WLX Plugin webengine_qt Shared OpenGL Contexts needed

[advice2020]

Debian based distro / GTK based DE
DC 1.2.0 alpha QT6.4.2 Standalone Version
Revision 11938 / Commit 8fd3f8780
Lazarus 3.6.0.0 / Free Pascal 3.2.2

I had mentioned this in the past that when trying out DC QT6, the WLX plugin webengine_qt QT6 version generated an error preventing the plugin from working. Was never able to figure it out and had hoped that it was just because of the QT6 version I was using at the time. I recently tried newer version QT6.4.2 and noticed that the same error still gets generated.
I was wondering if anyone knew why this error occurs?
The QT5 version of webengine_qt works fine.

---

DC is compiled with QT6.4.2
webengine_qt is compiled with QT6.4.2

I have the specific plugin dependencies installed
build-essential pkg-config qt6-base-dev qt6-webengine-dev
and there are no errors shown in terminal durning the compiling process.

Linking the plugin in Options - Plugins - WLX loads fine

---

When I hit QPP hotkey to show a saved .mhtml file in QPP an error dialog appears
Unhandled exception: EAccessViolation: Access violation

doublecmd.err Shows

Unhandled exception: EAccessViolation: Access violation
  Stack trace:
$$0000000000000 in /usr/lib/x86_64-linux-gnu/libQt6Gui.so.6
$00000000000000 in /lib/x86_64-linux-gnu/libQt6WebEngineCore.so.6
$00000000000000 in /lib/x86_64-linux-gnu/libQt6WebEngineCore.so.6
$00000000000000 in /lib/x86_64-linux-gnu/libQt6WebEngineCore.so.6
$00000000000000 in /lib/x86_64-linux-gnu/libQt6WebEngineCore.so.6

The 0000000 show different numbers for each, was not sure what these mean so did not want to post, if they are safe to post and needed let me know

---

I did a search for "webengine" in my package manager and it says I have the following installed already on my system
I have the following "webengine" libraries installed

libqt6webenginecore6
libqt6webenginecore6-bin
libqt6webengine6-data
libqt6webenginequick6
libqt6webenginequickdelegatesqml6
libqt6webenginewidgets6
qt6-webengine-dev
qt6-webengine-dev-tools
qt6-webchannel-dev

---

The DC error file mentioned
libQt6Gui.so.6
I have this library installed already as well
libQt6Gui6
I know they are not the same file types, so I do not think it matters but it has a "6" at the end
compared to the
libQt6Gui
mentioned in the DC error file

I really like this plugin, again works in QT5, but just want to know that it is going to continue to work in the future when QT6 becomes the standard version of QT used.

If anyone has any idea I can try, please let me know.
Thank You

[j2969719]

does this Debian based distro use systemd?
coredumpctl list does show anything related to doublecmd?

[advice2020]

Would systemd have something to do with how the plugin functions?

[j2969719]

dont think its a systemd issue, its just that systemd has a fancy coredumpctl tool
nwm

[advice2020]

Ahh thank you.
Hmmm still a mystery then.
So it works on Arch based systems when using QT6 DC, but not for Debian based DEs, or at least not for me anyways :)
I wonder, any users using DC QT6 with a Debian based DE where this plugin works for you, if so please mention.
Maybe I will mention this in DC site as well to see if anyone would be able to try this out.
Thank You

[advice2020]

@j2969719
I think this may be a helpful tool to have access to not just for webengine but in general.
I have systemd and I also have fancy coredumpctl tool.
Question for you, how do I use this fancy coredumpctl tool? :)
I tried various commands, here are some of them

coredumpctl -r
Hint: You are currently not seeing messages from other users and the system.
      Users in groups 'adm', 'systemd-journal' can see all messages.
      Pass -q to turn off this notice.
No coredumps found.

coredumpctl info 1908  (which was the PID assigned to DC at the time)
Hint: You are currently not seeing messages from other users and the system.
      Users in groups 'adm', 'systemd-journal' can see all messages.
      Pass -q to turn off this notice.
No coredumps found.

coredumpctl list <path-to-DC-QT6>/doublecmd
Hint: You are currently not seeing messages from other users and the system.
      Users in groups 'adm', 'systemd-journal' can see all messages.
      Pass -q to turn off this notice.
No coredumps found.

None of these seemed to generate anything, so that is why I am here seeking your help. Do you by any chance have any help you can provide maybe in the form of a command or maybe some kind of extra strength laxative?

[advice2020]

@Skif-off
Ohh Skif, I apologize, you do not have to confirm right now if you are busy, but when you get a chance, I saw in other post that you were testing out mpv_alt with QT6, when you have a chance would you be willing to test out the webengine_qt WLX plugin QT6 version also?

I think I remember that you had tried this out in the past and it did not work for you either. I was just wondering if this was still true.

I have a little information generated by gdb to share about this, but was trying to generate as much info as I can about this.

