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From: ari@eleazar.dartmouth.edu (Ari Halberstadt)
Newsgroups: comp.sys.mac.programmer
Subject: How do I write a screen saver?
Message-ID: <1991Jan11.013203.13763@dartvax.dartmouth.edu>
Date: 11 Jan 91 01:32:03 GMT
References: <13650002@hpspdra.HP.COM>
Sender: news@dartvax.dartmouth.edu (The News Manager)
Organization: Dartmouth College, Hanover, NH
Lines: 46

I know the basic idea of a screen saver: if nothing's happened for X
minutes, then blank the screen (gee whiz). I've written an application
which will blacken the entire screen (or screens), and wait till
there's a click or some other user event. I've even written a patch to
GetNextEvent which, for lack of anything better to do, beeped if
nothing had happened for several minutes. What I need is a screen
saver which will work both in Finder and in MultiFinder. It can be an
INIT, like AutoIdle.

I have several questions:

If I write it as an INIT, like AutoIdle, and patch GetNextEvent, then
I need some way to blacken the screen. AutoIdle seems to patch
InitGraf as well, so that it can find out if it's been called. If
InitGraf hasn't been called, then I guess AutoIdle calls it. To
blacken the screen, all I'd have to do is create a port and paint it
black. The problem is, how do I tell the application to redraw its
windows when it's time to unblacken the screen? Also, I'm not sure
that I can always create a graf port if InitGraf isn't called by the
application.

Under MultiFinder, assuming I wrote a background program, how do I
examine the event queues of all of the applications? And, how do I
force a background application's window to be the frontmost window
when it's time to blacken the screen? One technique, employed by a
shareware utility, is to launch another application as a foreground
application which will blacken the screen.

How do I make sure all of this works under A/UX 2.0? (This requirement
isn't that critical, but it's always nice to be compatible.) I
understand A/UX doesn't have the same type of event queue that regular
macs have.

Thanks folks. If I get enough replies, maybe I'll post a summary.

------- cut here if you think tail patches are good for your digestion ------

The following comment has had bloody battles fought over it, but since
I'm talking about patching GetNextEvent, I sort of feel it's my duty
to state this.

NOTICE MAC PROGRAMMERS: Tail patches are bad. Inside Macintosh says
you shouldn't do them (lookup SetTrapAddress). Please don't start a
flame war, it's just that I still see source code with tail patches in
it. Someday I'll post an assembly language and C stub showing how to
write friendly patches.