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)
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.
Hi Vladimir,
thanks for answering.
I just sent it on the support contact form.
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.
Thanks but I dont understand…
What will you update ?
Is there a parameter I need to modify in my scene?
What is VGPU-5171?
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.
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)
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.
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?
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.
Does anyone know if there is any update on this? I’m trying to set up something similar where I need the object to cast shadows on a matte surface but I’m getting the shadows of the matte surface as well making it useless. I’m getting other oddities too in a very simple scene setup to test it:
Shot of viewport with two planes, a teapot, and an cosmos hdri sun:
If I render this just with standard vray materials I get this (as expected). The HDRI sun is also invisible:
If I then make the two planes shadow catchers (either with the toolbar button or manually) I get this for the RGB which looks as expected but the alpha has a hard shadow from the HDRI sun:
Why is the sun still casting shadows on the alpha? There is a soft GI shadow under the teapot and a bit of a GI shadow on the back plane too which is good and what I’m after. The sun shadow makes this unusable though. The teapot looks correct though.
Continued in next post…
…continued…
If I turn off "no GI on other mattes the RGB looks the same but I get this for the Alpha mask:
I think this is somewhat expected behavior when no GI on other mattes is unchecked.
Lastly, and kind of unrelated, if I make the sun visible I get a weird highlight off the teapot onto the back wall. This happens if I have No GI on other mattes on or off (off in the image below):
It’s like the sun is still going through the plane and causing the teapot to generate GI but renders with no direct lighting on it. Weird.
OK, so, is there any way to get the alpha mask to just have the soft GI shadow at the base of the teapot and the little bit on the back plane? Complicating things is that this is really just a simple part of the overall scene - I’ve got objects that are fully in sun sitting on shadow catchers, objects that are partially in shadow, etc. Further, the planes in the example above are actually camera projection mapped with the photo so I’m using it for reflections and bounced GI lighting. I’m thinking that if there where a way to turn off self shadowing for the mattes I could get this to work (I’d have to merge all of them into one object though). Any ideas are greatly appreciated.
Simple scene attached too although it’s just like I described above.
Matte Test.zip (70.2 KB)
Yeah, I don’t think this is possible in one pass. What you basically want is the GI shadows only. I managed to extract them by rendering once without and once with the object present and its alpha = 0 (to ensure correct math when doing the comp). This gets complicated now since you need the alpha of the object again, which is a third pass… Attaching a gif of the setup in Nuke.
Thanks for the help. It seems like this should be simpler. Plus, the output is rather noisy since the alpha shadow mattes needs to not be denoised (the merge gets a lot of artifacts otherwise for me). Still trying to work out how to get some quick contact and gi shadows.
