Path: utzoo!attcan!uunet!wuarchive!brutus.cs.uiuc.edu!samsung!shadooby!mailrus!uflorida!gatech!utkcs2!cetus1a!mccaslan
From: mccaslan@cetus1a.cs.utk.edu (Donald McCasland)
Newsgroups: comp.sys.cbm
Subject: Re: Machine Language Smooth Scrolling Problem
Keywords: machine language, scrolling, C64, squid, gratification
Message-ID: <1274@utkcs2.cs.utk.edu>
Date: 29 Oct 89 13:10:45 GMT
References: <2317@jarthur.Claremont.EDU> <136@cbmtor.UUCP> <2823@husc6.harvard.edu> <1989Oct11.151724.18728@jarvis.csri.toronto.edu> <2911@husc6.harvard.edu>
Sender: news@utkcs2.cs.utk.edu
Reply-To: mccaslan@cetus1a.cs.utk.edu (Donald McCasland)
Organization: CS Dept -- University of TN, Knoxville
Lines: 34

>Regarding scrolling down.  This algorithm does it, starting from the top of
>the screen and working its way down: 
>
>1. Copy present character row into buffer B.
>2. Copy buffer A into present character row.
>3. Copy buffer B into buffer A.
>4. Go to next lower character row, if there is one; if not, end.
>5. Go to step 1.
>
>But the big question: is it fast enough to get to the bottom of the screen
>before the raster, released at the previous bottom edge, does?  I don't
>think so, after Marcel's analysis.  It should take about 3 times as long as
>Marcel's routine, or about 1/20 of a second.  Dang it, not fast enough!
>However, if it were possible to do this much computation in 1/60 of a
>second, and your normal down-scroll algorithm wasn't fast enough to beat
>the raster to the top of the screen, this one would do it.

Yes, I am an extremely unpracticed and unknowledgeable c64 user.
However, (this may seem stupid) has anyone thought of waiting for the
raster to be past the first 8 or so (far enough past so that the information
writing wouldn't catch up to the raster) character rows on the screen, and
then applying the aforementioned (I bet that's spelled wrong) buffering
algorithm.  In another words, what I'm trying to say is, would it be
possible to draw, smoothly, the screen while the raster is on another
part of the screen, rather than off the screen?

					Sincerely,
					Don McCasland
					The Priest at Nemi
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