Message-Id:	<m0x8uNS-0003COC@fwd09.btx.dtag.de>
Date:	Wed, 10 Sep 97 23:32 MET DST
To:	kovax AT cbhouse DOT fr, djgpp AT delorie DOT com
References:	<5v16bj$5cj AT snews3 DOT zippo DOT com>
Subject:	Re: Is it possible to make page flipping in VESA2 LINE MODE?
MIME-Version:	1.0
From:	Georg DOT Kolling AT t-online DOT de (Georg Kolling)

kovax AT cbhouse DOT fr schrieb:
> HI!
>
> i'm using allegro to make a spectacular game since about one year! 
> (a demo will out very soon...)
>
> I you like to use many graphic mode, and i've some problem with the VESA2L
>  mode...
>
> in fact does anybody know how to make page flipping in VESA2L.
>
since virtual height is only restricted by mem size in VESA modes, you can make
up two sub-BITMAPs of 'screen' eg at (0,0) and (0, physical_height).
write a function that swaps the two BITMAP pointers and sets up the correct
display start address via the scroll function of allegro. Swapping the pointers
makes you able to have one pointer always pointing to the visible screen and 
the other one pointing to the hidden page (where to draw).
Now you have to call this function every time you have completed one frame.
NOTE: Since it waits for a vertical retrace, it may waste a lot of time.

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