mode_setup;
 em#:=10pt#; cap#:=7pt#;
 thin#:=1/3pt#; thick#:=5/6pt#;
 o#:=1/5pt#;
define_pixels(em,cap);
define_blacker_pixels(thin,thick);
define_corrected_pixels(o);
 curve_sidebar=round 1/18em;
beginchar("O",0.8em#,cap#,0); "The letter O";
 penpos1(thick,10); penpos2(.1[thin,thick],90-10);
 penpos3(thick,180+10); penpos4(thin,270-10);
 x1l=w-x3l=curve_sidebar; x2=x4=.5w;
 y1=.49h; y2l=-o; y3=.51h; y4l=h+o;
 penstroke z1e{down}..z2e{right}
            ..z3e{up}..z4e{left}..cycle;
 penlabels(1,2,3,4); endchar;
def test_I(expr code,trial_stem,trial_width) =
 stem#:=trial_stem*pt#; define_blacker_pixels(stem);
 beginchar(code,trial_width*em#,cap#,0); "The letter I";
  penpos1(stem,15); penpos2(.9stem,12); penpos3(stem,10);
  x1=x2=x3=.5w; y1=h; y2=.55h; y3=0; x2l:=1/6[x2l,x2];
  penstroke z1e..z2e{down}..z3e;
  penlabels(1,2,3); endchar; enddef;