Not able to overload paintEvent() for QMainWindow to display SVG as backround, despite being able to do so for QWidget

[RaisinBread22]

I'm trying to set an SVG as the background for my QMainWindow based application. Previously I was using QWidget for my application, but I switched over to QMainWindow because I needed a status bar. I was able to set an SVG as a background when I was using QWidget by overloading paintEvent(). However, I'm not able to use the same approach for QMainWindow. What gives? I've created an example for both a QMainWindow and QWidget based application below.

from PySide2 import QtCore, QtGui, QtWidgets

class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName("Form")
        Form.resize(400, 300)
        contents = b"<svg width='44' height='12' viewBox='0 0 44 12' xmlns='http://www.w3.org/2000/svg'><path d='M20 12v-2L0 0v10l4 2h16zm18 0l4-2V0L22 10v2h16zM20 0v8L4 0h16zm18 0L22 8V0h16z' fill='#2c2c2c' fill-opacity='0.4' fill-rule='evenodd'/></svg>"
        file = QtCore.QTemporaryFile(Form)
        if file.open():
            file.write(contents)
            file.flush()
            Form.setStyleSheet("""CustomWidget#Form{background-color: #000000;
                                  background-image: url(%s);}""" % file.fileName())
        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        Form.setWindowTitle(QtWidgets.QApplication.translate("Form", "Form", None, -1))


class CustomWidget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(CustomWidget, self).__init__(parent)

    def paintEvent(self, event):

        opt = QtWidgets.QStyleOption()
        opt.init(self)
        painter = QtGui.QPainter(self)
        self.style().drawPrimitive(QtWidgets.QStyle.PE_Widget, opt, painter, self)

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    Form = CustomWidget()
    ui = Ui_Form()
    ui.setupUi(Form)
    Form.show()
    sys.exit(app.exec_())

from PySide2 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)

        contents = b"<svg width='44' height='12' viewBox='0 0 44 12' xmlns='http://www.w3.org/2000/svg'><path d='M20 12v-2L0 0v10l4 2h16zm18 0l4-2V0L22 10v2h16zM20 0v8L4 0h16zm18 0L22 8V0h16z' fill='#2c2c2c' fill-opacity='0.4' fill-rule='evenodd'/></svg>"
        file = QtCore.QTemporaryFile(MainWindow)
        if file.open():
            file.write(contents)
            file.flush()
            MainWindow.setStyleSheet("""CustomWidget#Form{background-color: #000000;
                                  background-image: url(%s);}""" % file.fileName())

        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        MainWindow.setCentralWidget(self.centralwidget)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QtWidgets.QApplication.translate("MainWindow", "MainWindow", None, -1))


class CustomWidget(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(CustomWidget, self).__init__(parent)

    def paintEvent(self, event):

        opt = QtWidgets.QStyleOption()
        opt.init(self)
        painter = QtGui.QPainter(self)
        self.style().drawPrimitive(QtWidgets.QStyle.PE_Widget, opt, painter, self)

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = CustomWidget()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

[mrjj]

Hi
Didn't read the code.
Just wanted to ask.
You are aware of centralWidget() for main window.
Unless you set SVG to that, it will be hidden.

[RaisinBread22]

I tried overloading paintEvent() for the centralwidget() as well, however the SVG still isn't displayed as the background. Here is the code for that attempt:

from PySide2 import QtCore, QtGui, QtWidgets


class CustomWidget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(CustomWidget, self).__init__(parent)

    def paintEvent(self, event):

        opt = QtWidgets.QStyleOption()
        opt.init(self)
        painter = QtGui.QPainter(self)
        self.style().drawPrimitive(QtWidgets.QStyle.PE_Widget, opt, painter, self)

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)



        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
     
        self.centralwidget = CustomWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        MainWindow.setCentralWidget(self.centralwidget)
        contents = b"<svg width='44' height='12' viewBox='0 0 44 12' xmlns='http://www.w3.org/2000/svg'><path d='M20 12v-2L0 0v10l4 2h16zm18 0l4-2V0L22 10v2h16zM20 0v8L4 0h16zm18 0L22 8V0h16z' fill='#2c2c2c' fill-opacity='0.4' fill-rule='evenodd'/></svg>"
        file = QtCore.QTemporaryFile(self.centralwidget)
        if file.open():
            file.write(contents)
            file.flush()
            self.centralwidget.setStyleSheet("""CustomWidget#Form{background-color: #000000;
                                  background-image: url(%s);}""" % file.fileName())
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(QtWidgets.QApplication.translate("MainWindow", "MainWindow", None, -1))




if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

[SGaist]

Hi,

Why are you doing a custom paint event if you are going to set a background image by stylesheet ?

[RaisinBread22]

@SGaist
Thanks for responding.

I initially tried the approach of not overriding paintEvent and using a temporary file to store the svg for the backround-image attribute of the stylesheet. However, I still couldn't get the SVG to display. This post on stackoverflow seems to indicate Pyside2(which I'm using) is a special case that requires the overloading of PaintEvent to display the SVG. This solution worked for QWidget(as shown above) but not for QMainWindow which is weirdly inconsistent. Any idea?

[SGaist]

QMainWindow does a lot of stuff to handle everything it does, therefore depending on what you want to do with it, you should rather customise its central widget.