Path: utzoo!censor!becker!cbmtor!jb
From: jb@cbmtor.UUCP (Jim Butterfield )
Newsgroups: comp.sys.cbm
Subject: Re: Machine Language Smooth Scrolling Problem
Summary: Use Two Screens
Keywords: machine language, scrolling, C64
Message-ID: <136@cbmtor.UUCP>
Date: 8 Oct 89 16:51:17 GMT
References: <2317@jarthur.Claremont.EDU>
Reply-To: jb@cbmtor.UUCP (Jim Butterfield )
Organization: via Amiga Unix from Commodore (CANADA)
Lines: 22

Question from: kfink@jarthur.Claremont.EDU (Kevin Fink)...

> My brother is working on smooth scrolling in machine language ...
>   [he says...] "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."  [more details omitted] 

    Even if he's using a character screen, you don't have time to move
a thousand characters and their corresponding color pixels within
retrace time... and on high resolution, you couldn't even make the
attempt.
    Set up two screen memory areas.  While one is displaying, draw the 
other one (say, with the screen characters pre-moved as desired).
When you're ready for that eighth-bit scroll, wait for retrace and
then flip to the other screen.
--jim

-- 
--
:  My boss doesn't understand me...  :  Jim Butterfield, Toronto  :
:   .. and I'm my own boss!          :    jb@cbmtor               :