Final Gathering & Primary Visibility

[gumboyaya]

Hi,

I found a strange behavior:

Since I am looking for a solution to get rid of those pesky black FG artifacts in my renderings for quite a while, I found out that the FG sampling behaves significantly different depending on the primary visibility.

You can see it clearly in the attached picture.

• On the left side the ground plane is visible. Everything renders nice and smooth.
• On the right side I just deactivated Primary Visibility for the ground plane and nothing else! In the reflections of the lower half of the sphere you can see some hardcore FG artifacts.

Is this how it is supposed to be? I doubt it.

Do I need to set special FG options when using Primary Visibility?

Any ideas?

Thanks
tom

[gumboyaya]

By raising the FG ray count the hardcore artifacts vanished (they are still there but almost not visible in this resolution) but there is still a tremendous difference between the left and right side of the picture.

It seems that the lower half of the sphere does not reflect the ground shadow when Primary Visibility is off.

How can I get this right? Am I missing anything?

[rray]

Hi gumboyaya,

in the FG precomp phase, MR shoots eye rays this is why the dark areas aren't visible in reflections (No FG points generated there).
The "Primary visibility" switch won't work - in order to turn off eye ray visibility of the ground plane, you'd first have to have a mip_rayswitch_stage in the ground's render tree to identify the FG precomp phase - plug your surface shader into all ports of that except "main render". That makes the ground visible to FG precomp eyerays.
Now plug a normal mip_rayswitch into "main render", again plug your surface shader into all ports of that one except eye.
Now put a transparency node into eye, that should do it hopefully :o
Ray

[gumboyaya]

Thanks a lot!

That works perfectly!
Good old MentalRay - you need to be a rocket scientist to handle it ;)