%!

% x1 y1 x2 y2 -> X1 Y1 X2Y2 X3 Y3 curveto
/quadto { 1 dict begin
  currentpoint                                        % x1 y1 x2 y2 x0 y0 
  4 index dup add add 3 div                    % x1 y1 x2 y2 x0 (y0+2 y1)/3
  6 1 roll                                                % Y1 x1 y1 x2 y2 x0 
  4 index dup add add 3 div                    % Y1 x1 y1 x2 y2 (x0+2 x1)/3
  6 1 roll                                                % X1 Y1 x1 y1 x2 y2 
  2 copy                                                % X1 Y1 x1 y1 x2 y2 x2 y2
  5 -1 roll dup add add 3 div                    % X1 Y1 x1 x2 y2 x2 (y2 + 2 y1)/3
  5 1 roll                                                % X1 Y1 Y2 x1 x2 y2 x2 
  4 -1 roll dup add add 3 div                    % X1 Y1 Y2 x2 y2 X2
  4 1 roll                                                % X1 Y1 X2 Y2 x2 y2
  curveto
end } def