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It is possible to have more than one media specified per object and it is legal to have more than one density per media. The effects are quite different. Consider this example:
object{MyObject
pigment{rgbf 1}
interior{
media{
density{Some_Density}
density{Another_Density}
}
}
}
As the media is sampled, calculations are performed for each density pattern at each sample point. The resulting samples are multiplied together. Suppose one density returned rgb<.8,.8,.4> and the other returned rgb<.25,.25,0>. The resulting color is rgb<.2,.2,0>. Note that in areas where one density returns zero, it will wipe out the other density. The end result is that only density areas which overlap will be visible. This is similar to a CSG intersection operation. Now consider
object{MyObject
pigment{rgbf 1}
interior{
media{
density{Some_Density}
}
media{
density{Another_Density}
}
}
}
In this case each media is computed independently. The resulting colors are added together. Suppose one density and media returned rgb<.8,.8,.4> and the other returned rgb<.25,.25,0>. The resulting color is rgb<1.05,1.05,.4>. The end result is that density areas which overlap will be especially bright and all areas will be visible. This is similar to a CSG union operation. See the sample scene scenes/interior/media/media4.pov for an example which illustrates this.
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