How to implement the special gesture event in widget

[mkdh]

I want to toggle my method after using finger to draw direction line.

Now, I can draw line in my widget using "bool event(QEvent *e);", "QEvent::TouchBegin:" and "QEvent::TouchEnd:" and "QTouchEvent",but that is not what I want to get.

I just want to using finger to draw simple direction line and toggle my method.

But I have no idea how to implement it....