POV-Ray : Newsgroups : povray.binaries.images : Granites Intermezzo : Re: Granites Intermezzo Server Time
15 May 2021 18:51:21 EDT (-0400)
  Re: Granites Intermezzo  
From: Bald Eagle
Date: 27 Apr 2021 06:40:00
Message: <web.6087e9d4cfb077e41f9dae3025979125@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:

> The original granite code contains turbulence. That is one of the
> reasons the original granite looks like a 'flow' pattern. The first
> thing I did was to comment out the turbulence; the granite became more
> 'crispy' and closer to the real thing.

Ah.  The pattern is also gradient noise based, which causes smooth blending
between the values, and creates a "roundness" - the rolling hills of a
heightfield.  I looked into modifying that, and I got something that's at least
good enough for some experiments to see if it's worth any more pursuit.


> That is a tedious exercise ;-) I did it years ago to get correct colour
> values for Mediterranean-style roof tiles (for which I used the cells
> pattern, btw). Can be done of course; I shall put it on my
> ToDo/ToExplore list.

Maybe eval_pigment and that histogram macro in .... math.inc?

> All the above: yes; might need additional investigation. Concerning the
> hexagon pattern: many if not most of the granite minerals are hexagonal.
> That would mean it would be more appropriate for granites. However, I am
> afraid it would look 'circular' in practice.

Yes, a slice down the side of a hexagonal basalt column would give a
rectangle...
Maybe layered patterns with all but the base having a mostly clear pigment in
the map.  That way we could just "sprinkle" a few different shapes in and not
have to do a lot of math / algorithms / pattern tweaking, and still get the
crisp grain boundaries.


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