The old Unreal engine was based on portal rendering. The game itself didn't use too much in the ways of non-euclidian geometry, but there were plenty of custom

The old Unreal engine was based on portal rendering. The game itself didn't use too much in the ways of non-euclidian geometry, but there were plenty of custom maps and demos of it. Most, if not all, of the stuff in this video could probably be recreated in that old tech. Not meant as a middlebrow dismissal, this is neat stuff and I wished it was explored more in games! https://www.youtube.com/watch?v=AEVSUIECY9Y https://www.youtube.com/watch?v=AEVSUIECY9Y