Finally, here it is: https://www.reddit.com/r/GearVR/comments/4a5a96/holokilo_positional_tracker_using_camera_flash/
I don’t know if it’s bad or good, but the dev said if UE4 devs will request support, he’d implement support for UE4. So, if you are a developer for mobile VR, you might want to go to reddit (or github) and ask for UE4 support.