import java.awt.*;

/**
 * Edge.java represents a half plane defined by an edge of a clip polygon for 
 * a polygon clipping algorithm
 *
 * Created: Mon Aug 16 23:40:36 1999
 *
 * @author Tim Lambert
 */

class Edge {
  private int x1,y1; //start point
  private int x2,y2; //end point
  private int a,b,c; // (x,y) is inside the edge if a*x + b*y + c > 0;
  //we use ints to store the equation to avoid round off problems

  Edge(int x1, int y1, int x2, int y2) {
    a = y2 - y1;
    b = x1 - x2;
    c = -a*x1 - b*y1;
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
  }

  /* is this point inside the half plane defined by the edge? */
  public boolean inside(Point p){
    return a*p.x + b*p.y + c > 0;
  }

  /* return the intersection of this edge with another one from p1 to p2 */
  /* rounded to nearest int */
  public Point intersect(Point p1, Point p2) {
    int d = p2.y - p1.y;
    int e = p1.x - p2.x;
    int f = -d*p1.x - e*p1.y;
    int denom = e*a - b*d;
    int x = Math.round((b*f - e*c)/(float)denom);
    int y = Math.round((d*c - a*f)/(float)denom);
    return new Point(x,y);
  }

  /* draw this edge on a Graphics object */
  /* We don't just draw from (x1,y1) to (x2,y2) because the half plane
     is bounded by an infinite line.  But we can't draw an infinite line
     so compromise by drawing one 5 times as long as (x1,y1)-(x2,y2) */
  public void draw(Graphics g){
    g.drawLine(x1+2*b,y1-2*a,x2-2*b,y2+2*a);
  }

  /* Convert to a string - handy for debugging */
  public String toString() {
    return "("+x1+","+y1+")-("+x2+","+y2+")";
  }

}