Bad rendering of Qrubberband in QGraphicsScene

Question

I have a bad display for q qrubberband thought the wanted coordinates are ok :

class Viewer(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()

        self.graphicsView = QtWidgets.QGraphicsView()
        self.hbox = QtWidgets.QVBoxLayout()
        self.scene = Scene(self)
        self.splitter = QtWidgets.QSplitter()
        self.splitter.addWidget(self.graphicsView)
        self.widget.setLayout(self.hbox)
        self.setCentralWidget(self.widget)

I load a pixmap in the scene:

def open_picture(self):
        self.scene.setSceneRect(0, 0, self.pixmap.width(), self.pixmap.height())
        self.scene.addPixmap(self.pixmap)                  
        self.graphicsView.setScene(self.scene)              
        self.graphicsView.show()

and I have the scene inheritated from QGraphicsScene mostly tp handle a qrubberband on the scene

class Scene(QtWidgets.QGraphicsScene):

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

    def mousePressEvent(self, event):
        self.originQPoint = event.scenePos()
        self.originQPoint = self.originQPoint.toPoint()
        self.currentQRubberBand = QtWidgets.QRubberBand(QtWidgets.QRubberBand.Rectangle)

    def mouseMoveEvent(self, event):
        self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, event.scenePos().toPoint()).normalized())
        self.currentQRubberBand.show()

    def mouseReleaseEvent(self, event):
        print(self.items)
        self.currentQRubberBand.hide()
        self.currentQRect = self.currentQRubberBand.geometry()
        print(self.currentQRect)

My problem is the rectangle is displaying on the screen of the my laptop but the coordinate are ok (scene coordinate) How can I draw the rubberband in the scene correctly without changing the self.currentQRect values ?

eyllanesc · Accepted Answer · 2017-09-08T12:29:18.013

According to the docs:

QPointF QGraphicsSceneMouseEvent::scenePos() const

Returns the mouse cursor position in scene coordinates.

From the above we can conclude that the point we get is relative to the scene and not to the screen so it is not what we want.

The method to use is screenPos():

QPoint QGraphicsSceneMouseEvent::screenPos() const

Returns the mouse cursor position in screen coordinates.

With the above we obtain the following code:

class Scene(QtWidgets.QGraphicsScene):
    def __init__(self, parent=None):
        super(Scene, self).__init__(parent)

    def mousePressEvent(self, event):
        self.originQPoint = event.screenPos()
        self.currentQRubberBand = QtWidgets.QRubberBand(QtWidgets.QRubberBand.Rectangle)
        self.originCropPoint = event.scenePos()

    def mouseMoveEvent(self, event):
        self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, event.screenPos()))
        self.currentQRubberBand.show()

    def mouseReleaseEvent(self, event):
        self.currentQRubberBand.hide()
        currentQRect = self.currentQRubberBand.geometry()
        self.currentQRect = QtCore.QRect(self.originCropPoint.toPoint(), event.scenePos().toPoint())
        print(self.currentQRect)

Nope , wiyh screenPos I get a qrubberband on the whole screen. scenePos is what I want and I make a then crop impage and it is OK. The pb is the rendering is not following the mouse cusor (?) — Sylvain Page, Sep 08 '17 at 11:58
seems, ok (I reimplented my signal and so on to crop the selection in table etc....). Last pb (:p), The qrubberband is 0% transparent whereas it was transluent before (I cannot see anything under the rubberband rect)... I guess I can fix it in the a dedicated method, but it strange. Anyway thanks a lot for screen and scene position — Sylvain Page, Sep 08 '17 at 19:09

Bad rendering of Qrubberband in QGraphicsScene

1 Answers1