Hi Aditya,
Sorry I forgot to attach the image of what I want to do. I know corner=number parameter of framed and framed text but I wanted to do it with Metafun.
Thank you
Fabrice

2017-08-23 0:50 GMT+02:00 Aditya Mahajan <adityam@umich.edu>:
On Wed, 23 Aug 2017, Fabrice Couvreur wrote:

Hello,
I would like to have three corners rounded as in the figure.

Not sure if you had simplified your example or not. But if all you want is a rounded corner, you can consider using corner=number parameter of framed and framed text:

http://wiki.contextgarden.net/Framed#Rounded_Corners

Here is an example (that does not use metapost).

\definecolor[MyColorA][r=0.8784, g=0.8784, b=0.8784]
\definecolor[MyColorB][c=0.00,m=0.27,y=1.00,k=0.00]

\defineornament
    [FrameTitle]
    [preset=lefttop]
    [
      frame=off,
      foregroundstyle=\bfx,
      foregroundcolor=white,
      background=color,
      backgroundcolor=MyColorB,
    ]

\defineframedtext
  [FramedText]
  [
    offset=0.6em,
    toffset=\lineheight,
    background=color,
    backgroundcolor=MyColorA,
    foregroundstyle={\switchtobodyfont[10pt]},
    align=verytolerant,
    frame=off,
    corner=01,
  ]


\showframe
\starttext

\FrameTitle{Info}{\startFramedText[width=10cm]
      L'équivalent vingt pieds (EVP) est une unité de mesure de conteneurs
(de longueur courante 20 pieds, soit environ \unit{6,1 meter}).

      1 EVP représente environ \unit{38,5 cubic meter}.
    \stopFramedText}

\stoptext
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