Re: master 5743b74d4b 1/2: Improve mouse dragging

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Fri, 13 May 2022 15:05:39 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I'm not sure I understand.  Do you remember the details of tis
> > interference?  If not, can you reimplement this using tooltip-show and
> > string copying, and tell what problems that yields?  I really don't
> > want to have the tricky code that sets up colors in tooltip-show to be
> > in more than one place, it's a maintenance problem waiting to happen.
> 
> The immediate problem is that the tooltip contents get displayed in a
> proportional font, which makes no sense when dragging monospace text.

This can be countermanded by using a variant of tooltip-face that
doesn't specify the variable-pitch inheritance.

In general, though, the text should have the same typeface as the
region you are dragging, right?  IOW, if the region you are dragging
uses variable-pitch, the tooltip should use that as well.

I would suggest refactoring tooltip-show and possibly the 'tooltip'
face as well, so that use of the variable-pitch attribute could be
controlled by the caller if the tooltips are used for something other
than their original goal.  As currently implemented, tooltip-show is
really unsuitable for being called in any other context, so our
recommendation to use it, and not x-show-tip, effectively stands on
the proverbial feet of clay.

> IIRC there was also a problem involving `tooltip-hide-delay' and
> help-echo events, but I don't remember the details of that well enough
> to reproduce it.

That is unfortunate.  I'd really prefer that we could call
tooltip-show in mouse.el, not x-show-tip.  So if you can afford that,
please try reproducing the problems, and let's convert mouse.el to
using tooltip-show.