PySide2 中的 QGraphicsItem.itemClipsChildrenToShape 问题

pyqtGraph by default creates cosmetic pens, which are pens that always have a width based on the device they're drawn: if you specify a cosmetic pen with a width equal to 0.5, it will always have that size no matter the scale used for the view.

Now, the source of the problem can be found in the documentation about QGraphicsItem.shape(), which specifies:

The outline of a shape can vary depending on the width and style of the pen used when drawing.

Qt cannot know the actual extent of a cosmetic pen (since it completely depends on the paint device, and the same scene can have multiple views, each one with its own transformation. The result is that it computes the shape based on the specified pen width, even if it's cosmetic.

Since you're using very small values, a 0.5 pen width actually becomes very big, and the extent of the shape is hugely augmented by that size, and that's why it seems that the children are not respecting the shape: if you have a 2x2 ellipse, with a pen of 0.5 the resulting shape will be a 2.5x2.5 ellipse (since the extent of the pen is half its width).

解决方案是完全忽略 的默认行为shape()，只使用子类返回椭圆的形状：

class Ellipse(QGraphicsEllipseItem):
    def shape(self):
        path = QPainterPath()
        path.addEllipse(self.rect())
        return path

circle1 = Ellipse(-1, -1, 2, 2)
# ...