Web pdp-10.trailing-edge.com

Trailing-Edge - PDP-10 Archives - decuslib20-10 - decus/20-189/squarelimit.ps
There are no other files named squarelimit.ps in the archive.
```% From ut-ngp!ut-sally!husc6!caip!clyde!watmath!watnot!watdcsu!bumbulis
% Thu Jul 24 08:15:07 CDT 1986
%
% The following is a translation to PostScript of Michael Parsons
% Miranda code.  It produces a level 2 picture on an Apple LaserWriter
% in about 10-15 minutes.  Edit the second last line to get different
% levels.
%
%Peter
%
%  The following are all the functions required to produce the famous
%  "Square Limit" drawing by M. C. Escher. These functions were derived by
%  Peter Henderson. See his paper in 1982 Conf. on LISP and Func. Prog.
%  (C) Miranda coding by Michael Parsons, September 1985
%  Translation to PostScript by Peter Bumbulis, July 1986
%

%  quartet combines 4 images, one image in each quadrant, to produce one image.
/quartet {
4 -1 roll 1 2 div   0   1 zoom
4 -1 roll 1 2 div   1   1 zoom
4 -1 roll 1 2 div   0   0 zoom
4 -1 roll 1 2 div   1   0 zoom
4 {exec} /repeat cvx
7 array astore cvx
} def

%  nonet arranges 9 images in equal sized squares to form 1 image.
/nonet {
9 -1 roll 1 3 div   0   1 zoom
9 -1 roll 1 3 div 0.5   1 zoom
9 -1 roll 1 3 div   1   1 zoom
9 -1 roll 1 3 div   0 0.5 zoom
9 -1 roll 1 3 div 0.5 0.5 zoom
9 -1 roll 1 3 div   1 0.5 zoom
9 -1 roll 1 3 div   0   0 zoom
9 -1 roll 1 3 div 0.5   0 zoom
9 -1 roll 1 3 div   1   0 zoom
9 {exec} /repeat cvx
12 array astore cvx
} def

%  cycle combines 4 smaller copies of an image, each rotated by a different
%  multiple of 90 degrees.
/cycle {dup 270 rot dup 180 rot dup  90 rot quartet} def

%  t is one of the basic fish rearrangements.
/t {{p} {q} {r} {s} quartet} def

%  u is another of the basic fish rearrangements.
/u {{q} 90 rot cycle} def

%  side defines one side of the picture at level n.
/side {
dup 0 le
{  pop   {} dup t 90 rot t quartet}
{1 sub side dup t 90 rot t quartet}
ifelse
} def

%  corner defines one corner of the picture at level n.
/corner {
dup 0 le
{  pop         {}        {}         {} u quartet}
{1 sub dup corner exch side dup 90 rot u quartet}
ifelse
} def

%  quadcorner forms one quarter of the image at level n;
dup corner exch side dup dup 90 rot dup u exch t 90 rot dup 3 1 roll
{q} 90 rot nonet
} def

%  squarelimit produces the fish drawing.
/squarelimit {quadcorner cycle} def

%  fish gives a border to produce the final drawing.
/fish {
squarelimit exec
newpath
0 0 moveto
0 1 lineto
1 1 lineto
1 0 lineto
closepath
stroke
} def

/flip {0.5 0.5 translate 1 -1 scale -0.5 -0.5 translate} def

%  All the data needed to draw the fish.
/p {
gsave flip
newpath
0 0.8125 moveto 0 0.5 lineto
0 0.8125 moveto 0.1875 0.75 lineto
0.75 0 moveto 0.8125 6.25e-2 lineto
0.1875 0.75 moveto 0 0.5 lineto
0.375 1 moveto 0.25 0.75 lineto
0.25 0.6875 moveto 0.4375 0.625 lineto
0.25 0.6875 moveto 0.25 0.375 lineto
0.4375 0.625 moveto 0.25 0.375 lineto
0.6875 1 moveto 0.625 0.75 lineto
0.6875 1 moveto 0.875 0.875 lineto
0.875 0.875 moveto 1 0.875 lineto
0.625 0.75 moveto 0.8125 0.6875 lineto
0.8125 0.6875 moveto 1 0.75 lineto
0.625 0.75 moveto 0.5 0.5 lineto
0.5625 0.625 moveto 0.75 0.5625 lineto
0.75 0.5625 moveto 1 0.625 lineto
0.5 0.5 moveto 0.75 0.4375 lineto
0.75 0.4375 moveto 1 0.5 lineto
0.5 0.5 moveto 0.25 0.1875 lineto
0.25 0.1875 moveto 0 0 lineto
0.5 0.25 moveto 1 0.375 lineto
1 0.25 moveto 0.75 0.25 lineto
0.75 0.25 moveto 0.5 0 lineto
0.5 0 moveto 0.375 6.25e-2 lineto
0.375 6.25e-2 moveto 0 0 lineto
0.625 0 moveto 0.75 0.125 lineto
0.75 0.125 moveto 1 0.1875 lineto
1 0.125 moveto 0.8125 6.25e-2 lineto
1 6.25e-2 moveto 0.875 0 lineto
stroke
grestore
