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<title>用Delphi实现远程屏幕抓取</title>
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            <br>
            &nbsp;&nbsp;用Delphi实现远程屏幕抓取 <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp山东巨力股份有限公司CAD中心 <br>
            &nbsp&nbsp檀革勤 <br>
            &nbsp&nbsp---- 在网络管理中，有时需要通过监视远程计算机屏幕来了解网上微机的使用情况。虽然，市面上有很多软件可以实现该功能，有些甚至可以进行远程控制，但在使用上缺乏灵活性，如无法指定远程计算机屏幕区域的大小和位置，进而无法在一屏上同时监视多个屏幕。其实，可以用Delphi自行编制一个灵活的远程屏幕抓取工具，简述如下。 
            <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- 一、软硬件要求。 <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- Windows95/98对等网，用来监视的计算机（以下简称主控机）和被监视的计算机（以下简称受控机）都必须装有TCP/IP 
            协议，并正确配置。如没有网络，也可以在一台计算机上进行调试。 <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- 二、实现方法。 <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- 编制两个应用程序，一个为VClient.exe，装在受控机上，另一个为VServer.exe，装在主控机上。VServer.exe指定要监视的受控机的IP地址和将要在受控机屏幕上抓取区域的大小和位置，并发出屏幕抓取指令给VClient.exe，VClient.exe得到指令后，在受控机屏幕上选取指定区域，生成数据流，将其发回主控机，并在主控机上显示出抓取区域的BMP图象。由以上过程可以看出，该方法的关键有二：一是如何在受控机上进行屏幕抓取，二是如何通过TCP/IP协议在两台计算机中传输数据。 
            <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- UDP(User Datagram Protocol，意为用户报文协议)是Internet上广泛采用的通信协议之一。与TCP协议不同，它是一种非连接的传输协议，没有确认机制，可靠性不如TCP，但它的效率却比TCP高，用于远程屏幕监视还是比较适合的。同时，UDP控件不区分服务器端和客户端，只区分发送端和接收端，编程上较为简单，故选用UDP协议，使用Delphi 
            4.0提供的TNMUDP控件。 <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- 三、创建演示程序。 <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- 第一步，编制VClient.exe文件。新建Delphi工程，将默认窗体的Name属性设为"Client"。加入TNMUDP控件，Name属性设为"CUDP"；LocalPort属性设为"1111"，让控件CUDP监视受控机的1111端口，当有数据发送到该口时，触发控件CUDP的OnDataReceived事件；RemotePort属性设为"2222"，当控件CUDP发送数据时，将数据发到主控机的2222口。 
            <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp---- 在implementation后面加入变量定义 <br>
            &nbsp&nbsp <br>
            &nbsp&nbspconst BufSize=2048;{ 发送每一笔数据的缓冲区大小 } <br>
            &nbsp&nbspvar <br>
            &nbsp&nbspBmpStream:TMemoryStream; <br>
            &nbsp&nbspLeftSize:Longint;{ 发送每一笔数据后剩余的字节数 } <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp为Client的OnCreate事件添加代码： <br>
            &nbsp&nbspprocedure TClient.FormCreate(Sender: TObject); <br>
            &nbsp&nbspbegin <br>
            &nbsp&nbspBmpStream:=TMemoryStream.Create; <br>
            &nbsp&nbspend; <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp为Client的OnDestroy事件添加代码： <br>
            &nbsp&nbspprocedure TClient.FormDestroy(Sender: TObject); <br>
            &nbsp&nbspbegin <br>
            &nbsp&nbspBmpStream.Free; <br>
            &nbsp&nbspend; <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp为控件CUDP的OnDataReceived事件添加代码： <br>
            &nbsp&nbspprocedure TClient.CUDPDataReceived(Sender: TComponent; <br>
            &nbsp&nbspNumberBytes: Integer; FromIP: String); <br>
            &nbsp&nbspvar <br>
            &nbsp&nbspCtrlCode:array[0..29] of char; <br>
            &nbsp&nbspBuf:array[0..BufSize-1] of char; <br>
