From: Ian Chapman <ichapman AT nortel DOT ca>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Help: What causes screen flash problem in Allegro 2.0?
Date: Fri, 03 Jan 1997 10:19:10 -0400
Organization: Nortel Technology
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Message-ID: <32CD15ED.35CB@nortel.ca>
References: <32ccb401 DOT 3331475 AT news DOT diac DOT com>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Hi,
     not too sure what your code does.  Looks like you are changing
pages.  Also not at all sure how modern vga type controllers do their
stuff.  Any chance that you are re initilizing the controller or other
hardware?  Also if you change pages in an unSYNCHRONOUS way could that
also do it?  Some of the older controllers had a flag you could test ...
like err um
reset video_refresh_flag;
while(video_refresh_flag == FALSE)
{do (nothing);
}
then do your code.
> 
> void flip_page() {
>         if (active_page==page1) {
>                 scroll_screen(0,0);
>                 active_page=page2;
>                 inactive_page=page1;
>         }
>         else {
>                 scroll_screen(0,SCREEN_H);
>                 active_page=page1;
>                 inactive_page=page2;
>         }
> }