Re: [NTG-context] Randomize control points in metapost/metafun?

1 Aug 2016


      On 8/1/2016 8:03 AM, Mikael P. Sundqvist wrote:
...
Hi!
I look for a way to randomize control points of a path, leaving the
coordinates themselves untouched.
The reason is the following: I want to draw (for example) a circle
with a triangle inside, and I want them to look slightly randomized.
If I do (see attached pdf for a typical result of this)
\startMPpage
draw fullcircle scaled 2cm randomized 0.1cm;
draw ((1cm,0)--(0,1cm)--(-1cm,0)--cycle) randomized 0.1cm;
\stopMPpage
then the corners of the triangle does not stay on the circle (and I
want them to). [I dont want the triangle to consist of perfectly
straight lines, so I cannot (directly) draw the triangle using
different points along the randomized circle] I imagine that one could
achieve what I want if one could randomize the control points only.
i'll add

primarydef p randomizedcontrols s = (
     if path p :
         for i=0 upto length(p)-1 :
              (point       i    of p) .. controls
             ((postcontrol i    of p) randomshifted s) and
             ((precontrol (i+1) of p) randomshifted s) ..
         endfor
         if cycle p :
             cycle
         else :
             (point length(p) of p)
         fi
     else :
         p randomized s
     fi
) enddef ;
...
Also, is it possible to randomize a picture (consisting of several
paths/points) somehow, without randomizing each part of it manually?
so:

vardef mfun_randomized_path(expr p,s) =
     for i=0 upto length(p)-1 :
          (point       i    of p) .. controls
         ((postcontrol i    of p) randomshifted s) and
         ((precontrol (i+1) of p) randomshifted s) ..
     endfor
     if cycle p :
         cycle
     else :
         (point length(p) of p)
     fi
enddef;

vardef mfun_randomized_picture(expr p,s) =
     save currentpicture ;
     picture currentpicture ;
     currentpicture := nullpicture ;
     for i within p :
         addto currentpicture
             if stroked i :
                 doublepath pathpart i randomizedcontrols s
                 dashed dashpart i
                 withpen penpart i
                 withcolor colorpart i
                 withprescript prescriptpart i
                 withpostscript postscriptpart i
             elseif filled i :
                 contour pathpart i randomizedcontrols s
                 withpen penpart i
                 withcolor colorpart i
                 withprescript prescriptpart i
                 withpostscript postscriptpart i
             else :
                 also i
             fi
         ;
     endfor ;
     currentpicture
enddef ;

primarydef p randomizedcontrols s = (
     if path p :
         mfun_randomized_path(p,s)
     elseif picture p :
         mfun_randomized_picture(p,s)
     else :
         p randomized s
     fi
) enddef ;

with

draw fullcircle scaled 2cm randomizedcontrols 0.1cm;
draw ((1cm,0)--(0,1cm)--(-1cm,0)--cycle) randomizedcontrols 0.1cm;

draw image (
     draw fullcircle scaled 2cm ;
     draw ((1cm,0)--(0,1cm)--(-1cm,0)--cycle);
) randomizedcontrols 0.1cm ;


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