Collisions & Triggers

Collision layers

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

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

Two bodies collide only if each 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 whose mask only includes enemies, and they will pass through everything else.

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

Define callbacks on a script to respond. Contacts come from solid colliders, overlaps from triggers:

function Script:OnContactBegin(Event: SCollisionEvent)
    print("hit", Event.Other, "at", Event.ImpactSpeed, "m/s")
end

function Script:OnOverlapBegin(Event: SCollisionEvent)
    print("entered trigger of", Event.Other)
end

The full callback set (OnContactBegin/End, OnOverlapBegin/End) and every SCollisionEvent field are in Scripting › Physics.