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gifwrite.c
2386 lines (1939 loc) · 63.7 KB
/
gifwrite.c
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/*
* xvgifwr.c - handles writing of GIF files. based on flgife.c and
* flgifc.c from the FBM Library, by Michael Maudlin
*
* Contains:
* WriteGIF(fp, pic, ptype, w, h, rmap, gmap, bmap, numcols, colorstyle,
* comment)
*
* Note: slightly brain-damaged, in that it'll only write non-interlaced
* GIF files (in the interests of speed, or something)
*
* Modified by Jan Wielemaker for integration in XPCE:
*
* - Replaced exit() calls by returning error-code
* - Replaced fprintf(stderr, ...) by Cprintf()
* - Replaced FILE * by IOSTREAM *
* - Replaced malloc(), etc. by pceMalloc()
*/
/*****************************************************************
* Portions of this code Copyright (C) 1989 by Michael Mauldin.
* Permission is granted to use this file in whole or in
* part for any purpose, educational, recreational or commercial,
* provided that this copyright notice is retained unchanged.
* This software is available to all free of charge by anonymous
* FTP and in the UUNET archives.
*
*
* Authors: Michael Mauldin (mlm@cs.cmu.edu)
* David Rowley (mgardi@watdcsu.waterloo.edu)
*
* Based on: compress.c - File compression ala IEEE Computer, June 1984.
*
* Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
* Jim McKie (decvax!mcvax!jim)
* Steve Davies (decvax!vax135!petsd!peora!srd)
* Ken Turkowski (decvax!decwrl!turtlevax!ken)
* James A. Woods (decvax!ihnp4!ames!jaw)
* Joe Orost (decvax!vax135!petsd!joe)
*****************************************************************/
#include <h/kernel.h>
#undef min
#include "gifwrite.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <setjmp.h>
#ifdef O_IOSTREAM
#define FILE IOSTREAM
#define fwrite Sfwrite
#define fputc Sputc
#define ferror Sferror
#define fflush Sflush
#define malloc(n) pceMalloc(n)
#define free(p) pceFree(p)
#define realloc(p,n) pceRealloc(p,n)
#endif /* IOSTREAM STUFF */
typedef long int count_int;
typedef unsigned char byte;
static int Width, Height;
static int curx, cury;
static long CountDown;
static int Interlace;
static void putword(int, FILE *);
static void compress(int, FILE *, byte *, int);
static void output(int);
static void cl_block(void);
static void cl_hash(count_int);
static void char_init(void);
static void char_out(int);
static void flush_char(void);
static int WriteGIF(FILE *, byte *, int, int, int, byte *, byte *, byte *,
int, int, char*);
static byte *Conv24to8(byte *,int,int,int,byte *,byte *,byte *);
static void FatalError (char*);
static byte pc2nc[256],r1[256],g1[256],b1[256],greymap[256];
/*************************************************************/
#define COLOURIMG 0
#define GREYSCALE 1
#define PIC8 0
#define PIC24 1
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Return-values:
0: ok
-1: error
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
int gifwrite_grey(fp, image, w, h)
FILE *fp;
unsigned char *image;
long w, h;
{
long i;
for (i = 0; i < 256; i++) greymap[i] = (byte) i;
return WriteGIF(fp, (byte *) image, PIC8, (int) w, (int) h,
greymap, greymap, greymap, 256, GREYSCALE, (char *) '\0');
}
int gifwrite_rgb(fp, rgbimage, w, h)
FILE *fp;
unsigned char *rgbimage;
