Is it possible to set the opacity of qt widgets?

SetWindowOpacity works for me in Linux. I used code like this to change window opacity, (value is from 0 to 100):

setWindowOpacity(qreal(value)/100);

Just use QGraphicsOpacityEffect in order to achieve this effect.

• Qt4: http://doc.qt.io/qt-4.8/qgraphicsopacityeffect.html
• Qt5: http://doc.qt.io/qt-5/qgraphicsopacityeffect.html

Well for widgets inside mainwidow appear to have setAutoFillBackground(False) by default.

to make it fade in fadeout u need to to use QGraphicsOpacityEffect along with setAutoFillBackground(True)

a small example: write inside the widget which is called inside the mainwindow

op=QGraphicsOpacityEffect(self)
op.setOpacity(1.00) #0 to 1 will cause the fade effect to kick in
self.setGraphicsEffect(op)
self.setAutoFillBackground(True)