/**
  * Return true if two triangles should be smoothed as one surface. cos_angle is the minumum angle
  * for smoothing. If the angle between the faces is > cos_angle, then the faces are considered to
  * be a continuous surface. Ie. 90 degrees is a sharp corner, 180 degrees is a flat surface.
  */
 public static boolean onSameSurface(GL_Triangle t1, GL_Triangle t2, float cos_angle) {
   float dot = GL_Vector.dotProduct(t1.n, t2.n);
   // System.out.println("surface: compare dot=" +dot + " cos-angle=" + cos_angle + " return " +
   // (dot > cos_angle));
   return (dot > cos_angle);
 }