`xrCreateActionSpace` fails with `XR_ERROR_PATH_UNSUPPORTED` for Vive trackers on SteamVR 2.12.3+

[nicoco007]

This may be related to #1899 but since it wasn't fixed by the latest version I thought I'd create a new issue. Since 2.12.3, xrCreateActionSpace fails with XR_ERROR_PATH_UNSUPPORTED for all Vive tracker roles. This is not the case on 2.12.2.

I've created a sample project in Unity to demonstrate the issue. It's a little weird because it's in C# but the important part is the RunTest method in the ViveTrackerOpenXRFeature which is essentially a recreation of the sample code provided in the spec. It'll run immediately when entering Play mode.

On SteamVR 2.12.2, you should see:

but on SteamVR 2.12.3 and 2.12.4, it's now:

(Unity has defined XR_ERROR_PATH_UNSUPPORTED as simply PathUnsupported)

[nicoco007]

This is still an issue as of SteamVR 2.12.7 and I haven't found any solutions other than reverting to 2.12.2.

[danwillm]

Hi,
I'm unfortunately not able to repro. I have made a sample here (in samples/) that is able to successfully query the pose input of the tracker: https://github.com/danwillm/openxr-actions-tester/

I am also not able to see your sample, but can you make sure that you're enabling the XR_HTCX_vive_tracker_interaction extension in your call to xrCreateInstance?

Thanks.

[nicoco007]

Sorry, I keep forgetting GitHub repos are private by default 🤦🏻‍♂️ It should be public now.

I can confirm your sample works on my end. I believe the reason why is that you're not passing a subactionPath when calling xrCreateActionSpace. If I remove that from my example, it starts working, and if I modify your sample to pass a subactionPath when calling xrCreateActionSpace it fails with Failed to create action space: -22 (i.e. XR_ERROR_PATH_UNSUPPORTED). I was passing /user/vive_tracker_htcx/role/waist (as an XrPath) to both xrCreateAction and xrCreateActionSpace because that's what the example in the spec does.

The spec says the following about subactionPath on xrCreateActionSpace:

subactionPath is XR_NULL_PATH or an XrPath that was specified when the action was created. If subactionPath is a valid path not specified when the action was created the runtime must return XR_ERROR_PATH_UNSUPPORTED. If this parameter is set, the runtime must create a space that is relative to only that subaction’s pose binding.

That second sentence makes me think this behaviour (xrCreateActionSpace not recognizing a subactionPath passed to xrCreateAction) is not following the spec. Am I misunderstanding that? It doesn't seem to be an issue with other devices (e.g. my Index controllers).

As far as I can tell, Unity doesn't support passing XR_NULL_PATH to xrCreateActionSpace through it's OpenXR package — it seems to require a non-empty userPath value that it passes to both xrCreateAction and xrCreateActionSpace no matter what. I could probably figure out a way to get it working by hooking into its methods and calling OpenXR's methods directly, but ideally I'd like to avoid that especially since it's been working fine with the subactionPaths for a couple of years already.

[danwillm]

Ah - thanks, I can repro the error when calling xrCreateActionSpace.

The fix for this should be in the next SteamVR beta update. Let me know if it works for you.

[nicoco007]

Awesome, thank you! I'll try it out as soon as I can once it's released.