{ RCSid $Id: Ashikhmin.cal,v 1.1 2014/03/24 20:51:16 greg Exp $ }
{
	Ashikhmin-Shirley BRDF model

	Includes Schlick estimate of Fresnel fraction,
	but unlike Radiance material, does not remove
	this from diffuse component.
}
		{ Parameters (change these) }
MF : 30;
lcorr(r,g,b) : MF*(.265*r + .670*g + .065*b);
rho_d : lcorr(0.0039510616569, 0.0036905000484, 0.0027494885161);
rho_s : lcorr(0.0090625419097, 0.0083144131101, 0.0060292909118);
f0 : 0.9999999990000;
nu : 962.839595;
nv : 72.3236783;
		{ Lobe calculation }
abs(x) : if(x, x, -x);
max(a,b) : if(a-b, a, b);
Schlick(odoth) : f0 + (1-f0)*(1-odoth)^5;
lobe2(iz,oz,hx,hy,hz,odoth) : Schlick(odoth)*sqrt((nu+1)*(nv+1)) /
			(8*PI*max(abs(iz),abs(oz))*odoth) *
			abs(hz)^((hx*hx*nu + hy*hy*nv)/(1-hz*hz));
lobe1(iz,ox,oy,oz,hx,hy,hz,nf) :
		lobe2(iz,oz,hx*nf,hy*nf,hz*nf,(ox*hx+oy*hy+oz*hz)*nf);
lobe(iz,ox,oy,oz,hx,hy,hz) : lobe1(iz,ox,oy,oz,hx,hy,hz,
						1/sqrt(hx*hx+hy*hy+hz*hz));

ashikhmin(ix,iy,iz,ox,oy,oz) : if( -iz*oz, 0,
		rho_d/PI + rho_s*lobe(iz,ox,oy,oz,ix+ox,iy+oy,iz+oz) );