bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

To reproduce:

1. emacs -Q
2. [customize 'scroll-conservatively' to 4]
3. [visit a file named tshark.c containing all the lines between the
     ====== lines in the following]
=====================================
/* tshark.c
  *
  * Text-mode variant of Wireshark, along the lines of tcpdump and snoop,
  * by Gilbert Ramirez <gram@alumni.rice.edu> and Guy Harris 
<guy@alum.mit.edu>.
  *
  * $Id: tshark.c 41542 2012-03-14 01:08:09Z morriss $
  *
  * Wireshark - Network traffic analyzer
  * By Gerald Combs <gerald@wireshark.org>
  * Copyright 1998 Gerald Combs
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2
  * of the License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 
02111-1307, USA.
  */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <locale.h>
#include <limits.h>

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <errno.h>
=================================================

4. Do repeated down-arrow (manually; auto-repeat not req'd)
5. The result is that as the screen scrolls up (by 1 line each time)
    that the "cursor" indication sometimes remains displayed on the
    the "last line just scrolled up" even as it is also displayed
    on the new last line of the buffer.

    So: the result might look like the following (except of course, that
    the cursor doesn't actually take up a character position):

...
#include <stdlib.h>
|#include <stdio.h>
#include <string.h>
|#include <ctype.h>
|#include <locale.h>
#include <limits.h>

This effect does not happen on my Emacs 23.3.1:

   GNU Emacs 23.3.1 (i386-mingw-nt6.1.7601)
   of 2011-03-10 on 3249CTO


In GNU Emacs 23.4.1 (i386-mingw-nt6.1.7601)
  of 2012-02-04 on MARVIN
Windowing system distributor `Microsoft Corp.', version 6.1.7601
configured using `configure --with-gcc (4.4) --cflags 
-ID:/devel/emacs/libs/libXpm-3.5.8/include 
-ID:/devel/emacs/libs/libXpm-3.5.8/src 
-ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include 
-ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include 
-ID:/devel/emacs/libs/giflib-4.1.4-1/include 
-ID:/devel/emacs/libs/jpeg-6b-4/include 
-ID:/devel/emacs/libs/tiff-3.8.2-1/include'

Important settings:
   value of $LC_ALL: nil
   value of $LC_COLLATE: nil
   value of $LC_CTYPE: nil
   value of $LC_MESSAGES: nil
   value of $LC_MONETARY: nil
   value of $LC_NUMERIC: nil
   value of $LC_TIME: nil
   value of $LANG: en_US.UTF-8
   value of $XMODIFIERS: nil
   locale-coding-system: cp1252
   default enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
   tooltip-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   blink-cursor-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Recent input:
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <down> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<up> <up> <up> <up> <up> <up> <up> <up> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> <up> <C-home> C-s s c
r o l l C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s
C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s
C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s
C-s C-s C-s C-s C-s C-s C-s C-s C-s C-s <C-home> C-s
c o n s e r C-x k <return> M-x r e p o r t - e m a
c s - b u g <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit [3 times]
For information about GNU Emacs and the GNU system, type C-h C-a.
Type C-x 1 to delete the help window, C-M-v to scroll help.
View mode: type C-h for help, C-h m for commands, M-x View-quit to quit.
Mark set [2 times]
Mark saved where search started
Mark set
Mark saved where search started

Load-path shadows:
None found.

Features:
(shadow sort mail-extr message ecomplete rfc822 mml mml-sec
password-cache mm-decode mm-bodies mm-encode mailcap mail-parse rfc2231
rfc2047 rfc2045 qp ietf-drums mailabbrev nnheader gnus-util netrc
time-date mm-util mail-prsvr gmm-utils wid-edit mailheader canlock sha1
hex-util hashcash mail-utils emacsbug multi-isearch goto-addr thingatpt
noutline outline easy-mmode kmacro two-column iso-transl help-mode
easymenu view apropos tooltip ediff-hook vc-hooks lisp-float-type mwheel
dos-w32 disp-table ls-lisp w32-win w32-vars tool-bar dnd fontset image
fringe lisp-mode register page menu-bar rfn-eshadow timer select
scroll-bar mldrag mouse jit-lock font-lock syntax facemenu font-core
frame cham georgian utf-8-lang misc-lang vietnamese tibetan thai
tai-viet lao korean japanese hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese case-table epa-hook jka-cmpr-hook help
simple abbrev loaddefs button minibuffer faces cus-face files
text-properties overlay md5 base64 format env code-pages mule custom
widget hashtable-print-readable backquote make-network-process multi-tty
emacs)

