code: public float distance2(float tx, float ty) {
  		float dx = tx - px;
  		float dy = ty - py;
  		
  		return ((dx*dx) + (dy*dy));
  	}
docs: Get the distance squared from this link to the given position
  
  @param tx The x coordinate of the target location
  @param ty The y coordinate of the target location
  @return The distance squared from this link to the target