Path: utzoo!utgpu!watserv1!watmath!att!att!linac!uwm.edu!rpi!zaphod.mps.ohio-state.edu!samsung!olivea!apple!well!shiva
From: shiva@well.sf.ca.us (Kenneth Porter)
Newsgroups: comp.lang.postscript
Subject: Re: A question about //add
Summary: Nesting systemdict replacements
Message-ID: <21858@well.sf.ca.us>
Date: 29 Nov 90 05:55:40 GMT
References: <1990Nov12.195235.13908@light.uucp> <321@heaven.woodside.ca.us> <3294@exodus.Eng.Sun.COM>
Lines: 123



flar@bendenweyr.Eng.Sun.COM (Jim Graham) writes:
 
> A robust method for performing this overriding behaviour would be the
> following (assuming you are writing a package referred to as "AA"):
> 
> /preAAshowpage	/showpage load def
> 
> /showpage {stuff preAAshowpage morestuff} bind def
> 
> If showpage were an operator prior to this code, then bind would
> still bind the operator into the procedure (in which case
> "/preAAshowpage" would be wasted").  If it were not an operator,
> then the new showpage procedure would still execute correctly.
 
This doesn't work if you nest the same file twice and the original
showpage has been redefined before:
 
% (in exit-server job)
/showpage {{sysop stuff} original-showpage} def
 
% (in user job)
/preAAshowpage	/showpage load def
/showpage {stuff preAAshowpage morestuff} bind def
/preAAshowpage	/showpage load def
/showpage {stuff preAAshowpage morestuff} bind def
 
The new showpage is now recursive:
 
{stuff {stuff ... preAAshowpage ... morestuff} morestuff}
 
Here's an nup script that illustrates a case where nesting is
necessary:
 
------------------------------nup.sh------------------------------
#!/bin/csh -f
# change following line to point to correct path for next file
set twoup=/home/ken/psfonts/ps/twoup.ps
set n=$argv[1]
set logn=0
while ($n > 1)
	@ logn++
	@ n /= 2
end
echo logn = $logn
cp /dev/null /tmp/nup.$$
while ($logn > 0)
	cat $twoup >> /tmp/nup.$$
	@ logn--
end
foreach i ($argv[2-])
	echo $i
	cat /tmp/nup.$$ $i | lpr
end
----------------------------twoup.ps----------------------------
%!  Two-up filter
% Redefine showpage to collect two pages per page.
% Make showpage a procedure if it's an operator.
% This allows us to use // unconditionally to replace
% showpage below with "//showpage exec".
 
/showpage load type /operatortype eq { /showpage { //showpage } bind def } if
 
% Support routines in private dictionary
 
/twoupdict 6 dict def
 
twoupdict begin
 
/inch { 72 mul } bind def
 
/rightpage false def		% doing right half of page
 
/twoupscale 5.5 8.5 div def
 
/offset				% fudge factor to center on half page
  11 4 div			% half page width
  8.5 twoupscale mul 2 div	% half scaled page width
  sub inch
def
 
/setup {			% This does the real work
  grestore
% matrix currentmatrix == flush	% observe previous transform for debugging
  gsave				% restore initial coords
  90 rotate
  -8.25 inch translate		% this eats argument
  offset 0 translate
  twoupscale dup scale
  0 0 moveto 8.5 inch 0 lineto 8.5 inch 11 inch lineto
  0 11 inch lineto closepath clip newpath
} bind def
 
/dofile {			% init and cleanup code
  gsave
  //twoupdict begin 0 setup end
  % this is how to do an end-of-file handler
  currentfile cvx exec		% process client file
  % issue paper for last page if necessary
  //twoupdict begin rightpage { //showpage exec } if end
} bind def
 
end				% close dictionary before running
 
% new two-up showpage
 
/showpage {
  //twoupdict begin
    /rightpage
      rightpage dup
      { grestore //showpage exec gsave 0 setup } { 5.5 inch setup } ifelse
    not def
  end
} def
 
twoupdict /dofile get exec
----------------------------------------------------------------
 
Ken (shiva@well.sf.ca.us)

P.S. Mention my name and email address when you distribute this --
my ego needs it :-)