: Optimizing how floors and ceilings were rendered to save processing power.
If you are looking for a deep dive into the code and architecture, the provides a comprehensive breakdown of the engine's internal logic, while Fabien Sanglard's Game Engine Black Book: DOOM is widely considered the ultimate "paper" or book on how the technical magic of DOOM was achieved. DOOM.part08.rar
: Using BSP trees to split a 2D map into sub-sectors, allowing the engine to determine which walls to draw first without sorting every frame. : Optimizing how floors and ceilings were rendered