#include "imager.h"

static int
rubthru_targ_noalpha(i_img *im, i_img *src,
                     int tx, int ty, 
                     int src_minx, int src_miny,
                     int src_maxx, int src_maxy) {
  int x, y, ttx, tty;
  int chancount;
  int chans[3];
  int alphachan;
  int ch;

  i_clear_error();

  if (im->channels == 3 && src->channels == 4) {
    chancount = 3;
    chans[0] = 0; chans[1] = 1; chans[2] = 2;
    alphachan = 3;
  }
  else if (im->channels == 3 && src->channels == 2) {
    chancount = 3;
    chans[0] = chans[1] = chans[2] = 0;
    alphachan = 1;
  }
  else if (im->channels == 1 && src->channels == 2) {
    chancount = 1;
    chans[0] = 0;
    alphachan = 1;
  }
  else {
    i_push_error(0, "rubthru can only work where (dest, src) channels are (3,4), (4,4), (3,2), (4,2), (1,2) or (2,2)");
    return 0;
  }

#code im->bits <= 8 && src->bits <= 8
  IM_WORK_T alpha;
  IM_COLOR pv, orig, dest;

  tty = ty;
  for(y = src_miny; y < src_maxy; y++) {
    ttx = tx;
    for(x = src_minx; x < src_maxx; x++) {
      IM_GPIX(src, x,   y,   &pv);
      IM_GPIX(im,  ttx, tty, &orig);
      alpha = pv.channel[alphachan];
      for (ch = 0; ch < chancount; ++ch) {
        dest.channel[ch] = (alpha * pv.channel[chans[ch]]
                            + (IM_SAMPLE_MAX - alpha) * orig.channel[ch])/IM_SAMPLE_MAX;
      }
      IM_PPIX(im, ttx, tty, &dest);
      ttx++;
    }
    tty++;
  }
#/code
  return 1;
}

static int
rubthru_targ_alpha(i_img *im, i_img *src, int tx, int ty, 
                   int src_minx, int src_miny,
                   int src_maxx, int src_maxy) {
  int x, y, ttx, tty;
  int chancount;
  int chans[3];
  int alphachan;
  int ch;
  int targ_alpha_chan;
  
  if (im->channels == 4 && src->channels == 4) {
    chancount = 3;
    chans[0] = 0; chans[1] = 1; chans[2] = 2;
    alphachan = 3;
  }
  else if (im->channels == 4 && src->channels == 2) {
    chancount = 3;
    chans[0] = chans[1] = chans[2] = 0;
    alphachan = 1;
  }
  else if (im->channels == 2 && src->channels == 2) {
    chancount = 1;
    chans[0] = 0;
    alphachan = 1;
  }
  else {
    i_push_error(0, "rubthru can only work where (dest, src) channels are (3,4), (4,4), (3,2), (4,2), (1,2) or (2,2)");
    return 0;
  }

  targ_alpha_chan = im->channels - 1;

#code im->bits <= 8 && src->bits <= 8
  IM_WORK_T src_alpha, orig_alpha, dest_alpha, remains;
  IM_COLOR pv, orig, dest;

  tty = ty;
  for(y = src_miny; y < src_maxy; y++) {
    ttx = tx;
    for(x = src_minx; x < src_maxx; x++) {
      IM_GPIX(src, x,   y,   &pv);
      src_alpha = pv.channel[alphachan];
      if (src_alpha) {
        remains = IM_SAMPLE_MAX - src_alpha;
        IM_GPIX(im,  ttx, tty, &orig);
        orig_alpha = orig.channel[targ_alpha_chan];
        dest_alpha = src_alpha + (remains * orig_alpha) / IM_SAMPLE_MAX;

        for (ch = 0; ch < chancount; ++ch) {
          dest.channel[ch] = 
            ( src_alpha * pv.channel[chans[ch]]
              + remains * orig.channel[ch] * orig_alpha / IM_SAMPLE_MAX 
              ) / dest_alpha;
        }
        /* dest's alpha */
        dest.channel[targ_alpha_chan] = dest_alpha;
        IM_PPIX(im, ttx, tty, &dest);
      }
      ttx++;
    }
    tty++;
  }
#/code
  return 1;
}

/*
=item i_rubthru(im, src, tx, ty, src_minx, src_miny, src_maxx, src_maxy )

=category Image

Takes the sub image I<src[src_minx, src_maxx)[src_miny, src_maxy)> and
overlays it at (I<tx>,I<ty>) on the image object.

The alpha channel of each pixel in I<src> is used to control how much
the existing colour in I<im> is replaced, if it is 255 then the colour
is completely replaced, if it is 0 then the original colour is left 
unmodified.

=cut
*/

int
i_rubthru(i_img *im, i_img *src, int tx, int ty, int src_minx, int src_miny,
	  int src_maxx, int src_maxy) {
  if (im->channels == 1 || im->channels == 3)
    return rubthru_targ_noalpha(im, src, tx, ty, src_minx, src_miny, 
                                src_maxx, src_maxy);
  else
    return rubthru_targ_alpha(im, src, tx, ty, src_minx, src_miny,
                              src_maxx, src_maxy);
}