Very nice – if only I could try it! :'-) Any chance this could be ported to Android, at least for high-end devices with a decent GPU?

The rotating black hole version that we implemented requires GPU code, and porting that to Android is nontrivial---though we'd love it if someone took our open-source code and ported it!

In the meantime, check out this code developed by Dominic Chang (grad student at Harvard) that implements lensing by a non-rotating (Schwarzschild) black hole in your browser: https://dominic-chang.com/bhi-filter/