Collisions I – Collision Volumes

Collision volumes in Unreal Engine are invisible shapes used to detect interactions between objects in the game world. They help define how objects should react when they come into contact, such as stopping movement, triggering events, or blocking visibility.

What Are Collision Volumes?

Collision volumes act as boundaries around objects. They don’t need to match the object’s exact shape and are usually simplified for better performance. These volumes are used to detect when objects overlap or collide, and they define the physical interactions between them.

Types of Collision Volumes

1. Box Collision
   A rectangular collision volume. It’s ideal for simple, box-shaped objects like crates or walls.
2. Sphere Collision
   A spherical collision volume. It’s useful for round objects like balls or simple areas of effect.
3. Capsule Collision
   A capsule-shaped collision volume. It is commonly used for characters because it provides a good balance of coverage for movement and interactions.
4. Custom Collision
   Complex shapes created to fit the specific geometry of an object. These are more accurate but can impact performance.

Setting Up Collision Volumes

1. Adding a Collision Volume
   • In the Content Browser, open your Actor or Blueprint.
   • Go to the Components panel, and add a collision volume (e.g., Box Collision, Sphere Collision, or Capsule Collision).
2. Adjusting the Volume
   • Select the collision volume in the viewport.
   • Use the scaling tools to resize it to fit the object.
3. Configuring Collision Settings
   • In the Details panel, configure how the volume interacts with other objects.
     • Collision Enabled: Choose whether the volume blocks, overlaps, or ignores other objects.
     • Object Type: Define the type of object (e.g., WorldStatic, Pawn).
     • Collision Responses: Customize how the volume responds to other object types.

Using Collision Volumes

1. Blocking Movement
   Collision volumes can stop a character or object from passing through. For example, walls have collision volumes to prevent players from walking through them.
2. Triggering Events
   You can use collision volumes to trigger events when objects overlap. For example:
   • Add a Begin Overlap event in Blueprints.
   • Use this event to trigger actions like opening a door or playing a sound.
3. Overlap Detection
   Detect when an object enters or leaves the volume. For example, a collectible item might detect when a player is close enough to pick it up.
4. Fine-Tuning Interactions
   You can combine multiple collision volumes for detailed control. For example, a character might have a large capsule collision for general movement and smaller box collisions for detecting foot placement.

Example: Setting Up a Door Trigger

1. Add a Box Collision to the door Blueprint.
2. Adjust its size to cover the area where the player should stand to open the door.
3. In the Blueprint, use the Begin Overlap event of the collision volume to play the door-opening animation.

Best Practices

• Simplify Shapes: Use simple collision volumes like boxes or spheres for better performance.
• Test Collisions: Check collision settings in the Viewport using the “Player Collision” view mode.
• Layer Collisions: Use different collision layers for objects to manage interactions easily.

They are essential for making your game world interactive and realistic. They provide the foundation for detecting and responding to player actions, object interactions, and environmental effects.