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/*
 *   NAME
 *     line_point
 *
 *   PURPOSE
 *     Find a point on a line a given distance from a specific point on the line.
 *
 *   NOTES
 *     
 *
 *   HISTORY
 *      wiener - May 8, 1995: Created.
 */

#include <euclid/copyright.h>
#include <euclid/geometry.h>

/*
 * Given two points p1 and p2.  Find the point p3 on the line from p1 to
 * p2 that is a given distance from p1.  If the distance is negative, p1
 * will lie between p3 and p2.  Return the distance from p1 to p2 or 0 if
 * p1 == p2.
 */
double EG_line_point(Point_d *p1, Point_d *p2, double dist, Point_d *p3)
{
  double len;
  double quot;

  /* find the distance between p1 and p2 */
  len = DIST(p1, p2);

  if (len < MACH_EPS)
    {
      p3->x = 0;
      p3->y = 0;
      return(0);
    }

  quot = dist/len;

  /* the equation of a line from p1 to p2 is p1 + t * (p2 - p1) */
  p3->x = p1->x + quot * (p2->x - p1->x);
  p3->y = p1->y + quot * (p2->y - p1->y);

  return(len);
}