Purpose of the property opacity

Purpose of the property opacity?
values 0 or 1 invisible or visible
it's good for something or you can delete it from the shape component.
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Purpose of the property opacity?

Set the opacity: values from 0=0% to 1=100%.
For example 0.5 will set opacity to 50%.

It is possible to add a frame as in the image, which does not intercept mouse events inside.
With a rectangle, if I use the mouse inside, I select the rectangle menu and if I try to select objects by dragging the rectangle moves.
Greetings

Found it!

Code:


    this->setFlag(QGraphicsItem::ItemIsSelectable, false);
    setAcceptedMouseButtons(Qt::NoButton);


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