Vray Translucency optimization?

[Mokiki]

This is probably a pretty wide question but oh well. I am currently working on a few sequences involving lots of chocolate materials. I have a look I am quite happy with (attachment) that does make heavy use of the translucency feature inside the vraymtl but I get some pretty "long" render times. (Using the term long quite loosely here because I don't know if its long or short based on how much calculation vray has to do)
Now my question is does anybody know any tips while working with translucency to maybe shave off some render time, or would I be better off trying to fake it? Which I don't really have an idea how, since I'd like to avoid painting custom diffuse maps especially since the geo I created does not really have usable UVs. (Using Triplanar at the moment)

[khoross]

I would suggest trying fastsss2, but i'm not sure it would render faster than translucency.

[vlado]

VRayScatterVolumeMtl is also an option, but again it might not render any faster.

Best regards,
Vlado

[vlado]

Also make sure you are not blending multiple materials where each of them has a scattering component (scattering should be done only by the base material).

Best regards,
Vlado

[Mokiki]

@Khoross
I started with fast sss2 and alsurface but I wasn't able to capture the same behavior. At least not in the same timeframe it took me to do it with the vraymtl. I don't know why but when it comes to the fastsss2 or alsurface shader something in my brain just shuts down and I have no idea what I am doing. :P

@vlado
It's just 1 translucent material for the chocolate and a simple reflective mat for the nuts.
I'll give the scatter material a try. I just use it as a base in a blend material and a reflective coat on top. Correct?

[vlado]

I'll give the scatter material a try. I just use it as a base in a blend material and a reflective coat on top. Correct?

VRayScatterVolumeMtl should be the base material, the coat material should be a VRayMtl material with some (glossy) refraction and reflection, without a diffuse component.

Best regards,
Vlado

[Mokiki]

Thanks for the pointers!

[Oleg_Budeanu]

Also make sure you are not blending multiple materials where each of them has a scattering component (scattering should be done only by the base material).

Best regards,
Vlado

So generally it is a bad idea to blend several SSS materials ? It will render too long or produce noise ?

[vlado]

So generally it is a bad idea to blend several SSS materials ? It will render too long or produce noise ?

It will just render slowly. The alSurface material has three SSS layers and they are calculated quite efficiently - you should use that

Best regards,
Vlado

[Mokiki]

Just tried the scattervolume and it brought the render time down from 30 to 26 minutes and I got even more detail for the very thin parts of the mesh. So thanks once again thanks for the tip.
Coloring is darker because I just plugged in the same textures from the vray mtl and the surface less reflective because of the blend but overall I am extremely happy with this. So thanks again Vlado.

*edit* Nvm I just noticed some weirdness. There are pixel missing in the beauty pass which are only represented in the rgb. All other render elements don't have this problem. I only really noticed it because they got blown up during the denoising process and show as large black squares. Any idea what the cause could be?

[kosso_olli]

I remember having these black pixel on the stochastic flakes in GGX mode. Do they have a negative value or NAN in the pixel info?

[Mokiki]

The pixel show: Color (Float): -1.#IO,-1.#IO,-1.#IO,

[vlado]

Can you get me the scene? I've been trying to reproduce this for a while now without much luck - if I get a reproducible case, I can fix it quickly and get you a build.

Best regards,
Vlado

[thanulee]

Hey Vlado, volumescatter has a dedicated render element now? I did a job while back and there was no element. Only fast sss had one. ty

[Mokiki]

Can you get me the scene? I've been trying to reproduce this for a while now without much luck - if I get a reproducible case, I can fix it quickly and get you a build.

Best regards,
Vlado

Sure thing. Once I get back in the office I'll pack it up for you. The file is pretty big so is a dropbox link okay?