[solved] Qt6 and the Save Dialog

[Bogen85]

@ rca

Interesting...

Code: Text  [Select][+][-]

1. $ find /usr/lib64/qt6/plugins/platformthemes -type f
2. /usr/lib64/qt6/plugins/platformthemes/libqgtk3.so
3. /usr/lib64/qt6/plugins/platformthemes/libqxdgdesktopportal.so
4. /usr/lib64/qt6/plugins/platformthemes/libqt6ct.so

Same on both Fedora 37 and AlmaLinux 9.1.

On AlmaLinux 9.1 there is no qgnomeplatform for qt6, only for qt5.
Fedora 37 has both.

I'll need to stick with libqt6ct theming/styling as AlmaLinux 9.x is my primary platform.

I've seen similar threads to this one, but with qt5.
For instance, this one: https://forum.lazarus.freepascal.org/index.php/topic,61582.0.html
Could be a related issue...

In my case the problem is that it stays in the loop, it fails indefinitely when painting the dialog.

Using @dbannon's example and his native Dialogs code the behavior is the same.

Thanks to your code I managed to verify that when using non-native Dialogs, it shows them right away without any delay.
The behavior of the native dialogs has a lot to do with the "platformthemes" installed and used.
...
With that, everything was settled for me.

All the dialogs are displayed, without delay, without any problem if they are native or not.

You are welcome. 
Even though I've not had this delay issue, I've had qt5 and qt6 appearance related issues, and troubleshooting in this thread is helping me through some of those.

Failure to paint when the "how to style the painting" is not available.... Sort of makes sense...

[rca]

I found the solution, disabling QtUseNativeEventLoop in lcl/interfaces/qt6/qtdefines.inc

Code: Pascal  [Select][+][-]

1. {.$DEFINE QtUseNativeEventLoop}

Go back to Build Lazarus and recompile the applications.

Both the Lazarus IDE dialogs, as well as those of applications built for Qt6 now work correctly, without delay, whether they are native or not.

[rca]

I see that the change was made to the main (trunk) branch about three months ago:
"Qt6: all platforms now use Qt native event loop."

https://gitlab.com/freepascal.org/lazarus/lazarus/-/commit/af2916c4bacea0e869e023915dfe8cec9cdd9ae3

Previously QtUseNativeEventLoop was only enabled for MacOSX cocoa 64.

And also in an issue, I read from @Željan Rikalo: https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues/40011#note_1179754793

"Also, try to disable QtUseNativeEventLoop in lcl/interfaces/qt6/qtdefines.inc, maybe that makes problem for you. Here it works ok for lazarus IDE and any app built for Qt6."

[dbannon]

No, I am sorry rca, there is more going on here than it appears.

disabling Qt native event loop does not solve the problem on my test setup.

Davo

[rca]

No, I am sorry rca, there is more going on here than it appears.

disabling Qt native event loop does not solve the problem on my test setup.

Davo

Using fedora 37 and Debian 12 with Gnome Desktop, I just had to disable QtUseNativeEventLoop.

On Debian 12, I had to install qt6-wayland.

Since by default the Gnome desktop and my applications are running on Wayland.


When Starting the Gnome desktop with Xorg (X11), the problem reappears.

[rca]

In X11, In addition to disabling QtUseNativeEventLoop, I fixed it with:

Reading "Qt defines" from https://wiki.freepascal.org/LCL_Defines

Add to Configure "Build Lazarus", the flag -dQT_NATIVE_DIALOGS

Code: Pascal  [Select][+][-]

1. -g -gl -dQT_NATIVE_DIALOGS -O1

The file lcl/interfaces/qt6/qtwsdialogs.pp has two errors:

Code: Pascal  [Select][+][-]

1. qtwsdialogs.pp(472,25) Error: Identifier not found "QFileDialogDontConfirmOverwrite"
2. qtwsdialogs.pp(546,25) Error: Identifier not found "QFileDialogReadOnly"

Change of QFileDialogDontConfirmOverwrite to QFileDialogOptionDontConfirmOverwrite

Change of QFileDialogReadOnly to QFileDialogOptionReadOnly

Rebuild your applications.

