Creating semitransparent widget over QGraphicsView

[Luc4]

Hi! I'm trying to overlap a transparent widget to a QGraphicsView. I created it with:

MyWidget* widget = new MyWidget(this);
widget->show();

MyWidget* widget = new MyWidget(this);
widget->show();

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and I noticed it results not to be semitransparent. If, instead, I create it in a subclass of the QGraphicsScene placed in the QGraphicsView whose parent is my QMainWindow, like:

MyWidget* widget = new MyWidget((QWidget*)this->parent());
widget->show();

MyWidget* widget = new MyWidget((QWidget*)this->parent());
widget->show();

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I get that it is semitransparent. Why?
Thanks!