From:	"Tim B" <aeronaut AT palacenet DOT net DOT REMOVE>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Still frustrated with mouse problem (actually a blitting prob)
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Message-ID:	<6A5W3.270$Up1.2636@newsfeed.slurp.net>
Date:	Tue, 9 Nov 1999 21:29:40 -0600
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Okay, this is my second attempt at trying to find some help with this
problem.  I originally thought this was a problem with the mouse functions
but after doing some tests I discovered the mouse droppings were only a
symptom of the real problem which seems to be that images blitted from the
screen (video memory) on occasion become slightly corrupted.  That's why the
mouse appeared to create extra random pixels because the image under the
mouse was originally blitted from the screen.

There doesn't seem to be any problem when blitting to the screen and the
problem only seems to happen in the svga modes.  In particular, if the image
is blitted from a horizontal screen position that can be divided by 4 and
any vertical position, the image is transferred accurately.  However, if
blitted from any other horizontal position the image sometimes becomes
corrupted.

The computer I'm currently using has a pc100 motherboard with a built in 3D
AGP graphics adapter and a vesa compliant video bios.  I've done the same
tests with the program on my 486/66 which has a Trident 8900 and there is no
problem.  Blits can be done anywhere from the screen with no corruption
which is of course what would be expected.

I also originally thought this might be due to a buggy vesa bios but I don't
seem to have this problem with other non-djgpp graphics programs I've used.
This includes an extended dos program created with dos/4gw.  So I'm
beginning to think maybe this is a problem with DJGPP (I'm using v2.01).

It seems questions are always encouraged, but it's pointless advice if
they're never answered.  So I'm asking again.  Please, if anyone has ever
come across this kind of thing or can suggest any possibilities for dealing
with it.  Is the problem in my graphics adapter?  Is it in DJGPP?  Is there
a patch for it?  Is it something I can fix myself?

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