[Radiance-general] an invisible glow

[Carsten Bauer]

Hi Alex !

To some extent, there is the possibility of having invisible glows. In
my workshop contribution (available from the workshop page on
radiance-online) there are patches to the standard Radiance version
providing some further features. One of them is the possibility to
assign a so called "secondary ambient material" (currently only to
plastic, metal and trans). This was originally implemented to save
calculation time in case of complicated mathematical textures applied to
the object, but it can be used for other purposes, too.

So, if for example you provide a blue plastic box and give a yellow glow
material for the secondary ambient mat., you will see the blue box and
the yellow shining on surfaces nearby stemming from the glow. (rather
freaky, though, but - why not??) This of course affects only the
indirect calculation, so the fourth glow parameter has to be zero, and
self-evidently there will be no direct contribution from this glow.

A real invisible glow comparable to the illum which works with the
direct calculation, too, should be not too difficult to implement as a
new primitive ("glow-illum"), at least I think so ... 

-Carsten