long w, h;
{
return WriteGIF(fp, (byte *) rgbimage, PIC24, (int) w, (int) h,
(byte *) '\0', (byte *) '\0', (byte *) '\0', 256, COLOURIMG,
(char *) '\0');
}
int gifwrite_colmap(fp, image, w, h, red_map, green_map, blue_map)
FILE *fp;
unsigned char *image, *red_map, *green_map, *blue_map;
long w, h;
{
return WriteGIF(fp, (byte *) image, PIC8, (int) w, (int) h,
red_map, green_map, blue_map, 256, COLOURIMG,
(char *) '\0');
}
static jmp_buf jmp_env;
static int WriteGIF(fp, pic, ptype, w, h, rmap, gmap, bmap, numcols,
colorstyle, comment)
FILE *fp;
byte *pic;
int ptype, w,h;
byte *rmap, *gmap, *bmap;
int numcols, colorstyle;
char *comment;
{
int RWidth, RHeight;
int LeftOfs, TopOfs;
int ColorMapSize, InitCodeSize, Background, BitsPerPixel;
int i,j,nc;
byte *pic8;
byte rtemp[256],gtemp[256],btemp[256];
int rval;
if ( (rval=setjmp(jmp_env)) ) /* Non-reentrant! */
return rval;
if (ptype == PIC24) { /* have to quantize down to 8 bits */
pic8 = Conv24to8(pic, w, h, 256, rtemp,gtemp,btemp);
if (!pic8) FatalError("Unable to malloc in WriteGIF()");
rmap = rtemp; gmap = gtemp; bmap = btemp; numcols=256;
}
else pic8 = pic;
Interlace = 0;
Background = 0;
for (i=0; i<256; i++) { pc2nc[i] = r1[i] = g1[i] = b1[i] = 0; }
/* compute number of unique colors */
nc = 0;
for (i=0; i<numcols; i++) {
/* see if color #i is already used */
for (j=0; j<i; j++) {
if (rmap[i] == rmap[j] && gmap[i] == gmap[j] &&
bmap[i] == bmap[j]) break;
}
if (j==i) { /* wasn't found */
pc2nc[i] = nc;
r1[nc] = rmap[i];
g1[nc] = gmap[i];
b1[nc] = bmap[i];
nc++;
}
else pc2nc[i] = pc2nc[j];
}
/* figure out 'BitsPerPixel' */
for (i=1; i<8; i++)
if ( (1<<i) >= nc) break;
BitsPerPixel = i;
ColorMapSize = 1 << BitsPerPixel;
RWidth = Width = w;
RHeight = Height = h;
LeftOfs = TopOfs = 0;
CountDown = w * h; /* # of pixels we'll be doing */
if (BitsPerPixel <= 1) InitCodeSize = 2;
else InitCodeSize = BitsPerPixel;
curx = cury = 0;
if (comment && strlen(comment) > (size_t) 0)
fwrite("GIF89a", (size_t) 1, (size_t) 6, fp); /* the GIF magic number */
else
fwrite("GIF87a", (size_t) 1, (size_t) 6, fp); /* the GIF magic number */
putword(RWidth, fp); /* screen descriptor */
putword(RHeight, fp);
i = 0x80; /* Yes, there is a color map */
i |= (8-1)<<4; /* OR in the color resolution (hardwired 8) */
i |= (BitsPerPixel - 1); /* OR in the # of bits per pixel */
fputc(i,fp);
fputc(Background, fp); /* background color */
fputc(0, fp); /* future expansion byte */
if (colorstyle == 1) { /* greyscale */
for (i=0; i<ColorMapSize; i++) {
/* j = MONO(r1[i], g1[i], b1[i]); */
j = (r1[i] + g1[i] + b1[i] + 1)/3;
fputc(j, fp);
fputc(j, fp);
fputc(j, fp);
}
}
else {
for (i=0; i<ColorMapSize; i++) { /* write out Global colormap */
fputc(r1[i], fp);
fputc(g1[i], fp);
fputc(b1[i], fp);
}
}
if (comment && strlen(comment) > (size_t) 0) { /* write comment blocks */
char *sp;
int i, blen;
fputc(0x21, fp); /* EXTENSION block */
fputc(0xFE, fp); /* comment extension */
sp = comment;
while ( (blen=strlen(sp)) > 0) {
if (blen>255) blen = 255;
fputc(blen, fp);
for (i=0; i<blen; i++, sp++) fputc(*sp, fp);
}
fputc(0, fp); /* zero-length data subblock to end extension */
}
fputc( ',', fp ); /* image separator */
/* Write the Image header */
putword(LeftOfs, fp);
putword(TopOfs, fp);
putword(Width, fp);
