Create a popup widget with a native shadow

Question

I'm on KDE Plasma 6.0.2 + Wayland. I need to create a widget that inherits from QWidget with the Qt::Popup window flag set and has a natural shadow (i.e., the shadow is drawn by the window manager). Actually, I could inherit my widget from QMenu (which inherits from QWidget with the Qt::Popup window flag set), but there are a lot of methods I don't need. The problem is that my custom widget (which, once again, is inherited from QWidget with the Qt::Popup window flag set) doesn't have a natural shadow, while QMenu does. And I can't understand why, because they are essentially two similar classes.

Answer 1

Got it. In Plasma 6, the presence of a shadow under the popup widget depends on the current style. For the Breeze style (which is default for Plasma 6), you need to add a dynamic property _KDE_NET_WM_FORCE_SHADOW and set it to true:

class CustomPopup : public QWidget
{
    Q_OBJECT

public:
    explicit CustomPopup(QWidget *parent = nullptr)
        : QWidget(parent, Qt::Popup)
    {
        setProperty("_KDE_NET_WM_FORCE_SHADOW", true);
    }
};

See here for details.