GIFDECOD.C

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/* --
OpenFX version 1.0 - Modelling, Animation and Rendering Package
Copyright (C) 2000 OpenFX Development Team

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

You may contact the OpenFX development team via elecronic mail
at core@openfx.org, or visit our website at http://openfx.org for
further information and support details.
-- */

#define MODULE_GIFDECOD

// This is a standard GIF decoder 


#include <stdio.h>
#include <string.h>
#include <math.h>

#ifndef TRUE
#define TRUE 1
#endif

#ifndef FALSE
#define FALSE 0
#endif

typedef struct Colour_Struct COLOUR;
typedef struct Colour_Map_Entry COLOUR_MAP_ENTRY;
typedef struct Colour_Map_Struct COLOUR_MAP;
typedef struct Image_Struct IMAGE;

struct Colour_Struct
   {
   double Red, Green, Blue, Alpha;
   };


struct Colour_Map_Entry
   {
   double start, end;
   COLOUR Start_Colour, End_Colour;
   };


struct Colour_Map_Struct
   {
   long Number_Of_Entries;
   COLOUR_MAP_ENTRY *Colour_Map_Entries;
   };


struct Image_Struct
   {
   double width, height;
   long iwidth, iheight;
   unsigned char *red, *green, *blue;
   };

/* Types for reading IFF files. */
typedef struct {
   unsigned short Red, Green, Blue;
   } IMAGE_COLOUR;

#define LOCAL static
#define IMPORT extern

#define FAST register

typedef short WORD;
typedef unsigned short UWORD;
typedef char TEXT;
typedef unsigned char UTINY;
typedef long LONG;
typedef unsigned long ULONG;
typedef long INT;


/* Various error codes used by decoder
 * and my own routines...   It's okay
 * for you to define whatever you want,
 * as long as it's negative...  It will be
 * returned intact up the various subroutine
 * levels...
 */
#define OUT_OF_MEMORY -10
#define BAD_CODE_SIZE -20
#define WRITE_ERROR -2
#define OPEN_ERROR -3
#define CREATE_ERROR -4


/* Prototypes for functions defined in gifdecod.c */
#ifdef _SUNSTYLE
static short init_exp ();
static short get_next_code();
short GIF_decoder();
IMPORT long get_byte();
IMPORT long out_line();
#else
static short init_exp (short size);
static short get_next_code (void);
short GIF_decoder(short linewidth);
IMPORT long get_byte(void);
IMPORT long out_line(unsigned char *pixels, long linelen);
#endif

/* IMPORT INT bad_code_count;
 *
 * This value is the only other global required by the using program, and
 * is incremented each time an out of range code is read by the decoder.
 * When this value is non-zero after a decode, your GIF file is probably
 * corrupt in some way...
 */
static INT bad_code_count;

#define MAX_CODES   4095

/* Static variables */
LOCAL WORD curr_size;                     /* The current code size */
LOCAL WORD clear;                         /* Value for a clear code */
LOCAL WORD ending;                        /* Value for a ending code */
LOCAL WORD newcodes;                      /* First available code */
LOCAL WORD top_slot;                      /* Highest code for current size */
LOCAL WORD slot;                          /* Last read code */

/* The following static variables are used
 * for seperating out codes
 */
LOCAL WORD navail_bytes = 0;              /* # bytes left in block */
LOCAL WORD nbits_left = 0;                /* # bits left in current byte */
LOCAL UTINY b1;                           /* Current byte */
LOCAL UTINY byte_buff[257];               /* Current block */
LOCAL UTINY *pbytes;                      /* Pointer to next byte in block */

LOCAL LONG code_mask[13] = {
     0,
     0x0001, 0x0003,
     0x0007, 0x000F,
     0x001F, 0x003F,
     0x007F, 0x00FF,
     0x01FF, 0x03FF,
     0x07FF, 0x0FFF
     };

#ifdef _SUNSTYLE
LOCAL WORD init_exp(size) WORD size; {
#else
LOCAL WORD init_exp(WORD size){
#endif
   curr_size = size + 1;
   top_slot = 1 << curr_size;
   clear = 1 << size;
   ending = clear + 1;
   slot = newcodes = ending + 1;
   navail_bytes = nbits_left = 0;
   return(0);
   }

