In a recent opinion article by James Portnow entitled The Problem Of Choice, the idea was posited that there are two types of decisions that a player can be faced with in a game: "problems" and"choices". The former is something that involves a "right answer" such as a mathematically optimal solution. Therefore, theoretically it can be solved. We are all familiar with such challenges ingames -- especially when designers make them all too transparent.The other type of decision is the "choice". These are a little more amorphous in that there is no "right answer". Games such as Bioshock (i.e. the Little Sisters) have these elements but others such as Black & White and the two Fable games are rife with them. In fact, the entire game mechanic is built upon the idea of "make a choice and change the whole experience."
While I agree with the excellent points that James made, I believethat this same mentality can be extended to the realm of AI as well. In fact, Imade this point in my lecture, Breaking the Cookie-Cutter: Modeling Individual Personality, Mood, and Emotion in Characters at the AI Summit at GDC a few weeks ago.  Specifically, I suggested that the incorporation of differences between characters can enable game design choices for us as developers which, in turn, enables gameplay choices for our audience. However, it is not simply the incorporation of personality, mood, and emotion that does this. It is often even simpler than that.
As programmers, we deal in a world of algorithms. Algorithms are, by definition, a series of steps designed to solve a particular problem. Even the ubiquitous yet humble A* pathfinding algorithm is sold as guaranteeing to"return the shortest path to a goal if a path exists." The emphasis is mine. It returns the shortest path -- the best decision. Now that we are using A* for other uses such as sifting through planning algorithms todecide on non-path-related actions, we are subscribing to the same approach. What is the best action I can take at this time? Unfortunately, that leads our AI agents along the same path as the player... "how can I solve this game?" The simple fact that our agents are looking for the one solution necessarily limits the variety and depth that they are capable of exhibiting.Â
The irony involved here is that, in designing things this way, we cause our agents to approach something that should be a choice (as defined by Portnow) and turn it into a problem (i.e. somethingthat can be solved). Whether there is any "best" decision or not, our agents believe that there is... "belief" in this case coming in the form of whatever decision algorithm we happened to design into their little brains.
The solution to this is not necessarily technical. It is more of a willingness by designers and AI programmers to allow our agents to either
a) not make the "best" decision all the time, or
b) include decisions in the design to which there is no"best" solution at all.
Unfortunately, we have established a sort of industry meme that "we can't allow our agents to do something that is not entirely predictable". We are afraid of losing control. Here's a startling tip, however... if we can predict what our agents are going to do, so can our players! And I nominate predictability as one of worst air leaks in the tires of replayability.
One of the quotes that I used in that lecture and in my book on behavioral AI is from Sid Meier who suggested that a game is "a series ofinteresting choices". It is a natural corollary that in order for the player to make interesting choices, he needs interesting options (not math problems). One of the ways that we can present those interesting options is to allow our agents to make interesting choices (not solve problems) as well.
In the first chapter of my book, "Behavioral Mathematics for Game AI," I actually use Poker as a sort of "jumping off point" for a discussion on why decision-making in AI is an important part of the game design. I compare it to games such as Tic-Tac-Toe where the only decision is "if you want to not lose, move here," Rock-Paper-Scissors where (for most people) the decision is essentially random, and Blackjack where your opponent (the dealer) has specific rules that he has to play by (i.e. < 17 hit, > 17 stand).
Poker, on the other hand (<- that's a joke), is interesting because your intelligent decisions have to incorporate the simple fact that the other player(s) is making intelligent decisions as well. It's not enough to look at your own hand and your own odds and make a decision from that. You have to take into account what the other player is doing and attempt to ferret out what he might be thinking. Conversely, your opponent must have the same perceptions of you and what it is you might be thinking and, therefore, holding in your hand.
Thankfully, there is no "perfect solution" that a Poker player can follow due to the imperfect information. However, in other games, there are "best options" that can be selected. If our agents always select the best options, not only do we run the risk of making them too difficult ("Boom! Head shot!) but they also all tend to look exactly the same. After all, put 100 people in the exact same complex situation and there will be plenty of different reactions. In fact, very few of them will choose what might be "the best" option. (I cover this extensively in Chapter 6 of my book, "Rational vs. Irrational Behavior."
Our computerized AI algorithms, however, excel greatly at determining "the best" something. Whether it be an angle for a snooker shot (the author's other example), a head shot, or the "shortest path" as determined by A*. After all, that is A*'s selling point... "it is guaranteed to return the shortest path if one exists." Congratulations... you inhumanly perfect. Therefore, as the author points out in his article, generating intelligent-looking mistakes is a necessary challenge. Thankfully, in later chapters of "Behavioral Mathematics..." I propose a number of solutions to this problem that can be easily implemented.
Anyway, I find it an interesting quandary that we have to approach behavior from both sides. That is, how do we make our AI more intelligent... and, how do we make our AI less accurate? Kind of an odd position to be in, isn't it?
