Hi! This response has been a long time coming.
You can access the source code here: https://www.lexaloffle.com/bbs/?tid=32397. Unfortunately, I made my own method for this, and it is pretty hard to follow.
If I come up with a cleaner way to make these visuals, I will probably make a notice/post on this game, so stay tuned here. Otherwise, I recommend reading up on "raycasters," which can give you a very similar effect: https://lodev.org/cgtutor/raycasting.html