Date: Thu, 15 May 1997 03:12:24 -0400 (EDT)
From: Pierre Phaneuf <pp AT 55-174 DOT hy DOT cgocable DOT ca>
Reply-To: pierre AT tycho DOT com
To: OpenDOS Mailing List <opendos AT delorie DOT com>
Subject: Re: OpenDOS graphics drivers
In-Reply-To: <199705150046.KAA23687@solwarra.gbrmpa.gov.au>
Message-ID: <Pine.LNX.3.95.970515025828.6880A-100000@55-174.hy.cgocable.ca>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk

On Thu, 15 May 1997, Leath Muller wrote:

> Ok, first off, if 32 bit isn't that much of an increase, why aren't we
> all still using 16 bit? :)  I just don't think there is any argument
> between the advantages/speed etc of 32bit and 16 bit... As for NT, a

Simply because it's easier to have a single 256KB chunk of memory to work
with, than working with four 64KB chunks to have a 640x480 frame buffer!
The cool thing about 32-bit protected mode is that you get all the memory
you need. This doesn't make it *twice* as fast! It makes it *efficient*,
which sometimes is smaller code (doesn't have to juggle small segments)...

> program run by a normal user (not the administrator) can update its
> priority to real time;  it uses a hack though... Its basically a program
> dependent thing which I have seen running, I just have no idea how to do
> it... :)  (Basically, the game sets itself to real-time priority, and
> then sets itself back to normal priority if alt-tab/alt-enter etc is
> hit) 

One of the thing I hate *MOST* about DOS and especially Microsoft in
general is the amount of "abnormal" things they do or you have to do to
achieve "normal" stuff! A "normal" app under NT doesn't have the right to
upgrade its priority, period.

> Wouldn't it be great though if OpenDOS had access to all the features of
> hardware acceleration? I have written tests to check on the speed of
> DirectX blits from a backbuffer and software blits under DOS (even using
> the FPU load/store method) and windows still outperformed DOS... Now if
> I could use the hardware acceleration of my card in DOS, I'm sure it
> would outperform the windows stuff, but remember, a 640x480x32
> framebuffer is 1,228,800 bytes;  at 30FPS thats 36Mb to transfer - if
> you have hardware accleration moving that around for you, thats a lot of
> spare time for the CPU - more than the overhead of scheduling and task
> switching (if the game is the only thing running) 

OpenDOS has *full* access to hardware acceleration. It just isn't used.
It's not because you don't know how to use the chip on your video card and
DirectX programmers (those who made the drivers) does that DOS is crappy!
And when was the last game you saw running at 640x480 in 32 bit color
depth, all this at 30FPS? DOS Quake with accelerated hardware (yep, it
DOES use accelerated hardware!) will do about 36FPS with 3dfx chipset at
640x480x16. WinQuake runs the low 20's.

In action video games, *ANY* overhead is too much overhead. You break the
cache pipeline. You f**kup your prefetch. You lose CLOCK CYCLES. You know
John Carmack has created over 20 diffenrent rendering engines for Quake
during its development? You wouldn't believe what saving a friggin' clock
cycle in an inner loop can give you in gameplay!

Pierre Phaneuf

"The use of COBOL cripples the mind; its teaching should, therefore, be
regarded as a criminal offense."
 - Edsger W. Dijkstra (Selected Writings on Computing)