[NTG-context] update old MP code

[Henning Hraban Ramm]

Am 01.09.22 um 15:40 schrieb Taco Hoekwater:
> Adding grouping makes sense:
>>
>> def Moire(expr size)(text densities)=
> 
> begingroup
> endgroup
> 
> As that at least makes it an expression instead of a statement list.
> 
> But also depthless() is never defined?

Oops, I forgot to copy that part (confusing source...)

It still doesn’t compile:

---

\setupbodyfont[plex,ss,8bp]

\startreusableMPgraphic{moiree}
% 1994 by Bogusław Jackowski (GUST)
defaultfont := "\truefontname{Sans}";
pickup pencircle scaled 0.3bp;

defaultscale := .8;
linecap := butt;
labeloffset := 1.5bp;
defaultthickness:=.3bp; % 5 pixels at 1200 dpi

% tertiarydef p ulshiftedto s = p shifted (s-ulcorner(p)) enddef;

vardef depthless(expr p) =
  save p_; picture p_;
  p_:=p if string p: infont defaultfont scaled defaultscale fi;
  setbounds p_ to (xpart(llcorner p_),0)--(xpart(lrcorner p_),0)--
   urcorner(p_)--ulcorner(p_)--cycle;
  p_
enddef;

def Moire(expr size)(text densities)=
   begingroup
   save dn,a,b,k,labit,n,p,q,s,xs;
   n := 32;
   dn := 0;
   for i := densities:
     d[incr dn] := abs(i);
     if i>1: labit[dn]:=1; fi
   endfor
   a := min(d[1],d[dn]);
   b := max(d[1],d[dn]);
   image(
     for i=-n upto n:
      draw (0,i*in/a)--(size,i*in/b);
       %withpen pencircle scaled 3/5defaultthickness;
     endfor
     for i=1 upto dn:
       k:=(a/d[i]-1)/(a/b-1);
       if known labit[i]:
         string s; s:=decimal(d[i]); xs:=0;
         picture p,q; q := p := depthless(s);
         if i=dn:
           q := depthless(s & "  lpi");
           xs := width(q)-width(p);
         fi
         label.top(q, (k*size+1/2xs, n*in/a+1.5mm));
       fi
       draw (k*size, n*in/a+1.5mm)--(k*size, k[n*in/a,n*in/b]+.5mm);
       draw (k*size, -n*in/a-1.5mm)--(k*size, -k[n*in/a,n*in/b]-.5mm);
     endfor
   )
   endgroup;
enddef;
draw Moire(57.5mm)(200, 175, 150, 125, 100, 75);
% ulshiftedto (142mm, 38.5mm);
\stopreusableMPgraphic

\starttext
\reuseMPgraphic{moiree}
\stoptext

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