anti-aliasing+hi-dpi Scaling -> The drawing area and the refresh area do not match

class TestWindow : public QWidget
{
public:
    explicit TestWindow(QWidget *parent = 0)
        : QWidget(parent)
    {

    }

    void mousePressEvent(QMouseEvent *e)
    {
        if (e->button() == Qt::LeftButton) {
            press_pos = e->pos();
        }
    }

    void mouseReleaseEvent(QMouseEvent *e)
    {

    }

    void mouseMoveEvent(QMouseEvent *e)
    {
        update(rect);

        rect.setLeft(qMin(press_pos.x(), e->pos().x()));
        rect.setTop(qMin(press_pos.y(), e->pos().y()));
        rect.setRight(qMax(press_pos.x(), e->pos().x()));
        rect.setBottom(qMax(press_pos.y(), e->pos().y()));

        update(rect);
    }

    void paintEvent(QPaintEvent *e)
    {
        QPainter pa(this);
        pa.setRenderHints(QPainter::Antialiasing);
        //pa.setRenderHints(QPainter::Antialiasing, false);
        pa.fillRect(rect, color);
    }

    QPoint press_pos;
    QRect rect;
    QColor color;
};