/* Copyright (C) 1995, 1996 Aladdin Enterprises.  All rights reserved.
  
  This file is part of AFPL Ghostscript.
  
  AFPL Ghostscript is distributed with NO WARRANTY OF ANY KIND.  No author or
  distributor accepts any responsibility for the consequences of using it, or
  for whether it serves any particular purpose or works at all, unless he or
  she says so in writing.  Refer to the Aladdin Free Public License (the
  "License") for full details.
  
  Every copy of AFPL Ghostscript must include a copy of the License, normally
  in a plain ASCII text file named PUBLIC.  The License grants you the right
  to copy, modify and redistribute AFPL Ghostscript, but only under certain
  conditions described in the License.  Among other things, the License
  requires that the copyright notice and this notice be preserved on all
  copies.
*/

/*$Id$*/
/* Epson Stylus-Color Printer-Driver */

/***
     This file holds a byte-Implementation of the Floyd-Steinberg error
     diffusion-algorithm. This algorithm is an alternative for high quality 
     printing in conjunction with the PostScript-Header stcolor.ps:

          gs -sDEVICE=stcolor -sDithering=fs2 <other options> stcolor.ps ...

     THIS ALGORIHM WAS WRITTEN BY STEVEN SINGER (S.Singer@ph.surrey.ac.uk)
     AS PART OF escp2cfs2. 
     THIS IMPLEMENTATION INCORPORATES ONLY FEW CHANGES TO THE ORIGINAL CODE.

 ***/

#include "gdevstc.h"

/*
 * escp2c_pick best scans for best matching color 
 */
private byte *
escp2c_pick_best(byte *col)
{
    static byte colour[8][3] = {
       {  0,  0,  0},{255,  0,  0},{  0,255,  0},{255,255,  0},
       {  0,  0,255},{255,  0,255},{  0,255,255},{255,255,255}};
    register int x, y, z, dx, dy, dz, dz2, dx2, dx3, dx4;
    register byte *p;
    register long md, d;

    md = 16777216; /* plenty */

/*
   Note that I don't use a simple distance algorithm. That can lead to a block
   of (130,127,127) being dithered as red-cyan. This algorithm should make
   it use black-white-red. This is very important, as a coloured block in
   the middle of a grey block can, via error diffusion, perturb the
   surrounding colours sufficiently for this to happen.
*/

/*
   The next bit is equivalent to this, but faster.

    x = col[0];
    y = col[1];
    z = col[2];
    for(n=8; n--; )
    {
	dx = x - colour[n][0];
	dy = y - colour[n][1];
	dz = z - colour[n][2];
	d = dx*(dx-(dy>>1)) + dy*(dy-(dz>>1)) + dz*(dz-(dx>>1));
	if (d < md)
	{
	    md = d;
	    p = n;
	}
    }
*/

/*
 * Test colours in gray code order to reduce number of recalculations.
 * I bet you can't find an optimiser that would do this automatically.
 */

    x = col[0];
    y = col[1];
    z = col[2];
    dx = x*(x-(y>>1));
    dy = y*(y-(z>>1));
    dz = z*(z-(x>>1));
    md = dx + dy + dz;
    p = colour[0];
    x -= 255;
    dx2 = x*(x-(y>>1));
    dz2 = z*(z-(x>>1));
    if ((d = dx2 + dy + dz2) < md) {md = d; p = colour[1];}
    y -= 255;
    dx3 = x*(x-(y>>1));
    dy = y*(y-(z>>1));
    if ((d = dx3 + dy + dz2) < md) {md = d; p = colour[3];}
    x += 255;
    dx4 = x*(x-(y>>1));
    if ((d = dx4 + dy + dz) < md) {md = d; p = colour[2];}
    z -= 255;
    dy = y*(y-(z>>1));
    dz = z*(z-(x>>1));
    if ((d = dx4 + dy + dz) < md) {md = d; p = colour[6];}
    x -= 255;
    dz2 = z*(z-(x>>1));
    if ((d = dx3 + dy + dz2) < md) {md = d; p = colour[7];}
    y += 255;
    dy = y*(y-(z>>1));
    if ((d = dx2 + dy + dz2) < md) {md = d; p = colour[5];}
    if ((d = dx + dy + dz) < md) {p = colour[4];}
    return(p);
}

/*
 * escp2c_conv_stc converts into the ouput format used by stcolor
 */
private void
escp2c_conv_stc(byte *p, byte *q, int i)
{
    for(; i; p+=3, i-=3)
        *q++ = (*p & RED) | (p[1] & GREEN) | (p[2] & BLUE);
}


