clipka <ano### [at] anonymousorg> wrote:

> I can imagine what patterns you have in mind, but I still only have a
> vague idea what "direct access" you envision for them.

As you say below, POV-Ray has internal methods of computing pattern values
computed from individual points.  I would guess that there may be a way to -
compute the 2nd derivative of such a function to get maxima/minima as inflection
points, and perhaps provide a general means for "pulling out" those values - so
that the user doesn't have to do a loop with sufficient fineness to test for a 0
or  1 ....

> That's a lot, I guess ;)
> Obviously, some of them are /not/ available as POV-Ray patterns, so what
> about them?

Add some of them?   :P

Where there's a discontinuity in value of nearby points, there's
> a node; where there is only a gradual change, there isn't.

True, though there maybe a way to narrowly specify values of 0, 0.5, 1 ....

> Various of the patterns you mentioned don't even have point-like nodes,
> and just have line-like or surface-like discontinuities. The wood
> pattern is one such example: It has one central line-like discontinuity,
> with concentric cylinder-like discontinuities at regular distances.

Yes.  I can envision rendering concentric cylinders by such a means, or
intersecting that locus of points with another pattern with point-like nodes, or
anything else to get only a subset of that - I'm just looking to get a few
different example to get started with an illustrate the possibilities.

> And even when patterns do exhibit point-like nodes, any application of
> even the slightest turbulence would make it impossible to identify their
> effective resulting location: "backtracking" POV-Ray's turbulence warp
> is, to my knowledge, not feasible.

You're working backwards in that case.  If there's a way to replicate the means
by which POV-Ray creates the pattern and applies the turbulence, then the user
could do that in a forward-fashion, which must be feasible since POV-Ray already
does it..


> > They could also form the basis for [...snip]

> Now you again have me at the disadvantage of not understanding what you
> mean :)

Let's suppose there's a pattern for a crystal structure, and a sphere is plotted
at the origin.  I might do something like use a slightly larger sphere to do
insidedness tests on the points of the crystal-pattern and place narrow
cylinders from the origin out to all of those points - to give a sort of defined
type of stellation.

like the following, only with non-random endpoints:
http://www.f-lohmueller.de/pov_tut/random/random8e.htm

If instead I used those points as bases of cones with all the peaks at the
origin, I could have cones radiate out from the center in a defined manner.
Maybe they're hollow - maybe they're subtracted from the sphere, maybe there's
no sphere and the cylinders are all just merged.

> > How will this work?  What will people use it for?
> > How the heck do I know?
>
> I guess that's the crux of the matter ;)

To me, it's the HOW.   The _what_ will follow.


> That may be a reasonable approach. Aside from the crackle pattern, I
> don't think it would be reasonable to even attempt to implement such
> stuff in POV-Ray proper.

I think Jerome would have a blast doing a few of these - he always seems like
he's up for the challenges   ;)  He's got some wild stuff on that wiki page of
his.

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