Build on Linux: -qt-xcb option?

Joshua Fletcher

I found that ensuring these packages were installed was sufficient for my purposes:
libxcb-devel
libxkbcommon-devel
xcb-util-devel
xcb-util-image-devel
xcb-util-keysyms-devel
xcb-util-renderutil-devel
xcb-util-wm-devel
mesa-libGL-devel

the only one I was actually missing was: xcb-util-renderutil-devel
but if you can, check and make sure all those are installed, and I think it should work for you.

ludek.vodicka

Hi, I just also trying to solve problems with -qt-xcb option.

I removed this switch and compiled the latest Qt 5.15.0. But my application didn't start with error:

qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.
Available platform plugins are: linuxfb, minimal, offscreen, vnc.

Directory qt\plugis\platforms contains only

libqlinuxfb.so
libqminimal.so
libqoffscreen.so
libqvnc.so

Thanks for any help

JoeCFD

https://forum.qt.io/topic/93247/qt-qpa-plugin-could-not-load-the-qt-platform-plugin-xcb-in-even-though-it-was-found

ludek.vodicka

@JoeCFD Thanks for the reply. I already saw this topic but it is a slightly different problem.

I do not have a message:

Qt platform plugin "xcb" in "" even though it was found.
but only
Qt platform plugin "xcb" in ""

My issue is that I don't have file libqxcb.so in Qt/plugins/platform directory at all.

I tried to compile it with -qt-xcb like several times before, but because this switch was removed, I tried it without that. Also, I tried "-xcb" switch too.

But although I have "X11 specific: XCB Xlib...yes" message during configuration, libqxcb.so file isn't created.

ludek.vodicka

Seems that adding following switches forces Qt to build libxcb.so

-xcb -xcb-xlib -bundled-xcb-input

(it's necessary to add all these switches based on my observations)

Jawsh

@ludek-vodicka, where do you specify those options? They are not part of configure, correct?

jsulm

@Jawsh said in Build on Linux: -qt-xcb option?:

They are not part of configure

They are. Call configure with -h parameter and you will see.

Jawsh

Actually, if I remove bundled-xcb-input it works on configure. However, I have run into a new error: "ERROR: Feature 'xcb' was enabled, but the pre-condition 'features.thread && libs.xcb && tests.xcb_syslibs && features.xkbcommon-x11' failed." Anyone have any ideas? I have installed as many of the prerequisite libs as I could find listed.

Jawsh

Found this on: https://github.com/RudolfCardinal/camcops/issues/3

sudo apt-get build-dep qt5-default

(having enabled "Source code" option in Software and Updates > Ubuntu Software)

After I did this, deleted config.cache, and reran configure then it worked.

SeanMurphy_6

I had this exact same problem and I found that if I combined the installing the packages listed by Joshua Fletcher on 16 Jun 2020:

libxcb-devel
libxkbcommon-devel
xcb-util-devel
xcb-util-image-devel
xcb-util-keysyms-devel
xcb-util-renderutil-devel
xcb-util-wm-devel
mesa-libGL-devel

And then running configure with the options suggested by Ludek Vodicka on 19 Jun 2020:

-xcb
-xcb-xlib
-bundled-xcb-xinput

Built Qt and correctly built the libqxcb.so under the platforms plugin directory, and now my applications compiled against Qt 5.15.2 launch without any errors.

nikhil-sethi

Hey everyone. I was facing the same issue on Ubuntu 20.04. This thread and @SeanMurphy_6's solution (23rd Nov) helped me a lot. Thanks for that.
Just wanted to add that it is important to use the 'dev' versions of the xcb libraries. In my case I had the latest 'xcb xinerama0' library installed but libqxcb.so still didn't compile. Fixed it by installing the dev version (libxcb-xinerama0-dev on Debian/Ubuntu). If all xcb libraries are installed correctly, you should

See a 'yes' for each xcb library on the CLI when running the configure command:

Checking XCB XINERAMA .... yes

See a 'succeeded' for tests in the config.log file:

test config.qtbase_gui.libraries.xcb_xinerama succeeded

When compiled you should see libqxcb.so in the qtbase/plugins/platforms directory
The original software ran perfectly after ensuring this.

jrb1

In case this might help someone, there appears to be a bug in configure with respect to the iccc such that with Qt-5.12.6 on RHEL7, despite having it installed the config log says:

loaded result for library config.qtbase_gui.libraries.xcb_icccm
Trying source 0 (type pkgConfig) of library xcb_icccm ...
+ /bin/pkg-config --exists --silence-errors xcb-icccm '>=' 0.3.9
pkg-config did not find package.
  => source produced no result.
Trying source 1 (type inline) of library xcb_icccm ...
xcb/xcb_icccm.h not found in [] and global paths.
  => source produced no result.
test config.qtbase_gui.libraries.xcb_icccm FAILED

I'm very sure I have that package installed (RHEL7's latest which is 0.27.1) which should have passed that version check, if I run that command myself I see it should have found it:

bash-4.2$ /bin/pkg-config --exists --silence-errors xcb-icccm '>=' 0.3.9
bash-4.2$ echo $?
0

Now pick a version I know I don't have to check pkg-config is working:

bash-4.2$ /bin/pkg-config --exists --silence-errors xcb-icccm '>=' 0.28.9
bash-4.2$ echo $?
1
bash-4.2$ /bin/pkg-config --version xcb-icccm
0.27.1
bash-4.2$ /bin/pkg-config --libs xcb-icccm
-lxcb-icccm -lxcb

echoing $? gives you the result of the last command, 0 is "success" on unix-like OSes, non-zero is fail. Something odd is happening in that test.

If you were looking to install this library on RHEL7 the package name you need is xcb-util-wm-devel. Unfortunately that doesn't help in this case.

mschilling

@jrb1 Using the latest version of RHEL7, I had this issue and found that I had to install xcb-util-wm-devel before installing other xcb* libraries. I tested this by removing xcb-util-wm-devel and xcb-util-wm then re-installing just xcb-util-wm-devel and re-configuring. There seems to be a bug in RHEL7 with the way this it is packaged.

Thank you for your post, you helped me fix my issue, along with @SeanMurphy_6 and @ludek-vodicka posts.

JonathonM

This thread helped me immensely. I found on my CentOS 7 system, I also had to install libxkbcommon-x11-devel.
Hope this helps someone.