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    i_img_dim min_x, max_x;
    IM_COLOR *srcp = src_line;
    IM_COLOR *destp = dest_line;
    IM_GLIN(src, src_minx, src_maxx, y, src_line);
    if (src->channels != want_channels)
      IM_ADAPT_COLORS(want_channels, src->channels, src_line, width);
    min_x = src_minx;
    max_x = src_maxx;

    while (min_x < max_x && srcp->channel[alphachan] == 0) {
      ++min_x;
      ++srcp;
    }
    while (max_x > min_x && src_line[max_x-1 - src_minx].channel[alphachan] == 0) {
      --max_x;
    }

    if (max_x > min_x) {
      i_img_dim work_left = tx + min_x - src_minx;
      i_img_dim work_width = max_x - min_x;
      ttx = work_left;
      IM_GLIN(im, work_left, work_left + work_width, tty, dest_line);
      
      for(x = min_x; x < max_x; x++) {
	src_alpha = srcp->channel[alphachan];
	if (src_alpha) {
	  remains = IM_SAMPLE_MAX - src_alpha;
	  orig_alpha = destp->channel[targ_alpha_chan];
	  dest_alpha = src_alpha + (remains * orig_alpha) / IM_SAMPLE_MAX;
	  
	  for (ch = 0; ch < im->channels-1; ++ch) {
	    IM_WORK_T samp = 
	      ( src_alpha * srcp->channel[ch]
		+ remains * destp->channel[ch] * orig_alpha / IM_SAMPLE_MAX 
		) / dest_alpha;
	    destp->channel[ch] = IM_LIMIT(samp);
	  }
	  /* dest's alpha */
	  destp->channel[targ_alpha_chan] = dest_alpha;
	}
	++srcp;
	++destp;
	ttx++;
      }
      IM_PLIN(im, work_left, work_left + work_width, tty, dest_line);
    }
    tty++;
  }
  myfree(dest_line);
  myfree(src_line);
#/code
  return 1;
}

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

=category Image

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

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

=cut
*/

int
i_rubthru(i_img *im, i_img *src, i_img_dim tx, i_img_dim ty, i_img_dim src_minx, i_img_dim src_miny,
	  i_img_dim src_maxx, i_img_dim src_maxy) {
  if (src_minx < 0) {
    tx -= src_minx;
    src_minx = 0;
  }
  if (src_miny < 0) {
    ty -= src_miny;
    src_miny = 0;
  }
  if (tx < 0) {
    src_minx -= tx;
    tx = 0;
  }
  if (ty < 0) {
    src_miny -= ty;
    ty = 0;
  }
  if (src_maxx > src->xsize) {
    src_maxx = src->xsize;
  }
  if (src_maxy > src->ysize) {
    src_maxy = src->ysize;
  }
  if (tx >= im->xsize || ty >= im->ysize
      || src_minx >= src_maxx || src_miny >= src_maxy) {
    i_clear_error();
    /* just do nothing, attempting to rubthrough outside the target isn't
       worth being an error */
    return 1;
  }

  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);
}