public void DrawCircle(int x0, int y0, int radius)
            {
                int x = 0;
                int y = radius;
                int delta = 1 - 2 * radius;
                int error = 0;
                while (y >= 0)
                {
                    this.arr[x0 + x, y0 + y -].fill = true;
                    this.arr[x0 + x, y0 - y].fill = true;
                    this.arr[x0 - x, y0 + y].fill = true;
                    this.arr[x0 - x, y0 - y].fill = true;
                    error = 2 * (delta + y) - 1;
                    if (delta < 0 && error <= 0)
                    {
                        ++x;
                        delta += 2 * x + 1;
                        continue;
                    }
                    error = 2 * (delta - x) - 1;
                    if (delta > 0 && error > 0)
                    {
                        --y;
                        delta += 1 - 2 * y;
                        continue;
                    }
                    ++x;
                    delta += 2 * (x - y);
                    --y;
                }