transparent Widget

CodeFreaks

I examined many ways,
But I can't make a transparent tabwidget (In Linux) :

Chris Kawa

It's a 3 step process.

Make the window widget transparent using attribute Qt::WA_TranslucentBackground, which gives you something like in your picture:
Make the tab header transparent. You can do that with stylesheet QTabBar::tab { background: transparent; }
Note that this is styling QTabBar, not QTabWidget.

You can modify the stylesheet to add the borders of the tab back if you like.
Make the tab content transparent. Note that QTabWidget itself doesn't have a background. It's the background of the widget inside it that you need to make transparent. The easiest way to do this is to tell Qt that the paint event takes care of all the painting and it does not need to fill the background with default color i.e. use Qt::WA_OpaquePaintEvent attribute.

So the entire example looks like this:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget* tab_content = new QWidget();
    tab_content->setAttribute(Qt::WA_OpaquePaintEvent); //makes the widget transparent

    QTabWidget* tw = new QTabWidget();
    tw->addTab(tab_content, "Example");
    tw->setStyleSheet("QTabBar::tab { background: transparent; }"); //makes the header transparent

    QWidget w;
    w.setAttribute(Qt::WA_TranslucentBackground); //makes the window transparent
    w.setLayout(new QVBoxLayout());
    w.layout()->addWidget(tw);
    w.show();

    return a.exec();
}

CodeFreaks

@Chris-Kawa
Hi Dear Chris Kawa
The method that you mentioned in previous post helped me a lot.
Thanks a lot.
But I tried to make a semi-transparent canvas (of qwtplot) . The canvas inherit from QFrame. I tried many days but I still can't do that.
A black background will appear instead of parent widget behind it.
QwtPlotCanvas Class Reference

8Observer8

@Chris-Kawa, I tried your code but it does not work on Windows 10 and Qt 5.15.2. Why? Maybe does somebody else know it?

Taytoo

@8Observer8 Were you able to resolve this issue? I'm having weird behavior even though i'm following the instructions, so not sure what am I doing wrong?

8Observer8

@Taytoo I am also waiting for a solution. Maybe someone knows what is the problem in the above example?

How to implement the same behavior as in ScreenToGif to take a screenshot inside a window?

JoeCFD

@Chris-Kawa Your code works nicely on my local computer. But the transparent feature is gone after I copy the executable from my machine to another computer. Any thoughts?

same OS: Ubuntu 22.04
same Qt version: 5.15.3

JoeCFD

@JoeCFD I lied. The desktop is different. One is gnome and another one is lxqt. It could be a qt bug.

Ronel_qtmaster

@JoeCFD you people may find this helpfull
https://github.com/jordanprog86/QtTransparentWindow.git

JoeCFD

@Ronel_qtmaster thanks for your post. Your code is not working on Lubuntu with LXQt desktop as well for Qt5/6. Chris Kawa's test code has the same issue.

The following example works
https://doc.qt.io/qt-5/qtwidgets-widgets-shapedclock-example.html

JoeCFD

@JoeCFD solved the transparency issue in my code with mask. but kind of awkward and unnecessary. Submit a bug report with Chris Kawa's test code here
https://bugreports.qt.io/browse/QTBUG-124722

Ronel_qtmaster

@JoeCFD i think on ubuntu it might depend on the windows manager

JoeCFD

@JoeCFD The ticket is set to Important.

JoeCFD

@JoeCFD My solution with mask for transparency works for LXQt desktop, but not for Gnome Desktop of Ubuntu. Reset of mask regions is wrong sometimes. Added this issue to the bug report.