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> Date: Mon, 09 Apr 2012 18:38:28 -0400
> From: Bill Meier <wmeier@newsguy.com>
> 
> To reproduce:
> 
> 1. emacs -Q
> 2. [customize 'scroll-conservatively' to 4]
> 3. [visit a file named tshark.c containing all the lines between the
>      ====== lines in the following]
> =====================================
> 
> 4. Do repeated down-arrow (manually; auto-repeat not req'd)
> 5. The result is that as the screen scrolls up (by 1 line each time)
>     that the "cursor" indication sometimes remains displayed on the
>     the "last line just scrolled up" even as it is also displayed
>     on the new last line of the buffer.
> 
>     So: the result might look like the following (except of course, that
>     the cursor doesn't actually take up a character position):
> 
> ...
> #include <stdlib.h>
> |#include <stdio.h>
> #include <string.h>
> |#include <ctype.h>
> |#include <locale.h>
> #include <limits.h>

I cannot reproduce this on my Windows XP box.  I see no artifacts at
all left after scrolling.

Do you perhaps have ClearType enabled?  If so, does the problem go
away when you disable it?

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

On 4/10/2012 3:26 AM, Eli Zaretskii wrote:
>> Date: Mon, 09 Apr 2012 18:38:28 -0400
>> From: Bill Meier<wmeier@newsguy.com>
>>
>
> I cannot reproduce this on my Windows XP box.  I see no artifacts at
> all left after scrolling.
>
> Do you perhaps have ClearType enabled?

Yes

> If so, does the problem go
> away when you disable it?
>

No

Additional info (which may or may not be relevant)

Note, in all cases below, I create an artifact by hitting down-arrow at 
the bottom of the screen (with scroll-conservatively > 0) until I get
a case where the cursor (aka artifact) shows (not blinking) at line N-1
with a blinking cursor at line N.

1. Minimize/Restore of the w32 window (aka EMacs "frame") clears the
    artifact;
2. Cover/Uncover of the w32 window (EMacs) with another w32 window
    does not clear the artifacts;
3. Hitting up-arrow puts the blinking cursor at line N-1.
    Then hitting down-arrow puts the blinking cursor back at line N.
    The cursor/artifact remains at line N-1 (not blinking).
4. If, after an artifact appears on a line, I scroll up a line
    (M-1 C-V) the artifact moves with the line.
5. If cursor is at column N (and at the bottow row (Line N) of the text
    on the screen), then after hitting down-arrow, if the
    artifact appears on the line just scrolled up it will be
    at column N.

    aaaaa|aaa
    bbb|
    cccccc
    ee
    fffff|ffffff

6. If an EMacs frame is showing multiple EMacs windows, no cursor
    appears in the non-selected EMacs window.
7. Changing a cursor setting (blink-cursor-mode, blink-cursor-interval)
    doen't seem to actually affect the cursor.

If there's anything I can do to help with debugging, please let me know.

(Just for the record, I'm running Windows 7 Ultimate, Service Pack #1 
with up-to-date patches).

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

Playing around a bit more:

1. Start Emacs (scroll-conservatively > 0)
2. Adjust w32 window height (aka EMacs frame) to show (say) 24 rows.
3. Fill *scratch* with with 32 lines of 'abc'

Move cursor to top; down-arrow to end of buffer;
Repeat;

No artifacts

Add 123 as last line of the buffer.
Move cursor to top, down-arrow and etc.

Artifact shows up (almost always) at the end of the buffer.

abc
123
|


Strange ....

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> Date: Tue, 10 Apr 2012 11:42:01 -0400
> From: Bill Meier <wmeier@newsguy.com>
> CC: 11210@debbugs.gnu.org
> 
> Note, in all cases below, I create an artifact by hitting down-arrow at 
> the bottom of the screen (with scroll-conservatively > 0) until I get
> a case where the cursor (aka artifact) shows (not blinking) at line N-1
> with a blinking cursor at line N.
> 
> 1. Minimize/Restore of the w32 window (aka EMacs "frame") clears the
>     artifact;
> 2. Cover/Uncover of the w32 window (EMacs) with another w32 window
>     does not clear the artifacts;
> 3. Hitting up-arrow puts the blinking cursor at line N-1.
>     Then hitting down-arrow puts the blinking cursor back at line N.
>     The cursor/artifact remains at line N-1 (not blinking).
> 4. If, after an artifact appears on a line, I scroll up a line
>     (M-1 C-V) the artifact moves with the line.
> 5. If cursor is at column N (and at the bottow row (Line N) of the text
>     on the screen), then after hitting down-arrow, if the
>     artifact appears on the line just scrolled up it will be
>     at column N.
> 
>     aaaaa|aaa
>     bbb|
>     cccccc
>     ee
>     fffff|ffffff

This all points to incomplete erasing of the portions of the screen
that are redrawn.  Perhaps changing some of your display properties or
the font(s) you use would fix that.  Also, is there anything special
about your monitor, like dimensions, or resolution?  Or maybe you have
more than one monitor connected?