Some of you have asked me questions about my new book, "Behavioral Mathematics for Game AI." The information that is on amazon and other retailers is not up to date. For one, there is no cover picture. There's a good reason for that. The cover is still being laid out and will be uploaded to the resellers soon. In the mean time, here's the cover art that I developed (click for a nicely detailed larger version).
The description text that you see on the resellers' sites is based on what I originally submitted to my publisher when I began the writing process. Things have changed a little bit since then. The following is likely what we are putting on the back of the book and will eventually be updated on Amazon, etc.
Human behavior is never an exact science. As a result, the design and programming of artificial intelligence that seeks to replicate human behavior is already an uphill battle. Usually, the answers can not be found in sterile algorithms that are often the focus of artificial intelligence programming. However, by analyzing why people humans (and other sentient beings) behave the way we do, we can break the process down into increasingly smaller components. We can model many of those individual components in the language of logic and mathematics and then reassemble them into larger, more involved decision-making processes.
Drawing from classical game theory, this book covers both the psychological underpinnings of human decisions and the mathematical modeling techniques that AI designers and programmers can use to replicate them. With examples from both "real life" and game situations, the author explores topics such as the fallacy of "rational behavior," utility, and the inconsistencies and contradictions that human behavior often exhibits. Readers are shown various ways of using statistics, formulas, and algorithms to create believable simulations and to model these dynamic, realistic, and interesting behaviors in video games.
Additionally, the book introduces a number of tools that the reader can use in conjunction with standard AI algorithms to make it easier to utilize the mathematical models. Lastly, the programming examples and mathematical models shown in the book are downloadable, allowing the reader to explore the possibilities in their own creations.
If you have any other questions about the book, feel free to ask! (And yes, it should be available at the Charles River Media booth at the Game Developers Conference next month. I'll be there quite a bit... flag me down!)
For those of you that have been wondering why this blog has been a little quiet in the past 6 months or why I haven't progressed on Airline Traffic Manager, I present to you my excuse...
My new book, Behavioral Mathematics for Game AI, is now available for pre-order on Amazon.com (and dozens of other resellers). Some of the details on the site are incorrect since the book is being finished up. As my publisher (Charles River Media/Cengage/Course PTR) updates their information (including art for a cover that we haven't even designed yet), the information at the resellers will be updated as well.
As it is scheduled now, the book will be available in mid-March. Thankfully, that means that it will also be on the shelf in time for GDC. Considering my role in the inaugural AI Summit, that will make for an exciting week for me.
Rather than the typical AI book which deals with the architecture of state machines and pathfinding, for example, I focus on behavioral AI. That is, what goes into a decision and how can we make those decisions more believable?
I begin by covering a lot of classical game and decision theory and explain how we can relate those examples into the video game world. I cover utility theory and marginal utility, how it manifests in the real world and how we can represent it in our AI agents. There's a healthy dose of technical material as well. There are chapters on constructing mathematical formulas and algorithms to help replicate behavioral patterns. Lastly, I offer solutions to prevent some of the problems that hamstring our AI agents. Throughout all of the book, I tried to make it an easy and even fun read. How often have you read a technical book that would keep you awake chuckling rather than put you to sleep with a headache? After all, we do program games, right?
All in all, it has been an enjoyable project that forced me to re-analyze things that we all often take for granted as AI programmers. I hope that you enjoy it as well.
Batman and Robin make an appearance in my Developer Discussion column at AIGameDev.com this week. In The Art of AI Sidekicks:Making Sure Robin Doesn’t Suck, I touch on the recent shift towards providing consistent, engaging sidekicks for the player. Certainly there are unique challenges in an AI agent that is so ever-present. To lift a segment from the column:
If we are going to have an AI that's tagging along behind us for hours on end, wouldn't it be better for us to love him/her/it? Let's face it, if you are playing 10 or 20 hours of game content, any form of repetitive AI may have you digging through the manual for scouring cheat codes online in order to find the "slap your sidekick upside the head" control. You can't simply get away with seven seconds... or even 5 minutes of believable behavior. Beyond that, the sidekick needs to be more than just something you are entertained and amused by. You need to be able to depend on it... as if it were your lifelong partner.
The ensuing discussion spurred many great comments. Take a gander at it and chime in with your opinion (or a solution?).
I was pointed to an interesting little observation/rant/commentary on the AI of FPS games on Blogo Profundo. Just a snippet heavily trimmed down to his main points:
I'm no expert here, so maybe one of my forty thousand readers can chime in, but these are just some problems I've noticed.
... Over the years, FPS's have definitely evolved both in graphics and mission complexity. ... One thing that has always been subpar however is the computer characters' AI.
... First criticism is that they tend to act as solitary agents, and don't usually form up into squads and act tactically like a rifle-team. There's no covering fire, there's no flanking, there's no suppression and calling in air-strikes.
... Second criticism is that even when they are acting as solitary agents, they're dumb as hell. They usually don't hear you, they don't make basic predictions about what you're likely to do, and they don't use the terrain to their advantage.
There's more to it than that. In fact, he asks some excellent questions of the development community. Certainly, the suggested solutions are a bit simplistic but it does show what I believe is the consensus of our audience... that they are grumpy about our lack of progress and/or dedication to realistic AI.
