incorrect X11 display update

incorrect X11 display update

[Marko Mäkelä]

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In GNU Emacs 21.3.2 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2003-04-24 on raven, modified by Debian
 configured using `configure  i386-linux --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes --with-x=yes
 --with-x-toolkit=athena --without-gif'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: C
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: C
  value of $LANG: fi_FI@euro
  locale-coding-system: iso-latin-9
  default-enable-multibyte-characters: nil

Emacs 21 has occasional problems with X11 display updates.  Last night,
I was able to reproduce one bug - alas, I don't know which font Emacs is
using, and this exact bug doesn't seem to appear with other fonts.
To reproduce, type m C-a m on an empty line.  The line should read "mm"
with the cursor above the second "m", but instead, it reads "_m", where
the "_" is a ghost image of the cursor.

A picture is worth 1000 words, or in this case 1000 bytes.
I've attached two screenshots in PNG format.

	Marko

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Re: incorrect X11 display update

[Marko Mäkelä]

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On Sun, Jun 01, 2003 at 11:53:35AM -0400, Richard Stallman wrote:
> Could you possibly get the latest sources from CVS on savannah.gnu.org
> so as to see if the problem still exists in the latest sources?
> That would be a big help.

This "ghost cursor" bug still exists after 3 years, and I've become used
to it.  Yesterday I come across a way to reproduce it almost always.
The reduced $HOME/.emacs and the custom X resources are attached.
This bug occurs with the attached file emacs-bug.c, but any lengthy
text file should do.

Here are the steps to reproduce this "ghost cursor" bug.

(0) Start emacs and execute M-: (blink-cursor-mode -1)
(1) Load a document at least 3 pages long [c-mode or fundamental-mode]
(2) Scroll down at least one page.
(3) Position the cursor on column 0 of the first visible line of the buffer
("line 1").  Make sure that there is text on that line.
(4) Switch to another X11 application.  Place the window so that
it will cover the left part of the Emacs window, from the bottom half
of line 2 [see (3)] downwards.  Ensure that the Emacs window is taller,
i.e., that the mode line won't be covered by the other window.
(5) Switch between these two windows a few times.  [Enable the
"popup focused window" setting of the window manager, so that an
expose event will be generated for the left part of the Emacs window
whenever switching back to Emacs.]
(6) Switch to the Emacs window and hit C-n. Now there should be a
"ghost cursor" on line 1.  You can get another ghost cursor by pressing
C-f C-p and going back to step 5.

Please note that the ghost cursor does not always appear in step 6.
When it does, it seems to appear consistently for the rest of the
Emacs session.  Here, the bug occurs at some 80% or 90% probability.

> I asked people to tell you how to determine what font is in use.

I've repeated the bug with three fonts: 'fixed' (selected from the Font menu,
more exactly, -misc-fixed-bold-r-normal--0-0-75-75-c-0-iso10646-1
or ...-iso8859-1) and -sony-fixed-medium-r-normal--16-*-*-*-*-*-*-*
(more exactly, -sony-fixed-medium-r-normal--16-150-75-75-c-80-iso8859-1),
and the default .Emacs.font when none has been specified in xrdb.

I'm using the Debian GNU/Linux unstable distribution with the package
emacs21, version 21.4a-6.  "M-x version" reports the following:
GNU Emacs 21.4.1 (i486-pc-linux-gnu, X toolkit, Xaw3d scroll bars) of
2006-05-15 on trouble, modified by Debian

I don't think that this bug is window manager specific.  Currently, I'm
using metacity 2.14.3 of the GNOME desktop.  In 2003, I most likely used
fvwm2.

Best regards,

	Marko Mäkelä

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(blink-cursor-mode -1)

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! before starting Emacs, feed this file to xrdb -load
.Emacs.background:      White
.Emacs.foreground:      black
.Emacs.cursorColor:     black

[-- Attachment #4: emacs-bug.c --]
[-- Type: text/x-csrc, Size: 1182 bytes --]

/******************************************************
Xxxxxxxxxx xxxx xxxxxxxxx

Xxxxxxxx Xx

Xxxxxxx Xxxxxx Xxxxx Xxxxxx
*******************************************************/

#xxxxxx XXXX_XXXXXX
#xxxxxxx "xxxx"
#xxxxx XXXX_XXXXXX
# xxxxxxx "xxxx"
#xxxxx
#xxxxx XXXX_XXXXXX
#xxxxxxx "xxxx"
#xxxxxxx "xxxx"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"
#xxxxxxx "xx.x"

/* Xxxxxx xxxxx xx ../xxxxxxx/xxxx0xxx.xx xxx x xxxxxxxxxxx xx xxx
xxxxxxxxxx xxxx xxxxxx. */

/* Xxx xxxxxxx xxx xxxxxxxx xxxxxxx xxx xxxxxxx xxxx xxx xxxxxxxxxx xxxx.
Xx xxxxxxxx, xx xxxxxxx xxxx xxx xxxxxxx xxx xxxxx, xxx xx xxxxxxxxxx xx
xxxxxxx xxx xxxxxxx. */
xxxxxx xxxxx xxxx xxxxxxx_xxxxx[] = {
	0x00,			/* xxxx_xxxx=0, x_xxxxx=1 */
	0x00, 0x00		/* xxxx_xx=0, xxxxxx=2 */
	/* ?, ?	*/		/* xxxx=(xxxxx xxxx xxx, xx xxxxxxxx) */
};
xxxxxx xxxxx xxxx xxxxxxx_xxxx[] = {
	0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00	/* "xxxxxxx\0" */
};
xxxxxx xxxxx xxxx xxxxxxxx_xxxxx_xxxx[] = {
	0x00, 0x00,		/* xxxx_xx=1, xxxxxx=3 */
	0x00, 0x00,		/* xxxx=0 */
	0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00	/* "xxxxxxxx" */
};

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