mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QPainter>
#include <QTime>
#include <QTimer>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
    QTimer *timer;

protected:
   void paintEvent(QPaintEvent *) override;
   void drawArrow(double line_width, double line_length, double rotate);
};
#endif // MAINWINDOW_H