I have a model I’m trying to render out with a matte object, but I’m having a bit of a problem.
As you can see in the attached image, there is a portion of the model that extends below the ground level.
I have placed a box (the light green box) around this and applied a VrayMtlWrapper material, so it will prevent the model that extends below ground level from being seen with low camera angles.
Problem is, the box just renders black. I just want it to be invisible on the image and alpha, and to make anything it covers invisible too. I don’t want it to cast or receive shadows or anything, just act like it’s not there at all.
Anyone got any suggestions?
Hmmm, that works for the image, but the box still affects the alpha…
Is there a way to stop it from affecting the alpha too??
In the material wrapper OR the vray properties of the object, (remember the material wrapper overrides the vray properties) do either:
1. Set your Alpha contribution to “0” -the object will not appear in the alpha channel.
2. Set your Alpha contribution to “-1” - the object will not appear in the alpha channel AND anything behind it will also appear invisible (cut a way).
Sweet. I’ll give that a try.
Thanks.
It seems I was jumping the gun a bit. With -1, When the irradiance map/light cache is being rendered the alpha is affected by the box, but when the final pass is calculated, the alpha is correct. I gotta play with this matte stuff to get my head around it. 
