BT Set Blackboard

Type: Exec (In → Out)
Category: AI_BT
Result: always SUCCESS

Writes a value to the blackboard (self._bt_bb). Always returns SUCCESS. It is the primary mechanism for passing data between BT nodes without connecting sockets.

Properties

Property	Type	Default	Description
Key	String	"my_key"	Blackboard key to write
Value	String	"True"	Python expression evaluated at execution time

Sockets

Socket	Direction	Type
In	Input	Exec
Out	Output	Exec

Value expressions

The Value field is evaluated as Python code in the component context. self is available.

Expression	Result
True	boolean True
42	integer 42
'patrol'	string "patrol"
self.own.worldPosition.copy()	current object position
self.own.scene.objects.get('Enemy').worldPosition	another object's position
self.own.get('hp', 100)	BGE property of the object

If the expression throws an exception, the key is set to None (no crash).

Results

Condition	_bt_last_result
Always	'SUCCESS'

Typical usage

Mark AI state

[BT Set Blackboard: mode = 'chase'] → [BT Move To: Player]

Capture target position

[BT Custom Task: find_player] → [BT Set Blackboard: target_pos = self.own.scene.objects.get('Player').worldPosition.copy()]

Reset cooldown

[BT Set Blackboard: attack_cooldown = 0.0] → [BT Sequence] → ...

Increment a counter

Key:   patrol_index
Value: (self._bt_bb.get('patrol_index', 0) + 1) % 4

Creates a cyclic counter from 0 to 3 without external code.

Graph position

BTSetBlackboard typically precedes the action that will use the written value, or is placed in condition branches to update state when a decision is made:

[BT Condition: enemy_visible]
    ├── True ──► [BT Set Blackboard: last_seen_pos = self.own.scene.objects.get('Player').worldPosition.copy()]
    │                   │
    │                   Out ──► [BT Move To: Player]
    └── False ──► [BT Move To: last_seen_pos_object]

Notes

• Always returns SUCCESS, making it safe in any position within a Sequence.
• The blackboard persists between frames — values written are available the next frame.
• To read the blackboard, use BTCondition or access directly with self._bt_bb.get('key', default) in a BTCustomTask.