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_())

alt text

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.