New BRDF model documentation

[tim_harding]

Hey folks,

Since going through Grant Warwick's Vray Training course, which goes over layer spec and glancing-angle reflection, I have been testing out the new BRDF models (GGX and Vray BRDF) in the more recent 3.0 versions. The GGX is working quite nicely, and its much cheaper to render than the layered Blinn technique. The Vray model, however, I'm very confused about. It seems to be doing some weird things, shifting around highlight placement and giving weird shapes. I haven't been able to find any documentation on these new BRDFs, so I was wondering if there was somewhere I could find out more information on how they work. Thanks,

-Tim Harding

[tashko.zashev]

Hi Tim,

What kind of information do you need for the Ggx Brdf ? How the code behind it works or render examples?

[vlado]

The Vray model, however, I'm very confused about.

Which V-Ray model? We only have Phong, Blinn, Ward and GGX exposed in the UI.

Best regards,
Vlado

[tim_harding]

I can see the GGX using multiple specular lobes, but I was curious how it handles glancing angle reflections with increased glossiness, and what sort of surface it's designed to simulate. The Vray BRDF I now notice is not available in Maya, however it is exposed in the Modo plugin. How is the Vray BRDF supposed to be used, and what does it do differently that creates its unique look? Thanks again.

[vlado]

The GGX does not really use multiple specular lobes; it's still just one lobe, however by controlling the hilight tail falloff, you can achieve many different looks, as you can see on this page:
http://help.chaosgroup.com/vray/imag...tr_render.html

The V-Ray BRDF was not supposed to be exposed, and I think it is hidden in subsequent builds of V-Ray for Modo. It has no relationship whatsoever to how materials behave in the real world.

Best regards,
Vlado