AI Bot for

First Person ShootersJoão Carlos Gonçalves

jcgonc@student.dei.uc.pt

OMNI-BOT - Resume• Bots• Resume Omni-Bot• Game functioning,• Framework• Agent structure,• Goals• Society and interaction between agents,• Waypoints and traversal,• Manual routing,• Scripting,• Problems and scripting,• Conclusion

What’s a bot? Everyone who has played a

computer game has encountered a bot.

Computer controlled game player.

Computational equivalent of a ‘robot’

Bot Agent

Why bots? Fill a game with more players.

Help humans to train.

Execute tasks boring for us.

Etc.

OMNI-BOT

Framework implementing bots in FPS Games supported:

Wolfenstein: Enemy Territory, Doom 3, Quake 4, Fortress Forever, Return To Castle Wolfenstein, Team Fortress 2

“BDI” agents, internally state machines. Oriented towards completing goals while sensing their environment.

Not ALL games fully working (currently).

Best implementation on W.E.T.

Enemy TerritoryEnemy Territory- Resume -- Resume -

Comprised of various environments (maps) usually set in WW2, with different goals (frequently contradictory) for the factions.

Two factions: Allies and Axis, equal in characteristics, spawning in pre-determinated locations.

Five classes: Soldier, Medic, Engineer, Field Ops, Covert Ops, each one with it’s advantages and disadvantages.

Wolfenstein – Enemy TerritoryWolfenstein – Enemy Territory- Goals -- Goals - Goals like stealing vehicles, escorting or not allowing them to move, destroying or constructing entities, healing and reviving teammates, etc.

Completing goals may create contradictory goals on the opposing faction.

Game development may also create or delete goals, possibly specific for some faction.

Show Demo.

Wolfenstein – Enemy TerritoryWolfenstein – Enemy Territory Limbo, with map’s goals for allied faction:

Wolfenstein – ET : MODsWolfenstein – ET : MODs SDK for changing game logic available

Various game modifications (mods) with different game plays:

ETPub

NoQuarter

ShrubMod

ETPro

Jaymod

True Combat Elite

PowerBall

etc.

Installed on the game’s directory

OMNI-BOT

Independent ‘Library’ installed on ET’s folder (usually “omni-bot”) “omnibot_et.dll has the implementation

“qagame_mp_x86.dll” = server side engine (game logic)

“cgame_mp_x86.dll” & “ui_mp_x86.dll” = client side engine and graphics (client side logic and corresponding graphics)

“Omnibot_et.dll” linked by the running mod (must support omni’s interface)

mod initializes omnibot and bots are connected to the engine as clients (like players)

supported mods: ETPub, Jaymod, NoQuarter

OMNI-BOT - agent structure List of goals, with execution states, positions, priorities and availability

Sensory memory, with list of attractive entities, like enemies or ‘aimable’ things.

Available weapons, with their preference and firing parameters.

Motor Control, executing the path following algorithm as well as the aiming mechanism.

OMNI-BOT - agent structure Simplified version of a BDI agent

Beliefs = Stored on sensory memory

Desires = List of goals

Intentions = desire selected for execution, being performed

Basically a state machine (deterministic finite automaton, DFA)

OMNI-BOT - State Tree

•Show bigger state tree

OMNI-BOT – Agent’s behaviourif(incapacitated) {

do {for(medic:team.medics) {

evaluation = avaliate(medic.proximity);}evaluation = avaliate(timer.spawn);decideRespawn(evaluation);selectEquipment();

} while(incapacitated);} else {

updateSensoryMemory(world.getNeighborhood());// additional behaviour scriptsexecuteScripts();selectEquipment();goal = getHighestPriorityAvailableGoal(); // goal may include alternative routepath = computePath(goal);// wait for world eventswhile(not(world.changed)) {

waypoint = nearestWaypoint(path);motorControl.setDestination(waypoint);if(near(waypoint)) {

do {execute(goal);

} while(not(executed(goal)));}

};};

• Simplified algorithm for bots' behaviour. Actually implemented in parallel threads, like path following, enemy aiming and firing, sensory information, etc. (external scripts)

OMNI-BOT – Agent’s behaviour

• Executed on each server frame (usually 20 per second, server side cvar “sv_fps”)

• ‘Threads’ and execution details on Debug’s window, section profiler

OMNI-BOT - Goals Retrieved from the map’s script and bsp’s entities

Following example: destroy ‘Side Door’, for axis

OMNI-BOT - Goals Example of map goals:

x: “goal” -> |bitflag| serial |y| priority |z|

bitflag specifying allowed team (axis, allies);

serial = internal goal identification;

priority = goal priority (relating to others).

and more properties

OMNI-BOT - Society By default goals are shared by different agents (excluding some cases).

