Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!well!wdh
From: wdh@well.sf.ca.us (Bill Hofmann)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How's the screen cleaned after _SysError?
Summary: set up DsAlertRect, BCLR #7,DsWndUpdate
Keywords: Hacks, The Debugger
Message-ID: <16461@well.sf.ca.us>
Date: 1 Mar 90 19:04:37 GMT
References: <34252@news.Think.COM>
Reply-To: wdh@well.UUCP (Bill Hofmann)
Organization: Flashpoint
Lines: 35

In article <34252@news.Think.COM> ephraim@Think.COM (Ephraim Vishniac) writes:
>How is the screen restored after a call to _SysError?
>
>The reason I'm asking about this is that I'd like to be able to display an
>alert at just about any time (much like the disk-swap alert, and for
>similar reasons) and then clean up nicely.  Right now, I'm waiting for the
>next call to _GetOSEvent and using _PaintBehind to get the alert rect
>redrawn.  This works, but it's not as smooth as whatever the disk-swap code
>does.
The Debugger is much handier for obscure trivia like this.  Its listing for
DSWndUpdate is "GetNextEvent not to paintBehind DS AlertRect", and looking
at the code for EventAvail and GetNextEvent, it does something like this:
	BSET	#7,DsWndUpdate
	BNE.S	out
	...GetPort(curPort) SetPort(WMgrPort)
	SUBQ	#4,a7
	_FrontWindow
	SUBQ	#4,a7
	_NewRgn
	MOVEA.L	(a7),a3
	PEA	DsAlertRect	; $3f8
	PUSH.L	a3
	_PaintBehind
	PUSH.L	a3
	_DisposRgn
	...SetPort(curPort)
So to force a cleanup, just BCLR #7,DsWndUpdate, being sure DsAlertRect
is properly set up.

But how about using the Notification Manager?  That'll let you put up an
alert in front of everything, in a much less hackish way.

-Bill Hofmann

PS: How're things?