POV-Ray : Newsgroups : povray.beta-test : Version 3.6 flag and SSLT Server Time
1 Jun 2024 16:48:47 EDT (-0400)
  Version 3.6 flag and SSLT (Message 1 to 4 of 4)  
From: Stephen
Subject: Version 3.6 flag and SSLT
Date: 12 Feb 2011 14:10:27
Message: <4d56db23@news.povray.org>
I rendered a scene with SSLT but forgot to add #version 3.7 to the 
scene. It rendered fine with little difference between them, just noise 
on the Mesh. There was no warning about the version, should there be?

I re-rendered the #version 3.7 again and there are differences on all 
the images as if I was using crand. Does it matter which noise generator 
you use. I was using Perlin.

-- 
Regards
     Stephen


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From: Stephen
Subject: Re: Version 3.6 flag and SSLT
Date: 12 Feb 2011 17:36:22
Message: <4d570b66$1@news.povray.org>
On 12/02/2011 7:10 PM, Stephen wrote:
> I re-rendered the #version 3.7 again and there are differences on all
> the images as if I was using crand. Does it matter which noise generator
> you use. I was using Perlin.

At higher aa settings it is hardly noticeable.

-- 
Regards
     Stephen


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From: clipka
Subject: Re: Version 3.6 flag and SSLT
Date: 12 Feb 2011 20:29:52
Message: <4d573410$1@news.povray.org>
Am 12.02.2011 20:10, schrieb Stephen:
> I rendered a scene with SSLT but forgot to add #version 3.7 to the
> scene. It rendered fine with little difference between them, just noise
> on the Mesh. There was no warning about the version, should there be?

As a general rule-of-thumb, the #version setting only affects /changed/ 
features (that would otherwise break backward compatibility), not new ones.

> I re-rendered the #version 3.7 again and there are differences on all
> the images as if I was using crand. Does it matter which noise generator
> you use. I was using Perlin.

No, the Perlin-alike-noise generator used for patterns (e.g. bozo) and 
turbulence (which is always Perlin-alike) has nothing to do with it; 
SSLT doesn't need a 3D random pattern - just a stream of pseudo-random 
numbers and vectors.

The difference in the noise is simply due to differences in the order in 
which pixels are rendered. In POV-Ray 3.6 that's line-by-line, and in 
POV-Ray 3.7 it's block-by-block (with the order of blocks being somewhat 
arbitrary due to the use of multiple parallel threads, making results 
differ even from render to render).


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From: Stephen
Subject: Re: Version 3.6 flag and SSLT
Date: 13 Feb 2011 07:44:19
Message: <4d57d223@news.povray.org>
On 13/02/2011 1:29 AM, clipka wrote:

> As a general rule-of-thumb, the #version setting only affects /changed/
> features (that would otherwise break backward compatibility), not new ones.
>

That is good to know.

> No, the Perlin-alike-noise generator used for patterns (e.g. bozo) and
> turbulence (which is always Perlin-alike) has nothing to do with it;
> SSLT doesn't need a 3D random pattern - just a stream of pseudo-random
> numbers and vectors.
>

Again, good to know.

> The difference in the noise is simply due to differences in the order in
> which pixels are rendered. In POV-Ray 3.6 that's line-by-line, and in
> POV-Ray 3.7 it's block-by-block (with the order of blocks being somewhat
> arbitrary due to the use of multiple parallel threads, making results
> differ even from render to render).

That makes sense as when comparing different rendering of the same 
scene, some blocks are identical.

Thanks for your reply/

-- 
Regards
     Stephen


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