Hi,
I discovered some macro Metafun particular.
I then wanted to outline, but it does not fit with the boundary of the quadrant.
Can I have some explanation ?

Best regards,

Fabrice

\starttext
\startMPcode
u:=1cm ;
pickup pencircle scaled 1pt ;
fill ulcircle scaled 8u withcolor lightgray ;
fill llcircle scaled 2u shifted (1u,0) withcolor lightgray ;
fill lrcircle scaled 4u shifted (1u,1u) withcolor lightgray ;
fill urcircle scaled 6u shifted (0,1u) withcolor lightgray ;
label.lft(btex $x$ etex, (0,0.5u)) ;
fill unitsquare scaled 1u withcolor lightgray ;
draw unitsquare scaled 1u ;
draw (-4u,0)--(0,0) dashed evenly ;
draw (0,1u)--(0,4u) dashed evenly ;
draw (1u,1u)--(3u,1u) dashed evenly ;
draw (1u,0)--(1u,-1u) dashed evenly ;
draw (-4u,0){up}..(0,4u)..(3u,1u){down} ;
\stopMPcode
\stoptext