%!PS
% Draw a spiral of squares
% Illustrates: for-loop, rotate, translate, scale.
% Joseph O'Rourke

5 setlinewidth
1 0 0 setrgbcolor % Red

/inch {72 mul} def

% Set scale to draw in inches:
4.25 inch 5.5 inch translate
% Too large!  Cut by 1/4:
0.25 0.25 scale

% Draw a 1x1 square, lower left corner at current origin
% Use gsave/grestore to both stroke and fill
/square {
    newpath
    0 0 moveto
    1 inch 0 lineto
    1 inch 1 inch lineto
    0 1 inch lineto
    closepath
    gsave
    1 0 0 setrgbcolor % Red
    stroke
    grestore
    0.75 0.75 0 setrgbcolor % Olive Green
    fill
    } def

% Draw a total of n squares
/n 24 def

gsave

% start incr end
1 1 n {
    % bind loop variable to x (always on top of stack):
    /x exch def
    square
    30 rotate
    0 x 10 mul translate
    1.1 1.1 scale
} for

% Unscale etc.: back to default coordinate system.
grestore 

% Circle the origin so we can see it
0 0 1 setrgbcolor % Blue
newpath
0 0 20 0 360 arc
stroke

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