Half life 2/ Counter Strike: Source bot

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Half life 2/ Counter Strike Source bot

• Charlie Cross
• CIS 488
• 2-14-05

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Background

• Counter Strike is a multiplayer modification for
  Half life, released in June of 1999.
• Valve software hired the counterstrike team and
  ported Counter Strike to their new Source engine.
• Outsourced a spin off single player product-
  Counter Strike Condition Zero.
• Ended up being finished at Turtle Rock Studios.

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Background (2)

• Turtle Rock developed artificial intelligence for
  condition zero.
• AI was ported to CS Source last month.

4
AI features

• Navigates map using automated systems (waypoints)
  combined with human teaching (navigation meshes).
• Communicates with human players, telling them
  where enemies are located.
• Follows human instructions (e.g. follow me, or
  team fall back)
• Selects best weapon for tactical situation.
  Avoids tactically disadvantageous situations.
• Conveys range of emotion-driven behaviors. Rushes
  aggressively when winning or retreats when
  outnumbered.

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Navigation Meshes
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Navigation

• Use of nav meshes allows bots to be less
  predictable and to use less structured behavior
  the way humans do.
• A pathfinding.
• Uses reactive obstacle avoidance (like the quake
  bots) To avoid crashing into walls and other
  objects.
• Monitors average velocity to detect when the bot
  is stuck, then uses a random wiggle to try to
  jerk free. (I have never seen this happen)

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Using the tools to build paths. (Source Mike
Booths presentation at GDC)
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Using and viewing the environment

• Nav meshes include hiding spots that are
  labeled by the programmer.
• When retreating or camping the bot will find a
  hiding spot to ambush the opponent.
• Looks around smoothly and avoid jerky movements.
• Looks around corners and checks openings.

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Tactics
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Tactics and Bot emotions

• Nav Areas hold a danger value.
• Increased danger means increased cost (A)
• This forces bots to change routes.
• Danger values are increased when bad things
  happen (such as team mates dying)
• Morale determines level of aggression.
• High morale Bot is on winning team, bot is
  killing enemies.
• Low morale Bot is on losing team, bot is killed,
  hurt.

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Combat and Weapon selection

• Since it is a rule based system, there are an
  elaborate collection of rules to determine combat
  actions.
• Examples
• Using the appropriate weapon for the range
  (Sniper rifles if enemy is far, pistol if close.)
• Aiming for the head.
• How to use grenades effectively (flush out
  enemies if attacking, slow them down if
  defending)

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Team awareness

• Follows the leader (you)
• Communicates enemy locations
• Uses stealth (sneaking slowly to reduce noise)
  when heavily outnumbered
• Avoids stupid problems like shooting teammates,
  (will yell at you if you do).

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Effects on Gameplay

• Why make a bot for a multi-player game?
• Some servers dont have a lot of players on them.
  Bots can fill in the gaps to make a full team.
• Lousy internet connection wont prevent players
  from enjoying game.
• Bots dont accuse you of cheating when you kick
  their ass.

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Strengths and weaknesses

• Strengths
• Bot is almost convincingly human.
• Bot difficulty is scalable to match different
  skill levels.
• Bots dont change flow of game, they are just
  like other players.
• Weaknesses
• Bots can see perfectly in dark areas.
• Bots often prioritize killing enemies over
  completing mission objectives. (Then again, so do
  most human players.)