/* get_next_code()
 * - gets the next code from the GIF file.  Returns the code, or else
 * a negative number in case of file errors...
 */
#ifdef _SUNSTYLE
LOCAL WORD get_next_code(){
#else
LOCAL WORD get_next_code(void){
#endif
   WORD i, x;
   ULONG ret;

   if (nbits_left == 0)
      {
      if (navail_bytes <= 0)
         {

         /* Out of bytes in current block, so read next block
          */
         pbytes = byte_buff;
         if ((navail_bytes = get_byte()) < 0)
            return(navail_bytes);
         else if (navail_bytes)
            {
            for (i = 0; i < navail_bytes; ++i)
               {
               if ((x = get_byte()) < 0)
                  return(x);
               byte_buff[i] = x;
               }
            }
         }
      b1 = *pbytes++;
      nbits_left = 8;
      --navail_bytes;
      }

   ret = b1 >> (8 - nbits_left);
   while (curr_size > nbits_left)
      {
      if (navail_bytes <= 0)
         {

         /* Out of bytes in current block, so read next block
          */
         pbytes = byte_buff;
         if ((navail_bytes = get_byte()) < 0)
            return(navail_bytes);
         else if (navail_bytes)
            {
            for (i = 0; i < navail_bytes; ++i)
               {
               if ((x = get_byte()) < 0)
                  return(x);
               byte_buff[i] = x;
               }
            }
         }
      b1 = *pbytes++;
      ret |= b1 << nbits_left;
      nbits_left += 8;
      --navail_bytes;
      }
   nbits_left -= curr_size;
   ret &= code_mask[curr_size];
   return((WORD)(ret));
   }


/* The reason we have these seperated like this instead of using
 * a structure like the original Wilhite code did, is because this
 * stuff generally produces significantly faster code when compiled...
 * This code is full of similar speedups...  (For a good book on writing
 * C for speed or for space optomisation, see Efficient C by Tom Plum,
 * published by Plum-Hall Associates...)
 */

/*
I removed the LOCAL identifiers in the arrays below and replaced them
with 'extern's so as to declare (and re-use) the space elsewhere.
The arrays are actually declared in the assembler source.
                                                    Bert Tyler
*/

LOCAL UTINY dstack[MAX_CODES + 1];      /* Stack for storing pixels */
LOCAL UTINY suffix[MAX_CODES + 1];      /* Suffix table */
LOCAL UWORD prefix[MAX_CODES + 1];      /* Prefix linked list */
extern UTINY *decoderline;              /* decoded line goes here */

/* WORD GIF_decoder(linewidth)
 *    WORD linewidth;               * Pixels per line of image *
 *
 * - This function decodes an LZW image, according to the method used
 * in the GIF spec.  Every *linewidth* "characters" (ie. pixels) decoded
 * will generate a call to out_line(), which is a user specific function
 * to display a line of pixels.  The function gets its codes from
 * get_next_code() which is responsible for reading blocks of data and
 * seperating them into the proper size codes.  Finally, get_byte() is
 * the global routine to read the next byte from the GIF file.
 *
 * It is generally a good idea to have linewidth correspond to the actual
 * width of a line (as specified in the Image header) to make your own
 * code a bit simpler, but it isn't absolutely necessary.
 *
 * Returns: 0 if successful, else negative.  (See ERRS.H)
 *
 */

#ifdef _SUNSTYLE
WORD GIF_decoder(linewidth) WORD linewidth; {
#else
WORD GIF_decoder(WORD linewidth){
#endif
   FAST UTINY *sp, *bufptr;
   UTINY *buf;
   FAST WORD code, fc, oc, bufcnt;
   WORD c, size, ret;

   /* Initialize for decoding a new image...
    */
   if ((size = get_byte()) < 0)
      return(size);
   if (size < 2 || 9 < size)
      return(BAD_CODE_SIZE);
   init_exp(size);

