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C# 读取CAD文件缩略图(DWG文件)

作者:大鹏 发布于:2009-7-19 12:01 Sunday 分类:Asp.Net 2.0
标签: c# cad

在不使用任务插件的情况下读取DWG文件的缩略图,以便在没有安装AutoCAD的计算机上浏览。
[code]
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace 浏览dwg
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, 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);
                }
            }
        }

    }
}[/code]


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