[dbannon]

No, I am sorry rca, there is more going on here than it appears.

disabling Qt native event loop does not solve the problem on my test setup.

Davo

Using fedora 37 and Debian 12 with Gnome Desktop, I just had to disable QtUseNativeEventLoop.

On Debian 12, I had to install qt6-wayland.

Since by default the Gnome desktop and my applications are running on Wayland.


When Starting the Gnome desktop with Xorg (X11), the problem reappears.

OK, thats interesting !  My test VM were XFCe and Mate. Be rather funny if we can get it working on Wayland only.

I have trashed those two VMs (disk space) but might, time permitting, rebuild them.

Thanks RCS, you are finding out some valuable stuff here.

Davo

[rca]

This behavior only affects save dialogs that are native to both Qt5 and Qt6:

Parsing the file lazarus/lcl/interfaces/qt6/qtwsdialogs.pp

Inside TQtWSOpenDialog.CreateHandle

Code: Pascal  [Select][+][-]

1. class function TQtWSOpenDialog.CreateHandle(const ACommonDialog: TCommonDialog): THandle;
2.  
3.     {$ifndef QT_NATIVE_DIALOGS}
4.     QFileDialog_setOption(QFileDialogH(FileDialog.Widget),
5.       QFileDialogOptionDontUseNativeDialog, True);
6.     FileDialog.initializePreview(TPreviewFileDialog(ACommonDialog).PreviewFileControl);
7.     {$endif}

But inside TQtWSFileDialog.CreateHandle

Code: Pascal  [Select][+][-]

1. class function TQtWSFileDialog.CreateHandle(const ACommonDialog: TCommonDialog): THandle;
2.  
3.   QFileDialog_setOption(QFileDialogH(FileDialog.Widget),
4.     QFileDialogOptionDontUseNativeDialog, False);

I changed from

Code: Pascal  [Select][+][-]

1.   QFileDialog_setOption(QFileDialogH(FileDialog.Widget),
2.     QFileDialogOptionDontUseNativeDialog, False);

for this

Code: Pascal  [Select][+][-]

1.   {$ifndef QT_NATIVE_DIALOGS}
2.   QFileDialog_setOption(QFileDialogH(FileDialog.Widget),
3.     QFileDialogOptionDontUseNativeDialog, True);
4.   {$endif}

Rebuild Lazarus and recompile your applications.

[dbannon]

Just thought I'd follow up a touch here to mark the release of Ubuntu 23.04.

On Ubuntu 23.04, Gnome (incredibly ugly by the way), using Qt6 6.4.2, problem is still there.

An app built on the above machine with today's Lazarus Main and using a freshly built libQt6pas built from todays Lazarus Main still goes off to never never land when you open a Save Dialog -

• if there is no platform theme set.
• if the platform theme is set to gtk2 or gtk3
• BUT WORKS OK, as it should, if qt6ct is installed and the platform theme is set to qt6ct

So, have to conclude that this problem is not going to go away with newer versions of Qt6.

And I tried rca's tricks too, same result.

Davo

 

[rca]

@Zeljko already fixed this issue. Thank you very much for your excellent work.

Save dialogs now open immediately without any delay.

[zeljko]

Glad to hear that

[dbannon]

No, sorry to bring bad tidings, I still see this on Ubuntu 23.04, Gnome in both Wayland and XOrg sessions. Using todays Lazarus Src.

