"Loren" <gre### [at] umnedu> wrote:
> Hello,
>
> I'm having great difficult getting emitting media (glowing red media, as in a
> laser), in my scenes. First, a simple example which doesn't work:
>
[snip]
>   hollow
>   interior{
>        media{ emission Red intervals 30 samples 100,100 }
>   }
> }

[I'm using v3.7.1 beta 9]
This may not be exactly on-topic, but I've also discovered some unexpected
behavior when trying to get a PURE-color media to render properly. (That is, a
pure-color SINGLE media.) The result shows 'transparent color', with no opacity.
For example, colors like <1,0,0> or even <1,1,0>. It happens with all three
media types-- emission, absorption and scattering (with or without extinction.)
Cranking up the 'density' of the media doesn't help.

An example with extreme values...
interior{
     media{
        scattering{1, 300*<1,0,0> extinction 300}

..... still shows no true opacity.

Adding an identical pure-color ABSORPTION media (or even its complementary
color)-- to try and *force* some opacity-- doesn't work either.

However, this CAN be worked around by adding absorption media with NO color (or
rather, to absorb *all* colors equally)...
     absorption 5 (or whatever) -- with no zeros in the color vector

.....OR, by making the zero value(s) of the original color some small positive
value instead. (But strickly speaking, the color will no longer be 'pure.')

Just from experimenting, it's obvious that one or more zero values in the color
are the cause of this. But I'm actually more curious to know the mechanism of
why this happens. My only guess is that a zero value is somehow multiplying the
'opacity' part of the underlying code by zero(?), either as part of the original
design of the media code long ago, or perhaps as a detail that was overlooked.

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