#include <QDebug>
#include <QPolygonF>

int main()
{
  QPolygonF high, low;
  high << QPointF(293, 0) << QPointF(406.102, 225) << QPointF(556, 0);
  low << QPointF(79, -1) << QPointF(182.303, 60) << QPointF(673, -1);

  QPolygonF low_first_unite(low.united(high));
  QPolygonF expected({ QPointF(79,-1), QPointF(182.303,60), QPointF(314.876,43.5194), QPointF(406.102,225), QPointF(546.162,14.7677), QPointF(673,-1), QPointF(79,-1) });

  qDebug() << low_first_unite.united(high); // error
  qDebug() << expected;
  qDebug() << (expected == low_first_unite);

  high[1].ry() = 230;
  qDebug() << low_first_unite.united(high); // right result

  return 0;
}