Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!ginosko!uunet!jarthur!kfink
From: kfink@jarthur.Claremont.EDU (Kevin Fink)
Newsgroups: comp.sys.cbm
Subject: Machine Language Smooth Scrolling Problem
Keywords: machine language, scrolling, C64
Message-ID: <2317@jarthur.Claremont.EDU>
Date: 6 Oct 89 01:45:42 GMT
Reply-To: kfink@jarthur.claremont.edu (Kevin Fink)
Organization: Harvey Mudd College, Claremont, CA
Lines: 37



My brother is working on smooth scrolling in machine language on the
Commodore 64. I don't understand what he's doing, but he sent me this to
post.

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	I have a problem with the smooth scrolling on the Commodore 64. I
have written a program in machine language that scrolls the screen down one
bit at a time in the Y-direction, using the VIC-II chip's automatic
scrolling capabilities. It works fine, except for when it scrolls down every
eighth bit, it jerks a little. It does this because you have to move the
whole screen down one line, then tell the VIC-II to move the whole screen up
seven lines. The Commodore 64 Programmer's Reference Manual says, "You can
use the raster register to set up timing changes in your display so that you
can get rid of screen flicker." I put a raster interrupt routine in my
program to move the line down and change the VIC-II chip's setting while the
raster is off the visible display area, but either I did it wrong or it
didn't work. I am out of ideas and need help badly.

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He's way out of my league in ML programming, but hopefully some of you can
help. Either reply to me here at Harvey Mudd and I'll forward it to him, or
if you're feeling really benevolent, mail him directly. His address is:

Steve Fink
23000 Grand Ronde Rd.
Grand Ronde, OR 97347
(503) 879-5354

Thanks.

Kevin Fink
kfink@jarthur.claremont.edu      -or-        kfink@hmcvax.bitnet
uunet!jarthur!kfink