gimp/app/core/gimpscanconvert.c

/* The GIMP -- an image manipulation program
 * Copyright (C) 1995-1999 Spencer Kimball and Peter Mattis
 *
 * 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.
 */

#include "config.h"

#include <string.h>

#include <gtk/gtk.h>

#include "libgimpmath/gimpmath.h"

#include "apptypes.h"

#include "gimpchannel.h"
#include "gimpdrawable.h"
#include "gimpimage.h"
#include "pixel_region.h"
#include "scan_convert.h"


#ifdef DEBUG
#define TRC(x) printf x
#else
#define TRC(x)
#endif


/* Reveal our private structure */
struct ScanConverterPrivate
{
  guint             width;
  guint             height;
  GSList          **scanlines;   /* array of height*antialias scanlines */

  guint             antialias;   /* how much to oversample by */

  /* record the first and last points so we can close the curve */
  gboolean          got_first;
  ScanConvertPoint  first;
  gboolean          got_last;
  ScanConvertPoint  last;
};



/* Local helper routines to scan convert the polygon */

static GSList *
insert_into_sorted_list (GSList *list,
			 gint    x)
{
  GSList *orig = list;
  GSList *rest;

  if (!list)
    return g_slist_prepend (list, GINT_TO_POINTER (x));

  while (list)
    {
      rest = g_slist_next (list);
      if (x < GPOINTER_TO_INT (list->data))
	{
	  rest = g_slist_prepend (rest, list->data);
	  list->next = rest;
	  list->data = GINT_TO_POINTER (x);
	  return orig;
	}
      else if (!rest)
	{
	  g_slist_append (list, GINT_TO_POINTER (x));
	  return orig;
	}
      list = g_slist_next (list);
    }

  return orig;
}


static void
convert_segment (ScanConverter *sc,
		 gint           x1,
		 gint           y1,
		 gint           x2,
		 gint           y2)
{
  gint     ydiff, y, tmp;
  gint     width;
  gint     height;
  GSList **scanlines;
  gfloat   xinc, xstart;

  /* pre-calculate invariant commonly used values */
  width     = sc->width * sc->antialias;
  height    = sc->height * sc->antialias;
  scanlines = sc->scanlines;    

  x1 = CLAMP (x1, 0, width - 1);
  y1 = CLAMP (y1, 0, height - 1);
  x2 = CLAMP (x2, 0, width - 1);
  y2 = CLAMP (y2, 0, height - 1);

  if (y1 > y2)
    {
      tmp = y2; y2 = y1; y1 = tmp;
      tmp = x2; x2 = x1; x1 = tmp;
    }

  ydiff = (y2 - y1);

  if (ydiff)
    {
      xinc = (float) (x2 - x1) / (float) ydiff;
      xstart = x1 + 0.5 * xinc;
      for (y = y1 ; y < y2; y++)
	{
	  scanlines[y] = insert_into_sorted_list (scanlines[y], ROUND (xstart));
	  xstart += xinc;
	}
    }
  else
    {
      /* horizontal line */
      scanlines[y1] = insert_into_sorted_list (scanlines[y1], ROUND (x1));
      scanlines[y1] = insert_into_sorted_list (scanlines[y1], ROUND (x2));
    }
}


/**************************************************************/
/* Exported functions */

/* Create a new scan conversion context */
ScanConverter *
scan_converter_new (guint width,
		    guint height,
		    guint antialias)
{
  ScanConverter *sc;

  g_return_val_if_fail (width > 0, NULL);
  g_return_val_if_fail (height > 0, NULL);
  g_return_val_if_fail (antialias > 0, NULL);

  sc = g_new0 (ScanConverter, 1);

  sc->antialias = antialias;
  sc->width     = width;
  sc->height    = height;
  sc->scanlines = g_new0 (GSList *, height * antialias);

  return sc;
}

void
scan_converter_free (ScanConverter *sc)
{
  g_free (sc->scanlines);
  g_free (sc);
}

/* Add "npoints" from "pointlist" to the polygon currently being
 * described by "scan_converter".  */
void
scan_converter_add_points (ScanConverter    *sc,
			   guint             npoints,
			   ScanConvertPoint *pointlist)
{
  gint  i;
  guint antialias;

  g_return_if_fail (sc != NULL);
  g_return_if_fail (pointlist != NULL);

  antialias = sc->antialias;

  if (!sc->got_first && npoints > 0)
    {
      sc->got_first = TRUE;
      sc->first = pointlist[0];
    }

