In preparation for the AI Summit that I am helping put on at the 2009 Game Developers Conference, I am rapidly cranking through some of the key games of the year. So, I signed up for GameFly just so I could putz with some games in the short term. I will likely buy some of these games down the road, but the research budget for IA doesn't cover spending $300 on games in only a few weeks!

Well, the first thing in my queue (along with Fable 2... check back later for that) was Gears of War 2. I had seen a number of the reviews in various places and I was impressed by not only what I saw but by what people were saying about it. Despite having Gears 1 sitting here, I had never really played it. (My son had.) So really, I had no idea what I was getting into.

Ok, wow.

Obviously, it is a very good looking game... but that's not what this column is about. After watching Yahtzee's take on the game, I was also fully prepared for plenty of "chest high walls". Of course, there's good reason for that given that the cover fire system is an integral part of the game. On the other hand, I have not seen the poor AI quirks that Yahtzee cracks on the same review. (Although I suppose referring to the generally satirical and sarcastic Zero Punctuation blurbs as "reviews" is a bit of a stretch now, isn't it?)

So far the AI seems pretty solid. Now note that I have only played the opening level up to just past the epic speech (<- unintentional pun for those of you who actually pay attention to the names of the game studios who crank out your entertainment products) so I haven't experienced too much of it. However, what I have seen has been pretty decent for a shooter. The enemies are frustratingly adept at using cover. I have often found myself flanking them just so I can get a shot around whatever "chest high wall"-like object they are behind. What's more, I have noticed that they will shoot from around different sides of the object. If the baddie is behind a desk, he may pop over it or around the side. This is a nice touch of realism that steps away from the typical method of 1-1 relationships of designer-tagged points. That is, there is no "and at this point, the AI can shoot over the object." There seems to be simply "here's a hiding spot... let him do what he needs to do."

My allies seem to be pretty proficient at using the cover as well. Of course, I haven't been paying too much attention to what they are doing since I have been concentrating more on saving my own ass. (Nota bene, I'm playing on the hard difficulty level.) However, as we move from battle to battle, I do notice that they are very conscientious of taking cover as we go... even when they are simply waiting for me to catch up.

All of this cover-taking is very refreshing in a shooter. I have (for 15 years?) been so tired of enemies (and allies) that simply stand out in the open and either wait to get shot or are so invincible that cover is unnecessary. (Yahtzee suggests this is possible in GoW2, but maybe he was on a different difficulty level than I am.)

For the most part, the animation seems clean. The transitions are pretty decent and any quirks seem to be more a result of the control system than the animation. That's a hard problem to solve, so I don't bitch about it too much. A better example is watching the animation of the AI characters rather than of myself. Everything seems smooth as they move, duck, fire, etc. I will pay more attention to that as I go.

I have yet to play enough to see how much of the enemy combat events are scripted and how many are dynamic. For example, early on the Locusts in the hospital are retreating... but that is obviously scripted as I have played through it three times (twice by myself and once in co-op with my son). I understand that. However, as I play on, I would like to see if there are places where the enemy retreats simply because I'm kicking his ass. I saw a lot of this in Halo 3, for example, which was controlled by Damian Isla and Max Dyckhoff's battle management system. Given the impressive use of cover in Gears, the inclusion of a good fall back or retreat system would be cool. We'll see.

That about covers it for the moment. More later. If you are jumping into this article, remember to check the Gears tag below to see if I have written anything else about this game.

Labels: Epic Games, Gears of War 2, Halo 3, scripting, using cover

Ok... this isn't necessarily going to be a full-fledged review of all of the AI in F.E.A.R. (Monolith studios) Actually, to do that justice may take an entire book anyway. However, I have been playing it for a few days. One of the reasons that I had to get a hold of it anyway (I bought the Platinum Collection) is that I also got my hands on the SDK. It is a special treat to be able to see the actual code that went into making this ground-breaking gem of a game.

Anyway, I had a taste of the game a few months back via the downloadable demo from Gamespot. Even with that brief glimpse I was impressed. Now that I have been able to "dork with it" (research term) a little more, I have found myself saying a few things that surprise me.

"Son of a bitch! Where did he come from?"

This usually occurs when I fall into old patterns of thinking that the enemies are going to generally either stay put or move toward me in something resembling a direct assault. The first time this happened was on one of the more open, but box-laden arenas (which I am realizing was a design decision to show off this exact effect). I was slowly closing on a group of enemies... or at least where I thought they were (more on that later) when I get pegged from behind.

Now this isn't a "Doom 3" sort of assault (see my post on the subject) where the game either spawns a monster directly behind me or pops open a completely illogical hidden panel in order to literally kick me in the ass. As I thought about where this dude could have come from, I realized that it was one of the enemies that had been in front of me... but off to one side. He actually had circled around some obstacles and come up behind me. Sure, he probably didn't realize that I had moved until he reached the spot where he had last seen me - but then rather than stand there, he continued on the only logical way I could have gone until he did discover me - and proceeded to politely pop a proverbial cap in my ass. Score one for the bad guys.

