x = a * cos(t)
y = b * sin(t)

public partial class Form1 : Form
{
    private Timer timer;
    private double angle = 0;
    private const double STEP = 1;  // 角度步進值  
    private const int A = 150;      // 長半軸  
    private const int B = 100;      // 短半軸  
    private Point center;           // 橢圓中心點  
    private Point currentPos;       // 運動物體當前位置  


    public Form1()
    {
        InitializeComponent();


        // 啟用雙緩沖,防止閃爍  
        this.DoubleBuffered = true;
        // 設置控件樣式為全部在WM_PAINT中繪制  
        // 這樣可以防止控件擦除背景時閃爍,提高繪制效率  
        this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);


        // 計算中心點  
        center = new Point(this.ClientSize.Width / 2, this.ClientSize.Height / 2);


        // 初始化定時器  
        timer = new Timer();
        timer.Interval = 20;  // 20ms更新一次  
        timer.Tick += Timer_Tick;
        timer.Start();
    }


    private void Timer_Tick(object sender, EventArgs e)
    {
        // 計算新位置  
        angle = (angle + STEP) % 360;
        double radian = angle * Math.PI / 180;


        currentPos = new Point(
            (int)(center.X + A * Math.Cos(radian)),
            (int)(center.Y + B * Math.Sin(radian))
        );


        this.Invalidate();  // 觸發(fā)重繪  
    }


    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        Graphics g = e.Graphics;


        // 設置高質量繪圖  
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;


        // 繪制橢圓軌跡  
        using (Pen pen = new Pen(Color.LightGray, 1))
        {
            g.DrawEllipse(pen,
                center.X - A, center.Y - B,
                2 * A, 2 * B);
        }


        // 繪制運動物體  
        using (SolidBrush brush = new SolidBrush(Color.Blue))
        {
            const int BALL_SIZE = 20;
            g.FillEllipse(brush,
                currentPos.X - BALL_SIZE / 2,
                currentPos.Y - BALL_SIZE / 2,
                BALL_SIZE, BALL_SIZE);
        }


        // 繪制中心點  
        using (SolidBrush brush = new SolidBrush(Color.Red))
        {
            g.FillEllipse(brush,
                center.X - 3, center.Y - 3,
                6, 6);
        }


        // 顯示當前角度  
        using (Font font = new Font("Arial", 12))
        using (SolidBrush brush = new SolidBrush(Color.Black))
        {
            g.DrawString($"Angle: {angle:F1}°",
                font, brush, new PointF(10, 10));
        }
    }
}