vraymtl2sided with matte material on backside?

[pechart]

Hi!

I'm trying to setup a scene where I render only the frontside of an object. As this object is also occluding itself I need to use the backside to cut away the alpha of the frontside. Is this possible?

Right now I'm using a 2sided material with my main material in the frontside slot and a material wrapper on the backside. The material wrapper is set to matte object with an alpha of -1. The RGB is fine, but the backsides is fully visible in the alpha, unfortunatly. Any ideas?

Thanks!

(When this is not possible in one pass I still can make a mask, of course.)

[Svetlozar Draganov]

A better approach would be to use VrayMtl with Opacity Map driven by Surface Normal.
With that setup you will be able to see the the front face correctly but when looking the backside of the object it will be invisible with no alpha channel.


Scene: http://ftp.chaosgroup.com/support/sc...kside_alpha.ma

[pechart]

Great, thanks a lot! That'll make it easier.

EDIT: but will the backward facing polys cut a hole into the front faces' alpha?

[Svetlozar Draganov]

No with that setup if a front-face polygon is behind a backface-one it will be visible in RGB and Alpha.

Here is another setup which is based on the previous one but instead of using alpha channel I am using VraySwitchMaterial with two sub-materials a normal material for the front-facing polys and a Wrapper material for the back-facing polys. The same sampler info node is used to determine which material should be applied on front and which on the back-facing polygons.



scene: http://ftp.chaosgroup.com/support/sc...sided_matte.mb