Qt5 developed app doesn't display correctly using Cinnamon desktop in VirtualBox

[te777]

Ctrl+Alt+F1, login, sudo service sddm stop (or lightdm, depending what your system is using), X &, Ctrl+Alt+F1, DISPLAY=:0 yourapp

I had stop mdm service. After entering "X &" then screen is just blank. Then if I choose Ctrl+Alt+F1 it says "Loading extension GLX" and just sits there.

Edit: I then just hit Return and got prompt. Then cd to my app directory, then DISPLAY=:0 ./myapp. It says failed to load magic3 and vboxvideo.

[wysota]

Does Alt+F7 show a gray screen with a cursor?

You can also try putting the full path to your application in ~/.xinitrc and restart your desktop session as usual. This should launch your app instead of DE. Just remember to remove the file afterwards (using the console) so that next time you start X your desktop gets loaded.

[te777]

Alt+F7 doesn't show anything. I guess it can't load some drivers out of a display manager, particularly vboxvideo, in VirtualBox. But my app works fine in other desktops, but not Cinnamon. I guess that tells me it's either a Cinnamon or VirtualBox problem. Seems like the problem started with VBox 4.3.18. I'm using VBox 5.0.0 RC2 now.

[wysota]

Alt+F7 doesn't show anything. I guess it can't load some drivers out of a display manager, particularly vboxvideo, in VirtualBox. But my app works fine in other desktops, but not Cinnamon. I guess that tells me it's either a Cinnamon or VirtualBox problem. Seems like the problem started with VBox 4.3.18. I'm using VBox 5.0.0 RC2 now.

As far as I understand, you have only tested your app with a single Cinnamon installation. I don't think that's enough to assume Cinnamon is to blame. Applications usually don't care about desktop environments they run in.

[te777]

I've tried Cinnamon with Ubuntu, Linux Mint and Debian, all with the same problem. The problem doesn't occur in Unity Ubuntu, Linux Mint Xfce or Debian Xfce. And I've tested on other distros as well, including: Fedora 18, openSuse 12.3, and Mageia 2, with no problems. My gut tells me it's a VirtualBox or Cinnamon problem, or possibly even a Qt problem. One of those 3. I've posted bug reports with those 3.

[te777]

Update: I tried my app with the latest Fedora (Xfce) and Mageia (gnome). The Fedora had no problems, but the Mageia had the problem with gnome desktop. I installed the Xfce desktop on Mageia and the problem didn't happen. Just in case someone is following this thread.

[wysota]

I still think you are looking in a wrong place. The desktop is not a problem. The configuration is.

[te777]

What do you mean by configuration? Settings in design mode for the app? Or problems with the libs deployed with the apps? I've tried several desktops in Mageia with the following results:

Desktop Problems

KDE No
Mate No
Openbox No
LXDE No
Xfce No
Gnome Yes
Gnome Classic Yes
Cinnamon Yes

The common factor seems to be VirtualBox. I've heard on the web that VBox doesn't do a good job with OpenGL drivers or display management. But if I can change the design of my app or how it is deployed to alleviate the problem, I haven't given up on that yet. Just at a roadblock here with that. Any suggestions on the configuration issue?

[Infinity]

For your tests you can also play around with some environment variables:
XDG_CURRENT_DESKTOP: Used by Qt to identify the desktop environment (KDE, gnome, cinnamon, ...).
QT_STYLE_OVERRIDE: Sets the Qt style to be used (breeze, oxygen, gtk, ...) independent from the recognized desktop environment. (See also anda_skoa's last post.)

Are other Qt 5 applications also affected by the bug (kwrite, konsole, systemsettings5, smplayer, ...)? If not, the problem is likely just somewhere in your specific application.
(When testing these applications, check whether the version you are using is already ported to Qt 5!)

[te777]

A very important fact is that I loaded Linux Mint Cinnamon into VMWare Player with 3D acceleration, and the problem doesn't occur. It only occurs in the desktops (Cinnamon and Gnome) with 3D acceleration in VBox. Those 2 desktops don't have any problems when 3D acceleration is disabled in VBox.

[Infinity]

Then don't use 3D acceleration with Cinnamon/Gnome in VirtualBox if this setup doesn't work.

Did you test other applications, just to be sure that the problem doesn't come from your own app?

What happens if you set the style to fusion using the mentioned environment variable?

You can try to get a newer version of Cinnamon/Gnome, VirtualBox, or Qt. (Maybe the problem is already fixed.)

[te777]

I've tested using the latest Cinnamon/Gnome, Vbox, and Qt. I was just trying fix a problem when my app gets downloaded from the web and the user has his/her system in VBox. The easiest thing I guess is to tell users on my download page just to disable 3D acceleration in VBox if they want to get my app to display properly. But that's not a solution, it's a stop-gap measure, a rough workaround. Advising to not use 3D acceleration in VBox isn't a real solution, especially since without 3D in VBox the Linux guest video is slow and lagging. But that's what I'll have to do until a real solution is found.

[wysota]

What do you mean by configuration?

Each Linux distribution has different maintainers who configure their distros differently. KDE installed on Linux Mint will be configured differently than KDE installed on Fedora or Debian. Freetype (responsible for font rendering) might be configured differently on Ubuntu and on Arch Linux. Fontconfig (responsible for font matching) might be configured differently on different systems. Each desktop environment might provide different overrides to many of the settings which are different too.

The common factor seems to be VirtualBox. I've heard on the web that VBox doesn't do a good job with OpenGL drivers or display management. But if I can change the design of my app or how it is deployed to alleviate the problem, I haven't given up on that yet. Just at a roadblock here with that. Any suggestions on the configuration issue?

I'm wondering whether someone else tested Qt apps on the same combinations as you did and had similar results. I understand that examples that come with Qt experience the same problems as your application, is that correct?

[te777]

I think the problem with my app is that it passes so many widgets as parameters to the output procedure and then the app asks the OS which asks the video drivers to display them all at one time. I think different desktops get confused with all those widgets to display at one time, i.e., the video driver's response to such a request. I haven't tested the Qt examples yet. I wouldn't think they have a similar design as mine.

[wysota]

I think the problem with my app is that it passes so many widgets as parameters to the output procedure and then the app asks the OS which asks the video drivers to display them all at one time. I think different desktops get confused with all those widgets to display at one time, i.e., the video driver's response to such a request.

No, that's silly. Desktops don't draw your applications, the apps do it by themselves, the compositor can at most receive a single bitmap with the whole window already rendered to it. And why would it garble text but not anything else?

I haven't tested the Qt examples yet.

That's the first thing you should have done.

[te777]

Can you suggest any Qt examples to compile and test with Linux distros in VirtualBox? By the way, I loaded Mageia in VMWare Player and it didn't have a problem with my app using Gnome. Nor did Ubuntu with the Gnome flashback desktop in VirtualBox. Cinnamon doesn't have a problem with 3D acceleration in VMWare Player either.

[wysota]

Can you suggest any Qt examples to compile and test with Linux distros in VirtualBox?

Any that displays text in QTextEdit