using System;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        Bitmap drawBitmap;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            InitDraw();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Draw();
        }

        private void InitDraw()
        {
            drawBitmap = new Bitmap(500, 500);
            pictureBox1.Image = drawBitmap;
        }

        private void Draw()
        {
            Graphics g = Graphics.FromImage(pictureBox1.Image);
            Pen myPen = new Pen(Color.Black);
            g.DrawLine(myPen, 0, 0, 100, 100);
            myPen.Dispose();
            g.Dispose();
            Invalidate();
        }
    }
}