Expanded client area in QMainWindow

[hexo]

I want my application to occupy the entire available screen (including the titlebar area). Normally I am able to achive this using ExpandedClientAreaHint and NoTitleBarBackgroundHint window flags like the following minimal example:

#include <QApplication>
#include <QPainter>
#include <QMainWindow>

class MyWidget : public QWidget
{
public:
    MyWidget(QWidget* parent=nullptr) : QWidget(parent) {}

    void paintEvent(QPaintEvent* event) override
    {
        QPainter painter(this);
        painter.fillRect(rect(), Qt::blue);
    }
};

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

    MyWidget* my_widget = new MyWidget();

    my_widget->setWindowFlag(Qt::ExpandedClientAreaHint, true);
    my_widget->setWindowFlag(Qt::NoTitleBarBackgroundHint, true);
    my_widget->show();

    return a.exec();
}

Which looks like this:

However, when I use a QMainWindow as the top level window of the application, the titlebar background is still rendered. Here is a minimal example:

#include <QApplication>
#include <QPainter>
#include <QMainWindow>

class MyWidget : public QWidget
{
public:
    MyWidget(QWidget* parent=nullptr) : QWidget(parent) {}

    void paintEvent(QPaintEvent* event) override
    {
        QPainter painter(this);
        painter.fillRect(rect(), Qt::blue);
    }
};

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

    MyWidget* my_widget = new MyWidget();

    QMainWindow window;
    window.setWindowFlag(Qt::ExpandedClientAreaHint, true);
    window.setWindowFlag(Qt::NoTitleBarBackgroundHint, true);
    window.setCentralWidget(my_widget);
    window.show();

    return a.exec();
}

and here is how it looks:

How can I achieve the original look while using QMainWindow?

This is on Qt 6.9.0 on MacOS.

[Pl45m4]

@hexo said in Expanded client area in QMainWindow:

How can I achieve the original look while using QMainWindow?

What's the point for QMainWindow then if you don't need title bars and so on?
QMainWindow is just an enhanced version of QWidget.

[hexo]

@Pl45m4 I want to have MacOS's integrated menubar (the one that is integrated with the system menubar) but I don't want the application titlebar.

[StudentScripter]

@hexo Not really possible with qt... i tried too for way to long. There is a frameless window example that goes into this direction but than u loose the ability for good docking of the window.

[hexo]

@StudentScripter I used to be able to do this using custom macos-specific code (see https://github.com/ahrm/sioyek/pull/1015) but it has stopped working in recent Qt versions (I think after 6.8 but I am not 100% sure).