Rendering on the CPU as opposed to the GPU.
Color: From Hexcodes to Eyeballs
A grand tour of the science behind color, color perception, and how colors are generated by computer displays. By Jamie Wong.
Excerpt: Quake Postmortem - Optimizing Level Viewing
Michael Abrash succinctly explains Quake's visibility precomputation algorithm using a sharpie and overhead projector.
Wolfenstein 3D's map renderer
Matt Godbolt's excellent explanation of the Wolfenstein 3D raycasting renderer