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From: gaynor@topaz.rutgers.edu (Silver)
Newsgroups: comp.emacs
Subject: Re: flow control by termcap
Message-ID: <13269@topaz.rutgers.edu>
Date: Fri, 10-Jul-87 23:13:19 EDT
Article-I.D.: topaz.13269
Posted: Fri Jul 10 23:13:19 1987
Date-Received: Mon, 13-Jul-87 03:46:20 EDT
References: <493@yetti.UUCP> <13255@topaz.rutgers.edu>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 48

ron@topaz writes:

> Changes EMACS makes to the screen are supposed to appear
> instantaneous.

This depends upon your environment.  It is impossible to perform
instantaneous screen updates in a "slow" atmosphere, ...

>                 You are not expected to try to read the screen
> during updates, so slowing the scroll down or making it smooth so
> you can see is not applicable.

... where the user *will* notice updates.  These may occur slowly
enough that the user may be able to still read the screen, and even
detect what updates are being made.  To keep from distracting the
user, these changes should be as innocuous as possible.

For an example, a redraw is disconcerting in a slow environment.  The
eyes follow the line insertions (just after registering a gap in the
material), and the thought "C'mon, c'mon..."  registers unbidden in
the mind.  Almost without fail.  With a (relatively) smooth scroll,
though, the eyes and grey matter tend to stay focused on the attended
material.

It is more appropriate to say "The user will hopefully disregard the
screen updates, so do them incognito.".

>                                 Scroll is only done because it is a
> cheap block move on most terminals.

Smooth-scroll is only done to maintain continuity in the display
during updates for the benefit of the user.  Normal scrolls and
redraws might be a little faster.  And a little uglier.

Don't get me wrong, though.  I'm NOT saying that everything should be
smooth-scrolled, because it can also be distracting - it's almost as
if material being smooth-scrolled has attention-glue on it if it's
overused and performed *too* slowly.  What I AM saying is that there
are other considerations to be taken into account besides display-
efficiency.  What is efficient for the display is not always efficient
for the user (although it seems that this is usually the case).

Silver.

name:  Andy Gaynor (Silver)
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