[cal85]

I've had a stab at decompressing the code by hand, adding comments and meaningful var names where possible. I still don't understand the maths in it...

https://github.com/callumlocke/bitwise-liminal-expanded

[gigabates]

Looks like the maths is a kind of raymarching loop if you want to read up on it.

[junon]

Just a guess, the speedup is probably due to you caching the 2d context.