Bos Wars Scripting API: Artificial Intelligence (AI)

Intro - Introduction to AI functions and variables

Warning: The AI documentation is slightly outdated. This documentation hasn't been fully converted to the lua API yet.

How does it work

• The main script. It starts buildings, ...
• The action/reaction scripts. They are started by the AI engine, under certain condition.
  

Variables

AiTypes

This table lists all the AI types defined in Lua. It is used by both the engine and the Lua code. In AiTypes, every AI type has an entry that is a table with these keys:

Ident = string

Unique, language-independent identifier of this AI type. By convention, each identifier should begin with "ai-". The Ident string is also the key of the entry within AiTypes. The map setup file sets e.g. Players[1].AiName = "ai-blitz" and the engine then finds the AI type whose identifier is that string; or if no such AI type exists, the engine falls back to "ai-passive". In saved games, these names are used in the "ai-type" parameter of DefineAiPlayer and the "ai-name" parameter of Player.

Name = string

Name of the AI the Player sees and which gets translated. The engine does not use this; only the Lua code does.

Init = function or nil

Initializes AiState[AiPlayer()] to whatever the AI type requires. When starting a new game, the engine calls the Init function for each player that is going to use this AI type. Typically, the Init function creates a table and writes it to AiState[AiPlayer()], and the EachSecond function will then maintain that table. Even if the AI type does not use AiState for its own purposes, the Init function must regardless write a non-nil value to AiState[AiPlayer()], so that the engine will know the AI state has been initialized and not call the Init function again if the game is later saved and loaded. (Of course, if the AI type has no Init function, then there is no such requirement.)

EachSecond = function

Decides AI actions: primarily, what to build. The engine calls the EachSecond function once per second (at the default game speed).

(other)

Lua code can add other keys in the table. The engine will ignore them. (Perhaps there should be a naming convention so that Lua-specific and engine-specific keys won't clash. Or we can just document all keys here.)

Lua code is free to read the AiTypes table but should not modify it or its elements directly. Instead, it should call DefineAiType, so that the engine knows to update its data structures accordingly.

AiState

The AI state of the map and each AI player. The AI scripts should write all persistent state into AiState, so that the engine will save and load it as part of the game, and so that the engine can easily clear the state when starting a new game.

AiState[AiPlayer()] = table

AI state of a single AI player. The Init function of the AI type creates this table, and the other functions of the AI type can then use the fields of the table as they please. If AiState[AiPlayer()] is nil, that means the engine has not called the Init function yet.

AiState.cache = table

Cached information shared by all AI players. Lua scripts of individual AI types should not access this directly. Instead, they should use shared functions.

Not in engine: The engine does not know about AiState.cache. Only the Lua code does.

The engine does not currently preserve object identity when saving and loading a game. That means, if the AI script does

local x = {}
AiState[AiPlayer()].first = x
AiState[AiPlayer()].second = x

then a comparison like AiState[AiPlayer()].first == AiState[AiPlayer()].second will initially return true, but if the game is saved and loaded, the comparison will start returning false because first and second now refer to different empty tables. However, scripts should not depend on this behavior.

Functions

DefineAiType(table)

Defines an AI type and adds it to AiTypes.

table

Describes the AI type, in the same format as an element of AiTypes.

Note: Individual maps should not call DefineAiType. Call it during global initialization instead. The engine does not provide any way to undefine an AI type and reacts poorly to redefinitions.

Example

-- Defines the passive computer AI, which does nothing.
DefineAiType({
  Ident = "ai-passive",
  Name = _("Passive"),
  Init = nil, -- which is the default anyway
  EachSecond = function() end })

DefineAiHelper(list)

list

A list of features:

{"build", builder-type, building-type-1, ... building-type-n}

Obsolete since r8101 (2006-06-21): Ignored. The AI instead gets this information from DefineButton calls that have Action = "build".

builder-type

Name of the unit-type that can build.

building-type-1

building-type-n

Names of the unit-types that can be built by the builder.

Note: If more units can build the same buildings you need the same list for all units.

{"train", trainer-type, unit-type-1, ... unit-type-n}

Obsolete since r8101 (2006-06-21): Ignored. The AI instead gets this information from DefineButton calls that have Action = "train".

trainer-type

Name of the unit-type that can train the units.

unit-type-1

unit-type-n

Names of the unit-types that can be trained by the trainer.

Note: If more units can train the same unit you need the same list for all units.

{"repair", worker-type, unit-type-1, ... unit-type-n}

Obsolete since r8101 (2006-06-21): Ignored. The AI instead gets this information from DefineButton calls that have Action = "repair".

worker-type

Name of the unit-type that can repair other units.

unit-type-1

unit-type-n

Names of the unit-types that can be repaired by the worker.

Note: If more units can repair the same units you need the same list for all units.

{"unit-equiv", unit-type, unit-type-1, ... unit-type-n}

Declares unit types as equivalent for AI purposes. When AiForce is asked to train any of them, it instead trains the best one it can; "best" here is controlled by the Priority setting in DefineUnitType.

unit-type

Name of the unit-type that have equivalent units.

unit-type-1

unit-type-n

Names of the unit-types that can be used by the AI equivalent.

