Cant move my widget properly

[tonnot]

I have a simple code (i think) to move a simple Widget placed at the central-widget of a window. I have subclass the mouseevents to do the work but it does not work properly.
( the widget flikks and on every movement of 1 pixel the mouse is 1 pixel from it have to be placed... )

Mousemove:

int mouse_x = event->pos().x();
    int mouse_y = event->pos().y();
      if (mouse_active==Qt::LeftButton) {
         mouse_prev= mouse_active;
         mouse_active=Qt::NoButton;      // to avoid re-call 
         event->accept();
   // mouse_rx, mouse_ry are private vars . First value is given by mousepress, the nexts from here
         this->move(this->geometry().left()+mouse_x-mouse_rx,this->geometry().top() +mouse_y-mouse_ry);
      mouse_rx=mouse_x;mouse_ry=mouse_y;  // remember
      mouse_active=mouse_prev;                   // restore the button type}

int mouse_x = event->pos().x();
    int mouse_y = event->pos().y();
      if (mouse_active==Qt::LeftButton) {
         mouse_prev= mouse_active;
         mouse_active=Qt::NoButton;      // to avoid re-call 
         event->accept();
   // mouse_rx, mouse_ry are private vars . First value is given by mousepress, the nexts from here
         this->move(this->geometry().left()+mouse_x-mouse_rx,this->geometry().top() +mouse_y-mouse_ry);
      mouse_rx=mouse_x;mouse_ry=mouse_y;  // remember
      mouse_active=mouse_prev;                   // restore the button type}

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Mousepress :

mouse_active = event->button();
    mouse_rx = event->pos().x();
    mouse_ry = event->pos().y();

mouse_active = event->button();
    mouse_rx = event->pos().x();
    mouse_ry = event->pos().y();

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Any idea ? (I'm tired to see how so simple thing does not work ....)