surface orange_curve2(float    Kfb = 1,
                            position = 0.5,
                            amp = 0.07,
                            freq = 20)
{
color    surfcolor = 1;
  
if (t - position <= amp*sin(s*freq))
    surfcolor = color(1, 0.5, 0);
  
Oi = Os;
  
Ci = Oi * Cs * surfcolor * Kfb;
}