% transformations.
%
-\startuniqueMPgraphic{box}
+\startuseMPgraphic{HLine}
+path a, b;
+% Create a rectangle of the full size
+a := origin -- (\MPvar{width}, 0mm);
+% Randomize it a bit
+b := a randomized (\overlaywidth / 25) ;
+% And draw it
+drawoptions (withpen pencircle scaled .75mm withcolor black) ;
+draw b;
+\stopuseMPgraphic
+
+% Draw a line with the given options. Accepts only the 'width' option. Be
+% careful that these are metapost options, so use \the\textwidth instead of
+% textwidth, and a metapost expression for arithmethic (e.g. 0.5 *
+% \the\textwidth instead of 0.5\textwidth).
+\def\HLine[#1]%
+ {\setupMPvariables[HLine][#1]%
+ \useMPgraphic{HLine}}
+
+\startuseMPgraphic{box}
path a, b;
% Create a rectangle of the full size
a := unitsquare xyscaled(\overlaywidth,\overlayheight);
% Randomize it a bit
-b := a randomized 10pt ;
+b := a randomized (\overlaywidth / 25) ;
% And draw it
drawoptions (withpen pencircle scaled .75mm withcolor black) ;
draw b;
-\stopuniqueMPgraphic
+\stopuseMPgraphic
-\defineoverlay[box][\uniqueMPgraphic{box}]
+\defineoverlay[box][\useMPgraphic{box}]
% Define \{start,stop}boxed with a nice metapost box around it.
\defineframedtext[boxed][background=box,frame=off]