"In general, I think game AI has gone from the stage where it was an achievement if it did not stand out negatively to the point where AI in most big games is solid, and some titles are using innovative new ideas. More development teams have also moved from simple state machines to behaviour trees and using planners in NPC AI systems describing knowledge of the world around the NPCs have improved with better knowledge for navigation over changing terrain, and more knowledge about strategic properties of the world such as cover. I also think advances in animation systems with better ways to combine various animations and physics have become available, which now allows for more realistic movement and responses to being hit [in combat AI]. Most of these systems were not around 10 years ago or simply could not run on the hardware available."
The terrain-reasoning systems we generate have also evolved over our various titles. We are now able to deal with much more dynamic terrain (like obstacles moving around or changing shape) than ever before. Our data on where there is cover has also become more detailed, something that allows NPCs to deal with more complex environments such as multistory buildings, etc."
Back when Straatman and Guerrilla began work on Killzone and Shellshock, the team’s goal was to make the AI system as capable of making its own decisions as possible, realising this would make things all the more fun for players. However, doing this in a consistent way proved to be a lot more work than the team anticipated, particularly when dealing with combat AI. While the goal of normal AI is to emulate the real-life behaviour of a particular nature (for example, doctor, civilian, or shopkeeper), combat AI works very differently. Firstly, its main objective is to be as entertaining as possible. In some cases this means being efficient at killing players; in other cases, it's more about making intentional mistakes and "overacting" by way of signalling to players what is about to happen.
According to Straatman, the area that needs most improvement in the game AI field is buddy AI. Because buddy AI systems often have contradictory constraints, getting this system right is often a big challenge: the buddies should be visible and close to the player but not get in his line of fire; they should stay close and respond to the player movement but not move around all the time; and so on. Buddy AI is also much closer in view to players than enemy AI, making any errors easier to spot.
"Enemy NPCs know what other NPCs of the same faction are going to do because they are all computer-controlled and can tell each other what they will do next. However, players are much harder to predict--if you would look at movement patterns of players, you will see they are quite strange at times. This is made worse by the fact that player turn rates, movement speeds, and acceleration are very high. The last point is the expectation of the player: enemies are only supposed to shoot at you, whereas buddies are supposed to fight and interact with you in a sensible way. We are working hard to make the buddies work better, because we feel that they can add a lot to the player experience when done right."
Straatman believes the struggle to make NPCs as human as possible is still very much at the top of the list for many AI programmers, with the future set to change the way we think about in-game interaction.
"The ideal is always to immerse the player in the game: the NPCs should feel like they are living and breathing creatures, and this illusion should not be spoiled anywhere. Within the relatively limited interaction you have in a game, it may be achievable to make the distinction very small. I think human behaviour is so interesting, and yet subtle interactions such as conversations are still out of reach of autonomous AI; games rely on clever scripting or cutscenes to get that across. If we as a field will master these types of interactions, more parts of the game can be interactive, and possibly whole new game genres may become feasible."
