The Looking Glass Buttons can be accessed just like any other default input method in UE4. There are two ways to access the button events:
Direct Event Access
In the event graph if you right click and search “HoloPlay Button” you will be provided with the Gamepad events for all four buttons.
Input Binding Settings
In the Project Settings under the Engine->Input subsection you can bind the HoloPlay button press to either an action or axis input mapping.
The buttons are organized from left to right in naming convention
- HoloPlay Button 0 - Square Button
- HoloPlay Button 1 - Left Arrow
- HoloPlay Button 2 - Right Arrow
- HoloPlay Button 3 - Circle Button
Each button event provides access to both Pressed and Released events.
You can read more about input in Unreal Engine in the UE4 Documentation here: https://docs.unrealengine.com/en-US/Gameplay/Input/index.html