For all these times we talked about Super Mario, we never covered another important game, Doom.

Here’s a 17-minute video from decino explaining how the Doom monsters move and attack the player (the “AI” in the old sense of the word):

What’s really fun about this video is how it uses annotated source code (in contrast to Super Mario, the Doom source code was officially released and open sourced), and particularly how it tasks the engine with explaining itself, setting sometimes elaborate stages just to show a principle or an algorithm – an absolutely perfect example of “show, don’t tell.”

decino has tons more of these kinds of videos (click on Popular!), distinguishable by their yellow covers, if you want to pick another aspect of Doom that interests you.