In writing this post to the v4.0 forum:

http://news.povray.org/povray.pov4.discussion.general/thread/%3C67471126%241%40news.povray.org%3E/

I discovered weird differences in results between using the wood pattern 
directly within a normal and wrapping it in pigment_pattern{} or 
function{pattern{}}.

In other words, the following:

normal {
   wood
   rotate*90
}

Results in behavior different than either:

#declare Fn = function {
   pattern {
     wood
     rotate x*90
   }
}
...
normal { Fn(x,y,z) }

     or

normal {
   pigment_pattern {
     wood
     color_map {
       [0 rgb 0]
       [1 rgb 1]
     }
     rotate x*90
}

In the attached image the left column is using one of the wood {} 
wrapped forms. The middle column uses 'wood' directly in the normal{}.
The right column showing a 4x multiple of differences which should not 
exist. No AA used. The image results are from v3.8 beta 2, but this 
issue exists in the yuqk fork too.

The top row is just the wood base normal. The bottom row showing the 
wood based normal used in a slope map{}.

Real life keeping me busy over the next few days, but I plan to dig into 
this when I get some time. My guess at the moment is it is some 
numerical difference near values of 0 and/or 1, but we'll see.

Bill P.

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