HighQualityAntialiasing

When drawing a rounded rectangle then applying it as the windows shape using

Code:

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def resizeEvent(self, event):
        pixmap = QtGui.QPixmap(self.size())
        pixmap.fill(QtCore.Qt.transparent)
        painter = QtGui.QPainter(pixmap)
        painter.setBrush(QtCore.Qt.black)
        painter.drawRoundedRect(pixmap.rect(), 8, 8)
        painter.end()
 
        self.setMask(pixmap.mask())

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It comes out very poor quality, and it seems that I should be using OPENGl or is there is a way to have it set to HighQualityAntialiasing

You can set antialiasing modes in the painter. Check the documentation.