ScrimismsPresently suffering a dearth of witticisms
A.I. and Games and Musings04 Dec 2005

I’ve been thinking about game AI lately. I suppose this is natural: I like games, and I like AI.

I recently played through Halo single player and was fairly impressed by the enemies. Enemies run for cover, try to flank you, dodge your grenades, retreat when wounded. Having written a little game code now and again, I can appreciate how hard it is to make AI characters move around the game world in an intelligent way, let alone do the things the Halo enemies do.

I found this neat talk given by some of the Halo AI programmers. One of the things that they stressed was that it is less important to make an unbeatable AI and more important to make an understandable AI: The player should be able to tell why the AI character did what it did.


From the article:

In Halo the Grunts run away when an Elite is killed

Initially nobody noticed so we had to keep adding clues to make it more obvious
By the time we shipped we had made it so not only does _every single_ Grunt run away _every single_ time an Elite is killed but they all have an outrageously exaggerated panic run where they wave their hands above their heads

  • they scream in terror
  • and half the time one of them will say “Leader Dead, Run Away!”
  • I would still estimate that less than a third of our users made the connection
  • I think this is an important point, and it’s one that is fortunately not lost on a lot of game developers. Another game I’ve been playing lately is Robin Hood: Legend of Sherwood, in which Robin and his Merry Men spend most of their time trying to outwit the Sheriff of Nottingham’s various guards and soldiers. Like Halo, the AI soldiers have a lot of dialog that is triggered based on what they are doing and thinking. The designers even went a step further and added a little animation above the head of each soldier to tell you his mood. For example: when a squad of soldiers spot something that interest them (like a coin purse or a flagon of Ale that you left in their path), the following happens: They stop walking. Spinning question marks appear above their heads for a few seconds while realization dawns on them. The question marks are replaced by bright “sun” icons to indicate excitement, and they shout things like “Hey look! A coin!”. They all rush in and start collecting the loot. However, as money is quickly scooped up by their pals, the “sun” is replaced by a “storm cloud”. Often a brawl ensues, with shouts of “That’s mine!” and “Hands off the money, squadie!”. My favorite is when a sergeant comes along and sees this. He chastises them, and they quickly become contrite, helping fallen comrades to their feet and offering excuses like “We were just having a little fun” and “I was only showing him a new move”.

    The behaviour is a little complex, but it’s not that complex. What makes it easy to appreciate is how overtly the machinations of the soldier’s brains are conveyed to the player.

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