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Thread: The problem of paint() function in Qgraphicsitem?

  1. #1
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    Unhappy The problem of paint() function in Qgraphicsitem?

    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:
    Qt Code:
    1. # show image
    2. painter.drawPixmap(0, 0, self.__display)
    3.  
    4. # draw image
    5. self.painter = QPainter()
    6.  
    7. self.painter.begin(self.__transparent)
    8. radialGrad = QRadialGradient(self.pos, 50)
    9. radialGrad.setColorAt(0, QColor(255, 0, 255, 255))
    10. radialGrad.setColorAt(1, QColor(255, 0, 255, 0))
    11. brush = QBrush(radialGrad)
    12. self.painter.setBrush(brush)
    13. self.painter.setPen(Qt.NoPen)
    14. self.painter.drawEllipse(self.pos, 50, 50)
    15. self.painter.end()
    16.  
    17. self.painter.begin(self.__display)
    18. if self.__painterMode is 0: # Draw color on image
    19. self.painter.drawImage(0, 0, self.__image)
    20. self.painter.setCompositionMode(QPainter.CompositionMode_SourceAtop)
    21. self.painter.drawImage(0, 0, self.__transparent)
    22. elif self.__painterMode is 1: # Draw alpha on image
    23. self.painter.drawImage(0, 0, self.__image)
    24. self.painter.setCompositionMode(QPainter.CompositionMode_DestinationOut)
    25. self.painter.drawImage(0, 0, self.__transparent)
    26.  
    27. self.painter.end()
    28. self.update()
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    Last edited by d_stranz; 14th January 2021 at 20:36. Reason: missing [code] tags

  2. #2
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    Default Re: The problem of paint() function in Qgraphicsitem?

    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.
    I have no idea what you mean by "draw the process".

    The whole process of the mouse drawing is very slow and stuck
    image size: 10000 * 10000
    What do you expect? You apparently have two images, each of them with 100 million pixels, and you are using an interpreted language to draw them. Of course it will be slow.

    And if by "mouse drawing" you mean that you are updating the image with every mouse move, then of course it will deadly slow in any programming language.

    You should consider using a QPainterPath to capture the mouse movements instead of setting individual pixels, which is what I think you are doing.
    <=== The Great Pumpkin says ===>
    Please use CODE tags when posting source code so it is more readable. Click "Go Advanced" and then the "#" icon to insert the tags. Paste your code between them.

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