Blender Git Loki

XR: Fix for Viewport Denoising Artifacts

Addresses T76003. When using VR with Eevee and viewport denoising,
scene geometry could sometimes be occluded for one eye. Solution is
to use a separate GPUViewport/GPUOffscreen for each VR view instead
of reusing a single one for rendering.

Reviewed By: Julian Eisel, Cl�ment Foucault

Differential Revision: https://developer.blender.org/D11858