From:	pmonks AT iname DOT com (Peter Monks)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Questions about Allegro
Date:	Thu, 27 Feb 97 06:53:38 GMT
Organization:	Financial Market Software Consultants pty ltd
Lines:	54
Message-ID:	<5f3b1i$2gk_002@fmsc.com.au>
References:	<01bc2460$9a92bee0$8c081ecb AT sly>
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

In article <01bc2460$9a92bee0$8c081ecb AT sly>, "Sly" <sly AT aussie DOT net> wrote:

>1. Why do the timer routines have to be installed in order to be able to
>see the mouse on SVGA resolutions?

AFAIK, graphics operations can't be performed from within the mouse event 
callback.  Therefore Allegro merely updates some position variables in the 
callback, and then polls these variables and draws the cursor from within the 
timer interrupt.

I'm not 100% sure, but I think this is the reason why.  Someone please correct 
me if I'm mistaken.

>2.  What is happening when install_timer() is called, and Win95 complains
>about the program should be run in MS-DOS mode?  Cancel this requester and
>the program looks like it is running normally, and any subsequent execution
>of programs in that DOS box do not show this warning.  Is the program
>*really* running normally, or is something screwy going on in the
>background?

As of v2.2, when Allegro detects Windows it runs in a way that is more 
compatible.  Win95 will probably still complain (since it doesn't like 
programs mucking about with the timer interrupt at all), but nothing screwy 
should be happening.

The warning only appears the first time because Win95 recognises the program 
the subsequent times you run it, and doesn't bother asking again.  I think 
that if you recompile the program, Win95 will ask again (unless you save the 
option into a PIF file).

>3. I have read elsewhere that the timer should be reset to normal (ie. 18.2
>ticks/sec) before any disk access.  Is this still necessary?

Sorry, can't help you!  :-)   Anyone know the answer to this one?

>4. Are the various ModeX screen modes restricted to use the first 256k of
>video memory only?  Or do I have to use the VESA modes to access the rest
>of video memory?

Yes and yes.  Since ModeX only uses the standard VGA hardware (which can only 
access up to 256Kb of VRAM), only 256K of video memory is available.  UniVBE 
provides low resolution VESA modes which give you all available memory, with 
the disadvantage that other VESA manufacturers don't usually provide these 
modes.

Cheers,
Peter


----------------------------------------------------------------------
Peter Monks                    http://www.geocities.com/Yosemite/4455/
pmonks AT iname DOT com
pmo AT fmsc DOT com DOT au
Peter_Monks AT australia DOT notes DOT pw DOT com

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