class Obstacle {
  
  Vec P1, P2;
  double x1, y1, x2, y2;
  double x2_x1, y2_y1;
  double dir;
  public double WALL_DRAG = 0.6;
  public boolean ACTIVE = true;
  
  Obstacle(Obstacle o) {
    P1 = new Vec(o.P1);
    P2 = new Vec(o.P2);
    x1 = P1.X; 
    y1 = P1.Y;
    x2 = P2.X; 
    y2 = P2.Y;
    x2_x1=o.x2_x1;
    y2_y1=o.y2_y1;
    dir=o.dir;
    WALL_DRAG=o.WALL_DRAG;
    ACTIVE=o.ACTIVE;
  }
  
  Obstacle(double _x1, double _y1, double _x2, double _y2) {
    P1 = new Vec(_x1,_y1);
    P2 = new Vec(_x2,_y2);
    x1 = P1.X; 
    y1 = P1.Y;
    x2 = P2.X; 
    y2 = P2.Y;
    x2_x1 = x2-x1;
    y2_y1 = y2-y1;
    dir = Math.atan2(y2_y1,x2_x1);
  }
  
  
  // http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/
    
  public Vec getIntersectionPoint(Vec P3, Vec P4) {
    double x3 = P3.X, y3 = P3.Y;
    double x4 = P4.X, y4 = P4.Y;
    double denom = (y4-y3)*(x2_x1) - (x4-x3)*(y2_y1);
    if (denom==0) return null;
    double numA = (x4-x3)*(y1-y3) - (y4-y3)*(x1-x3);
    double numB = (x2_x1)*(y1-y3) - (y2_y1)*(x1-x3);
    double uA = numA/denom;
    double uB = numB/denom;
    if (uA>=0&&uA<=1&&uB>=0&&uB<=1) {
      // INTERSECTION!
      return new Vec(x1+uA*(x2_x1),y1+uA*(y2_y1));
    }
    return null;
  }
  
  public void draw() {
    if (ACTIVE) line(P1,P2);
  }
  
}