Forms CopyFromScreen不'；它不显示图像中的省略号吗

我正在试验这个代码

我在设计时有一个面板和一个按钮。另一个按钮和面板正在动态生成。我得到的结果图像不是显示省略号，而是显示按钮，我想知道为什么

    private void Form3_Load(object sender, EventArgs e)
    {

    }

    private void Form3_Paint(object sender, PaintEventArgs e)
    {
        Graphics g = this.CreateGraphics();
        Pen pen = new Pen(Color.Black, 2);
        Brush brush = new SolidBrush(Color.White);
        Rectangle rect = new Rectangle(50, 50, 100, 200);
        Ellipse el = new Ellipse();
        el.Rectangle = rect;
        //g.DrawRectangle(pen, rect);
        g.DrawEllipse(pen, rect);

    }

    private void button1_Click(object sender, EventArgs e)
    {
        Bitmap printscreen = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);

        Graphics graphics = Graphics.FromImage(printscreen as Image);

        graphics.CopyFromScreen(0, 0, 0, 0, printscreen.Size);

        printscreen.Save(@"C:\Temp\temp.jpg", ImageFormat.Jpeg);
    }

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我最终使用了SendKeys.Send（{PRTSC}）； 这要简单得多。确保在开始之前至少睡眠2秒钟： 系统线程线程睡眠（2000）