bug#63271: 29.0.90; broken mouse-face

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: Gregory Heytings <gregory@heytings.org>,  juri@linkov.net,
>>   63271@debbugs.gnu.org,  stephen.berman@gmx.net
>> Date: Thu, 11 May 2023 08:51:05 +0800
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > Po Lu, was that change intentional?  If not, let's remove that line or
>> > move it under some conditional that doesn't include all Cairo builds.
>> > If it was intentional, please explain why, and let's take it from
>> > there.
>> 
>> It was needed to prevent drawing overhangs as part of the cursor from
>> overwriting surrounding characters with the glyph string background.
>> 
>> Unfortunately, I don't remember why it was needed, though I think the
>> underlying reason has been fixed.
>
> So can we undo that now?  If there is still a reason for doing
> something special there, it will pop up sooner or later, and we can
> deal with it at that time.  At the very least, the setting of
> s->background_filled_p should not be done when s->hl is one of the
> last 3 values in enum draw_glyphs_face, I think, and maybe also when
> s->for_overlaps is zero.
>
> I'd like to fix this soon, because I want to make another pretest of
> 29.1.

Yes, but please wait a day or two for me to get to a machine where I can
test this.  Thanks.