Support OpenHMD

[lboklin]

We don't want to be tied to Valve's unfree Vive drivers and OpenVR implementation, so it would be preferable if Simula worked out of the box using the only reasonable FLO alternative: OpenHMD.

Blockers:

• The OpenHMD plugin for Godot does not work with multi-threading: Crashes with multithreading GodotVR/godot_openhmd#27. This makes it impossible to run Simula with OpenHMD.

Lacking features:

• It doesn't have fully featured support for Vive controllers (see Controllers in demo scene GodotVR/godot_openhmd#6 and 3D render models for HMDs, controllers, ... OpenHMD/OpenHMD#119). It should however be possible to use Simula without VR controllers.

• No support for positional tracking, only rotational (see device support table). May cause discomfort when looking around.

• No support for direct rendering, so the user must resort to using extended desktop.

[georgewsinger]

Is there any update on this? I believe we have disabled Godot multithreading for the time being, which might help us get around the first blocker.

[lboklin]

Simula no longer requires multithreading?

[georgewsinger]

We had to disable it to fix a texturing error race condition (textures were showing up as black).