William F Pokorny <ano### [at] anonymousorg> wrote:

> The patterns agate, marble, spiral1, spiral2 where turbulence is used
> will be getting violent shifts both on use of turbulence where not a
> default and on omega changes. Aside: wood uses turbulence too by in x
> and y so DTurbulence() and is OK. The plan is to do nothing with the
> affected patterns post Turbulence() change unless something pops.

I (and likely others) would like some way to better understand the distribution
of values in the pigment patterns.   That's from the perspective of "I would
like a bit more of THAT tone in my wood pattern ....   so what portion of my
texture map do I need to adjust...?"

I bring that up because I'm trying to envision omega, octaves, lamda, etc, and
I'd need a graph of that to better understand what knobs to fiddle with when I'm
crafting a turbulated pattern.

Specifically with respect to noise and turbulence, and the range of values that
functions return, it would be nice to have a way to know or be reminded that an
inbuilt function, where the calculations are invisible to the user, deviate from
a 0-1 range.

I'd say that from an isosurface perspective, it would be MOST helpful in
determining where to set the threshold, or what to subtract from the equation in
order to get a zero-value surface.

http://wiki.povray.org/content/Documentation:Tutorial_Section_3.2#Noise_and_pigment_functions
"Using this simple noise3d function results in the image on the right. The value
-0.5 matches the default threshold value of zero. The f_noise3d function returns
values between 0 and 1:

function { f_noise3d(x,y,z)-0.5 }"

(Most folks would be tempted to just use noise and a 0 threshold, and then waste
a lot of time trying to "debug" the isosurface object.

> 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.

I would very much like a function that "scales space" prior to passing world
space cooordinates into functions.
Having had to grapple with that issue, I'm wondering what the best
implementation of that would be.  I'm also curious what your approach is when
you use functions.
I haven't figured out how to graph a function with the native (x,y,z) - so I
define all my functions with capitals, which just act as containers for the
lowercase I pass to it on invocation.
Then I can graph them using a #for (X, 0, tau) loop ....

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 think
given numerical accuracy there should be some >=0 clamping to not
sometimes get negative thicknesses

maybe abs() ?


> Not tested to confirm, but the fog features using turbulence I suspect
> are in bad shape. There is a min(1.0,Turbulence(..)... bit used a ouple
> places which I believe will make it very hard to get much turbulence
> given the distribution center is way the heck out at 4.0 with defaults!

yeah wow - that's WAY out there...

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