AI is A-OK in new games

Our video-game enemies are smart — and getting smarter. The artificial intelligence that guides in-game characters today leads to far more natural actions and realistic friends and foes than in the past. "As graphics improvements top out, artificial intelligence will (drive) game innovation," says University of California-Santa Cruz professor Michael Mateas. A look at AI evolution:

Halo 3

Players will notice more enemies aiming to thwart the Master Chief — and more artificially intelligent marines to help him along in this new campaign.

Where battlefields in previous Halo games might have had 15 or so combatants, Halo 3 will feature as many as 40 enemies and allies fighting intelligently. Typical Halo 2 enemies or squad mates had at most about 50 behaviors; in Halo 3, programmers have upped that to as many as 70. Each character has more rules attached to each behavior — up to 10,000, compared with 10 in the past.

The computer-controlled characters use their AI brains to calculate all these rules in milliseconds just as humans' can, and their actions are harder to predict. In the past, a Covenant "brute" (an alien attacker) would likely seek cover when you fired on him. Now the enemy can deploy a bubble shield, hold its ground, assess the situation and perhaps find a method of attack.

Microsoft, out today, for Xbox 360, $59.99, $69.99 limited edition, $129.99 Legendary Edition with Spartan helmet case. Rated M (mature) for ages 17 and older.

•Developer comment:"The interaction of all those rules is absolutely unpredictable," says Dàmiàn Isla of developer Bungie. "There is simply no way that I as a programmer can predict what is going to happen next. What we get is 'emergence,' one of the holy grails of AI: some really complex, interesting results out of very, very simple rules."

Enemy Territory: Quake Wars

The Earth-invading Strogg are id Software's craftiest enemies yet, having evolved from basic hunters with a limited understanding in Quake II into tactically aware combatants who might use disguises, are aware of their teammates' status, can revive them and instantly begin a retaliatory response.

Your computer-controlled "bot" teammates are just as smart and will aggressively provide cover for you rather than simply act as escorts. Playable as an online multiplayer game, Quake Wars also has enough AI capacity to let you simulate an online game offline, pitting you and 15 AI teammates against 16 AI opponents. Choose what class you want to play as — soldier, field ops, medic, covert ops or engineer — and the game automatically fills out the rest of your squad. (Players can also play as the Strogg.)

Previous id games could devote no more than 10% of the hardware's processing power to AI. Now that PCs and game systems have multiple processors, nearly an entire processor can be dedicated to handling AI.

Developer comment:"The more processing power you have to allocate to AI, the more time you can have (AI characters) thinking about interesting tactical actions," says John Dean, id's artificial-intelligence programmer.

Activision, out Oct. 2, for Windows PC, $50, $60 for limited collectors edition, also in development for PS3 and Xbox 360, rated T (teen) for ages 13 and up.

Call of Duty 4: Modern Warfare

In 2005's Call of Duty 2, the last game developed by Infinity Ward, the Nazis were your World War II enemy. This new game is set in the present day with two foes: ultra-nationalist Russians and a Middle Eastern army.

That means players and the AI enemies have access to more advanced weaponry and vehicles. The amount of processing power and memory capacity devoted to the AI alone in Call of Duty 4 is equal to the horsepower needed to run all of Call of Duty 2.

Foes are more likely to act of their own accord, choosing between weapons and tactics, whereas enemies in Call of Duty 2 were scripted to use certain weapons. Players can choose their own path, perhaps retreating rather than simply charging on.

Your troops are smarter and will reward proper tactics. Previously, if a player charged into an unsafe firefight, his band of brothers charged right along. Now, they will analyze the situation and may decide to hold their position, letting you suffer the consequences.

Developer comment:"It makes for a much more dynamic playground of battle," says Jason West, an Infinity Ward studio head. "You can try different things and the enemies will counterbalance you, and you and your friends then must counterbalance them."

Activision, out Nov. 5, for Xbox 360 and PS3, $59.99, for Windows PCs, $49.99, rated M.