Редактор блок-схем, как сделать так, чтобы линии соединяющие блоки сохранялись при перемещении блоков

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
 
namespace block_shemi
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        PictureBox[] vichisl = new PictureBox[30];
        PictureBox[] log = new PictureBox[30];
        PictureBox[] vvod_vivod = new PictureBox[30];
 
        int i = 0;
        int j = 0;
        int z = 0;
        int x1, y1, x2, y2;
        int x1_line, y1_line, x2_line, y2_line;
        int ilabelX, ilabelY, ilabelX_Line, ilabelY_Line;
        bool isDragging = false;
 
        bool is_line = false;
        int start_x1, start_y1, start_x2, start_y2;
 
        private void button1_Click(object sender, EventArgs e)
        {
            vichisl[i] = new PictureBox(); 
            vichisl[i].Location = new System.Drawing.Point(100, 100);
            vichisl[i].Size = new System.Drawing.Size(150, 83);
            vichisl[i].Image = new Bitmap("image/vichesl_box.png");
            vichisl[i].MouseDown += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseDown);
            vichisl[i].MouseMove += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseMove);
            vichisl[i].MouseUp += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseUp);
            vichisl[i].Paint += new System.Windows.Forms.PaintEventHandler(this.Paint_text);
            vichisl[i].MouseDoubleClick += new System.Windows.Forms.MouseEventHandler(this.MouseDoubleClick);
            vichisl[i].MouseClick += new System.Windows.Forms.MouseEventHandler(this.Right_MouseClick);
 
            Controls.Add(vichisl[i]);
 
            i++;
        }
 
        private void Vichisl_MouseDown(object sender, EventArgs e)
        {
            isDragging = true;
            PictureBox link = (PictureBox)sender;
 
            ilabelX = link.Location.X;
            ilabelY = link.Location.Y;
            x1 = System.Windows.Forms.Cursor.Position.X;
            y1 = System.Windows.Forms.Cursor.Position.Y;
        }
 
        private void Vichisl_MouseMove(object sender, EventArgs e)
        {
            if (isDragging)
            {
                x2 = System.Windows.Forms.Cursor.Position.X;
                y2 = System.Windows.Forms.Cursor.Position.Y;
 
                PictureBox link = (PictureBox)sender;
 
                link.Location = new Point(ilabelX + (x2 - x1), ilabelY + (y2 - y1));
                Controls.Add(link);
            }
        }
        //________________________________________
        //Рисуем линию при двойном клике
        //____________________________________
        private void MouseDoubleClick(object sender, EventArgs e)
        {
            if(is_line == false)
            {
                is_line = true;
 
                PictureBox link = (PictureBox)sender;
 
                int pol_shirini = link.Width / 2;
                int pol_visoti = link.Height / 2;
 
                start_x1 = link.Location.X + pol_shirini;
                start_y1 = link.Location.Y + pol_visoti;
            }
            else
            {
                is_line = false;
 
                PictureBox link = (PictureBox)sender;
 
                int pol_shirini = link.Width / 2;
                int pol_visoti = link.Height / 2;
 
                start_x2 = link.Location.X + pol_shirini;
                start_y2 = link.Location.Y + pol_visoti;
 
                Graphics g = CreateGraphics();
 
                Pen p = new Pen(Color.Black, 1);
 
                g.DrawLine(p, start_x1, start_y1, start_x2, start_y2);
            }
        }
 
        private void Right_MouseClick(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right)
            {
                PictureBox link = (PictureBox)sender;
 
                link.Size = new System.Drawing.Size(link.Width + 10, link.Height + 10);
                link.SizeMode = PictureBoxSizeMode.StretchImage;
            }
            
        }
 
        private void Vichisl_MouseUp(object sender, EventArgs e)
        {
            isDragging = false;
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
            log[j] = new PictureBox();
            log[j].Location = new System.Drawing.Point(100, 100);
            log[j].Size = new System.Drawing.Size(150, 83);
            log[j].Image = new Bitmap("image/log_box.png");
            log[j].MouseDown += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseDown);
            log[j].MouseMove += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseMove);
            log[j].MouseUp += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseUp);
            log[j].Paint += new System.Windows.Forms.PaintEventHandler(this.Paint_text);
            log[j].MouseDoubleClick += new System.Windows.Forms.MouseEventHandler(this.MouseDoubleClick);
            log[j].MouseClick += new System.Windows.Forms.MouseEventHandler(this.Right_MouseClick);
 
            Controls.Add(log[j]);
 
            j++;
        }
 
        private void button3_Click(object sender, EventArgs e)
        {
            vvod_vivod[z] = new PictureBox();
            vvod_vivod[z].Location = new System.Drawing.Point(100, 100);
            vvod_vivod[z].Size = new System.Drawing.Size(145, 87);
            vvod_vivod[z].Image = new Bitmap("image/vvod_vivod_box.png");
            vvod_vivod[z].MouseDown += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseDown);
            vvod_vivod[z].MouseMove += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseMove);
            vvod_vivod[z].MouseUp += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseUp);
            vvod_vivod[z].Paint += new System.Windows.Forms.PaintEventHandler(this.Paint_text);
            vvod_vivod[z].MouseDoubleClick += new System.Windows.Forms.MouseEventHandler(this.MouseDoubleClick);
            vvod_vivod[z].MouseClick += new System.Windows.Forms.MouseEventHandler(this.Right_MouseClick);
 
