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Behavior Trees for Modelling Artificial Intelligence in Games: A Tutorial

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The Computer Games Journal


We provide a tutorial introduction to behavior trees, which are a useful way of structuring artificial intelligence in games. A behavior tree is a model of plan execution that is graphically represented as a tree. A node in a tree either encapsulates an action to be performed or acts as a control flow component that directs traversal over the tree. Behavior trees are appropriate for specifying the behavior of non-player characters and other entities because of their maintainability, scalability, reusability, and extensibility. We describe the main features of behavior trees, show an example of how to create a behavior tree, and briefly survey existing packages for editing behavior trees. We recommend that behavior trees be used when some game designers are not programmers, the conditions governing the behavior are complex, and the NPCs have aspects of behavior in common.

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Correspondence to Howard J. Hamilton.

Appendix: Pseudo-Code and Icons for Decorator Components

Appendix: Pseudo-Code and Icons for Decorator Components

See Figs. 7, 8, 9, 10, 11, 12 and 13.

Fig. 7
figure 7

The succeeder decorator

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figure 8

The failer decorator

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figure 9

The basic repeater decorator

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figure 10

The repeat-until-success decorator

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figure 11

The repeat-until-failure decorator

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figure 12

The count-based limit decorator

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figure 13

The timer-based limit decorator

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Marcotte, R., Hamilton, H.J. Behavior Trees for Modelling Artificial Intelligence in Games: A Tutorial. Comput Game J 6, 171–184 (2017).

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