Op 13-5-2021 om 20:40 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> All right! This is going to be the *last* test image of the pre-macro
>> Dakota Red Granite, closing also this Intermezzo.
>>
>> Shown here, is the current implementation of the quartz veins through
>> the granite, using the marble pattern. Please note that this feature
>> will remain /experimental/ in the upcoming beta macro which I shall
>> provide tomorrow.
> 
> This is looking very nice!  :)
> 
I had been writing an answer to this post, and then it was lost... drat! 
Have to do it again. :-/

> Just going to jot down some observations and thoughts, some which we may
> address, and some we might not.
> 
> I think the pattern we have is better that the previous stock pattern.  The
> grain size is still too uniform, but maybe if several adjacent grains were
> textured identically, using the hexagon/bricks trick, then we could get a less
> homogeneous size distribution.
> 
You have to realise that granites in general /are/ rather uniform in 
grain size, only a certain class of rocks show marked size differences 
('phenocrysts', 'porphyritic') where the large crystals are represented 
by feldspars rather than quartz. So, the size distribution in the 
present concept is about right.

> Next I guess would be crafting the textures of the individual minerals composing
> the grains.
> 
No, I would advise against doing that, for the simple reason that it 
would be overkill for most of the uses of the material. Additionally it 
would burden memory and parser/render time to unacceptable levels. Much 
better would be to find a 'fast' way to add a believable sslt 
(conundrum, I know).

> Aside:
> I took the boy outside last weekend - the oxygen and sunlight surely burned his
> lungs and skin - and we explored the retaining wall of the local dam
>
https://www.nae.usace.army.mil/Missions/Civil-Works/Flood-Risk-Management/New-Hampshire/Hop-Ev/
> Lots of granite, big chunks of quartz, and other things yet to be identified "Is
> that andesite?" (smart kid - or maybe it's Minecraft...)

Excellent exercise! To be recommended for everybody in 'rocky' country. 
Beautiful landscape btw. I like it.
As said above, the big chunks are probably feldspars rather quartz, and 
no, no 'andesite', which would be a fine-grained, dark, extrusive rock 
and no granite. However, a smart suggestion indeed. The big chunks may 
point to a porphyry or a gabbro instead of a true granite.

> I noticed that the quartz, while appearing translucent white in small samples,
> took on an agate gray/purple cast as the veins or chunks got larger and deeper
> and Beer's law started to really kick in.  There were also striations
> perpendicular to the vein line, and some of the quartz was bordered by a
> different mineral that was more chalky / portland cement solid white, whatever
> that might be.
> 
Yes, those characteristics seem to point to feldspars. the 'chalky' 
colour might point to 'weathering' of the minerals.

> There were also "rust spots" in some of the rocks, as well as plates of of mica.
>   And mixed in with the granites were a few very smooth fine-grained/grainless
> stones that had a dark grey transitioning to red color, such that they almost
> looked like they were rusting.
> 
Hmmm... inclusions of stones... maybe we are not dealing with a true 
granite here. Granites do not have such inclusions.

> I can return and take samples, photos, closeups if we think such would assist.
> 
Well, a few photos would do no harm indeed. Remember however, that we 
are dealing here with /Dakota/ granites! If taking photos, remember to 
put in a coin or something recognisable for size. Good practice for such 
things!

> I would imagine that the quartz veins will be the most challenging to implement,
> as there will be the issue of presence, thickness, number of veins, orientation,
> amount of turbulence, etc.  Maybe that's best handled by an optional array that
> the macro checks to see if present.
> 
Yes, the veins are a problem. I was wondering if we should not need some 
kind of function to do this well. Not sure how to do this correctly.

-- 
Thomas

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