bug#16129: 24.3.50; Emacs slow with follow-mode when buffer ends before last window

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 14 Jan 2014 13:34:23 +0100
> From: Anders Lindgren <andlind@gmail.com>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, 16129@debbugs.gnu.org
> 
> I mean the implementation -- adding this to the display engine is a major
> undertaking.

Depending on the requirements, it might not be that major.

> Basically, it is supposed to do whatever Follow mode does today

That is not specific enough, especially if you take into consideration
that I have only a vague idea about what Follow mode does.  Moreover,
I'm not sure we should ask the display engine do everything it does.
For example, selecting the next/previous window when point moves off
the limits of the current window seems to be something that is easy to
do in Lisp.

So please do try to come up with a list of requirements that should be
moved to the display engine.  I guess setting the window start point
when scrolling would be one; what else?

> > I would suggest that we also post feature requests for things that would
> > > help the situation on a shorter time scale. Primarily, I would like to be
> > > able, on a window-by-window basis, control whether or not a window should
> > > be recentered, when empty.
> >
> > What should Emacs do instead of recentering a window?
> >
> 
> It should keep the window empty.

Shouldn't be hard to implement, given some buffer-local variable.