I would be grateful for some help with what I hope is a simple question.

I know that in Carrara one can add distance fog to a scene that will attenuate the intensity of a light ray in proportion to its path length. But can one do the same within an object shader, so that the thick parts of a glass object will be proportionately less transparent than the thin parts?

Thank you, in advance, for any information you can provide.

Attached Link: Digital Carvers Guild

I think you are referring to te fresnel effect. Eric Winemiller's Digital Carvers Guild has the Shader Ops plug-in, that does a fake fresnell effect you can use in the transparancy/reflection channels of your shaders. Look it up!

Thanks for your reply, Hoofdcommissaris. However, Im not referring to the Fresnel effect -- but I probably didnt word my question well.

What I would like to know is how to build an object shader that makes the object less transparent in direct proportion to how thick the object is. A thin piece of coloured glass will transmit more light than a thick one. Similarly, if one excludes Fresnel and refraction effects, a sphere of coloured glass will be more transparent near its edges than near its centre, where the glass is thickest.

Can you, or anyone else, help me out with this?

Attached Link: Subsurface scattering

This reeks like subsurface scattering, a render/shading option that is not available in Carrara. I think it will not be in the near future, because Carrara does not handle it's objects as solids. But I might be brabbling now... You can google more on that of course...

Thanks again, Hoofdcommissaris. Certainly subsurface scattering would be one way to model the effect Im after -- though, I think, an unnecessarily complicated way. As for other methods, you probably hit the target exactly when you said, Carrara does not handle its objects as solids. The distance fog option works according to the path length light travels between an object and the camera. If a light ray travels twice a given distance through the fog, it is dimmed by twice the amount. But there just doesnt seem to be any way to create a shader in Carrara that will do this within the boundaries of an object, attenuating the light passing through in proportion to the distance the light travels through an object of varying thickness. Sigh.

Attached Link: "And by combining Lit and Angle, you can fake translucence!! "

Good news! Look at the link, I think translucency is the thing?

Thanks, yet again, Hoofdcommissaris! I deeply appreciate all your help! I will check out that link immediately.

Your link still didn't lead me to quite what I'm looking for, Hoofdcommissaris -- but it did lead me to a great deal of other interesting and very useful stuff! I'm definitely going to buy Shoestring Shaders today. But I still don't know how to create a shader where transparency decreases with the object's thickness . . .

This may be too coarse for what you are after but this was done using Elevation (Local space) as the mixer for two glass shaders, one with transparency reduced to zero to exaggerate the effect. You'll need to play with Height, Blend and Axis depending on your shape but at least it *does* reduce the transparency with the object's thickness...

HTH

Mark

Message edited on: 10/08/2004 12:22

That is so very clever, Mark! It will indeed produce the effect I'm after for any object on which the side opposite the camera is flat, and can be adapted for any object whatsoever -- discounting slight inaccuracies created by perspective if I don't use an isometric camera and assuming I account for the addition of next object sides -- by splitting that object in half along a plane perpendicular to the direction to the camera. Great!!! Thanks, very much, Mark!

That's good, I'm glad you can use it!