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:
case kNoiseGen_Default: // <---- ????
temp = 0.5 - Noise (tv2, noise_generator);
temp = fabs(temp);
temp = 1.0 - 2.0 * Noise (tv2, noise_generator);
temp = fabs(temp);
if (temp>0.5) temp=0.5;
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
The above issue got me looking more at the noise code and CPU specific
optimizations. The AMD optimization file:
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
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
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.
(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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