The 2D Visibility tutorial is about sweeping an angle across polar coordinates. This could be “unfolded” into sweeping x across cartesian coordinates. Once you see that sweep pattern, you might wonder, why not sweep y? That’d then “fold” back into sweeping across radii. I wanted to build the animation to see what it looked like. Then I can decide whether/how to integrate it into the visibility page.
Conclusion: it was a neat idea but I didn’t really like the animation I made at first. I redesigned it and like this one better. I still don’t know if it’s useful to show in the tutorial.