AI FSM – Arma 2: Operation Arrowhead
AI FSM
Summary page to gather community knowledge about the exposed AI FSM and the modification possibilities.
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
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. 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.
Next cause
The FSM can get multiple events supplied by the engine. Assumption: The FSM is meant to loop through all of them, yet it seems the looping is broken or disabled intentionally. See the technical details section below for more details.
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.
formationEntity.fsm
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
Unknown. Was yet to log an occurrence for non Civilian infantry.
formationC.fsm
At mission start executed for every Civilian unit. Assumption: Seems to run permanently until the unit dies.
formationCDanger.fsm
On danger / threat events close to civilian units. The distance and frequency are unknown. Also unknown which danger causes actually work / are implemented.
formationEntity.fsm
Technical details
comm.fsm
- _who = _this select 0;
- _state = _this select 1;
danger.fsm
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)
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's 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. Assumption: It could be the danger target position.
- A float. Assumption: It looks like the timeout timestamp. It always has +5 seconds or less to the event call time.
- An unit. Assumption: Most likely the unit the threat is coming from. Can be <NULL-object>.
//Note 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.
The strange thing is that the _queue gets emptied in the init state. So either the _queue can get refiled while the FSM is processed, or it will always exit.
TODO: Log the value of _queue once in the state to determine how it works.
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";
comment "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.