Moving a frameless QDialog with a MouseMoveEvent

So I have a frameless QDialog that I want to be able to move around simply by clicking and dragging it. Given the code below, dragging the dialog always snaps the ve开发者_StackOverflowry top-left (0,0) of the dialog to the mouse. How might I circumvent this, or rather, what might the math be for it?

Standard QDialog with the following basic subclass:

class Main(QtGui.QDialog):
    def __init__(self, args):
        QtGui.QDialog.__init__(self)

    def mouseMoveEvent(self, event):
        super(Main, self).mouseMoveEvent(event)
        if self.leftClick == True: self.moveWindow(event.globalPos())

    def mousePressEvent(self, event):
        super(Main, self).mousePressEvent(event)
        if event.button() == QtCore.Qt.LeftButton:
            self.leftClick = True

    def mouseReleaseEvent(self, event):
        super(Main, self).mouseReleaseEvent(event)
        self.leftClick = False

Instead of event.pos(), try calling event.globalPos(). From the QMouseEvent reference, "If you move the widget as a result of the mouse event, use the global position returned by globalPos() to avoid a shaking motion."

Proposed solution moves Window, but mouse cursor jumps to 0,0 of Window. I wanted mouse cursor to stay on x,y of the Window all the time.

Here is upgraded version of the code [in QT5]:

X=0
X2=8  #!!!!
Y=0
Y2=30 #!!!!
class Main(QtWidgets.QMainWindow):
    leftClick = False #! IMPORTANT

    def __init__(self, parent=None):
        QtWidgets.QWidget.__init__(self, parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

    def mouseMoveEvent(self, event):
        super(Main, self).mouseMoveEvent(event)
        if self.leftClick == True: 
            self.move(event.globalPos().x()-X-X2,event.globalPos().y()-Y-Y2)

    def mousePressEvent(self, event):
        super(Main, self).mousePressEvent(event)
        if event.button() == QtCore.Qt.LeftButton:
            self.leftClick = True
            global X,Y
            X=event.pos().x()
            Y=event.pos().y()

    def mouseReleaseEvent(self, event):
        super(Main, self).mouseReleaseEvent(event)
        self.leftClick = False

For frameless window (made with window.setMask()) I need some constants like X2 and Y2, because "masked" frameless window is a bit smaller than a real framed window. Don't know how to calculate this difference yet.

UP. After long time I've found one critical bug. If you press Left Mouse Button on any pushbutton (just after the application start) and drag the mouse cursor away from that pushbutton, your application will crash, because we refer to nonexistent variable LeftClick. That's why in class Main we need to create LeftClick.