%
% Labels point i of mypath with (start+i).
%
def test( expr mypath, start ) =
  draw mypath
       withcolor red;
  for i = 0 upto length mypath:
    dotlabel ( decimal( i + start ),point i of mypath );
  endfor;
enddef;

%
% Circles pic with a circle scaled s.
%
def scaledcircleit( expr pic, s ) =
  (unitcircle shifted (-0.5,-0.5) scaled s
              shifted 0.5[ llcorner( pic ), urcorner( pic )])
enddef;

def widthofbox( expr b ) =
  (xpart( lrcorner( b ) ) - xpart( llcorner( b ) ))
enddef;

def heightofbox( expr b ) =
  (ypart( ulcorner( b ) ) - ypart( llcorner( b ) ))
enddef;

def centreofbox( expr b ) =
  (0.5[ ulcorner( b ), lrcorner( b ) ])
enddef;