{ RCSid $Id: LaFortune.cal,v 1.1 2014/03/18 16:16:37 greg Exp $ }
{ LaFortune reflectance model with N lobes }

	{ Sample parameters (change these) }
rho_d : 0.136465483630983;
rho_s(i) : select(i, 0.144594472775860);
Cx(i) : select(i, -0.605122636448704);
Cy(i) : select(i, -0.664960041454502);
Cz(i) : select(i, 0.586571000768196);
n(i) : select(i, 29.629194300125050);
NL : n(0);

			{ Useful functions }
max(a,b) : if(a-b, a, b);
abs(x) : if(x, x, -x);
noneg(x) : if(x, x, 0);

	{ Normalization factor based on parameters }
snf(i) : (n(i)+2)/(2*PI*max(abs(Cx(i)),max(abs(Cy(i)),abs(Cz(i))))^n(i));

	{ CHANGE THE FOLOWING TO MATCH NL }
snfk(i) : select(i, snf(1));

{ Note that we assume i and o vectors are normalized, both pointing away }

sum(i,dx,dy,dz) : if(.5-i, 0, sum(i-1) +
		rho_s(i)*snfk(i)*noneg(Cx(i)*dx + Cy(i)*dy + Cz(i)*dz)^n(i));

lafortune(ix,iy,iz,ox,oy,oz) : if( -iz*oz, 0, rho_d/PI + sum(NL,ix*ox,iy*oy,iz*oz) );