Filling an ellipse with a QRadialGradient brush

[Caius Aérobus]

Hello,
I would like to draw an ellipse and fill it with a QRadialGradient brush. So I have 2 questions:

• what is the difference between focal and center points in a QRadialGradient?
• here is my code, which draws a classical - empty - ellipse, what should I add to fill it with the selected brush?

  QRadialGradient rg(this->fire_point, this->fire_size);
      rg.setColorAt(0, Qt::red);
      rg.setColorAt(1, Qt::white);
      pen.setBrush(QBrush(rg));
      painter.setPen(pen);
      painter.drawEllipse(this->fire_point.x(), this->fire_point.y(), this->fire_size*2, this->fire_size*2);

  QRadialGradient rg(this->fire_point, this->fire_size);
      rg.setColorAt(0, Qt::red);
      rg.setColorAt(1, Qt::white);
      pen.setBrush(QBrush(rg));
      painter.setPen(pen);
      painter.drawEllipse(this->fire_point.x(), this->fire_point.y(), this->fire_size*2, this->fire_size*2);

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