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Overview

The Modular Behavior Tree (MBT) is a decision making system for individual AI characters. It allows the AI to perform actions and react to its environment. The structure of the tree is specified by certain nodes and gets defined in XML.

Basically, an MBT consists of:

  • Variables
  • SignalVariables
  • Timestamps
  • The Root node (which is where the actual tree starts)

Regarding the Root node, the most commonly used nodes in here are:

  • Sequences
  • Selectors
  • Priorities
  • Actions

Example Tree Structure

ExampleTree.xml
<BehaviorTree>
    <Variables>
        <Variable name="HasTarget"/>
    </Variables>
    <SignalVariables>
    </SignalVariables>
    <Timestamps>
    </Timestamps>
    <Root>
        <Sequence>
            <Log message="Test" />
            <WaitForEvent name="OnEnemySeen" />
            <Move to="Target" speed="Walk" stance="Stand" fireMode="BurstWhileMoving" />
            <Halt />
        </Sequence>
    </Root>
</BehaviorTree>

Tree Files

The XML files need to reside in Scripts/AI/BehaviorTrees. Some sample trees that ship with SDK can be found in there already.

Every XML file that is located in that folder will automatically appear in the drop-down list of the entity's ModularBehaviorTree property in Sandbox (you may need to restart Sandbox to make new files appear).

Make sure the SelectionTree property is empty (only one type of tree can run)

Specification (draft)

Download: Documentation (PDF)

 

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