vec3 beam(vec3 px, vec2 coord){
   vec3 pixel = pow(px, vec3(2.2));
   vec3 black = vec3(0.,0.,0.);
   vec3 beam_profile[9][4] = {
      {black, black, black, black},
      {black, black, black, black},
      {black, black, pixel, pixel},
      {black, pixel, pixel, pixel},
      {pixel, pixel, pixel, pixel},
      {black, pixel, pixel, pixel},
      {black, black, pixel, pixel},
      {black, black, black, black},
      {black, black, black, black}
   };

   int j = int(floor(mod(coord.y * 9.0, 8.9999)));
   int k = int(floor(max(max(px.r, px.g), px.b) * 3.9999));

   return pow(beam_profile[j][k], vec3(1./2.2));
}