Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!mit-eddie!uw-beaver!tektronix!decvax!spray!anson
From: anson@spray.CalComp.COM (Ed Anson)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Multifinder: how do I patch GetNextEvent?
Message-ID: <2459@spray.CalComp.COM>
Date: 14 Oct 88 14:17:00 GMT
References: <2453@spray.CalComp.COM> <749@ttrdf.UUCP>
Reply-To: anson@spray.UUCP (Ed Anson)
Organization: CalComp, A Lockheed Company, Hudson, NH, USA
Lines: 21

In article <749@ttrdf.UUCP> fjo@ttrdf.UUCP (Frank Owen ) writes:
>
>  Apple is not leaving us without a workaround however. There is this
>low-memory global called "jGNEfilter" which points to a filter routine
>that GNE will jump to prior to returning. When GNE jumps to this address,
>register A1 contains a pointer to the EventRecord.

Yes, there is the GNE filter. Yes, TN #85 says how to use it. But NO, Apple
also warns that modifying low-memory globals is dangerous. Even looking at
them is officially discouraged, but permitted "if really necessary".

Another alternative to a tail patch of GNE, is a (permitted) patch of
SystemEvent, which is called by both GNE and WNE after other processing is
completed. I have tried this, and it works well. I can find no reason for
any future compatibility problems. Or is it dangerous to rely on the fact
that this trap gets called under these circumstances, even though it is
documented by Inside Macintosh? :-|
-- 
=====================================================================
   Ed Anson,    Calcomp Display Products Division,    Hudson NH 03051
   (603) 885-8712,      anson@elrond.CalComp.COM