The problem of paint() function in Qgraphicsitem?

[tom_1]

I want to make a function of drawing image content after pressing the mouse. You can draw color and transparent channels

1:The painter parameter in the paint() function can only display images, but not the contents of the drawing process. So I created a new painter to draw the process.

2:The whole process of the mouse drawing is very slow and stuck

3:image size: 10000 * 10000

python code:

# show image
        painter.drawPixmap(0, 0, self.__display)
 
        # draw image
        self.painter = QPainter()
 
        self.painter.begin(self.__transparent)
        radialGrad = QRadialGradient(self.pos, 50)
        radialGrad.setColorAt(0, QColor(255, 0, 255, 255))
        radialGrad.setColorAt(1, QColor(255, 0, 255, 0))
        brush = QBrush(radialGrad)
        self.painter.setBrush(brush)
        self.painter.setPen(Qt.NoPen)
        self.painter.drawEllipse(self.pos, 50, 50)
        self.painter.end()
 
        self.painter.begin(self.__display)
        if self.__painterMode is 0:     #  Draw color on image
            self.painter.drawImage(0, 0, self.__image)
            self.painter.setCompositionMode(QPainter.CompositionMode_SourceAtop)
            self.painter.drawImage(0, 0, self.__transparent)
        elif self.__painterMode is 1:  #  Draw alpha on image
            self.painter.drawImage(0, 0, self.__image)
            self.painter.setCompositionMode(QPainter.CompositionMode_DestinationOut)
            self.painter.drawImage(0, 0, self.__transparent)
 
        self.painter.end()
        self.update()

# show image
        painter.drawPixmap(0, 0, self.__display)

        # draw image
        self.painter = QPainter()

        self.painter.begin(self.__transparent)
        radialGrad = QRadialGradient(self.pos, 50)
        radialGrad.setColorAt(0, QColor(255, 0, 255, 255))
        radialGrad.setColorAt(1, QColor(255, 0, 255, 0))
        brush = QBrush(radialGrad)
        self.painter.setBrush(brush)
        self.painter.setPen(Qt.NoPen)
        self.painter.drawEllipse(self.pos, 50, 50)
        self.painter.end()

        self.painter.begin(self.__display)
        if self.__painterMode is 0:     #  Draw color on image
            self.painter.drawImage(0, 0, self.__image)
            self.painter.setCompositionMode(QPainter.CompositionMode_SourceAtop)
            self.painter.drawImage(0, 0, self.__transparent)
        elif self.__painterMode is 1:  #  Draw alpha on image
            self.painter.drawImage(0, 0, self.__image)
            self.painter.setCompositionMode(QPainter.CompositionMode_DestinationOut)
            self.painter.drawImage(0, 0, self.__transparent)

        self.painter.end()
        self.update()

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