{"unit-limit", unit-type, resource}

Obsolete since r8101 (2006-06-21) and r8658 (2007-04-01): Ignored. The engine no longer limits the number of units according to resources.

unit-type

Name of the unit-type that must be produced to increase the unit limit.

resource

Name of the resource producing the shortage.

I think we should swap the arguments: "resource", "unit-type".

Example

DefineAiHelper(
  {"build", "unit-peasant", "unit-farm"},
  {"train", "unit-town-hall", "unit-peasant"},
  {"repair", "unit-peasant", "unit-town-hall"},
  {"unit-limit", "unit-farm", "food"},
  {"unit-equiv", "unit-town-hall", "unit-keep"})

A peasant can build a farm.

The town hall can train a peasant.

A peasant can repair the town hall.

To fix the food shortage the AI must build farms.

For the AI is a keep equivalent to a town hall.

AiAttackWithForce(force)

Attack the opponent with the given force. The place is choosen by the AI. If there are flyers, ships and land units in the force they could attack different goals.

force

ID of the force to which the attacking units belong. The force ids 0 to 9 are currently supported.

returns

False.

Example

-- Force 0 is built with one assault unit. The script continues processing, when
-- the assault unit is ready. When ready, the script attacks the opponent
-- with force 0.
{
  function() return AiForce(0, "unit-assault", 1) end,
  function() return AiWaitForce(0) end,
  function() return AiAttackWithForce(0) end
}

AiCheckForce(force)

Check if a force is complete.

force

Number of the force to which the units should belong. 0 - 9 is currently supported.

returns

True if the force is complete, false if not yet.

Example

-- Force 0 is build with one assault. 
AiForce(0, "unit-assault", 1)
...
-- If the force is ready, use it to attack.
if (AiCheckForce(0)) then AiAttackWithForce(0) end

-- Prints now the commands of this computer player.
AiDebug(true)

AiDebugPlayer("self")

AiForce(force, unit-type-1, count-1, ... ,unit-type-N, count-N)

Define a force, what and how many units should belong to a force. Up to 10 forces are currently supported.
Force 0 is currently fixed to be the defence force. Send to a building or unit under attack.
If there are any unassigned units of the requested unit-type, than they are assigned to the force.
Note: The low-level didn't support the reduce of a force.

force

Number of the force to which the units should belong. 0 - 9 is currently supported.

unit-type-1

unit-type-N

Unit-type that should be in the force. Currently only mobile (trained) units are allowed.

count-1

count-N

How many of this units should be in the force.

returns

False.

Example

-- First the force 0 is filled up with 4 assaults and 5 bazoos, after this
-- force 1 is filled with 3 assaults and 2 bazoos.
AiForce(0, "unit-assault", 4, "unit-bazoo", 5)
AiForce(1, "unit-assault", 3, "unit-bazoo", 2)

-- Sets the role of force 0 to attack.
AiForceRole(0, "attack")

AiNeed(unit-type)

unit-type

Name of the unit-type required.

returns

False.

Example

-- The magmapump must be build before a powerplant.
AiNeed("unit-magmapump")
AiNeed("unit-powerplant")

AiPlayer()

Example

-- If the player of the running AI has insufficient magma
-- then build a magmapump:
player = AiPlayer()
if (Players[player].MagmaStored < 300) then
  AiNeed("unit-magmapump")
end

AiSet(unit-type, count)

unit-type

Name of the unit-type(s) required.

count

Number of unit-types(s) required. Zero is not allowed.

returns

False.

Example

-- Request two assault units.
AiSet("unit-assault", 2)

AiSleep(frames)

Wait some frames, to let the opponent (you) recover.

The first time this function is called, the frames value is stored, and "true" is returned. The next times, also "true" is returned, until the timeout is over: then "false" is returned.

The frames parameter is ignored except during the first call.

frames

How many frames (~1/30s) the AI shouldn't proceed with the script.

returns

True if we need to wait longer.

False if the waiting period is over.

Example

{
  -- Wait 500 frames ~16s.
  function() return AiSleep(500) end,
}

AiWait(type)

type

The unit type name string.

returns

True if this unit type is not yet available.

False if at least one instance of this unit-type exists.

Example

{
  -- Proceed only if an engineer is ready:
  function() return AiNeed("unit-engineer") end,
  function() return AiWait("unit-engineer") end,
  -- Proceed only if two magmapumps are ready:
  function() return AiSet("unit-magmapump", 2) end,
  function() return AiWait("unit-magmapump") end,
}

AiWaitForce(force)

Check if a force is complete.

The forces are build in force number order. First 0, than 1, last 9.

force

Number of the force to which the units should belong. 0 - 9 is currently supported.

returns

False if the force is complete, true if not yet.

Example

-- Force 0 is build with one assault unitn. The script continues processing, if the
-- unit is ready trained.
AiForce(0, "unit-assault", 1)
AiWaitForce(0)

Notes