{
	Wood grain texture:

	A1 = roughness (0 < roughness < 1).
}

xgrain_dx = 0;				{ dx along x axis }
xgrain_dy = A1 * Rdot * sin(wztexang);	{ dy along x axis }
xgrain_dz = A1 * Rdot * cos(wztexang);	{ dz along x axis }
wxtexang = PI * fnoise3(Px/10, Py, Pz);

ygrain_dx = A1 * Rdot * cos(wztexang);	{ dx along y axis }
ygrain_dy = 0;				{ dy along y axis }
ygrain_dz = A1 * Rdot * sin(wztexang);	{ dz along y axis }
wytexang = PI * fnoise3(Px, Py/10, Pz);

zgrain_dx = A1 * Rdot * cos(wztexang);	{ dx along z axis }
zgrain_dy = A1 * Rdot * sin(wztexang);	{ dy along z axis }
zgrain_dz = 0;				{ dz along z axis }
wztexang = PI * fnoise3(Px, Py, Pz/10);