Emacs 26.1 RC1 display issues over SSH/X11 with xming/vcxsrv

Question

I can compile Emacs 26.1 RC1 ok, and use it locally on the host fine.

However, when attempting to ssh -X to host via PuTTY 0.70 and launch the Emacs gui, emacs is not displaying correctly. See screenshot below - no default welcome screen, and missing minibuffer too. Using Windows xserver program VcXsrv (1.19.6.3).

I suspect this issue is related to some combination of GTK and Xming/VcXsrv, however the behavior does change between Emacs 25.3 and 26.1 RC1, see table below:

| emacs    | x-toolkit | result
+----------+-----------+-------
| 26.1 RC1 | gtk3      | bad
| 26.1 RC1 | gtk2      | bad
| 26.1 RC1 | motif     | ok
| 25.3     | gtk3      | ok
| 25.3     | gtk2      | ok

• emacs -Q produces the same result.
• freshly compiled on Opensuse Leap 43.2 and CentOS 7 produces same result
• XLIB_SKIP_ARGB_VISUALS=1 emacs same result
  • References: Link1, Link2

./configure options I ultimately desire:

--with-x-toolkit=gtk3 --with-xwidgets --with-modules --with-mailutils

Where gtk3 is required for xwidgets, so motif or other x-toolkits are not the best solution.

Note: with Xming 6.9.0.31 (not vcxsrv) I get core dumps with error messages referencing this GTK bug: https://bugzilla.gnome.org/show_bug.cgi?id=85715

Can anyone else replicate this problem or have any ideas how to resolve?

wget ftp://alpha.gnu.org/gnu/emacs/pretest/emacs-26.1-rc1.tar.xz
tar -xvf emacs-26.1-rc1.tar.xz
cd emacs-26.1
./configure --with-x-toolkit=gtk3 --with-xwidgets --with-modules --with-mailutils --prefix=/home/test/emacs_26.1_gtk3
make && make install 
# launch emacs, confirm ok
# login to windows, launch ssh -X putty session to linux host, + vcxsrv/xming
# launch emacs - compare to screenshot

Thanks!

Answer 1

Emacs 26 by default switches on double buffering for X servers when it finds the Xdbe header on the build machine. (See Emacs 26 release notes at the GitHub mirror.) Some X servers don’t support this.

Therfore switching off double buffering by adding '(inhibit-double-buffering . t) to your frame parameters might fix this. Safest way is to add it to default-frame-alist:

(setq default-frame-alist
         (append default-frame-alist '((inhibit-double-buffering . t))))

Credit: This tip comes originally from the bug-gnu-emacs list. (Thanks Eli and Robert!)