putword(Height, fp);
if (Interlace) fputc(0x40, fp); /* Use Global Colormap, maybe Interlace */
else fputc(0x00, fp);
fputc(InitCodeSize, fp);
compress(InitCodeSize+1, fp, pic8, w*h);
fputc(0,fp); /* Write out a Zero-length packet (EOF) */
fputc(';',fp); /* Write GIF file terminator */
if (ptype == PIC24) free(pic8);
if (ferror(fp))
return -1;
return (0);
}
/******************************/
static void putword(w, fp)
int w;
FILE *fp;
{
/* writes a 16-bit integer in GIF order (LSB first) */
fputc(w & 0xff, fp);
fputc((w>>8)&0xff, fp);
}
static void xvbcopy(src, dst, len)
char *src, *dst;
size_t len;
{
/* Modern OS's (Solaris, etc.) frown upon the use of bcopy(),
* and only want you to use memcpy(). However, memcpy() is broken,
* in the sense that it doesn't properly handle overlapped regions
* of memory. This routine does, and also has its arguments in
* the same order as bcopy() did, without using bcopy().
*/
/* determine if the regions overlap
*
* 3 cases: src=dst, src<dst, src>dst
*
* if src=dst, they overlap completely, but nothing needs to be moved
* if src<dst and src+len>dst then they overlap
* if src>dst and src<dst+len then they overlap
*/
if (src==dst || len<=0) return; /* nothin' to do */
if (src<dst && src+len>dst) { /* do a backward copy */
src = src + len - 1;
dst = dst + len - 1;
for ( ; len>0; len--, src--, dst--) *dst = *src;
}
else { /* they either overlap (src>dst) or they don't overlap */
/* do a forward copy */
for ( ; len>0; len--, src++, dst++) *dst = *src;
}
}
static void xvbzero(s, len)
char *s;
size_t len;
{
for ( ; len>0; len--) *s++ = 0;
}
static void FatalError (identifier)
char *identifier;
{
Cprintf("GifWrite(): %s\n", identifier);
longjmp(jmp_env, -1);
}
/***********************************************************************/
static unsigned long cur_accum = 0;
static int cur_bits = 0;
#define min(a,b) ((a>b) ? b : a)
#define RANGE(a,b,c) { if (a < b) a = b; if (a > c) a = c; }
#define XV_BITS 12 /* BITS was already defined on some systems */
#define MSDOS 1
#define HSIZE 5003 /* 80% occupancy */
typedef unsigned char char_type;
static int n_bits; /* number of bits/code */
static int maxbits = XV_BITS; /* user settable max # bits/code */
static int maxcode; /* maximum code, given n_bits */
static int maxmaxcode = 1 << XV_BITS; /* NEVER generate this */
#define MAXCODE(n_bits) ( (1 << (n_bits)) - 1)
static count_int htab [HSIZE];
static unsigned short codetab [HSIZE];
#define HashTabOf(i) htab[i]
#define CodeTabOf(i) codetab[i]
static int hsize = HSIZE; /* for dynamic table sizing */
/*
* To save much memory, we overlay the table used by compress() with those
* used by decompress(). The tab_prefix table is the same size and type
* as the codetab. The tab_suffix table needs 2**BITS characters. We
* get this from the beginning of htab. The output stack uses the rest
* of htab, and contains characters. There is plenty of room for any
* possible stack (stack used to be 8000 characters).
*/
#define tab_prefixof(i) CodeTabOf(i)
#define tab_suffixof(i) ((char_type *)(htab))[i]
#define de_stack ((char_type *)&tab_suffixof(1<<XV_BITS))
static int free_ent = 0; /* first unused entry */
/*
* block compression parameters -- after all codes are used up,
* and compression rate changes, start over.
