> There is no real point in "previewing" a filter or transmit value as the
> result does not depend on the color but that what you call the
"background",
> which actually means the recursive ray-tracing result color.  BUT, that is
> what you cannot just compute by one simple mathematical formula ...


Well, if you display the color over the typical checkerboard background,
then you can filter and transmit that as the background to demonstrate the
color.

I believe the formula Allen is looking for would be something along the
lines of

red = color.red * (1 - color.transmit) * (1 - color.filter) + color.transmit
* whateversbehind.red + color.filter*color.red*whateversbehind.red
(same for green, blue)

I'm not sure if that's right. It should be in the source somewhere (though
not as clearly as this)...

 - Slime
 [ http://www.slimeland.com/ ]

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