Ah, you&#x27;re most likely talking about Wenzel Jakob&#x27;s wonderful 2D tool for demonstrating Manifold Walks.<p>Wenzel was actually one of my thesis advisors, and his tool was the inspiration behind this project. :) I was writing an implementation of Manifold Walks out of personal interest and reproduced his 2D tool for debugging purposes. Eventually I realized that caustics in 2D actually look kinda neat, so I spent some time doing research and then fleshed it out into this article + demo.