Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!usc!wuarchive!psuvax1!rutgers!att!cbnewsm!nsw
From: nsw@cbnewsm.ATT.COM (Neil Weinstock)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Fast Scrolling
Keywords: scrolling,spam
Message-ID: <7182@cbnewsm.ATT.COM>
Date: 29 Nov 89 17:58:34 GMT
References: <6072@ucdavis.ucdavis.edu>
Reply-To: nsw@cbnewsm.ATT.COM (Neil Weinstock)
Organization: The Flying Squid Patrol
Lines: 45

In article <6072@ucdavis.ucdavis.edu> rogers@iris.ucdavis.edu (Brewski Rogers) writes:
>In article <762@milton.acs.washington.edu> zeno@milton.acs.washington.edu (Sean Lamont) writes:
[ ... stuff about horizontal scrolling ... ]
>>2) It's TOO SLOW!  A SCROLLRASTPORT takes far too much time to scroll
>>anything of any substance. (like a 400 x 200 5-plane bitmap) I know
>>it's possible to move bitmaps much faster (for example, Screen sizing)
>>How would one go about making a FAST scroll?
>
>The only really *FAST* (That I know of, anyhow) way to scroll a view
>is to take control of the copper list, or create your own copper list.
>
>Once you have done this, you can simply change a couple of bytes in the
>copper list, which takes almost zero cpu time, and you will have smooth
>scrolling. Of course the whole thing tends to be a major pain in the
>ass if you want intuition compatibility, but at least its possible.
[ ... ]

One method I have used successfully is to first have Intuition allocate a 
screen for you, then you create your own "second screen" and make a 
dual-playfield display.  You can then manipulate the second playfield and 
Intuition won't even know about it.  You can double buffer, smooth scroll, 
anything.  Intuition will live happily on the first playfield.  If you use 
color 0 as your background color on the Intuition playfield, you can get cool 
effects like transparent menus, where your animation will be visible 
(and still animating) "through" the menus.  I believe the freeware program
"Tapestry" does something like this, though it doesn't do any animation.

You do have to be careful about screen depth arrangement.  I assumed that I
could do pretty much whatever I wanted with the copper lists while my screen 
was on top (note that I did not allow my screen to be dragged down; that would
have been a mess).  If I ever found that my screen was not on top, I stopped
animating.  You also have to be careful with locking IntuitionBase;  for a 
while I was having some problems with Dmouse guruing when trying to unblank 
the screen, but eventually I managed to make everything behave.

As far as I know, I wasn't being "unfriendly" to the OS once I had everything
worked out.

Dual playfield screens:  don't leave home without them!

    ________________    __________________    ____________________________
////                \\//                  \\//                            \\\\
\\\\ Neil Weinstock //\\ att!cord!nsw  or //\\ "Oh dear, now I shall have ////
//// AT&T Bell Labs \\// nsw@cord.att.com \\//  to create more Martians." \\\\
\\\\________________//\\__________________//\\____________________________////