Ted Vessenes wrote a nifty little post on his blog where he compared designing and programming AI to being a parent. Here's the opening paragraph:
"Writing artificial intelligence is a lot like being a parent. It requires an unbelievable amount of work. There are utterly frustrating times where your children (or bots) do completely stupid things and you just can't figure out what they were thinking. And there are other times they act brilliantly, and all the effort feels satisfying and well spent."
I have to agree with a lot of the points he makes in his post. I would like to take the analogy one step farther.
I've occasionally made the point about both parenting and AI that your job is to not define what your progeny should do but convey an understanding of why. If, as a parent, you tell your child not to run in the street, they will hopefully carry that lesson into the future. However, they may not apply that same edict to driveways, parking lots or any other places where they could get plowed over by a car. This is analogous to the scripted AI methodology. However, if you explain the why of the situation - i.e. "be careful anywhere that cars are moving because the driver may not see you in time to stop and you could get badly hurt" - then the simple rule can be applied to any situation where there are cars (or even car-like objects). This, of course, maps over to rule-based systems or even planning systems.
However, going back to Ted's point, it is an interesting similarity to put all those rules into place and hope that your little bots realize the appropriate situations in which to use them. I actually wrote a column about this scary process on my weekly column over at AIGameDev.
Anyway, if you are an AI developer, I hope that you are blessed with many children who all grow up to be accomplished in their chosen lives (or deaths).
I noticed this GamePro blurb about the upcoming sequel to F.E.A.R. Here's an excerpt...
"The most obvious difference that will hit the player right away is in the visual density of the world," said Mulkey. "F.E.A.R. looked really great, but where F.E.A.R. would have a dozen props in a room to convey the space, Project Origin will have five times that much detail.
"Of course, this will only serve to further ratchet up that 'chaos of combat' to all new levels with more breakables, more debris, more stuff to fly through the air in destructive slow motion beauty."
OK... I can dig that. One thing I noticed as I played through F.E.A.R. is that things were kinda sparse. (I really got tired of seeing the same potted cactus, too.)
The part that I am curious about, however is this:
... Mulkey says improved enemy behavior is at the top of the list.
"We are teaching the enemies more about the environment and new ways to leverage it, adding new enemy types with new combat tactics, ramping up the tactical impact of our weapons, introducing more open environments, and giving the player the ability to create cover in the environment the way the enemies do," he says.
Now that is the cool part. When the enemies in the original moved the couches, tables, bookshelves, etc. it was cool... but rather infrequent. I was always expecting them to do more with it. If they are both adding objects to the environment and then "teaching" the agents to actually use those objects, we may see a level of environment interactivity that we've never experienced before.
The cool thing about their planning AI structure is that there isn't a completely rediculous ramp-up in the complexity of the design. All one needs do is tag an object that it can be used in a certain way and it gets included into the mix. On the other hand, having more objects to use and hide behind does increase the potential decision space quite a bit. It's like how the decision tree in chess is far greater than that of Tic-tac-toe because there are so many more options. The good news is that the emergent behavior level will go through the roof. The bad news is that it will hit your processor pretty hard. Expect the game to be a beast to run on a PC.
I certainly am looking forward to mucking about with this game!
I happened upon this blog entry by a reviewer of the new Far Cry 2 by Ubisoft (note, not Crytek). I include this paragraph here but please visit the blog for more information.
Ubisoft also makes some very grandiose claims about Far Cry 2's AI, which makes me far more leery than any promises of beautiful graphics or realistic physics. Every game I've seen that promises realistic artificial intelligence has fallen short. It's not about bad AI, but more about developers making promises they can't back up. According to Ubisoft, Far Cry 2 will sport complex, nonscripted artificial intelligence that has enemies and NPCs reacting to personal needs. I've heard that enemy soldiers will seek shade when it's hot, take breaks then they're tired, and seek out food when they're hungry. Combine these claims with a sprawling world and I find myself having flashbacks of the buildup to The Elder Scrolls IV: Oblivion. Bethesda Softworks promised some amazingly realistic behavior in its NPCs, but it didn't quite make it. The game was still very good and its characters occasionally showed glimpses of intelligence, but it didn't live up to the hype. I saw an enemy medic pick up a wounded soldier to carry him to safety in Far Cry 2 and was impressed by the action, but until I play the final game myself and see that sort of behavior manifest consistently, I'll take the promises of AI with a generous spoonful of salt.
I seriously agree with the skepticism. One thing that Far Cry 2 has going for its AI is that Crytek is not doing it. Far Cry had gaping holes in it and Crysis continues that trend (see my observations on Crysis at Post-Play'em.). That being said, I would seriously like to see the claims come true, of course. Anything that advances the technology of autonomous agent-based AI is cool with me.
, is now available for pre-order on Amazon.com (and dozens of other resellers). Some of the details on the site are incorrect since the book is being finished up. As my publisher (Charles River Media/Cengage/Course PTR) updates their information (including art for a cover that we haven't even designed yet), the information at the resellers will be updated as well.
