Collisions, Overlaps, and Traces

In this article, we explain everything to do with collisions, overlaps, and traces.

Related Material

• https://www.unrealengine.com/en-US/blog/collision-filtering

Special Behavior

There is some unexpected (at least for me) behavior that might be confusing at first:

• Collision detection (blocking) while sweeping an Actor seems to work only for translation and not for rotation. (UE 2.26) That is, bSweep=true in AActor::AddActorLocalRotation does not trigger collision detection, while for AActor::AddActorLocalOffset it works fine. In the documentation of AActor::AddActorWorldRotation it even says that it is “not currently supported for rotation.”
• When sweeping an AActor with AActor::AddActorLocalOffset or AActor::AddActorWorldOffset, collision will only be calculated for its root component. All other components will not trigger collision events. For example, if we have a UCapsuleComponent as the RootComponent and a UStaticMeshComponent attached to it, the UCapsuleComponent will block movement on collision with other actors, while the MeshComponent will clip through other actors.
• When scaling a Component in one or two dimensions, the collision volume seems to stay on the unscaled version.

General Overview