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#QRubberBand

A rubber band is often used to show a new bounding area (as in a QSplitter or a QDockWidget that is undocking). Historically this has been implemented using a QPainter and XOR, but this approach doesn’t always work properly since rendering can happen in the window below the rubber band, but before the rubber band has been “erased”.
You can create a QRubberBand whenever you need to render a rubber band around a given area (or to represent a single line), then call setGeometry(), move() or resize() to position and size it. A common pattern is to do this in conjunction with mouse events. For example:
void Widget::mousePressEvent(QMouseEvent *event)
{
origin = event->pos();
if (!rubberBand)
rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
rubberBand->setGeometry(QRect(origin, QSize()));
rubberBand->show();
}
void Widget::mouseMoveEvent(QMouseEvent *event)
{
rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
}
void Widget::mouseReleaseEvent(QMouseEvent *event)
{
rubberBand->hide();
// determine selection, for example using QRect::intersects()
// and QRect::contains().
}
If you pass a parent to QRubberBand’s constructor, the rubber band will display only inside its parent, but stays on top of other child widgets. If no parent is passed, QRubberBand will act as a top-level widget.
Call show() to make the rubber band visible; also when the rubber band is not a top-level. Hiding or destroying the widget will make the rubber band disappear. The rubber band can be a Rectangle or a Line (vertical or horizontal), depending on the shape() it was given when constructed.