{
	Wood grain pattern:

	A1 - magnitude (0 to 1)
}

xgrain = woodgrain(Ring(Py,Pz));	{ along x axis }
ygrain = woodgrain(Ring(Px,Pz));	{ along y axis }
zgrain = woodgrain(Ring(Px,Py));	{ along z axis }

woodgrain(r) = hermite(.6-A1/2,.6+A1/2,2,.5,2*tri(r,.5));

Ring(a,b) = sqrt( 25 + sq(mod(a,50)-25) + sq(mod(b,50)-25)) +
		  7 * fnoise3(Px/40,Py/40,Pz/40) ;
