From: nitehawk91 AT aol DOT com (NiteHawk91)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: What's ModeX?
Date: 4 May 1997 12:00:42 GMT
Organization: AOL Bertelsmann Online GmbH & Co. KG http://www.germany.aol.com
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To: djgpp AT delorie DOT com
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Hi,

>Gautam N. Lad wrote:
>> 
>> Hi,
>> 
>> What's ModeX?  Is it the SVGA modes (i.e. 640x480x256,
800x600x65536,etc.)?
>> 
>> Thanks!
>> Bye!

Well, ModeX is a ceartain VGA mode. Possible resolutions are 320x200 &
320x400.
What's good about ModeX is, that you have 4 screen pages(2 if you use
320x400) -
e.g. if you want to move a sprite along the screen. While the sprite is
displayed you can calcluate the next movement on page 2 and then during
the vertical retrace just flip the pages. This is neccessary to avoid
flickering(or worse things), as lots of graphic calculations can't be done
in the short period of a retrace.
This can't be done e.g. in mode 13h, because there one screen page is
already 64kb big (= the whole viedo memory 0a0000h-0affffh) and so the cpu
cannot access the 2nd screen page.
And its even faster (ca. 10%) as mode 13h, cause when copying an screen
page, there are copyed 4 pixels at once, and you can use fast ReadMode 0
and WriteMode 1 which don't use address calulations nor sticking data into
the cpu.
That makes it so cool ;-)
ModeX is widely used in Demos for example...

Bye,
Matthias
<NiteHawk91 AT aol DOT com>

*Artificial intelligence is better than natural stupidity