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From: pochron@cat37.cs.wisc.edu (David Pochron)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Scrolling in 512K - Advice?
Keywords: amiga 512k scrolling bitmap graphics
Message-ID: <1990Nov16.222133.23158@daffy.cs.wisc.edu>
Date: 16 Nov 90 22:21:33 GMT
References: <1149@xroads.UUCP> <2259@exodus.Eng.Sun.COM>
Sender: news@daffy.cs.wisc.edu (The News)
Organization: U of Wisconsin CS Dept
Lines: 46

In article <2259@exodus.Eng.Sun.COM> cmcmanis@stpeter.Eng.Sun.COM (Chuck McManis) writes:

{stuff deleted}
>on systems with more than .5K) You keep in memory the "view" bitmap and
>bitmaps for the four edges of that bitmap. This allows you to scroll
>on one of the edges when they are needed. When the edge bitmap is scrolled
>on, you can then start another task to begin loading a new "edge" into 
>the area vacated by this scrolled on portion. (ASCII image follows :)

{more stuff deleted}

>smoothly onto the next panel. The size of the panels will be determined
>by how fast you scroll across them. Because in this example the
>on a 512K machine. 

{yet more stuff deleted}

I also have been experimenting with scrolling huge screens (with AMOS, of
course) and have a few additional comments I would like to add:

Both of these methods appear similar except the first one is just getting the
data from disk, and the second is assuming you have the data in memory, right?

Okay, this appears fine for coarse scrolling, but how does one go about doing
fine scrolling - using the hardware pointers, of course.  It seems you would
need to double buffer everything and redraw one buffer completely every time
an entire panel was uncovered.  (ie. redraw logical buffer in direction of
scroll, fine scroll physical buffer, switch to logical buffer when entire block
is revealed (now the physical buffer), go back to step 1 with the new logical
buffer)

Phew!  Sure wish they had just put multicolor text modes in the Amiga! :-)


If there is an easier way, please tell me - timing the redraw blits with the
hardware scroll pointers is a real pain.

>--
>--Chuck McManis					    Sun Microsystems


--
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David M. Pochron	    |  from Rescue Rangers, _A Fly in the Ointment_
pochron@garfield.cs.wisc.edu|  Gadget to Dale:  "Keep the hands off the body!"
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