I think pass two is intended to introduce additional regions of concavity (mostly by replacing straight lines), which in effect introduces a bunch of inflection points, helping creating the organic "spiny" feel, as opposed a "bubbly" feel. Without it, the resulting caves look a bit more like if you spilled liquid on a waxy surface, and less like thorns.<p>If you go into the javascript and replace "for(let p=0;p<3;p++)" with "for(let p=1;p<3;p++)", and then re-execute the block in the console, you can generate run through a bunch of generations without step 2
Oh wow. I had no idea this was based on cellular automata. It really does give a totally different feel versus the other sections of the dungeon.
This is my favorite kind of procgen blog post: here's what we did, and here's a little widget you can play with to see how it works.
I always have a lot of respect for people who are really good at procedural generation
Related, TNNT starts in 9 days (Nov 1), anyone can join the tournament.<p><a href="https://tnnt.org/" rel="nofollow">https://tnnt.org/</a>