POV-Ray : Newsgroups : povray.beta-test : v3.8+ crackle instability (facets?) with >1 uses per thread. : Re: v3.8+ crackle instability (facets?) with >1 uses per thread. Server Time
2 Dec 2024 17:44:56 EST (-0500)
  Re: v3.8+ crackle instability (facets?) with >1 uses per thread.  
From: William F Pokorny
Date: 18 Nov 2024 06:51:54
Message: <673b2a5a@news.povray.org>
On 11/17/24 21:52, Bald Eagle wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
>> On 11/17/24 06:51, William F Pokorny wrote:
>>> No attempt wrap the cylinder - just punching out a thin part of the
>>> crackle cell outlines.
> 
> Huh.  And what happens if you do the same sort of thing with something like the
> Stanford bunny?
> 

If the aim is seeing the outlines rather than creating an isosurface 
shape from them, the quick thing would be to create a pigment from the 
crackle pattern set up to show outlines - the parts of the pattern not 
outlines would be set transparent. Ignoring that we can define an inside 
vector for a well formed / closed mesh, a mesh surface is already 
infinitely thin for the purposes of sampling.

If you want to play with isosurfaces based upon a mesh, one of the 
techniques to turn them into value fields would be the up front 
approach. There are a couple SDL only ones. A method I posted in the mid 
to late 2000s and one Sam B posted in the early 2010s. The yuqk fork has 
hard_object{} and soft_object{} inbuilt features for turning shapes into 
value fields / patterns.

The recent filling a shape with random noise approach might work for a 
noisier result. There is too a way to pre-sample a shapes interior 
saving the result as a df3 file which can then be used as a value 
pattern suitable for an isosurface.

A straight intersection with a mesh having a clean inside region or any 
object with an defined inside is an option too. The gradients will be 
bad and the result, visually, less interesting as the outer layer of 
cell outlines will hide everything to the interior.

Bill P.

Aside: I've wondered some what an intersection of two crackle value 
pattern intersected might look like - where one crackle changes ip_seed, 
is rotated or scaled differently such that the cells walls intersect 
sparsely.

With the ip_strength option set up asymmetrically we might also be able 
to define certain patterns or shapes. One crackle ip_repeat, repeating 
differently than the other where both have identical ip_seed, seeds...


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