*/
static int clear_flg = 0;
static long int in_count = 1; /* length of input */
static long int out_count = 0; /* # of codes output (for debugging) */
/*
* compress stdin to stdout
*
* Algorithm: use open addressing double hashing (no chaining) on the
* prefix code / next character combination. We do a variant of Knuth's
* algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
* secondary probe. Here, the modular division first probe is gives way
* to a faster exclusive-or manipulation. Also do block compression with
* an adaptive reset, whereby the code table is cleared when the compression
* ratio decreases, but after the table fills. The variable-length output
* codes are re-sized at this point, and a special CLEAR code is generated
* for the decompressor. Late addition: construct the table according to
* file size for noticeable speed improvement on small files. Please direct
* questions about this implementation to ames!jaw.
*/
static int g_init_bits;
static FILE *g_outfile;
static int ClearCode;
static int EOFCode;
/********************************************************/
static void compress(init_bits, outfile, data, len)
int init_bits;
FILE *outfile;
byte *data;
int len;
{
register long fcode;
register int i = 0;
register int c;
register int ent;
register int disp;
register int hsize_reg;
register int hshift;
/*
* Set up the globals: g_init_bits - initial number of bits
* g_outfile - pointer to output file
*/
g_init_bits = init_bits;
g_outfile = outfile;
/* initialize 'compress' globals */
maxbits = XV_BITS;
maxmaxcode = 1<<XV_BITS;
xvbzero((char *) htab, sizeof(htab));
xvbzero((char *) codetab, sizeof(codetab));
hsize = HSIZE;
free_ent = 0;
clear_flg = 0;
in_count = 1;
out_count = 0;
cur_accum = 0;
cur_bits = 0;
/*
* Set up the necessary values
*/
out_count = 0;
clear_flg = 0;
in_count = 1;
maxcode = MAXCODE(n_bits = g_init_bits);
ClearCode = (1 << (init_bits - 1));
EOFCode = ClearCode + 1;
free_ent = ClearCode + 2;
char_init();
ent = pc2nc[*data++]; len--;
hshift = 0;
for ( fcode = (long) hsize; fcode < 65536L; fcode *= 2L )
hshift++;
hshift = 8 - hshift; /* set hash code range bound */
hsize_reg = hsize;
cl_hash( (count_int) hsize_reg); /* clear hash table */
output(ClearCode);
while (len) {
c = pc2nc[*data++]; len--;
in_count++;
fcode = (long) ( ( (long) c << maxbits) + ent);
i = (((int) c << hshift) ^ ent); /* xor hashing */
if ( HashTabOf (i) == fcode ) {
ent = CodeTabOf (i);
continue;
}
else if ( (long)HashTabOf (i) < 0 ) /* empty slot */
goto nomatch;
disp = hsize_reg - i; /* secondary hash (after G. Knott) */
if ( i == 0 )
disp = 1;
probe:
if ( (i -= disp) < 0 )
i += hsize_reg;
if ( HashTabOf (i) == fcode ) {
ent = CodeTabOf (i);
continue;
}
if ( (long)HashTabOf (i) >= 0 )
goto probe;
nomatch:
output(ent);
out_count++;
ent = c;
if ( free_ent < maxmaxcode ) {
CodeTabOf (i) = free_ent++; /* code -> hashtable */
HashTabOf (i) = fcode;
}
else
cl_block();
}
/* Put out the final code */
output(ent);
out_count++;
output(EOFCode);
}
/*****************************************************************
* TAG( output )
*
* Output the given code.
* Inputs:
* code: A n_bits-bit integer. If == -1, then EOF. This assumes
* that n_bits =< (long)wordsize - 1.
* Outputs:
* Outputs code to the file.
* Assumptions:
* Chars are 8 bits long.
