Xref: utzoo comp.graphics:9912 comp.sys.ibm.pc:44279
Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!nsc!pyramid!infmx!lorena
From: lorena@infmx.UUCP (Lon Anderson)
Newsgroups: comp.graphics,comp.sys.ibm.pc
Subject: Re: VGA - direct memory access question
Message-ID: <3351@infmx.UUCP>
Date: 12 Feb 90 17:06:55 GMT
References: <90039.091705IAP@PSUVM.BITNET>
Reply-To: lorena@infmx.UUCP (Lon Anderson)
Organization: Informix, Menlo Park, Ca. U.S.A.
Lines: 11


The VGA adapter uses a concept knows as memory planes.  These memory
planes map th the same location in memory and hold the "other" bits
associated with a pixel in the color modes.  You need to toggle the
planes on and off to read the individual bits that make up the 4 bits
of the pixel.  This is done by manipulating the VGA registers.

The code to do this is available in a number of books on VGA
programming.  Two I would recomend are Programmers guide to the EGA
and VGA and Programming the VGA adapter by Brady.  These are available
at most good computer book stores.