Рисование лининий на форме - C#

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Drawing;
 
namespace pros
{
    public class Program:Form 
    {
        private PictureBox pictureBox1;
        private PictureBox pictureBox2;
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.Run(new Program());
        }
        Rectangle line;
        bool flag = false;
        Random rnd = new Random();
        Program()
        {
            InitializeComponent();
            line = new Rectangle(pictureBox1.Left + pictureBox1.Width, pictureBox1.Top + pictureBox1.Height /2,
                pictureBox2.Left, pictureBox2.Top + pictureBox2.Height /2);
            this.Paint += new PaintEventHandler(Program_Paint);
        }
 
        void Program_Paint(object sender, PaintEventArgs e)
        {
            e.Graphics.DrawLine (new Pen(Color.FromArgb(rnd.Next(255), rnd.Next(255), rnd.Next(255)),5),
                line.Left, line.Top ,line.Width, line.Height);
        }
 
        private void InitializeComponent()
        {
            this.pictureBox1 = new System.Windows.Forms.PictureBox();
            this.pictureBox2 = new System.Windows.Forms.PictureBox();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox2)).BeginInit();
            this.SuspendLayout();
            // 
            // pictureBox1
            // 
            this.pictureBox1.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
            this.pictureBox1.Location = new System.Drawing.Point(43, 58);
            this.pictureBox1.Name = "pictureBox1";
            this.pictureBox1.Size = new System.Drawing.Size(48, 48);
            this.pictureBox1.TabIndex = 0;
            this.pictureBox1.TabStop = false;
            this.pictureBox1.Click += new System.EventHandler(this.pictureBox1_Click);
            // 
            // pictureBox2
            // 
            this.pictureBox2.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
            this.pictureBox2.Location = new System.Drawing.Point(205, 46);
            this.pictureBox2.Name = "pictureBox2";
            this.pictureBox2.Size = new System.Drawing.Size(54, 59);
            this.pictureBox2.TabIndex = 1;
            this.pictureBox2.TabStop = false;
            this.pictureBox2.Click += new System.EventHandler(this.pictureBox2_Click);
            // 
            // Program
            // 
            this.ClientSize = new System.Drawing.Size(292, 273);
            this.Controls.Add(this.pictureBox2);
            this.Controls.Add(this.pictureBox1);
            this.Name = "Program";
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox2)).EndInit();
            this.ResumeLayout(false);
        }
 
        private void pictureBox1_Click(object sender, EventArgs e)
        {
            flag = true;
        }
 
        private void pictureBox2_Click(object sender, EventArgs e)
        {
            if(flag)
                Invalidate();
            flag = false;
        }
    }
}