{ RCSid $Id: aniso.cal,v 1.3 2019/02/01 16:20:00 greg Exp $ }
{ Ward-Geisler-Moroder-Duer anisotropic BSDF model }

{ Final 5 real arguments are alpha_x and alpha_y roughnesses and Up vector }

ax = arg(AC-4);		{ ax is roughness in Up orientation }
ay = arg(AC-3);

arefl(hx,hy,hz) = Exp(-(hx*hx/(ax*ax) + hy*hy/(ay*ay))/(hz*hz)) *
			(hx*hx + hy*hy + hz*hz) /
			(PI*ax*ay*hz*hz*hz*hz);

axmit(hx,hy,hz) = Exp(-(hx*hx/(ax*ax) + hy*hy/(ay*ay))/(hz*hz)) /
			(4*PI*ax*ay);

dobsdf(sdx,sdy,sdz) = if(sdz, arefl(Idx+sdx, Idy+sdy, Idz+sdz),
			axmit(Idx+sdx, Idy+sdy, Idz-sdz) / sqrt(-sdz*Idz) );

absdf(ox,oy,oz) = dobsdf(Ldx(ox,oy,oz), Ldy(ox,oy,oz), Ldz(ox,oy,oz));