Stereoscopic optimization: Single plane 3D

Stereoscopic rendering in Qt 3D Studio runtime is fully 3D meaning that whole scene is rendered 2 times with different cameras and z-position of each vertice defines how much eye separation it gets (so how far it appears to be).

Alternative would be supporting only single 3D distance at a time: Render scene only single time into fbo and blit it 2 times with configurable eye separation. Performance of this should be quite close to normal mono rendering. Limitation is that there would be only single 3D distance for the whole scene (or for each layer if we want to support that), but that might be enough for some use-cases?