "end of GIF data stream\n");
      return(imagecount);
    }

    if (c == GIFextension) {    /* Extension */
      if (! ReadOK(fd,&c,1)) {
        fprintf(stderr, "EOF / read error on extention function code\n");
        return check_recover(FALSE);
      }
      if(DoExtension(fd, c))
        return check_recover(FALSE);
      continue;
    }

    if (c != GIFimage) {                /* Not a valid start character */
      fprintf(stderr, "bogus character 0x%02x\n",
              (int)c);
      return check_recover(FALSE);
    }

    if (! ReadOK(fd,buf,9)) {
      fprintf(stderr,"couldn't read left/top/width/height\n");
      return check_recover(FALSE);
    }

    useGlobalColormap = ! BitSet(buf[8], LOCALCOLORMAP);

    bitPixel = 1<<((buf[8]&0x07)+1);

    x_off = LM_to_uint(buf[0],buf[1]);
    y_off = LM_to_uint(buf[1],buf[2]);
    w = LM_to_uint(buf[4],buf[5]);
    h = LM_to_uint(buf[6],buf[7]);

    if (! useGlobalColormap) {
      if (ReadColorMap(fd,bitPixel,localColorMap)) {
        fprintf(stderr, "error reading local colormap\n");
        return check_recover(FALSE);
      }

      if(!ReadImage(fd, x_off, y_off, w, h, bitPixel,
                    localColorMap, BitSet(buf[8], INTERLACE))) {
        imagecount++;
      }
    } else {
      if(!GifScreen.ColorMap_present) {
        fprintf(stderr, "neither global nor local colormap, using default\n");
      }

      if(!ReadImage(fd, x_off, y_off, w, h, GifScreen.BitPixel,
                    GifScreen.ColorMap,  BitSet(buf[8], INTERLACE))) {
        imagecount++;
      }
    }

    /*
     * reset GIF89 extensions after image
     */
    Gif89.transparent = -1;
    Gif89.delayTime = -1;
    Gif89.inputFlag = -1;
    Gif89.disposal = 0;
  }
}

static int
ReadColorMap(FILE *fd, int number, GifColor colors[MAXCMSIZE])
{
  int   i;
  byte  rgb[3];

  for (i = 0; i < number; ++i) {
    if (! ReadOK(fd, rgb, sizeof(rgb))) {
      fprintf(stderr, "bad colormap\n");
      return(TRUE);
    }

    colors[i].red   = rgb[0];
    colors[i].green = rgb[1];
    colors[i].blue  = rgb[2];
  }

  for (i = number; i<MAXCMSIZE; ++i) {
    colors[i].red   = 0;
    colors[i].green = 0;
    colors[i].blue  = 0;
  }

  return FALSE;
}

static int
DoExtension(FILE *fd, int label)
{
  static char   buf[256];
  char *str;
  char *p,*p2;
  int size;
  int last_cr;

  switch (label) {
  case GIFplaintext:            /* Plain Text Extension */
    str = "Plain Text Extension";
    /*
     * reset GIF89 extensions after Plain Text
     */
    Gif89.transparent = -1;
    Gif89.delayTime = -1;
    Gif89.inputFlag = -1;
    Gif89.disposal = 0;
    if(skip_pte) {
      fprintf(stderr, "got a 'Plain Text Extension' extension (skipping)\n");

      while (GetDataBlock(fd, (unsigned char*) buf) > 0)
        ;
      return (0);
    } else {
      fprintf(stderr, "Plain Text Extensions are currently not supported\n");
      fprintf(stderr, "if you actually have such files, please wait for an update of gif2png\n");
      fprintf(stderr, "or use option -t to discard all ptes\n");
      return (-1);
    }

  case GIFapplication:/* Application Extension */
    str = "Application Extension";
    break;

  case GIFcomment:      /* Comment Extension */
    allocate_element(); /* current now points to new element struct */

