Message-ID: <F77915E7F086D31197F4009027CC81C90DB7D9@probe-2.as-london.acclaim.com>
From: Shawn Hargreaves <SHargreaves AT acclaimstudios DOT co DOT uk>
To: djgpp AT delorie DOT com
Subject: Re: fprintf() and using under graphic modes
Date: Tue, 23 Nov 1999 14:36:19 -0000
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Reply-To: djgpp AT delorie DOT com

Chaos writes:
>> VESA is buggy. Allegro successfully works around the bugs.
>
> ???
> What you meen? My philosophy is that: If Allegro can do it 
> I can do it too.

Of course. But the trouble with writing VESA code is that many
(probably most) VESA drivers are extremely buggy, so no matter
how well you write your code, it will still fail on some machines
due to things that are outside your control. It would be nice if
we could get away with this, but in the real world when your
program crashes, most users will blame you for it, so it is nice
if you can try to work around some of the more common driver bugs.

Allegro certainly isn't perfect in this respect: if a driver is
truly broken, there isn't anything you can do about that. But it
has been through several years of intensive testing and tweaking
to make it work on many different setups, which is hard to
duplicate yourself unless you have a huge test lab (I couldn't
have done it all myself either, but many people have debugged
various parts of the code on different machines, and found fixes
for specific problems that were affecting them). Writing your
own code is very likely to produce more compact results, and
you should easily be able to make your code 'correct', but it
is unlikely that you can replicate all the obscure tweaking that
has subsequently gone into the Allegro routines...

>>> 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.
>
>> They don't work on all cards.
>
> Why?

Because not all VESA drivers bother to provide any text output
functions. And this isn't actually a bug: the spec says that they
are allowed not to do this. So if you want your program to work
reliably on all machines, you cannot use printf() type functions
in VESA graphics modes, and must write your own text plotting code
instead. Store your own font graphics as part of the code, and
draw them to the screen as a series of pixels in the same way as
for any other graphics: that's not hard to do, and far safer than
just hoping the BIOS will do this for you.


	Shawn Hargreaves.