Xref: utzoo comp.graphics:9861 comp.sys.ibm.pc:44104
Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!sdrc!scjones
From: scjones@sdrc.UUCP (Larry Jones)
Newsgroups: comp.graphics,comp.sys.ibm.pc
Subject: Re: VGA - direct memory access question
Message-ID: <1128@sdrc.UUCP>
Date: 9 Feb 90 22:14:13 GMT
References: <90039.091705IAP@PSUVM.BITNET>
Followup-To: comp.sys.ibm.pc
Organization: SDRC, Cincinnati
Lines: 26

In article <90039.091705IAP@PSUVM.BITNET>, IAP@psuvm.psu.edu (Kirk Hanawalt) writes:
>     I'm trying to write a program (TurboC 2.0, IBM PS/2 Model 50
> with VGA adapter, HP LaserJet II) to dump a bitmap image of the
> high resolution VGA screen to a LaserJet printer.  Using the
> TurboC getpixel function, the 640x480 graphics screen can be
> dumped in about 35 seconds.  I would like to access memory
> directly, and dispense with getpixel() altogether.
> Unfortunately, I can't figure out how the pixels are mapped in
> memory.

Both the EGA and VGA need more memory than there is room for in
the reserved address space.  To get around the problem, they have
a number of different mapping schemes which allow access to some
of the bits at a time.  Precisely which bits and where in memory
they are depends on the particular mapping scheme which has been
invoked.  I suggest you get a good book such as Programmer's
Guide to PC and PS/2 Video Systems (Microsoft Press, if I
remember correctly) and study it.  The mapping schemes are
incredibly complex.
----
Larry Jones                         UUCP: uunet!sdrc!scjones
SDRC                                      scjones@SDRC.UU.NET
2000 Eastman Dr.                    BIX:  ltl
Milford, OH  45150-2789             AT&T: (513) 576-2070
"You know how Einstein got bad grades as a kid?  Well MINE are even WORSE!"
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