/**
  * Ray stores a ray origin point and direction vector.
  *
  * @author Anthony Steed
  * @version 1.0
  */

public class Ray {

  /** 
    * Holds the ray origin
    */
  public Point Origin;

  /** 
    * Holds the ray direction
    */
  public Vector Direction;
    
  /** 
    * Create a default ray
    */
  Ray() {
    Origin = new Point();
    Direction = new Vector(0.0, 0.0, 1.0);
  }

  /** 
    * Create a ray by copying an existing ray
    */
  Ray(Ray r) {
    Origin = new Point(r.Origin);
    Direction = new Vector(r.Direction);
  }

  /** 
    * Create a ray from a point and a direction. 
    *
    * Values are referenced not copied
    * @param p the point to reference
    * @param v the vector to reference
    */
  Ray(Point p, Vector v) {
    Origin = p;
    Direction = v;
  }

  /** 
    * Get a point along a ray.
    *
    * The return point is given by Origin + (t.Direction).
    * @param t the distance along the ray of the point
    * @return a the point on the ray as specified.
    */
  public Point getPointAt(double t) {
    return new Point(Origin.X + t*Direction.X,
		     Origin.Y + t*Direction.Y,
		     Origin.Z + t*Direction.Z);
  }
}