Blackboard

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Share values through the blackboard

A blackboard is the variable list shared by tasks in a behavior tree. Behavior Designer implements it with Shared Variables. One task can discover a target and write Current Target; later tasks can read the same value without directly referencing the first task.

Assign one variable to several tasks

  1. Open the tree’s Variables tab.
  2. Add a variable with a unique, purpose-based name such as Current Target or Last Known Position.
  3. Select a task with a compatible Shared Variable field.
  4. Change that field from a constant value to the named variable.
  5. Assign the same variable to every task that should read or write it.

At runtime, watched fields and the Variables tab help confirm which value is currently shared.

Keep ownership narrow

Prefer a local variable when only one tree needs the value. Use a dynamic variable for a temporary named connection and a global variable only when unrelated trees intentionally share ownership. External Behavior Trees can expose variables that the owning Behavior Tree maps to its own values.

Continue

Variables covers scopes, property mapping, code access, custom variable types, synchronization, and scene references. External Behavior Trees explains variable overrides on reusable tree assets.