clipka <ano### [at] anonymousorg> wrote:
> You know why both filter and transmit are there?
>
> Because a single coefficient is not enough to describe transparency.
>
> Now Gues why that is?
>
> Because strictly speaking it would require *three* coefficients: Red,
> blue and green transparency :-P
>
> With those three, you could do everything filter and transmit do right
> now - plus some.
>
> And when going for spectral math, it would require as many coefficients
> as there are wavelengths: Each could be attenuated differently.

This makes a good case for actually stripping filter and transmit out of the SDL
entirely (or at least deprecating them) and throwing in a separate
"transparency" keyword under pigments.

....especially if we _are_ going to have spectral coloring/lighting.  (For the
time being, I'm leaning towards an implementation that's strictly peak/width
pairs.  It'd be extended later, but it's at least a start towards a "good"
system for this.)

> > For the SDL, at least it would allow a refraction on a black reflecting
> > glass.
>
> ??

Obsidian, at present, is one of the more pain-in-the-neck RL substances to
model.  I assume this is what he's trying to get at, but I could be wrong.

> > And should we bother for pleochroism ? what about birefringence ?
>
> A bit of p[l]eochroism would be neat. Some 6 instead of 3 color channels
> would be a start. Plus a UV channel of course.

Pleochroism pretty well falls under the requests for an AOI pigment pattern,
doesn't it? :-D

> > Maybe that's a part for media, not pigment.
>
> Birefringence is definitively neither a media nor pigment thing, but a
> straightforward interior thing, and would have to join ranks with ior
> and dispersion (as a matter of fact it's a difference in ior depending
> on polarization with respect to the "optical axis" of the (AFAIK
> necessarily) crystalline material).

Dispersion is an ugly hack at present, just like iridescence.  :-D  (Technically
it should be implemented as the spectral variant of ior...  yet another thing on
The List (tm) for this.)  Birefringence seems like it'd require an extension to
ior as well (similar to the current two-value reflection form - specify an axis
of anisotropy and a second ior), though maybe I'm loading a bit much on the ior
keyword now...

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