Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!mcsun!sunic!tut!po87553
From: po87553@tut.fi (Ojala Pasi Juhani)
Newsgroups: comp.sys.cbm
Subject: Re: Another Smooth-Scrolling ML question
Message-ID: <2829@alva.tut.fi>
Date: 11 Dec 89 08:53:11 GMT
References: <3408@jarthur.Claremont.EDU>
Reply-To: po87553@alva.UUCP (Ojala Pasi Juhani)
Organization: Tampere University of Technology, Finland
Lines: 31

You talked about scrolling the screen downwards.
I know what could be wrong in your approach. You see, VIC-chip is
not very complicated, in fact, it is quite silly..

It is fairly easy to make VIC think that it should do something it
wasn't designed to do. For example: opening borders, using more than
8 sprites, scrolling the whole screen FAST.. And this last
one is related to your 'problem'. I try to make clear how this
fast scroll is made and then you find out this problem also..

Just before VIC is going to start drawing the screen, we scroll it one
pixelline down, so VIC thinks it is not time to start drawing the
screen, and when the screen is scrolled to 7, the next value is 0,
and the poor VIC will never start to draw the screen.. So, you can
very fast scroll e.g. a hi-res picture off the screen, and I mean
FAST..

And if you change the y-scroll register when the VIC is drawing a
text-line, it won't start drawing another until it reaches that
line in scroll register (the lower 4 bits), so there may be some
space between those textlines. It is possible to change every line's
distance to the other and so on.



 -- Pasi Ojala, 39230 Osara, Finland --
-- 
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 Pasi Ojala       Pasbox v2.6     Why does my signature keep changing??
 po87553@tut.fi   C64 forever     Am I doing something wrong?
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