bug#24567: 25.1; Cursor flickering with large margin

bug#24567: 25.1; Cursor flickering with large margin

[Vasilij Schneidermann]

Hello,

I've noticed this bug in an IRC buffer with a minor mode enabled that
sets up the window margins to make the contents appear as if they have
been soft-wrapped with the value of `fill-column'.  Quick typing makes
the cursor disappear and reappear erratically.  Restoring the window
margins to their original value of 0 makes it go away again.

To reproduce this in a minimal Emacs session, I've used the following in
the scratch buffer:

    (blink-cursor-mode -1)
    (set-window-margins nil 0 (- (window-width) 50))

Then one can hold down a key and watch the cursor carefully as it starts
flickering until you let go of it.

Is anyone else able to reproduce this?  What would be suitable debugging
steps to find out the reason behind this glitch?  Could it be the fault
of my graphics setup?



In GNU Emacs 25.1.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.20.9)
 of 2016-09-18 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

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

Recent messages:
Making completion list... [2 times]
nil
t
Making completion list...
Quit
Making completion list... [2 times]
Type C-x 1 to delete the help window.
230 (#o346, #xe6, ?æ)
t
Undo! [3 times]
t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils info thingatpt
help-fns help-mode easymenu cl-loaddefs pcase cl-lib debug time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd fontset
image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 94201 6780)
 (symbols 48 20135 0)
 (miscs 40 51 196)
 (strings 32 16654 4240)
 (string-bytes 1 458316)
 (vectors 16 12355)
 (vector-slots 8 438292 5950)
 (floats 8 169 502)
 (intervals 56 885 68)
 (buffers 976 20))

bug#24567: 25.1; Cursor flickering with large margin

[Vasilij Schneidermann]

As I've suspected, the reason lies within my graphics setup.  The glitch
disappeared after changing the Xorg driver from "intel" to "modesetting".