I managed to fix this using StyleSheets.
The strange thing is that a StyleSheet with "background-color: transparent;" or "background-color: rgba(0, 0, 0, 0);" wouldn't make the background transparent. But when I tried a random gradient, voila! The background was transparent!
So, I simply grabbed the linear black to white gradient from Qt Designer, got it from the autogenerated .h and placed in my QWidget like this:
That seemed to do the trick! Now my background is transparent.
my_qwidget->setStyleSheet(QString::fromUtf8("background-color: qlineargradient(spread:pad, x1:0, y1:0, x2:1, y2:0, stop:0 rgba(0, 0, 0, 0), stop:1 rgba(255, 255, 255, 0));"));
The only left issue is that now I get a world of Painter not active errors or warnings in the console. Some examples:
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setWorldTransform: Painter not active
QPainter::worldTransform: Painter not active
QPainter::setBrush: Painter not active
QPainter::setRenderHint: Painter must be active to set rendering hints
And so on, and so on.
Since I'm still a newbie in Qt, I really can't decipher those errors. Perhaps there is something Very wrong going on, but everything seems to be working just fine on the Simulator and the actual Phone.
Hope this quasi-solution helps anyone with my same issue, though.