From:	Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Callbacks
Date:	Sun, 8 Jun 1997 18:12:23 +0100
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Distribution:	world
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To:	djgpp AT delorie DOT com
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Goretec3 writes:
>I was looing through the Allegro code to maye learn something and, as I
>looked through the mouse section, I saw a funciotn that installs a
>callback. What is a callback? 

Just what the name implies: it's a function of your own which you
specify to be called by some other routine. Callbacks are used quite
often in the Allegro API, for example when you use the timer routines
you pass a function to install_int(), which is then called at regular
intervals by the timer interrupt.

In the case of the mouse code, I pass a callback function to the DOS int
0x33 mouse driver, telling it to call this routine every time the mouse
moves (so I can update the mouse position variables, redraw the pointer,
etc). It's complicated by the fact that the DOS driver runs in real
mode, so I have to construct a wrapper around the function that will
handle the switch into protected mode before running my code...


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
Beauty is a French phonetic corruption of a short cloth neck ornament.

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