Simulating subsurface scattering

[richard-sher]

Tom Sporer has created a little shader that does an excellent job of simulating subsurface scattering in XSI. (thanks Tom) It looks great and it's really quite fast. (It renders in just a few seconds) While it may not be "real" subsurface scattering it looks so good and it renders so quickly that it does not really matter.

You can download the shader and view a tutorial on how to use it here: http://www.tomsporer.comhttp://www.tomsporer.com
This is great, however, I'm still searching for a way to create "real" subsurface scattering in XSI. According to the Mental Images web site mental ray can do subsurface scattering. If any one knows how, please tell me. I'd like to do so comparisons between the "real" thing and "fake" shaders like this one.

Ed
XSI Videos, Classes, Tutorials, Tools, Shaders....
Available at:http://www.EdHarriss.comhttp://www.EdHarriss.com

[sonne]

Hi Ed,

It sounds really cool, but www.tomsporer.com doesn't work.. Are you sure it's the right link?

Thanx,
Peter

[wolfinger]

How does this shader and/or the real mr SSS work actually? Will it still render when the camera is inside the object?

What I'm going after is that there's no decent fog in XSI/mr, because there's no real volumetric objects. SSS is volumetric/solid rendering, so if it's done right I bet it could be used to make a nice fog. Then you wouldn't need a "volumic light shader", just point a normal light towards an SSS object and you get the volumetric effect inside the object. Also the camera could then move from outside the object to inside the object naturally (using the XSI fog the fog just dissappears when the camera moves inside the fog object).

[devdoka]

mental ray does have volumic objects, but in order to see the volume effects applied, the surface needs to be at least semi-transparent. When you're modifying a volume shader, what you're doing is adjusting the color of space according to the ray attributes and/or changing the ray's direction at each sample. Using the rendertree, you can create fog like effects very easily.

Fog only disappears if you place the volume shader on an object because the camera is not allowed into a fixed volume. If you place the shader on the pass, however, then fog is applied to the entire scene and the camera can move around freely. Read the mental ray manual!!!

If you're tired of dealing with fog, then try the "Volume Effects" shader. It's the "March_Volume" shader from SI3D. The default settings won't produce anything desireable (or visible), but play around with the scattering lights and volumic density and you'll get some nice results very quickly.

Matt

---

Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com

[wolfinger]

In reply to:Fog only disappears if you place the volume shader on an object because the camera is not allowed into a fixed volume. If you place the shader on the pass, however, then fog is applied to the entire scene and the camera can move around freely. Read the mental ray manual!!!

This is exactly what I want to avoid. I need a camera that can move from outside a localized fog to inside a localized fog, and back outside again. Now I have to do this in several passes or scenes, with one pass having a universal fog, and the others having a localized fog shader. Plus the fake is never perfect.

MAX can do it just fine... (so why am I not using MAX? it sucks, I know, that's why I have XSI now, but it's still a good gripe)

Also it would be great to get other realistic volumic effects (like volumic light visible in fog), but I've never seen any 3D package do that, at least not without simulating fog with particles.

[richard-sher]

In reply to:
Hi Ed,

It sounds really cool, but www.tomsporer.com doesn't work.. Are you sure it's the right link?

Thanx,
Peter

It does work. I just went there. Perhaps it was down (or bogged down) when you tried earlier. It's somewhat slow to access here in the US, so it might be slow in your part of the world too. Open a browser and let it sit there while you do some work. Eventually it will pop up.

Ed
XSI Videos, Classes, Tutorials, Tools, Shaders....
Available at:http://www.EdHarriss.comhttp://www.EdHarriss.com

[devdoka]

Did you even try the Volume Effects shader like I suggested?

It comes with a bounding box parameter so you don't need to use actual geometry for the localized fog (so you can fly in and out of the fog). It also supports volumic lighting if you pick the desired lights and add them to the scattering and shadowing lists on the last tab of the shaders' PPG.

Do some tests before you gripe, you might discover you can do it afterall.

Also, read the mental ray manual (not the softimage manual describing mental ray). You'll learn a lot of how mental ray thinks/works and therefore achieve your desired effects much quicker with less effort. The html docs are part of your XSI v2.0 installation.

Matt

---

Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com

[wolfinger]

No, I haven't had time to test it yet, but I will. Just need more time.

Is it actually possible to use this shader you mention with geometry (or some shape(s) other than a bounding box)? I'd like to use real geometry as fog bounds if possible... Nevertheless it sounds like it could do the job.

To my defense I have to say I HAVE done a lot of tests before griping, albeit on XSI 1.5. I sat a long time trying to make a fog which I could fly into, but couldn't manage. Of course I know that doesn't mean it's not possible, but They sure as hell haven't made it too easy. Once again the manuals were of no help, but I haven't read any mental ray specific manuals - just the XSI 1.5 ones.

I found the mental ray manual now, on the XSI 2 Docs CD (couldn't find anything in the actual XSI installation directory besides the command reference etc). I'll read it through as time allows.

Thanks for the help anyway! I do appreciate it.

Edited by Fess on 01/15/02 10:29:31 AM.

[sonne]

Hi,

It would be extremely cool, if someone could upload this shader somewhere, because I've tried www.tomsporer.com a LOT of times now, and it just doesn't work.

Thanx,
Peter

[jesperk]

The site seems to be working now.
I can mail it if anybody needs it!

Best regards
Jesper

[nurbousbreakdown]

In reply to:
Hi,

It would be extremely cool, if someone could upload this shader somewhere, because I've tried www.tomsporer.com a LOT of times now, and it just doesn't work.

Thanx,
Peter

it was having extreme bandwidth problems....

I guess Tom didn't expect the hordes and mobs that turned up on his doorstep )

but he said it should be working now.

Balgillow

[sonne]

Hi,

I have downloaded everything now, so no need to mail it to me.
Thanx for the help - looking forward to trying it out.

Peter