AI FSM – Arma 2: Operation Arrowhead

Summary page to gather community knowledge about the exposed AI FSM and the modification possibilities.

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NOTE: None of the information on this page is guaranteed to be correct.

The provided information is from research, testing and guesswork.

You are most welcome to contribute yourself!

What are they about

It seems they expose certain areas of the AI behavior outside the core engine. This means the community can modify some parts of the AI behavior this one. That said in the config space a lot of values permitted tweaking AI as well, yet on a different level.

The available FSM are about:

• Behavior while in formation.
• Behavior while in danger/from danger events.

TODO: Needs more research, testing and specific information.

What are they NOT about

• Micro AI
• Low(est) level AI behavior system

TODO: Clarify and add more details.

Where to find them

ca\characters\scripts

Where are they used

Following FSMs can be defined for a unit in Arma 2:

• behaviour (formation) FSM (lowest priority)
• conversation FSM
• reaction (danger) FSM (highest priority)

comm.fsm

No reference.

danger.fsm

class CAManBase : Man
{
	// ...
	fsmDanger = "Ca\characters\scripts\danger.fsm";
	// ...
};

formationC.fsm

class Civilian : CAManBase
{
	// ...
	fsmFormation = "ca\characters\scripts\formationC.fsm";
	// ...
}:

formationCDanger.fsm

class Civilian : CAManBase
{
	// ...
	fsmDanger = "ca\characters\scripts\formationCDanger.fsm";
	// ...
}:

formationEntity.fsm

No reference. However it is the equivalent to the config definition of:

class CAManBase : Man
{
	// ...
	fsmFormation = "Formation";
	// ...
};

Formation itself is also defined, for unknown reasons, in the config space rather as FSM file.

class CfgFSMs - class Formation

How to edit them

Get the FSM Editor part of the BI Tools 2 suite, or Arma 3 Tools from Steam. It allows you to open, study and modify the FSM files.

What do they do

comm.fsm

Makes an unit communicate his action:

• "Reloading! Cover me!"
• "Running!"
• "Covering!"

danger.fsm

Seems to be an event hook to make AI react to various danger events.

Right now only few events are used to initiate actions:

Cause 0 "ENEMY DETECTED"

Signal enemy via gesture.

Cause 8 "CAN FIRE"

Stop to fire makes the unit no longer move to return fire more effectively. If the threat is dead or after 4 to 8 seconds delay the unit moves on.

formationC.fsm

It forces initially Civilian units to stand (setUnitPos "UP") permanently unless instructed otherwise by another script/FSM (like formationCDanger.fsm).

In addition it makes non leader Civilian units to have a five meter radius offset to their actual destination.

The code comment says:

Lowering the formation precision for civilians

formationCDanger.fsm

Seems to be an event hook to make Civilian AI react to various danger events.

If the unit is the leader (isFormationLeader _this), it will react to danger causes 0 to 6 - NOT 7 (Scream) and 8 (CanFire). If inside a vehicle and (canUnloadInCombat _this), the unit will eject it, drop down to the ground (60% chance) and not move for a while (360 seconds or till _dangerUntil if not in combat mode). After that it will move again and switch to auto stance. If it ejected a vehicle, it will enter it again.

In practice the same happens for non leader units. Expect the chance to drop down is higher (85%) and it will keep on moving. There are two additional features in there, but currently not active.

• 'Go to cover': Disabled as findCover and setHideBehind currently do not work.
• 'Inspect dead body': Not working as the 'Inspect body' condition is broken and therefore this tree will not be used.

The non leader Civilian will react to the highest threat, but will ignore all others. In general it ignores danger causes 7 (Scream) and 8 (CanFire) too like a leader unit Civilian.

When are they run

comm.fsm

Assumption: Not at all. Seems like a test version and the actual system is integrated into the engine nowadays.

danger.fsm

On (seemingly) each danger / threat events close to non civilian units. The distance and frequency are unknown.

Next cause

If a new danger event happens to the unit, while the current danger event handling is processed, the event will be added to the units danger events queue. Next cause checks makes the highest prio danger event in the queue processed after the former has been completed.

[Source reference _{(dead link)}]

Observed instances

TODO

formationC.fsm

At mission start executed for every Civilian unit. Assumption: Seems to run permanently until the unit dies.

formationCDanger.fsm

On (seemingly) each danger / threat events close to civilian units. The distance and frequency are unknown. Also unknown which danger causes actually work / are implemented.

Technical details

comm.fsm

• _who = _this select 0;
• _state = _this select 1;

danger.fsm

Disabling

Suma: When you use fsmDanger = "", there are some built-in reactions to danger, but there is no danger FSM running (...).

[Source reference _{(dead link)}]

Danger causes

The FSM contains this description block:

DEFINE_ENUM_BEG(DangerCause)
(0) DCEnemyDetected,	// the first enemy detected
(1) DCFire,			// fire visible
(2) DCHit,				// vehicle hit
(3) DCEnemyNear,		// enemy very close to me
(4) DCExplosion,		// explosion detected
(5) DCDeadBodyGroup,	// dead soldier from my group found
(6) DCDeadBody,		// other dead soldier found
(7) DCScream			// hit soldier screaming
DEFINE_ENUM_END(DangerCause)

See Arma 2: FSM Danger Causes for more information.

