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

From: Lars Ingebrigtsen <[email-masked]>
Date: Fri, 06 May 2022 14:52:25 +0200

Eli Zaretskii <[email-masked]> writes:

> I'm not sure.  This was supposed to be a nifty feature.  If some users
> are annoyed by its effect, the easy way to handle that is to let those
> users disable the cause of the annoyance.  After all, we don't show
> anything comparable for non-rectangular regions, do we?

That's a good point.

> What other uses could this have, except fill-column indication, which
> is another minor feature?
>
> Adding capabilities to the Emacs display that operate on
> sub-character-cell resolution will mean serious complications.  For
> example, what would we do when displaying color Emoji at that place?
> Or what about images?  Or what if the character in question is
> currently highlighted by mouse-face?
>
> IOW, I'm asking whether these marginal features are worth a serious
> surgery and complications in the display engine, which currently has
> the canvas-based design?

display-fill-column-indicator-mode was the only one that sprang
immediately to mind, but I think it could be useful when displaying
tabular data, and you want to mark boundaries without taking up extra
space, for instance.

And speaking off the fill indicator -- bug#54598 talks a bit about the
problems with the current implementation.  But that mode does show how a
box cursor and a region could behave with these vertical lines.

And I don't think colour emojis or images would represent that much of a
problem -- I think we'd draw the line on top of the glyph?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no