If not, the goal is assigned by the framework to some agent (actually, first come, first served).

An agent may require support from others (ammunition and health / revival). In this case, it creates a specific goal (like ‘heal me’).

No negotiation of goals between the agents.

Individual behaviour

OMNI-BOT - Waypoints Goals are reached by following paths

Paths created using waypoints

Directed graphs (typically cyclic)

Diagonal descending edge = connection direction

OMNI-BOT - Waypoints

Travelling properties (flags):

Crouch, prone, sprint, walk, jump, route, radius, etc.

radius of waypoint affects path cornering

waypoint flag affects bot‘s behaviour when it’s approaching the node or when reaches it’s radius

OMNI-BOT – Path travelling

Uses Dijkstra's algorithm for waypoint selection

Essentially uses the shortest path from the source (where the agent selected the goal) to it’s destination (where goal resides or next route point if used)

OMNI-BOT – Routing Path travelling easily expected

Boring for humans

Solution = Manual routing

Basically a human ‘codes’ different paths for different map traversal

Goal X = travel through waypoint 1, then 2 OR 3, then 4, etc. until reach destination

Define waypoint selection probability

Route is chosen when goal acquired near ‘first’ route waypoint.

OMNI-BOT – Routing

If ‘goal’ got when at ‘spawn’ waypoint, choose next waypoint from A, B or C, with probabilities of 2, 1 and 0.66. Calculate shortest path to chosen route point and travel the path;

When arrive to A or B, travel shortest path to ‘goal’s waypoint;

If chose waypoint C and reached it, choose B or D (with corresponding probabilities) and calculate shortest path to ‘goal’. Then travel it.

From ‘SPAWN’ to ‘GOAL’:

MapRoutes = { GOAL = { ROUTE_SPAWN = { ROUTE_A = {Weight = 2.0,}, ROUTE_B = {}, ROUTE_C = {Weight = 0.66 ROUTE_B = {Weight = 0.5} ROUTE_D = {},},},},};

OMNI-BOT – Scripting Written in GameMonkey language

Add functionality to goals, maps, weapons, bots, utils, etc.

Goal scripts: Tells or helps the bot how to achieve some goal (map or another);

Map scripts: Control the logic of the map, like enabling or disabling routes and goals (for instance according to the game’s progress);

Weapon scripts: Configure how to use and handle some weapon or item

Bot scripts: Stores a behaviour which can be associated to some bots.

Utils: implement some usefull functions for been called in other scripts.

OMNI-BOT – Map scriptsGoal script example: goal_askforhealth.gm

this.GetPriority()

if my health < threshold and I’m alive (me, the bot) then

increase this goal’s priority

get nearest health pack

if no pack near, and my team has medics, request medical support

this.update()

if acquired pack, get pack’s position, aim towards it and try to acquire the pack

OMNI-BOT – Goal scripts

Goal script example: bunker.gm

Store the logic of the map (the bots don’t know the goal’s dependencies as well as their importance)

• If objective taken → leave the stairs and attack the radio;

• If objective returned → leave the radio and attack the stairs;

• On map start → start attacking the stairs, forget the radio;

OMNI-BOT – ProblemsHuman waypointing, quite boring. Done manually. Detailed waypoints take time as well as routing them.

Proposed navigational mesh, detailed version of waypoints, but with the problem of the mesh resolution.

OMNI-BOT – Problems Can’t plan a sequence of intentions; No objectives negotiation between agents (assigned FCFS); Objectives are not assigned to the nearest agent; Human coded intentions’ order and priorities; Don’t ‘learn’ the best paths (currently and in the past); Don’t predict (and learn) actions taken by others (cooperation and synchronization); …

OMNI-BOT – Referencehttp://www.omni-bot.com/wiki/index.php?title=Main_Pagehttp://en.wikipedia.org/wiki/Wolfenstein:_Enemy_Territoryhttp://www.omni-bot.dehttp://www.gamasutra.com/gdc2005/features/20050311/isla_01.shtml

OMNI-BOT – Questions

Tuesday, 16 December 2008