Support for VrayScatterVolume on GPU

[Midiaeffects]

I love VrayScatterVolume material and would be very nice to have support for it on the GPU. Also, improvements regarding performance are always welcome, since it's a generally slow material to render (and somewhat prone to fireflies in my experience). And last but not least, a way (maybe another map slot) to texture the volume itself and not just the surface, similar to mapping environment fog.

Regards,
-Eugenio

[vlado]

It's on the "to do" list. Out of curiosity, what are you using it for?

Best regards,
Vlado

[Midiaeffects]

Oh I've been using it for most SSS needs I had in a while. Other methods seem to fall apart on complicated situations like these (everything is using ScatterVolume for SSS):

However, I find it's only viable for stills not just for the rendertime, but especially because of fireflies. On the cookies in particular I had a lot of trouble removing them in Photoshop, and in the second image they look like sugar, but it's not .

-Eugenio

[^Lele^]

Well, all i can say is **** ****!
Superb stuff.

[Midiaeffects]

Thank you so much Lele

-Eugenio

[MANUEL_MOUSIOL]

Would you mind giving some Intel about how create delicious cookies?
I'm trying with alsurface now, but it seems you have great recipe already!

[Macker]

I'm curious as to how you achieved the wafer in the fourth image - is it geometry? (if so, how?) or is it noise & scattervolume?

[stevejjd]

Why is there no scattervolumeshader for Maya ?

[Midiaeffects]

So sorry for such a late reply guys. I totally forgot about this post.

Would you mind giving some Intel about how create delicious cookies?
I'm trying with alsurface now, but it seems you have great recipe already!

There isn't any secret I can think of. The only important one is precisely the use o VrayScatterVolume since it manages to capture those high frequency details where SSS looks brighter and sort of refractive. The nugget image shows that very well. Other methods tend to look too harsh/diffuse like.

I'm curious as to how you achieved the wafer in the fourth image - is it geometry? (if so, how?) or is it noise & scattervolume?

The wafer is a geometry made in Zbrush. I made by modeling simple basic shapes and scattering lots of spheres with nanomesh, converting to poly and subtracting them with dynamesh. I had to do it in multiple passes to get the proper look, first some bigger holes, then smaller, then some additive, etc. Also added some noises on top to avoid any smooth part. It's not perfect but worked ok.

Kind regards,
Eugenio

[MANUEL_MOUSIOL]

Interesting, from reading the docs, scattervolume sounds like a more physically correct fastsss2, but not with huge improvements or changes in appearance. Have to check it out. How does it compare to alsurface in your opinion?

[stevejjd]

The reason people are using the Scatter Volume Shader is because you can do multiple scattering with it - The other SSS models available are only single scatter.

The scatter volume shader offers a bounce controller with a default value of 5 bounces. You could potentially crank it to something stupid like 50 bounces. If you set it to a value of 1 bounce it will become a single scatter shader like VRayFastSSS2 and ALSurface. So the reason why people use it is mainly because of the bounce parameter. You can see a massive difference when Comparing the look of a material with multiple bounces VS a single scatter.

(I think Chaos made the shader as a benchmark to test a more accurate SSS moddel perhaps - sort of like how they have a bidirectional path tracer that no one uses. It could be for diagnostic purposes?)

Light decays exponentially - so a single scatter gives the shader only 1 data-point to represent the falloff of light.......But adding more bounces means that the Inverse square falloff of light can more accurately be depicted.

A bounce value of 1 will produce a shader that looks darker and a bounce value of 50 will produce a brighter look (But I don't think it's MAKING it brighter - There is simply more data to sample and so its able to describe what the material should look like with more accuracy)

I'm using V-ray for Maya Beta and they don't have the Scatter Volume Shader ! - But I really wanted it test fabrics - ScatterVolumeShader is very computationally expensive and my CPU is so shit - so the only way I can test it is with VRayForMayaNext because it supports IPR with DR.

[MANUEL_MOUSIOL]

Thanks for the explanation! Awesome. Sounds like it could really help with my cookie shading,
I am really craving GPU support already ☺️

[Jiri.Matys]

Looks fantastic. Its just scattervolume material + Vraymtl and thats all?