#include <QtCore>
#include <QtGui>

class MyWidget: public QWidget
{
public:
    explicit MyWidget(QWidget *parent = NULL) : QWidget(parent) {}

protected:
    virtual void mousePressEvent(QMouseEvent *event)
    {
        qDebug() << "press" << event->pos();
        startPos = event->pos();
    }

    virtual void mouseMoveEvent(QMouseEvent *event)
    {
        qDebug() << "move" << event->pos();
        if ((event->pos() - startPos).manhattanLength() > 5) {
            qDebug() << "drag";
            QDrag *drag = new QDrag(this);
            QMimeData *mimeData = new QMimeData;
            mimeData->setText("Data");
            drag->setMimeData(mimeData);
            drag->start();
        }
    }

    virtual void mouseReleaseEvent(QMouseEvent *event)
    {
        qDebug() << "release" << event->pos();
        qDebug() << "click";
    }

private:
    QPoint startPos;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    MyWidget myWidget;
    myWidget.resize(100, 100);
    myWidget.show();

    return app.exec();
}