Out of sync VR camera with lens flares

[SimonTrushkin]

Forum
https://forum.babylonjs.com/t/vr-and-lens-flares/17665

Repro

• PG: https://playground.babylonjs.com/#ZEB7H6#28:
• Expected result: Lens flares was attached on each rig cameras in VR:
• Current result: Lens flares was attached only at one rig camera

Screenshots
https://aws1.discourse-cdn.com/business7/uploads/babylonjs/optimized/2X/0/0edfcc03e06a676912a81bd3fa3fe84ec97e5d51_2_657x500.jpeg

Device
Oculus Quest 2

[RaananW]

According to my tests (and the attached image) - lens flare was added to both cameras.

This is not a bug, but the right behavior according to the current implementation. The problem is that each camera has a different position and rotation, so the lens flare is positioned incorrectly when viewed in a headset (each eye sees something else, it feels very odd).
The camera that should be used to calculate the lens flare's positions is the xr camera and not the rig camera. The rig camera should only render.

[SimonTrushkin]

@RaananW Yes, I'm sorry, I put it wrong, flares really added to both cameras but attached to only one (on second camera flares are rendered like at first camera how i understand).

[RaananW]

This feature, together with others like post processing (god rays is a good example) require the projection layer of the layer API to work correctly - #10588 . Once integrated this issue will be dealt with