View Full Version : Alpha contribution of double sided surfaces

02-26-2009, 03:41 AM
How can I control the alpha contribution of materials created in the node editor? In the layer system we can control the amount a surface contributes to the alpha channel in the advanced tab, but how do you do that in the node editor?

I have a double sided material for which the inside must have an alpha but the outside must not. I've given them different colors so I can create a mask in Shake, but I'd rather have LW create the mask. Does anybody know how to do this?

02-26-2009, 05:08 AM
should be quite easy using the polyon side property of spot info with either a multiply node if you have a complex nodal network or mixer with polygon side plugged in opacity if you just want an image on one side.

02-26-2009, 07:56 AM
Thanks for the reply Bytehawk, but I can't seem to get it to work. I've made the network the same as you have but it still gives me a solid alpha channel.
The idear is to have the alpha channel of the green or the black transparent.

02-26-2009, 01:16 PM
have you tried plugging in the polygon side straight to transparency ?

If it still doesn't work I'll whip up a fast scene for you to show this but it is quite easy.

If polygon side isn't the right way round you can use a math->scalar->invert node inbetween

02-26-2009, 01:32 PM
If you could create a scene for me that would be fab, I can't seem to get it myself :)

02-26-2009, 06:50 PM
Yes but there is no way to control alpha in a surface right.
It would be cool to have a Alpha input in the main Surface Node. It might do wonders for compositing all in one render.

I mean.... without aftecting the visibility, meaning, to make trasnparent.

02-26-2009, 06:59 PM
I hope I'm wrong, but I don't see how Bytehawk's method can affect the rendered alpha channel.

02-26-2009, 07:03 PM
Yea what he said. Would be even better if LW allowed some extra buffers for us to use for what we want, like, make a fresnel buffer, plug it into misc buffer 1. Make masks for characters that go in front and behind each other, plug that into misc buffer 2, etc.