Improve VR/AR camera experience

[slimbuck]

According to @simonbethke the following issues with AR/VR persist:

• The initial height above 0 is always ~1.5m although the goggles DO know the actual height (works for example in three.js). So if you enter the experience sitting down, everything is off and keeps being off
• The inability to move with the controller. Teleporting works and is nice, but it doesn't allow to get the the correct height
• I wish there were VR authoring-tools that help to get the ground-level and starting position right

[RudminDrones]

Also, on meta quest 3, large scenes of about 2M gaussians produce noticeable lag.
Modifying the viewer to only update the scene sorting when moving the head past a rotation or translation threshold removed this lag while holding the head still, so the issue is the sorting of the scene, not directly the actual display of the scene.

[willeastcott]

That's really interesting that sorting can affect frame rate, since I thought sorting was completely async.

[MisterE123]

That's really interesting that sorting can affect frame rate, since I thought sorting was completely async.

I'm no expert, but I attempted to solve the issue with AI, and while I did not manage to, it's analysis was that the data being transfered between the worker and the main thread after sorting finished was on the order of 8 MB and was the culprit. Splitting the model into several sections with a worker for each, will transfer less data at once

(I'm another account of rudmindrones, sorry)

[Mozoloa]

Very glitchy experience on my side too with the quest 3 browser, where the splats just disappear from a certain distance, if we get too close but sometimes it's not even that close. Doesn't happen on the desktop view. It's also very laggy using native Quest browser vs my PC with Link (obviously) but really it's laggy af for some very basic pretty light splats