Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display

glamis

I have successfully cross-compiled Qt5.15.0 with HW accelerated OpenGL (eglfs) so that Qt apps can run without x11. I know that I was able to cross-compile and install qt5.15.0 successfully on pi0 because I am able to cross-compile and deploy remotely non GUI application from QtCreator.

However when I run GUI application (for example qopenglwidget example project that comes with qt source code), I get the following error:

qt.qpa.screen: QXcbConnection: Could not connect to display 
Could not connect to any X display.

As the application compiled without any error I assume that the problem comes error while linking to some dynamic library. Has any had similar issues and does anyone know how to fix this ? The following observation may be useful for answering my query

After installing qt5 library I have updated ldconfig by running:

echo /usr/local/qt5pi/lib | sudo tee /etc/ld.so.conf.d/qt5pi.conf
sudo ldconfig

When configuring Qt5 for install I had put the option -opengl option and I had obtained the following options (only relevant ones shown here) :

Desktop OpenGL ....................... no
OpenGL ES 2.0 ........................ yes

EGLFS .................................. yes
  EGLFS Raspberry Pi ................... yes

X11 specific:
  XLib ................................. no
  XCB Xlib ............................. no
  EGL on X11 ........................... no
  xkbcommon-x11 ........................ no

Raspberry Pi zero W is running : Raspbian Buster (Linux kernel 5.

glamis

@sierdzio said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

@glamis said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

How can I force it to use my version of Qt5 ?

Set the LD path before running (does not require recompilation):
export LD_LIBRARY_PATH=/path/to/your/qt
./yourAppBinary
Or you can link with rpath (does require recompilation).

Thanks for the suggestion. Modifying LD_LIBRARY_PATH did indeed work. Addiotionaly I had to add the currect user to video group (and login/logout to apply changes):

usermod -aG video $USER

I will recompile with -rpath option to fix this issue permanently.

sierdzio

are you running with your Qt or the one built-into Raspbian (check with ldd)
you can force correct platform plugin using command line switch: ./yourAppBinary -platform eglfs

glamis

@sierdzio said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

ldd

Thanks for the suggestion. Indeed the application is using the built-in qt5 and not rhe one I used:

dietpi@pifotoframe:~$ ldd qopenglwidget 
	/usr/lib/arm-linux-gnueabihf/libarmmem-${PLATFORM}.so => /usr/lib/arm-linux-gnueabihf/libarmmem-v6l.so (0xb6f95000)
	libQt5Widgets.so.5 => /usr/lib/arm-linux-gnueabihf/libQt5Widgets.so.5 (0xb6a39000)
	libQt5Gui.so.5 => /usr/lib/arm-linux-gnueabihf/libQt5Gui.so.5 (0xb65b9000)
	libQt5Core.so.5 => /usr/lib/arm-linux-gnueabihf/libQt5Core.so.5 (0xb613f000)
	libGLESv2.so => /opt/vc/lib/libGLESv2.so (0xb611a000)
	libpthread.so.0 => /lib/arm-linux-gnueabihf/libpthread.so.0 (0xb60f0000)
	libstdc++.so.6 => /usr/lib/arm-linux-gnueabihf/libstdc++.so.6 (0xb5fa9000)
	libm.so.6 => /lib/arm-linux-gnueabihf/libm.so.6 (0xb5f27000)
	libgcc_s.so.1 => /lib/arm-linux-gnueabihf/libgcc_s.so.1 (0xb5efa000)
	libc.so.6 => /lib/arm-linux-gnueabihf/libc.so.6 (0xb5dac000)
	/lib/ld-linux-armhf.so.3 (0xb6fa8000)
	libpng16.so.16 => /usr/lib/arm-linux-gnueabihf/libpng16.so.16 (0xb5d70000)
	libharfbuzz.so.0 => /usr/lib/arm-linux-gnueabihf/libharfbuzz.so.0 (0xb5c72000)
	libz.so.1 => /lib/arm-linux-gnueabihf/libz.so.1 (0xb5c47000)
	libatomic.so.1 => /usr/lib/arm-linux-gnueabihf/libatomic.so.1 (0xb5c2e000)
	libicui18n.so.63 => /usr/lib/arm-linux-gnueabihf/libicui18n.so.63 (0xb59e0000)
	libicuuc.so.63 => /usr/lib/arm-linux-gnueabihf/libicuuc.so.63 (0xb585a000)
	libpcre2-16.so.0 => /usr/lib/arm-linux-gnueabihf/libpcre2-16.so.0 (0xb57de000)
	libdouble-conversion.so.1 => /usr/lib/arm-linux-gnueabihf/libdouble-conversion.so.1 (0xb57ba000)
	libdl.so.2 => /lib/arm-linux-gnueabihf/libdl.so.2 (0xb57a7000)
	libglib-2.0.so.0 => /usr/lib/arm-linux-gnueabihf/libglib-2.0.so.0 (0xb5697000)
	libEGL.so => /opt/vc/lib/libEGL.so (0xb565e000)
	libbcm_host.so => /opt/vc/lib/libbcm_host.so (0xb5634000)
	libvchiq_arm.so => /opt/vc/lib/libvchiq_arm.so (0xb561e000)
	libvcos.so => /opt/vc/lib/libvcos.so (0xb5605000)
	librt.so.1 => /lib/arm-linux-gnueabihf/librt.so.1 (0xb55ee000)
	libfreetype.so.6 => /usr/lib/arm-linux-gnueabihf/libfreetype.so.6 (0xb554b000)
	libgraphite2.so.3 => /usr/lib/arm-linux-gnueabihf/libgraphite2.so.3 (0xb551a000)
	libicudata.so.63 => /usr/lib/arm-linux-gnueabihf/libicudata.so.63 (0xb3b1c000)
	libpcre.so.3 => /lib/arm-linux-gnueabihf/libpcre.so.3 (0xb3aa5000)

How can I force it to use my version of Qt5 ?

I have already tried

./yourAppBinary -platform eglfs

But I'm getting the following error :

dietpi@pifotoframe:~$ ./qopenglwidget -platform eglfs
Could not open display
Aborted

sierdzio

@glamis said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

How can I force it to use my version of Qt5 ?

Set the LD path before running (does not require recompilation):

export LD_LIBRARY_PATH=/path/to/your/qt
./yourAppBinary

Or you can link with rpath (does require recompilation).

glamis

@sierdzio said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

@glamis said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

How can I force it to use my version of Qt5 ?

Set the LD path before running (does not require recompilation):
export LD_LIBRARY_PATH=/path/to/your/qt
./yourAppBinary
Or you can link with rpath (does require recompilation).

Thanks for the suggestion. Modifying LD_LIBRARY_PATH did indeed work. Addiotionaly I had to add the currect user to video group (and login/logout to apply changes):

usermod -aG video $USER

I will recompile with -rpath option to fix this issue permanently.

Pablo J. Rogina

@glamis said in Qt5 with OpenGL (on Raspberry Pi 0) getting error QXcbConnection: Could not connect to display Could not connect to any X display:

did indeed work

great, please don't forget to mark your post as solved!