%% half-dimer pointing up
% name, width, height, depth
beginchar("a",1.5pt#,7pt#,0);
  pickup pencircle scaled 4;

  x1=y1=x2=x3=0;
  y2=h;
  x4=-x5=-y4=-y5=w;
  y3=2y4;

  draw z1..z2;
  draw z1..z4..z3..z5..cycle;
endchar;

%% half-dimer pointing down
beginchar("b",1.5pt#,7pt#,0);
  pickup pencircle scaled 4;

  x1=x2=x3=0;
  y1=h-2w;
  y2=-2w;
  x4=-x5=w;
  y4=y5=h-w;
  y3=h;

  draw z1..z2;
  draw z1..z4..z3..z5..cycle;
endchar;

%% radius for horizontal dimers
r=1.5pt;

%% half-dimer pointing right
beginchar("c",10pt#,4.5pt#,0);
  pickup pencircle scaled 4;

  y1=y2=y3=h-r;
  x3=0;
  y4=h;
  y5=h-2r;
  x4=x5=r;
  x1=2r;
  x2=w;

  draw z1..z2;
  draw z1..z4..z3..z5..cycle;
endchar;

%% half-dimer pointing left
beginchar("d",10pt#,4.5pt#,0);
  pickup pencircle scaled 4;

  y1=y2=y3=h-r;
  x3=w;
  y4=h;
  y5=h-2r;
  x4=x5=w-r;
  x1=w-2r;
  x2=0;

  draw z1..z2;
  draw z1..z4..z3..z5..cycle;
endchar;

end