Grafik i C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        Graphics lærred;
        Pen blyant;

        private void btnTegn_Click(object sender, EventArgs e)
        {
            int x1 = int.Parse(txtX1.Text);
            int y1 = int.Parse(txtY1.Text);
            int x2 = int.Parse(txtX2.Text);
            int y2 = int.Parse(txtY2.Text);

            lærred.DrawLine(blyant, x1, y1, x2, y2);

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            lærred = this.CreateGraphics();
            blyant = new Pen(Color.Blue, 1.0f);
        }
    }
}