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.     SaveExport : TSaveDialog;
4. begin
5.     SaveExport := TSaveDialog.Create(self);
6.     SaveExport.DefaultExt := 'md';
7.     SaveExport.InitialDir := '.';
8.     SaveExport.Filename := 'blar';
9.     if SaveExport.Execute then
10.         showmessage(SaveExport.FileName);
11.     SaveExport.Free;
12. end;

Davo

Edit: zeljko, I did not build new libraries, is a rebuild necessary (from 6.2.5) ?
 

[rca]

I built with the lazarus trunk version and with libQt6Pas 6.2.5

On fedora 38 with Gnome 44, work fine in both Wayland and XOrg sessions.

And I can confirm your same results on Ubuntu 23.04 with Gnome 44. (Delay in both sessions)


I have noticed that currently the systems have different version of Qt6:

• Fedora 38, Qt6 has version: 6.5.0
• Ubuntu 23.04, Qt6 has version: 6.4.2

Perhaps it is the reason why despite having the same Gnome 44 it does work on Fedora.

[dbannon]

Yes, rca, that probably makes sense.

Debian has Qt6 6.4.2 in Bullseye Backports, Bookworm and even Sid. To me thats almost certain that bookworm release will be 6.4.2. A later one 'might' appear in backports later on. So, won't really know until then.

Confirmed problem also exists still in Debian Gnome as we'd expect. But, to my surprise, Debian Bookworm KDE does not exhibit the problem ! The same Qt6 6.4.2.  So, are we missing a package that gets pre-installed on KDE ?

Davo

[dbannon]

Ok, as zeljko has introduced some new stuff to both Qt5 and Qt6 (needing, incidentally, new libraries) I thought I'd summarize where we are with this problem using my favorite recently released distros.

Tested against Ubuntu 23.04 and Debian 12 Bookworm (both using Qt5 5.15.8 and Qt6 6.4.2)  using Gnome, KDE, XFCe, Mate, Cinnamon and Budgie

Firstly, on all tested systems, in the Font Dialog, we cannot set the Preview Text Programmatically.

Here is the results using the TSaveDialog with a file name filter set :

Ubuntu
U23.04 - Gnome. Qt5 and Qt5 slow, use qt5ct/qt6ct and its fast. Or install qt6-wayland and Qt6 is fast.
U23.04 - XFCe, Mate, Cinnamon, Budgie.  Qt5 and Qt6 slow, using qt5ct or qt6ct fixes.
U23.04 - KDE Plasma. Qt5 and Qt6 fast out of the box.
.
Debian
12 Bookworm - Gnome. Qt5 and Qt5 slow, use qt5ct/qt6ct fixes. Or install qt6-wayland and Qt6 is fast.
12 Bookworm - KDE Plasma. Qt5 and Qt6 fast out of the box.
12 Bookworm - XFCe, Mate, Cinnamon, Budgie.  Qt5 and Qt6 slow, using qt5ct or qt6ct fixes.

Terms
"using qt5ct or qt6ct fixes" - qt5ct or qt6ct must be installed and app started with the environment variable,eg,  QT_QPA_PLATFORM=qt5ct set. Setting, from with in the qt5ct or qt6ct app, Dialogs=gtk3 will break the fix.

"qt6-wayland" is a package that brings in some 18Meg of dependencies but does fix the TSaveDialog problem on Gnome systems. Does not help on non-Wayland. Its not installed by default as part of Qt6 libraries and is not a dependency of the libQt5/6Pas libraries because its useful only on Gnome. Maybe its worth adding as a dependency ?? Comments ?

Conclusions

• If you know your users will only use Gnome then add qt6-wayland to your app dependencies list, all good.
• If you know your users will only use KDE Plasma, no problems.
• For a general solution, add qt5ct or qt6ct to your dependencies list and in the desktop file start your app with something like "QT_QPA_PLATFORMTHEME=qt5ct  /some/path/myapp".  The user has now lost the opportunity to select a gtk2 or gtk3 theme and if they start you app in some other way, well, bad luck !

Be nice if users of other distributions could add what ever their favorite is, I have attached my test app.

Davo