Bob Hughes <inv### [at] aolcom> wrote in message
news:37dcfecc@news.povray.org...
> I think the basic thing to do is use 'density' and 'density_map' like
> you would with 'color_map' in 'halo', putting the type (spherical for
> example) into the density statement.  And use emission or absorption
> in place of the rgbt -1 and dust type.  It's no direct exchange but
> once you learn the workings a halo can be faked fairly okay.  Like Ken
> said though probably better to move into media entirely and just skip
> halo "conversion".  Don't forget about 'scattering' if you need to
> interact with light.

    Halo had the "glowing" keyword ( = emitting and absorbing) , which
probably ought to be done as a macro in 3.1, becuae it is very often the
Right Thing.   Specifically, thermodynamics tells us that glowing media
(flames, red hot glass, neon, etc.) absorb and emit the same spectrum. This
means that in most places where one might naively expect to use "emission 1"
one should in fact use "emission 1 absorption 1".  Emitting media on their
own almost always look wrong. (Perhaps Fluorescent media might be an
exception? I'm not sure here.)  Pure absorbing media, on the other hand, do
have their place, as do scattering media...

    But when in doubt, use equal parts of emission and absorbtion rather
than pure emission.

    -Robert Dawson

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