%!PS, siehe https://digitalartarchive.siggraph.org/artwork/georg-nees-gravel-stones/
% $Id: schotter.ps,v 1.5 2024/01/12 11:30:32 oj14ozun Exp $
% https://wwwcip.cs.fau.de/~oj14ozun/src+etc/schotter.ps

% parameters
/rows 24 def			%number of rows
/cols 12 def			%number of columns
/unit 24 def			%size of a square

% golden ratio (because of course)
/phi 5 sqrt 1 add 2 div def

% ensure a new random seed for every run
realtime srand

% draw a square
/square {
    currentpoint unit unit rectstroke
} def

% generate a random real in an interval [0;i]
/randi {
    rand 2 31 exp 1 sub div mul
} def

% add attribution
10 10 moveto
/Helvetica findfont 10 scalefont setfont
(Nach "Schotter" von Georg Nees) show

% draw the grid downwards
currentpagedevice /PageSize get dup
dup 0 get exch 1 get translate	%the origin is ↗
180 rotate			%draw downwards
 
% try to centre the unjittered grid
dup 0 get			%page width
cols unit mul			%grid width
sub 2 div
exch 1 get			%page height
rows unit mul			%grid height
sub 2 div
moveto				%use as start point

% draw the grid, restarting the jitter for each column
cols {
    gsave
    rand 3 mod 1 sub rotate	%initial jitter

    0 1 rows {
	phi mul dup randi
	exch 2 div sub

	gsave
	dup dup rmoveto rotate square
	grestore

	0 unit rmoveto
    } for
    grestore
    unit 0 rmoveto
} repeat
showpage