UEFN Scene Graph Touch Detection: Collision Sensors and Limitations

UEFN Scene Graph touch detection is part of Fortnite 43.10’s experimental Perception API. It reports contact between collidable Scene Graph meshes through touch emitters and detectors. Players and NPC characters don’t trigger these sensors in this release, and islands using the experimental feature cannot be published.

That rules out treating the new API as an instant solution for a player-operated pressure plate. If your design needs a player to enter a trigger or step on a pad right now, use the supported devices suited to that behaviour.

Scene Graph Touch is more useful as a technical prototype for mesh-to-mesh contact, with gameplay reacting when two objects meet or separate.

How UEFN Scene Graph touch detection is set up

Put a touch_detector_component on the entity doing the sensing and make sure its configured mesh can collide. The entity you want to detect needs a collidable mesh carrying a touch_emitter_component, or the touch emitter must exist on an ancestor in the entity hierarchy. Subscribe a receiver to the detector with a filter.

Without a subscription, the detector will not listen to mesh collision events. Without a qualifying emitter in the collision ancestry, no perception touch event is raised.

What UEFN Scene Graph touch detection reports

Touch begins with Active when contact is established and moves to Inactive when the final contact is separated. Unlike the sight and hearing family, built-in Touch does not emit Instant events. The event’s touch data can contain contact information from the underlying collision, including location and normal.

If multiple meshes touch, be careful about assuming that the first separation means everything has stopped touching; the detector tracks the overall contact state.

Test UEFN Scene Graph touch detection with two meshes

For a UEFN Scene Graph touch detection test, put a detector on one collidable mesh and an emitter on another. Bring them together using movement that produces Scene Graph collision events, then separate them. Log the Active and Inactive events. Keyframed entity movement does not produce the needed collision events in v43.10, so it isn’t a valid test.

UEFN Scene Graph touch detection: why a player pressure plate will not work

A player-operated pressure plate sounds like an obvious use, but the built-in Touch sense cannot detect player or NPC characters yet. Use a supported trigger or volume device for that kind of published island mechanic. Test experimental Touch with mesh objects instead.

What to check when nothing happens

If nothing happens, check that both meshes have collision enabled, the emitter is attached to the correct entity and the detector watches the right mesh. Then check the event subscription and filter. Start with two objects in an otherwise empty test scene.

How mesh hierarchy affects touch detection

A touch emitter can sit on the collidable mesh’s entity or on an ancestor in the Scene Graph hierarchy. If you’ve moved objects into nested entities, check where the emitter ended up. The detector must also be configured to watch the correct collidable meshes. A visible overlap between two models isn’t enough if their collision setup does not produce the events the API needs.

Use two simple meshes first. Bring them into contact and watch for Active, then separate them fully and check for Inactive. If several mesh contacts exist at once, the last separation is what ends the touch. The event can include the contact location and normal, which can help you tell whether the collision happened where you expected. Player and NPC characters remain unsupported in this experimental version.

UEFN Scene Graph touch detection FAQ

Can the built-in touch detector sense Fortnite players? No. In 43.10, neither players nor NPCs emit the required Scene Graph collision events.

What are the touch states? Active when contact begins and Inactive when the final contact ends. The built-in detector does not send Instant events.

Will keyframed movement trigger detection? Epic says keyframed movement does not generate the collision events this experimental sense needs.

Official source: Epic Games documentation.