C# 实现预览dwg文件完整源代码(无需autocad环境)

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.IO;
namespace WindowsApplication3
{
 /// <summary>
 /// Form1 的摘要说明。
 /// </summary>
 public class Form1 : System.Windows.Forms.Form
 {
  private System.Windows.Forms.Timer timer1;
  private System.Windows.Forms.PictureBox pictureBox1;
  private System.ComponentModel.IContainer components;
  public Form1()
  {
   //
   // Windows 窗体设计器支持所必需的
   //
   InitializeComponent();
   //
   // TODO: 在 InitializeComponent 调用后添加任何构造函数代码
   //
  }
  /// <summary>
  /// 清理所有正在使用的资源。
  /// </summary>
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }
  #region Windows Form Designer generated code
  /// <summary>
  /// 设计器支持所需的方法 - 不要使用代码编辑器修改
  /// 此方法的内容。
  /// </summary>
  private void InitializeComponent()
  {
   this.components = new System.ComponentModel.Container();
   this.timer1 = new System.Windows.Forms.Timer(this.components);
   this.pictureBox1 = new System.Windows.Forms.PictureBox();
   this.SuspendLayout();
   //
   // pictureBox1
   //
   this.pictureBox1.Location = new System.Drawing.Point(16, 16);
   this.pictureBox1.Name = "pictureBox1";
   this.pictureBox1.Size = new System.Drawing.Size(416, 272);
   this.pictureBox1.TabIndex = 0;
   this.pictureBox1.TabStop = false;
   //
   // Form1
   //
   this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
   this.ClientSize = new System.Drawing.Size(472, 310);
   this.Controls.AddRange(new System.Windows.Forms.Control[] {
                    this.pictureBox1});
   this.Name = "Form1";
   this.Text = "Form1";
   this.Load += new System.EventHandler(this.Form1_Load);
   this.ResumeLayout(false);
  }
  #endregion
  /// <summary>
  /// 应用程序的主入口点。
  /// </summary>
  [STAThread]
  static void Main()
  {
   Application.Run(new Form1());
  }
  private void Form1_Load(object sender, System.EventArgs e)
  {
   ViewDWG viewDWG=new ViewDWG();
   pictureBox1.Image =viewDWG.GetDwgImage("c:\\\\1.dwg");
  }
 }
 class ViewDWG
 {
  struct BITMAPFILEHEADER
  {
   public short bfType;
   public int bfSize;
   public short bfReserved1;
   public short bfReserved2;
   public int bfOffBits;
  }
  public  Image GetDwgImage(string FileName)
  {
   if (!(File.Exists(FileName)))
   {
    throw new FileNotFoundException("文件没有被找到");
   }
   FileStream DwgF;  //文件流
   int PosSentinel;  //文件描述块的位置
   BinaryReader br;  //读取二进制文件
   int TypePreview;  //缩略图格式
   int PosBMP;       //缩略图位置
   int LenBMP;       //缩略图大小
   short biBitCount; //缩略图比特深度
   BITMAPFILEHEADER biH; //BMP文件头，DWG文件中不包含位图文件头，要自行加上去
   byte[] BMPInfo;       //包含在DWG文件中的BMP文件体
   MemoryStream BMPF = new MemoryStream(); //保存位图的内存文件流
   BinaryWriter bmpr = new BinaryWriter(BMPF); //写二进制文件类
   Image myImg = null;
   try
   {
    DwgF = new FileStream(FileName, FileMode.Open, FileAccess.Read);   //文件流
    br = new BinaryReader(DwgF);
    DwgF.Seek(13, SeekOrigin.Begin); //从第十三字节开始读取
    PosSentinel = br.ReadInt32();  //第13到17字节指示缩略图描述块的位置
    DwgF.Seek(PosSentinel + 30, SeekOrigin.Begin);  //将指针移到缩略图描述块的第31字节
    TypePreview = br.ReadByte();  //第31字节为缩略图格式信息，2 为BMP格式，3为WMF格式
    if (TypePreview == 1)
    {
    }
    else if (TypePreview == 2 || TypePreview == 3)
    {
     PosBMP = br.ReadInt32(); //DWG文件保存的位图所在位置
     LenBMP = br.ReadInt32(); //位图的大小
     DwgF.Seek(PosBMP + 14, SeekOrigin.Begin); //移动指针到位图块
     biBitCount = br.ReadInt16(); //读取比特深度
     DwgF.Seek(PosBMP, SeekOrigin.Begin); //从位图块开始处读取全部位图内容备用
     BMPInfo = br.ReadBytes(LenBMP); //不包含文件头的位图信息
     br.Close();
     DwgF.Close();
     biH.bfType = 19778; //建立位图文件头
     if (biBitCount < 9)
     {
      biH.bfSize = 54 + 4 * (int)(Math.Pow(2, biBitCount)) + LenBMP;
     }
     else
     {
      biH.bfSize = 54 + LenBMP;
     }
     biH.bfReserved1 = 0; //保留字节
     biH.bfReserved2 = 0; //保留字节
     biH.bfOffBits = 14 + 40 + 1024; //图像数据偏移
     //以下开始写入位图文件头
     bmpr.Write(biH.bfType); //文件类型
     bmpr.Write(biH.bfSize);  //文件大小
     bmpr.Write(biH.bfReserved1); //0
     bmpr.Write(biH.bfReserved2); //0
     bmpr.Write(biH.bfOffBits); //图像数据偏移
     bmpr.Write(BMPInfo); //写入位图
     BMPF.Seek(0, SeekOrigin.Begin); //指针移到文件开始处
     myImg = Image.FromStream(BMPF); //创建位图文件对象
     bmpr.Close();
     BMPF.Close();
    }
    return myImg;
   }
   catch(Exception ex)
   {
    throw new Exception(ex.Message);
   }
  }
 }
}