declare shader 
    color "ground_fog_layers" (
	color   "fog_color"          default 1 1 1,
	color   "fog_density"        default 1 1 1,
	scalar  "fade_start"         default 0,
	scalar  "fade_end"           default 1,
	scalar  "unit_density"       default 1,
	scalar  "march_increment"    default 0.1,
	boolean "show_layers"        default off,
	color   "full_fog_marker"    default 1.1 .9 .9,
	color   "partial_fog_marker" default .9 1.1 .9
    )
    version 1
    apply volume
end declare