import java.awt.*;
import java.awt.event.*;
import java.util.*;  

public class Vedge implements java.io.Serializable{
  InsertionP p1,p2;   
  Vedge einv = null;
  Vedge enext = null;
  Vedge hnext = null;
  Dtriangle tri = null; 
  /* explicit form of vector to line expression ax + by +c = 0 */
  double a,b,c;             
  public Vedge(InsertionP p1, InsertionP p2){ 
    Update(p1,p2); 
  }
  public void Update(InsertionP dp1, InsertionP dp2){ 
    p1 = dp1; 
    p2 = dp2; 
    this.setLineCoefficients();
    this.setp1edge(); 
  }
  public Vedge getReverse(){ 
    Vedge e = new Vedge(p2,p1); 
    this.setInverse(e); 
    return e; 
  }
  public void setLineCoefficients(){
    a = (p2.y - p1.y); 
    b = (p1.x - p2.x); 
    c = (p2.x*p1.y - p1.x*p2.y); 
  }
  public void setp1edge(){ 
    p1.edge = this;
  }
  public Vedge getHead(){ 
    Vedge dedge;
    Vedge medge = this;
    while(((dedge = next(next(medge)).einv) != null )&&(dedge != this)){
      medge = dedge;
    }
    return next(next(medge));
  }
  public void setInverse(Vedge v){ 
    this.einv = v; 
    if(v != null)v.einv = this; 
  }
  public int Region(InsertionP ds){ 
      double dv = (a*ds.x+b*ds.y+c);
      if(dv > 0.0){
	return 1;
      }else if(dv < 0.0){
	return -1;
      }else{
	return 0;
      }
    }
  private Vedge next(Vedge dv){
    return (dv.enext);
  }
}