On 10/01/10 15:30, David Given wrote:
[...]
> - I want to play with the atmospheric density function (to allow for the
> moon's very low gravity gradient). This means I need to adjust Bruno
> Cabasson's original code so that it doesn't depend on the height of the
> atmosphere. Unfortunately there's something about how to scale media
> that I'm just not getting --- the bigger I make the object containing
> the atmosphere, the less dense the atmosphere gets, regardless how I
> modify the density function. (Code below.)

I now realise that I forgot to attach the relevant bit of code for the
atmosphere that I wanted people to lookat. Whoops.

Nominal_Terrain_Radius and Sea_Level describe the size of the planet.
Atmospheric_Scale and Atmospheric_Depth describe the size of the
atmosphere. Atmospheric_Scale is a scale factor indicating the nominal
depth of the atmosphere; this should correspond to the original TerraPOV
'depth of atmosphere' field. Atmospheric_Depth describes the depth of
the actual atmosphere object. I want to be able to adjust
Atmospheric_Depth arbitrarily and have my media remain looking (largely)
the same.

#local Bottom_Of_Atmosphere = Nominal_Terrain_Radius + Sea_Level;
#local Top_Of_Atmosphere = Bottom_Of_Atmosphere
	+ Atmospheric_Depth;

#local Base_Rayleigh_Power = 6.7;
// don't know what the following line means.
#local Rayleigh_Factor = 1 / Atmospheric_Scale;
#local Rayleigh_Scale = 1;
#local Rayleigh_Power = Base_Rayleigh_Power * Rayleigh_Factor;

#local Rayleigh_Density =
	density
	{
        #local height_from_centre =
	        function(x, y, z) {
	            sqrt(x*x + y*y + z*z)
	        }
	
	    #local height_from_surface =
	        function(x, y, z) {
	            height_from_centre(x, y, z) - Bottom_Of_Atmosphere
	        }
	
		function
		{
			Rayleigh_Scale * exp(
				-Rayleigh_Power *
				height_from_surface(x, y, z)
		            )
			    // this line doesn't work
		            * (Atmospheric_Scale / Atmospheric_Depth)
		}
	}

#local Rayleigh_Colour = rgb <0.2061, 0.3933, 1.0>;

#local Rayleigh_Media =
	media
	{
		method 3 // adaptive
		intervals 3
		samples 3
		scattering
		{
			RAYLEIGH_SCATTERING
			color Rayleigh_Colour / Atmospheric_Scale
			extinction 1
		}
		density
		{
			Rayleigh_Density
		}
	}

#local Sky_Object =
	sphere
	{
		<0, 0, 0>, 1

		pigment
		{
			rgbt 1
		}

		hollow
		scale Top_Of_Atmosphere
		
		interior
		{
			media
			{
				Rayleigh_Media
			}
		}
	}

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│ "There does not now, nor will there ever, exist a programming
│ language in which it is the least bit hard to write bad programs." ---
│ Flon's Axiom

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