I recently worked up a bump_map{} scene for the yuqk fork documentation.

Attached is an image with positive and negative bump_size crackle 
pattern in the top row. Lower left is wrinkles. Lower right leopard.

All of the pattern implementations used are somewhat different in the 
yuqk fork, but I've attached a scene file which will work with v3.8 beta 
2 should folks want to play (it 'probably' works back to v3.7).

Of note there is some sort of top / right bug in the way the bump_map{} 
is being handled for use in the normal{} block which has existed for a 
long time. In the attached 'yuqk' fork generated image the seam has been 
rotated into full view. I've not attempted to debug it. There is a note 
in the code about samples falling outside the mapped area needing to be 
handled correctly.

The bump_size as applied to bump_map{}s is a bit funky in that for many 
image types coming in with values in the 0 to 1 range, very large 
bump_size multipliers are needed.

Internally there is a value/255 kind of thing going on. Guess is some 
formats / options (idexed?) come in as integers where the divisions by 
255 makes sense. The bump_size of +-127 equates to an effective 
bump_size of +-0.5 internally where values in the 0-1 range.

Due the sampling, the normals at changes in slope direction are 
sometimes noisy.

Bill P.

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Attachments:
Download 'bump_mapstory.jpg' (151 KB) Download 'bump_map_v38.pov.txt' (2 KB)

Preview of image 'bump_mapstory.jpg'

On 2/3/25 18:44, William F Pokorny wrote:
> Of note there is some sort of top / right bug in the way the bump_map{} 
> is being handled for use in the normal{} block which has existed for a 
> long time.

I'd aimed to quickly fix this and post back here pointing to detail to 
povray.beta-test... What is going on is proving difficult to completely 
understand. I'll post more to povray.beta-test when (and if) I can 
figure it out.

Bill P.

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William F Pokorny <ano### [at] anonymousorg> wrote:
> On 2/3/25 18:44, William F Pokorny wrote:
> > Of note there is some sort of top / right bug in the way the bump_map{}
> > is being handled for use in the normal{} block which has existed for a
> > long time.
>
> I'd aimed to quickly fix this and post back here pointing to detail to
> povray.beta-test... What is going on is proving difficult to completely
> understand. I'll post more to povray.beta-test when (and if) I can
> figure it out.
>
> Bill P.

I don't know if this is in any way related, but maybe this (and there is a link
in the article to similar) will spark some ideas:

https://iquilezles.org/articles/tunnel/

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On 2/10/25 06:39, Bald Eagle wrote:
> I don't know if this is in any way related, but maybe this (and there is a link
> in the article to similar) will spark some ideas:
> 
> https://iquilezles.org/articles/tunnel/

Thank you Bill W. I appreciate the reference. It might well be part of 
all that has me confused.

Bill P.

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