/* Libart_LGPL - library of basic graphic primitives
 * Copyright (C) 1999 Raph Levien
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/* Apply a dash style to a vector path. */

#include <math.h>
#include <stdlib.h>

#include "art_misc.h"

#include "art_vpath.h"
#include "art_vpath_dash.h"


/* Return the length of the largest subpath within vpath */
static int
art_vpath_dash_max_subpath (const ArtVpath *vpath)
{
  int max_subpath;
  int i;
  int start;

  max_subpath = 0;
  start = 0;
  for (i = 0; vpath[i].code != ART_END; i++)
    {
      if (vpath[i].code == ART_MOVETO || vpath[i].code == ART_MOVETO_OPEN)
	{
	  if (i - start > max_subpath)
	    max_subpath = i - start;
	  start = i;
	}
    }
  if (i - start > max_subpath)
    max_subpath = i - start;

  return max_subpath;
}

/* This implementation has two known flaws:

   First, it adds a spurious break at the beginning of the vpath. The
   only way I see to resolve this flaw is to run the state forward one
   dash break at the beginning, and fix up by looping back to the
   first dash break at the end. This is doable but of course adds
   some complexity.

   Second, it does not suppress output points that are within epsilon
   of each other.  */

ArtVpath *
art_vpath_dash (const ArtVpath *vpath, const ArtVpathDash *dash)
{
  int max_subpath;
  double *dists;
  ArtVpath *result;
  int n_result, n_result_max;
  int start, end;
  int i;
  double total_dist;

  /* state while traversing dasharray - offset is offset of current dash
     value, toggle is 0 for "off" and 1 for "on", and phase is the distance
     in, >= 0, < dash->dash[offset]. */
  int offset, toggle;
  double phase;

  /* initial values */
  int offset_init, toggle_init;
  double phase_init;

  max_subpath = art_vpath_dash_max_subpath (vpath);
  dists = art_new (double, max_subpath);

  n_result = 0;
  n_result_max = 16;
  result = art_new (ArtVpath, n_result_max);

  /* determine initial values of dash state */
  toggle_init = 1;
  offset_init = 0;
  phase_init = dash->offset;
  while (phase_init >= dash->dash[offset_init])
    {
      toggle_init = !toggle_init;
      phase_init -= dash->dash[offset_init];
      offset_init++;
      if (offset_init == dash->n_dash)
	offset_init = 0;
    }

  for (start = 0; vpath[start].code != ART_END; start = end)
    {
      for (end = start + 1; vpath[end].code == ART_LINETO; end++);
      /* subpath is [start..end) */
      total_dist = 0;
      for (i = start; i < end - 1; i++)
	{
	  double dx, dy;

	  dx = vpath[i + 1].x - vpath[i].x;
	  dy = vpath[i + 1].y - vpath[i].y;
	  dists[i - start] = sqrt (dx * dx + dy * dy);
	  total_dist += dists[i - start];
	}
      if (total_dist <= dash->dash[offset_init] - phase_init)
	{
	  /* subpath fits entirely within first dash */
	  if (toggle_init)
	    {
	      for (i = start; i < end; i++)
		art_vpath_add_point (&result, &n_result, &n_result_max,
				     vpath[i].code, vpath[i].x, vpath[i].y);
	    }
	}
      else
	{
	  /* subpath is composed of at least one dash - thus all
	     generated pieces are open */
	  double dist;

	  phase = phase_init;
	  offset = offset_init;
	  toggle = toggle_init;
	  dist = 0;
	  i = start;
	  if (toggle)
	    art_vpath_add_point (&result, &n_result, &n_result_max,
				 ART_MOVETO_OPEN, vpath[i].x, vpath[i].y);
	  while (i != end - 1)
	    {
	      if (dists[i] - dist > dash->dash[offset] - phase)
		{
		  /* dash boundary is next */
		  double a;
		  double x, y;

		  dist += dash->dash[offset] - phase;
		  a = dist / dists[i - start];
		  x = vpath[i].x + a * (vpath[i + 1].x - vpath[i].x);
		  y = vpath[i].y + a * (vpath[i + 1].y - vpath[i].y);
		  art_vpath_add_point (&result, &n_result, &n_result_max,
				       toggle ? ART_LINETO : ART_MOVETO_OPEN,
				       x, y);
		  /* advance to next dash */
		  toggle = !toggle;
		  phase = 0;
		  offset++;
		  if (offset == dash->n_dash)
		    offset = 0;
		}
	      else
		{
		  /* end of line in vpath is next */
		  phase += dists[i - start] - dist;
		  i++;
		  dist = 0;
		  if (toggle)
		    art_vpath_add_point (&result, &n_result, &n_result_max,
					 ART_LINETO, vpath[i].x, vpath[i].y);
		}
	    }
	}
    }

  art_vpath_add_point (&result, &n_result, &n_result_max,
		       ART_END, 0, 0);

  art_free (dists);

  return result;
}