How to Build AI Characters in Unreal Engine

Why Use Unreal Engine for AI Development?

Unreal Engine provides a powerful suite of tools that simplifies the AI development process, from basic behaviors to advanced character intelligence. Key benefits include:

1. Behavior Trees

Behavior Trees are one of Unreal Engine’s standout features for AI development. These hierarchical structures allow developers to define a series of tasks or behaviors that AI characters can perform based on conditions or player input. Behavior Trees are highly flexible, making them ideal for managing complex AI logic.

2. Blackboard System

The Blackboard system works alongside Behavior Trees, acting as a data repository for storing and retrieving information that drives AI decisions. For instance, an AI character can use the Blackboard to store information about player positions, health levels, or items of interest. This allows for more dynamic and responsive AI behavior.

3. NavMesh for Pathfinding

Navigation Mesh, or NavMesh, is essential for AI character movement. NavMesh allows AI characters to move intelligently around obstacles, taking into account different terrains and environmental features. Unreal Engine’s built-in NavMesh support makes pathfinding straightforward, enabling AI characters to navigate through complex game environments seamlessly.

4. Perception System

Unreal Engine’s Perception System gives AI characters sensory abilities, such as sight, hearing, and touch. This allows them to react to their surroundings based on what they detect, leading to more realistic and challenging encounters for players.

Step-by-Step Guide to Building AI Characters in Unreal Engine

Building AI characters in Unreal Engine can be broken down into a few key steps. Below is a step-by-step guide that will help you get started on creating AI for your Unreal Engine game development project.

Step 1: Setting Up an AI Controller

The AI controller in Unreal Engine acts as the “brain” of the AI character, responsible for managing the character’s behavior and decisions. To create an AI controller:

1. Create a new AI Controller Blueprint: In the Unreal Engine editor, create a new AI Controller Blueprint and assign it to your AI character.
2. Implement basic control logic: You can now set up basic movement and actions, such as wandering or patrolling, using the AI Controller.

Step 2: Implementing Behavior Trees

Behavior Trees form the core of your AI logic. To create one:

1. Set up a new Behavior Tree: Create a new Behavior Tree asset in Unreal Engine.
2. Define tasks and conditions: Add nodes to the Behavior Tree that represent tasks, such as moving to a location or attacking a target. Use conditions to determine when these tasks should execute.
3. Connect the Behavior Tree to the AI Controller: Ensure that your AI Controller is linked to the Behavior Tree so that the AI character can execute the defined behaviors.

Step 3: Using the Blackboard System

The Blackboard system works hand-in-hand with Behavior Trees to store key information for your AI character.

1. Create a Blackboard asset: In the Unreal Engine editor, create a new Blackboard asset.
2. Add data keys: Add data keys such as player location, health levels, or other environmental information that the AI will need to access.
3. Link the Blackboard to the Behavior Tree: Connect the Blackboard to your Behavior Tree so that your AI can read and write data as part of its decision-making process.

Step 4: Setting Up NavMesh for Pathfinding

For AI characters to move realistically through the environment, they need access to a Navigation Mesh (NavMesh).

1. Enable NavMesh: In your Unreal Engine project settings, make sure NavMesh is enabled.
2. Bake the NavMesh: Unreal Engine will automatically generate a NavMesh for the environment, allowing AI characters to move around obstacles.
3. Use MoveTo Task: In the Behavior Tree, use the MoveTo task to direct the AI character to a specific location. The character will navigate around obstacles using the NavMesh.

Step 5: Implementing Perception

The Perception System enables AI characters to detect their environment using sensory inputs like sight and hearing.

1. Add an AI Perception Component: Attach the Perception component to your AI character.
2. Set up sensory inputs: Define what the AI character can detect, such as sight for detecting players or hearing for detecting sounds.
3. Respond to stimuli: Use the Behavior Tree and Blackboard to define how the AI character responds to what it detects.

Advanced AI Features in Unreal Engine

Once you’ve mastered the basics of AI in Unreal Engine, there are several advanced features you can implement to make your AI characters more sophisticated.

1. Dynamic Decision Making

Unreal Engine supports dynamic decision-making systems like Utility AI, where AI characters evaluate multiple options and choose the best course of action based on changing circumstances.

2. Learning AI

For more advanced AI, you can integrate machine learning models into Unreal Engine, allowing AI characters to learn from player actions and adapt their behavior over time.

3. Squad and Group AI

Using Unreal Engine’s Group AI features, you can manage the behavior of groups of AI characters, allowing them to act cooperatively, such as in tactical combat scenarios.

Unreal Engine vs Unity for AI Development

When comparing Unreal Engine vs Unity for AI character development, both engines have their strengths, but Unreal Engine stands out for a few key reasons.

1. Behavior Trees

Unreal Engine’s built-in Behavior Tree system is more advanced than Unity’s native AI tools. While Unity provides support for state machines and nav agents, its Behavior Tree implementation requires third-party plugins, adding complexity to the process.

2. Graphics and Performance

Unreal Engine excels in rendering high-fidelity environments, which is essential for AI characters that interact with detailed worlds. Unity is capable of good graphics as well, but Unreal Engine’s superior real-time rendering ensures that AI behaviors remain fluid and responsive in high-performance settings.

3. AI Customization

Both engines allow for a high degree of customization, but Unreal Engine’s visual scripting system (Blueprint) gives developers more flexibility to tweak AI behaviors without needing to dive deep into code. Unity has similar functionality with its Playmaker plugin, but Blueprint is more integrated and easier to use.