Contest: Capture The Flag

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Contest Capture The Flag

• Martin C. Martin
• with Jon Klein

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Capture The Flag

• 10 agents per side
• If you touch the enemys flag, you pick it up
• The first team to bring a flag to the center line
  wins
• You cant pick up or move your own flag
• If you touch an enemy on your side, they go to
  jail
• If you touch an enemy on their side, you go to
  jail
• If one of your agents touches the enemy jail, all
  your agents are released, placed randomly on your
  side

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Basics of Agent Based Simulation

• Time is broken into discrete segments called
  timesteps
• 0.05 sec long for the capture the flag tournament
• At each timestep, breve calls every agents
  iterate method
• This is what you write
• In breves Capture The Flag, this simply decides
• The speed of each player
• Whether to turn right, left, or not turn at all

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breves Main Loop

• At each timestep, breve
• Computes all sensor values (e.g. who is touching
  who who has the flag etc.)
• Calls each agents iterate method
• Moves every agent according to its speed and
  heading
• Draws the graphics

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Available Information

• get-id-number an int from 0 to 9.
• sense-my-team list of agents on same team in
  sensor range.
• sense-other-team list of other teams agents in
  sensor range.
• sense-my-flag agents teams flag, if in sensor
  range
• sense-other-flag other teams flag, if in sensor
  range.
• sense-my-jail jail where team is held, if in
  sensor range.
• sense-other-jail jail where other team is held,
  if in the sensor range.
• get-my-home-location closest point to agent on
  agent's home-side.
• get-angle to location angle to location in
  radians
• get-location the location of any object, a vector

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Available Info/Actions

• Information
• get-time current time in simulated seconds
• get-jailed-red-count the number of Red agents in
  jail.
• get-jailed-blue-count the number of Blue agents
  in jail.
• Action
• turn-left Turns the agent left by a small amount
• turn-right Turns the agent right by a small
  amount
• set-speed to speed Sets speed of agent to speed
  units.

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breves coordinate system
25
x axis
-25
25
-25
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Heading To A Given Location
desired
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Demonstration
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A Taste of Bot AI in Unreal Tournament 2004

• All written in UnrealScript, very similar to Java
• If you can read C or Java, you can read
  UnrealScript
• AI code consists mostly of if statements to
  select between competing objectives

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OrdersForFlagCarrier

• function bool OrdersForFlagCarrier(Bot B)
• if ( B.Pawn.Health lt 40 )
• B.TryCombo("xGame.ComboDefensive")
• else
• B.TryCombo("xGame.ComboSpeed")
• if ( !FriendlyFlag.bHome (FriendlyFlag.Holder
  
• None) B.LineOfSightTo(FriendlyFlag.Positi
  on())
• (VSize(B.Pawn.Location -
  FriendlyFlag.Location) lt
• 1500.f) GoPickupFlag(B) )
• return true

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OrdersForFlagCarrier

• If my health is lt 40, try a defensive combo,
  otherwise a speed combo
• If my flag isnt at its base, and nobody is
  carrying it, and I have line of sight to the
  flag, and Im within 1500 units, head toward it
• If my skill level is gt 2, and Im not within 2000
  units of the friendly flag, and there is a super
  pickup within 800 units that hasnt been taken,
  head toward it
• If Im being attacked and my health is lt 60,
  broadcast a need backup message
• Head to home base

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CheckSquadObjectives

• If my flag isnt home, and I have line of sight
  to it
• If nobodys holding it, head toward it
• If Im not attacking the flag carrier, then call
  FindNewEnemyFor(B)
• Broadcast Enemy flag carrier is here if its
  been at least 6 seconds since the last time
• If Im not sniping, TryToIntercept the enemy flag
  holder, assuming theyre heading to their base

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Information Used In If Statements

• Health
• What I have line of sight to
• Orders attack, defend, follow, freelance,
  sniping
• My skill level
• Status of flags at base, being carried, dropped
• Whether I need a weapon
• Whether pickups are nearby
• Am I attacking/pursuing someone?
• Times when I respawned, when flag was taken, how
  long its been since Ive seen the enemy Im
  trying to pursue
• Distance to various things (flag, my base, enemy
  base, etc.)
• Whether youve just reached a desired location

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Tactical

• Programmer can define states for an object
• Can override functions within those states
• Bots have states RestFormation, MoveToGoal,
  Roaming, Retreating, Charging, StakeOut,
  RangedAttack, etc.
• state Charging extends MoveToGoalWithEnemy
• function bool TryToDuck(vector duckDir, bool
  bReversed)
• if ( FRand() lt 0.6 )
• return Global.TryToDuck(duckDir, bReversed)
• if ( MoveTarget Enemy )
• return TryStrafe(duckDir)

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Contest A Few Last Things

• Submission a single text file, containing a
  subclass of CaptureTheFlagPlayer
• breve has no notion of data hiding all fields
  are public.
• Call only the functions listed in the rules.
• E.g. calling move on agents other team or yours
  is cheating.
• Two conditions
• Best performance (i.e. wins largest percentage of
  games)
• Most creative
• Prizes book and/or T-shirt

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Sharing your source code

• We encourage people to share source code, to
  learn from one another, and to bounce ideas back
  and forth
• If someone submits a modified version of someone
  elses code, then both will win the same prize
• As long as the change is substantial, decided
  primarily on ability to win
• Maximum 2 prizes per condition
• Join us on the breve forums!