Simon Lemieux <lem### [at] yahoocom> wrote:
> I've not played with the media since the halo statement doesn't exist
> anymore...
> I'll make it simple, how can I make a halo sphere...  on a black
background a
> white spherish cloud should apear as the light flows through (ie: constant
> density, reflect color of light as rgb 1)

Simple answer:

   sphere {0, 1 hollow
      pigment {rgbf 1}
      interior {media {emission rgb 1}}
      }

You can vary the colour and density by adjusting the emission.  If you want
to do more with the ball of media (such as apply turbulence), use a density
map:

   sphere {0, 2 hollow
      pigment {rgbf 1}
      interior {media {emission rgb 1
         density {spherical
            color_map {[0 rgb 0] [1 rgb 1]}
            turbulence 0.5 lambda 3
            }}}}

The values in the color map(s) of your density map(s) are multiplied by the
emission, absorption and scattering values of your media, so using rgb 0
gives a transparent media (and rgb 1 gives media having the values you
originally specified).  As soon as you use a density map, however, you will
notice the poor results of the default sampling methods.  This is where
MegaPOV's extra sampling methods make a huge difference (and just wait till
you start using scattering media...!).

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