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Mail Archives: djgpp/1999/11/22/05:21:51

From: "Kalum Somaratna aka Grendel" <kalum AT newmail DOT net>
To: djgpp AT delorie DOT com
Date: Mon, 22 Nov 1999 14:56:54 +0600
MIME-Version: 1.0
Subject: Re: fprintf() and using under graphic modes
In-reply-to: <8195o6$qfc$1@portraits.wsisiz.edu.pl>
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On 21 Nov 99, at 17:12, Chaos wrote:

> My philosophy is that: If Allegro can do it I can do it too.
> BTW. I'm treating that game as learning in programming C and Asm using
> various algorithms.

Way to go Chaos! It's nice to see someone trying to learn by 
experimenting instead of relying blindly on high level library API's.

Sure, Allegro is a great library (my favourite) but one must not 
depend on library's without having a understanding of what they do. 
for ex;- If you have a understanding about various algorithm's for 
texture mapping ...etc you can think of other faster, innovative 
ways of doing it....(and maybe write a new 3D rendering engine 
which will get you lot's of $$$) . 

>>None of VESA works when compiling for M$ Windows 

If the video card supports VESA then you shouldn't have any 
problems acessing it under Win95/98. AFAIK NT doesn't allow  
direct access so this might not be possible under NT. 

Some card's have buggy VESA implementations however this can 
be corrected by installing SciTech Software's Display Doctor.
The great game Quake v1.00 uses VESA 2.0 for video acess.

>Now i'm wondering if I can do it safelly. Can I stick with printing >text messages such as timer or player name using only printf->family functions. Are there any limitations in using those functio
ns >in graphics modes?

AFAIK printf is dependent on the BIOS to print the strings. So the 
BIOS must be able to acess the video memory you are using for 
your graphics at the same time (it must understand the graphics 
mode).

In my video card the bios writes to 0xA000 segment for printf call's. 
So when you use bank switching printf will work (the BIOS writes 
text to 0xA000 and the video card also uses 0xa000 for the 
screen). 

However if you are using the Linear frame buffer mode the buffer 
may be located somewhere around 128MB so the video card will 
be using the 128MB location for the screen. So when you use printf 
my BIOS will still be writing text to 0xa000 and there will be no text 
output on the screen because my video card in LFB mode ignores 
what is written to 0xa000 (because it reads the LFB located at 
128MB).

Regards,
Kalum

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