specular Distribution

Using V-Ray and the V-Ray Material, you have the choice to use Blinn, Phong or Ward for the BRDF (Bidirectional reflectance distribution function) parameter for the material, which is what describes how light is reflected off the surface of the material – or how the specular highlight component of the material looks when rendered.

Representing Surfaces

Technically, the harder, more even and smooth the surface is, the more the specular reflection will be shaper. If the specular reflectance appears to be blurred or diffused in anyway, this is typically seen with materials that are not smooth nor as hard. In thing a zoomed in look at the surface of some objects will reveal that they are being composted of micro facets.

This changes the distribution of the specular reflectance into something more “blurry” or diffused, and in V-Ray, this can be handled by the Blinn or even Phong models to an extent.

Ggx is a microfacet model which is very successful for modeling light reflection from surfaces. In other words it’s a shader like Blinn but 10x more awesome


However, Back in 2007 Bruce Walter, Stephen R. Marschner, Hongsong Li, and Kenneth E. Torrance proposed a new method for modeling light reflection from surfaces using a much more true micro facet model that better matches the measured response of real light transmission from real surfaces. In their paper “Microfacet Models for Refraction through Rough Surfaces” they review the microfacet theory and demonstrate some systems for sampling microfacet models and the corresponding density functions. This new microfacet distribution they called the GGX.


GGX for V-Ray

Borrowing the distribution models from Bruce Walter et al, Sergey Shlyaev developed a shader that can be used with V-Ray, that uses the GGX, the new micro facet distribution described in the paper, which provides a closer match for surfaces than the standard Beckmann distribution function used by Blinn or Phong.

The GGX Shader for V-Ray is a physically correct shader with importance sampling, and works as a BRDF plugin for VRay, available for Autodesk Maya and 3ds Max. The render times are negligibly larger with the GGX shader, but the resulting image is much more true to real life “rough” materials.


Check out the page for the GGX Shader for V-Ray from Sergey Shlyaev’s site here, for some examples and a contact for purchase.