Message-ID: <37CC1600.E9ABA4A0@cyberoptics.com>
From: Eric Rudd <rudd AT cyberoptics DOT com>
Organization: CyberOptics
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Newsgroups: comp.os.msdos.djgpp
Subject: Re: Nearptr putpixel method?
References: <199908242311 DOT TAA09745 AT delorie DOT com> <7q0kfa$rot$1 AT news DOT adamastor DOT ac DOT za> <7q19jj$ajq$1 AT news DOT adamastor DOT ac DOT za> <7qcucs$78c$1 AT solomon DOT cs DOT rose-hulman DOT edu> <37cb760e DOT 9341261 AT newsserver DOT cc DOT monash DOT edu DOT au>
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Date: Tue, 31 Aug 1999 12:50:56 -0500
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Davin McCall wrote:

> >It brings with it general
> >protection faults, page faults, and other things that, if you use nearptr,
> >are your fault, up to and including data loss.
>
> I successfully used the nearptr "hack" when writing a game last year.
> Most programming erros (access violations etc) were still caught, and I
> certainly didn't suffer any data loss.

If one is using a linear frame buffer (usually located high in 32-bit memory
space), one other option is to write a modified __djgpp_nearptr_enable() that
opens the segment limit just wide enough to include the video card address.
This at least prevents a stray pointer from wrapping and accessing DOS memory.
Thus, a buggy program may crash, but at least it's unlikely to bring down DOS.
I have been using this technique for several years now (both under DOS and
under Win95), and have yet to have a problem with it.

I haven't had any success in using this under NT, and I am curious if anyone
else has managed to write directly to video memory under NT.

-Eric Rudd
rudd AT cyberoptics DOT com