How to change color in QPainter::CompositionMode_DestinationIn?

[qwe3]

Hi,

I have someWidget class ( inherits QWidget ) and paintEvent() on it.

void someWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHints(QPainter::Antialiasing);
    painter.setPen(Qt::NoPen);

    painter.fillRect(0, 0, width(), height(), Qt::white);


    int radius = 100;
    painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);

    QRadialGradient radialGrad(QPoint(200,200), radius);
    radialGrad.setColorAt(0, QColor(255, 0, 0, 0));
    radialGrad.setColorAt(1, QColor(255, 0, 0, 255));
    painter.setBrush(radialGrad);

    painter.drawEllipse(QPoint(200,200), radius, radius);
}

And I would like to have red ellipse. Now I have black ellipse.

I tried to set:

    radialGrad.setColorAt(0, QColor(255, 0, 0, 0));
    radialGrad.setColorAt(1, QColor(255, 0, 0, 255));

To other colors: blue, green, but result is the same - black ellipse. So how can I get the red one?

EDIT:
Even simpler code:

void someWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHints(QPainter::Antialiasing);
    painter.setPen(Qt::NoPen);

    painter.fillRect(0, 0, width(), height(), Qt::white);

    int radius = 100;
    painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);

    painter.setBrush(QColor(255,0,0,200));

    painter.drawEllipse(QPoint(200,200), radius, radius);
}