irregular shaped widget problem with X11BypassWindowManagerHint flag

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Hi,
I'm a new commer of Qt, I have a QWidget based irregular shaped window that needs to be TOP MOST on linux. The flags of the widget are set as:
setWindowFlag(Qt:: Qt::Widget | Qt::WindowStaysOnTopHint | Qt::FramelessWindowHint | Qt::X11BypassWindowManagerHint );
and the shape of the widget is defined by the mask of a QPixMap image.

It is ok until now, but I need to change dynamically the shape of the widget every time I get a new image. The problem I have is that the shape of widget can not change accordingly with setMask of the image.

I know, setMask() works if I remove X11BypassWindowManagerHint flag from the widget, but I need to keep this flag so as that the widget might stay TOP MOST.

Do you have any idea to solve this problem? I'am using Qt5.2.1

Any hints will be welcome!