// set global atmospheric fog effect in the scene.
// at the fog distance, there will be 63% visibility
fog {
  fog_type 1               // 1=constant, 2=ground_fog
  distance 10
  color Gray               // can also have 'filter' and 'transmit'
  // (---turbulence---)
  //turbulence <0.5, 0.5, 1.0>
  //turb_depth 0.5
  //omega 0.5
  //lambda 2.0
  //octaves 6
  // (---ground fog---)
  //fog_offset 0.5         // height of constant fog
  //fog_alt 0.5            // at fog_offset+fog_alt: density=25%
}