public class Direction {
  public float dx;
  public float dy;
  public float dz;

  public Direction() {
    dx = dy = 0.0F;
    dz = 1.0F;
  }

  public Direction(float dx,float dy,float dz) {
    this.dx = dx;
    this.dy = dy;
    this.dz = dz;
  }

  public Direction(Direction d) {
    dx = d.dx;
    dy = d.dy;
    dz = d.dz;
  }

  public Direction(Position p1,Position p2) {
    dx = p2.x-p1.x;
    dy = p2.y-p1.y;
    dz = p2.z-p1.z;
  }

  public float norme() {
    return((float) Math.sqrt(dx*dx + dy*dy + dz*dz));
  }

  public void normalise() {
    float norme = norme();
    if ( norme != 0 ) {
      dx /= norme;
      dy /= norme;
      dz /= norme; }
  }

  public Direction produitVectoriel(Direction d) {
    return(new Direction(dy*d.dz - dz*d.dy,
                         dz*d.dx - dx*d.dz,
                         dx*d.dy - dy*d.dx));
  }
  
  public String toString() {
    return("["+dx+","+dy+","+dz+"]");
  }
}