Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!udel!princeton!phoenix!bskendig
From: bskendig@phoenix.Princeton.EDU (Brian Scott Kendig)
Newsgroups: comp.sys.cbm
Subject: Re: Machine Language Smooth Scrolling Problem
Message-ID: <10755@phoenix.Princeton.EDU>
Date: 8 Oct 89 19:27:33 GMT
References: <2317@jarthur.Claremont.EDU>
Reply-To: bskendig@phoenix.Princeton.EDU (Brian Kendig)
Organization: Systems Engineering, NASA Space Station Freedom Project
Lines: 34

In article <2317@jarthur.Claremont.EDU> kfink@jarthur.claremont.edu (Kevin Fink) writes:
]	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.
] ...
]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:

No, better yet - post replies here to the net, please!  I've tried to
do smooth ML scrolling on a 128 (*very* similar to doing it on a 64)
several times, with no success.  I'd like to be able to define a
playing-field for a game, and have the field be several times larger
than the size of the computer monitor.  First of all, how do I
represent the playfield in memory (it's a low-res color bitmap), and
second of all, how do I scroll through it smoothly?

Replies are more than welcome, but code samples would be *heavenly*!

Thank you.
     << Brian >>
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| Brian S. Kendig       |  I feel more like I   | bskendig                   |
| Computer Engineering  |  did when I got here  | @phoenix.Princeton.EDU     |
| Princeton University  |       than I do now.  | @PUCC.BITNET               |
| Systems Engineering, NASA Space Station Freedom / General Electric WP3     |