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The Hitman And Individual AI Personalities

Musings on different AI "personalities" and reactions inspired by the Hitman Absolution gameplay video.

(This article is a repost from my personal blog at www.gamearch.com - visit that site for other posts and discussion)

So, I’ve seen that 17 minute Hitman Absolution walkthrough of the library level. It basically shows what looks like most of one level and Agent 47 expertly evading the police that’s on his tail. Now that gameplay section looks well crafted and interesting but what stuck out to me, in a good way, was the NPC dialogue that features prominently. In case you haven’t seen the video, here’s the YouTube version.

So in the video you can hear a lot of the policemen talking while the player hides in the shadows. That’s nothing uncommon in games with a stealth focus. Be it Splinter Cell or Deus Ex, if you’re quiet you can overhear some conversations and learn more about the world. That serves as a pointer that these guards are busy and can be surprised and a sort of reward for the careful player. However these dialogues usually consist of two henchmen/mercenaries standing around talking about the setting world. In a few cases they might even mention some details in the game world that a careful player could pick up on. And that’s pretty much it, a sort of water cooler talk between hired guns working for the bad guy.

However the NPC barks in this gameplay demo seemed to be doing much more than that. Without knowing what the actual mechanics behind the Hitman AI system are there are some obvious differences in their behavior from which we can infer some ideas, maybe if not for this game then for another one. So, what was different?

For starters, the dialogue seemed to encompass large parts of the scene. Clearly not every policeman or NPC had his own set of lines but it felt like the group was talking on a scope beyond a water-cooler talk. This is doable because the entire group operates on a script that is probably kept until the player triggers an alarm or something similar. This makes the entire scene seem a lot more realistic and (dare I say) cinematic.

In the scene from the video what comes up most prominently is the conflict between the boss policeman and the rookie. The former is being quite a hardass to the latter while generally having only very little patience. Later in the video when Agent 47 takes a policeman hostage and the boss orders his team to open fire after only a short time. This seemed entirely in character for the boss with a temper and my brain made a connection between the two events:

Individual AI personalities

From http://www.flickr.com/photos/35638902@N02/4403123217/sizes/z/in/photostream/

Now as said, I’m not sure if this is being done in Hitman but the idea it might be worth some thought. Imagine a game where individual NPCs have different AI personalities: some with more patience while others might be angrier. And then expose those personalities to the player through their dialogue. So when interacting with them the player can infer what their reactions could be based on his observations. Of course this only makes sense in a game where you actually spend time observing characters and where their actual behavior in response to your possible actions matters. Stealth games would be particularly suited to this as the personalities might make some actions harder or easier.

This requires a certain “personality” model that is based on the possible actions of the player. It makes little difference whether a grizzled mercenary has a romantic streak or likes to collect stamps in his spare time when this is unlikely to affect his behavior in response to the player. More obvious character traits would be patience, aggressiveness, caution, courage etc. Of course you could differentiate it even more and actually build relationships for NPCs, so someone might react more strongly if the player killed or kidnapped their best buddy.

Now for all this work to make any sense the personalities and results need to be communicated to the player. This means that characters have to be painted with broad strokes so players quickly understand who they could be and see the differences in their reaction. It might be worth the work though, as it adds another layer to gameplay that is based on the player's empathy. That plus the fact that I'm sure this will contribute to the believability of your virtual world.

So which game will be the first to implement this?

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