PHP script exec() on QT App - errors with Could not load the Qt platform plugin "xcb" in "" even though it was found.

[JonB]

@StrandedFox said in PHP script exec() on QT App - errors with Could not load the Qt platform plugin "xcb" in "" even though it was found.:

loaded library "/home/virtual-tertius/Qt/5.15.2/gcc_64/plugins/xcbglintegrations/libqxcb-glx-integration.so"

@jsulm has beaten me to it (as usual)! I think the above line is telling you it's going for some kind of xcb, but your server application has no xcb/X11/X display accessible to it, hence the final error qt.qpa.xcb: could not connect to display.

You must design/link as a non-UI application for this, and cannot make any calls which demand a UI.

[StrandedFox]

I'm not sure how to proceed from this point.
The application is a procedural portrait generator/editor. It uses discrete drawn assets to compose a whole.
Due to my inexperience with MVCs and design in general, there is some coupling when a portrait is generated with the actual display of the portrait.
Therefore, without DISPLAYING first the portrait, I cannot issue the PNG export...

The generator caught some attention within various communities and I wanted to offer a quick way to test it online without the need to actually download it (and also get my hands on what it means to host a server and some basic html/php).

The idea was to expose to the web-user an html 'generate' button and then send the request in backend, generate the png and then post it for the user to see.

In this case, should I look into webAssembly / javascript and try to compile the project for browsers instead?
I am totally at a loss where to start with this and I lack experience in such matters, but I think this is the only option I have left?

Thank you for your support so far...!

[JonB]

@StrandedFox said in PHP script exec() on QT App - errors with Could not load the Qt platform plugin "xcb" in "" even though it was found.:

Therefore, without DISPLAYING first the portrait, I cannot issue the PNG export...

In a word: are you prepared to look at this and consider changing code to decouple display from export (if it's possible), which is the right way to proceed, or are you not prepared to do that and code must stay as-is?

Expert @lorn-potter might disagree, but I would caution against trying to turn into WebAssembly. In practice there are many limitations on what WASM can cope with in an already-written Qt application, you might do the work only to find something in your app is quite incompatible with moving to a WASM app....

[StrandedFox]

@JonB

Thanks! That bit of information regarding the limitations of WASM calibrated my expectations...
I've given a thought and I guess you're right. I'll go ahead and try to decouple the display from the portrait exporting process.

But, suppose I can now invoke from the CLI ./myApp -genRandPng which should just create a png...
That still isn't enough, right? I somehow need to get rid of the app from starting its GUI modules...?

[jsulm]

@StrandedFox said in PHP script exec() on QT App - errors with Could not load the Qt platform plugin "xcb" in "" even though it was found.:

I somehow need to get rid of the app from starting its GUI modules...?

That's why I suggested to change your app to a console app...

[JonB]

@StrandedFox said in PHP script exec() on QT App - errors with Could not load the Qt platform plugin "xcb" in "" even though it was found.:

I somehow need to get rid of the app from starting its GUI modules...?

That's why you want to change it to a CLI app as @jsulm says. You might start by doing that, then you'll soon find what you're calling calling UI-wise which you're not allowed to do, because you'll get link errors now! Work backward from there.

[StrandedFox]

I have a dull question: how would I go about to strip my project of GUI elements and turn it into a console app?

[jsulm]

@StrandedFox Simplest way: create a standard console app in QtCreator and check the differences.
For example you have to use https://doc.qt.io/qt-5/qcoreapplication.html instead of QApplication.
Also remove "QT += gui" from pro file and add "QT += core" instead.

[JonB]

@StrandedFox
As I said, if you follow @jsulm's advice to change to QCoreApplication and change from QT += gui to QT += core when you then rebuild/relink you'll get a starting overview (from errors) of what you currently use which is going to need to be changed. I'd start from there to get a rapid idea of the size of the task.

[Pablo J. Rogina]

@StrandedFox said in PHP script exec() on QT App - errors with Could not load the Qt platform plugin "xcb" in "" even though it was found.:

I somehow need to get rid of the app from starting its GUI modules...?

At some extent, you may want to have the same only Qt app running as GUI or console given a CLI argument at startup, see this article.
However, that approach won't free you from changing your current Qt app to decouple some GUI parts from the PNG generation parts.