I grokked it too over a few weeks a few months ago, then rewrote it all in a sane language: C. There are also a few mistakes in the code, where it is clear what the author intended, but it is not what he wrote. After fixing them, the fences around buildings, for example, look correct. I then replaced a lot of the O(n^4) algorithms with faster ones for that one: O(n^2logn). This made it go from needing ~1e10 floating ops to render an image to 1e7, allowing me to do it on a small microcontroller, producing this: https://twitter.com/dmitrygr/status/1470934354712928257