FIRST PERSON SHOOTER ARTIFICIAL INTELLIGENCE

Xavier Otero Keil

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

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

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

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=UZf89

ejZavc (example of bad dynamic obstacle handling) Quake 2.

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

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

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)

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

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

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)

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

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

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

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

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

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.

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

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.

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

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

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

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

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

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

Thank You