The index numbers in brackets are added for easier viewing only in this article. It seems that later an ninth (index 8) event was added: DCCanFire. It looks like an event when the unit has a target in sight and is able to fire it is weapon.

Engine parameters

The FSM gets supplied by the engine the following parameters:

• _this: References the unit.
• _dangerCause: An integer to specify the "first" danger event type. Assumption: First could be most recent or oldest or with the highest priority.
• _queue: An array that contains multiple danger events and their details. One queue element contains:
  • The danger cause (integer).
  • A position of the event.
  • A current time + random 3-7 seconds offset
  • A danger source (can be <NULL-object>)

This data was retrieved assigning the FSM to civilian units as it never triggered so far for non-Civilian units:

diag_log["danger.FSM", time, _this, _dangerCause, _queue];

"danger.FSM",0.05,C 1-1-A:8,3,[[3,[1665.17,1686.23,1.31488],5.60283,O 1-1-A:5],[3,[1665.17,1686.23,1.31488],5.79803,O 1-1-A:5]]

FSM Init

It seems only the highest priority event is handled:

// Retrieve the highest priority event from the _queue private ["_priors","_priorCur"]; _priors = [3, 4, 5, 1, 4, 1, 1, 2, 2]; if (_dangerCause > 0) then { _priorCur = _priors select _dangerCause } else { _priorCur = -1 }; { private ["_cause"]; _cause = _x select 0; if ((_priors select _cause) > _priorCur) then { _dangerCause = _cause; _dangerPos = _x select 1; _dangerUntil = _x select 2; _dangerCausedBy = _x select 3; } } forEach _queue; _queue = [];

Danger cause events ordered by priority. Highest comes first:

(2) DCHit,				5
(1) DCFire,			4
(4) DCExplosion,		4
(0) DCEnemyDetected,	3
(7) DCScream			2
(8) DCCanFire			2
(3) DCEnemyNear,		1
(5) DCDeadBodyGroup,	1
(6) DCDeadBody,		1

Queue

After handling an event the FSM gets into the 'Check queue' state. In the condition 'Next cause', it checks 'count _queue>0' and returns to the init state if true; otherwise exits.

Suma: There is always only one Danger FSM running per unit. If the Danger FSM is already running
when there is a new danger cause, new FSM is not spawned, rather a new item is inserted
into the _queue variable for the FSM to process.
The default FSM always processes the whole queue at once and discards all items but the one with
most priority (see characters\scripts\danger.fsm - initial state Reacting on danger).

[Source reference _{(dead link)}]

formationC.fsm

• _this: References the unit.

Infinite loop. Seems to have no effect on Civilian leader units (isFormationLeader (effectiveCommander (vehicle _this))).

formationCDanger.fsm

Danger causes

See danger.fsm.

Engine parameters

See danger.fsm.

FSM Init

It seems only the highest priority event is handled (for non Civilian leader units):

private ["_vehicle","_commander"]; _vehicle = vehicle _this; _commander = effectiveCommander _vehicle; private ["_maxTime","_timeNow"]; _maxTime = 360; _this setUnitPos "UP"; // Function to retrieve the highest priority event from the _queue private ["_priors", "_oldDangerCause"]; _priors = [3, 3, 4, 5, 2, 1, 1, 1, 1]; _oldDangerCause = -1; private ["_funcBiggestDanger"]; _funcBiggestDanger = { private ["_priorCur"]; _priorCur = _priors select _dangerCause; for "_i" from 0 to ((count _queue) - 1) do { private ["_event","_cause","_priorNew"]; _event = _queue select _i; _cause = _event select 0; _priorNew = _priors select _cause; if (_priorNew > _priorCur) exitWith { _oldDangerCause = _dangerCause; _dangerCause = _cause; _dangerPos = _event select 1; _dangerUntil = _event select 2; }; }; _queue = []; };

Note the forced standup (setUnitPos "UP") and high delay (_maxTime = 360).

Danger cause events ordered by priority. Highest comes first:

(3) DCEnemyNear,		5
(2) DCHit,				4
(0) DCEnemyDetected,	3
(1) DCFire,			3
(4) DCExplosion,		2
(5) DCDeadBodyGroup,	1
(6) DCDeadBody,		1
(7) DCScream			1
(8) DCCanFire			1

Queue

See danger.fsm.

The Civilian leader only check the initial/first danger event. The non Civilian leader unit will only handle the highest priority even and ignore the rest.

formationEntity.fsm

Modification

So for no luck here assigning an external FSM:

fsmFormation = "ConfigFSM\formationEntity.fsm";

lead to

Warning Message: No entry 'ConfigFSM\formationEntity.fsm.FSM'.

and

fsmFormation = "ConfigFSM\formationEntity";

lead to

Warning Message: FSM 'ConfigFSM\formationEntity' cannot be loaded.

So it might be only possible to modify the CAManBase's fsmFormation by editing the configs based definition in 'class CfgFSMs - class Formation'.