[NTG-context] Code that run in Metapost but not in starMPcode enviroment

[Hans Hagen]

On 2/1/2015 12:29 PM, DesdeChaves wrote:
>
> I'm trying to draw some random arrows using Metapost. For that I use a
> piece of code from fpast that in found at stackexchange
> <http://tex.stackexchange.com/questions/179745/generating-random-arrows-in-tikz/180111#180111>
>
> Unfortunately this code does not work in context (request for a solution
> <http://tex.stackexchange.com/questions/225864/metapost-error-related-with-context>)
> because the freelabel() function. If I disable it the result is the
> expected.
> What is wrong with this code?
>
>
> \starttext
>
> \startMPcode
> numeric u, nb_vectors, wd;
> u := 1cm; % unit length
> nb_vectors := 20; wd = .5;
> boolean intersect; pair random_origin; color random_color; path
> candidate, random_vector[];
> %
> vardef bb(expr p) =
>    save orig, extr; pair orig, extr; orig = point 0 of p; extr = point 1
> of p;
>    pair v,w; v = wd*unitvector(extr-orig)*u; w = v rotated 90;
>    (orig - v + w) -- (extr + v + w) -- (extr + v - w) -- (orig - v - w)
> -- cycle
> enddef;
> %
>
>    pickup pencircle scaled 2bp;

   numeric i ;
   i = 1 ;

>    i = 1;

or

  i := 1 ; % never assume variable is not set global (such is mp)

>    forever:
>      exitunless (i <=  nb_vectors);
>      intersect := false;
>      random_length := u*(2+uniformdeviate(1));
>      random_angle := uniformdeviate(359);
>      random_origin := u*(uniformdeviate(wd*nb_vectors),
> uniformdeviate(wd*nb_vectors));
>      random_color := (uniformdeviate(1), uniformdeviate(1),
> uniformdeviate(1));
>      candidate := random_origin -- (random_origin +
> random_length*dir(random_angle));
>      j := 1;
>      forever:
>        exitif (j = i) or (intersect = true);
>        if bb(random_vector[j]) intersectiontimes bb(candidate) <>  (-1, -1):
>          intersect := true;
>        fi;
>        j := j+1;
>      endfor;
>      if intersect = false:
>        random_vector[i] = candidate;
>        drawarrow candidate withcolor random_color;
>        freelabel(btex $v$ etex, point .5 of candidate, point .5 of
> candidate + dir (random_angle + 90));
>        i := i+1;
>      fi;
>    endfor;
> \stopMPcode
>
>
> \stoptext
>
>
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