surface
leaf ( float Ka = 1, Kd = .8, Ks = .0, roughness = .3;
		 color specularcolor = 1;
		 string texturename = ""; )
{
    Ci = Cs;
    Oi = Os;
    if (texturename != "") {
	Ci = color texture (texturename);
	Oi *= float texture (texturename[3], "fill", 1.0, "width", 0.0);
    }

    normal Nf = faceforward (normalize(N),I);
    Ci = Ci * (Ka*ambient() + Kd*diffuse(Nf)) +
	 specularcolor * Ks*specular(Nf,-normalize(I),roughness);
    Ci *= Oi;
}