Build on Linux: -qt-xcb option?

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.