How to make lines not overlap shapes (Windows Forms)?

Question

Programming

I am making a graph editor, and I ran into one problem - when drawing graph edges, the lines overlap the vertex, since I draw a line from the center to the center of the circle:

Can I somehow make the lines not overlap the circles? Those. like this:

Code (C#):

//рисует вершину графа
        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            // проверка флага нажатия
            if (!crc_OK)
                return;

            if (step == 9)
                button1.Enabled = false;

            Point pointLocation = pictureBox1.PointToClient(Cursor.Position);
            if (pictureBox1.Image == null) { pictureBox1.Image = new Bitmap(pictureBox1.Width, pictureBox1.Height); }
            var bmp = new Bitmap(pictureBox1.Image);
            var g = Graphics.FromImage(bmp);
            g.DrawString(step.ToString(), DefaultFont, Brushes.Black, e.X - 5, e.Y - 5);
            g.DrawEllipse(Pens.Black, e.X - 10, e.Y - 10, 20, 20);
            label1.Text = "Добавлена вершина " + Convert.ToString(step);
            pictureBox1.Image = bmp;
            masX[step] = e.X;
            masY[step] = e.Y;
            label3.Text = "X:" + Convert.ToString(masX[step]);
            label2.Text = "Y:" + Convert.ToString(masY[step]);
            step++;
            crc_OK = false;
        }

        //рисует ребро
        private void button2_Click(object sender, EventArgs e)
        {
            int first_toop = Convert.ToInt16(textBox1.Text);
            int second_toop = Convert.ToInt16(textBox2.Text);
            if (first_toop > 9 || second_toop > 9)
            {
                MessageBox.Show("Недопустимое значение.", "Ошибка", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
            }
            if (pictureBox1.Image == null) { pictureBox1.Image = new Bitmap(pictureBox1.Width, pictureBox1.Height); }
            var bmp = new Bitmap(pictureBox1.Image);
            var g = Graphics.FromImage(bmp);
            g = Graphics.FromImage(pictureBox1.Image);
            g.DrawLine(Pens.DarkGray, masX[first_toop], masY[first_toop], masX[second_toop], masY[second_toop]);
            label1.Text = "Добавлено ребро " + Convert.ToString(first_toop) + " - " + Convert.ToString(second_toop);
            pictureBox1.Refresh();
        }

Answer 1

Actually two options.
1. Draw the vertices at the end and fill them with the background using FillEllipse
2. Since the size of the graph vertex is known, draw lines to the vertex border.