First Person Shooter Artificial Intelligence - PowerPoint Presentation

Slide1

First Person Shooter Artificial Intelligence

Xavier Otero Keil Slide2

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 moveSlide3

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 LayersSlide4

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 Slide5

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.

Slide6

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=FA6SYhFHS6MSlide7

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 Slide8

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)Slide9

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 Slide10

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 frustratingSlide11

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)Slide12

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.

T

his is a poor solution, if it becomes obvious players feel cheatedSlide13

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 AISlide14

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 searchesSlide15

Idle searching

W

ander 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=3nzMdPwO2QwSlide16

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 Slide17

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. Slide18

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 Slide19

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. Slide20

Teaming Up

With 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 Slide21

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 purposeSlide22

Correct Movement Continued

When there are multiple targets there are two options for staying out of the players field of view.

smallest angle

viewing angleSlide23

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 annoyanceSlide24

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-09OcIP0Slide25

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 dynamicSlide26

Thank You