Artificial Intelligence in Game Design

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Artificial Intelligence in Game Design

• Content Generation

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Content Generation

• Creating world for game
• Terrain for battle games
• Levels for shooters
• Tracks for racing games
• Most expensive part of development!
• Goal Generate content automatically
• Cheaper, faster
• Infinite replayability

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Terrain Maps

• Most commonly applied to terrain maps in
  civilization games
• Goals (possibly contradictory)
• Realistic appearing terrain
• Continents, islands, mountains, beaches, deserts,
  etc.
• Fair to all players
• Equal amounts of resources, water, and flat areas
  for building cities near initial position for
  each player

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Land Mass Generation

• One method
• Grow land clumps from each player location
• Initial territory each player given chance to
  expand into before running into other players

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Land Mass Generation

• Each iteration grows clump by 1 tile
• After given number of tiles, rest of map becomes
  water
• Chosen randomly from tiles adjacent to existing
  clump
• Must not be part of another players clump
• Evaluated using fitness criteria
• Nearness to initial player position
• Number of adjacent tiles already part of
  players clump
• Distance from other players clumps
• If tile fails, choose another
• Goal avoid peninsulas

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Island Map Generation

• Each player initially given separate island
• Can be built like land clumps
• Additional criteria New land tiles for player
  not allowed within some distance of tiles for
  other players (keep islands separated)
• Additional islands can be generated in empty
  spaces after player islands created

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Terrain Generation

• Creating realistic looking map of land masses
• Generally height based
• Defining h(x, y) for points on the map
• Low at beaches
• High in mountains
• Flat areas for city development

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Fractals

• Shapes which appear the same at any scale
  (self-similar)
• Based on some variance applied at each level of
  detail
• Modify area by some variance v
• Subdivide into sub areas
• Higher v ? more jagged look

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Fractals

• One dimensional example
• Start with line
• Vary height of center of line by random value
  between v and v
• Vary height of center of each segment by v/2 and
  v/2

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Fractals

• One dimensional example
• Vary height of center of each segment by v/4 and
  v/4
• And so on, until have as much detail as necessary

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Fractals

• Create random terrain by doing this in two
  dimensions

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Adding Detail

• Smoothing used to level out terrain in areas that
  should be flat
• Beaches at interface of land/water tiles
• Flat areas designed to allow players to build
  cities, etc.
• Done by averaging heights in flat areas

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Adding Detail

• Create mountains in non-flat areas
• Choose a location and increase its height
• Use averaging to affect height of nearby
  locations (foothills)
• Use wander behavior to create a mountain range
  over a certain distance

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Adding Details

• Create rivers as paths from mountains to ocean
• Choose random point on coast
• Seek nearest point at base of a mountain
• Add wander to avoid a straight line

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Resource Distribution

• Must make sure resources are distributed fairly
  among all players
• Gold, oil, uranium, etc.
• Land on which structures can be built
• Goals
• Each player should have same amount of resources
  available at any stage of game (depending on
  amount of territory captured)
• Players should be encouraged to explore
  increasingly further from their initial position

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Resource Distribution

• Generate rings around player initial position
• Randomly place r resources within each ring
• r increases with each ring

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Generate and Test

• Generate level content in some random way
• Evaluate that content
• How playable/fun/challenging is it?
• Is the level of difficulty appropriate for that
  point in game?
• Modify that content
• Change features that are not appropriate

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Track Generation

• Track generated as sequence of randomly generated
  spline curves
• AI driver used to evaluate the difficulty level
  track
• Overall time to drive the track
• Variation in speed needed to drive the track
• Individual spline curvatures modified for track
  sections which vary from the rest of the level

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Mario Level Generation

• Two-dimensional level generated
• Pits, coins, enemies, etc.
• Evaluated by human players
• Fun time moving right, enemies stomped, etc
• Frustration time standing still, falls into
  pits, etc.