Op 24/05/2020 om 18:16 schreef Bald Eagle:
> William F Pokorny <ano### [at] anonymousorg> wrote:
> 

[snip]

>> The finish irid feature ....
>> ... This feature has some
>> other issues like lack of ability to scale relative to the incoming
>> coordinates which will make it tricky to get something which always
>> works with respect to scene dimensions.
> 
[snip]

> 
> Yeah - iridescence seems ... "special".
> Using Iridescence
> "Iridescence is what we see on the surface of an oil slick when the sun shines
> on it. The rainbow effect is created by something called thin-film interference
> (read section Iridescence for details). For now let's just try using it.
> Iridescence is specified by the irid statement and three values: amount,
> thickness and turbulence. The amount is the contribution to the overall surface
> color. Usually 0.1 to 0.5 is sufficient here. The thickness affects the busyness
> of the effect. Keep this between 0.25 and 1 for best results. The turbulence is
> a little different from pigment or normal turbulence. We cannot set octaves,
> lambda or omega but we can specify an amount which will affect the thickness in
> a slightly different way from the thickness value. Values between 0.25 and 1
> work best here too."
> 

I am probably wrong, but I seem to recall that Christoph did some 
massive work in overhauling iridescence a number of years ago...? Indeed 
in 2011:

http://news.povray.org/povray.binaries.images/thread/%3C4ed6f24c@news.povray.org%3E/

...there should be more about this.

Or is this unrelated to the present problem?

-- 
Thomas

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