   /* Initialize in case they forgot to put in a clear code.
    * (This shouldn't happen, but we'll try and decode it anyway...)
    */
   oc = fc = 0;

   buf = decoderline;

   /* Set up the stack pointer and decode buffer pointer
    */
   sp = dstack;
   bufptr = buf;
   bufcnt = linewidth;

   /* This is the main loop.  For each code we get we pass through the
    * linked list of prefix codes, pushing the corresponding "character" for
    * each code onto the stack.  When the list reaches a single "character"
    * we push that on the stack too, and then start unstacking each
    * character for output in the correct order.  Special handling is
    * included for the clear code, and the whole thing ends when we get
    * an ending code.
    */
   while ((c = get_next_code()) != ending)
      {

      /* If we had a file error, return without completing the decode
       */
      if (c < 0)
         return(0);

      /* If the code is a clear code, reinitialize all necessary items.
       */
      if (c == clear)
         {
         curr_size = size + 1;
         slot = newcodes;
         top_slot = 1 << curr_size;

         /* Continue reading codes until we get a non-clear code
          * (Another unlikely, but possible case...)
          */
         while ((c = get_next_code()) == clear)
            ;

         /* If we get an ending code immediately after a clear code
          * (Yet another unlikely case), then break out of the loop.
          */
         if (c == ending)
            break;

         /* Finally, if the code is beyond the range of already set codes,
          * (This one had better NOT happen...  I have no idea what will
          * result from this, but I doubt it will look good...) then set it
          * to color zero.
          */
         if (c >= slot)
            c = 0;

         oc = fc = c;

         /* And let us not forget to put the char into the buffer... And
          * if, on the off chance, we were exactly one pixel from the end
          * of the line, we have to send the buffer to the out_line()
          * routine...
          */
         *bufptr++ = c;
         if (--bufcnt == 0)
            {
            if ((ret = out_line(buf, linewidth)) < 0)
               return(ret);
            bufptr = buf;
            bufcnt = linewidth;
            }
         }
      else
         {

         /* In this case, it's not a clear code or an ending code, so
          * it must be a code code...  So we can now decode the code into
          * a stack of character codes. (Clear as mud, right?)
          */
         code = c;

         /* Here we go again with one of those off chances...  If, on the
          * off chance, the code we got is beyond the range of those already
          * set up (Another thing which had better NOT happen...) we trick
          * the decoder into thinking it actually got the last code read.
          * (Hmmn... I'm not sure why this works...  But it does...)
          */
         if (code >= slot)
            {
            if (code > slot)
               ++bad_code_count;
            code = oc;
            *sp++ = fc;
            }

         /* Here we scan back along the linked list of prefixes, pushing
          * helpless characters (ie. suffixes) onto the stack as we do so.
          */
         while (code >= newcodes)
            {
            *sp++ = suffix[code];
            code = prefix[code];
            }

         /* Push the last character on the stack, and set up the new
          * prefix and suffix, and if the required slot number is greater
          * than that allowed by the current bit size, increase the bit
          * size.  (NOTE - If we are all full, we *don't* save the new
          * suffix and prefix...  I'm not certain if this is correct...
          * it might be more proper to overwrite the last code...
          */
         *sp++ = code;
         if (slot < top_slot)
            {
            suffix[slot] = fc = code;
            prefix[slot++] = oc;
            oc = c;
            }
         if (slot >= top_slot)
            if (curr_size < 12)
               {
               top_slot <<= 1;
               ++curr_size;
               }

         /* Now that we've pushed the decoded string (in reverse order)
          * onto the stack, lets pop it off and put it into our decode
          * buffer...  And when the decode buffer is full, write another
          * line...
          */
         while (sp > dstack)
            {
            *bufptr++ = *(--sp);
            if (--bufcnt == 0)
               {
               if ((ret = out_line(buf, linewidth)) < 0)
                  return(ret);
               bufptr = buf;
               bufcnt = linewidth;
               }
            }
         }
      }
   ret = 0;
   if (bufcnt != linewidth)
      ret = out_line(buf, (linewidth - bufcnt));
   return(ret);
   }