    /* the GIF89a spec defines comment extensions to contain ASCII text,
       but doesn't specify what end-of-line delimiter is to be used.
       Most programs use DOS style (CR/LF), at least one uses CR (Graphic
       Workshop for Windows), unix programs probably use LF. We just delete
       CRs unless they are not followed by a LF, then we convert CR to LF.
       Even though 7 bit ASCII is specified, there are some GIF files with
       comments that use codepage 437 and most DOS GIF readers display this
       in the DOS charset (e.g. VPIC). We convert the characters both in
       cp437 and latin1 and try to approximate some of the box drawing chars.
    */

    last_cr=0;

    while ((size=GetDataBlock(fd, (unsigned char*) buf)) > 0) {

      p2=p=buf;

      /* take care of CR as last char of one sub-block and no LF at first of
         the next */
      if(last_cr && *p!='\n') {
        store_block("\n",1);
        last_cr=0;
      }

      while(p-buf<size) {
        if(last_cr) {
          if(*p!='\n')
            *p2++='\n';
          last_cr=0;
        }
        if(*p=='\r')
          last_cr=1;
        else
          *p2++=c_437_l1[(unsigned char)*p];
        p++;
      }
      size=p2-buf;

      store_block(buf, size);
    }

    fprintf(stderr, "got a 'Comment Extension' extension\n");

    current->GIFtype=label;

    fix_current();
    return 0;

  case GIFgraphicctl:           /* Graphic Control Extension */
    str = "Graphic Control Extension";
    size = GetDataBlock(fd, (unsigned char*) buf);
    Gif89.disposal    = (buf[0] >> 2) & 0x7;
    Gif89.inputFlag   = (buf[0] >> 1) & 0x1;
    Gif89.delayTime   = LM_to_uint(buf[1],buf[2]);
    if ((buf[0] & 0x1) != 0)
      Gif89.transparent = (int)((unsigned char)buf[3]);

    if(Gif89.disposal==0 && Gif89.inputFlag==0 &&
       Gif89.delayTime==0) {

      /* do not keep GCEs only indicating transparency */

      while (GetDataBlock(fd, (unsigned char*) buf) > 0)
        ;

      return (0);
    } else {
      /* copy block already read */
      allocate_element(); /* current now points to new element struct */

      goto copy_block;
    }
  default:
    fprintf(stderr, "skipping unknown extension 0x%02x\n",
            (unsigned char)label);
    while (GetDataBlock(fd, (unsigned char*) buf) > 0)
      ;
    return (1);
  }

  allocate_element(); /* current now points to new element struct */

  while ((size=GetDataBlock(fd, (unsigned char*) buf)) > 0) {
copy_block:
    store_block(buf, size);
  }

  fprintf(stderr, "got a '%s' extension\n", str);

  current->GIFtype=label;

  fix_current();

  return (0);
}

static int      ZeroDataBlock = FALSE;

static int
GetDataBlock(FILE *fd, unsigned char *buf)
{
  unsigned char count;

  count = 0;
  if (! ReadOK(fd, &count, 1)) {
    fprintf(stderr, "error in getting DataBlock size\n");
    return -1;
  }

  ZeroDataBlock = count == 0;

  if ((count != 0) && (! ReadOK(fd, buf, count))) {
    fprintf(stderr, "error in reading DataBlock\n");
    return -1;
  }

  return((int)count);
}

/*
**  Pulled out of nextCode
*/
static  int             curbit, lastbit, get_done, last_byte;
static  int             return_clear;
/*
**  Out of nextLWZ
*/
static int      stack[(1<<(MAX_LWZ_BITS))*2], *sp;
static int      code_size, set_code_size;
static int      max_code, max_code_size;
static int      clear_code, end_code;

static void initLWZ(int input_code_size)
{
  set_code_size = input_code_size;
  code_size     = set_code_size + 1;
  clear_code    = 1 << set_code_size ;
  end_code      = clear_code + 1;
  max_code_size = 2 * clear_code;
  max_code      = clear_code + 2;

  curbit = lastbit = 0;
  last_byte = 2;
  get_done = FALSE;

