Phong shading issue with refractive SSS?

[greymiura]

The new refractive translucency options inside the V-Ray Material are great, thanks a lot for the implementation! But I really can't figure out why the translucency portion of the material seems to totally ignore the phong or vertex normal tags of the object.

In this scene I tried to emphasize this strange facetting effect for the object on the right. The one on the left is identical but has a similar looking FastSSS2 Material applied to it instead. I uploaded just the objects with their materials here https://we.tl/t-k722ELqwIZ

I know that the FastSSS2 effect is for a certain part fake while the refractive translucency is calculated more physically accurate. And I know that you can reduce the issue by increasing the subdivisions of the object. But when working with CAD models you'll easily end up with a ridiculous polycount even for fairly simple objects.

Is there a solution to this? Did I choose a wrong setup?

Another question which may probably be better suited for the wishlist section: Are there any chances that the FastSSS2 effect will be reimplementated into the V-Ray Material at some point? I know that that was a V-RayforC4D exclusive solution by LaubLab, but in my opinion it was a great possibility to easily soften the surfaces especially of fabrics, plants, food assets etc. That's one thing I really miss...

[fixeighted]

I remember wondering the same thing using Max....the solution was to use a Vray Displacement modifer set to 0 to subdivide the mesh, so maybe that'll
be good for you here too. The translucency crucially needs the denser mesh for it to work, as it's as you said, more physically based.

[greymiura]

Hey fixeighted,

thanks for your suggestion! At first I thought cool, that's it. But then I realized that the V-Ray Displacement modifier can either subdivide the geometry with this Catmull-Clark like method, which doesn't work with meshed CAD data, or it just subdivides every single polygon without smoothing the angles between them, which also doesn't help with this facetted look. Or did I miss something here?

[sirio76]

Hi,
I’ll check the scene tomorrow and see if this can be fixed somehow.

[greymiura]

I appreciate that very much, Sirio! And as I said, it's not so much about this particular object, but rather about meshed CAD data or low resolution 3D scans.

[fixeighted]

Here's the post where Vlado linked to a pdf with an explanation https://forums.chaos.com/forum/v-ray...shading-errors

[greymiura]

fixeighted, thanks a lot! And please excuse, I could have found that by myself.

So if I'm getting this right, you can only get rid of the artifacts by using geometry that can be subdivided with a Catmull-Clark like method, using the V-Ray Geometry tag or a subdivision surface / turbosmooth modifier or other methods like the cloth modifier. But all of this doesn't work with existing CAD meshes or lowpoly scans...

[fixeighted]

You'd need to retopo stuff to have it work properly. A hassle, but worthwhile if you need the nice result

[greymiura]

No thanks, retopo is a nightmare, at least if you're not familiar with the really sophisticated tools For the current project I'll be fine with just remeshing the STEP data or simply abandoning the SSS effect. It's a device with a translucent plastic case where the material thickness is reduced to 0.2 mm around the buttons. When the light is off, the buttons are totally invisible. I was kind of impressed that V-Ray could actually reproduce this effect, but you can fake it as well.

[sirio76]

I appreciate that very much, Sirio! And as I said, it's not so much about this particular object, but rather about meshed CAD data or low resolution 3D scans.

Hi,
it seems there's no proper solution for this issue, I found a "workaround" but is not perfect, if you turn off the affect shadow option and you play with your color then it sort of work.

[greymiura]

Sirio, thank you so much for your efforts! You're right, the artifacts nearly dissapear, though the material looks quite dull at first glance and loses this vivid SSS look. Strange... And the contrast between the edges, where the light actually passes through the object and the rest looks unnaturally intense. But maybe adjusting the colors will help - I'll give it a try!

[sirio76]

Yes is not perfect since the new SSS is not supposed to work without the affect shadow option, but maybe with some work on colors and SSS depth radius you may get close to what you need