A Qt/C++ application that draws a cardioid

main.cpp

#include <QApplication>
#include <QWidget>
#include <QTimer>
#include <QElapsedTimer>
#include <QPoint>
#include <QPainter>
#include <QObject>
#include <algorithm>
#include <cmath>

class Window : public QWidget
{
    Q_OBJECT
public:
    Window()
        : m_radius(400), m_num_lines(150), m_counter(0.0f), m_inc(0.01f)
    {
        setWindowTitle("Cardioid Qt C++");
        resize(1000, 600);
        m_translate = QPoint(size().width()/2, size().height()/2);

        QObject::connect(&m_timer, &QTimer::timeout, this, &Window::animationLoop);
        m_timer.start(1000.f/60.f); //60 times per second
        m_elapsedTimer.start();
    }
    virtual ~Window(){}
    QColor getColor(){
        m_counter += m_inc;
        if (!(0.009 < m_counter && m_counter < 1)) {
            m_counter = std::max(std::min(m_counter, 1.0f), 0.0f);
            m_inc = -m_inc;
        }
        //interpolate
        QColor c1 = Qt::red;
        QColor c2 = Qt::green;
        int r = (c2.red()-c1.red())*m_counter + c1.red();
        int g = (c2.green()-c1.green())*m_counter + c1.green();
        int b = (c2.blue()-c1.blue())*m_counter + c1.blue();

        return QColor(r,g,b);
    }
    void drawCardioid(QPainter& painter){
        painter.save();
        painter.setRenderHint(QPainter::Antialiasing);
        painter.setPen(QColor(getColor()));
        painter.setBrush(Qt::NoBrush);
        qint64 time = m_elapsedTimer.elapsed();
        m_radius = 250 + 50 * std::abs(std::sin(time * 0.004) - 0.5);
        float factor = 1 + 0.0001 * time;
        for(int i = 0; i < m_num_lines; ++i)
        {
            float theta = ( (2 * M_PI) / m_num_lines) * i;
            int x1 = m_radius * std::cos(theta) + m_translate.x();
            int y1 = m_radius * std::sin(theta) + m_translate.y();

            int x2 = m_radius * std::cos(factor*theta) + m_translate.x();
            int y2 = m_radius * std::sin(factor*theta) + m_translate.y();

            painter.drawLine(QPoint(x1, y1), QPoint(x2, y2));
        }
        painter.restore();
    }
private:
    QTimer m_timer;
    QElapsedTimer m_elapsedTimer;

    int m_radius;
    int m_num_lines;
    QPoint m_translate;
    float m_counter;
    float m_inc;
private slots:
    void animationLoop()
    {
        update();
    }
private:
    void paintEvent(QPaintEvent *event)
    {
        Q_UNUSED(event);
        QPainter qp(this);
        qp.setBrush(QBrush(Qt::black));
        qp.drawRect(0,0,size().width(), size().height());
        drawCardioid(qp);
    }
};

#include "main.moc"

int main(int argc, char** argv)
{
    QApplication a(argc, argv);
    Window *w = new Window();
    w->show();
    a.exec();
}