Qt - cross platform behaviour - c++

Question

I am trying to deploy a cross platform Qt application written in c++. It works fine on my Ubuntu Linux but when I run it on Windows the application's main window's position gets set on the very top left point of the screen with the upper frame (that holds the minimize, maximize, close buttons) missing.
That is it until i resize the main window (in this case making the width smaller from the right). When this happens the upper frame and the control buttons appear as in the visualization I provided.
Note: I've removed all widgets on the app so they do not аppear as a distraction.
Note2: It appears the maximize button is disabled, which is not the case inside Ubuntu. I have not set any window flags.
How do i visualize the upper frame at the very start of the application without the need to resize the window. I understand its an OS specific behaviour. Setting the main window's geometry with a starting point with a higher y value does NOT help. It still pops at the very top left of the screen.

Answer 1

try to use QWidget::move to set the Window position after setGeometry.
If the widget is a window, the position is that of the widget on the
desktop, including its frame.

Answer 2

You ask a question about cross-platform UI code, and then you don't show the full code. Please show the full code.
The one line of code you do show does something in the wrong way: if you want to maximize a window, call the appropriate function, instead of setting its absolute size that you think shows the window maximized. Windows, their decorations and their placement are very very platform specific, and you should prefer their cross-platform abstractions over trying to do them yourself.
Concretely: the window positioning handles the decorations (title bar) differently on Windows and on Ubuntu. There is absolutely nothing you can do about it except not position your windows absolutely like this.

Answer 3

In the MainWindow constructor at the end this->setGeometry(0, 0, 1336, 600);
That's the problem. setGeometry deals with the geometry of the client area. This is well documented. You should use move to change the position of the widget frame. To set the size of the frame requires the knowledge of the frame's incremental width and height:
bool setWidgetFrameGeometry(QWidget *w, const QRect &r) {
auto frame = w->frameGeometry().size();
auto client = w->size();
auto delta = frame - client;
auto maxDelta = 128;
if (delta.width() > 0 && delta.width() < maxDelta
&& delta.height() > 0 && delta.height() < maxDelta) {
w->move(r.topLeft());
w->resize(r.size() - delta);
return true;
}
return false;
}
The call may need to be deferred to when the event loop had a chance to run:
auto setter = [this]{ return setWidgetFrameGeometry(this, {0,0,1336,600}); };
if (!setter())
QTimer::singleShot(0, this, setter);