Setting or unsetting the Qt::WindowTransparentForInput flag on the main window causes the window to hide

Lucas64_t

I have an application where you can toggle on a feature to make the main window transparent for inputs. However, while the user holds the Alt-key, then the window can receive inputs again. My problem is that whenever I set or unset the Qt::WindowTransparentForInput flag, the main window sets its visibility to false. I then have to manually turn the visibility back on. It is unfortunately still very much noticable that the window hides for a moment. Does somebody know what causes the window to hide and if there is a way to prevent that?

In the main window constructor I set these flags

setWindowFlag(Qt::FramelessWindowHint, true);
setWindowFlag(Qt::WindowStaysOnTopHint);
setAttribute(Qt::WA_TranslucentBackground, true);

This is the function which sets or unsets the Qt::WindowTransparentForInput flag. When the feature is enabled, this function is called every 100 miliseconds, based on a QTimer.

void MainWindow::checkHoldKeyState()
{
    bool held = qApp->queryKeyboardModifiers().testFlag(Qt::AltModifier); // is the Alt-key held?
    Qt::WindowFlags flags = windowFlags();
    bool transparent = flags & Qt::WindowTransparentForInput; // is the WindowTransparentForInput flag set?
    if(held == transparent)
    {
        // If the Alt-key is held and the flag is set, remove the flag.
        // If the Alt-key is not held and the flag is not set, apply the flag.
        setWindowFlag(Qt::WindowTransparentForInput, !transparent);
    }

    if(isHidden()) // When the WindowTransparentForInput flag was set or unset, the window always is hidden.
    {
        show(); // Setting the window to visible again causes flickering
    }
}

Lucas64_t

Interestingly this does not affect the visibility of a QDialog which is a direct child of the main window.