Yes, it's a set of facing angles, and then mirror'd for the other side. I played with Doom modding tools back in my youth, I've seen the sprite-sheets. The Cacodemon isn't a good example, though, since it doesn't have a walk cycle.

Every monster that can walk needs to have a fully animated walk for going towards the player and away from the player and every angle in between. Ditto firing anims. That's a lot of walk cycles. They cheat with the death anims since the monster always faces the player to die. Still, lots of walk and firing anims.

The approach also fails for PVP models because players can fire and move at the same time, which creates the "skating" effect from Doom/Quake1/Quake2.

It's a lot of work, but there is nothing complicated about getting it done. You tell the art guys the specs and they spend a few days getting all the images and then move on to the next monster.

There's a lot of complication about getting it done. You're just offloaading all the complexity to the art people.

- signed, an art person.

Why yes, yes I did. But for Doom there were about 10-15 kinds of sprites (monsters, lamps, trash cans). I didn't say it was easy, I said it was straight forward. The code took a lot of time back then, and I'm sure the art guy(s) were busy the whole time.

Indie titles means clever/complicated is better than labour-intensive, because labour-intensive costs money but cleverness just needs one brilliant programmer/artist.