Cannot Connect to QML Emulation Layer (QML Puppet)

[BGrimaud]

Hi,

I have a fresh install of Qt 6.5.2 with Qt Creator on Ubuntu 23, using the unified Linux online installer.

Whenever I start Qt Design Studio, I get the following error :

Cannot Connect to QML Emulation Layer (QML Puppet)
The executable of the QML emulation layer (QML Puppet) may not be responding. Switching to another kit might help.

If I try to get back to Design mode afterwards, the same error pops up.

I have tried uninstalling and reinstalling Qt as a whole, and reverting to the LTS version of Qt Design Studio.

Every other topic that mentions this issue is a few years old and mentions changing parameters that don't appear in the settings UI anymore.

Any help would be appreciated !

[JKSH]

Hi @BGrimaud, and welcome!

First, try running the QML Puppet from the console, e.g.:

~/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/bin/qml2puppet-4.2.0 --test

What error messages do you see? If it's something about the "xcb plugin", then most likely you're missing a dependency. Try running ldd on libqxcb.so to see if anything is "Not found":

ldd ~/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/libqxcb.so

[BGrimaud]

@JKSH Seems you were correct :

QML debugging is enabled. Only use this in a safe environment.
Info: Starting QML Puppet ((null):0, (null))
Info: Could not load the Qt platform plugin "xcb" in "" even though it was found. ((null):0, (null))
Fatal: This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: wayland, offscreen, minimal, wayland-egl, xcb, linuxfb, minimalegl, vnc, vkkhrdisplay, eglfs.
 ((null):0, (null))

ldd returns :

	linux-vdso.so.1 (0x00007ffed5dfb000)
	libQt6XcbQpa.so.6 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libQt6XcbQpa.so.6 (0x00007f3bda977000)
	libxkbcommon-x11.so.0 => /lib/x86_64-linux-gnu/libxkbcommon-x11.so.0 (0x00007f3bda955000)
	libxkbcommon.so.0 => /lib/x86_64-linux-gnu/libxkbcommon.so.0 (0x00007f3bda90f000)
	libxcb-cursor.so.0 => not found
	libxcb-icccm.so.4 => /lib/x86_64-linux-gnu/libxcb-icccm.so.4 (0x00007f3bda908000)
	libxcb-image.so.0 => /lib/x86_64-linux-gnu/libxcb-image.so.0 (0x00007f3bda900000)
	libxcb-keysyms.so.1 => /lib/x86_64-linux-gnu/libxcb-keysyms.so.1 (0x00007f3bda8fb000)
	libxcb-randr.so.0 => /lib/x86_64-linux-gnu/libxcb-randr.so.0 (0x00007f3bda8e9000)
	libxcb-render-util.so.0 => /lib/x86_64-linux-gnu/libxcb-render-util.so.0 (0x00007f3bda8e2000)
	libxcb-shm.so.0 => /lib/x86_64-linux-gnu/libxcb-shm.so.0 (0x00007f3bda8dd000)
	libxcb-sync.so.1 => /lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007f3bda8d4000)
	libxcb-xfixes.so.0 => /lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007f3bda8c9000)
	libxcb-render.so.0 => /lib/x86_64-linux-gnu/libxcb-render.so.0 (0x00007f3bda8bb000)
	libxcb-shape.so.0 => /lib/x86_64-linux-gnu/libxcb-shape.so.0 (0x00007f3bda8b6000)
	libxcb-xkb.so.1 => /lib/x86_64-linux-gnu/libxcb-xkb.so.1 (0x00007f3bda898000)
	libxcb.so.1 => /lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f3bda86e000)
	libQt6OpenGL.so.6 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libQt6OpenGL.so.6 (0x00007f3bda7cc000)
	libQt6Gui.so.6 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libQt6Gui.so.6 (0x00007f3bd9e00000)
	libGL.so.1 => /lib/x86_64-linux-gnu/libGL.so.1 (0x00007f3bd9d79000)
	libQt6Core.so.6 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libQt6Core.so.6 (0x00007f3bd9600000)
	libX11-xcb.so.1 => /lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007f3bda7c5000)
	libX11.so.6 => /lib/x86_64-linux-gnu/libX11.so.6 (0x00007f3bd94c2000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f3bd9d72000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f3bd9d6d000)
	libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f3bd9200000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f3bd9117000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f3bd9d49000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3bd8e00000)
	libxcb-cursor.so.0 => not found
	libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f3bd8cb9000)
	libgthread-2.0.so.0 => /lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007f3bd9d42000)
	libxcb-util.so.1 => /lib/x86_64-linux-gnu/libxcb-util.so.1 (0x00007f3bd9d39000)
	libXau.so.6 => /lib/x86_64-linux-gnu/libXau.so.6 (0x00007f3bd9d33000)
	libXdmcp.so.6 => /lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f3bd9d29000)
	libEGL.so.1 => /lib/x86_64-linux-gnu/libEGL.so.1 (0x00007f3bd9d16000)
	libfontconfig.so.1 => /lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f3bd9cc8000)
	libQt6DBus.so.6 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libQt6DBus.so.6 (0x00007f3bd9051000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f3bd9caa000)
	libfreetype.so.6 => /lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f3bd8bef000)
	libGLdispatch.so.0 => /lib/x86_64-linux-gnu/libGLdispatch.so.0 (0x00007f3bd8b37000)
	libGLX.so.0 => /lib/x86_64-linux-gnu/libGLX.so.0 (0x00007f3bd9490000)
	libicui18n.so.56 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libicui18n.so.56 (0x00007f3bd8600000)
	libicuuc.so.56 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libicuuc.so.56 (0x00007f3bd8200000)
	libicudata.so.56 => /home/user/Qt/Tools/QtDesignStudio/qt6_design_studio_reduced_version/plugins/platforms/./../../lib/libicudata.so.56 (0x00007f3bd6800000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f3bd9ca1000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f3bdaa32000)
	libpcre2-8.so.0 => /lib/x86_64-linux-gnu/libpcre2-8.so.0 (0x00007f3bd8a9d000)
	libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007f3bd9c8c000)
	libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f3bd9026000)
	libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007f3bd67b2000)
	libpng16.so.16 => /lib/x86_64-linux-gnu/libpng16.so.16 (0x00007f3bd85c8000)
	libbrotlidec.so.1 => /lib/x86_64-linux-gnu/libbrotlidec.so.1 (0x00007f3bd9483000)
	libmd.so.0 => /lib/x86_64-linux-gnu/libmd.so.0 (0x00007f3bd9476000)
	libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f3bd66e2000)
	libbrotlicommon.so.1 => /lib/x86_64-linux-gnu/libbrotlicommon.so.1 (0x00007f3bd66bf000)
	libcap.so.2 => /lib/x86_64-linux-gnu/libcap.so.2 (0x00007f3bd901a000)
	libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f3bd6577000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f3bd6545000)
	libzstd.so.1 => /lib/x86_64-linux-gnu/libzstd.so.1 (0x00007f3bd6491000)
	liblz4.so.1 => /lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f3bd646e000)
	libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f3bd6448000)

I installed libxcb-cursor and the problem is solved, thanks a lot !