POV-Ray : Newsgroups : povray.beta-test : v3.8 Clean up TODOs. kNoiseGen_Default switch use. Server Time: 28 May 2020 20:31:32 GMT
  v3.8 Clean up TODOs. kNoiseGen_Default switch use. (Message 1 to 1 of 1)  
From: William F Pokorny
Subject: v3.8 Clean up TODOs. kNoiseGen_Default switch use.
Date: 4 Apr 2020 10:26:12
Message: <5e8860c4$1@news.povray.org>
Documenting some cleanup which I think should happen on any resumption 
of v3.8 work. It's work I am doing in my cut down povr.

In working on pattern / function handling changes (documented mostly in 
the non-web presented newsgroup povray.beta-test.binaries(1)) the 
following code caught my eye in the granite pattern:

         switch (noise_generator)
         {
             case kNoiseGen_Default:  // <---- ????
             case kNoiseGen_Original:
                 temp = 0.5 - Noise (tv2, noise_generator);
                 temp = fabs(temp);
                 break;

             default:
                 temp = 1.0 - 2.0 * Noise (tv2, noise_generator);
                 temp = fabs(temp);
                 if (temp>0.5) temp=0.5;
                 break;
         }

kNoiseGen_Default "Indicates that the scene's global settings noise 
generator should be used." It's not the local pattern noise default
and should not be used as such. The coding is harmless to result, but 
not completely to performance - the case statement should be removed and 
also in wrinkles. Perhaps there are other such uses - turbulence??? Not 
looked.

The above issue got me looking more at the noise code and CPU specific 
optimizations. The AMD optimization file:

       platform/x86/avxfma4/avxfma4noise.cpp

is missing the #if CHECK_FUNCTIONAL test blocks comparing results to the 
non-optimized portable Noise and DNoise code which exists in the other 
optimization files. Looks like the check existed when Noise / DNoise was 
in texture.cpp - so this I think missed when the file above was created 
in the v3.8 / master branch.

Lastly, I'll ramble a little about what look to me to be less than clear 
statements in comments about mean, media and ranges which led me to take 
detailed looks at the distributions on my machine 
(platform/x86/avx2fma3/avx2fma3noise.cpp). All three generators end up 
with gaussian like distributions centered near 0.5 and in a 0-1 range as 
expected.

The Perlin-Skinner distributions are a little asymmetric, but smoother 
than the implemented Perlin version. All three have still visible 
artifacts, though the current generator 2 default is the best in this 
respect.

Aside: In the granite call I coded up a version which alternates between 
Perlin and Perlin-Skinner(2) as it sums up the scaled, fractional noise 
and to me looks really good artefact wise. Have others tried this? 
Thinking I might keep it as a noise option in my cut down povr code. 
We'll see.

Bill P.

(1) - Partial lie as images to this group show up in the 100 most recent 
images group until no longer in the most recent 100. I started to use 
the group so as not to present noise to most web interface users while 
still storing what I see where other hackers / developers (and I) can 
find stuff by news group search...

(2) - Granite introduces clamping as part of the pattern. (Something 
never really optimized for Perlin(3) it looks. Perhaps the Skinner(2) 
clamping good enough with Perlin too?)


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