Path: utzoo!attcan!uunet!nfsun!eklektik!danbabcock
From: danbabcock@eklektik.UUCP (/dev/tty000)
Newsgroups: comp.sys.amiga.tech
Subject: Scrolling with the copper (in a text editor)
Message-ID: <1656@eklektik.UUCP>
Date: 9 Apr 90 22:02:17 GMT
Reply-To: danbabcock@eklektik.UUCP (/dev/tty000)
Organization: Computers, Gerbils, and Games in the Basement, Pgh, PA
Lines: 30

Jonathan Abbey (jonabbey@ccwf.cc.utexas.edu) wrote in message ID
<27737@ut-emx.UUCP>:

> Good advice at the last, but how do you intend for him to use the copper?

Consider writing out a new line of text at the bottom of the screen and
scrolling. Most editors just rewrite the entire screen from the ASCII
buffer, or else use the blitter to copy the bitmap to itself, offset one
line, and write out the new line to replace the last line in the bitmap.

However, the most efficient approach is to use the copper to simulate a
circular buffer-type display, much like the VIDC in the Archimedes.
In this scheme, the new line is placed where line 1 used to be, and the
copper list is adjusted so that line 1 (in memory) is displayed at the
bottom of the screen. Only one line (i.e. 640 bytes) in the bitmap needs
to be rewritten, and no memory needs to be physically moved. No "extra"
memory is required, besides the few words needed for the copper list.
(please note that when I say "line" I mean a line of text, not a line
of the bitmap)

Admittedly, using such a copper list could result in intuition menus
popping up in unusual areas of the screen, so it might be neccesary to
write custom menu code.

I agree that adding an ARexx port is a good idea.

-- Dan Babcock
1106 Jefferson Road
Pittsburgh, PA 15235
(412)-373-1753