Adding random walk SSS to alsurface please

[Bigguns]

Hi,

Like the title says it, can you guy's add the random walk sss to the alsurface sss shader, so we would have the choice between 3 method of sss. Random walk is very good, especially for strong sss but also for skin etc. Even blender has it now. here's a link to it :

https://developer.blender.org/D3054#72261

[jasonhuang1115]

I am wondering if you have tried the VrayScatterVolume for sss of face skin?

[^Lele^]

scatterVolume *is* random walk.

[vlado]

The VRayScatterVolume material is an implementation of random walk SSS and has been in V-Ray for quite a while. There is more information about it here:
https://docs.chaosgroup.com/display/...yScatterVolume

To make it easier to use, at some point it will be integrated into the VRayMtl material, along with a second coat reflection layer.

Best regards,
Vlado

[jasonhuang1115]

vlado lele cheers, thanks for the clarifications. It's great to learn it will be part of VrayMtl in the future.

What would be the main pros and cons of using VRayScatterVolume for sss than VrayAlsurface? One feature I see in VRayScatterVolume is the forward/backward scattering through phase function, which seems to not existent in VRrayAlsurface.

[vlado]

What would be the main pros and cons of using VRayScatterVolume for sss than VrayAlsurface? One feature I see in VRayScatterVolume is the forward/backward scattering through phase function, which seems to not existent in VRrayAlsurface.

The scatter volume behaves much more realistically with complex shapes with thin translucent details, but may require quite a large number of volume bounces to look right (20-25), which will take up render time. While the phase function is there, it is actually very very slow to calculate for anything other than isotropic scattering.

Best regards,
Vlado

[jasonhuang1115]

The scatter volume behaves much more realistically with complex shapes with thin translucent details, but may require quite a large number of volume bounces to look right (20-25), which will take up render time. While the phase function is there, it is actually very very slow to calculate for anything other than isotropic scattering.

Best regards,
Vlado

vlado so essentially the VRayScatterVolume yields more realistic results, especially for thin translucent surfaces, but takes longer to render.
Is the phase function map-able? I tried to plug a Maya file node via a couple of ways but in vain. In the connection editor, the phase function isn't in the list of attributes for accepting input connection. I only see overall_color, color, scatter_color, and radius_mult available as input connection.

[^Lele^]

a few samples.
Most are just achieved using the two colors and the radius, without any texturing.
Murex_Romosus_01.jpg has the radius mapped with a curvature texture, and view-dependent gradients in the scatterVolume colors.

[^Lele^]

A few more, showing also the (non-mappable) phase, and the other scatter mode, better suited to liquids and such.
The first two are the same shader and lighting conditions as the shell.
The B versions are with the other scatter mode, and cues of what i did to the shader in the file names (f.e. "fwd" "fwd_higherRadius", etc.).

[^Lele^]

continued from the previous post

[^Lele^]

and more still.

[jasonhuang1115]

lele Thanks for the examples. Very interesting!

On a tangent, is there a phase function in VRayAlsurface? I see in Ander Langland's documentation, there is a "scattering_direction" for forward/backward scattering control but didn't see that in VRayAlsurface.

[DaveKW]

It's worth noting that the scattervolume shader has no reflection component and so if you want to use it as an alSurface replacement you need to use it in a blend material with scattervolume as a base and a refractive shader as a coat with the blend colour set to white. I'm doing some tests with this to see how useful it is as a skin shader. I will post some tests soon.

[^Lele^]

David, some of my samples indeed had the setup you described.

[jasonhuang1115]

It's worth noting that the scattervolume shader has no reflection component and so if you want to use it as an alSurface replacement you need to use it in a blend material with scattervolume as a base and a refractive shader as a coat with the blend colour set to white. I'm doing some tests with this to see how useful it is as a skin shader. I will post some tests soon.

I am curious about how it works on skin. The white blend is for blending refractive shader as a coat. Is it how one should blend two spec lobes for skin (white color for both blend color)? Should it be "additive" blend?