doily.c Example C Language Program

/*
doily.c:

Draws a doily depending on how many points you give
it (range is
currently set between 3..100).  point count is equivale
nt to how
many line segments make up the circle's edge.
*/

#include <gl/gl.h>
#include <gl/device.h>
#include <math.h>

#define PI 3.1415926535

float points[100][2];

main(argc, argv)
int argc;
char *argv[];
{

  int val,dev;
  long numpts;            /* First figure out how many points there are. */

  if (argc != 2) {
    printf("Usage: %s <point_count>\n", argv[0]);
    exit(0);
  }

  numpts = atoi(argv[1]); /* convert argument to internal format */
  if (numpts > 100) {
    printf("Too many points\n");
    exit(0);
  }
  else if (numpts < 3) {
    printf("Too few points\n"); exit(0);
  }

  initialize(numpts);    
  while (TRUE) {       
    if (qtest()) {           
      dev = qread(&val);           
      if (dev == ESCKEY) {
        gexit();
        exit(0);
      }
      else if (dev == REDRAW) {
        reshapeviewport();
        drawdoily(numpts);
      }
    }
  }

}

initialize(numpts)
long numpts;
{

  int gid;
  long i;    /* Now get the x and y coordinates of numpts equally-
              * spaced points around the unit circle.
              */
  for (i = 0; i < numpts; i++) {

    points[i][0] = cos((i*2.0*PI)/numpts);
    points[i][1] = sin((i*2.0*PI)/numpts);
  }
  keepaspect(1,1);
  prefposition(XMAXSCREEN/4,XMAXSCREEN*3/4,YMAXSCREEN/4,
      YMAXSCREEN*3/4);
  gid = winopen("doily");    
  qdevice(ESCKEY);
  qdevice(REDRAW);
  qenter(REDRAW,gid);    
  ortho2(-1.2, 1.2, -1.2, 1.2);

}

drawdoily(numpts)
long numpts;
{

  long i,j;    

  color(BLACK);
  clear();
  color(RED);    
  for (i = 0; i < numpts; i++)
    for (j = i+1; j < numpts; j++) {
      move2(points[i][0], points[i][1]);
      draw2(points[j][0], points[j][1]);
    }

}

/*
  Changes:
  - exit(); to exit(1);
*/

Related Information

The keepaspect subroutine, prefposition subroutine.