Debian: after upgrading the system the program became unusable. How to approach the problem?

Pl45m4

Might be helpful to read:

https://github.com/githubuser0xFFFF/Qt-Advanced-Docking-System/issues/288

SGaist

@JanuszSB if memory serves well, you can use X application under Wayland. You can try forcing your application to use xcb backend.

JanuszSB

@Pl45m4 Very interesting link, but the solutions suggested there (XDG_SESSION_TYPE=x11, QT_QPA_PLATFORM=xcb) don't work for me.

JanuszSB

@SGaist said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

@JanuszSB if memory serves well, you can use X application under Wayland. You can try forcing your application to use xcb backend.

Yes, this should solve the problem. Unfortunately it is not clear how to do it. As I said above, QT_QPA_PLATFORM=xcb doesn't work for me.

For the time being switching to X at the login time is acceptable, but I will continue to look for a more elegant solution.

Pl45m4

@JanuszSB

On that linked page someone also mention that it might be fixed in Qt6.3+
At least the error message was gone, it I understand this right...
What version are you using? Can you upgrade?

JanuszSB

@Pl45m4 said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

@JanuszSB

On that linked page someone also mention that it might be fixed in Qt6.3+
At least the error message was gone, it I understand this right...
What version are you using? Can you upgrade?

qmake -query QT_VERSION reports 5.15.8 but I installed also qt6-base-dev .

The question "How do I install Qt 6 in Debian Bookworm?" (https://unix.stackexchange.com/questions/752145/how-do-i-install-qt-6-in-debian-bookworm) has practically no answer since 6 months :-(
QT is split on Bookworm into over 20 packages, installing all of them doesn't seem reasonable. I have no idea which of them I really need.
There is an option to install it from https://www.qt.io/download-qt-installer-oss, but I'm afraid of creating a mess by mixing various versions.

SGaist

For the packages you need: look at the modules your application uses and just install those.

The Qt online installer does not mess with your system. It either install Qt in your home folder or in /opt so unless you do some pretty convoluted things, it will have no impact on your system.

JanuszSB

@SGaist said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

For the packages you need: look at the modules your application uses and just install those.

The Qt online installer does not mess with your system. It either install Qt in your home folder or in /opt so unless you do some pretty convoluted things, it will have no impact on your system.

Thanks for the information. Looks like I have some mess already :-(

I prefer to focus now on xcb. I have both
/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so and
/usr/lib/x86_64-linux-gnu/qt6/plugins/platforms/libqxcb.so.

qtchooser reports 7 (!) versions:
4
5
default
qt4-x86_64-linux-gnu
qt4
qt5-x86_64-linux-gnu
qt5

All of them has been installed some time ago just to compile two programs: djview4shapes discussed here and djview4poliqarp (https://github.com/jsbien/djview-poliqarp_fork); they share a lot of code, so it is a little strange that the latter has no problem with opening panels.

QTCreator reports 5.15.8 twice: /usr/lib/qt5/bin/qmake and /usr/lib/x86_64-linux-gnu/qt5/bin/qmake

So the question is: when I write QT_QPA_PLATFORM=xcb on the command line what actually happens? How to check whether the plugin is activated?

I noticed mentions of the platform parameter. Does it work for all programs? Should djview-shapes -platform xcb' work?

ChrisW67

@JanuszSB said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

So the question is: when I write QT_QPA_PLATFORM=xcb on the command line what actually happens? How to check whether the plugin is activated?

QT_QPA_PLATFORM=xcb djview-shapes will start djview-shapes with QT_QPA_PLATFORM in the environment. When QApplication initialises it forces the xcb Qt Platform Abstraction (QPA) plugin where it would normally auto-select Wayland.

If you add QT_DEBUG_PLUGINS you see much more information about plugins found and loaded.
QT_DEBUG_PLUGINS=1 QT_QPA_PLATFORM=xcb djview-shapes

I noticed mentions of the platform parameter. Does it work for all programs?

Yes for anything using QGuiApplication or the QApplication subclass.

