Desktop wallpaper Fade In

[Dan`]

Hi everyone

I'm pretty much new to the QT world, so I'm trying to learn something by reading codes and stuff. My main problem now is that I need to set a wallpaper, showing it slowly from a black background.
I googled and tested some methods, but couldn't get it working.
So I'll just post my little code and ask if someone can explain me a way to make the effect I'm looking for

void Desk::set_wall() {
	setPixmap(wall_img);
	setScaledContents(true);
	setGeometry(0, 0, 1280, 1024);
}

void Desk::set_wall() {
	setPixmap(wall_img);
	setScaledContents(true);
	setGeometry(0, 0, 1280, 1024);
}

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Thanks!