From: Shawn Hargreaves <shawn AT talula DOT demon DOT co DOT uk>
To: djgpp AT delorie DOT com
MMDF-Warning:  Parse error in original version of preceding line at relay-11.mail.demon.net
Subject: Re: Measuring frame rate more often
Date: Wed, 23 Apr 1997 18:17:35 +0100
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Ian D Romanick writes:
> This is *NOT* the right way to do this.  The right way uses a single
> timer interrupt going at whatever your target rate is.  Just update your
> position values during the interrupt.  You will need to be careful to
> make sure that the position values don't get modified while you're using
> them.

I used to use that technique all the time, but have recently gone off it 
because of the hassles with unexpected modifications, and also because
running large chunks of code inside a timer interrupt handler results
in you having to lock large amounts of memory, which is a huge pain.

IMHO a better technique is to just have the timer interrupt increment
a global variable, and then have a main control loop along the lines of:

    timer_variable = 0;

    while (!game_over) {
        while (timer_variable > 0) {
            move_all_objects(); 
            timer_variable--;
        }

        redraw_display();
    }

That handles changing frame rates, avoids all problems with reentrancy,
and means there's only one little increment going on inside the
interrupt...


--
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"