Mail Archives: djgpp/1997/03/01/08:55:14

From: ao950 AT FreeNet DOT Carleton DOT CA (Paul Derbyshire)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Questions about Allegro
Date: 1 Mar 1997 05:05:28 GMT
Organization: The National Capital FreeNet
Lines: 44
Message-ID: <5f8deo$>
References: <01bc2460$9a92bee0$8c081ecb AT sly>
Reply-To: ao950 AT FreeNet DOT Carleton DOT CA (Paul Derbyshire)
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

"Sly" (sly AT aussie DOT net) writes:
> These are a few questions that I have concerning the Allegro library...
> 1. Why do the timer routines have to be installed in order to be able to
> see the mouse on SVGA resolutions?

I can answer this... it's because timer routines are used to interrupt
program flow periodically in order to restore what was under the cursor,
and redraw the pointer at an updated location. It was a choice between
either calling an install_timers once, or having to remember to call a
"redraw_pointer()" or something every time around any loops of your program.

> 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?

Windows 95 is like Bill Gates: it wants a monopoly, in this case over the
CPU timer. Complain to Bill, not Shawn or Roehne (sp?) :) 

> 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?
> 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?

I have 512K S3 superVGA card; however, anytime I tried to get a ModeX
screen with a virtual screen bigger than 262144 pixels all told,
set_gfx_mode has balked, so yes, ModeX seems to think you have only
regular non-super VGA and is ignorant of any video memory you have above 256k.
This made things hairy for a while for my pet project, but I got around it

    .*.  Where feelings are concerned, answers are rarely simple [GeneDeWeese]
 -()  <  When I go to the theater, I always go straight to the "bag and mix"
    `*'  bulk candy section...because variety is the spice of life... [me]
Paul Derbyshire ao950 AT freenet DOT carleton DOT ca,

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