  return_clear = TRUE;

  sp = stack;
}

static int nextCode(FILE *fd, int code_size)
{
  static unsigned char    buf[280];
  static int maskTbl[16] = {
    0x0000, 0x0001, 0x0003, 0x0007,
    0x000f, 0x001f, 0x003f, 0x007f,
    0x00ff, 0x01ff, 0x03ff, 0x07ff,
    0x0fff, 0x1fff, 0x3fff, 0x7fff,
  };
  int i, j, end;
  long ret;

  if (return_clear) {
    return_clear = FALSE;
    return clear_code;
  }

  end = curbit + code_size;

  if (end >= lastbit) {
    int     count;

    if (get_done) {
      if (curbit >= lastbit) {
        fprintf(stderr, "ran off the end of my bits\n");
      }
      return -1;
    }
    buf[0] = buf[last_byte-2];
    buf[1] = buf[last_byte-1];

    if ((count = GetDataBlock(fd, &buf[2])) == 0)
      get_done = TRUE;

    if (count<0) return -1;

    last_byte = 2 + count;
    curbit = (curbit - lastbit) + 16;
    lastbit = (2+count)*8 ;

    end = curbit + code_size;
  }

  j = end / 8;
  i = curbit / 8;

  if (i == j)
    ret = (long)buf[i];
  else if (i + 1 == j)
    ret = (long)buf[i] | ((long)buf[i+1] << 8);
  else
    ret = (long)buf[i] | ((long)buf[i+1] << 8) | ((long)buf[i+2] << 16);

  ret = (ret >> (curbit % 8)) & maskTbl[code_size];

  curbit += code_size;

  return (int)ret;
}

#define readLWZ(fd) ((sp > stack) ? *--sp : nextLWZ(fd))

static int nextLWZ(FILE *fd)
{
  static int       table[2][(1<< MAX_LWZ_BITS)];
  static int       firstcode, oldcode;
  int              code, incode;
  register int     i;

  while ((code = nextCode(fd, code_size)) >= 0) {
    if (code == clear_code) {

      /* corrupt GIFs can make this happen */
      if (clear_code >= (1<<MAX_LWZ_BITS)) {
        return -2;
      }

      for (i = 0; i < clear_code; ++i) {
        table[0][i] = 0;
        table[1][i] = i;
      }
      for (; i < (1<<MAX_LWZ_BITS); ++i)
        table[0][i] = table[1][i] = 0;
      code_size = set_code_size+1;
      max_code_size = 2*clear_code;
      max_code = clear_code+2;
      sp = stack;
      do {
        firstcode = oldcode = nextCode(fd, code_size);
      } while (firstcode == clear_code);

      return firstcode;
    }
    if (code == end_code) {
      int             count;
      unsigned char   buf[260];

      if (ZeroDataBlock)
        return -2;

      while ((count = GetDataBlock(fd, buf)) > 0)
        ;

      if (count != 0) {
        fprintf(stderr, "missing EOD in data stream (common occurence)\n");
      }
      return -2;
    }

    incode = code;

    if (code >= max_code) {
      *sp++ = firstcode;
      code = oldcode;
    }

    while (code >= clear_code) {
      *sp++ = table[1][code];
      if (code == table[0][code]) {
        fprintf(stderr, "circular table entry BIG ERROR\n");
        return(code);
      }
      if ((int)sp >= ((int)stack + sizeof(stack))) {
        fprintf(stderr, "circular table STACK OVERFLOW!\n");
        return(code);
      }
      code = table[0][code];
    }

    *sp++ = firstcode = table[1][code];

    if ((code = max_code) <(1<<MAX_LWZ_BITS)) {
      table[0][code] = oldcode;
      table[1][code] = firstcode;
      ++max_code;
      if ((max_code >= max_code_size) &&
          (max_code_size < (1<<MAX_LWZ_BITS))) {
        max_code_size *= 2;
        ++code_size;
      }
    }

    oldcode = incode;

    if (sp > stack)
      return *--sp;
  }
  return code;
}

/* find the nearest line above that already has data in it */

static byte *
get_prev_line(int width, int height, int line)
{
  int prev_line;
  byte *res;
#ifdef TMPFILE
  long filepos;
#endif

  prev_line=inv_interlace_line(height,line)-1;
  while(interlace_line(height, prev_line)>=line)
    prev_line--;

