First Person Shooter Artificial Intelligence

1. First Person Shooter Artificial Intelligence Xavier Otero Keil

2. Four Layered AI • Animation • Control characters body • makes sure that animation fits situation • handles requests to perform actions • Combat • Possibly most important subsystem • Determine tactics • Behavior • Highest level, has precedence over other systems • Sets broad goals like a CEO • Movement • Determine how to move (path finding) • Not where to move

3. Animation Controller • Plays pregenerated animation mostly • Some animations take control of entire character such as dying • Others require only a specific part • Arm waving • Head turning • These are more complex because more than one can be applied at one time • Needs to be aware of which animations are playing (if currently arm waving stop before attacking) • Gathers information from other Layers

4. Animation Continued • Generation of context related animations on the fly. • Generalizing the position of objects. • Causes problems with believability. • Modern games do not take this shortcut • Solution similar to robotic arm movement

5. Movement • Basically a path finding system • Given a starting point uses a database of how the level is laid out and the A* search • Dynamic obstacles create a problem • http://www.youtube.com/watch?v=UZf89ejZavc (example of bad dynamic obstacle handling) Quake 2.

6. Local Path finding • You can use Local path finding to solve this problem • Integration of physics system and movement system • Uses global path finding as a guideline then polls the physics system for dynamic obstacles and adjusts accordingly • Crysis with local path finding turned off http://www.youtube.com/watch?v=FA6SYhFHS6M

7. Combat • Spatial Reasoning • Humans are very good at this almost second nature • Most games embed hints for the AI into the levels like the anchors in Far Cry • This creates a tactical database that allows the computer to simulate an understanding of Spatial Reasoning • Again problems with Dynamic Obstacles

8. Combat Continued • Solved with geometrical analysis. • Uses a lot of processor power • Dynamic object tagging • Changing Battle Environments • http://www.youtube.com/watch?v=pWyoQoEgPBA&NR=1 (Crysis Nuke Gun)

9. Combat Tactics • Very basic selection of combat tactics • Camp • Joust • Circle of death • Ambush • Flee and ambush • Generally a FPS will have far more tactics in its arsenal. However these basic ones give insight into how the tactical selection is done

10. Firing • To-hit roll random number • If in the hit threshold attempt to hit • Otherwise attempt to miss • With high damage weapons always miss first shot • Takes into account environmental variables • Prevents perfect accuracy which can be frustrating

11. Where to shoot • When attempting to hit • Angle of animation does not have to match angle of shot • Most games use bounding boxes for collisions with bullets and other objects • Choose random point near the center • When attempting to miss • Shoot too close to the target could possibly hit • Too far away AI looks stupid • Want shot to be visible and audible. Alert player to enemy presence and create feel of tension • Some games place invisible markers in player character models of good places to shoot at in order to miss • Always test shots (ray-testing)

12. Friendly Fire • Makes the AI look really bad if it happens too often • Use ray-testing to avoid this • Sometimes it can be used as a player reward • Player dodges out of the way so a rocket launch hits an enemy behind him • In this situation auditory acknowledgment by the offending NPC is a good idea “Ohh **** sorry Hank” • Some games solve this problem by simply not accepting damage from friendly fire. This is a poor solution, if it becomes obvious players feel cheated

13. Firing Continued • If a hit is necessary use dead reckoning • Can produce over accurate fire • Radius testing is a another way • Projectiles should report back to the AI

14. Searching for the player • Should be range of searching behaviors • Not sure player is even in the search area (Idle searching) • Maybe the player is there (normal searching) • Sure the player is there (intense searching) • Multiple Paths • Low efficiency searches

15. Idle searching • Wander about aimlessly or follow a set patrol schedule • Should not use the players location in calculations at all as this is usually detectable by the player • If the player is seen do not immediately drop into combat unless the player is very obvious or firing at you • http://www.youtube.com/watch?v=3nzMdPwO2Qw

16. normal searching • NPC has caught a glimpse of the player • Should scan the area where it “saw” the player and then give up after a short time • Should immediately drop into combat mode if the player is seen in this stage • At this point upholstering of weapons or unsheathing of swords is appropriate

17. Intense searching • This should be activated if the NPC sees the player go somewhere where there is no escape or has attacked or been attacked by the player • At this stage for believability the NPC should not give up until it finds the player or a very large period of time has elapsed. • Games where the give up time is too low seem unrealistic. • Should use actual player location in calculations but add a randomness factor so the NPC does not make a bee line to the players location.

18. Stealth • Sensory Perception • Darkness levels and sound levels • Alertness levels • Auditory cues • Thief 3 http://www.youtube.com/watch?v=9sSICYp8ssI • Perceptual Modeling • Visual • Auditory • Tactile • Increasingly all first person shooters are employing stealth elements for believability

19. Behavior • High Level command issuer • Chooses between states such as Idle, Patrolling, Combat, Searching etc… then notifies the other layers of what they need to do. • Generally a Finite State Machine • Very important for believability especially in idle and combat modes • Often times uses triggers in order to choose a state.

20. Teaming UpWith the Player • Has become very popular in recent years • When done well highly increases the immersion of the player • What the AI needs • Follow commands • Not get in the way • Follow logical rules • Interact with the player • Survive until the end of the game

21. Correct Movement • Generally stay out of field of view • Prevents friendly fire and view obstruction • During points of non combat teammates should occasionally appear in the field of view to reassert that they are there • Use auditory cues during combat for this same purpose

22. Correct Movement Continued • When there are multiple targets there are two options for staying out of the players field of view. • smallest angle • viewing angle

23. More on Movement • Should be maximum distance set that the NPC’s can wander away from the player. • Let the player be the hero • take no risk unless ordered to • Don’t be first through doors, choke points, over hills etc… • Generally good practice to match the player’s actions. • Many games “cheat” • Rainbow Six Vegas • Match player speed to avoid annoyance

24. Player is important • NPC’s should be secondary to the player • Should never perform better than the player • Select weapons that are similar or less powerful than the players weapons • Always allow the player first chance to collect items • Should report all sightings of enemies before attacking unless currently under attack http://www.youtube.com/watch?v=yxQ-09OcIP0

25. Enemy Teams • All these rules can apply to enemy teams as well • One NPC should be team leader and treated as the player • Mimics normal team dynamic

26. Thank You