#413Disco Ball

A faceted mirror ball turns at the center of a dark room. The view ray is sphere-traced to either the ball or the surrounding walls: on the ball the surface normal is quantized into a lattice of flat mirror tiles that each catch the key light as a hard specular glint; on a wall each point solves for the facet whose reflection would land there — the required half-vector, snapped to the same rotating tile grid, lights up as a crisp pointillist dot. As the ball spins, those hundreds of warm/cool dots sweep across the walls and floor. Scroll to change the spin, move the pointer to swing the ball and light, press to brighten the room.