File: tri.c

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//  Quelle:    http://reality.sgi.com/employees/atul_asd/code/chapter.html


#include "triangul.h"
#include <string.h>


static int initialise(n)
     int n;
{
    int i;

  for (i = 1; i <= n; i++)
    seg[i].is_inserted = FALSE;

  generate_random_ordering(n);
  
  return 0;
}

#ifdef STANDALONE

int main(argc, argv)
     int argc;
     char *argv[];
{
  int n, nmonpoly, genus;
  int op[SEGSIZE][3], i, ntriangles;

  if ((argc < 2) || ((n = read_segments(argv[1], &genus)) < 0))
    {
      fprintf(stderr, "usage: triangulate <filename>\n");
      exit(1);
    }

  initialise(n);
  construct_trapezoids(n);
  nmonpoly = monotonate_trapezoids(n);
  ntriangles = triangulate_monotone_polygons(n, nmonpoly, op);

  for (i = 0; i < ntriangles; i++)
    printf("triangle #%d: %d %d %d\n", i, 
	   op[i][0], op[i][1], op[i][2]);

  return 0;
}


#else  /* Not standalone. Use this as an interface routine */


/* Input specified as contours.
 * Outer contour must be anti-clockwise.
 * All inner contours must be clockwise.
 *  
 * Every contour is specified by giving all its points in order. No
 * point shoud be repeated. i.e. if the outer contour is a square,
 * only the four distinct endpoints shopudl be specified in order.
 *  
 * ncontours: #contours
 * cntr: An array describing the number of points in each
 *	 contour. Thus, cntr[i] = #points in the i'th contour.
 * vertices: Input array of vertices. Vertices for each contour
 *           immediately follow those for previous one. Array location
 *           vertices[0] must NOT be used (i.e. i/p starts from
 *           vertices[1] instead. The output triangles are
 *	     specified  w.r.t. the indices of these vertices.
 * triangles: Output array to hold triangles.
 *  
 * Enough space must be allocated for all the arrays before calling
 * this routine
 */


int triangulate_polygon(ncontours, cntr, vertices, triangles)
     int ncontours;
     int cntr[];
     double (*vertices)[2];
     int (*triangles)[3];
{
    int i;
  int nmonpoly, ccount, npoints;
  int n;

  memset((void *)seg, 0, sizeof(seg));
  ccount = 0;
  i = 1;
  
  while (ccount < ncontours)
    {
      int j;
      int first, last;

      npoints = cntr[ccount];
      first = i;
      last = first + npoints - 1;
      for (j = 0; j < npoints; j++, i++)
	{
	  seg[i].v0.x = vertices[i][0];
	  seg[i].v0.y = vertices[i][1];

	  if (i == last)
	    {
	      seg[i].next = first;
	      seg[i].prev = i-1;
	      seg[i-1].v1 = seg[i].v0;
	    }
	  else if (i == first)
	    {
	      seg[i].next = i+1;
	      seg[i].prev = last;
	      seg[last].v1 = seg[i].v0;
	    }
	  else
	    {
	      seg[i].prev = i-1;
	      seg[i].next = i+1;
	      seg[i-1].v1 = seg[i].v0;
	    }
	  
	  seg[i].is_inserted = FALSE;
	}
      
      ccount++;
    }
  
  n = i-1;

  initialise(n);
  construct_trapezoids(n);
  nmonpoly = monotonate_trapezoids(n);
  triangulate_monotone_polygons(n, nmonpoly, triangles);
  
  return 0;
}


/* This function returns TRUE or FALSE depending upon whether the 
 * vertex is inside the polygon or not. The polygon must already have
 * been triangulated before this routine is called.
 * This routine will always detect all the points belonging to the 
 * set (polygon-area - polygon-boundary). The return value for points 
 * on the boundary is not consistent!!!
 */

int is_point_inside_polygon(vertex)
     double vertex[2];
{
  point_t v;
  int trnum, rseg;
  trap_t *t;

  v.x = vertex[0];
  v.y = vertex[1];
  
  trnum = locate_endpoint(&v, &v, 1);
  t = &tr[trnum];
  
  if (t->state == ST_INVALID)
    return FALSE;
  
  if ((t->lseg <= 0) || (t->rseg <= 0))
    return FALSE;
  rseg = t->rseg;
  return _greater_than_equal_to(&seg[rseg].v1, &seg[rseg].v0);
}


#endif /* STANDALONE */