MtlWrapper catches unwanted self-shadows

[fabrice_barbey]

Hi all,
I want to put a 3d teapot in a photo of a concrete.
When ,rendering the VrayMtlWrapper material of the mesh wall should be only catching the shadows it projects on the wall.
But it seems it also catches its own self shadows
and I dont want that.

How to make the MtlWrapper only catch the shadow/GI/reflection from the teapot please?
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(Max 2025 + Vray 6 up 2.1)

[vladimir_krastev]

Hi, thanks for posting. I am not able to reproduce this in a simple scene. Could you send us your scene for review? You can do that here or trough the support contact form.

[fabrice_barbey]

Hi Vladimir,
thanks for answering.
I just sent it on the support contact form.

[vladimir_krastev]

Hi, the issue is with Incorrect alpha when having matte objects which cast shadows on themselves. The issue is logged as a bug in our system (VGPU-5171) I will update it with this thread.

[fabrice_barbey]

Thanks but I dont understand...

What will you update ?
Is there a parameter I need to modify in my scene?
What is VGPU-5171?

[vladimir_krastev]

I will update the status of the issue with your complaint so hopefully it gets fixed sooner.
VGPU-5171 is our internal tracker for this issue.
I don't see a good workaround for this issue unfortunately. We might have to wait for the fix.

[Joelaff]

Could you just disable shadow casting for the wall? Or render a version without the teapot and subtract it from the one with the teapot in post?

I have long wanted an option to disable self shadow for objects so they cannot cast shadows on themselves. This used to be a standard thing in all 3d software, frequently used as an optimization. (Possibly due to the use of shadow mapped shadows)

[vladimir_krastev]

Could you just disable shadow casting for the wall?

I've tried it yesterday before posting. It does not work in this case. Also disabling GI does not work.

[Joelaff]

I've tried it yesterday before posting. It does not work in this case. Also disabling GI does not work.

Oh, wow. Ok. So a pretty big bug of some sort, I take it?

What about light exclusions? Exclude the wall from shadow casting that way?

[fabrice_barbey]

That wouldnt be correct because then the wall wont cast shadows on the teapot.
The only good solution would be a per-object "no self-shadows" option.