bug#47360: 27.1; using 'bar cursor, mouseclick is rounded to the wrong char position

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 28 Mar 2021 07:15:38 +0000
> From: Julian Rohrhuber <rohrhuber@protonmail.com>
> Cc: larsi@gnus.org, 47360@debbugs.gnu.org
> 
> 
> >> There is one more case where one can feel the difference: when selecting with the mouse and dragging to the right, the selection jumps to each character a little "too late", that is, after you have already crossed the position you want the selection to end at. You have to point to a character *after* the one you want to include. The current selection always is up to one character behind the cursor barline.  This results in a "sticky" feeling.
> >
> > Yes, selection in Emacs works on per-character granularity, because it
> > uses the faces infrastructure.  We'd need to do something very
> > different to make that use pixel granularity.  Patches are welcome.
> 
> I don't think that a change of granularity would be necessarily at all to improve what I describe. All what would have to be done is to change at what *cursor* position the selection jumps to the next character (namely when it crosses its middle). So it would only another application of the solution to the current issue.

Sorry, I thought you were talking about the jumps, not about when the
jump is done.

However, with your proposal, the jump will be too early, so instead of
"lagging" the selection would sometimes "lead" the mouse pointer,
i.e. be ahead of it.  As long as the changes are one character at a
time, there's no way around that basic fact.