Re: The future of Follow Mode - a proposal.

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Thu, Feb 25, 2016 at 06:28:18PM +0200, Eli Zaretskii wrote:
> > From: Stefan Monnier <monnier@iro.umontreal.ca>
> > Cc: emacs-devel@gnu.org
> > Date: Wed, 24 Feb 2016 19:30:55 -0500

> > I live in a world where wrapped lines are sufficiently rare that I don't
> > really care and rarely think about what can happen in those cases.

> > But now that I think about it: I'm not sure how vertical-motion could
> > handle a "multiple-window" case where the windows don't have the same
> > width (same thing in other similar cases, such as with overlays with
> > a `window' property that make them only apply to some of the multiple
> > windows, or when the windows aren't all in the same frame and don't use
> > the same font).  The desired semantic seems undefined except for the
> > case where the vertical motion is applied to the "currently displayed
> > state" (so we know when to use which window data).

> Actually, vertical-motion completely breaks in that case.  I don't
> even see a way that will allow to solve that situation in principle,
> except in some very specific and restricted use cases.  Which is why I
> strongly suggest to change Follow Mode so that it forces all of its
> windows be of the same width.  With the current pixelwise control of
> window dimensions, this is easy.

On a tty, a pixel has the thickness of a character.  It could easily
happen that to make all the windows of equal width, it's necessary to
put a "terminator" vertical line on the RH window, or even double width
window separators in.  This would be ugly.

> I think this will magically remove many of the problems that currently
> plague Follow Mode, and leave us with something we can reasonably easy
> to solve and maintain.

> However, Alan disagrees, and insists on supporting windows of unequal
> width.

If it can be done without undue difficulty, then yes.

-- 
Alan Mackenzie (Nuremberg, Germany).