* Algorithm:
* Maintain a BITS character long buffer (so that 8 codes will
* fit in it exactly). Use the VAX insv instruction to insert each
* code in turn. When the buffer fills up empty it and start over.
*/
static
unsigned long masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F,
0x001F, 0x003F, 0x007F, 0x00FF,
0x01FF, 0x03FF, 0x07FF, 0x0FFF,
0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };
static void output(code)
int code;
{
cur_accum &= masks[cur_bits];
if (cur_bits > 0)
cur_accum |= ((long)code << cur_bits);
else
cur_accum = code;
cur_bits += n_bits;
while( cur_bits >= 8 ) {
char_out( (int) (cur_accum & 0xff) );
cur_accum >>= 8;
cur_bits -= 8;
}
/*
* If the next entry is going to be too big for the code size,
* then increase it, if possible.
*/
if (free_ent > maxcode || clear_flg) {
if( clear_flg ) {
maxcode = MAXCODE (n_bits = g_init_bits);
clear_flg = 0;
}
else {
n_bits++;
if ( n_bits == maxbits )
maxcode = maxmaxcode;
else
maxcode = MAXCODE(n_bits);
}
}
if( code == EOFCode ) {
/* At EOF, write the rest of the buffer */
while( cur_bits > 0 ) {
char_out( (int)(cur_accum & 0xff) );
cur_accum >>= 8;
cur_bits -= 8;
}
flush_char();
fflush( g_outfile );
#ifdef FOO
if( ferror( g_outfile ) )
FatalError("unable to write GIF file");
#endif
}
}
/********************************/
static void cl_block () /* table clear for block compress */
{
/* Clear out the hash table */
cl_hash ( (count_int) hsize );
free_ent = ClearCode + 2;
clear_flg = 1;
output(ClearCode);
}
/********************************/
static void cl_hash(hsize) /* reset code table */
register count_int hsize;
{
register count_int *htab_p = htab+hsize;
register long i;
register long m1 = -1;
i = hsize - 16;
do { /* might use Sys V memset(3) here */
*(htab_p-16) = m1;
*(htab_p-15) = m1;
*(htab_p-14) = m1;
*(htab_p-13) = m1;
*(htab_p-12) = m1;
*(htab_p-11) = m1;
*(htab_p-10) = m1;
*(htab_p-9) = m1;
*(htab_p-8) = m1;
*(htab_p-7) = m1;
*(htab_p-6) = m1;
*(htab_p-5) = m1;
*(htab_p-4) = m1;
*(htab_p-3) = m1;
*(htab_p-2) = m1;
*(htab_p-1) = m1;
htab_p -= 16;
} while ((i -= 16) >= 0);
for ( i += 16; i > 0; i-- )
*--htab_p = m1;
}
/******************************************************************************
*
* GIF Specific routines
*
******************************************************************************/
/*
* Number of characters so far in this 'packet'
*/
static int a_count;
/*
* Set up the 'byte output' routine
*/
static void char_init()
{
a_count = 0;
}
/*
* Define the storage for the packet accumulator
*/
static char accum[ 256 ];
/*
* Add a character to the end of the current packet, and if it is 254
* characters, flush the packet to disk.
