qt simple angle rotation

#include <QApplication>
#include <QWidget>
#include <QTimer>
#include <QPainter>
#include <qmath.h>

class MyWidget : public QWidget {
    Q_OBJECT

public:
    MyWidget() : m_angle(0) {
        QTimer * animTimer = new QTimer(this);
        connect(animTimer, SIGNAL(timeout()), this, SLOT(animate()));
        animTimer->start(33);
    }

protected:
    void paintEvent(QPaintEvent * e) {
        QWidget::paintEvent(e);
        QSize s = size();
        float radius = qMin(s.width(), s.height()) * 0.49;
        QPointF center(s.width() / 2.0, s.height() / 2.0);
        enum { Sides = 3 };
        QPointF vertices[Sides];
        for(int i = 0; i < Sides; ++i) {
            double angle = m_angle + (2.0 * M_PI) * (i / (double)Sides);
            vertices[i] = QPointF(
                        radius * cos(angle),
                        radius * sin(angle));
            vertices[i] += center;
        }
        QPainter painter(this);
        painter.setBrush(Qt::black);
        painter.drawPolygon(vertices, Sides);
    }

private slots:
    void animate() {
        m_angle += 0.05;
        if(m_angle > M_PI * 2) {
            m_angle -= M_PI;
        }
        update();
    }

private:
    double m_angle;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    MyWidget w;
    w.show();

    return a.exec();
}

#include "main.moc"