This is work in progress!
 
Shader: plank.sl 
Author: Larry Gritz 
Date: 27 Jun 1994 
 
Description: 
Makes texture of wooden planks in s-t space. This wood looks rather like oak planks. 
 

Parameters: 
 *   Ka, Kd, Ks, specular, roughness - work just like the plastic shader 
 *   txtscale - overall scaling factor for the texture 
 *   ringscale - scaling for the ring spacing 
 *   grainscale - scaling for the fine grain 
 *   plankwidth - width of each plank (in terms of s/t) 
 *   planklength - length of each plank (in terms of s/t) 
 *   groovewidth - width of the grooves between the planks (in terms of s/t) 
 *   lightwood, darkwood - surface colors for the wood itself 
 *   groovecolor - the color of the "grooves" between the planks 
 *   plankvary - controls how much wood color varies from plank to plank 
 *   grainy - relative graininess (0 = no fine grain) 
 *   wavy - relative wavyness of the ring pattern