*/
static void char_out(c)
int c;
{
accum[ a_count++ ] = c;
if( a_count >= 254 )
flush_char();
}
/*
* Flush the packet to disk, and reset the accumulator
*/
static void flush_char()
{
if( a_count > 0 ) {
fputc(a_count, g_outfile );
fwrite(accum, (size_t) 1, (size_t) a_count, g_outfile );
a_count = 0;
}
}
#define CONV24_FAST 0
#define CONV24_BEST 1
#define CONV24_SLOW 2
#define TRUE 1
#define FALSE 0
static int conv24 = CONV24_BEST;
#define u_long unsigned long
static int quick_check (byte*, int,int, byte*, byte*,byte*,byte*,int);
static int quick_quant (byte*, int,int, byte*, byte*,byte*,byte*,int);
static int ppm_quant (byte *,int,int, byte*, byte*,byte*,byte*,int);
static int slow_quant (byte*, int,int, byte*, byte*,byte*,byte*,int);
/****************************/
static byte *Conv24to8(pic24,w,h,nc,rm,gm,bm)
byte *pic24;
byte *rm, *gm, *bm;
int w,h,nc;
{
/* returns pointer to new 8-bit-per-pixel image (w*h) if successful, or
NULL if unsuccessful */
int i;
byte *pic8;
if (!pic24) return NULL;
pic8 = (byte *) malloc((size_t) (w * h));
if (!pic8) {
Cprintf("GIFwrite: Conv24to8() - failed to allocate 'pic8'\n");
return pic8;
}
if (nc<=0) nc = 255; /* 'nc == 0' breaks code */
if (quick_check(pic24, w,h, pic8, rm,gm,bm, nc)) {
return pic8;
}
switch (conv24) {
case CONV24_FAST:
i = quick_quant(pic24, w, h, pic8, rm, gm, bm, nc);
break;
case CONV24_BEST:
i = ppm_quant(pic24, w, h, pic8, rm, gm, bm, nc);
break;
case CONV24_SLOW:
default:
i = slow_quant(pic24, w, h, pic8, rm, gm, bm, nc);
break;
}
if (i) { free(pic8); pic8 = NULL; }
return pic8;
}
/****************************/
static int quick_check(pic24, w,h, pic8, rmap,gmap,bmap, maxcol)
byte *pic24, *pic8, *rmap, *gmap, *bmap;
int w,h,maxcol;
{
/* scans picture until it finds more than 'maxcol' different colors. If it
finds more than 'maxcol' colors, it returns '0'. If it DOESN'T, it does
the 24-to-8 conversion by simply sticking the colors it found into
a colormap, and changing instances of a color in pic24 into colormap
indicies (in pic8) */
unsigned long colors[256],col;
int i, nc, low, high, mid;
byte *p, *pix;
if (maxcol>256) maxcol = 256;
/* put the first color in the table by hand */
nc = 0; mid = 0;
for (i=w*h,p=pic24; i; i--) {
col = (((u_long) *p++) << 16);
col += (((u_long) *p++) << 8);
col += *p++;
/* binary search the 'colors' array to see if it's in there */
low = 0; high = nc-1;
while (low <= high) {
mid = (low+high)/2;
if (col < colors[mid]) high = mid - 1;
else if (col > colors[mid]) low = mid + 1;
else break;
}
if (high < low) { /* didn't find color in list, add it. */
if (nc>=maxcol) return 0;
xvbcopy((char *) &colors[low], (char *) &colors[low+1],
(nc - low) * sizeof(u_long));
colors[low] = col;
nc++;
}
}
/* run through the data a second time, this time mapping pixel values in
pic24 into colormap offsets into 'colors' */
for (i=w*h,p=pic24, pix=pic8; i; i--,pix++) {
col = (((u_long) *p++) << 16);
col += (((u_long) *p++) << 8);
col += *p++;
/* binary search the 'colors' array. It *IS* in there */
low = 0; high = nc-1;
while (low <= high) {
mid = (low+high)/2;
if (col < colors[mid]) high = mid - 1;
else if (col > colors[mid]) low = mid + 1;
else break;
}
if (high < low) {
FatalError("GIFwrite: quick_check: impossible situation!\n");
}
*pix = mid;
}
/* and load up the 'desired colormap' */
for (i=0; i<nc; i++) {
rmap[i] = colors[i]>>16;
gmap[i] = (colors[i]>>8) & 0xff;
bmap[i] = colors[i] & 0xff;
}
return 1;
}
/************************************/
static int quick_quant(p24,w,h, p8, rmap,gmap,bmap, nc)
byte *p24, *p8, *rmap, *gmap, *bmap;
int w,h,nc;
{
/* called after 'pic8' has been alloced, pWIDE,pHIGH set up, mono/1-bit
checked already */
/* up to 256 colors: 3 bits R, 3 bits G, 2 bits B (RRRGGGBB) */
#define RMASK 0xe0
#define RSHIFT 0
#define GMASK 0xe0
#define GSHIFT 3
#define BMASK 0xc0
#define BSHIFT 6
byte *pp;
int r1, g1, b1;
int *thisline, *nextline, *thisptr, *nextptr, *tmpptr;
int i, j, val, pwide3;
int imax, jmax;
pp = p8; pwide3 = w * 3; imax = h-1; jmax = w-1;
/* load up colormap:
* note that 0 and 255 of each color are always in the map;
* intermediate values are evenly spaced.
