From: "Tony O'Bryan" <aho450s AT nic DOT smsu DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Orbiting Spheres?
Date: Sat, 02 May 1998 17:10:43 +0000
Organization: Southwest Missouri State Universtiy
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References: <000401bd75d9$069ac040$cf4b08c3 AT arthur>
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Arthur wrote:

> Is there an easy way of patching the keyboard to register a number of
> different keys (say 6) being pressed at the same time? Of course there is,
> but how is it done?

With interrupts, of course. :)  The most reliable way is to intercept the
keyboard interrupt and keep track of which keys are down and which are not.
Allegro uses an efficient method of using an array to track the state of each
key.  When a key is pressed, set the corresponding byte in the array.  When the
key is released, clear the appropriate byte in the array.

Be aware that not all keyboards are created equal.  Keyboards have a tendency
to report only a few simultaneous keypresses, and the allowances vary among
keyboards.