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Op 24/05/2020 om 18:16 schreef Bald Eagle:
> William F Pokorny <ano### [at] anonymous org> 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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On 5/25/20 2:33 AM, Thomas de Groot wrote:
> 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?
>
Thank you for the newsgroup pointer.
His updates - assuming they are the code I see - are tangle with this
problem because Turbulence() wasn't - or isn't now in any case -
returning the distribution and range assumed in the code.
Christoph's changes were - I believe made for the v37 release. The
documentation notes changes to actual physical dimensions for v37(1).
Which, on more thought, means I need to yank my fudge matching, magic
factor back out of the code and update the scenes for the proper end
thicknesses given the turbulence instead!
He mentions being unable to scale for the same effect - which I believe
is correct with respect to the viewer frame. I'm suggesting when using
turbulence adding some method to scale and/or shift the turbulence of
the thickness a good idea given the difficulty matching up with changing
scene scaling of some object. Like media and density, if you want the
turbulence to be constant (maybe yes, maybe some, maybe no) you'd need
to 'counter' adjust it in some way on scene scaling - we cannot do this.
(1) The documentation in r3_6.html#r3_6_1_3_7 has this 3.7 note:
"Note: The version 3.7 iridescence feature has had a major overhaul. The
syntax remains the same, however, both the thickness and amount values
are now specified in microns. Consequently, iridescence effects will
vary from previous versions."
which emphasizes 'both' thickness and amount being in microns. The
'thickness amount' is, and the 'turbulence amount' is, but the
irid_amount is just a color intensity multiplier for the irid_wavelength
color specified in global_settings. We could likely help new to irid
users by making this clearer.
The "See also the global setting Irid_Wavelength for additional
information." sentence I think should probably be up in the paragraph
with irid_amount because - indirectly - this is the 'amount' of color,
color to which it's related.
Anyway, this rushed so apologies for the mistakes. Off to real life for
a few days. Thanks again for the prompt. I need to yank that fudge
factor in my povr code.
Bill P.
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On 5/24/20 12:18 PM, William F Pokorny wrote:
...
>
> I also tried for a matching fudge factor to match the breadth of the old
> Turbulence() distribution. Cannot match previous precisely, but not bad
> in my view.
>
...
In povr, irid updated to yank fudge factor and scenes updated with
accurate base thicknesses. Thanks Thomas.
When I looked at the fixed internal turbulence() with fog picked up
additional bugs I expect kept folks from doing a lot especially with
turbulence (copy constructor was creating new, but not copying old
turbulence values, for example).
Anyway. In povr I've got the turbulence() fix in - with fixes to irid
and a significant re-work of fog updating and adding features/keywords.
Image attached showing some of the fixed and extended features.
The agate pattern looks different, but OK, with the turbulence() fix.
Not looked in detail at marble or the two spiral patterns as yet. Still
some f_turbulence() work to finish off.
Bill P.
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Attachments:
Download 'fogstory.jpg' (148 KB)
Preview of image 'fogstory.jpg'
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