MPgraphic with rounded corners

[Duncan Hothersall <dh@capdm.com>]

Hello all.

I have adapted a bit of MP code from Aditya from a mailing list message 
dated 2006-05-19 
(http://archive.contextgarden.net/message/20060519.214124.9174ac0e.en.html) 
to ensure that when a page break occurs in a textbackground there is a 
forced vertical space inside the box at the top of the new page.

This code works fine for me (although interestingly not in the garden):


\setupcolors[state=start]

\startuseMPgraphic{mpos:par:myexample}
path p;
for i = 1 upto nofmultipars :
p := multipars[1] topenlarged 8pt bottomenlarged 8pt;
fill p withcolor 0.9white ;
draw p withcolor black
withpen pencircle scaled \MPvar{linewidth};
endfor;
\stopuseMPgraphic

\definetextbackground[ExampleBackground]
        
[mp=mpos:par:myexample,location=paragraph,leftoffset=1em,rightoffset=1em,rulethickness=1pt]

\starttext
\input knuth \endgraf
\starttextbackground[ExampleBackground]
\dorecurse{13}{\input knuth \endgraf}
\stoptextbackground
\input knuth \endgraf
\stoptext


But now I need to make this box have rounded corners, and I am very 
confused when reading core-pgr.tex because that is a level of MP code I 
just don't understand.

Would somebody please be able to tell me what to change in the above to 
make the corners of the box rounded (with a radius of 2mm)?

Thank you very much!

Duncan

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