[PyQt] qgraphicsitem not cleared before paint(...) ?

[Mads]

Hi,

I'm trying to implement a selection marker so the user can see the
selected area in a QGraphicsView. The selection is drawed from a
mousePressEvent(..) until a mouseReleaseEvent(..). However the
QGraphicsItem isn't always cleared before the next selection? Is there
a flush() or something else I need to call?

I have attached the code. The following link points to an image
showing the selections not being cleared:
http://img263.imageshack.us/img263/6339/marker.png.

Thanks!

Best regards,
Mads

import sys, math
from PyQt4.QtGui import *
from PyQt4.QtCore import *


class SelectionMarker(QGraphicsItem):

	def __init__(self, parent=None):
		super(SelectionMarker, self).__init__(parent)
		self.clearSelection()

	def boundingRect(self):
		return self.bRect

	def clearSelection(self):
		self.bRect = QRectF(0,0,0,0)
		self.update()

	def paintSelection(self, c1, c2): # Scene coords
		w = qAbs(c1.x()-c2.x())
		h = qAbs(c1.y()-c2.y())

		centerPosX = min(c1.x(), c2.x())+w/2.0
		centerPosY = min(c1.y(), c2.y())+h/2.0
		self.setPos( QPointF(centerPosX, centerPosY) )

		topLeft = self.mapFromScene( QPointF( min(c1.x(), c2.x()), min(c1.y(), c2.y()) ) )
		self.bRect = QRectF( topLeft, QSizeF(w, h) )
		
		self.update()	

	def paint(self,  painter=None, qStyleOptionGraphicsItem=None, qWidget=None):
		painter.setOpacity(0.5)
		painter.fillRect(self.bRect, QBrush(Qt.blue))
		painter.drawRect(self.bRect)



class MarkerWidget(QGraphicsView):

	
	def __init__(self, parent=None):
		super(MarkerWidget, self).__init__(parent)

		self.scene = QGraphicsScene(self)

		self.cm = SelectionMarker()
		self.scene.addItem(self.cm)

		self.setScene(self.scene)

		self.clickedPos = None

	def mousePressEvent(self, event):
		self.clickedPos = QPointF(event.pos())

	def mouseReleaseEvent(self, event):
		self.clickedPos = None
		self.cm.clearSelection()

	def mouseMoveEvent(self, event):
		if self.clickedPos:
			p1 = self.mapToScene( QPoint(self.clickedPos.x(), self.clickedPos.y()) )
			p2 = self.mapToScene( QPoint(event.x(), event.y()) )
			self.cm.paintSelection(p1, p2)
			
	def drawBackground(self,painter, qRectf):
		sceneRect = self.sceneRect()
		painter.drawRect(sceneRect)


if __name__ == "__main__":
	app = QApplication(sys.argv)

	m = MarkerWidget()
	m.show()
	app.exec_()


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