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From Gearbox Software webpage: "...Patrick comes to Gearbox Software after working previously at Ion Storm on Anachronox. Prior to that he has contributed to many titles including Dominion, Monty Python And The Quest For The Holy Grail, and Arcade America. He started down the path of a game developer by programming home games on the Apple II in 1982. But, before getting into professional game programming Deupree worked on two non-game commercial products: Actor, an object oriented programming language for Windows, and PyWare 3D, a tool to choreograph marching band drills in a 2D/3D environment). In Patrick's spare time he managed to earn a black belt in Tae Kwon Do and he's healing up nicely..."

G5: When designing the Opposing Forces AI, what were your main objectives?

The #1 objective was to make it fun. Toward this end we wanted to have the various monsters and companions have unique capabilities and characteristics, while also maintaining consistency with what had already been introduced in Half-Life.

G5: What sort AI of techniques were utilized in Opposing Forces?

A lot of the AI techniques used were those already present in the Half-Life engine. The existing path finding, sound detection, and visual detection code present made our job a lot easier. Some tweaks were done to this logic to accomodate new weapons. For example, the sniper rifle allows for an instant kill without any noise from the kill, so a special case had to be added for enemies near them to realize something had dropped dead next to them. However, rather than have them instantly know where you sniped them from, they will go into a "hunting" mode.

We also used some techniques to "cheat" a bit. For instance, if you have a companion following you and you get shot, that companion will acquire the attacker as a potential target and they will try to rush in to defend you. Some people commented on the fact that our companion soldiers would often run into a situation and get themselves killed, but for what we were trying to accomplish, it was the better solution.

G5: Were you ever surprised at what your AI achieved?

We have a test map that I still use to this day to test AI that is called test_grunt. It was something one of the other developers here made, and I continue to modify. It's a lot of fun to make a change to the AI, or to add a new feature, and then hop into this map with some AI companions. Seeing how a team of human grunts would do when fighting a team of ShockTroopers would result in a different outcome just about every time. I think the coolest thing I saw was in one of our maps where you could have 2 grunts, a medic, and a guy with a blow torch but no weapon. I had the torch guy follow me into a hall containing a bunch of Black Ops and Ninja's and the torch guy took off down the hallway. I'd forgotten about him until I rounded the corner and saw him kicking the heck out of one of the ninja's until she was dead. I certainly hadn't expected it, though I had specifically put in code to make the grunts more inclined to use a melee attack in certain circumstances.

G5: How would you like to see AI in first-person shooters evolve over the next 2-3 years?

In all honesty, I would prefer to see things move into a semi-scripted AI system. I'm not a big fan of trying to completely use pure AI for character behavior in a single player game. It seems that many of the games that have done this involved less fun and more babysitting. I think that there are some moments where you just really want to coax the AI to do something specific and that the level designer is the best person to know where and when they should do it. An example would be an AI opponent or companion kicking down a door to get to a target, or falling a certain way if killed at the edge of a high place. These are things where attempts to dynamically detect the right environment for that action often lead to something that doesn't look quite right.

So, I would like to see the marriage of AI with hints placed by level designers to suggest a good place to die, or a good place to clear a path. I think this would make the single player experience much more impressive.

G5: Do you see "research techniques" (neural network, genetic algorithms) becoming a major part of gaming AI in the near future? Why or why not?

I do see such techniques playing an important role in certain styles of game in the near future. To enhance squad members to a point where they learn your patterns and evolve to work with them, or around them would be very cool. I think it would be very impressive to see a game where, for at least some portion of time, you are being led intelligently by the AI, and to have that AI react to you based upon how you have followed them.

G5: Outside of the first-person shooter genre, which gaming field provides the most interesting AI?

It would be hard to really say. On a personal level, I would really like to see a Role Playing game make decent use of a more dynamic AI system, so I think that genre has the most potential for growth in the field of AI.

Looking at current AI in games, I would have to say that sports games probably offer the most sophisticated AI (assuming it's a good sports game).

G5: To write AI as impressive as the HalfLife/Opposing Forces AI, what kind of experience and knowledge is required?

This is really a tough question to nail down. A certain amount of base experience that isn't specifically relevant to AI would be required. For example, good, structured C or C++ programming skills would be a must, and object oriented design experience would be very helpful as well.

Experience specifically related to AI would be things such as path planning, knowledge of the animation system and the event scheduling of the engine being used, and knowledge of how the engine handles "testing" the environment.

I really can't say what classes to take at college. I took classes in AI at my college, but everything we did in that class used LISP and Prolog. So, while the basic concepts were relevant, those languances are not practical for game development of this type. I'm sure other colleges might offer classes in developing AI using C++.

Ultimately, the type of experience required really depends on the person.

G5: Any funny stories about the development of the Opposing Forces AI?

One of the funniest things is a behavior that the enemy soldiers had in Half-Life that didn't work that well when used with friendly characters. In Half-Life the Grunts will sometimes kneel down, put a grenade on the ground, then run away while also telling their team mates to stay away. In one of the maps someone here was in a fight when one of his friendly Grunts ran over to him, bent down, put a grenade right at his feet, then stood up and stared at him until it blew up. You kinda had to be there, but it was very funny to watch.

Ultimately we removed that behavior from the friendly Grunt since laying a grenade down with an unpredictable player running around was just trouble waiting to happen.