draw ellipse at runtime and use widen metod.

public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        Rectangle r;
        bool isDown = false;
        int initialX;
        int initialY;
        bool IsDrowing =true;
        GraphicsPath gp1;
        GraphicsPath gp2;
        GraphicsPath gp3;
        GraphicsPath gp;
        Graphics g;
        bool contained;
        bool containedE;
        bool containedC;
       
        private void Form2_MouseDown(object sender, MouseEventArgs e)
        {
            isDown = true;
            IsDrowing = true;

            initialX = e.X;
            initialY = e.Y;
        }

        private void Form2_MouseMove(object sender, MouseEventArgs e)
        {
            //IsDrowing = true;
            if (isDown == true)
            {
                int width = e.X - initialX, height = e.Y - initialY;
                r = new Rectangle(Math.Min(e.X, initialX),
                               Math.Min(e.Y, initialY),
                               Math.Abs(e.X - initialX),
                               Math.Abs(e.Y - initialY));

                this.Invalidate();
            }
        }

        private void Form2_Paint(object sender, PaintEventArgs e)
        {
            g = this.CreateGraphics();
            gp = new GraphicsPath();
            Pen pen = new Pen(Color.Red);
            gp.AddEllipse(r);
            gp.Widen(pen);
            pen.DashStyle = DashStyle.Dash;
            if (IsDrowing)
            {
                g.DrawPath(pen, gp);
            }


            Rectangle rect=new Rectangle(100,200,100,90);
            gp1 = new GraphicsPath();
            gp1.AddRectangle(rect);
            gp1.Widen(Pens.Red);
            e.Graphics.DrawPath(Pens.Red,gp1);

            Rectangle rect1 = new Rectangle(300, 200, 100, 90);
            gp2 = new GraphicsPath();
            gp2.AddEllipse(rect1);
            gp2.Widen(Pens.Red);
            e.Graphics.DrawPath(Pens.Red, gp2);

            List<point> points = new List<point>();
            points.Add(new Point(10, 10));
            points.Add(new Point(100, 30));
            points.Add(new Point(200, 80));
            points.Add(new Point(500, 15));
            gp3 = new GraphicsPath();
            gp3.AddCurve(points.ToArray());

            gp3.Widen(Pens.Blue);
            e.Graphics.DrawPath(Pens.Blue, gp3);


            Region r1 = new Region(gp1);
            contained = r1.IsVisible(r);
            Region r2 = new System.Drawing.Region(gp2);
            containedE = r2.IsVisible(r);
            Region r3 = new Region(gp3);
            containedC = r3.IsVisible(r);
        }

        private void Form2_MouseUp(object sender, MouseEventArgs e)
        {
            IsDrowing = false;
            this.Refresh();
            isDown = false;
            g=this.CreateGraphics();
            if (contained)
            {
                g.DrawPath(Pens.Black, gp1);
            }
            if (containedE)
            {
                g.DrawPath(Pens.Black, gp2);
            }
            if (containedC)
            {
                g.DrawPath(Pens.Black, gp3);
            }
        }
    }