Time for action – creating an item where transformations can easily be seen

First we set up a playground. To do this, we subclass a QGraphicsRectItem item and customize its paint function as follows:

void ScaleItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) {
  Q_UNUSED(option)
  Q_UNUSED(widget)
  const QPen oldPen = painter->pen();

  const QRectF r = rect();
  const QColor fillColor = Qt::red;
  const qreal square = r.width() / 10.0;
  painter->fillRect(QRectF(0, 0, square, square), fillColor);
  painter->fillRect(QRectF(r.width() - square, 0, square, square), fillColor);
  painter->fillRect(QRectF(0,r.height() - square, square, square), fillColor);
  painter->fillRect(QRectF(r.width() - square, r.height() - square,square, square), fillColor);

  painter->setPen(Qt::black);
  painter->drawRect(r);
  painter->drawLine(r.topLeft(), r.bottomRight());
  painter->drawLine(r.topRight(), r.bottomLeft());
  const qreal padding...