  /* link from previous point */
  if (sc->got_last && npoints > 0)
    {
      TRC (("|| %g,%g -> %g,%g\n",
	    sc->last.x, sc->last.y,
	    pointlist[0].x, pointlist[0].y));
      convert_segment (sc,
		       (int)sc->last.x * antialias,
		       (int)sc->last.y * antialias,
		       (int)pointlist[0].x * antialias,
		       (int)pointlist[0].y * antialias);
    }

  for (i = 0; i < (npoints - 1); i++)
    {
      convert_segment (sc,
		       (int) pointlist[i].x * antialias,
		       (int) pointlist[i].y * antialias,
		       (int) pointlist[i + 1].x * antialias,
		       (int) pointlist[i + 1].y * antialias);
    }

  TRC (("[] %g,%g -> %g,%g\n",
	pointlist[0].x, pointlist[0].y,
	pointlist[npoints-1].x, pointlist[npoints-1].y));

  if (npoints > 0)
    {
      sc->got_last = TRUE;
      sc->last = pointlist[npoints - 1];
    }
}


/* Scan convert the polygon described by the list of points passed to
 * scan_convert_add_points, and return a channel with a bits set if
 * they fall within the polygon defined.  The polygon is filled
 * according to the even-odd rule.  The polygon is closed by
 * joining the final point to the initial point.
 */
GimpChannel *
scan_converter_to_channel (ScanConverter *sc,
			   GimpImage     *gimage)
{
  GimpChannel *mask;
  GSList      *list;
  PixelRegion  maskPR;
  guint        widtha;
  guint        heighta;
  guint        antialias;
  guint        antialias2;
  guchar      *buf;
  guchar      *b;
  gint        *vals;
  gint         val;
  gint         x, x2, w;
  gint         i, j;

  antialias = sc->antialias;
  antialias2 = antialias * antialias;

  /*  do we need to close the polygon? */
  if (sc->got_first && sc->got_last &&
      (sc->first.x != sc->last.x || sc->first.y != sc->last.y))
    {
      convert_segment (sc,
		       (int) sc->last.x * antialias,
		       (int) sc->last.y * antialias,
		       (int) sc->first.x * antialias,
		       (int) sc->first.y * antialias);
    }

  mask = gimp_channel_new_mask (gimage, sc->width, sc->height);

  buf = g_new0 (guchar, sc->width);
  widtha  = sc->width * antialias;
  heighta = sc->height * antialias;
  /* allocate value array  */
  vals = g_new (gint, widtha);

  /* dump scanlines */
  for (i = 0; i < heighta; i++)
    {
      list = sc->scanlines[i];
      TRC (("%03d: ", i));
      while (list)
	{
	  TRC (("%3d ", GPOINTER_TO_INT (list->data)));
	  list = g_slist_next (list);
	}
      TRC (("\n"));
    }

  pixel_region_init (&maskPR, gimp_drawable_data (GIMP_DRAWABLE (mask)), 0, 0, 
		     gimp_drawable_width (GIMP_DRAWABLE (mask)), 
		     gimp_drawable_height (GIMP_DRAWABLE (mask)), TRUE);

  for (i = 0; i < heighta; i++)
    {
      list = sc->scanlines[i];

      /*  zero the vals array  */
      if (!(i % antialias))
	memset (vals, 0, widtha * sizeof (int));

      while (list)
	{
	  x = GPOINTER_TO_INT (list->data);
	  list = g_slist_next (list);
	  if (!list)
	    {
	      g_message ("Cannot properly scanline convert polygon!\n");
	    }
	  else
	    {
	      /*  bounds checking  */
	      x = CLAMP (x, 0, widtha);
	      x2 = CLAMP (GPOINTER_TO_INT (list->data), 0, widtha);

	      w = x2 - x;

	      if (w > 0)
		{
		  if (antialias == 1)
		    {
		      gimp_channel_add_segment (mask, x, i, w, 255);
		    }
		  else
		    {
		      for (j = 0; j < w; j++)
			vals[j + x] += 255;
		    }
		}
	      list = g_slist_next (list);
	    }
	}

      if (antialias != 1 && !((i+1) % antialias))
	{
	  b = buf;
	  for (j = 0; j < widtha; j += antialias)
	    {
	      val = 0;
	      for (x = 0; x < antialias; x++)
		val += vals[j + x];

	      *b++ = (guchar) (val / antialias2);
	    }

	  pixel_region_set_row (&maskPR, 0, (i / antialias), sc->width, buf);
	}
    }

  g_free (vals);
  g_free (buf);

  return mask;
}