I've just started on another where each pixel is coloured according to how many reflections a ray starting from that point goes through before escaping the system, but at the moment it's still a bit buggy:

Oh, of course. That's what happens when I'm not reading what I'm typing. In threecircles1 the line direction=cos(theta)+i*sin(theta) ; We'll use a vector representaion ; of the direction should of course be direction=cos(theta)+(0,1)*sin(theta) ; We'll use a vector representaion ; of the direction Morgan L. Owens "I'm so sorry, I was miles away."