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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.sys.apple2
Subject: Re: updating windows fast
Message-ID: <15212@smoke.brl.mil>
Date: 15 Feb 91 19:04:55 GMT
References: <7566@crash.cts.com>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 13

In article <7566@crash.cts.com> mdavis@pro-sol.cts.com (Morgan Davis) writes:
>The fastest way to scroll a window is to calculate the actual video RAM
>locations for its content, and then use a fast 65816 routine to do the
>pixel shifting on your own, preferably by using a table of offsets, or even
>faster, by generating code at runtime that moves pixels in an unrolled loop
>of load-store instructions.  Takes up a bit of RAM, but can result in
>blindingly fast scrolls, albeit against the rules.

This is basically the technique that the developers of AT&T's "Blit"
terminal ended up using to implement the fundamental operation "bitblit".
(The processor was an MC68000 but the principles were the same.)  Details
were published in some issue of Software - Practice and Experience, if I
recall correctly.