} def

/q {
gsave flip
newpath
0 0 moveto 0 0.25 lineto
0 0.5 moveto 0 1 lineto
0 1 moveto 0.5 1 lineto
0.75 1 moveto 1 1 lineto
0.125 1 moveto 0.25 0.6875 lineto
0.25 1 moveto 0.375 0.6875 lineto
0.375 1 moveto 0.5 0.6875 lineto
0.5 1 moveto 0.625 0.625 lineto
0.25 0.6875 moveto 0.25 0.5625 lineto
0.375 0.6875 moveto 0.375 0.5625 lineto
0.5 0.6875 moveto 0.5 0.5 lineto
0.625 0.625 moveto 0.625 0.4375 lineto
0.625 1 moveto 0.875 0.3125 lineto
0.75 1 moveto 0.8125 0.75 lineto
0.8125 1 moveto 1 0.625 lineto
0.875 1 moveto 1 0.75 lineto
0.9375 1 moveto 1 0.875 lineto
0 0.25 moveto 0.1875 0.1875 lineto
0 0.375 moveto 0.4375 0.3125 lineto
0 0.5 moveto 0.25 0.5625 lineto
0.125 0 moveto 0.1875 0.1875 lineto
0.1875 0.1875 moveto 0.3125 0.125 lineto
0.3125 0.125 moveto 0.25 0 lineto
0.3125 0.125 moveto 0.4375 6.25e-2 lineto
0.4375 6.25e-2 moveto 0.5 0 lineto
0.5 6.25e-2 moveto 0.6875 6.25e-2 lineto
0.6875 6.25e-2 moveto 0.5625 0.1875 lineto
0.5625 0.1875 moveto 0.5 6.25e-2 lineto
0.5625 0.25 moveto 0.75 0.25 lineto
0.75 0.25 moveto 0.625 0.375 lineto
0.625 0.375 moveto 0.5625 0.25 lineto
1 0 moveto 0.75 0.375 lineto
0.375 0 moveto 0.4375 6.25e-2 lineto
0.75 0.375 moveto 0.375 0.5625 lineto
0.375 0.5625 moveto 0.25 0.5625 lineto
1 0 moveto 0.9375 0.375 lineto
0.9375 0.375 moveto 1 0.5 lineto
1 0.5 moveto 0.8125 0.75 lineto
stroke
grestore
} def

/r {
gsave flip
newpath
0.5 0.5 moveto 0.125 0.25 lineto
0.125 0.25 moveto 0 0 lineto
0 0.5 moveto 0.125 0.25 lineto
0 0.25 moveto 6.25e-2 0.125 lineto
0 1 moveto 0.5 0.5 lineto
0 0.75 moveto 0.3125 0.375 lineto
6.25e-2 0.9375 moveto 0.25 1 lineto
0.125 0.875 moveto 0.5 1 lineto
0.1875 0.8125 moveto 0.5 0.875 lineto
0.3125 0.6875 moveto 0.75 0.8125 lineto
0.5 0.875 moveto 0.75 1 lineto
0.75 0.8125 moveto 1 1 lineto
0.5 0.5 moveto 0.875 0.625 lineto
1 0.625 moveto 0.6875 0.375 lineto
0.6875 0.375 moveto 0.375 0 lineto
1 0.5 moveto 0.75 0.25 lineto
1 0.75 moveto 0.875 0.625 lineto
0.75 0.25 moveto 0.6875 0 lineto
0.75 0.25 moveto 1 0 lineto
1 0.375 moveto 0.8125 0.1875 lineto
1 0.25 moveto 0.875 0.125 lineto
1 0.125 moveto 0.9375 6.25e-2 lineto
stroke
grestore
} def

/s {
gsave flip
newpath
0 1 moveto 0.25 0.875 lineto
0.125 0.9375 moveto 0 0.75 lineto
0.25 0.875 moveto 0.5 0.875 lineto
0.5 0.875 moveto 1 1 lineto
1 1 moveto 0.625 0.75 lineto
0.625 0.75 moveto 0.5 0.625 lineto
0 0.625 moveto 0.4375 0.75 lineto
0 0.5 moveto 0.5 0.625 lineto
0 0.375 moveto 0.4375 0.5 lineto
0 0.25 moveto 0.4375 0.375 lineto
0 0.125 moveto 0.4375 0.1875 lineto
0.5 0.625 moveto 0.4375 0.5 lineto
0.4375 0.5 moveto 0.4375 0.1875 lineto
0.4375 0.1875 moveto 0.5 0 lineto
0.625 0 moveto 0.6875 0.375 lineto
0.75 0 moveto 0.8125 0.1875 lineto
0.8125 0.1875 moveto 0.9375 0.4375 lineto
0.9375 0.4375 moveto 1 0.5 lineto
1 0.125 moveto 0.8125 0.1875 lineto
1 0.25 moveto 0.875 0.3125 lineto
1 0.375 moveto 0.9375 0.4375 lineto
0.75 0.5625 moveto 0.75 0.75 lineto
0.75 0.75 moveto 0.625 0.625 lineto
0.625 0.625 moveto 0.75 0.5625 lineto
0.8125 0.5625 moveto 0.9375 0.5 lineto
0.9375 0.5 moveto 0.9375 0.6875 lineto
0.9375 0.6875 moveto 0.8125 0.5625 lineto
stroke
grestore
} def

%  rot rotates an image by th radians anti-clockwise, about the image centre.
/rotcode {gsave 0.5 0.5 translate rotate -0.5 -0.5 translate exec grestore} def

/rot { /rotcode cvx 3 array astore cvx } def

%  zoom scales an image up or down with one fixed point.
/zoomcode {
gsave 2 copy neg exch neg exch 5 2 roll translate dup scale translate exec grestore
} def
/zoom { /zoomcode cvx 5 array astore cvx} def

/setup {72 8 mul dup scale .25 8 div dup translate .001 setlinewidth} def

%  display a level 2 fish

% letter % ??
setup
2 fish
showpage
```