Anyway, unfortunately I see none of these problems here.  (Does anyone
else see this on MS-Windows?)

Could you perhaps try the latest pretest of Emacs 24.1, which is
available from here:

  http://alpha.gnu.org/gnu/emacs/pretest/windows/emacs-24.0.95-bin-i386.zip

> 6. If an EMacs frame is showing multiple EMacs windows, no cursor
>     appears in the non-selected EMacs window.

You mean, there's no empty rectangle in the non-selected windows?  Do
you _ever_ see a cursor in non-selected windows on this system?

> (Just for the record, I'm running Windows 7 Ultimate, Service Pack #1 
> with up-to-date patches).

Yes, thanks, your original bug report shows this info.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> Date: Tue, 10 Apr 2012 12:58:08 -0400
> From: Bill Meier <wmeier@newsguy.com>
> CC: 11210@debbugs.gnu.org
> 
> Playing around a bit more:
> 
> 1. Start Emacs (scroll-conservatively > 0)
> 2. Adjust w32 window height (aka EMacs frame) to show (say) 24 rows.
> 3. Fill *scratch* with with 32 lines of 'abc'
> 
> Move cursor to top; down-arrow to end of buffer;
> Repeat;
> 
> No artifacts
> 
> Add 123 as last line of the buffer.
> Move cursor to top, down-arrow and etc.
> 
> Artifact shows up (almost always) at the end of the buffer.
> 
> abc
> 123
> |
> 
> 
> Strange ....

Probably because of the different dimensions of the letters and the
digits.

If you go to one of the 'a' characters and type "C-u C-x =", what font
does Emacs show as being used for this character?  Please also do the
same for '1' and see what it says then.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Juanma Barranquero]

On Tue, Apr 10, 2012 at 19:06, Eli Zaretskii <eliz@gnu.org> wrote:

> Anyway, unfortunately I see none of these problems here.  (Does anyone
> else see this on MS-Windows?)

I cannot reproduce it either.

    Juanma

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Tue, 10 Apr 2012 19:39:47 +0200
> Cc: Bill Meier <wmeier@newsguy.com>, 11210@debbugs.gnu.org
> 
> On Tue, Apr 10, 2012 at 19:06, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > Anyway, unfortunately I see none of these problems here.  (Does anyone
> > else see this on MS-Windows?)
> 
> I cannot reproduce it either.

Thanks for testing.  Maybe Bill could compare his setup with yours,
and that could give a clue.

I will try to study the code involved to see if I see some difference
between a complete redraw (which evidently doesn't have this problem)
and partial redraw (which does).  But I'm not familiar with the
display-specific code of the Windows port, so chances that I will find
something by staring at the code are slim at best.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

Ok: To answer various comments/questions in 1 EMail (and to summarize)_


> Could you perhaps try the latest pretest of Emacs 24.1, which is
> available from here:
>
>    http://alpha.gnu.org/gnu/emacs/pretest/windows/emacs-24.0.95-bin-i386.zip
>

Same effect.

Summary: OK in 23.3; NG in 23.4 & 24.0.95

-------------------
>> 6. If an EMacs frame is showing multiple EMacs windows, no cursor
>>      appears in the non-selected EMacs window.
>
> You mean, there's no empty rectangle in the non-selected windows?  Do
> you _ever_ see a cursor in non-selected windows on this system?
>

No (AFAICT).

Note: This might (or might not) be a different unrelated problem. I've 
just realized that this is true for my Emacs 23.3 also.

Also, as noted, changing cursor configuration (e.g., "blinking cursor") 
has no apparent effect.

If others using Windows 7 do see an empty rectangle in non-selected 
windows and/or are able to change the cursor config from within Emacs, 
then obviously there's something special/different about my configuration.

