[NTG-context] How to run Typesetting in MetaPost example (MetaFun)?

Aditya Mahajan adityam at umich.edu
Wed Jan 19 18:42:42 CET 2011


On Tue, 18 Jan 2011, Verhaag, G.C.H.M. wrote:

> Hi,
>
> I wanted to try (using ConTeXt minimals MkIV) the example on page 228 of the 
> MetaFun manual, dealing with typesetting in MetaPost.

I haven't look at the metapost manual ... but

> The code is given as:
>
> \resetMPdrawing
> \startMPdrawing
> picture pic[] ;
> numeric wid[], len[], pos[], n ;
> wid[0] := len[0] := pos[0] := n := 0 ;
> \stopMPdrawing
>
> \def\whatever#1%
> {\appendtoks#1\to\MPtoks
> \setbox\MPbox=\hbox{\bfd\the\MPtoks}%
> \startMPdrawing
>  n := n + 1 ; len[n] := \the\wd\MPbox ;
> \stopMPdrawing
> \startMPdrawing[-]
>  pic[n] := textext("\bfd\setstrut\strut#1") ;
>  pic[n] := pic[n] shifted - llcorner pic[n] ;
> \stopMPdrawing}
>
> \handletokens MetaPost is Fun!\with\whatever
>
> But is won't run. The following message is generated:

The actual error message said

! Undefined control sequence.
\@@toks ->\MPtoks

So add

\newtoks\MPtoks

After which you get

! Undefined control sequence.
\whatever ...endtoks #1\to \MPtoks \setbox \MPbox

so add

\newbox\MPbox

After that the file compiles but you get an empty image. There are two 
things missing in the code. First you don't tell actually draw the 
metapost drawing. for that, add

\MPdrawingdonetrue \getMPdrawing \resetMPdrawing


Still an empty page. Again the pic[n] is calculated but never drawn. So 
add

   draw p[n] shifted (n*1cm,0) ;

(or perhaps along a more sophisticated path),

and now you have a working example:

\newtoks\MPtoks
\newbox\MPbox

\resetMPdrawing
\startMPdrawing
   picture p[] ;
   numeric wid[], len[], pos[], n ;
   wid[0] := len[0] := pos[0] := n := 0 ;
\stopMPdrawing

\def\whatever#1%
{\appendtoks#1\to\MPtoks
  \setbox\MPbox=\hbox{\bfd\the\MPtoks}%
  \startMPdrawing
   n := n + 1 ; len[n] := \the\wd\MPbox ;
   p[n] := textext("\bfd\setstrut\strut#1") ;
   p[n] := p[n] shifted - llcorner p[n] ;
   draw p[n] shifted (n*1cm,0) ;
  \stopMPdrawing}

\starttext
\handletokens MetaPost is Fun!\with\whatever

\MPdrawingdonetrue \getMPdrawing \resetMPdrawing

\stoptext

You could also have just used the macros from meta-txt:

\useMPlibrary[txt]

\startMPdefinitions
   newpath RotPath ;
   RotPath = fullcircle scaled 3cm ;
\stopMPdefinitions

\starttext
\followtokens{Metapost is fun \quad}
\stoptext

@Hans: Perhaps we can have a more ConTeXtist interface to this macro:

\definetextonepath
    [whatever]
    [color=...,
     style=...,
     mp=..., % path specification
    ]

\whatever{Metapost is fun}

Aditya


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