[PC VR/ XR Elite] OpenXR UE 5.1 Windows app not launching to an XR Elite connected over VIVE Streaming Hub

[Jeromee]

The two Unreal 5.1.1 projects below (set up with ViveOpenXR_1.6.0.r2 plugin) launch well to a connected XR Elite, via the VR Preview of UE Editor. 

However the resulting Windows target build (a Windows EXE) does not launch to the connected XR Elite. It only launches in a desktop window.

Concerned projects:
- 'ViveOpenXR_1.6.0.r2_UE51_Project' sample OR
- Epic VR Template 5.1.1 with 'ViveOpenXR_1.6.0.r2_UE51_Plugin'

Configuration:
- XR Elite software: VR 1.0.999.350
- SteamVR 1.26.3 with OpenXR runtime = 'SteamVR'
- VIVE Streaming Hub 1.1.8, via USB VIVE Streaming Cable, OR via Wifi 6E

Log output by the Windows app

Quote

LogHMD: Optional extension XR_KHR_vulkan_swapchain_format_list is not available
LogHMD: Optional extension XR_VARJO_quad_views is not available
LogHMD: Optional extension XR_KHR_binding_modification is not available
LogHMD: Optional extension XR_EPIC_view_configuration_fov is not available
LogHMD: Optional extension XR_EXT_dpad_binding is not available
LogHMD: Warning: Required extension XR_HTC_vive_focus3_controller_interaction is not available
LogHMD: Could not enable all required OpenXR extensions for OpenXRExtensionPlugin on current system. This plugin will be loaded but ignored, but will be enabled on a target platform that supports the required extension.
LogHMD: Warning: Required extension XR_HTC_vive_cosmos_controller_interaction is not available
LogHMD: Could not enable all required OpenXR extensions for OpenXRExtensionPlugin on current system. This plugin will be loaded but ignored, but will be enabled on a target platform that supports the required extension.
LogViveOpenXR: Entry SU GetRequiredExtensions.
LogHMD: Initialized OpenXR on Oculus runtime version 1.86.0
LogHMD: Failed to get an OpenXR system, result is XR_ERROR_FORM_FACTOR_UNAVAILABLE. Please check that your runtime supports VR headsets.

 

[Jeromee]

Problem solved.

The cause was I have installed on my PC both HTC Vive Streaming Hub and Oculus Desktop environments, meaning two OpenXR runtimes that may conflict with each other:
- C:\Program Files (x86)\VR\Steam\steamapps\common\SteamVR\steamxr_win64.json (for VIVE)
- C:\Program Files\Oculus\Support\oculus-runtime\oculus_openxr_64.json (for Oculus)

In this situation, this OpenXR runtime path must be assigned...:
- not only to the 'HKEY_LOCAL_MACHINE\SOFTWARE\Khronos\OpenXR\1\ActiveRuntime' registry key
- but also to the 'XR_RUNTIME_JSON' environment variable

The second point was the missing point for me.