Local Illumination Models..which one do you use?

[jeremybirn]

What do you mean: like Phong vs. Blinn vs. Lambert - that kind of thing?

-j

[kpalazov]

Hi jeremybirn,
Thank you for your reply :))...You are right on track with what I was thinking. I was interested in finding what other people are using for shading their objects; say maybe a specialized metal luminance function or maybe something special for dino or human skin. As mentioned I was primarily aiming at addressing the customization of the luminance function in Renderman SL.
Basically how you implement it and when?...that being said I'm open to any other models, or sources where I can find them?

What forced me to change what I had written in my first thread is my reading on ray marching in one of the siggraph papers, explaining the shader for the human and I guess monkey heart in Hollow man.
Please add to this if I'm making wrong assumptions, but it seemed that the majority of the shader, the calculation of the subsurface effect was achieved outside the luminance loop.
This really got me to thinking that really the luminance loop is not necessarily describing the local illumation of the shader.
( From the 2002 Rman Siggraph Paper: Two processes in shaders, the creation of patterns over the surface and desribing the surfaces reaction to light(luminance loop)....My confusion is that its possible to describe surface properties like translucence outside the luminace loop??...not simply pattern generation??
I thought a subsurface shader would be implemented into a luminance loop as another color function and then composite, just like the diffuse and secular functions.

If anyone wants to add or correct what I said, or better yet share with us your philosophy on the use of the luminance function and or general shader writing, I would be very grateful.

All the best

Kiril

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Ps....Mr.Birn I will add that I am a big fan of yours:)!!..thankyou kindley for your fantastic book !!

[fxjeane]

I believe that only if your shader requires gather information like color or intensity and add it to the shaded polygon then it will need an illuminance loop.

There are many functions and ways to gather SSS information for a shader. Some of them are done outside the illuminance loop since they are not trying to set the "color" of the micropolygon been shaded, they are just trying to set how much light will be transported to a micropolygon based on the SSS algorythm.

Please, those of your more experienced, step in and correct me if im wrong. (I hate sending people down a wrong path) :)


Go to renderman.org and read this year's Siggraph RenderMan course.. There are 2 Chapters that are ALL SSS stuff.

good luck

FxJeane

[kpalazov]

Hi fxjeane ,
THanks for your reply. I was wondering where I could find the 2003 Sigraph course...it will no doubt be very helpful in clarifying this issue of myn. For those that are interested here is the link to its location, just scroll down:

http://www.renderman.org/RMR/Books/index.html (36 mg!!)

I will have a read over these and post my resolution hopefully in the next couple of days.

If anyone else has something to add to this subject in concern to the use of the luminance loop or and any other idea i would love to here them:))

thank once again

Kiril

[stew]

Thanks for the link. Has renderman.org been redesigned recently? I was looking for such papers a few weeks ago and couldn't find anything on renderman.org. It looks much better now.

If you want to see examples for using SSS, AO or photon mapping shaders, I found that Pixie (http://pixie.sourceforge.net) comes with some nice examples.

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