bug#18793: 24.4; zero width rectangular selection displaces text

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: monnier@iro.umontreal.ca,  carlosjosepita@gmail.com,  
> 18793@debbugs.gnu.org
> Date: Fri, 06 May 2022 13:05:45 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I'm not sure: how would such a vertical line indicate that it's
> > region?
> 
> The same way the current one-pixel-wide thing does?  I.e., not very
> well.

The current one-pixel thing is displayed outside of the character
cell, and it has the color of the region face.

> > And how will it be visible, given that the cursor is displayed on that
> > same character?  Or maybe I don't understand what you mean by "a
> > vertical line through a character"?
> 
> The cursor usually blinks, so the line will be somewhat visible.

Usually, but not always.  More generally, I'm not sure the visual
effect will be satisfactory, when it blinks.

> But I was thinking that perhaps the box cursor would also react to that
> line in some way, for instance by using a reverse colour where the
> vertical line is.

That'd mean we need to display the cursor specially there.  IOW, it is
no longer a simple face.

It might be better and easier to introduce a defcustom that disables
the visualization of zero-width rectangles.  Was that considered as a
solution to this issue?