I am trying to paint on a QPixmap inside a QGraphicsView. The painting works fine, but the QGraphicsView doesn't update it.

Here is some working code:

#!/usr/bin/env python

from PyQt4 import QtCore
from PyQt4 import QtGui

class Canvas(QtGui.QPixmap):
    """ Canvas for drawing"""
    def __init__(self, parent=None):
        QtGui.QPixmap.__init__(self, 64, 64)
        self.parent = parent
        self.imH = 64
        self.imW = 64
        self.fill(QtGui.QColor(0, 255, 255))
        self.color = QtGui.QColor(0, 0, 0)

    def paintEvent(self, point=False):
        if point:
            p = QtGui.QPainter(self)
            p.setPen(QtGui.QPen(self.color, 1, QtCore.Qt.SolidLine))
            p.drawPoints(point)

    def clic(self, mouseX, mouseY):
        self.paintEvent(QtCore.QPoint(mouseX, mouseY))    

class GraphWidget(QtGui.QGraphicsView):
    """ Display, zoom, pan..."""
    def __init__(self):
        QtGui.QGraphicsView.__init__(self)
        self.im = Canvas(self)
        self.imH = self.im.height()
        self.imW = self.im.width()
        self.zoomN = 1            
        self.scene = QtGui.QGraphicsScene(self)
        self.scene.setItemIndexMethod(QtGui.QGraphicsScene.NoIndex)
        self.scene.setSceneRect(0, 0, self.imW, self.imH)
        self.scene.addPixmap(self.im)
        self.setScene(self.scene)
        self.setTransformationAnchor(QtGui.QGraphicsView.AnchorUnderMouse)
        self.setResizeAnchor(QtGui.QGraphicsView.AnchorViewCenter)
        self.setMinimumSize(400, 400)
        self.setWindowTitle("pix")

    def mousePressEvent(self, event):
        if event.buttons() == QtCore.Qt.LeftButton:
            pos = self.mapToScene(event.pos())
            self.im.clic(pos.x(), pos.y())
            #~ self.scene.update(0,0,64,64)
            #~ self.updateScene([QtCore.QRectF(0,0,64,64)])
            self.scene.addPixmap(self.im)
            print('items')
            print(self.scene.items())
        else:
            return QtGui.QGraphicsView.mousePressEvent(self, event)

    def wheelEvent(self, event):
        if event.delta() > 0:
            self.scaleView(2)
        elif event.delta() < 0:
            self.scaleView(0.5)

    def scaleView(self, factor):
        n = self.zoomN * factor
        if n < 1 or n > 16:
            return
        self.zoomN = n
        self.scale(factor, factor)

if __name__ == '__main__':
    import sys
    app = QtGui.QApplication(sys.argv)
    widget = GraphWidget()
    widget.show()
    sys.exit(app.exec_())

The mousePressEvent does some painting on the QPixmap. But the only solution I have found to update the display is to make a new instance (which is not a good solution).

How do I just update it?