            &nbsp&nbspTmpStr:string; <br>
            &nbsp&nbspSendSize,LeftPos,TopPos,RightPos,BottomPos:integer; <br>
            &nbsp&nbspbegin <br>
            &nbsp&nbspCUDP.ReadBuffer(CtrlCode,NumberBytes);{ 读取控制码 } <br>
            &nbsp&nbspif CtrlCode[0]+CtrlCode[1]+CtrlCode[2]+CtrlCode[3]='show' 
            then <br>
            &nbsp&nbspbegin { 控制码前4位为"show"表示主控机发出了抓屏指令 } <br>
            &nbsp&nbspif BmpStream.Size=0 then { 没有数据可发，必须截屏生成数据 } <br>
            &nbsp&nbspbegin <br>
            &nbsp&nbspTmpStr:=StrPas(CtrlCode); <br>
            &nbsp&nbspTmpStr:=Copy(TmpStr,5,Length(TmpStr)-4); <br>
            &nbsp&nbspLeftPos:=StrToInt(Copy(TmpStr,1,Pos(':',TmpStr)-1)); <br>
            &nbsp&nbspTmpStr:=Copy(TmpStr,Pos(':',TmpStr)+1,Length(TmpStr) <br>
            &nbsp&nbsp-Pos(':',TmpStr)); <br>
            &nbsp&nbspTopPos:=StrToInt(Copy(TmpStr,1,Pos(':',TmpStr)-1)); <br>
            &nbsp&nbspTmpStr:=Copy(TmpStr,Pos(':',TmpStr)+1,Length(TmpStr)- <br>
            &nbsp&nbspPos(':',TmpStr)); <br>
            &nbsp&nbspRightPos:=StrToInt(Copy(TmpStr,1,Pos(':',TmpStr)-1)); <br>
            &nbsp&nbspBottomPos:=StrToInt(Copy(TmpStr,Pos(':',TmpStr <br>
            &nbsp&nbsp)+1,Length(TmpStr)-Pos(':',TmpStr))); <br>
            &nbsp&nbspScreenCap(LeftPos,TopPos,RightPos,BottomPos); { <br>
            &nbsp&nbsp截取屏幕 } <br>
            &nbsp&nbspend; <br>
            &nbsp&nbspif LeftSize&gt;BufSize then SendSize:=BufSize <br>
            &nbsp&nbspelse SendSize:=LeftSize; <br>
            &nbsp&nbspBmpStream.ReadBuffer(Buf,SendSize); <br>
            &nbsp&nbspLeftSize:=LeftSize-SendSize; <br>
            &nbsp&nbspif LeftSize=0 then BmpStream.Clear;{ 清空流 } <br>
            &nbsp&nbspCUDP.RemoteHost:=FromIP; { FromIP为主控机IP地址 } <br>
            &nbsp&nbspCUDP.SendBuffer(Buf,SendSize); { 将数据发到主控机的2222口 } <br>
            &nbsp&nbspend; <br>
            &nbsp&nbspend; <br>
            &nbsp&nbsp <br>
            &nbsp&nbsp其中ScreenCap是自定义函数，截取屏幕指定区域， <br>
            &nbsp&nbsp代码如下： <br>
            &nbsp&nbspprocedure TClient.ScreenCap(LeftPos,TopPos, <br>
            &nbsp&nbspRightPos,BottomPos:integer); <br>
            &nbsp&nbspvar <br>
            &nbsp&nbspRectWidth,RectHeight:integer; <br>
            &nbsp&nbspSourceDC,DestDC,Bhandle:integer; <br>
            &nbsp&nbspBitmap:TBitmap; <br>
            &nbsp&nbspbegin <br>
            &nbsp&nbspRectWidth:=RightPos-LeftPos; <br>
            &nbsp&nbspRectHeight:=BottomPos-TopPos; <br>
            &nbsp&nbspSourceDC:=CreateDC('DISPLAY','','',nil); <br>
            &nbsp&nbspDestDC:=CreateCompatibleDC(SourceDC); <br>
            &nbsp&nbspBhandle:=CreateCompatibleBitmap(SourceDC, <br>
            &nbsp&nbspRectWidth,RectHeight); <br>
            &nbsp&nbspSelectObject(DestDC,Bhandle); <br>
            &nbsp&nbspBitBlt(DestDC,0,0,RectWidth,RectHeight,SourceDC, <br>
            &nbsp&nbspLeftPos,TopPos,SRCCOPY); <br>
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