Collisions II – Collision Events

Collision events in Unreal Engine define what happens when two objects in the game world interact. These events trigger specific actions, such as stopping movement, playing a sound, or starting an animation. Collision events are essential for creating dynamic and interactive gameplay.

What Are Collision Events?

Collision events occur when objects with collision volumes overlap, collide, or come into contact. Unreal Engine provides several built-in collision events that you can use in your Blueprints or C++ scripts.

Types of Collision Events

1. Begin Overlap
   Triggered when one object begins overlapping another. For example, when a player enters a trigger zone to open a door.
2. End Overlap
   Triggered when one object stops overlapping another. For example, when a player leaves a trigger zone.
3. Hit Event
   Triggered when two objects collide. For example, when a projectile hits a wall or an enemy.
4. Blocking Event
   Triggered when an object is blocked by another. For example, a character cannot move through a wall.

Setting Up Collision Events

1. Add a Collision Volume
   Attach a collision component (e.g., Box Collision, Sphere Collision) to your object or actor.
2. Configure Collision Settings
   In the Details panel:
   • Enable Generate Overlap Events to detect overlaps.
   • Set the collision type (e.g., Overlap, Block, Ignore).
   • Choose the object types the collision should interact with (e.g., WorldStatic, Pawn).
3. Use Collision Events in Blueprints
   Open the Blueprint of the object and find the collision component. Add the following events:
   • On Component Begin Overlap
   • On Component End Overlap
   • On Component Hit

Example Scenarios

1. Opening a Door
   • Add a Box Collision around the door.
   • In the Blueprint, use the Begin Overlap event to play the door opening animation when the player enters the trigger zone.
2. Collecting Items
   • Add a Sphere Collision to the item.
   • Use the Begin Overlap event to make the item disappear and increase the player’s score when the player touches it.
3. Projectile Collision
   • Add a Sphere Collision to the projectile.
   • Use the Hit Event to destroy the projectile and deal damage to the object it hits.
4. Enemy Detection
   • Add a Box Collision to the enemy.
   • Use the Begin Overlap event to trigger an attack animation when the player enters the enemy’s range.

Blueprint Example: Collectible Item

1. Add a Sphere Collision to the item.
2. Enable Generate Overlap Events in the Details panel.
3. Add the On Component Begin Overlap event in the Blueprint.
4. Connect logic to destroy the item and update the player’s score when the overlap occurs.

Event On Component Begin Overlap
→ Destroy Actor (Item)
→ Add to Player Score

Best Practices

• Optimize Collision Settings: Use simple shapes and only enable necessary collision events to improve performance.
• Debug Collisions: Use the “Player Collision” view mode in the editor to check how collision volumes interact.
• Organize Layers: Use collision layers to group similar objects and control interactions more easily.

Collision events are a powerful tool for making your game interactive. By using these events, you can trigger actions that respond to player movements, object interactions, and environmental changes, creating engaging and dynamic gameplay.