k3d/share/shaders/k3d_superplank.sl:32: *   graindepth - depth of grain and ring grooves
k3d/share/shaders/k3d_superplank.sl:80:			float graindepth = 0.0001;	/* Depth of divots where grains are */
k3d/share/shaders/k3d_superplank.sl:277:      disp -= graindepth * (.75 * grain + ring);
