this is more modern (the method, not the font):

How filling the number ?
 

2016-07-12 17:56 GMT+02:00 Hans Hagen <pragma@wxs.nl>:
On 7/12/2016 5:21 PM, Fabrice Couvreur wrote:
Compiling this file returns files ntg46-mpgraph.log ntg46-mpgraph.tex
ntg46-mpgraph.mpy ntg46-mpgraph.pdf  ntg46-mpgraph.tuc

this is more modern (the method, not the font):

\startusableMPgraphic{NumberHead}
      draw outlinetext.d
        ("\bf\namedheadnumber{chapter}")
        (withpen pencircle scaled .1)
        ysized 60pt ;
\stopusableMPgraphic



% macros=mkvi

\setuppagenumbering[location=footer]

\startusableMPgraphic{NumberHead}
      picture r ;
      r := image ( graphictext
        "\bf\namedheadnumber{chapter}"
        scaled 5pt
        withfillcolor \MPcolor{lightgray}
        withpen pencircle scaled 1pt ; ) ;
      draw r ;
\stopusableMPgraphic

\def\processMPheadnumber#1%
  {\useMPgraphic{NumberHead}}

\setuphead
   [chapter]
   [command=\HeadTitle,
    headstyle=\ss,
    numbercommand=\processMPheadnumber]


\unexpanded\def\HeadTitle#1#2%
  {\framed
    [frame=off,
    bottomframe=on,
    width=broad,
    align={broad,nothyphenated,left}]
    {#1\blank[nowhite]#2}}

\starttext

\startchapter
  [title={Fist chapter}]

\input knuth

\stopchapter

\stoptext

2016-07-12 16:45 GMT+02:00 Hans Hagen <pragma@wxs.nl
<mailto:pragma@wxs.nl>>:

    On 7/12/2016 3:30 PM, Fabrice Couvreur wrote:

        Thank youfor the information, but it remains to delete the files ...
        mpgraph.log


    fwiw, mkiv normally doesn't have such files

    Hans


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                                              Hans Hagen | PRAGMA ADE
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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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--

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                                          Hans Hagen | PRAGMA ADE
              Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
       tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
archive  : http://foundry.supelec.fr/projects/contextrev/
wiki     : http://contextgarden.net
___________________________________________________________________________________