*/
for (i=0; i<256; i++) {
rmap[i] = (((i<<RSHIFT) & RMASK) * 255 + RMASK/2) / RMASK;
gmap[i] = (((i<<GSHIFT) & GMASK) * 255 + GMASK/2) / GMASK;
bmap[i] = (((i<<BSHIFT) & BMASK) * 255 + BMASK/2) / BMASK;
}
thisline = (int *) malloc(pwide3 * sizeof(int));
nextline = (int *) malloc(pwide3 * sizeof(int));
if (!thisline || !nextline) {
if (thisline) free(thisline);
if (nextline) free(nextline);
Cprintf("GIFwrite: unable to allocate memory in quick_quant()\n");
return(1);
}
/* get first line of picture */
for (j=pwide3, tmpptr=nextline; j; j--) *tmpptr++ = (int) *p24++;
for (i=0; i<h; i++) {
tmpptr = thisline; thisline = nextline; nextline = tmpptr; /* swap */
/* if ((i&0x3f) == 0) WaitCursor(); */
if (i!=imax) /* get next line */
for (j=pwide3, tmpptr=nextline; j; j--)
*tmpptr++ = (int) *p24++;
for (j=0, thisptr=thisline, nextptr=nextline; j<w; j++,pp++) {
r1 = *thisptr++; g1 = *thisptr++; b1 = *thisptr++;
RANGE(r1,0,255); RANGE(g1,0,255); RANGE(b1,0,255);
/* choose actual pixel value */
val = (((r1&RMASK)>>RSHIFT) | ((g1&GMASK)>>GSHIFT) |
((b1&BMASK)>>BSHIFT));
*pp = val;
/* compute color errors */
r1 -= rmap[val];
g1 -= gmap[val];
b1 -= bmap[val];
/* Add fractions of errors to adjacent pixels */
if (j!=jmax) { /* adjust RIGHT pixel */
thisptr[0] += (r1*7) / 16;
thisptr[1] += (g1*7) / 16;
thisptr[2] += (b1*7) / 16;
}
if (i!=imax) { /* do BOTTOM pixel */
nextptr[0] += (r1*5) / 16;
nextptr[1] += (g1*5) / 16;
nextptr[2] += (b1*5) / 16;
if (j>0) { /* do BOTTOM LEFT pixel */
nextptr[-3] += (r1*3) / 16;
nextptr[-2] += (g1*3) / 16;
nextptr[-1] += (b1*3) / 16;
}
if (j!=jmax) { /* do BOTTOM RIGHT pixel */
nextptr[3] += (r1)/16;
nextptr[4] += (g1)/16;
nextptr[5] += (b1)/16;
}
nextptr += 3;
}
}
}
free(thisline);
free(nextline);
return 0;
#undef RMASK
#undef RSHIFT
#undef GMASK
#undef GSHIFT
#undef BMASK
#undef BSHIFT
}
/***************************************************************/
/* The following code based on code from the 'pbmplus' package */
/* written by Jef Poskanzer */
/***************************************************************/
/* ppmquant.c - quantize the colors in a pixmap down to a specified number
**
** Copyright (C) 1989, 1991 by Jef Poskanzer.
**
** 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