/* cross */
surface
constant_test(float    Kfb = 1    /* fake brightness */)
{
color    surfcolor = 1;
  
if(s >= 0.35 && s <= .65)
    surfcolor = color(0.2,0.8,1.0);
else 
    surfcolor = color(0.6,0.6,0.6);
if(t >= 0.35 && t <= .65)
    surfcolor = color(0.2,0.8,1.0);
  
    
/* STEP 1 - set the apparent surface opacity */
Oi = Os;
  
/* STEP 2 - calculate the apparent surface color */
Ci = Oi * Cs * surfcolor * Kfb;
}