POV-Ray : Newsgroups : povray.beta-test : benchmark scene mesh buggy? Server Time: 30 Mar 2017 08:52:21 GMT
  benchmark scene mesh buggy? (Message 1 to 2 of 2)  
From: clipka
Subject: benchmark scene mesh buggy?
Date: 3 Sep 2016 20:12:26
Message: <57cb2eaa@news.povray.org>
Hi folks,

does anyone have time to examine the mesh in the benchmark scene, and
check whether the surface normals make any sense? I have reason to
believe they don't, at least not at the kink in the generating function.


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From: Le Forgeron
Subject: Re: benchmark scene mesh buggy?
Date: 4 Sep 2016 15:03:58
Message: <57cc37de$1@news.povray.org>
Le 03/09/2016 à 22:12, clipka a écrit :
> Hi folks,
> 
> does anyone have time to examine the mesh in the benchmark scene, and
> check whether the surface normals make any sense? I have reason to
> believe they don't, at least not at the kink in the generating function.
> 
You mean :

#macro L_GetVN(ResSpl)
   #local I = 0;
   #local A = array[ResSpl+1][2]
   #while (I<=ResSpl)
      #local P0 = 0+<FnA(I/ResSpl), I/ResSpl, 0>;
      #if (P0.x=0 & P0.z=0)
         #local P0 = <1e-25,P0.y,1e-25>;
      #end
      #if (I=0)
         #local P1 = 0+<FnA(((I-0.5)/ResSpl)), I/ResSpl, 0>;
         #local P2 = 0+<FnA(((I+0.5)/ResSpl)), I/ResSpl, 0>;
      #else
         #local P1 = P2;
         #local P2 = 0+<FnA(((I+0.5)/ResSpl)), I/ResSpl, 0>;
      #end
      #local P3 = vrotate(P0,<0,1,0>);
      #local P4 = vrotate(P0,<0,-1,0>);
      #local B1 = P4-P0;
      #local B2 = P2-P0;
      #local B3 = P3-P0;
      #local B4 = P1-P0;
      #local N1 = vcross(B1,B2);
      #local N2 = vcross(B2,B3);
      #local N3 = vcross(B3,B4);
      #local N4 = vcross(B4,B1);
      #local N = vnormalize((N1+N2+N3+N4)*-1);
      #local A[I][0] = P0;
      #local A[I][1] = N;
      #local I = I+1;
   #end
   A
#end

P0 is the point to compute, P1 is the previous intermediate point
P2 is the next intermediate point
P3 & P4 are a bit strange, rotation around y for 1 degree of P0, so kind of sideway
(from origin)
B1,B2,B3,B4 are "diagonal" from P0
N1,N2,N3,N4 are normal computation from 2 neighbouring diagonals.
N is the average of all contributions (negated)

As the original P0 is with .z = 0, the small rotation for P3 & P4 seems ok. as long as
FnA avoid 0.


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