qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""

RobertB

Trying to compile a QtWidgets application in docker, statically, using Qt 5.15.0.

My application:

./helloworld
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""

In my docker container I seem to be missing libQt5XcbQpa.a

I configure Qt5 like this:

./configure --prefix=/usr -platform linux-g++-64 -opensource -confirm-license -release -static -no-avx \
    -opengl desktop -qpa xcb -system-freetype -fontconfig -glib \
    -no-dbus -no-openssl -no-sql-sqlite -no-use-gold-linker \
    -qt-harfbuzz -qt-libjpeg -qt-libpng -qt-pcre -qt-zlib \
    -skip qt3d -skip qtandroidextras -skip qtcanvas3d -skip qtcharts -skip qtconnectivity -skip qtdatavis3d \
    -skip qtdoc -skip qtquickcontrols -skip qtquickcontrols2 -skip qtspeech  -skip qtgamepad \
    -skip qtlocation -skip qtmacextras -skip qtnetworkauth -skip qtpurchasing -optimize-size \
    -skip qtscript -skip qtscxml -skip qtsensors -skip qtserialbus -skip qtserialport -skip qtspeech -skip qttools \
    -skip qtvirtualkeyboard -skip qtwayland -skip qtwebchannel -skip qtwebengine -skip qtwebview \
    -skip qtwinextras -skip qtx11extras -skip gamepad -skip serialbus -skip location -skip webengine \
    -skip qtdeclarative -skip qtmultimedia  \
    -no-feature-cups -no-feature-ftp -no-feature-pdf -no-feature-animation \
    -nomake examples -nomake tests -nomake tools

Result:

Features used by QPA backends:
  evdev .................................. yes
  libinput ............................... no
  INTEGRITY HID .......................... no
  mtdev .................................. no
  tslib .................................. no
  xkbcommon .............................. yes
  X11 specific:
    XLib ................................. no
    XCB Xlib ............................. no
    EGL on X11 ........................... no
    xkbcommon-x11 ........................ no
QPA backends:
  DirectFB ............................... no
  EGLFS .................................. yes
  EGLFS details:
    EGLFS OpenWFD ........................ no
    EGLFS i.Mx6 .......................... no
    EGLFS i.Mx6 Wayland .................. no
    EGLFS RCAR ........................... no
    EGLFS EGLDevice ...................... no
    EGLFS GBM ............................ no
    EGLFS VSP2 ........................... no
    EGLFS Mali ........................... no
    EGLFS Raspberry Pi ................... no
    EGLFS X11 ............................ no
  LinuxFB ................................ yes
  VNC .................................... yes

question 1: Does this look OK?

question 2: How do I get libQt5XcbQpa ? Assuming that this produces my application's error.

CMake also notices Qt5XcbQpa is absent:

find_library(Qt5XcbQpa_LIBRARY Qt5XcbQpa PATHS REQUIRED)

CMake Error:

CMake Error at CMakeLists.txt:74 (find_library):
  Could not find Qt5XcbQpa_LIBRARY using the following names: Qt5XcbQpa

RobertB

This post is deleted!

RobertB

I was able to get rid of the error by installing a lot of xcb libraries statically; Starting from:

All of them (or almost?) can be compiled like:

CFLAGS='-fPIC' CXXFLAGS='-fPIC' ./autogen.sh --disable-shared --enable-static && \
make -j4
make install

At which point you get the necessary xcb .a libs in /usr/local/. Find the right version for each. Yes, it's a big pain.

RobertB

When I try to compile my application I now get:

/usr/local/lib/libxcb-image.a(xcb_image.o): In function `xcb_create_pixmap_from_bitmap_data':
xcb_image.c:(.text+0x1c69): undefined reference to `xcb_aux_create_gc'
collect2: error: ld returned 1 exit status
CMakeFiles/hello2.dir/build.make:310: recipe for target 'hello2' failed
make[2]: *** [hello2] Error 1
CMakeFiles/Makefile2:94: recipe for target 'CMakeFiles/hello2.dir/all' failed
make[1]: *** [CMakeFiles/hello2.dir/all] Error 2
Makefile:102: recipe for target 'all' failed

I've made an issue here: https://bugreports.qt.io/browse/QTBUG-86287

TL;DR: If you get "Could not find the Qt platform plugin "xcb"" then make sure that you have libQt5XcbQpa.a or libQt5XcbQpa.so, if that's not the case, you should compile the required xcb libraries and recompile Qt.