---------------------------------------
 >> abc
 >> 123
 >> |
 >>
 >>
 >> Strange ....
 >
 > Probably because of the different dimensions of the letters and the
 > digits.
 >
 > If you go to one of the 'a' characters and type "C-u C-x =", what font
 > does Emacs show as being used for this character?  Please also do the
 > same for '1' and see what it says then.
 >
 >

Actually: I see the same problem using 'def' (or seemingly any set of 
characters) instead of '123'.   :)

         character: a (97, #o141, #x61)
preferred charset: ascii (ASCII (ISO646 IRV))
        code point: 0x61
            syntax: w 	which means: word
          category: .:Base, a:ASCII, l:Latin, r:Roman
       buffer code: #x61
         file code: #x61 (encoded by coding system utf-8-dos)
           display: by this font (glyph code)
     uniscribe:-outline-Courier 
New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1 (#x44)

Character code properties: customize what to show
   name: LATIN SMALL LETTER A
   general-category: Ll (Letter, Lowercase)

There are text properties here:
   fontified            t

-------------------------

The problem seems very "phase of the moon" related.

Only happens some fraction of the time (i.e. not on every down-arrow 
past the end of the buffer).

Seems definitely dependent upon the contents of the buffer.

I even got a fail (artifacts) once (even with scroll-conservatively set 
to 0) with a 24 line screen and a buffer of 50 lines of 'abc' and just 
repeatedly doing M-S-< followed by M-S->  .

---------------------------

My comment: maybe let this simmer for a while and see if anyone else 
reports a similar issue (or eventually decide the issue is something 
about my system).

(It's not the end of the world for me to run emacs with
'scroll-conservatively= 0')

Bill

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> Date: Tue, 10 Apr 2012 17:37:13 -0400
> From: Bill Meier <wmeier@newsguy.com>
> CC: 11210@debbugs.gnu.org
> 
> My comment: maybe let this simmer for a while and see if anyone else 
> reports a similar issue (or eventually decide the issue is something 
> about my system).

I would suggest to try to modify the hardware acceleration level of
your video adapter.  On XP, you can get there by right-clicking on the
desktop, selecting "Properties", then clicking on the "Setting" tab,
then "Advanced", and then click the "Troubleshoot" tab.  Try lowering
the hardware acceleration level there.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

On 4/10/2012 5:37 PM, Bill Meier wrote:
>
> Summary: OK in 23.3; NG in 23.4 & 24.0.95
>


Update:

With a little bisecting (doing builds from a local copy of the the emacs 
bazaar repository), I've determined that revision 100582 (which was 
became part of the 23.4 release) is the one that results in the change 
in behavior (artifacts) on my system.


em $bzr log -v -r 100582
------------------------------------------------------------
revno: 100582
committer: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>
branch nick: emacs-23
timestamp: Sat 2011-05-21 10:56:45 +0900
message:
   * dispnew.c (scrolling_window): Don't exclude the case that the
   last enabled row in the desired matrix touches the bottom boundary.
modified:
   src/ChangeLog
   src/dispnew.c

----------------------------------------------------------------

Re:

 > I would suggest to try to modify the hardware acceleration level of
 > your video adapter.  On XP, you can get there by right-clicking on the
 > desktop, selecting "Properties", then clicking on the "Setting" tab,
 > then "Advanced", and then click the "Troubleshoot" tab.  Try lowering
 > the hardware acceleration level there.

Apparently disabling graphics hardware acceleration on Windows 7 isn't 
so easy: in fact, I haven't yet found a way.  I'll keep looking.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> Date: Fri, 13 Apr 2012 01:07:51 -0400
> From: Bill Meier <wmeier@newsguy.com>
> CC: 11210@debbugs.gnu.org
> 
> With a little bisecting (doing builds from a local copy of the the emacs 
> bazaar repository), I've determined that revision 100582 (which was 
> became part of the 23.4 release) is the one that results in the change 
> in behavior (artifacts) on my system.
> 
> 
> em $bzr log -v -r 100582
> ------------------------------------------------------------
> revno: 100582
> committer: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>
> branch nick: emacs-23
> timestamp: Sat 2011-05-21 10:56:45 +0900
> message:
>    * dispnew.c (scrolling_window): Don't exclude the case that the
>    last enabled row in the desired matrix touches the bottom boundary.

Can you run Emacs you built under a debugger?  If so, please make an
unoptimized build ("configure --no-opt" in the nt/ directory to
configure the package before compiling), and please show the values of
yb and last_new on line 5021 of dispnew.c, when you press down-arrow
on the "123" line in this recipe:

> 1. Start Emacs (scroll-conservatively > 0)
> 2. Adjust w32 window height (aka EMacs frame) to show (say) 24 rows.
> 3. Fill *scratch* with with 32 lines of 'abc'
> 
> Move cursor to top; down-arrow to end of buffer;
> Repeat;
> 
> No artifacts
> 
> Add 123 as last line of the buffer.
> Move cursor to top, down-arrow and etc.
> 
> Artifact shows up (almost always) at the end of the buffer.
> 
> abc
> 123
> |

For the record, the values I see are yb = 384 and last_new = 24.

