limboai/doc/source/classes/class_blackboard.rst

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.. _class_Blackboard:

Blackboard
==========

**Inherits:** 

A key/value storage for sharing among :ref:`LimboHSM<class_LimboHSM>` states and :ref:`BehaviorTree<class_BehaviorTree>` tasks.

.. rst-class:: classref-introduction-group

Description
-----------

Blackboard is where data is stored and shared between states in the :ref:`LimboHSM<class_LimboHSM>` system and tasks in a :ref:`BehaviorTree<class_BehaviorTree>`. Each state and task in the :ref:`BehaviorTree<class_BehaviorTree>` can access this Blackboard, allowing them to read and write data. This makes it easy to share information between different actions and behaviors.

Blackboard can also act as a parent scope for another Blackboard. If a specific variable is not found in the active scope, it looks in the parent Blackboard to find it. A parent Blackboard can itself have its own parent scope, forming what we call a "blackboard scope chain." Importantly, there is no limit to how many Blackboards can be in this chain, and the Blackboard doesn't modify values in the parent scopes.

New scopes can be created using the :ref:`BTNewScope<class_BTNewScope>` and :ref:`BTSubtree<class_BTSubtree>` decorators. Additionally, a new scope is automatically created for any :ref:`LimboState<class_LimboState>` that has defined non-empty Blackboard data or for any root-level :ref:`LimboHSM<class_LimboHSM>` node.

.. rst-class:: classref-reftable-group

Methods
-------

.. table::
   :widths: auto

   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                                | :ref:`bind_var_to_property<class_Blackboard_method_bind_var_to_property>` **(** StringName var_name, Object object, StringName property **)**                   |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                                | :ref:`erase_var<class_Blackboard_method_erase_var>` **(** StringName var_name **)**                                                                             |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`Blackboard<class_Blackboard>` | :ref:`get_parent<class_Blackboard_method_get_parent>` **(** **)** |const|                                                                                       |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Variant                             | :ref:`get_var<class_Blackboard_method_get_var>` **(** StringName var_name, Variant default=null, bool complain=true **)** |const|                               |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | bool                                | :ref:`has_var<class_Blackboard_method_has_var>` **(** StringName var_name **)** |const|                                                                         |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                                | :ref:`link_var<class_Blackboard_method_link_var>` **(** StringName var_name, :ref:`Blackboard<class_Blackboard>` target_blackboard, StringName target_var **)** |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                                | :ref:`set_parent<class_Blackboard_method_set_parent>` **(** :ref:`Blackboard<class_Blackboard>` blackboard **)**                                                |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                                | :ref:`set_var<class_Blackboard_method_set_var>` **(** StringName var_name, Variant value **)**                                                                  |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`Blackboard<class_Blackboard>` | :ref:`top<class_Blackboard_method_top>` **(** **)** |const|                                                                                                     |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                                | :ref:`unbind_var<class_Blackboard_method_unbind_var>` **(** StringName var_name **)**                                                                           |
   +-------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+

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----

.. rst-class:: classref-descriptions-group

Method Descriptions
-------------------

.. _class_Blackboard_method_bind_var_to_property:

.. rst-class:: classref-method

void **bind_var_to_property** **(** StringName var_name, Object object, StringName property **)**

Establish a binding between a variable and the object's property specified by ``property`` and ``object``. Changes to the variable update the property, and vice versa.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_erase_var:

.. rst-class:: classref-method

void **erase_var** **(** StringName var_name **)**

Removes a variable by its name.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_get_parent:

.. rst-class:: classref-method

:ref:`Blackboard<class_Blackboard>` **get_parent** **(** **)** |const|

Returns a Blackboard that serves as the parent scope for this instance.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_get_var:

.. rst-class:: classref-method

Variant **get_var** **(** StringName var_name, Variant default=null, bool complain=true **)** |const|

Returns variable value or ``default`` if variable doesn't exist. If ``complain`` is ``true``, an error will be printed if variable doesn't exist.

.. rst-class:: classref-item-separator

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.. _class_Blackboard_method_has_var:

.. rst-class:: classref-method

bool **has_var** **(** StringName var_name **)** |const|

Returns ``true`` if the Blackboard contains the ``var_name`` variable, including the parent scopes.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_link_var:

.. rst-class:: classref-method

void **link_var** **(** StringName var_name, :ref:`Blackboard<class_Blackboard>` target_blackboard, StringName target_var **)**

Links a variable to another Blackboard variable. If a variable is linked to another variable, their state will always be identical, and any change to one will be reflected in the other. You can use this method to link a variable in the current scope to a variable in another scope, or in another Blackboard instance.



A variable can only be linked to one other variable. Calling this method again will overwrite the previous link. However, it is possible to link to the same variable from multiple different variables.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_set_parent:

.. rst-class:: classref-method

void **set_parent** **(** :ref:`Blackboard<class_Blackboard>` blackboard **)**

Assigns the parent scope. If a value isn't in the current Blackboard scope, it will look in the parent scope Blackboard to find it.

.. rst-class:: classref-item-separator

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.. _class_Blackboard_method_set_var:

.. rst-class:: classref-method

void **set_var** **(** StringName var_name, Variant value **)**

Assigns a value to a Blackboard variable.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_top:

.. rst-class:: classref-method

:ref:`Blackboard<class_Blackboard>` **top** **(** **)** |const|

Returns the topmost **Blackboard** in the scope chain.

.. rst-class:: classref-item-separator

----

.. _class_Blackboard_method_unbind_var:

.. rst-class:: classref-method

void **unbind_var** **(** StringName var_name **)**

Remove binding from a variable.

.. |virtual| replace:: :abbr:`virtual (This method should typically be overridden by the user to have any effect.)`
.. |const| replace:: :abbr:`const (This method has no side effects. It doesn't modify any of the instance's member variables.)`
.. |vararg| replace:: :abbr:`vararg (This method accepts any number of arguments after the ones described here.)`
.. |constructor| replace:: :abbr:`constructor (This method is used to construct a type.)`
.. |static| replace:: :abbr:`static (This method doesn't need an instance to be called, so it can be called directly using the class name.)`
.. |operator| replace:: :abbr:`operator (This method describes a valid operator to use with this type as left-hand operand.)`
.. |bitfield| replace:: :abbr:`BitField (This value is an integer composed as a bitmask of the following flags.)`