Behavior Tree
Behavior Trees (BTs) are a versatile and modular mathematical model used to design and implement dynamic decision-making and task execution systems in fields such as computer science, robotics, control systems, and video game development. BTs organize tasks into a hierarchical tree structure, where each node represents a task, decision, or control flow element.
This structure allows for the composition of complex behaviors from simpler, reusable tasks, facilitating clear and manageable development of behavior logic. Unlike hierarchical state machines, which are centered around states, BTs focus on tasks as the primary building blocks, making them inherently action-oriented.
This task-centric approach, combined with the tree's hierarchical nature, enables straightforward representation of complex decision-making processes and provides clear pathways for task prioritization, sequencing, and execution based on the system's current state and external inputs. The modularity and intuitiveness of BTs contribute to their popularity, particularly in game development, where they are used to script nuanced behaviors for non-player characters (NPCs).
In robotics, a BT might be used to govern an autonomous robot's behavior for a search-and-rescue mission. The tree's root might begin with a high-level decision node evaluating the robot's current situation. Child nodes could represent tasks like scanning the environment, navigating to points of interest, or performing rescue actions.
Each task can be further broken down into smaller sub-tasks, allowing the robot to adapt its behavior in real-time to the complexities of the rescue scenario. In video game AI, BTs are employed to control NPC behavior, providing a rich interaction experience for the player.
For instance, an NPC's BT might include nodes for basic behaviors like patrolling an area, with branches for more complex behaviors like investigating noises or engaging in combat when an enemy is detected. This allows NPCs to exhibit behaviors that appear thoughtful and responsive to the player's actions and the game environment, enhancing the game's immersion and challenge.