How to render faces occluded by front facing object

[craigdvance]

is it possible to, or what configuration could you use to render faces on an object that are occluded by geometry in front of it. For example drapery, you want the folds rendered for a specific purpose, that are behind other folds.
Is there a sampler info mode that would make the first set of faces the camera sees invisible and only render out the geo behind the first set of rays.....
I need to render out backing information on a single object to comp later and change opacity of the first set of geo. Its all one piece of geo which is the challenging part so I thought maybe there was a ray math config that could be used but I am not very knowledgeable about the math part of shaders.

[oglu]

Could you share an image? Its not clear to me.

[Morbid Angel]

You probably have only two choices there. One is to use a camera clipping plane, switch from auto to manually define the near clip, this will omit rendering anything that falls below (in front) of the near clip value. I typically would setup two layers, one with near clip set to 0.001 and far clip set to (whatever the foreground you want), then second layer would be the near clip would be set to the same value as the far clip of the first layer and the far clip would be set to a high value to encompass the whole scene. The other option is to render deep, but again deep won't see objects that are behind other objects and you would have to do some kind of zslice anyway.

[craigdvance]

Morbid Angel, yeah I think you are right. I can't really think of another way around it. I thought about z-depth but that won't really do what I need.

[fixeighted]

Maybe it's as simple as a face selection of the front faces, which you can hide in order to render the back faces.
Or is it more complex than that?

[Morbid Angel]

Ok how about this: something can be achieved with the 2sided material, where each side is a separate material, and for one render layer you switch the opacity off for the front material so it only renders backside, and for the other render layer your reverse the process.