%!PS
% Fill the paper with S's.
% Illustrating: procedures & loops
% Joseph O'Rourke

/inch {72 mul} def

2 setlinewidth
/red 1 def
/blue 0 def
/green 0 def
red green blue setrgbcolor
1 setlinecap  % 1=rounded cap (as opposed to 0=butt, 2=projecting square)


%--------------------------------
% L is radius of 'S' arc.
% arcs are 270 deg, one forward, one reverse,
% both centered on (0,L) so that leftmost coord is 0,
% rightmost is 2L. 
/L 12 def
% procedure S draws one S
/S {0 L L 0 270 arc
    0 L neg L 90 -180 arcn
    stroke
} def
%--------------------------------

%--------------------------------
% For-loop params to fill page:
% nx = number of S's that will fit horizontally
% ny = number of S's that will fit vertically
/nx 8.5 inch L div floor def
/ny 11 inch 4 L mul div floor 1 add def

% For-loop over all rows
% start incr end
0 1 ny {
    % One row
    gsave % Save origin on y-axis.
    % Prepare for first S (move over -2L, width of S):
    % First step in loop translates.
    L neg 2 L mul translate
    % For-loop to fill one row:
    % start incr end
    0 1 nx {
	2 L mul 0 translate  % Move over width of S
	S} for
    grestore % Reset origin on y-axis

    % Move up height of S.
    0 4 L mul translate

    % Adjust the color slightly: red down, blue up.
    /red red 0.05 sub def
    /blue blue 0.05 add def
    red green blue setrgbcolor
    
} for


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