[Bug]: tigervnc: Unable to setup a Compose Key

[Iey4iej3]

Problem description

The compose key is not working properly.

There are two issues, as far as I see:

• Emptiness of Compose files: the Compose files in ${PREFIX}/share/X11/locale are all empty for all locales. It seems that the package libx11 is not built correctly;
• TigerVNC does not work even with Compose file: I copied a Compose file from my Debian Linux to $HOME/.XCompose. Then under termux-x11, the compose key is activated after setxkbmap -option "compose:ralt". However, under TigerVNC, it does not work.

What steps will reproduce the bug?

1. vncserver :0;
2. export DISPLAY=:0;
3. setxkbmap -option "compose:ralt";
4. Try to press a compose sequence, say, Alt_R+'+e

What is the expected behavior?

Produce é

System information

termux-info:

Termux Variables:
TERMUX_API_VERSION=0.50.1
TERMUX_APK_RELEASE=F_DROID
TERMUX_APP_PACKAGE_MANAGER=apt
TERMUX_APP_PID=30173
TERMUX_IS_DEBUGGABLE_BUILD=0
TERMUX_MAIN_PACKAGE_FORMAT=debian
TERMUX_VERSION=0.118.0
Packages CPU architecture:
aarch64
Subscribed repositories:
# sources.list
deb https://packages-cf.termux.dev/apt/termux-main stable main
# x11-repo (sources.list.d/x11.list)
deb https://packages-cf.termux.dev/apt/termux-x11 x11 main
Updatable packages:
All packages up to date
termux-tools version:
1.35.0
Android version:
12
Kernel build information:
Linux localhost 4.14.299-gcd41c6b2be18 #1 SMP PREEMPT Sun Dec 18 22:07:16 UTC 2022 aarch64 Android
Device manufacturer:
samsung
Device model:
SM-P610

[xtkoba]

Partially a duplicate of #13362 I suppose.

[Iey4iej3]

I don't see how that one is related. If I understand correctly, that issue is about a different keyboard layout under which one could input accents directly, and the x11 captures the signal but failed to deal with it.

I am talking about a different issue: the compose key is not recognized at all. It is not a low-level issue: the Alt_R is recognized by xev, and if I understand correctly, it is treated as a normal Alt by x11, but not as a compose key.

[xtkoba]

In that locale support is broken in libX11. So I thought the first one of the two issues might be related. I suppose the second one is not much related.

Of course I might be wrong, but the directory name $PREFIX/share/X11/locale suggested that.

[xtkoba]

Some observation:

• $PREFIX/share/X11/locale/C/Compose being empty seems to be normal, as that is the same as in my Gentoo GNU/Linux environment.

• Bionic libc does not have proper locale support. Other than C (POSIX) locale, only C.UTF-8 is supported. But directory $PREFIX/share/X11/locale/C.UTF-8/ does not exist.

[Iey4iej3]

• $PREFIX/share/X11/locale/C/Compose being empty seems to be normal, as that is the same as in my Gentoo GNU/Linux environment.

What is abnormal is that all of them are empty. I checked by find -name Compose -exec ls -l {} \;.

[xtkoba]

What is abnormal is that all of them are empty. I checked by find -name Compose -exec ls -l {} \;.

I'm aware of it. As I wrote above, Bionic can only handle C or C.UTF-8 locales. Directories for other locales are not supposed to be handled in the first place.

[xtkoba]

The first issue has been resolved. It was due to misconfiguration of RAWCPP. My guess in the discussion above was completely wrong, to my shame.

[xtkoba]

Is TigerVNC/tigervnc#962 related to the second issue?

[Iey4iej3]

-RawKeyboard (or -RawKeyboard=1) does not seem to work (on AVNC or MultiVNC).

I tried to see what happens under xev. Without extra setup, when I press right Alt, it is recognized as Alt_R. If setxkbmap -option "compose:ralt" is run, when I press right Alt, it shows as Alt_L (on a Linux device, when the compose key is correctly set, it should be MultiKey).

[xtkoba]

Quoted from TigerVNC/tigervnc#962 (comment):

Fortunately there is also an extension that allows switching to a key based system. You can enable it by setting -RawKeyboard=1 on the server. It requires support in the client though.

So presumably those VNC viewer apps for Android do not support this extension. In fact, I can make some key (Left Control; because Right Alt does not exist on my keyboard) shown as Multi key in xev with TigerVNC viewer 1.12.90 from Gentoo GNU/Linux.

[xtkoba]

Enhancement on the client side. Strictly this is a third-party issue unless we provide a VNC viewer app on our own.

FYI, there is another issue in which the situation is similar: #14647.

[Iey4iej3]

I confirm that Compose Keys are working with RawKeyboard parameter and a compatible client.