Volumetric fog is shifted in screenspace when XR is enabled on the viewport.

[luzader]

Godot version

4.0beta16

System information

Windows 10, Vulkan API 1.3.205, NVIDIA - NVIDIA GeForce RTX 3080, Valve Index, Steam VR

Issue description

When XR is enabled FogVolumes (and probably all volumetric fog but it is not obvious for large homogenous volumes) are rendered to the wrong location in both eyes once XR is enabled on the viewport. Here's a unit-cube dense fog volume stacked between two mesh cubes.

Here it is correctly positioned in the editor:

But once XR is enabled on the viewport, the volume is shifted to the left in the left eye and to the right in the right eye:

It is also shifted to the left in the main game window (presumably because the game window is rendering the left eye).

The shift is in screenspace as you can see if I rotate my head:

Steps to reproduce

Create a small fog volume and enable XR on the viewport.
I have also observed this on large fog volumes if using a fog shader which creates small clumps of fog, the clumps are shifted wrongly which breaks stereopsis .

Minimal reproduction project

FogVolume.zip

[BastiaanOlij]

Fog is indeed still on the list of effects to add stereo support for

[jakes1403]

Would this be fixed by the time 4.0.0 is fully released?

[Calinou]

Would this be fixed by the time 4.0.0 is fully released?

No, as this is technically a missing feature for XR (the current implementation of volumetric fog wasn't designed to account for XR).

In the meantime, you can use the good old fake volumetric fog approach using transparent billboards with a StandardMaterial3D that has Proximity Fade and Distance Fade enabled.