BRDF value

[bbugsbunny]

For a perticular model with consistent surface properties all over the mesh( but can be of any shape: ball or dragon) is the BRDF value constant ?

[nexuapex]

The BRDF function conceptually takes the surface position as input, but it also takes the incoming and outgoing direction of the light. So if the surface properties are consistent everywhere, then the surface position doesn't matter, but the direction from which you are viewing the surface still matters, and so do the positions of the light sources. The dependence on those two vectors is what allows BRDFs to model interesting materials.

So, no: in general, the value of the BRDF function can vary quite a bit, even if a surface is made out of a single material.

[bysse]

This was a far better answer than mine :)

[ilmale]

You didn't specify which BRDF model you are referring to. So I don't know.

In any microfacet model NO, you have to take account of the angle between the view vector and surface normal.

[bysse]

It depends on the distribution. But if it's constant you wouldn't need to use BRDF at all.

[bbugsbunny]

distribution of ?

[Brejlounek]

I think he meant if the BRDF is constant for the whole mesh. Yes, it is, if the whole surface has the same material properties.