Again only if you have minute to try.
Thank You

[j2969719]

dunno much about debian w/o systemd, always thought that coredumpctl is part of systemd. on arch if something crases then a tarball appears in /var/lib/systemd/coredump and if type coredumpctl list then you can see something like

TIME                          PID  UID  GID SIG     COREFILE EXE                                                           SIZE
Sat 2025-03-22 07:44:52 +03  2206 1000 1000 SIGABRT present  /usr/lib/doublecmd/doublecmd                                 14.6M
...

so you can take eg PID from this table and enter eg
coredumpctl info 2206
or
coredumpctl debug 2206
and see what kind of gibberish it will show

but apparently you either dont have coredumps or the user dosent have enough privileges

[advice2020]

Sorry to bother you but, really like this plugin and cannot imagine it not working when QT6 becomes the standard, so just trying to figure out what this could be.
Trying to generate any information possible to hopefully help narrw this down.

COREDUMPCTL
Strange, I have systemd and coredumpctl and the folder you mention but it does not seem to generate anything when DC error occurs when try to use webengine_qt plugin in DC QT6.
So I guess for now will skip this solution.

DC SITE
I tried asking on DC page if there were any QT6 users who would be willing to try this out but no responses. Most are probably using QT5 and also Windows & Mac are not probably as easy to compile for?

DC OFFICIAL QT6 VERSION
Did not realize there was an official QT6 version available, tested it out recently with this plugin issue, and it still occurs, so probably not a compiling issue on my part.

GDB RESULTS
I was able to get the gdb command to work and here are the results it produced

Qt WebEngine seems to be initialized from a plugin. Please set Qt::AA_ShareOpenGLContexts using QCoreApplication::setAttribute and QSGRendererInterface::OpenGLRhi using QQuickWindow::setGraphicsApi before constructing QGuiApplication.
WebEngineContext used before QtWebEngineCore::initialize() or OpenGL context creation failed.

Thread 1 "doublecmd" received signal SIGSEGV, Segmentation fault.
0x00007ffff6be3fb6 in QOpenGLContext::format() const ()
   from /usr/lib/x86_64-linux-gnu/libQt6Gui.so.6

DOUBLECMD.ERR
As mentioned in original thread above this file always mentions these two items
libQt6Gui.so.6
libQt6WebEngineCore.so.6
which the gdb command results above also mention

PACKAGES/LIBRARIES
I mentioned above the dependencies I have installed.
I also recently installed any qt6 based packages that sounded like they had anything to do with web/internet related actions but no difference

The gdb command results above also mentioned OpenGL items
Here are the dependencies I have installed that contain keyword opengl
All the qt6 = 6.4.2
libqt6openglwidgets6
libqt6opengl6
libqt6opengl6-dev
libopengl0 (1.6.0-1)
libopengl-dev (1.6.0-1)

Not sure if any of this helps to narrow down this issue?
Thanks again

[j2969719]

src.tar.gz

try to replace this file rebuild dc. you can roll back changes with git restore /path/to/file

[Skif-off]

you can roll back changes with git restore /path/to/file

git reset --hard HEAD, sternly and decisively, for the glory of the God Emperor of Man.

[advice2020]

@j2969719
Thank you for providing this but did not work for me.

Not sure if I did something incorrectly?
-I extracted DC source code
-Replaced existing file with this new file provided
-Compiled DC QT6
-Linked webengine QT6
-Same error

doublecmd.err
file shows same style error as it did before

GDB
When I run this that error dialog does not show up, the cursor just spins
gdb in the terminal shows the same exact message that it did the last time (posted above)

If you guys have anything else I can try let me know, I do not mind, I will try any ideas I could.
Thanks again

[j2969719]

Qt WebEngine seems to be initialized from a plugin. Please set Qt::AA_ShareOpenGLContexts using QCoreApplication::setAttribute and QSGRendererInterface::OpenGLRhi using QQuickWindow::setGraphicsApi before constructing QGuiApplication.
WebEngineContext used before QtWebEngineCore::initialize() or OpenGL context creation failed.

is this message also present? is linux installed on bare metal or in a virtual machine/wsl? what video driver is used?

[advice2020]

@j2969719
Thank You
Yes that is the same message I mentioned above that was generated by gdb, that same message still shows up with the new replace file solution you mentioned to try. Test on real Linux machine not virtual/wsl.
Question is, it is the same machine/video/dependencies/etc that the DC QT5 is being run on along with the QT5 version of webengine_qt plugin and that plugin works perfectly.

So would probably have to be something with one of the following?....
-Interaction between Debian and something QT6 (DC / DC plugin related) (because you do not experience in Arch)
-webengine_qt QT6 coding is somehow different then QT5 version (even though both compile fine)
-Some kind of missing QT6 based dependency that the plugin requires to run but not to compile (I tried a bunch of random QT6 dependencies before and could never find anything that fixed it, but again they were just guesses.
-Some kind of missing QT6 based dependency that DC requires to run this plugin but not needed to compile DC itself.
-DC QT6 version itself / how it interacts with this plugin.

To make things less complicated, I would like to be able to just start using DC QT6 only and this plugin is the only thing I do not have a solution for, really enjoy this plugin (better of the two qt web based plugins).
As mentioned I will try anything you can think of, if anything else comes to mind.

Thanks again for continuing to help
I will try to see if I can get anyone else to replicate this behavior.

[j2969719]

forgot to say that to compile dc with that file, use the command ./build.sh qt6 in the root folder with dc sources. the executable file should appear there too.

both versions of this plugin use the same code.