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

> Thanks for digging through the details here. I was traveling and I'm
> just seeing your recent posts.

No problem - I was wanting to understand what the fundamental problem was, and
was only able to attack it piecemeal in the odd little spurts of free time.

> Could I get a copy of your SDL for the
> 'all/most' patterns post prior to this last one? The one with the
> pattern names to the left and the patterns shown to the right.

I believe that's in the .pov file immediately preceding the image post.

> What you say about POV-Ray often defining a default color/pigment 0-1
> map is true. At the moment I am a little surprised wood's default map
> isn't what you defined. Some patterns, like agate(1), are other than
> above - but why would wood's be?

I think maybe it's just an old hold-over from the earlier versions, where the
basic wood pigment's default mapping was 2 colors.
I'll have to think some on if/how that can be undone and still be prior-version
friendly.

> I'll put this on my to look at list and let it rattle around in my head
> meanwhile.
>
> Bill P.
>
> (1) WAY down my list is another question whether the agate map
> needs/needed a tweak due the 3.7 assumed_gamma default change... I know
> brick's color_map defaults for example did not get adjusted and the
> default colors don't look that good running at an assumed_gamma of 1.0.
> Not many folks use the in-built defaults in practice I suppose, and they
> can always override with their own maps; Excepting maybe agate where to
> my recollection something extra was going on I didn't understand in a
> quick look.

Well, now that you mention it, I actually was thinking a bit about why the wood
pigment map was the way it was, and how that was done, and that led me to
tangentially go a step further from the SDL that I posted to give:

#declare Hyp = function {sqrt(pow(x,2)+pow(y,2))}
#declare Freq = 1;
#declare Gamma = 1;
#declare Rings = pigment {function
{pow(1-((2*Freq)*abs(mod(Hyp(x,y,0),(1/Freq))-(1/(Freq*2))) ), Gamma)} }

So now the "spread" of the pigment map can be changed.

I'd love to be able to read the source code better than I can at the present,
and look more closely at how the pigments and functions are implemented.

I think it would be a nice collection of patterns, perhaps as an include, to
rewrite all of the internal POV-Ray patterns as SDL versions, so that people can
see how they work, better understand how to use them, and have the code right
there for the user to modify, play with, and come up with their own variations.



I'm presently wondering if there's a way to implement a reaction-diffusion type
/ cellular automata pattern using parameters.   That can apparently give leopard
spots, zebra stripes, giraffe crackle-type patterns, and the usual chemical
petri dish looking pattern.

https://people.maths.ox.ac.uk/~maini/PKM%20publications/212.pdf
https://phys.org/news/2015-12-mathematical-animal-stripes.html
https://plus.maths.org/content/how-leopard-got-its-spots



ALSO,
A while back, when I was fixated on working out the Dupin cyclide, I eventually
dug out the source for the internal function, and discovered that it generates
the shape by doing a geometric inversion of a torus!  :O

I think it ought to be possible to write an f_inversion function that others can
be processed by - which would give people a powerful tool to explore different
shapes in away that's vastly more difficult to do at the present.

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