Sight and Light: how to create 2D visibility/shadow effects for your game

Nice tutorial and here is the online game: http://demo.nothingtohide.cc/

I remember seeing a nice web page where you could play around with lights and walls in real time and see the results. Something like a lights and shadows on-line real time simulation, but I can't remember the address and couldn't find it by searching. Anyone knows the page I'm talking about?