Introduction

In this module, we will delve into the world of Artificial Intelligence (AI) within Unreal Engine, focusing on Behavior Trees. Behavior Trees are a powerful tool for creating complex AI behaviors in a structured and manageable way. By the end of this module, you will understand the basics of AI in Unreal Engine, how to set up and use Behavior Trees, and how to create intelligent and responsive AI characters.

Key Concepts

AI Controllers: Special controllers that manage AI characters.
Behavior Trees: A hierarchical structure used to define the behavior of AI characters.
Blackboards: Data storage used by Behavior Trees to store and retrieve information.
Tasks, Services, and Decorators: Components of Behavior Trees that define specific actions, conditions, and logic.

Setting Up AI Controllers

Step-by-Step Guide

Create an AI Controller:
- Right-click in the Content Browser.
- Select Blueprint Class.
- Choose AIController as the parent class.
- Name it MyAIController.
Assign the AI Controller to a Character:
- Open your AI character Blueprint.
- In the Details panel, find the Pawn section.
- Set the AI Controller Class to MyAIController.

Creating a Behavior Tree

Step-by-Step Guide

Create a Behavior Tree:
- Right-click in the Content Browser.
- Select Artificial Intelligence > Behavior Tree.
- Name it MyBehaviorTree.
Create a Blackboard:
- Right-click in the Content Browser.
- Select Artificial Intelligence > Blackboard.
- Name it MyBlackboard.
Link the Blackboard to the Behavior Tree:
- Open MyBehaviorTree.
- In the Details panel, set the Blackboard Asset to MyBlackboard.

Understanding Behavior Tree Components

Tasks

Tasks are the actions that the AI will perform. For example, moving to a location, attacking, or patrolling.

Example Task: Move To

// MoveToTask.cpp
#include "MoveToTask.h"
#include "AIController.h"
#include "BehaviorTree/BlackboardComponent.h"

EBTNodeResult::Type UMoveToTask::ExecuteTask(UBehaviorTreeComponent& OwnerComp, uint8* NodeMemory)
{
    AAIController* AIController = OwnerComp.GetAIOwner();
    if (AIController)
    {
        FVector Location = OwnerComp.GetBlackboardComponent()->GetValueAsVector("TargetLocation");
        AIController->MoveToLocation(Location);
        return EBTNodeResult::Succeeded;
    }
    return EBTNodeResult::Failed;
}

Services

Services run periodically and can be used to update Blackboard values or perform checks.

Example Service: Update Target Location

// UpdateTargetLocationService.cpp
#include "UpdateTargetLocationService.h"
#include "AIController.h"
#include "BehaviorTree/BlackboardComponent.h"

void UUpdateTargetLocationService::TickNode(UBehaviorTreeComponent& OwnerComp, uint8* NodeMemory, float DeltaSeconds)
{
    AAIController* AIController = OwnerComp.GetAIOwner();
    if (AIController)
    {
        FVector NewLocation = // Logic to determine new location
        OwnerComp.GetBlackboardComponent()->SetValueAsVector("TargetLocation", NewLocation);
    }
}

Decorators

Decorators are conditional checks that determine whether a branch of the Behavior Tree should be executed.

Example Decorator: Check Health

// CheckHealthDecorator.cpp
#include "CheckHealthDecorator.h"
#include "AIController.h"
#include "BehaviorTree/BlackboardComponent.h"

bool UCheckHealthDecorator::CalculateRawConditionValue(UBehaviorTreeComponent& OwnerComp, uint8* NodeMemory) const
{
    AAIController* AIController = OwnerComp.GetAIOwner();
    if (AIController)
    {
        float Health = OwnerComp.GetBlackboardComponent()->GetValueAsFloat("Health");
        return Health > 50.0f;
    }
    return false;
}

Practical Exercise

Exercise: Create a Patrolling AI

Create a new AI Controller and assign it to your AI character.
Create a Behavior Tree and Blackboard.
Add a Move To task to the Behavior Tree.
Create a Service to update the target location periodically.
Add a Decorator to check if the AI should continue patrolling.

Solution

AI Controller:
- Create PatrolAIController and assign it to your AI character.
Behavior Tree and Blackboard:
- Create PatrolBehaviorTree and PatrolBlackboard.
Move To Task:
- Implement a MoveToTask that moves the AI to a location stored in the Blackboard.
Update Target Location Service:
- Implement UpdatePatrolLocationService to update the target location.
Health Check Decorator:
- Implement CheckHealthDecorator to ensure the AI only patrols if health is above a certain threshold.

Conclusion

In this module, we covered the basics of AI in Unreal Engine, focusing on Behavior Trees. We learned how to set up AI Controllers, create and configure Behavior Trees, and use Tasks, Services, and Decorators to define AI behavior. By completing the practical exercise, you should now have a solid understanding of how to create intelligent and responsive AI characters in Unreal Engine.

AI and Behavior Trees

Introduction

Key Concepts

Setting Up AI Controllers

Step-by-Step Guide

Creating a Behavior Tree

Step-by-Step Guide

Understanding Behavior Tree Components

Tasks

Example Task: Move To

Services

Example Service: Update Target Location

Decorators

Example Decorator: Check Health

Practical Exercise

Exercise: Create a Patrolling AI

Solution

Conclusion

Unreal Engine Course

Module 1: Introduction to Unreal Engine

Module 2: Basic Concepts

Module 3: Intermediate Blueprints

Module 4: Advanced Blueprints

Module 5: C++ Programming in Unreal Engine

Module 6: Advanced C++ Programming

Module 7: Advanced Topics

Module 8: Project Development