It is clear that there has been a lot of updates on the subject, however not much documentation is (yet) available, as far as I'm aware of. I downloaded the most recent commit from the feature/spectatorview branch of MixedrealityToolkit-Unity, and copied the MixedRealityToolkit.Extensions into my MRTK folder.
Now some of the noticable changes has to do with the PlatformSwitcher-holding prefab "SpectatorView - HoloLens". The script is marked as "SpectatorViewOld" and it could be interpreted as this is a deprecated prefab. There's also SpectatorView.ASA.HoloLens/Android, however these prefabs are seemingly having missing scripts, which prevents them from being usable in a project.
My question is, if there's an up-to-date guide on how to implement the SpectatorView, and if so, where can I find this/How do I go about it? Should I stick with an earlier commit?
Update:
We have migrated to a new repository with samples and better documentation, please take a look here: https://github.com/microsoft/MixedReality-SpectatorView.
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Yes, we currently have a stable branch that matches what we showcased at //BUILD: https://github.com/microsoft/MixedRealityToolkit-Unity/tree/prerelease/2019.build.spectatorView
And, documentation for it here: https://github.com/microsoft/MixedRealityToolkit-Unity/blob/prerelease/2019.build.spectatorView/Assets/MixedRealityToolkit.Extensions/SpectatorView/SpectatorView.md
Please give that a try.
We are still in active development as we push towards a V1, and soon will be cleaning up all the deprecated files and polishing of our documentation.