            Controls.Add(vvod_vivod[z]);
 
            z++;
        }
 
        private void Paint_text(object sender, System.Windows.Forms.PaintEventArgs e)
        {
            Graphics g = e.Graphics;
 
            g.DrawString(textBox1.Text, new Font("Arial", 10), System.Drawing.Brushes.Blue, new Point(30, 30));
 
            textBox1.Text = String.Empty;
        }
 
        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            x1_line = e.X;
            y1_line = e.Y;
 
           
        }
 
        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            Graphics g = CreateGraphics();
 
            Pen p = new Pen(Color.Black, 1);
 
            x2_line = e.X;
            y2_line = e.Y;
 
            g.DrawLine(p, x1_line, y1_line, x2_line, y2_line);
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            
            PictureBox start = new PictureBox();
            start.Location = new System.Drawing.Point(250, 100);
            start.Size = new System.Drawing.Size(150, 40);
            start.Image = new Bitmap("image/start_stop.png");
            start.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseDown);
            start.MouseMove += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseMove);
            start.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseUp);
            start.Paint += new System.Windows.Forms.PaintEventHandler(this.Paint_text_start);
            start.MouseDoubleClick += new System.Windows.Forms.MouseEventHandler(this.MouseDoubleClick);
            start.MouseClick += new System.Windows.Forms.MouseEventHandler(this.Right_MouseClick);
 
            Controls.Add(start);
 
            PictureBox finish = new PictureBox();
            finish.Location = new System.Drawing.Point(250, 550);
            finish.Size = new System.Drawing.Size(150, 40);
            finish.Image = new Bitmap("image/start_stop.png");
            finish.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseDown);
            finish.MouseMove += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseMove);
            finish.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Vichisl_MouseUp);
            finish.Paint += new System.Windows.Forms.PaintEventHandler(this.Paint_text_finish);
            finish.MouseDoubleClick += new System.Windows.Forms.MouseEventHandler(this.MouseDoubleClick);
            finish.MouseClick += new System.Windows.Forms.MouseEventHandler(this.Right_MouseClick);
 
            Controls.Add(finish);
        }
        private void Paint_text_start(object sender, System.Windows.Forms.PaintEventArgs e)
        {
            Graphics g = e.Graphics;
 
            g.DrawString("START", new Font("Arial", 12), System.Drawing.Brushes.Blue, new Point(50, 10));
 
        }
        private void Paint_text_finish(object sender, System.Windows.Forms.PaintEventArgs e)
        {
            Graphics g = e.Graphics;
 
            g.DrawString("FINISH", new Font("Arial", 12), System.Drawing.Brushes.Blue, new Point(50, 10));
 
        }
    }
}

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
 
namespace WindowsFormsApplication1 {
    public class Form1 : Form {
        [STAThread]
        static void Main() {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
 
        private const int NodeRadius = 5;
 
        private static readonly Pen ArrowPen = new Pen(Color.Black, 2) {
            StartCap = LineCap.Round, 
            EndCap = LineCap.ArrowAnchor,
            CustomEndCap = new AdjustableArrowCap(7, 7)
        };
 
        private readonly List<Node> _nodes = new List<Node>();
 
        private Node _currentNode;
 
        protected override void OnPaint(PaintEventArgs e) {
            e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
 
            foreach (var node in _nodes) {
                e.Graphics.FillEllipse(node == _currentNode ? Brushes.Red : Brushes.Black, new Rectangle(node.Position.X - NodeRadius, node.Position.Y - NodeRadius, NodeRadius * 2, NodeRadius * 2));
                foreach (var next in node.Dependencies) {
                    e.Graphics.DrawLine(ArrowPen, node.Position, next.Position);
                }
            }
            base.OnPaint(e);
        }
 
        public Node GetNode(Point point) {
            foreach (var node in _nodes)
                if (Math.Abs(node.Position.X - point.X) < NodeRadius && Math.Abs(node.Position.Y - point.Y) < NodeRadius)
                    return node;
 
            return null;
        }
 
        protected override void OnMouseClick(MouseEventArgs e) {
            if (e.Button == MouseButtons.Left && _currentNode == null) {
                _nodes.Add(new Node() { Position = e.Location });
                Invalidate();
            }
 
            base.OnMouseClick(e);
        }
        protected override void OnMouseDown(MouseEventArgs e) {
            var currentNode = GetNode(e.Location);
 
            if (e.Button == MouseButtons.Right && _currentNode != null && currentNode != null && !_currentNode.Dependencies.Contains(currentNode)) {
                _currentNode.Dependencies.Add(currentNode);
                Invalidate();
 
            } else if (e.Button == MouseButtons.Left) {
                _currentNode = currentNode;
                Invalidate();
 
            }
 
            base.OnMouseDown(e);
        }
 
        protected override void OnMouseMove(MouseEventArgs e) {
            if (e.Button == MouseButtons.Left && _currentNode != null) {
                _currentNode.Position = e.Location;
                Invalidate();
 
            }
            
            base.OnMouseMove(e);
        }
 
    }
 
    public class Node {
        private readonly List<Node> _dependencies = new List<Node>();
 
        public List<Node> Dependencies { get { return _dependencies; } }
        public Point Position { get; set; }
    }
}