c# 滚动网页截图

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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
       
        private int _currentWidth = 1024;
        private Bitmap _currentBitmap = null;
        public Form1()
        {
            InitializeComponent();
        }
       

private void button1_Click(object sender, EventArgs e)
{
    if (webBrowser1.Document == null)
        return;
    try
    {
        int width = _currentWidth;
        int height = webBrowser1.Document.Body.ScrollRectangle.Height;
        webBrowser1.Width = width;
        webBrowser1.Height = height;
        _currentBitmap = new Bitmap(width, height);
        webBrowser1.Stop();
        webBrowser1.DrawToBitmap(_currentBitmap, new Rectangle(0, 0, width, height));
        pictureBox1.Image = _currentBitmap;

    }
    catch (Exception ex)
    {

        MessageBox.Show(ex.ToString(), "遇到错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}
    }
}