Do Once

Type: Branch (True / False)
Category: FLOW

Executes the True path only the very first time it is triggered. On all subsequent calls it executes the False path. Useful for one-time initializations or entry effects that must not repeat.

Properties

None — the node only maintains an internal flag.

Sockets

Socket	Direction	Type
In	Input	Exec
True	Output	Exec (first call)
False	Output	Exec (subsequent calls)

Behavior

if not hasattr(self, '_do1_<name>'):
    self._do1_<name> = False
if not self._do1_<name>:
    self._do1_<name> = True
    # → True path
else:
    # → False path

• First call: the flag doesn't exist → created as False → set to True → executes True.
• All subsequent calls: the flag is already True → executes False.

The state persists as long as the object exists in the scene.

Typical usage

Blackboard initialization

[OnUpdate] → [Do Once]
                ├── True  ──► [BT Set Blackboard: patrol_idx = 0]
                │                   → [BT Set Blackboard: initialized = True]
                └── False ──► [normal logic]

Entry sound when entering a zone

[OnCollision: zone_trigger] → [Do Once]
                                  ├── True  ──► [BTCustomTask: play_sound('alert')]
                                  └── False ──► (silence)

Loot spawn on death (only once)

[BT Condition: ai_is_dead]
    └── True ──► [Do Once]
                    ├── True  ──► [BTCustomTask: self.own.scene.addObject('Coin', self.own, 0)]
                    └── False ──► (already dropped)

Resetting the state

To reset Do Once from code:

# In a BTCustomTask:
var = '_do1_' + 'NodeName'.replace(' ', '_')
if hasattr(self, var):
    delattr(self, var)

Or directly:

self._do1_NodeName = False

Notes

• The node name in the editor determines the variable name. Renaming the node is equivalent to resetting its state.
• If two Do Once nodes in the same component share the same name, they will share the variable — always give them unique names.
• The False path fires from the second call onwards, not only when the node has already been triggered. Connecting to False is useful for continuing normal execution without re-doing the initialization.