Date: Tue, 6 Jan 1998 13:20:34 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: Anthony DOT Appleyard AT umist DOT ac DOT uk
cc: DJGPP AT delorie DOT com
Subject: Re: Getting the fastest running
In-Reply-To: <1B174837C8E@fs2.mt.umist.ac.uk>
Message-ID: <Pine.SUN.3.91.980106131545.2550C-100000@is>
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On Tue, 6 Jan 1998, Anthony.Appleyard wrote:

> keep flashing in and out of view. How can I tell the PC's graphics card not to
> redisplay the screen while I am writing a display to it?

I don't think you can.  The video circuitry is scanning the video ram 
dedicated to the currently-displayed page at its own rate and displays 
whatever it finds there.  The only ways of preventing it which are known 
to me are (1) to prepare the display on a different page, then flip pages 
when it is ready; or (2) turn off the screen while you update it.  The 
second way will probably cause worse flickering than writing directly to 
the screen without waiting.

Another technique is to wait for the retrace time (when the CRT beam 
moves from the lower-right corner to the upper-left, for the next scan) 
and only update them, since at that time, the display is automatically 
turned off.