Newsgroups: comp.windows.ms
Path: utzoo!utgpu!watserv1!sunee!gpsteffl
From: gpsteffl@sunee.waterloo.edu (Glenn Patrick Steffler)
Subject: Re: Video wrap-around at 800x600x256
Message-ID: <1991Mar12.175630.25051@sunee.waterloo.edu>
Organization: Gold Disk Inc.
References: <1991Mar8.154238.28637@cbnews.att.com>
Date: Tue, 12 Mar 1991 17:56:30 GMT
Lines: 33

In article <1991Mar8.154238.28637@cbnews.att.com> shurr@cbnews.cb.att.com (larry.a.shurr) writes:
>[video "wraps" around the screen such that some stuff appears on both
 top and bottom, etc]

I would guess the problem lies in the video driver which deals with the 
video 800x600x256 mode uses a technique commonly seem on windows graphics
drivers:

The drivers configure the card to display only 800 bits wide, meanwhile, the
memory is composed of lines which are 1024 bits wide.  Since this allows`
easy segment calculations (since the whole half megabyte must appear
within a 64k segment at 0A000) for the driver.  Otherwise, the segmetn
boundries for the driver could appear partways on a scanline, causing
the video driver to have to test for lots o' special cases, as opposed to 
one case, going vertically, and not having to wroy about the horizontal case 
at all.

Then again, I could just be blowing sunshine up yer butt.

>Can anyone help.  I will take email or postings and I will gladly summarize
>if others are interested.
>
>Larry
>-- 
>Larry A. Shurr (cbnmva!las@att.ATT.COM or att!cbnmva!las)
>The end of the world has been delayed due to a shortage of trumpet players.
>(The above reflects my opinions, not those of AGS or AT&T, but you knew that.)

-- 
Co-Op Scum                            "Bo doesn't know software" - George Brett

"The galaxial hearth steams the sea as the sky blood red embrasses darkness"
-John Constantine (HellBlazer)                          Glenn Steffler