D3 A.I. Could Use a Rewrite

I read that one of the reasons why Doom 3 was criticized was because the monsters were mainly script animated, and had nothing more to their A.I. behavior. That becomes painfully clear in some recent
Doom 3 mods, where the enemies can't climb ladders, walls, or ceilings on their own accord.

Since the source code to Doom 3 is released, I wonder if the A.I. can possibly be elevated to the expectation fans originally had for the game. How would one be able to successfully program a A.I. system which would allow the imps to crawl upon all surfaces on its own inclination, lurk in the shadows observing you patiently, and finding clever ways to attack you when you least expect it?

Those capabilities for PC game A.I. probably haven't been invented yet, but what programming techniques do we have available now which could bring about significant improvments to Doom 3's A.I.? A pathway net system similar to HL2's (if that is possible to implement)? What can be done?

Search for the paper on the AI in F.E.A.R., it will give you some pointers.

Frankly, this was painfully obvious in the original game and in RoE in particular - in the latter, when you use the artifact, the enemies gotta do their little actions they started whether or not you're half way across the map by the time they'll finish. So you can run around them and punch them in the back, for example, cuz they're scripted to roar in a particular direction.

More important would be to first design the maps that would give a chance to the AI to act more dynamically. The stock levels are too one-sided and controlled to show much.

Quasar said:

Frankly, this was painfully obvious in the original game and in RoE in particular

The Grabber allowed you to fuck with scripted actions and doors/machinery in a lot of interesting ways, e.g. like getting the skytram stuck.

And, in general, you can do a lot of stupid or disruptive things. The difference being that with the latter, you can sometimes gain an actual advantage, when the game doesn't break that is, while the former are usually asymptomatic. Killing NPCs is usually side-effect free, but there are exceptions: e.g. killing Dr. Ishii before he's zombified results in him being, well, not zombified :-p

Maes said:

The Grabber allowed you to fuck with scripted actions and doors/machinery in a lot of interesting ways, e.g. like getting the skytram stuck.

And, in general, you can do a lot of stupid or disruptive things. The difference being that with the latter, you can sometimes gain an actual advantage, when the game doesn't break that is, while the former are usually asymptomatic. Killing NPCs is usually side-effect free, but there are exceptions: e.g. killing Dr. Ishii before he's zombified results in him being, well, not zombified :-p

You can also send revenant rockets back at him, no manual aiming required, just one click. Wish I could do that in Doom 1 and 2, they annoy the fuck out of me.

Id love to see the zombie soldiers behave more like the HECU in the first Half-Life.

Didn't Doom 3 creators brag about the AI back before it came out... like they did with Rage too.

I think AI needs to be programmed based on trial and error from what players do. Like if a player stays hidden or pinned down. Throw some sort of explosive device to get the player to move. If you've got 3 enemies in 1 room have 1 distract while the other 2 flank. If there is cover around... take cover (but zombies aren't the smartest out there). Like how Trites will jump away from your fire.

If enemies could climb ladders it would just look weird unless they had some good animations, that's why stairs and elevators are good :-)

A big problem with the AI seems to be most of the time everything is stuck in a hallway.

Having an enemy run from you to find its friends would also be nice. Like a cherub that will hop away until it finds a pack of cherubs to attack you. Or having 1 Z-SEC run while firing or wait for you around a corner might be helpful. Or heck in the future a Z-ENG that sets up turrets and traps for you then runs to them. That might feel unDoom... so just make it an Arch Vile that will run from you, hide and spawn in enemies then you come running in and find a wall of bodies.

Testing AI

A good way to test AI first is to put a player vs enemy in an empty room. How do they react? Just shoot ala old Doom1 or strafe and shoot? Is there a game mechanic where kneeling means more accuracy?

Then put a box in the room. What happens with your AI do they stand shooting at you or do they take cover and shoot at you? In Uncharted 1 the enemies were great for finding cover and finding wacky and weird ways of coming out from it. They'd use blind fire, they'd peak out of the top and the side, they'd jump out, they'd do some jump and low crouching fire to react weirdly so you wouldn't be able to insta-kill them.

Perhaps put a better weapon in the room.... does the enemy try to go for the better weapon, pick it up and start using it?

Then put the player on a bunch of boxes with no gun and the player has no gun. Does the AI try to climb or jump to get on the boxes with you?

Next give the player a gun, but the enemy has no weapon? Does the AI have a sense of self sustainability where they hide from you with the gun ontop of boxes with the better vantage point?

After that... are the boxes destroyable? Give the player a gun, and the enemy a grenade, does the enemy try to blow up the boxes from beneath the player and hopefully the fall or explosion would stun the player and then the enemy can run in for the attack. Fire... can they burn down the boxes and the player on them?

Injury. Shoot someone in the leg, destroy a leg, can they zombie crawl? Do they limp. I think they solved this issue in Quake 2 I remember limping enemies. Then they talked so highly about it when Rage came out... they limp!

Threat assessment... The first Doom had infighting. Do Z-secs think imps are threats? Do demons attack lost souls? What's the bigger threat? Can they strafe to cover if getting attacked by a distant enemy so they can keep fighting the closer enemy without the distant one getting shots in.

Put the player on a platform with a ladder... can the AI even climb the ladder? Does the AI judge the distance the player with a gun is from the side of the platform, because if there's a risk of getting shot off the ladder, the AI shouldn't just rush in.

Can the enemy alert something to have a whole legion coming after you. Does gunfire draw attention from zombies?

More interestingly, since Doom is in space can they shoot windows out even if it means their own death just to make stuff tougher for you with 0 oxygen. What does a cacodemon care about air?

Three Benefits of Planning
The previous case study illustrates the first of three benefits of a planning system. The first
benefit is the ability to decouple goals and actions, to allow different types of characters to
satisfy goals in different ways. The second benefit of a planning system is facilitation of
layering simple behaviors to produce complex observable behavior. The third benefit is
empowering characters with dynamic problem solving abilities.

Source:
http://alumni.media.mit.edu/~jorkin/gdc2006_orkin_jeff_fear.pdf

Three States and a Plan: The A.I. of F.E.A.R.
Jeff Orkin
Monolith Productions / M.I.T. Media Lab, Cognitive Machines Group
http://www.jorkin.com

Dr. Durr said:

Id love to see the zombie soldiers behave more like the HECU in the first Half-Life.

I'd like to see them act with any intelligence, period. They are incredibly predictable. I've always been surprised at how slowly they even reacted to the player and how scripted their animations were. Sometimes they would run away if they took damage, making them irritating, but they were too spaced away from each other to be a threat. FEAR was so much superior in group battles but Doom 3 was often more about one-on-one - I don't know why they bothered with zombie soldiers at all.