Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!saxony!dgil
From: dgil@pa.reuter.COM (Dave Gillett)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: CGA Memory Locations
Message-ID: <393@saxony.pa.reuter.COM>
Date: 6 Sep 90 21:21:34 GMT
References: <29496@nigel.ee.udel.edu>
Organization: Reuter:file Inc  (A Reuter Company) Palo Alto, CA
Lines: 24

In <29496@nigel.ee.udel.edu> boutell@freezer.it.udel.edu (Tom Boutell) writes:

>Where does the CGA medium- resolution graphics screen start in memory on
>PC compatibles? I'll have a glorious time figuring out the mapping of
>it for myself, but if you know that information also I'd appreciate it.

>(I'm working on some high- performance graphics code to go around the
>speed limitations of the getimage/ putimage functions provided with
>Quick C. I expect having a copy of each image at each possible bit
>shift position and strncpy'ing them into place should do nicely.)

It starts at the same place all of the memory on the CGA starts: B800:0000.
Note, however, that that's where the first line starts.  The second line
starts at B800:2000, the third at B800:0050, the fourth at B800:2050, and
so on.

So strncpy'ing the whole buffer is easy, but grabbing a little piec of it
is harder.  I'm also not sure what you mean by bit shift positions, unless
you know that your strncpy is allowed to blot out a few pixels to left and
right...

If you're trying to do graphics stuff on the PC, you need a copy of Wilton's
"Programmer's Guide to PC and PS/2 Video Systems", from Microsoft Press.
                                       Dave