% Cookbook Example Program from First Printing, Revised 7 Jan 1985
% Program: Drawing Arrows     Number: 8
%-----------------------------------------------------------------------------
%
/arrowdict 13 dict def                      % Local storage for the procedure
					    % ``arrow.''
							
/arrow                                      % The procedure ``arrow'' adds an
  { arrowdict begin                         % arrow shape to the current path.
      /headlength exch def                  % It takes seven arguments: the x
      /halfheadthickness exch 2 div def     % and y coordinates of the tail
      /halfthickness exch 2 div def         % (imagine that a line has been
      /tipy exch def /tipx exch def         % drawn down the center of the
      /taily exch def /tailx exch def       % arrow from the tip to the tail,
					    % then x and y lie on this line),
					    % the x and y coordinates of the
					    % tip of the arrow, the thickness
					    % of the arrow in the tail
					    % portion, the thickness of the
					    % arrow at the widest part of the
					    % arrowhead and the length of the
					    % arrowhead.
							
      /dx tipx tailx sub def                % Compute the differences in x and
      /dy tipy taily sub def                % y for the tip and tail. These
      /arrowlength dx dx mul dy dy mul add  % will be used to compute the
	sqrt def                            % length of the arrow and to
      /angle dy dx atan def                 % compute the angle of direction
					    % that the arrow is facing with
					    % respect to the current user
					    % coordinate system origin.
      /base arrowlength headlength sub def  % Compute where the base of the
					    % arrowhead will be.
								
      /savematrix matrix currentmatrix def  % Save the current user coordinate
					    % system. We are using the same
					    % strategy to localize the effect
					    % of transformations as was used
					    % in the program to draw an
					    % ellipse.
      tailx taily translate                 % Translate to the starting point
					    % of the tail.
      angle rotate                          % Rotate the x-axis to correspond
					    % with the center line of the
					    % arrow.
      0 halfthickness neg moveto            % Add the arrow shape to the
					    % current path.
      base halfthickness neg lineto
      base halfheadthickness neg lineto
      arrowlength 0 lineto
      base halfheadthickness lineto
      base halfthickness lineto
      0 halfthickness lineto
      closepath
	       
      savematrix setmatrix                  % Restore the current user
					    % coordinate system.
    end
  } def

/len 160 def
/l1   40 def
/l2  120 def

5.625 72 mul len sub 2 div 60 translate

2 setlinewidth
0 0 moveto
len 0 lineto stroke
1 setlinewidth
l1 25 moveto
l1 -25 lineto
l2 25 moveto
l2 -25 lineto
stroke

l2 20 sub 35 l2 20 add 35 2 12 10 arrow gsave fill grestore stroke

/Helvetica findfont 14 scalefont setfont

(right) dup stringwidth pop 2 div l2 exch sub -40 moveto show
(edge) dup stringwidth pop 2 div l2 exch sub -55 moveto show

(left) dup stringwidth pop 2 div l1 exch sub -40 moveto show
(edge) dup stringwidth pop 2 div l1 exch sub -55 moveto show

.