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Adrian

A way to render overlapping geometry as a single SSS volume?

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Hello. I was wondering – can anyone think of a way to compute a SSS point cloud that treats closed, overlapping geometry as a single volume. I have meshes that would be very tedious to unify, and I doubt poly -> VDB -> union -> poly -> reduce can give me a crisp enough result.

Alas I don't have enough insight into the workings of how SSS point clouds are mapped onto polygonal geometry, but wondered if a volumetric approximation of the meshes with sufficient resolution could serve as the basis (somehow).

Any ideas / suggestions welcome.

overlapping_meshes.jpg

Edited by Adrian

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Hi,
I am not sure how it does work in Mantra, but in Arnold you can set SSS groups which I believe solves this task.

I am curious if something similar is also in Mantra.

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I don't have much experience with SSS point clouds in Mantra, but using ray traced SSS your above model should render fine if merged into a single geometry OP.

Give it a try, object merge your objects into a single one and use the full ray trace setting on the SSS shader VOP.

Hope this helps,

Andy

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Juraj, something like that, yeah. Arnold looks really cool btw, very intuitive SSS parameters!

Andy58, unless I made some other mistake, I don't think you suggestion works. I tried the "Full Ray Traced" model (though that would be too slow for my needs anyway), but it shows identical artifacts to the "Global Point Cloud" (fast). I've attached two images, only differing by the amount of attenuation set in the shader. The scene is lit from the front by a point light, as you can see by the shadow thrown from the top cylinder onto the one behind/right to it. However there are also dark see-through like shapes that wouldn't be there in a unified volume; there should be no cylinder going though that box anymore. The artifacts don't behave like shadows or reflections, which I suspected at first.

Even though the second image looks much better in this regard, it essentially suffers from the same problem, just masking it out more.

low_attenuation.jpg

high_attenuation.jpg

p.s. Sorry for not aligning the images, the forum software doesn't seem to allow me to specify that.

Edited by Adrian

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Hey Adrian

I don't seem to get those dark lines where objects intersect, except where the angle is somewhere around 90 degrees. AFAIK this is a limitation of the algorithm used for SSS.
Try not to use single scattering, It will show dark lines at intersections. Play with the IOR, even set it to 1.0. 

I usually work on characters where merging solves the SSS flow across objects. Perhaps as characters usually have a smooth surface I've not encountered these artifacts. I'm sorry to not be of more help.

Andy

 

sss_merged_traced.png

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Andy58, Not using Single Scattering made the key difference. Without it, the material lost a lot of definition/contrast, but with more tweaking I think I'll be able to get a satisfying result. Thanks a lot for your help!

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