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On 07/15/2018 08:21 AM, Bald Eagle wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
>
>
http://news.povray.org/povray.general/thread/%3Cweb.441831a9134eb929e606030f0%40news.povray.org%3E/
>
>> I did some function based pigment thing too a long while back, but don't
>> quite remember details - and I cannot find it.
>>
>> Mike's solution simpler - if it works for for seventy goats ;-).
"for for" Ah the junk I write... So wish my eye-brain circuitry was
better. On writing I can read something like that fifty times and not
"see" the mistake. I come back to it later and it's obvious. Aging is
not helping - I'm headed for complete gibberish. :-)
>>
>> Bill P.
>
> Yes, that would be along the lines of situation (a) where he could just define a
> grid as a layered texture in space and have the object "in" it.
>
> What I'm envisioning / speculating / projecting his question is: if he had a
> grid composed of loose lines - like the unwoven warp and weft of a loom, then if
> he placed a ball on the surface of that grid, then as the object slipped between
> the cords, they would move to allow the passage of the object through a hole
> that got stretched out of the way.
>
> I think simplistically, if a repeating linear texture like wood were applied to
> the plane, and then a black hole warp were added with a strength proportional to
> the proximity of the object to the plane, then that might do it. Then just
> layer the same texture rotate y*90.
>
> Style points for scaling the black hole warp in x and z according the cross
> sectional dimensions of the object's bounding box.
>
> I tried the complicated pattern function method, and just got a blank black
> render. I think pattern just returns 1 or 0 ?
Patterns - except the new potential pattern in 3.8 - are clamped to a 0
to 1 range as I recall.
So I suppose I'd have to use
> that as a multiplier function rather than the base function.
>
> It would be helpful to know how the actual black hole warp is implemented as a
> pattern modifier - more info to dig up. :)
Patterns are evaluated at a point in space. The warp feature moves that
point before doing the pattern evaluation. The black_hole warp is the
same except the point's movement - only push or pull relative to the
origin currently - is constrained so as to happen only within one or
more spherical spaces.
>
> If a 3D grid is needed, perhaps there's a way to do something based on
> electrostatic repulsion, and have the grid be constructed from an array of
> points that are use to build splines / sphere sweeps.
>
Somewhere on the newsgroups is a series of postings regarding point
charges and plotting equal-potential contours and field lines about
them. The calc got rolled into one large function so performance
degraded badly as the number of points increased.
Bill P.
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