Vertical scrolling, and emulating the weird side-effects of the registers being written to, was the hardest part of recreating the NES using 3D meshes. It took

Vertical scrolling, and emulating the weird side-effects of the registers being written to, was the hardest part of recreating the NES using 3D meshes. It took me a few weekends to get Zelda 2's intro working reliably. I wrote about it a bit myself (probably got a few details wrong or simplified them) here: http://n3s.io/index.php?title=How_It_Works http://n3s.io/index.php?title=How_It_Works