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From: pts@faraday.clas.Virginia.EDU (Paul T. Shannon)
Newsgroups: comp.sys.next
Subject: postscript: returning values to my application
Message-ID: <1991Mar21.160137.13875@murdoch.acc.Virginia.EDU>
Date: 21 Mar 91 16:01:37 GMT
Sender: usenet@murdoch.acc.Virginia.EDU
Distribution: na
Organization: University of Virginia
Lines: 33

I sent this to the next programmers' mailing list, but it doesn't
seem to have been distributed -- it didn't come back to me as my messages
have before.  I apologize if you're seeing this for the second time.

I'm doing some very straightforward postscript programming, using single-
operator functions from Objective-C.  My problem comes when I need to 
return to a specific point on the screen (or page) after drawing a string.
The length of the string is only known at run-time.  

I've tried two techniques: 

     1.  calling PScurrentpoint (&x, &y) before drawing the string
     2.  calling PSstringwidth (string, &width, &height), so that I
         can then call PSrmoveto (-width, 0.0) after the string is 
         drawn.

Both of these work fine with Display PostScript.  However neither work
with a printer or with Preview.  The printer (an Apple LaserWriter) 
prints nothing; Preview gives this error message:

    The PostScript code of the document erroneously tried to 
    return values to the application...

So it seems that while it's no problem for DPS to tell my application
what it asks for (either current position or a string's width), it's
impossible for either the LaserWriter or Previewer to send this 
information back to me.  

Can someone suggest an approach that works in all 3 contexts, DPS,
Previewer, and a printer?  Thanks.

 - Paul Shannon
   pts@Virginia.EDU