bug#13011: 24.2; Text flickering moving cursor with box around text enabled

[Eli Zaretskii <eliz@gnu.org>]

> From: Kenichi Handa <handa@gnu.org>
> Cc: eliz@gnu.org,  mario.giovinazzo@virgilio.it,  13011@debbugs.gnu.org
> Date: Mon, 03 Dec 2012 18:29:18 +0900
> 
> In article <jwvhao8z0y8.fsf-monnier+emacs@gnu.org>, Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> > > I made a provisional change that behaves with left and right borders
> > > like it does with horizontal ones, and it seems to work, at least with
> > > character display (didn't text with images, image slices, composite
> > > characters, etc.).  But I'd like to ask Handa-san (CC'ed), who wrote
> > > the code for this feature (almost 12 years ago!), whether he might
> > > remember why the code deliberately makes the left and right borders
> > > behave differently from top and bottom ones.
> 
> > I'm curious as well.  The only think that comes to mind is that in most
> > fonts, there's usually some empty pixel-line(s) at the top and the
> > bottom, whereas there often't isn't any empty pixel-lines at all on the
> > left (and/or on the right) side.  So there's more risk of overwriting
> > useful pixels on the left&right than at top&bottom.
> 
> Yes.  That's the reason of this asymmetry.  The original
> intention of this feature was to make modeline occupy only
> canonical line height even with the current style.

So does anyone object to lifting this limitation, even though it might
degrade the quality of displaying the first and the last characters in
the run of characters that have the box face?