C#中在picturebox中实时画矩形框

        Point rectPoint = new Point();
        Point startPoint = new Point();
        Point endPoint = new Point();
        Point ptMouse = new Point();//鼠标相对图像框位置
        Point pointMove1 = new Point();
        Point pointPick2 = new Point();
        Point pointMove2 = new Point();
        Rectangle MouseRect = Rectangle.Empty;
        List<Point> AllPoint = new List<Point>();//存储当前窗体中的所有轮廓点       
        bool inOrOut = false;
        bool DrawingStart = false;
        bool MouseIsDown = false;

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            this.pictureBox1.Focus();
            if (e.Button == MouseButtons.Left)
            {
                startPoint.X = e.X ;
                startPoint.Y =e.Y ;
            }
            MouseIsDown = false;
        }

        private void pictureBox1_MouseEnter(object sender, EventArgs e)
        {
            inOrOut = true;
        }