Parallel Behavior Plugin - Unreal Engine 5.6+

Description

ParallelBehavioris a lightweight Unreal Engine plugin that allows a single AI-controlled Pawn (or AIController) to run multiple independent Behavior Trees simultaneously, each with its own isolated Blackboard.

This solves a common limitation of the default UBehaviorTreeComponent: only one tree can be active at a time on an AIController. With this component you can easily implement layered AI architecture such as:

• Combat logic (main BT)
• Locomotion / movement overrides
• Emotional state / mood system
• Dialogue / interaction layer
• Environmental awareness (e.g. weather reactions)

Each layer runs completely in parallel without key conflicts because every tree has its own UBlackboardComponent.

Features

• Run unlimited parallel Behavior Trees on the same Pawn/AIController
• Each tree has a fully independent Blackboard instance
• Blueprint-exposed API (Authority-only where required)
• Automatic startup of default trees defined in component defaults
• Unique ID system for runtime management (add/stop/restart/remove by name)
• Safe cleanup on EndPlay
• Works in multiplayer (authority checks included)

Usage

1. Add the Component
   • Create ParallelBehaviorManagerComponent to your AIController or directly to your Pawn (recommended on AIController).
2. Define Default Trees (optional)
   • In the component's details panel you will see an array Behaviors (default trees).
   • Add entries and assign Behavior Tree assets. These will automatically start on BeginPlay.
   • Each entry can have a custom Id (FName).

Runtime Control (Blueprints or C++)

Function	Description
Add Tree	Dynamically spawn and start a new parallel BT from a setup struct
Get Tree	Retrieve the UBehaviorTreeComponent for a specific ID
Stop Tree	DAbort execution of a specific tree (keeps component alive)
Restart Tree	Stop + start again
Remove Tree	Stop + destroy component for a specific ID
Remove all Trees	Full cleanup of all parallel trees (called on EndPlay)

API Quick Reference

// Add a new tree at runtime
FParallelBehaviorSetup Setup;
Setup.Id = FName("TemporaryAlert");
Setup.BTAsset = LoadObject<UBehaviorTree>(nullptr, TEXT("/Game/AI/BT_Alert.BT_Alert"));
ManagerComponent->AddTree(Setup);

// Get component
UBehaviorTreeComponent* AlertComp = ManagerComponent->GetTree("TemporaryAlert");

// Stop / Restart / Remove
ManagerComponent->StopTree("TemporaryAlert");
ManagerComponent->RestartTree("EmotionLayer");
ManagerComponent->RemoveTree("DialogueLayer");

Overriding GetPawn()

The default implementation already returns GetOwner<AController>()->GetPawn()

You normally don't need to override it. The function is marked as BlueprintNativeEvent if you ever need custom logic.

Known Limitations

• Parallel trees do not have built-in priority system (you must implement arbitration in your trees or via events)
• Very large numbers of parallel trees (>20) may impact performance – use reasonably

License

This project is licensed under the MIT License - see the LICENSE file for details.