JanuszSB

@ChrisW67 said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

If you add QT_DEBUG_PLUGINS you see much more information about plugins found and loaded.
QT_DEBUG_PLUGINS=1 QT_QPA_PLATFORM=xcb djview-shapes

Nothing changed, no output. However if instead of xcb I write some other string then I get an error report.

In https://stackoverflow.com/questions/55731797/custom-plugin-for-qt-is-not-loaded-how-to-debug I found "you apparently have QT to build with debug information". Can it be relevant for my case?

ChrisW67

@JanuszSB I get plugin debug information for both debug and release builds of a small example. For example:

$ ~/Qt/6.6.1/gcc_64/bin/qmake CONFIG+=release

$ make
...

$ file ./simple_example
./simple_example: ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=89d8e1eca37d300fbcfd802cd1f2bb82ce9e708c, for GNU/Linux 3.2.0, not stripped

$ QT_DEBUG_PLUGINS=1 QT_QPA_PLATFORM=xcb ./simple_example 
qt.core.plugin.factoryloader: checking directory path "/home/chrisw/Qt/6.6.1/gcc_64/plugins/platforms" ...
qt.core.plugin.factoryloader: looking at "/home/chrisw/Qt/6.6.1/gcc_64/plugins/platforms/libqminimal.so"
qt.core.plugin.loader: Found metadata in lib /home/chrisw/Qt/6.6.1/gcc_64/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "archlevel": 1,
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 394752
}
...
qt.core.library: "/home/chrisw/Qt/6.6.1/gcc_64/plugins/platforms/libqxcb.so" loaded library
...

I guess your application could be doing something creative to trash the output.

JanuszSB

@ChrisW67 said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

@JanuszSB I get plugin debug information for both debug and release builds of a small example. For example:
$ ~/Qt/6.6.1/gcc_64/bin/qmake CONFIG+=release

What is it for?

$ make
...

$ file ./simple_example
./simple_example: ELF 64-bit LSB pie executable, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=89d8e1eca37d300fbcfd802cd1f2bb82ce9e708c, for GNU/Linux 3.2.0, not stripped

Can you somehow share the program?

$ QT_DEBUG_PLUGINS=1 QT_QPA_PLATFORM=xcb ./simple_example

I guess your application could be doing something creative to trash the output.

The program was written12 years ago, can this be relevant?

SGaist

@JanuszSB can you share your own build ?

Tested on KDE Neon with wayland as backend and it looks like it's working as expected. The widget on the left is a scroll area where widgets are added. It does not do anything special.

JanuszSB

@SGaist said in Debian: after upgrading the system the program became unusable. How to approach the problem?:

@JanuszSB can you share your own build ?

If a Debian package will do, it is available in the repository https://github.com/jsbien/djview4shapes in the Releases. I can also upload somewhere just the binaries.

On the other hand it seems the problem is not reproducible on KDE...

JanuszSB

@SGaist After upgrading yesterday to Debian 11.9, the situation changed slightly. The left panel still doesn't open but QT_DEBUG_PLUGINS=1 produced some output. I uploaded it to
https://github.com/jsbien/djview4shapes/issues/5#issuecomment-1938158253

SGaist

@JanuszSB It's something else, if it was a plugin problem, you wouldn't see the application at all. There's no error in the logs.

JanuszSB

Any idea how to diagnose the problem? BTW, does this forum have a function of mail notification?

ChrisW67

@JanuszSB Your code saves and restores the main window and splitter geometry. Are you absolutely sure you have not just collapsed the left panel of the splitter entirely? This would persist by virtue of the state save/restore.

Find the save configuration and remove/move it sideways before starting the application.
One or more of these locations:

~/.config/djview-poliqarp/djview-poliqarp.conf
~/.config/djview-poliqarp.conf
for D in $(echo $XDG_CONFIG_DIRS | tr ':' ' ') 
do 
  echo $D/djview-poliqarp/djview-poliqarp.conf
  echo $D/djview-poliqarp.conf
done

SGaist

@ChrisW67 Interesting take, I didn't think of that one !