BehaviourTreeEditor for Unity

A behaviour tree executes from a root node and traverses down through its children. Each node returns one of three states:

• success
• failure
• running

When a child returns running, the tree traversal typically stops for the current frame, and the state bubbles back up to the root. Parent nodes interpret these return states to decide the next course of action.

Nodes are categorized into three main types:

1. Action Nodes: Leaf nodes with no children. They represent the agent's capabilities (e.g., MoveToPosition, Wait).
2. Composite Nodes: Control flow nodes that can have multiple children (e.g., Sequencer, Selector).
3. Decorator Nodes: Nodes with exactly one child used to modify or hide the child's return state (e.g., Inverter, Repeat).

The Blackboard is a centralized data store that allows Nodes to pass information to each other across the behaviour tree. For example, one node can write a target position to the blackboard, and a subsequent node can read that position to move to it.

Managing Blackboard Keys

• Adding Keys: In the Blackboard view, enter a unique name in the Name field and select a type from the Type dropdown.
• Deleting Keys: Right-click on a node's value in the Blackboard view and select delete.
• Blackboard Key Overrides: You can override specific key values for individual GameObjects. Select the GameObject containing a BehaviourTreeInstance component, add a new override, select the desired key from the dropdown, and enter the override value.

When opening the editor for the first time, a prompt will appear allowing you to:

1. Select an existing tree from a dropdown menu to continue work.
2. Create a new tree by specifying a file path for the new asset.

The Node Inspector View displays all public properties of the currently selected node.

Tips:

• To ensure properties are displayed, select the middle of the node (over the node's title).
• All nodes include a description field. You can set this in the inspector to provide context that appears under the node's title in the tree.

To install the BehaviourTreeEditor, use the Unity Package Manager to add the package from a git URL.

Requirements:

• Minimum Unity version: 2023.2
• A working installation of git (if you encounter the error No 'git' executable was found, install it from https://git-scm.com/download/win).

Steps:

1. In Unity, open the Package Manager.
2. Select the Add Package From git URL... command.
3. Paste the following URL: https://github.com/thekiwicoder0/UnityBehaviourTreeEditor.git

While in Play Mode, you can select a GameObject to analyze its current behaviour tree state via color coding in the editor:

• Red: The node failed.
• Green: The node succeeded.
• Yellow: The node is currently running.
• No Highlight: The node was aborted and returned to its default state.

The editor interface can be opened via the Unity menu: Window -> AI -> BehaviourTree...

Main Panels:

• TreeView: Used for creating and organizing nodes.
• Inspector View: Displays public properties of the selected node.
• Blackboard View: Manages shared data used by nodes.
• Assets Menu: Accesses project assets.

To interact with the blackboard from within a custom Node, add a public NodeProperty<T> variable to your class. Use the .Value property to perform read and write operations.

In the Node Inspector, you can then select the specific Blackboard key from a dropdown. Alternatively, you can select [Value] to set a fixed default value directly on the node, bypassing the blackboard for that specific parameter.

[System.Serializable]
public class TestNode : ActionNode
{
    public NodeProperty<int> myInt;

    ... 

    protected override State OnUpdate() {
        int value = myInt.Value;
        Debug.Log("Value:" + value);
        myInt.Value = value + 1;
        return State.Success;
    }
}

To extend the editor, you can create custom nodes by inheriting from one of the three base C# classes:

• ActionNode
• CompositeNode
• DecoratorNode

Methods of creation:

1. Manual: Write a standard C# script inheriting from one of the base types.
2. Template: Right-click in the TreeView canvas and use the context menu to generate a new script from a template. Templates are located at: Assets/TheKiwiCoder/BehaviourTree/ScriptTemplates.

The Blackboard automatically includes all common Unity types. To register a custom type so it appears in the Blackboard Type dropdown, create a class that inherits from BlackboardKey<T>.

[System.Serializable]
public class MyTypeKey : BlackboardKey<MyType> {

}