POV-Ray : Newsgroups : povray.binaries.images : A povr branch image using new inv_pnormal_cure keyword. : Re: A povr branch image using new inv_pnormal_cure keyword. Server Time
13 Jul 2024 08:29:02 EDT (-0400)
  Re: A povr branch image using new inv_pnormal_cure keyword.  
From: William F Pokorny
Date: 16 Feb 2022 22:09:51
Message: <620dbc7f$1@news.povray.org>
On 2/16/22 09:33, s.day wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
>> An image result using povr's new reflection block inv_pnormal_cure
>> keyword. Using inv_pnormal_cure 5.22, so 22% of the perturbed rays are
>> forced into the spheres as if the surface somewhat porous to light.
>> More detail in povray.pov4.discussion.general.
>> Bill P.
> Looks good, I have no idea what it means ;-) Is this similar to the SSLT
> feature? If so is it quicker to render?
> Sean

While pushing feature boundaries in povr, I'm often not sure what it 
means. :-) What might users do after a new option is available. How 
might some new enabled behavior interact with other features. I might 
have ideas but, I don't really know.

I added this mode(5.probability) thinking about reflections with porous 
surfaces, say, a fabric weave on a lamp shade(a). Some of the rays at a 
ray-surface intersection reflect through openings to what is behind.

For this image I was thinking, some, about a faked subsurface effect 
but, as modeled, it's only one surface behind the outer one. A simple 
set up like this is probably faster than SSLT(b). However, other than 
fixing some SSLT bugs which were really solver / code set up bugs, I've 
not much used SSLT - so I don't know for certain.

Your question got me thinking. What if we model more surface layers? I 
don't think there is any fundamental reason we couldn't model more 
depth, with more layers. Could we get a result close to or, perhaps 
sometimes, better than the existing SSLT? There are issues for more 
complex geometries where I think the current SSLT code is not very 

Bill P.

(a) - This happens too where certain wavelengths of light see through a 
surface which to other wavelengths might be opaque, etc.

(b) - This method uses both the new 'normal { micro }' pattern and the 
inv_pnormal_cure option which grabs some portion of the reflected rays 
and pushes (re-directs) them through the surface. The overall effect 
only 'activates' with anti-aliasing (AA) on because the micro normal 
pattern is set up to lean on the AA mechanism to control the number of 
samples. Where AA is off or at a coarse setting, the renders will be 
much faster but, look noisy.

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