GNU bug report logs - #23478
25.0.93; Mouse region selection asymmetry

Previous Next

Full log

Message #11 received at 23478 <at> debbugs.gnu.org (full text, mbox):

From: Stephen Berman <stephen.berman <at> gmx.net>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 23478 <at> debbugs.gnu.org
Subject: Re: bug#23478: 25.0.93; Mouse region selection asymmetry
Date: Sun, 08 May 2016 20:31:04 +0200

On Sun, 08 May 2016 19:23:17 +0300 Eli Zaretskii <eliz <at> gnu.org> wrote:

>> From: Stephen Berman <stephen.berman <at> gmx.net>
>> Date: Sun, 08 May 2016 17:44:49 +0200
>> 
>> When you select a region by double-clicking with mouse-1 and the end of
>> the region is below the last visible line of the window, Emacs recenters
>> the display, making the entire selected region visible (unless it's
>> larger than half the window's height).  But when you select a region by
>> double-clicking with mouse-1 and the beginning of the region is above
>> the first visible line of the window, Emacs does not recenter the
>> display, so the entire selected region is not visible.
>
> Isn't this because Emacs always makes sure point is visible, but
> there's no such requirement about the mark?  

I'm sure it is.

>                                              If I type "C-x C-x" after
> item 5 in your recipe, the entire region becomes visible, as expected.

Yes, and you also see the whole region when you type `S-C-M-b' on `)' in
step 5 instead of double clicking on it, because backward-sexp changes
point, but double-clicking does not (or rather, it puts point one
position after region-end).

>> This is not a program bug, since Emacs is behaving as intended, but it
>> is a UX asymmetry that I think it would be preferable to eliminate.  The
>> patch below does that, but I'm not sure it's the best way to handle
>> this, since I don't know whether calling `recenter' from Lisp may have
>> undesirable side effects that the automatic recentering Emacs redisplay
>> does when point moves out of the visible portion of the window does not
>> have.
>
> I don't think calling 'recenter' is TRT.  First, the fact that you see
> the display recentering after item 3 in your recipe is only the
> default behavior; if you set scroll-conservatively to 101 before
> repeating your recipe, you will see that Emacs instead scrolls the
> display just one line, i.e. the minimum amount required to bring point
> back into view.  Users that set scroll-conservatively like that will
> lynch us if we recenter display in this situation.

Good point, I think I had that vaguely in mind when I expressed my
doubts about `recenter', but couldn't remember just what needed to be
taken account of.  I did try an alternative to `recenter', using
`goto-char' instead, which changes point and hence induces recentering
by redisplay, but it also loses the region highlighting.  I tried (with
several variants involving redisplay-highlight-region-function and
redisplay--update-region-highlight) but failed to figure out how to keep
the highlighting, but if that's a better way to handle this, maybe
someone more familiar with the region highlighting code will be able to
do that.

> Bottom line, I don't think we should behave like that by default.  I
> think this could be an optional feature, but it must obey
> scroll-conservatively (and maybe also other related variables).

Definitely.  Thanks for the feedback.

Steve Berman

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.