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From: sara@mcvax.cwi.nl (SARA)
Newsgroups: comp.sys.mac
Subject: Re: Animated watch cursor.
Message-ID: <1500@mcvax.cwi.nl>
Date: Wed, 4-Feb-87 16:31:38 EST
Article-I.D.: mcvax.1500
Posted: Wed Feb  4 16:31:38 1987
Date-Received: Sat, 7-Feb-87 14:57:48 EST
References: <7488@decwrl.DEC.COM> <603@runx.OZ> <607@runx.OZ> <176@trwspf.UUCP> <881@aecom.UUCP>
Organization: CWI, Amsterdam
Lines: 58
Summary: How animated watch cursors are really implemented..



I have written (and posted) the very first running watch
for Macintosh (back in 1985) so I'll explain how I did it...

Implementing an animated cursor using some predefined
cursors and doing a setcursor of these cursors will only
work for certain cursor shapes like wheels etc, but NOT
for a watch cursor that has both hands running. That
would require a huge number of cursors...

Now, to make the hands running you could just use QuickDraw
for drawing the hands in a small bitmap, the Cursor data.
Performing a SetCursor will display   the cursor with the
updated hands. This way an application can make the hands
of a cursor spin. So, here no vertical retrace tasks are
used here. This only works WITHIN an application, the
application itself must periodically update the cursor.
(This was implemented in my TeX Preview program, and
before that in a tiny demo program that did nothing but
displaying 'Wait' in the Menu Bar and animating the cursor.)
Now Servant and the new Finder use this method.

To make the hands spin over all applications you need to
do more. The only way to get control over the cursor when
another application is running is by using a vertical
retrace task, that is installed one way or the other.
A natural way to install a VR task is using an INIT that
installs this task at system startup.

However, Vertical retrace tasks are severely limited, for
example they cannot even use QuickDraw, as they are not
allowed to use any routine that (indirectly) uses the
memory manager. First of all the task must determine
whether the cursor IS a watch. If it IS it must periodically
update the hands to make them spin. The problem is to find
out how to do this without using QuickDraw   8-).

I have posted the lastest version of my Watch Installer
to the moderator of mod.mac.binaries. It installs an
INIT in the system that will animate the hands of the
watch cursor using the vertical retrace method.

Whether ot not you like to have an animated watch on the
screen is not only a matter of taste. It depends on the
speed of the rotating hands whether it really draws your
attention or not. The Finder doen't display a watch cursor
very often, and in most cases not very long either. Other
applications, like Kermit when down loading a file, display
watch cursors at great length. *I* happen to like gently
spinning hands, most people don't even notice it until
they are told the hands are spinning...

Rick Jansen
SARA, Amsterdam Universities

Bitnet: Rick@hasara5
UUCP: mcvax!rick@hasara5.bitnet