From: Eli Zaretskii <eliz@gnu.org>
To: Dmitry <dgutov@yandex.ru>
Cc: 18285@debbugs.gnu.org
Subject: bug#18285: 24.3.92; A combination of `display' on text and `invisible' and `before/after-string' leads to the before/after string being displayed twice
Date: Mon, 18 Aug 2014 18:07:15 +0300 [thread overview]
Message-ID: <83k365defw.fsf@gnu.org> (raw)
In-Reply-To: <86d2bypwx1.fsf@yandex.ru>
> From: Dmitry <dgutov@yandex.ru>
> Date: Mon, 18 Aug 2014 02:35:06 +0400
>
> (let ((pt (point)))
> (insert (propertize "a" 'display "bbb"))
> (let ((o (make-overlay pt (point))))
> (overlay-put o 'invisible t)
> (overlay-put o 'after-string "foo\nbar")))
>
> The result looks like this:
>
> foo
> barbbbfoo
> bar
Believe it or not, but this is how the code was written 14 years ago,
although perhaps this particular consequence wasn't intended. But it
follows logically from how the display engine works.
The fundamental issue here is that the 'invisible' property makes all
the character positions between the start and the end of the overlay
indistinguishable. Therefore, the display engine considers the
'before-string' and 'after-string' of an overlay that spans invisible
text to be applicable to both the start and the end of the overlay,
something it wouldn't do if the 'invisible' property were not present.
So what happens is this:
. we find the 'display' property and arrange for it to be displayed
. before displaying the 'display' property string, we check for
overlay strings, and find the 'after-string' whose overlay starts
at the same position; since its overlay has the 'invisible'
property, we consider the 'after-string' in effect for the start of
the overlay, and display that string
. we display the 'display' string
. we are going to continue display of the buffer starting at the
position where the 'display' property ends
. we check for overlays at that position, and again find the same
'after-string' because its overlay _ends_ at that buffer position,
so we display that string again
So you are actually shooting yourself in the foot by using the
'invisible' property here. Doing that is redundant here, because the
'display' property already makes the text it "covers" invisible.
I think it's not worth to try to fix this (by complicating the heck
out of the display engine) on the account of this use case.
If you have other similar use cases, where simply refraining from
using 'invisible' won't help, please show them.
> It's the same if I use `before-string' instead of `after-string', but
> not `display'.
>
> If I don't set the `invisible' property, it's just
>
> bbbfoo
> bar
My crystal ball says you get
bbbfoo
bar
only with 'after-string'. With 'before-string', you should get
foo
barbbb
instead. IOW, without the 'invisible' property getting in the way,
the 'before-string' is displayed before the display property, and
the 'after-string' is displayed after it.
Btw, there was a discussion of a similar issue starting at
http://lists.gnu.org/archive/html/emacs-devel/2011-04/msg00674.html
It was inconclusive.
next prev parent reply other threads:[~2014-08-18 15:07 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-17 22:35 bug#18285: 24.3.92; A combination of `display' on text and `invisible' and `before/after-string' leads to the before/after string being displayed twice Dmitry
[not found] ` <handler.18285.B.140831493931056.ack@debbugs.gnu.org>
2014-08-18 1:06 ` bug#18285: Acknowledgement (24.3.92; A combination of `display' on text and `invisible' and `before/after-string' leads to the before/after string being displayed twice) Dmitry Gutov
2014-08-18 15:07 ` Eli Zaretskii [this message]
2014-08-21 14:07 ` bug#18285: 24.3.92; A combination of `display' on text and `invisible' and `before/after-string' leads to the before/after string being displayed twice Dmitry Gutov
2014-08-21 14:57 ` Eli Zaretskii
2014-08-21 15:40 ` Dmitry Gutov
2014-08-21 16:06 ` Eli Zaretskii
2014-08-22 0:58 ` Dmitry Gutov
2014-08-22 6:41 ` Eli Zaretskii
2014-08-22 11:41 ` Dmitry Gutov
2014-08-22 13:31 ` Eli Zaretskii
2014-08-22 20:01 ` Dmitry Gutov
2014-08-22 20:55 ` Eli Zaretskii
2014-08-24 1:28 ` Dmitry Gutov
2014-08-24 2:44 ` Eli Zaretskii
2014-08-23 23:21 ` Dmitry Gutov
2014-08-24 2:40 ` Eli Zaretskii
2014-08-24 2:48 ` Dmitry Gutov
2022-04-18 11:39 ` Lars Ingebrigtsen
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