Collisions & Triggers

Collision layers

Every body has a Collision Profile with a Layer and a Mask.

• Layer is the category this body belongs to.
• Mask is the categories this body collides against.

Two bodies collide if either one’s mask includes the other’s layer. The built-in layers are Static, Dynamic, and Channel 0 through Channel 13 for your own gameplay categories. For example, put bullets on a channel and give them a mask of only the layers they should hit, so they pass through everything else.

By default a body’s Layer is Dynamic and its Mask is Static + Dynamic, so ordinary bodies collide with the world and each other.

Solid colliders vs triggers

By default a collider is solid. Bodies bounce off it, and you receive contact events.

Turn on a collider’s Is Trigger flag and it stops being solid. Bodies pass through it, but you receive overlap events. Use triggers for pickups, checkpoints, and damage volumes. The rigid body’s Is Sensor flag does the same thing at the whole-body level.

Reacting in a script

Bind a handler to the rigid body’s collision events. Cache the SRigidBodyComponent with [RequireComponent] and bind in OnReady. Contacts come from solid colliders, overlaps from triggers.

[RequireComponent] private SRigidBodyComponent _Body = null!;

public override void OnReady()
{
    _Body.OnContactBegin.Bind(OnHit);
    _Body.OnOverlapBegin.Bind(OnEnterTrigger);
}

private void OnHit(SCollisionEvent Event)
{
    Debug.Log($"hit {Event.Other} at {Event.ImpactSpeed} m/s");
}

private void OnEnterTrigger(SCollisionEvent Event)
{
    Debug.Log($"entered trigger of {Event.Other}");
}

The full event set (OnContactBegin/OnContactEnd, OnOverlapBegin/ OnOverlapEnd) and every SCollisionEvent field are in Scripting › Physics.