Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!mtunx!whuts!homxb!ho7cad!wjc
From: wjc@ho5cad (Bill Carpenter)
Newsgroups: comp.sys.att
Subject: Re: UNIX PC Graphics Questions
Message-ID: <328@ho7cad.ATT.COM>
Date: 11 May 88 14:20:28 GMT
References: <2271@inco.UUCP>
Sender: nuucp@ho7cad.ATT.COM
Reply-To: wjc@ho5cad (Bill Carpenter)
Organization: AT&T Bell Laboratories
Lines: 25
In-reply-to: todd@inco.UUCP (Todd O'Connell)

In article <2271@inco.UUCP>, todd@inco (Todd O'Connell) writes:
>2) Is there any way to directly access screen memory?  I would like to
>   bring up a segmented graphics package on my 7300 but find it a little
>   abhorrent to do pixrect ops to display a single pixel in a vector draw
>   routine.  I would use the graphics driver except that I also want to
>   do some raster work and I don't want to waste 16 bits/pixel for a b/w
>   display.

The screen memory on the UnixPC is a whole different set of chips from
regular old program memory.  To  access it, you'd  have to  get  right
down there to the hardware, and Unix won't let you do that except in a
privileged kernel mode.  If  you  were especially  clever,   you could
write a  device driver  for a device that  fiddled with  screen memory
directly.  But, when I say clever, I mean with a capital C.  Also, you
wouldn't be  that far  ahead,  since you would  still  have  to make a
system  call (which  is  what you're  already  doing).  Good chance of
clobbering the rest of the system as well.

BTW, if you do  write that kind of device  driver  (or find some other
way of writing to  an arbitrary  spot on the  screen without regard to
the window  boundaries, etc),  I'd give you at  least a  nickel  for a
copy.
--
	Bill Carpenter
	(AT&T gateways)!ho5cad!wjc