/*
 * Limit byte-values
 */
#define LIMIT(a) if (a > 255) a = 255; if (a < 0) a = 0
#define LIMIT2(a) if (a > 127) a = 127; if (a < -128) a = -128; \
                if (a < 0) a += 256
/*
 * Main routine of the algorithm
 */
int 
stc_fs2(stcolor_device *sd,int npixel,byte *in,byte *buf,byte *out)
{
   int fullcolor_line_size = npixel*3;

/* ============================================================= */
   if(npixel > 0) {  /* npixel >  0 -> scanline-processing       */
/* ============================================================= */

/*    -------------------------------------------------------------------- */
      if(in == NULL) { /* clear the error-buffer upon white-lines */
/*    -------------------------------------------------------------------- */

         memset(buf,0,fullcolor_line_size);

/*    ------------------------------------------------------------------- */
      } else {                 /* do the actual dithering                 */
/*    ------------------------------------------------------------------- */
    int i, j, k, e, l, i2, below[3][3], *fb, *b, *bb, *tb;
    byte *p, *q, *cp;
    static int dir = 1;

    p = buf;
    if (*p != 0 || memcmp((char *) p, (char *) p + 1, fullcolor_line_size - 1))
    {
	for(p = in, q=buf, i=fullcolor_line_size;
	    i--; p++, q++ )
	{
	    j = *p + ((*q & 128) ? *q - 256 : *q);
	    LIMIT(j);
	    *p = j;
	}
    }

    p = in;

	fb = below[2];
	b = below[1];
	bb = below[0];
	*b = b[1] = b[2] = *bb = bb[1] = bb[2] = 0;

	if (dir)
	{
	    for(p = in, q=buf-3,
		i=fullcolor_line_size; i; i-=3)
	    {
		cp = escp2c_pick_best(p);
		for(i2=3; i2--; p++, q++, fb++, b++, bb++)
		{
		    j = *p;
		    *p = *cp++;
		    j -= *p;
		    if (j != 0)
		    {
			l = (e = (j>>1)) - (*fb = (j>>4));
			if (i > 2)
			{
			    k = p[3] + l;
			    LIMIT(k);
			    p[3] = k;
			}
			*b += e - (l = (j>>2) - *fb);
			if (i < fullcolor_line_size)
			{
			    l += *bb;
			    LIMIT2(l);
			    *q = l;
			}
		    }
		    else
			*fb = 0;
		}
		tb = bb-3;
		bb = b-3;
		b = fb-3;
		fb = tb;
	    }
	    *q = *bb;
	    q[1] = bb[1];
	    q[2] = bb[2];
	    dir = 0;
	}
	else
	{
	    for(p = in+fullcolor_line_size-1,
		q = buf+fullcolor_line_size+2, i=fullcolor_line_size; 
                i; i-=3)
	    {
		cp = escp2c_pick_best(p-2) + 2;
		for(i2=3; i2--; p--, q--, fb++, b++, bb++)
		{
		    j = *p;
		    *p = *cp--;
		    j -= *p;
		    if (j != 0)
		    {
			l = (e = (j>>1)) - (*fb = (j>>4));
			if (i > 2)
			{
			    k = p[-3] + l;
			    LIMIT(k);
			    p[-3] = k;
			}
			*b += e - (l = (j>>2) - *fb);
			if (i < fullcolor_line_size)
			{
			    l += *bb;
			    LIMIT2(l);
			    *q = l;
			}
		    }
		    else
			*fb = 0;
		}
		tb = bb-3;
		bb = b-3;
		b = fb-3;
		fb = tb;
	    }
	    *q = *bb;
	    q[1] = bb[1];
	    q[2] = bb[2];
	    dir = 1;
	}
	
    escp2c_conv_stc(in, out, fullcolor_line_size);

/*    ------------------------------------------------------------------- */
      }                        /* buffer-reset | dithering                */
/*    ------------------------------------------------------------------- */


/* ============================================================= */
   } else {          /* npixel <= 0 -> initialisation            */
/* ============================================================= */


/*
 * check wether the number of components is valid
 */
      if(sd->color_info.num_components != 3)                       return -1;

/*
 * check wether stcdither & TYPE are correct
 */
      if(( sd->stc.dither                    == NULL) ||
         ((sd->stc.dither->flags & STC_TYPE) != STC_BYTE))         return -2;

/*
 * check wether the buffer-size is sufficiently large
 */
      if((sd->stc.dither->flags/STC_SCAN) < 1)                     return -3;

/*
 * finally clear the buffer
 */
      memset(buf,0,-fullcolor_line_size);

/* ============================================================= */
   } /* scanline-processing or initialisation */
/* ============================================================= */

   return 0;
}