5-or-so years ago I came across a raytracing simulator that looked a bit like this, but did a full spectrograph IC light simulation on top. I haven't been able to find it since, but it was a fascinating little toy to play around with.

Was it Tantalum, by any chance? https://benedikt-bitterli.me/tantalum/

Yes, that's exactly it. Thank you!

Very nice, color me impressed. A presentation with a button to run the thing, and a button to get to the sources. Have you seen the sources? Pure JS, no NPM hell, no build steps. And finally someone making use of the fact that our sources are all UTF-8 now :)

you can try to simulate the Penrose unilluminable room, see https://www.youtube.com/watch?v=x3VluzZTReE

There was a fun game for the Zune HD reminiscent of this called Dr. Optics Light Lab. The only record of it seems to be these poor-quality YouTube videos: https://www.youtube.com/watch?v=xKvLCDMe2Og https://www.youtube.com/watch?v=zeUYFhT68E4

I just discovered this game on steam that looks vaguely similar https://store.steampowered.com/app/1511140/Laser_Attraction/

I looked a while back to see if there was some open source equivalent to professional optical CAD software (think Zemax)

Sadly, anything I found was already total abandonware.

Nice one, very well done and with many options to play around.

I've used this for reasoning about our ROV's underwater optics.

nice to see a desktop style application with interactive canvas working in the browser.

fun toy! Just wasted 15 mins without realising

so great!