public void MidPoint(int x0, int y0, int a, int b, Color FrontClr)
            {
                int a2 = a * a;
                int b2 = b * b;
                int Twoa2 = 2 * a2;
                int Twob2 = 2 * b2;
                int p;
                int x = 0;
                int y = b;
                int px = 0;
                int py = Twoa2 * y;


                DrawPoint(x0 + x, y0 + y, FrontClr);
                DrawPoint(x0 - x, y0 + y, FrontClr);
                DrawPoint(x0 - x, y0 - y, FrontClr);
                DrawPoint(x0 + x, y0 - y, FrontClr);
                /* For Region 1 */

                p =(int) Math.Round(b2 - (a2 * b) + (0.25) * a2);

                while (px < py)
                {
                    DrawPoint(x0 + x, y0 + y, FrontClr);
                    DrawPoint(x0 - x, y0 + y, FrontClr);
                    DrawPoint(x0 - x, y0 - y, FrontClr);
                    DrawPoint(x0 + x, y0 - y, FrontClr);
                    x++;
                    px += Twob2;
                    if (p < 0)
                    {
                        p += b2 + px;
                    }
                    else
                    {
                        y--;
                        py -= Twoa2;
                        p += b2 + px - py;
                    }

                }


                /* For Region 2*/

                p = (int)Math.Round(b2 * (x + 0.5) * (x + 0.5) + a2 * (y - 1) * (y - 1) - a2 * b2);

                while (y>0)
                {
                    DrawPoint(x0 + x, y0 + y, FrontClr);
                    DrawPoint(x0 - x, y0 + y, FrontClr);
                    DrawPoint(x0 - x, y0 - y, FrontClr);
                    DrawPoint(x0 + x, y0 - y, FrontClr);
                    y--;
                    py -= Twoa2;
                    if (p > 0)
                    {
                        p += a2 - py;
                    }
                    else
                    {
                        x++;
                        px += Twob2;
                        p += a2 - py + px;
                    }

                }
            }
        }