You can use QBalloonTip
which is an internal class defined in
QtDir/5.2.1/Src/qtbase/src/widgets/util/qsystemtrayicon_p.h
QBalloonTip
inherits QWidget
and it is implemented in qsystemtrayicon.cpp
at the same directory. It has the following method to show a balloon tip:
void QBalloonTip::balloon(const QPoint& pos, int msecs, bool showArrow)
You can modify the source code of this class to have your desired balloon tip.