Implement support for virtual reality headsets via version 0.3 of the
osgXR[1] library I've been working on which uses OpenXR.
Add a new VRManager class based on osgXR::Manager to implement its
callbacks. When osgXR needs a new view created, we build a new camera in
the default camera group, and notify osgXR of each new "scene" typed
render pass. It also hooks into the CameraInfo's new compositor reload
callback to ensure osgXR is updated when the compositors are reloaded.
VR settings are controlled by properties, and new --enable-vr /
--disable-vr options are implemented to enable/disable VR at start.
This is enough to get basic VR for looking around the cockpit, but more
work will be required to support a desktop mirror of VR view, VR splash
screen, VR GUI, controller interaction, and correct positional sound.
[1] https://github.com/amalon/osgXR
Print an error message and exit if --{enable,disable}-enhanced-lighting
or --adf are used (those deprecated options will be removed in a future
version of FlightGear).