# Schlick's model

I am trying to implement schlick’s illumination model in hardware. To simplify the formula I make an assumption that my material is perfectly diffuse and isotropic. So I eliminate azimut and zenith terms (they are both 1). I assume also that my spectral term is constant.
So, I’m left with
R = Color * 1/(4piv, v’) there v= dot(normal, eye),v’= dot(normal, light)

I don’t understand this formula. At the end I get inverted diffuse light(it’s dark where it should be hell). Also it is very dark(1/(4pi) does the job). If I use R = v*v’ instead it looks good. I am really confused about it. Would appeciate an advice of some kind.

If you use the Schlick model with pure diffuse, then you are just doing diffuse lighting. So the answer would just be R = Color * v’ / pi.

I don’t quite understand it. If I use roughtness of one, is is also only diffuse lighing then, right? In this case the formula will apeear as I’ve shown in the previous post. So why v’/pi? Isn’t is darkened Phong lighing? Sorry if I don’t get something, I greately luck knowledge of optical physics…

I am not sure what your source is, but here:
http://dept-info.labri.u-bordeaux.fr/~schlick/DOC/eur2.html

Equation 32. In your case l = 1, b = f = 0 (diffuse assumption), so R = 1 / pi is the BRDF. Then you multiply by the cosine of the light vector to get the display value.

Thanks, I’ve got it. My tests where based on a earlier paper; the equation 32 was not included there BTW, I completely forgot that integral… I guess I’m going to start it anew.

Another question: what should I do to that differential angle based integral? (BRDF equation) Never dealed with that kind of stuff…

To evaluate the integral, just sum over all lights, multiplying the BRDF by the light power and the cosine of the light angle.

For more complicated situations, read a book on global illumination.

Thank you a lot!