drawdot fails?

[David Arnold <dwarnold45@cox.net>]

All,

I am wondering why my dots are not filled with the drawdot command.

\startuseMPgraphic{yeqx2}
   %define function
   vardef f(expr x)=
     x*x
   enddef;
   %define clipping path
   path cpath;
   cpath:=(-5,-5)--(5,-5)--(5,5)--(-5,5)--cycle;
   %create function path
   path p; p:=(-5,f(-5));
   for x=-5 step .1 until 5:
     p:=p--(x,f(x));
   endfor;
   p:=p--(5,f(5));
   %clip function path to clipping path
   p:=p cutbefore cpath;
   p:=reverse p;
   p:=p cutbefore cpath;
   %initialize scale
   numeric u; 10u=2in;
   %draw the grid
   for k=-5u step 1u until 5u:
     draw (k,-5u)--(k,5u) withcolor 0.85white;
     draw (-5u,k)--(5u,k) withcolor 0.85white;
   endfor;
   %draw axes
   drawdblarrow (-5.2u,0)--(5.2u,0);
   drawdblarrow (0,-5.2u)--(0,5.2u);
   %label axes
   label.rt(btex $x$ etex, (5.2u,0));
   label.top(btex $y$ etex, (0,5.2u));
   label.bot(btex $5$ etex, (5u,0));
   label.lft(btex $5$ etex, (0,5u));
   %scale function path
   p:=p scaled u;
   %draw function path
   drawdblarrow p withcolor blue;
   %draw plotted points
   for x=-2 step 1 until 2:
     drawdot ((x,f(x)) scaled u) withpen pencircle scaled 4pt;
   endfor;
\stopuseMPgraphic

\placefigure{The simple parabola.}{\useMPgraphic{yeqx2}}