"Get your butt back here, wimp!"

Again, unlike shooters that I have played in the past, I encountered something that was actually almost frustrating in the novelty of it. It was realistic... which actually took some getting used to. When I would engage an enemy, they were just as likely to fall back as they were to move forward. I may take a shot or two at them only to see them walk, run, or dive around corners. They weren't just going to cover, they were pulling back. This left me in the uncomfortable spot of having to move into a hostile environment where I knew dudes were camping for me... a position that I have always tried to put the enemy AI in. Now I know how effective it is - since I don't really relish having to be the one doing the hunting.

"I don't have all freakin' day!"

Rather the opposite of above, I have tried to fall back to patterns of "agro-ing" the enemy and then dropping back to wait. As often as not, they don't fall for it. If they know I'm there, they may very well not come for me - especially if I have nowhere to go. I'm used to being quite comfortable simply waiting around a corner with a shotgun to my shoulder ready to multi-perforate the first moving object that shows itself. I wait... and I wait... until I hear "Flush him out!" followed by that delightful ping of a grenade rattling around at my feet. Crap! But do they just come running dumbly around a corner like my cat hearing the food in his bowl? Nope... I gotta come to them.

"Would you show yourself, damnit?!?"

Somewhat related to the above is their stubborn insistence on using cover. Yeah, using cover is cool. We've been talking about it at GDC roundtables and message boards for years. For a while, AI programmers were all happy to use preset "cover points". In a general sense, they looked good... but they were easy to exploit by just being in a place where that specific cover point was not truly a cover point at all. I get a feeling that these assholes would be perfectly comfortable playing hide-and-seek in a round room with a round pillar in the center of it. They seem to process cover the same way that a human does... "can this specific spot be seen by that dude over there?"

It gets really frustrating when I get into peek-a-boo mode with a guy. The enemy may position itself in the shadow zone of a strip of wall, a column or something to take cover. If I peek around one side, he will move a little to keep the cover between us. If I move to look around the other side, he moves also. There isn't any invisible pre-defined spot that he's on, he's simply trying to not be seen. It pisses me off! Game AI is not supposed to act this way!!

"Quit acting like you guys like each other!"

[Cascade this from above...] If Ol' Chuck there is running to cover like the little bitch that he is (my language gets salty when I'm pwning), do me a favor and let me gun him down like an arcade ducky. Do NOT annoy me with suppressing fire and all that military squad nonsense. He's got his back turned and I want to blast him before he gets to that box because, once he gets there, we have already determined that he's not going to show me anything more than the barrel of his gun for the next 20 minutes. You really are not helping me out by scattering an endless cornucopia of metal alloy in my general direction. It really is distracting and makes it awfully hard for me to jump out here in the middle of the doorway and calmly aim down the sight at his weenie little ass. You act as if he's on the same team as you or something! What the hell is wrong with you, anyway? Sheesh!

"OK... that's not funny anymore!"

This was my latest little adventure. I finally met up with one of these "Watchers". They are like freakin' Spiderman The Rabbit Puncher. The first time I saw one, I thought it was one of the hallucinations again so I didn't think to actually shoot it until it walked up and bitch-slapped me... and then disappeared into the damn ceiling before I could blink. Uh. Ok... that was odd. Until, from the corner of my eye, I saw him (or his buddy) swing down from the ceiling, off the wall, over the desk, smack me on the butt again, and then perform a similarly frenetic egress.

For the next 3 minutes, I was twitching around all over the place like I was going through the DTs while on LSD. These two dudes were zipping up, down, "over, under, around and through" so as to keep striking me from behind. If I turned and saw them in time, they were just as likely to about face and retreat and replan. I began to realize that "replan" is exactly what they were doing. This wasn't a pre-set script to whack me when I got to a certain location... they were making this up on the fly (crawl, leap, cling, whatever)! I finally managed to pop one with the shotgun but the other got me. I was too shaken by the fact that they were actually being clever that I had to quit... and start writing.

Damn.

I'm not sure what I want to do now. Crawl through a billion lines of AI code spread across 100 different AI classes so I know what they are doing... or keep playing so I can experience it more and maybe put myself into a position where I can actually understand some of the more esoteric stuff that I encounter in the code. Right now I'm too shaken up by my encounter with real AI to do either one.

Maybe I'll go play Doom 3 instead. For some reason, creepy lighting and environments and stupid enemies is not as daunting as generically bland lighting and environments and monsters that actually act like they have a brain for a change.

Congrats to Jeff Orkin and company - I'll see you next month at GDC. I will be honored and excited to meet you and "talk shop" such as it is. But don't be surprised if I have a PTSD reaction and slug you before you get a chance flip over that damn table and hide behind it.

(More on F.E.A.R. AI at AIGameDev.com)

Labels: Doom 3, F.E.A.R., FPS, line of sight, Monolith, planning, using cover