Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!att!poseidon!ech
From: ech@poseidon.ATT.COM (Edward C Horvath)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Multifinder: how do I patch GetNextEvent?
Message-ID: <529@poseidon.ATT.COM>
Date: 14 Oct 88 16:21:41 GMT
References: <749@ttrdf.UUCP>
Organization: AT&T Bell Laboratories, Lincroft, NJ
Lines: 31

In article <10050022@eecs.nwu.edu> bob@eecs.nwu.edu (Bob Hablutzel) writes:
!   What is the proper way to patch the GetNextEvent() trap for
! compatibility with MultiFinder?...

In article <2453@spray.CalComp.COM>, anson@spray.CalComp.COM (Ed Anson) says:
! The problem here is that you have written a "tail patch"...
! forbidding a very useful type of patch? 

From article <749@ttrdf.UUCP>, by fjo@ttrdf.UUCP (Frank Owen ):
! ...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.
!   I have changed my INIT so that now it no longer patches GetNextEvent,
! but rather "inserts" code to be executed just before the jGNEfilter
! routine. The address of my code is inserted into the low-memory
! global, and when I'm done mangling the EventRecord, my routine jumps to 
! the address that had been there prior to my patch. simple. And it works.

!   I think tech-note #85 spells out all the rules for this. I don't have
! that particuliar note, but if anyone on the net does, I'd appreciatte it
! if you'd send me a copy. I'd like to abide by the rules if at all possible.

You've got it exactly right, Frank: the only detail is to make sure you set
the Boolean result at 4(sp) to TRUE if you replace a null event with one you
created (or to FALSE if you "eat" a non-null event that would otherwise
be returned).

I'll send a copy of TN 85 in the BTL mail; look for it around Christmas...

=Ned Horvath=