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    Unsolved Qt::Popup window in debugger seizes up whole windowing system

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    • Christian Ehrlicher
      Christian Ehrlicher Lifetime Qt Champion last edited by

      Feel free to provide a patch for it...

      Qt has to stay free or it will die.

      JonB 1 Reply Last reply Reply Quote 0
      • JonB
        JonB @Christian Ehrlicher last edited by JonB

        @Christian-Ehrlicher
        I don't know where exactly to look/search for what Qt::Popup does about the next click in Qt code, and @SGaist's mention of "in the xcb backend". I don't have/compile source, so only via woboq. I think I had a look at the time, and gave up when I saw hundreds of uses of Qt::Popup. So if you happen to know either what the behaviour is (X11 for me) of exactly which part of Qt source I should be looking at, please tell! :)

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          iynaur @iynaur last edited by iynaur

          @iynaur But with -platform wayland this issue is gone! Must be xcb platform plugin issue.

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          • Christian Ehrlicher
            Christian Ehrlicher Lifetime Qt Champion last edited by

            I already told somewhere else that 'popup' and debugging doesn't work together. You will likely get the same problems with other gui frameworks.

            Qt has to stay free or it will die.

            JonB 1 Reply Last reply Reply Quote 0
            • JonB
              JonB @Christian Ehrlicher last edited by JonB

              @Christian-Ehrlicher
              Yes, and that is a nightmare for debugging, if you cannot help but have a popup and need to debug while it's on-screen. As I have found, and almost have to give up on debugging my code since a lot happens when this popup is up :(

              I seem to recall in the distant past that this was an issue from e.g. Visual Studio if you had a combo box's drop down visible when you need to break, because in Windows that popup-box-of-choices is a special kind of "top-level desktop window" which blocks all input till the user does next click, and you can't access it or the debugger. Which caused us problems while developing code. I don't remember whether a later version of Windows (or VS) made this issue go away.

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                iynaur @JonB last edited by

                @JonB You can try debug with -platform wayland

                JonB 1 Reply Last reply Reply Quote 0
                • JonB
                  JonB @iynaur last edited by

                  @iynaur said in Qt::Popup window in debugger seizes up whole windowing system:

                  @JonB You can try debug with -platform wayland

                  Now this is totally beyond me! "wayland" means nothing to me. All I know is I have a Ubuntu VM (VirtualBox) running on my Windows 7 host. I believe it uses X11. Maybe that is "xcb", I don't know.

                  In a word, are you saying I have/can try/will work using "wayland"? I cannot test atm....

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                    iynaur @JonB last edited by

                    @JonB Could try this:
                    https://linuxconfig.org/how-to-enable-disable-wayland-on-ubuntu-20-04-desktop
                    and just run your app with
                    ./yourapp -platform wayland
                    in terminal

                    JonB 2 Replies Last reply Reply Quote 1
                    • JonB
                      JonB @iynaur last edited by JonB

                      @iynaur
                      Thank you! Will try tomorrow, if I remember....

                      Though there are comments to the link you reference:

                      I think I have followed this tutorial step by step, but I am still missing the Wayland option in the login menu…

                      Same here. I followed the steps but the only options I see are “Ubuntu” and “Gnome Classic”.

                      Note! Do not forget that the gpu drivers (nvidia, amd or intel) should allow the use of Wayland. If you have proprietary nvidia drivers uninstall them and install nouveau drivers.

                      (Hopefully the last one is not relevant to me.)

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                      • JonB
                        JonB @iynaur last edited by JonB

                        @iynaur , or @ anyone else who knows!
                        Well, I followed those instructions. Wayland was already enabled. I logged in using Wayland on Ubuntu. (Seems fine, all looked much the same as when I use X.) Did the ./yourapp -platform wayland. I get warning

                        Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.

                        so did export QT_QPA_PLATFORM=wayland and ran again. Get same warning, it didn't make any difference. I get

                        qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

                        So I did what I tell everyone else: export QT_DEBUG_PLUGINS=1.

                        It reports finding the metadata for each of the mentioned available platform plugins. Final line:

                        QFactoryLoader::QFactoryLoader() checking directory path "/home/jon/AtH/debug/platforms" ...
qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""

                        Since wayland is not listed among the Available platform plugins I presume this means I am supposed to have/install something to make Qt app run under Wayland? I do not compile Qt, I use the version (5.12) which is supplied with Ubuntu 20.04.

                        So, what am I supposed to do now? Am I supposed to get some Qt support for Wayland from somewhere?

                        Meanwhile I will do some further Googling....

                        UPDATE
                        I come across https://wiki.archlinux.org/index.php/wayland#Qt for Arch stating:

                        To enable Wayland support in Qt 5 or 6, install the qt5-wayland or qt6-wayland package, respectively.

                        So I get I need to install something. But under Ubuntu apt-get install qt5-wayland gets me E: Unable to locate package qt5-wayland, so now what...?

                        UPDATE2
                        OK, so I discover under Ubuntu it has to be

                        apt-get install qtwayland5

                        Sigh :)

                        OK, so now my app does run under Wayland! Yippee!!

                        I will soon try debugging now with Qt::Popup and see if I no longer "hang"!

                        Meanwhile, I don't much like the way it looks under Wayland display manager, compared to GNOME :( For one thing, the fonts look bigger, it looks horrible compared to xcb. Maybe I need to configure Wayland somewhere to alter.....

                        OK, I agree debugging no longer "freezes whole machine" with code Qt::Popup, which is great. But the Wayland layout/look/fonts are so horrible I cannot use this unless I can configure something somehow. Which I'm not getting from Googling? I don't even know that under Wayland app is using the default Fusion style I had under X11? Anyone know what to do to "configure" for Wayland, or is this not possible? Thanks!

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                          iynaur @JonB last edited by

                          @JonB you may use wayland just for debug your app and use your app in xcb mode (xcb mode can run in wayland desktop env). unless you are debugging ui rendering related code.
                          i dont know how to configure wayland ui either.

                          JonB 1 Reply Last reply Reply Quote 1
                          • JonB
                            JonB @iynaur last edited by

                            @iynaur
                            Thanks, yes. I have to switch to that "log onto Wayland Ubuntu" to be able to use it all (I think so, anyway?), I think you're right that you can still run xcb mode for there though, but I don't much like logging in that way. I will keep it for emergency debugging. Shame, but better than nothing!

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