19. GLSL Geometric functions

• Overloaded for all vecN data types:

  
      float length (vec x);
      float distance (vec p0, vec p1);
      float dot (vec x, vec y);
      vec3 cross (vec x, vec y);
      vec normalize (vec x);
      vec reflect (vec I, vec N); // I is incident vector (light/view) and N is normal
      vec refract(vec I, vec N, float eta);
      vec faceForward (vec N, vec I, vec nRef);// if dot(Nref, I) < 0, return N, else return -N