On 10-5-2019 17:53, Norbert Kern wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Last February, I presented some early renders of this scene. It has now
>> been "finished" (my scenes are never finished).
>>
>> --
>> Thomas
> 
> 
> 
> The sky is really nice - how did you made it?
> 
> Regards,
> Norbert
> 
> 

Three elements compose the sky (and atmosphere) from base to top:
1) a ground fog, slightly tilted to fill the distant valleys more);
2) An atmospheric haze;
3) a cloud layer.

All three are made up of non-interpenetrating media. The code looks like 
this (watch out for unwanted line feeds!):

//--start code------------------------------------------
#if (Atmos)
// An atmosphere composed of a ground fog and an haze:

#local Murkiness = 1.5; //best somewhere between 0.5 and 2.9 approximately

#local GroundFog =
difference {
   sphere {<0,0,0>, 6.0}
   plane {<0,1,0>, 0.0}
   scale <1, 0.14/6, 1>
   //scale 5000
   rotate -1.5*x
}
//----------------------------------------
#if (Debug)
#declare Min = min_extent(GroundFog);
#declare Max = max_extent(GroundFog);
#debug concat("\n  min_extent GroundFog: <",vstr(3, Min, ", ", 0,3),">\n")
#debug concat("  max_extent GroundFog: <",vstr(3, Max, ", ", 0,3),">\n\n")
#end
//----------------------------------------

#local Haze =
difference {
   sphere {<0,0,0>, 6.0}
   plane {<0,1,0>, 0.0}
   scale <1, 0.15/6, 1>
   //scale 5000
   rotate -1.5*x
   translate 0.14002*y
}
//----------------------------------------
#if (Debug)
#declare Min = min_extent(Haze);
#declare Max = max_extent(Haze);
#debug concat("\n  min_extent Haze: <",vstr(3, Min, ", ", 0,3),">\n")
#debug concat("  max_extent Haze: <",vstr(3, Max, ", ", 0,3),">\n\n")
#end
//----------------------------------------

#declare Atmosphere =
union {
   object {
     GroundFog
     hollow
     pigment {rgb <1,1,1> transmit 1.0}
     interior {
       media {
         scattering {5 rgb <0.6, 0.6, 0.8>*Murkiness/5000 extinction 1.0
           eccentricity 0.01
         }
         samples 20
         density {
           spherical
           density_map {
             [0.00 rgb 0.1]
             [0.45 rgb 1.0]
             [0.50 rgb 0.1]
             [0.60 rgb 0.1]
             [0.65 rgb 0.9]
             [1.00 rgb 1.0]
           }
           scale 11
           warp {turbulence <2.0, 3.0, 2.0>}
           scale <1.0, 1.0, 2.0>
           scale 1/11
         }
       }
     }
     scale 5000
     translate <CamLoc.x, 0.0, CamLoc.z>
   }
   object {
     Haze
     hollow
     pigment {rgb <1,1,1> transmit 1.0}
     interior {
       media {
         scattering {5, rgb <1,1,1>*0.10/5000
           eccentricity 0.4
         }
         samples 20
         density {
           spherical
           density_map {
             [0.00 rgb 1.0]
             [0.90 rgb 0.0]
           }
         }
       }
     }
     scale 5000
     translate <CamLoc.x, 0.0, CamLoc.z>
   }
} //end of Atmosphere union

//----------------------------------------
#if (Debug)
#declare Min = min_extent(Atmosphere);
#declare Max = max_extent(Atmosphere);
#debug concat("\n  min_extent Atmosphere: <",vstr(3, Min, ", ", 0,3),">\n")
#debug concat("  max_extent Atmosphere: <",vstr(3, Max, ", ", 0,3),">\n\n")
#end
//----------------------------------------

Atmosphere
#end  //of Atmos

//--------------------------------------------------
#if (Clouds)
#local CloudScale = 1000*10;

#declare Density_in =
density {
	wrinkles
	frequency 4
   color_map {
     [0.30 rgb <0.00, 0.00, 0.00>]
     [0.48 rgb 0.9]
     [0.52 rgb 0.9]
     [0.70 rgb <0.00, 0.00, 0.00>]
   }
   scale 0.5
	//rotate 90*x	//when using spirals; either here or:
   scale 30
   warp {turbulence <3, 4, 2>*0.9}
   scale 1/30
	//rotate 90*x	//when using spirals; here
}

#declare Density_out =
density {
     rgb <0.00, 0.00, 0.00>
}

#declare CloudScape =
   difference {
     sphere {0, 1.0}
     sphere {0, 0.75}
     hollow
     material {
       texture {pigment {rgb 1 transmit 1.0} finish {ambient 0 diffuse 0}}
       interior {
         media {
           // (---general values---)
           intervals 1
           samples 50
           //absorption rgb <0.5, 0.5, 0.5>*0.00001/CloudScale
           scattering {1, rgb <1, 1, 1>*8.00/CloudScale}

           // (---density---)
           density {
             spherical
			  	  density_map {
			  	    [0.1 Density_out]
				      [0.9 Density_in]
				    }
				    warp {turbulence 0.3}
			  	  scale 1
           }
         }
       }
     }
   scale CloudScale
   scale <5, 1.0, 5>
	rotate -20*z
   rotate 15*y
   translate <CamLookAt.x, CamLoc.y, 0>
   }

CloudScape
#end  //of Clouds
//--end code------------------------------------------


-- 
Thomas

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