How to smoothing jagged edges on curved lines and diagonals on pyqt4?

Question

I am drawing a line, but how keep the line ‘jag’ free and clean?

This is the code which draws the image above. Here we may notice the image is full of jagged edges.

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys
from PyQt4 import QtGui, QtCore

class Example(QtGui.QWidget):

    def __init__(self):
        super(Example, self).__init__()
        self.initUI()

    def initUI(self):
        self.drawingPanel = DrawingPanel(self)

        verticalLayout = QtGui.QVBoxLayout( self )
        verticalLayout.addWidget( self.drawingPanel )

        self.setLayout( verticalLayout )
        self.resize( 400, 300 )

        self.setWindowTitle('Review')
        self.show()


class DrawingPanel(QtGui.QGraphicsView):

    def __init__( self, parent ):
        super( DrawingPanel, self ).__init__( parent )

        scene = QtGui.QGraphicsScene()
        self.setScene( scene )

        pencil = QtGui.QPen( QtCore.Qt.black, 2, QtCore.Qt.SolidLine )
        self.scene().addLine( QtCore.QLineF(0, 0, 300, 600), pencil )


def main():

    app = QtGui.QApplication( sys.argv )
    ex = Example()
    sys.exit( app.exec_() )


if __name__ == '__main__':
    main()

Here there is a zoom on the image:

Some other questions about it:

1. Smoothing jagged edges without anti-aliasing - Unity3D
2. How to enable anti-aliasing in A-Frame?

Answer 1

You must enable antialiasing in QGraphicsView:

class DrawingPanel(QtGui.QGraphicsView):

    def __init__(self, parent):
        QtGui.QGraphicsView.__init__(self, parent)
        self.setRenderHint(QtGui.QPainter.Antialiasing)
        [...]