#ifdef TMPFILE
  filepos=ftell(tempfile);
#endif

  res=access_data(current, width*interlace_line(height, prev_line), width);

#ifdef TMPFILE
  fseek(tempfile, filepos, SEEK_SET);
#endif

  return res;
}

static int
ReadImage(FILE *fd, int x_off, int y_off, int width, int height, int cmapSize,
          GifColor cmap[MAXCMSIZE], int interlace)
{
  unsigned char *dp, c;
  int           v;
  int           xpos = 0, ypos = 0;
  unsigned char *image;
  int i;
  unsigned long *count;

  /*
   **  Initialize the Compression routines
   */
  if (! ReadOK(fd,&c,1)) {
    fprintf(stderr, "EOF / read error on image data\n");
    return(1);
  }

  initLWZ(c);

  fprintf(stderr, "reading %d by %d%s GIF image\n",
          width, height, interlace ? " interlaced" : "" );

  allocate_image();
  /* since we know how large the image will be, we set the size in advance.
     This saves a lot of realloc calls, which may require copying memory. */

  set_size((long)width*height);

  image=xalloc(width);

  current->imagestruct->offset_x = x_off;
  current->imagestruct->offset_y = y_off;
  current->imagestruct->width    = width;
  current->imagestruct->height   = height;
  current->imagestruct->trans    = Gif89.transparent;
  current->imagestruct->interlace= interlace;

  memcpy(current->imagestruct->colors, cmap, sizeof(GifColor)*MAXCMSIZE);

  count=current->imagestruct->color_count;

  for(i=0;i<MAXCMSIZE;i++) {
    count[i]=0;
  }

  for (ypos = 0; ypos < height; ypos++) {
    dp=image;
    for (xpos = 0; xpos < width; xpos++) {
      if ((v = readLWZ(fd)) < 0 || v>=cmapSize) {
        if(v>=cmapSize)
          fprintf(stderr, "reference to undefined colormap entry\n");

        if(xpos>0 || ypos>0) {
          if(recover) {
            if(!interlace) {
              /* easy part, just fill the rest of the `screen' with color 0 */
              memset(image+xpos,0, width-xpos);
              store_block(image,width);
              ypos++;

              memset(image, 0, width);
              for( ; ypos < height ; ypos++)
                store_block(image,width);
            } else {
              /* interlacing recovery is a bit tricky */

              if(xpos>0) {
                if((inv_interlace_line(height, ypos)&7)==0) {
                  /* in 1st pass */
                  memset(image+xpos, 0, width-xpos);
                } else {
                  /* pass >=2 */
                  memcpy(image+xpos, get_prev_line(width, height, ypos)+xpos,
                         width-xpos);
                }
                store_block(image,width);
                ypos++;
              }

              /* fill rest of 1st pass with color 0 */
              memset(image, 0, width);
              for( ; (inv_interlace_line(height, ypos)&7)==0 ; ypos++)
                store_block(image,width);

              /* all other passes, copy from line above */
              for( ; ypos<height ; ypos++) {
                memcpy(image, get_prev_line(width, height, ypos), width);
                store_block(image,width);
              }
            }
            goto fini;
          } else {
            check_recover(TRUE);
            return(1);
          }
        } else {
          return(1);
        }
      }

      count[v]++;

      *dp++=v;
    }
    store_block(image,width);
  }
 fini:

  while(readLWZ(fd)>=0)
    ;

  free(image);

  fix_current();

  /*
   * reset GIF89 extensions after image
   */

  Gif89.transparent = -1;
  Gif89.delayTime = -1;
  Gif89.inputFlag = -1;
  Gif89.disposal = 0;

  return(0);
}