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From: z@cca.UUCP (Steve Zimmerman)
Newsgroups: net.emacs
Subject: EMACS vs. reverse video
Message-ID: <6020@cca.UUCP>
Date: Tue, 1-Nov-83 09:09:54 EST
Article-I.D.: cca.6020
Posted: Tue Nov  1 09:09:54 1983
Date-Received: Fri, 4-Nov-83 00:11:43 EST
Lines: 31

Although most terminals with reverse video are handled properly by the
various EMACSes, there are two types of reverse video that cause
problems.  The first is that used by the hp's, which is denoted by the
"xs" capability.  As Warren Montgomery pointed out, the only way to
clear out reverse video from a location on such a terminal is to send a
"clear line" sequence somewhere in the line before that location.  This
is a side effect of the fact that in these terminals reverse video is an
attribute associated with the screen location, not with the character as
in most terminals.  Another side effect of this is that if the terminal
also supports character insert, inserting a character on a line
somewhere in front of a reverse video character (such as a highlighted
mark) will cause the following characters to shift down normally, but
the reverse video mark will stay firmly rooted, thereby highlighting the
previous character.  The solution is not to use character insert on
these terminals when there is a reverse video character farther down the
line, but instead to clear out the rest of the line and redisplay it
with the reverse video character properly positioned.

The second type of problem terminal is typified by the Televideo; these
terminals all have the "sg" capability.  The terminal automatically
inserts one or two spaces on the screen whenever it turns reverse video
on or off; these spaces are actually used to store the information that
the display mode is changing as of the next character, and it is
impossible to get around their presence.  As most programs cannot
tolerate extraneous spaces in the display like this, the reverse video
mode on these terminals is essentially useless.  Generally, the proper
thing to do is simply for programs not to use reverse video on terminals
where "sg" is present.

	Steve Zimmerman
	{decvax,linus}!cca!z