[Sidefx-houdini-list] Anisotropic work around?

Ivan DeWolf ivan at martian-labs.com
Mon Feb 20 13:55:54 EST 2006

I have altered the MT_brushedmetal shader that you can get of of odforce's codex
in the renderman rewrites .zip file to handle polygons many times in the last
several years. You just replace the derivatives (dPdu and dPdv) with some
vectors that you pass in, and create the vectors on the SOP level (same as
Marios current thread).  

I don't have enough spare time to make simplified production-ready shaders that
anyone can just use, I put out shaders as source code so they can be modified
to fit any specific production needs. Production-ready, documented, easy to use
shaders take the most effort to write, and are usually the most difficult to
read, so I try to put together nice legible source code as a starting point for
a shader writer.  If you don't have access to a shader writer that can help you
at your facility, you can always pay myself or any number of other capable
shader writers to whip out an anisotropic shader for your production. It should
only take about an hour.

Quoting Peter Riel <peter at basecampvfx.com>:

> Hey Jim,
>   Yes, it's surprising there is no updated anisotropic shader that works on 
> polys. Especially since polys are pretty much all conquering these days.
>  I use anisotropic highlights often, not just on metals... it gives you yet 
> another way of hiding that awesome CG phong specular we get by default... ;)
> As far as I can understand from the topic on the forum, there is a way to 
> calculate smooth tangents for the highlight shader, but for a fool like me to
> implement it in a vop network is another story. 
> Peter
> måndag 20 februari 2006 01:17 skrev jrutherford at stclaircollege.ca:
> > Hey Peter:
> > I think that the default anisotropic lighting model is based on Greg
> > Ward's lighting model which is .... ahhhhh...
> > anyways for something like brushed metal, you are getting that long thin
> > specular because the shader is finding the x direction and the y direction
> > using something like
> >  vector xdir = normalize (dPdu);
> > Anyways that works great for a surface but with polygons, the houdini
> > default gives you that kind of specular on every single polygon which
> > looks like crap ....but is exactly what the shader is supposed to do...
> > so what is the workaround and why doesn't Sesi have a default that works
> > on polys like Maya...hmmm...probably some patent thing...
> > I think Maya is using some sort of Photon Tracing to get it to work but
> > I'm probably wrong...
> > You'll have to talk to the overly caffeinated ex oboe player for that one
> > which I think in my own humble way is what he has been sort of talking
> > about in his other thread.
> > Jim
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