Behavior Graph

A visual graph editor facilitating the creation of simple and complex AI behaviors

Features

• A dynamic, user-friendly editor window
• Support for fundamental node transitions
• Easily create custom nodes and transitions
• Quick and easy integration to other MonoBehaviour components, enabling dynamic field modifications for nodes and transitions

Installation

This repository is installed as a package for Unity.

1. Open Window > Package Manager.
2. Click +.
3. Select Add Package from git URL.
4. Paste https://github.com/Tramshy/trashy-behavior-graph.git.
5. Click Add.

NOTE: To do this you need Git installed on your computer.

Editor Usage

Using the graph editor

1. Create a new BehaviorPanel scriptable object using the context menu.
2. Double click scriptable object, or click Window -> Behavior Graph Editor and select scriptable object.
3. Press Space, or Right click -> Create Nodes, to open search window for nodes.
4. Right click any node for more options, like creating transitions.
5. Select any node or edge to see values in the inspector to the left.

Integrating separate MonoBehaviour component for dynamic field updates

1. Create a new script and inherit BehaviorData.
2. Variables that can be accessed, and used by, behavior graph should be created using the generic DataField<T> class.
3. Add logic as usual.
4. Select the desired BehaviorPanel and drag in the new class, before clicking Link Behavior Data.
5. You can now see all the serialized fields in the blackboard of the graph editor!
6. To use fields, select the desired node or edge.
7. Click on a variable in the blackboard and then click on the variable you wish to link it to in the inspector.
8. You can unlink fields by just clicking them again.

Creating custom nodes and node transitions

Nodes

1. In the context menu under Behavior Graph choose Custom Node Script.
2. This creates a script which inherits from the Node class.
3. Node contains a Start, Update and Exit method, use as necessary.
4. Node also contains an enum, Statuses, which contain Success, Running and Failure. Each Node has a CurrentStatus, there are base transitions which exits a node depending on whether or not the node's CurrentStatus is in Success or Failure.
5. All fields that you wish to serialize to the inspector, that should be linked to the blackboard, should be of the generic type DataField<T>, variables that are not of this type will be shown in the inspector and can still be used within the node, but it cannot be linked to the blackboard fields.
6. Search for your new node in the graph editor and use as you please! Note: If you want your node to be considered a base node by the system, use the BaseBehaviorElement attribute in your node.

Transitions

1. In the context menu under Behavior Graph choose Custom Transition Script.
2. This creates a script which inherits from the NodeTransitionObject class.
3. The Condition method will tell the system to switch nodes when it returns true.
4. You also need to use DataField<T> here in the same way as you would for Node objects.
5. Transitions can by default only be used once per node; however, if your new transition should be able to be used by the same node multiple times, then use the AllowMultipleTransition attribute.
6. Right click a node and you can find your new transition within the context menu, under the custom section! Note: You can also use the BaseBehaviorElement attribute here to get your new transition to show up under the base section.

Triggers

1. In the context menu under Behavior Graph choose Custom Trigger Script.
2. This creates a script which inherits from the TriggerTransition class.
3. The Condition method will tell the system to switch nodes when it returns true.
4. Triggers are not checked automatically, instead you will have to use the CallTrigger method when you want to attempt a switch. This will then switch if the Condition returns true.
5. The BaseBehaviorElement and AllowMultipleTransition attributes can be used for Triggers as well.

Runtime Usage

1. Add a BehaviorTree component to the game object, also add the class that derives BehaviorData if linking between blackboard is used.
2. Reference your BehaviorPanel in the Panel field of the BehaviorTree.

Using Triggers

Triggers act very similar to regular transitions, the big difference is that triggers will not be checked automatically. This means you will need to get a reference to the triggers you wish to call. For this you can use the GetNode method in a Panel and then the GetTrigger, or GetTriggers, method in the specific node. When you have your reference just use the CallTrigger method to attempt a switch.

There are several base triggers that you can use by default. Most of them are self explanitory, but the SimpleTrigger can be quite unclear what it does without looking in the code. Its Condition always returns true. This means that whenever you use the CallTrigger method, it will switch.

License

This package is licensed under the MIT License. For more information read: LICENSE.

Additional Notes

The tool is surprisingly performant, but it works using a lot of reflection, and cloning of Scriptable Objects in some cases, which is inherently quite costly.

You can use the ReadOnlyInspector attribute on the fields you intend to link, this will make it very clear what fields you need to link.

When you try to link integers, floats and similar fields, you may run into an issue that prevents you from clicking the field in the inspector. If you try to click on the field in the inspector, it will instead result in you dragging the value of the field and will not link the fields. To fix this, all you need to do is click at the very edge of the field or use the ReadOnlyInspector attribute.

Due to the fact that the system uses Scriptable Objects as nodes and transitions, you may have to use the [NonSerialized] attribute to avoid Unity from serializing the runtime data and thus overriding your default values for variables. This is not a problem for all fields, but if you notice the issue just use the attribute.