Random Map Generation and Transport Unit AI for Strategy Games

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Random Map Generation and Transport Unit AI for
Strategy Games

• By Russell Kuchar

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Random Map GenerationFocusing on Empire Earth
(RTS)

• A system must generate maps for tile-based, real
  time strategy games for 2-16 players
• Must be fair with land and resources
• Maps of the same size, type, and number of
  players must be similar but allow for different
  results
• 7 different types continental, large islands,
  small islands, highlands, plains, tournament
  islands, and Mediterranean
• 6 different sizes tiny, small, medium, large,
  huge, and gigantic

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Basic Solution

• Map Generation uses number of players, number of
  teams, map size, map climate, type of random map,
  and random number seed
• Players are placed on a blank map, teammates are
  placed adjacent, enemies opposite and symmetrical
• Land is built around the players, flat land as
  well as rough terrain, then water fills the
  remaining area
• Resources are added evenly for each player
• Map is colored and textured
• Player starting units and buildings are placed

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Scripts and Testing

• Application is tested by creating an array of all
  possible combinations of the map generation
  results
• Combines all land water arrays, height map
  arrays, and flat map arrays
• Scripting languages allow for different map
  variations with only small changes
• Uses master scripts for each map type and
  different subscripts for each map size

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Player Placement

• First step in map generation is player placement
• An algorithm is used to place players around the
  map in an optimal position
• Algorithm does place players in predictable
  positions, but keeps map balanced
• Teammates are placed into adjacent positions
• Dummy players are created for the purpose of map
  generation to create additional, unclaimed,
  resource-rich areas for the growth of players
  colonies

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Clump Details

• Fair land allocation is a priority
• Land must have a natural appearance
• Land is grown in the map generator in clumps
• Clumps are defined by a clump size, number of
  clumps, and clump chaos level
• Uses the completion method, growing a clump tile
  by tile, and the step method, growing a clump one
  tile per iteration
• Clumps grow to their clump size, with the
  specified number of clumps and as random as the
  chaos level

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Clump Details

• A land clump is created for each player
• Land Clumps
• Uses step method to ensure equal land for each
  player and ensuring that no players clump
  surrounds another
• Land clumps are restricted to a certain distance
  from a players starting position and cannot
  overtake opponents land clumps

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Clump Details

• Island Land Clumps
• Land clumps are restricted to a certain distance
  from opponents land
• Flat Elevation Clumps
• Flat land is created within a players existing
  land
• Ensures each player has adequate flat land to
  build buildings

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Height Map Details

• After land is grown, realistic terrain is added
• Fractals generate realistic looking elevation
  using map attributes resulting in height map
  array
• Filter is applied to smooth out jagged terrain
  artifacts in the height map array
• The height map array is combined with the land
  water array and adjustments are made to raise or
  lower some of the height map values to fit the
  terrain of the land water array

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Resource Allocation

• Resources (berries, iron, gold, stone, and
  wildlife) are placed, each player receiving the
  same amount of each
• Resources must maintain a certain distance from
  others and from players starting positions
• Random locations for resources are selected until
  acceptable locations are found
• Trees are the final resource placed since they
  are the most abundant and are used to also
  restrict pathfinding

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Random Maps

• Multi-Island
• Continent

• Lake
• Large Island

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Transport Unit AI Focusing on Empire Earth (RTS)

• Transports move passengers (land-based units)
  around the map
• Air, land, naval, and building transports are
  needed
• Passengers are instructed to load into
  transports, the transports move to the desired
  location and the passengers are unloaded from the
  transport
• System must adhere to existing RTS transport
  standards that players expect

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Transport Definitions

• Air Transports flies above the terrain and can
  move anywhere on the map but can only load and
  unload on valid flat land
• Land Transports limited to the same level
  terrain as land units
• Building Transports any stationary unit like a
  bunker or tower
• Naval Transports limited to moving in the water
  and loading and unloading on the shores

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Basic Solution

• All transports have high level goals that are
  broken down and implemented through a
  finite-state machine (FSM)
• Loading involves instructing units to become
  passengers, interacting with each other to
  appropriately load into the transports
• Unloading involves the transport moving within a
  certain range of the unload location and unload
  the passengers while following rules about valid
  unload locations

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Passenger FSM

• When given the load command, passengers are
  responsible for moving to the rendezvous point,
  wait for the transport and load into the
  transport
• Passengers are responsible for making sure that
  the transport is still on its way to the
  rendezvous point and that they are able to make
  it to the rendezvous point
• Once in the transport the passengers are idle and
  it is up to the transport to unload the
  passengers

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Transport FSM

• When given the load command, transports are
  responsible for moving to the rendezvous point,
  waiting for the passengers and loading all the
  passengers or until the transport is full
• When given the unload command, transports must
  move within range of the unload point and attempt
  to unload the passengers

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Loading

• Both passengers and transports have the load
  command and must meet at a rendezvous point
• An initial rendezvous point is determined and
  adjusted based on validity
• If passengers cannot reach location based on a
  wall, mountains, etc., or the location is not
  valid, over water, a building, etc., a new
  rendezvous point is selected
• Pathfinding is used to determine the proper path
  for the passengers and transports to take to make
  sure that they dont move over invalid terrain
• While moving to the rendezvous point, passengers
  must test to see if they are in range to load
  into the transport

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Loading

• Air Transports can move regardless of terrain so
  they move to the location of the nearest
  passenger which acts as the rendezvous point
• Land Transports the rendezvous point is located
  at the middle point between the transport and
  the nearest passenger based on maximum velocity
  of the units so they arrive at the same time

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Loading

• Building Transports cannot move, the rendezvous
  point is the building
• Naval Transports there are two rendezvous point,
  one land tile and one water tile, the distance
  of which must be less than the units load
  range. Passengers move to the nearest shore
  tile and the transport moves to the adjacent
  water tile to rendezvous

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Unloading

• The transport has the unload command and heads
  toward the unload point
• Unload point can be adjusted to another location
  if original is invalid
• While moving to the unload point, transports must
  test to see if they are in range to unload the
  passengers
• Sub-tile placement is used to prevent unloading
  passengers from colliding with other units or
  terrain and makes sure that illegal movement is
  not exploited

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Unload Point

• Given transport point (T) and players click
  point (CP) there are three unload points
• Transport Destination Point (TDP) point where
  transport moves to unload passengers
• First Passenger Point (FPP) first tile adjacent
  to the TDP where passengers unload to and must
  pathfind from
• Unload Point (UP) final destination of
  passengers which may be adjusted from the CP
  depending on pathfinding and validity of the UP

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Unloading

• Air Transports not restricted in pathfinding so
  FPP and UP are the same, only restrictions are on
  passengers to find valid terrain to unload upon
• Land Transports pathfinding is restricted the
  same as passenger pathfinding so the TDP, FPP,
  UP and CP are the same assuming the CP is a
  valid location

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Unloading

• Building Transports since these are immobile,
  the TDP, FPP, and UP are the same as the
  buildings location. Sub-tile placement code
  handles the unloading to make sure that placement
  is valid
• Naval Transports closest water tile to the CP
  is selected as the TDP and the adjacent land
  tile is the FPP. The UP is the closest tile on
  a straight line to the CP but within the unload
  range of the transport

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Summary

• Random Map Generation considers player placement,
  clump detail growth, and resource allocation to
  ensure a fair but random map each time
• Random Map Generation uses scripts and subscripts
  for the generation process
• Transport Unit AI must control the Passengers in
  addition to the Transports
• Transport Unit AI mainly considers loading and
  unloading, and uses pathfinding for movement of
  the transport and passengers