Mental Ray SSS Skin Shader Multi/Sub-Object Problem


I’m not 100% on this, but as I understand it the Fast SSs shaders use a lightmap to render the SSS effect. This lightmap is refered to in the shader itself. The Lightmap is automatically produce by this shader at rendertime. The issue is that Mental Rays architechture is such that it cannot handle creating multiple light maps for a multi-sub-object material, as it need to only create ONE lightmap per object, and the mutlisub would requite it creating one per SSS shader in the multi-sub. As a result it bails on lightmap creation and the SSS effect does not render.

I understand there could be a hack, to pre-render the lightmaps and assign them manually to the SSS shaders in the multi-sub, but I’ve never done this myself and I think it needs .mi file hacking, basically its bit of a PITA.


I must just be missing the big picture here. Yes, MR creates a single lightmap for the mesh, but I don’t see where that would be a problem? (unless the mesh gets chopped up during an animation?) I don’t consider this technique a PITA (more difficult than it should’ve been…sure).

Here’s a simple test animation:

I animated the mesh, used 5 different skin materials in a multi-subobject map placed in a shellac material, and also animated the light. I had no crashes or any problems for that matter setting this up. Mental Ray simply updated the lightmap each frame. Also, the render time was surprisingly fast (16 minutes for 100 frames).

Now, I can’t verify how well this works across a network, but Mitch stated it worked for him. I’m just not sure how it would update an animated lightmap like I have created here over a LAN…I guess if you use a mapped drive?


hey Jeff thax for sharing! :thumbsup:


is that done as is, with no mi alteration???


no, it was made possible due to mods I made in the .mi file. I describe those modifications in post #13.


Hi Jeff, any chance you could post your “multi-skin” scene, or something similar?



Using mentalray material instead of standard material, in multisub material slot is working.
SSSFast material
–> Overall difuse coloration --> material to shader map --> multisub material / mentalray materials in id slots.
I used rgb multiply map in surface slots of mental ray materials in multisub material.


I have an exisiting character with several materials in a multi sub object material. I would like
to use the fast skin material, but I must be kind of dense, I am lost here.

Several approaches in this thread, but maybe because I am new to MR, I cant get any
of them working. I tried dragging and dropping my multi mat into a shellac top slot with
0 % blend, then using fast sss mat in the seperate slots of the multi mat that are skin.
Still dosent work right.

If someone gets it to work right, could you post a small example file for MR dummies like
myself please?



Using mentalray material instead of standard material, in multisub material slot is working.

So is this a way to avoid the workaround discussed previously?

Your render is not looking all that SSS to me, maybe it is just compression. Or maybe you rendered the light animating around and are about to post it?


All they are maximum jpeg quality and there is only one omni light source in the scene which you can see and there is not another light source and this is SSS.

I was looking for how to use id channel with SSS material.I found this topic and i found a sloution and i thought it is nice to share.
Standard materials didnt work for me using them in multisub material with SSS.So i tried with mental ray material and it worked and i posted it here.
I can send max file if these are not enough.


Ok, cool - good job. Always up for a new way, and please do zip up that scene and post/link.



Hi Emrea!
This is what I did.

  1. Create a fast skin mat.
  2. In the “overall diffuse coloration”, use a “material to shader” map.
  3. In the “material to shader” map use a “multi sub object material”.
  4. Drag the new “multi sub object material” to a new material slot and select instance.
  5. In the “multi sub object material” slots, use a “mental ray” material. (set diffuse prop here)
  6. Apply the fast skin to the multi ID’ed object.

Is this correct? So far it does seem to work!


Maybe this is a basic question for MR veterans, but, using Emrea’s approach, can anyone
please help me with were to put the SSS map to control the amount of SSS of each sub-object
material applied?


Has anybody found a way to make the fast sss material work with a Blend material??
Maybe thats the same trick used for shellac but I dont really understand where you get your lightmaps.


i am interested too in knowing how to get those lightmaps.
they seem view dependant, and strange too me.
they involve any kind of pass render?
thanks for all this information.


I just want clarification, like the other guys, of what exactly a lightmap is and does. I’m assuming it’s a greyscale map that controls the the intensity off SSS in one area?

It’d be great if I could get and answer thanks.



my apology to make gone up the this postbut i do not understand the way of making works the shader sss in multi sub objects material

I understood that it is necessary:

1: Create has fast skin chechmate

2: In the “overall diffuses colouring”, uses has “material to shader” map

3: In the “material to shader” creat has “multi sub object material”

4: Drag the new “multi sub object material” to has new material slot and select instance

I am lost and I do not understand any more what it is necessary to do if you could explain me more clearly, can be by joining a file example.I do not have can be understood owing to the fact that I do not speak good English!

[size=2]PS: sorry for my poor English!!!


hey everybody,

I’ve got the same problem as posted originally here (see post #1) BUT with max 8.0… anybody know if the engineers fixed this already?

(I haven’t had the time to test the solution mentioned here yet, sorry about that)

hoping for some input,



I’ve heard that this is still an issue in Max8. I’m still using 7.5 so I can’t verify. As far as my workaround goes (using light maps), I’ve also heard that doesn’t work in 8 either.


well, that’s good news :hmm: …

I just tested the approach emrea discribed but I can’t get it to work, maybe if he (or someone else who’s managed to make it work) could describe the proces again (nice and clean) so I can test this setup in Max 8 and tell you guys what I found.