Rim light attribute

[sharktacos]

In the new "all purpose" renderman shader, there is a "rim light" parameter of the shader. It would be awesome to have something like that in Vray as well (maybe as part of the VrayMtl). Is there such a thing, or are there any plans to add this kind of functionality?

Also, I think it would be helpful to discuss how rim lighting functions physically, and who that might be best applied in Vray. My understanding is that rim lights are due to a combination of fresnel reflections on the glancing angles of objects, and light exposure. Cook-Torrance seems to especially address those edge reflections, possibly Ashikmin-Shirley as well (I'm just getting used to that model). So it would be neat to have that as one of the spec models. Currently, of the 3 types (Blinn, Phong, Ward) Phong seems to give the best results for rim highlights.

Also I'm wondering if working with the physical camera and exposure settings might be important to getting accurate rim lights. I have not really done much with this, so if anyone has any insights and tips here, that would be great!

[vlado]

Well, we are working on an implementation of the Cook-Torrance BRDF model, so hopefully it will help with this...

Best regards,
Vlado

[sharktacos]

That sounds cool.

One thing I noticed with the rman rim parameter is that it appears to add a second diffuse component applied to the glancing angle of the geo, and so therefore is more of a lambertian broad rim, rather than a highlight "dot" that a specular model (like phong) would produce.

[sharktacos]

Following up on this... apparently the rim light in the Renderman material is basically a trick where they add a second diffuse term which brightens the edge of an object opposite the incoming light direction. Is there a way to wire up the current vray material to get it to do this?

[vlado]

Can you show me what it looks like?

Best regards,
Vlado

[sharktacos]

Here a page that outlines the use of both a rim light effect as well as light wrap in rman:
https://www.sfdm.scad.edu/faculty/mk...htShaders.html

The above has movie examples of the looks, and code samples. It is based on the work of Sony here:
http://rendermansite.pixar.com/view/renderman-on-film

[bigbossfr]

With OSL, all of this will be possible no ?

[Morbid Angel]

Well, we are working on an implementation of the Cook-Torrance BRDF model, so hopefully it will help with this...

Best regards,
Vlado

Vlado do you think it would be possible to have Cook-Torrance available in vray material soon? the current implementation is not very user friendly

[vlado]

With OSL, all of this will be possible no ?

Not really, unless we implement and provide the respective BRDF. However, an approximation can be done through vrayGLSL for experiments.

Best regards,
Vlado

[vlado]

Vlado do you think it would be possible to have Cook-Torrance available in vray material soon? the current implementation is not very user friendly

Yes, it's somewhere on the "to do" list.

Best regards,
Vlado

[Morbid Angel]

vlado does current implementation of cook-torrance has both diffuse and reflection in the shader?