fix(VR): fix eye mismatch for screenspacegi

[alandtse]

partially closes #667

[alandtse]

Ok, since I'm going to take a break for a while, this probably does need to get merged in since it does fix the common VR functions and also makes SSGI partially usable in VR. Without, the eyes are completely mismatched. @FlayaN mind getting this in or finishing up?

The one remaining bug is tied when the blending algorithm stops blending colors because one eye has become occluded. In that case, it reverts to the original color which is a different color then the blended color resulting in brighter areas near foreground objects delineated with sharp edge. The width of the artifact can be further reduced by looking at the depth of the transformed UV and making sure they're at least close to each other. This avoid trying to blend when one eye has a significantly different distance due to the occlusion.

The current blending is actually a stop gap, a more robust fix would be to fix it during the radiance or gi CS passes so that the eyes are the same before ambient or . The blending technique can be useful when dealing with masks so the functions are good to keep. It also fixes a potential bug in determining the eye index because it needs to happen before dynamic resolution adjustment.

[alandtse]

I still recommend VR default SSGI off until a full solution is available both for performance and correctness reasons.

One last thing, because VR is much more jittery than flat, the motion threshold is really too low and must be increased if using the temporal denoiser. Otherwise the accumulated vectors end up always have bad data resulting in grid or mosaic like black patterns.

[doodlum]

I still recommend VR default SSGI off until a full solution is available both for performance and correctness reasons.

One last thing, because VR is much more jittery than flat, the motion threshold is really too low and must be increased if using the temporal denoiser. Otherwise the accumulated vectors end up always have bad data resulting in grid or mosaic like black patterns.

I'm not sure that we exactly have a system to disable a feature by default only on VR. I guess when creating a new JSON, on VR we could set the disabled on boot option.