Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!math.lsa.umich.edu!sharkey!itivax!dhw
From: dhw@itivax.iti.org (David H. West)
Newsgroups: comp.sys.ibm.pc
Subject: MSDOS's recognition (?) of screen modes
Message-ID: <4703@itivax.iti.org>
Date: 28 Dec 89 23:02:17 GMT
Organization: The Forgotten Legions of ... um ... er ...
Lines: 37


 
A while ago, someone asked what he called a "weird question" -
does MSDOS have or recognise "a graphics mode".  The posted answers
were inconclusive.  

I used to think that this was quite straightforward: every display
adaptor has 1 or more text modes and 0 or more graphics modes, and
MSDOS itself (i.e. excluding utilities such as ansi.sys and 
graphics.com) concerns itself with this only to the extent that 
command.com wants (forces?) the screen to be in text mode when 
prompting for input.

Well, I've just discovered the inadequacy of this model.  I'm using
an Everex Viewpoint VGA, which comes with a utility to set its
modes.  Normally I keep it set to a high-resolution (9 x 14 cell)
text mode, but I find that some graphics programs, which claim to
work with VGA or EGA, will not set an appropriate mode with this
card (instead they hang - why?), but will work if an appropriate mode is
set before they are invoked.

The part I don't understand is as follows: I invoke the utility to
set the card into, say, EGA graphics mode - I think the mode number
is 16, but the manual is at home.  I then get a DOS prompt in a
different text font.  What is happening here - is command.com
temporarily returning the screen to (some other) text mode?  Or is
the card clever enough to know it needs to simulate text even though
it's "really" in a graphics mode?  Or does the card vendor's utility 
not actually set a specific graphics mode, but rather enable a
particular kind of emulation (even though I'm passing it a "mode 
number", specifying number of pixels and colors, as a parameter)?
And how does this square with the fact that if I set a "wrong"
graphics mode, I don't even get a DOS prompt afterwards?

-David West

"You are in a maze of twisty little graphics modes, all different".