Also, since you seem to have problems with cursor display, do you see
any change in the artifacts left after scrolling if you play with the
value of cursor-type?  E.g., try

          M-: (setq cursor-type 'hbar) RET
or even
          M-: (setq cursor-type nil) RET

before you repeat the above recipe.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

On 4/13/2012 9:04 AM, Eli Zaretskii wrote:
>
> Can you run Emacs you built under a debugger?

Certainly. (It may be a few days before I report back).

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Jason Rumney]

Bill Meier <wmeier@newsguy.com> writes:

> If others using Windows 7 do see an empty rectangle in non-selected
> windows and/or are able to change the cursor config from within Emacs,
> then obviously there's something special/different about my
> configuration.

Are you using screen reader or other accessibility software?

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

On 4/15/2012 10:43 AM, Jason Rumney wrote:
> Bill Meier<wmeier@newsguy.com>  writes:
>
>> If others using Windows 7 do see an empty rectangle in non-selected
>> windows and/or are able to change the cursor config from within Emacs,
>> then obviously there's something special/different about my
>> configuration.
>
> Are you using screen reader or other accessibility software?
>
>

No .....


On a separate note:

I disabled the display adapter in the device manager; this caused a 
switch to a low resolution display. (I'm guessing that this would be 
equivalent to "disabling graphics hardware acceleration").

The issue with artifacts still occurred.

Unfortunately, I didn't check to see if the empty rectangle showed in 
the non-selected window. I'll check that tomorrow.

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Bill Meier]

On 4/15/2012 1:27 PM, Bill Meier wrote:
> On 4/15/2012 10:43 AM, Jason Rumney wrote:
>> Bill Meier<wmeier@newsguy.com> writes:
>>
>>> If others using Windows 7 do see an empty rectangle in non-selected
>>> windows and/or are able to change the cursor config from within Emacs,
>>> then obviously there's something special/different about my
>>> configuration.
>>
>> Are you using screen reader or other accessibility software?
>>
>>
>
> No .....
>
>

Um...

After reading the code in w32term.c and checking the value of
w32-use-visible-system-caret in my Emacs, I found it had a value of 1.

So: Jason asked the right question.

It turned out that (unremembered by me) I once tried out
speech-recognition/text-to-speech which was still enabled (but not 
actually being used).

When I disabled same, my Emacs cursor was "normal" (and no artifacts 
appeared when I downarrowed off the bottom of the screen).

However, if I set w32-use-visible-system-caret to 1 and
scroll-conservatively to 1, I get artifacts.

So: this bug should actually be entitled:

(scroll-conservertively > 0) && (w32-use-visible-system-caret == 1) 
results in multiple cursors ....

Re:
 > Can you run Emacs you built under a debugger?  If so, please make an
 > unoptimized build ("configure --no-opt" in the nt/ directory to
 > configure the package before compiling), and please show the values of
 > yb and last_new on line 5021 of dispnew.c, when you press down-arrow
 > on the "123" line in this recipe:

 > For the record, the values I see are yb = 384 and last_new = 24.
 >

I see the same values.

Note: To reliably (90% of the time) get artifacts I actually used 32 
lines as follows:
001
002
003
...
032
123

Using abc,abc,...,123 now doesn't give artifacts for some reason.
Actually: the breakpoint is never hit in this case.
So: I'm no longer sure about my originally stated test case (abc,...,123).

Note: Just for the record, I put the breakpoint at
r 100582: dispnew.c: line 5016

5016      i = first_old + 1;
5017      while (i < current_matrix->nrows - 1)

bug#11210: Windows emacs 23.4.1: scroll-conservatively > 0 results in multiple cursors being displayed after scrolling

[Eli Zaretskii]

> Date: Thu, 19 Apr 2012 13:00:10 -0400
> From: Bill Meier <wmeier@newsguy.com>
> CC: Jason Rumney <jasonr@gnu.org>, 11210@debbugs.gnu.org
> 
> So: this bug should actually be entitled:
> 
> (scroll-conservertively > 0) && (w32-use-visible-system-caret == 1) 
> results in multiple cursors ....

Reproducible.