利用UDP协议传输图象

 　　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。
　　在implementation后面加入变量定义

const BufSize=2048;{ 发送每一笔数据的缓冲区大小 }
var
BmpStream:TMemoryStream;
LeftSize:Longint;{ 发送每一笔数据后剩余的字节数 }

为Client的OnCreate事件添加代码：
procedure TClient.FormCreate(Sender: TObject);
begin
BmpStream:=TMemoryStream.Create;
end;

为Client的OnDestroy事件添加代码：
procedure TClient.FormDestroy(Sender: TObject);
begin
BmpStream.Free;
end;

为控件CUDP的OnDataReceived事件添加代码：
procedure TClient.CUDPDataReceived(Sender: TComponent;
NumberBytes: Integer; FromIP: String);
var
CtrlCode:array[0..29] of char;
Buf:array[0..BufSize-1] of char;
TmpStr:string;
SendSize,LeftPos,TopPos,RightPos,BottomPos:integer;
begin
CUDP.ReadBuffer(CtrlCode,NumberBytes);{ 读取控制码 }
if CtrlCode[0]+CtrlCode[1]+CtrlCode[2]+CtrlCode[3]='show' then
begin { 控制码前4位为“show”表示主控机发出了抓屏指令 }
if BmpStream.Size=0 then { 没有数据可发，必须截屏生成数据 }
begin
TmpStr:=StrPas(CtrlCode);
TmpStr:=Copy(TmpStr,5,Length(TmpStr)-4);
LeftPos:=StrToInt(Copy(TmpStr,1,Pos(':',TmpStr)-1));
TmpStr:=Copy(TmpStr,Pos(':',TmpStr)+1,Length(TmpStr)
-Pos(':',TmpStr));
TopPos:=StrToInt(Copy(TmpStr,1,Pos(':',TmpStr)-1));
TmpStr:=Copy(TmpStr,Pos(':',TmpStr)+1,Length(TmpStr)-
Pos(':',TmpStr));
RightPos:=StrToInt(Copy(TmpStr,1,Pos(':',TmpStr)-1));
BottomPos:=StrToInt(Copy(TmpStr,Pos(':',TmpStr
)+1,Length(TmpStr)-Pos(':',TmpStr)));
ScreenCap(LeftPos,TopPos,RightPos,BottomPos); {
截取屏幕 }
end;
if LeftSize>BufSize then SendSize:=BufSize
else SendSize:=LeftSize;
BmpStream.ReadBuffer(Buf,SendSize);
LeftSize:=LeftSize-SendSize;
if LeftSize=0 then BmpStream.Clear;{ 清空流 }
CUDP.RemoteHost:=FromIP; { FromIP为主控机IP地址 }
CUDP.SendBuffer(Buf,SendSize); { 将数据发到主控机的2222口 }
end;
end;

其中ScreenCap是自定义函数，截取屏幕指定区域，
代码如下：
procedure TClient.ScreenCap(LeftPos,TopPos,
RightPos,BottomPos:integer);
var
RectWidth,RectHeight:integer;
SourceDC,DestDC,Bhandle:integer;
Bitmap:TBitmap;
begin
RectWidth:=RightPos-LeftPos;
RectHeight:=BottomPos-TopPos;
SourceDC:=CreateDC('DISPLAY','','',nil);
DestDC:=CreateCompatibleDC(SourceDC);
Bhandle:=CreateCompatibleBitmap(SourceDC,
RectWidth,RectHeight);
SelectObject(DestDC,Bhandle);
BitBlt(DestDC,0,0,RectWidth,RectHeight,SourceDC,
LeftPos,TopPos,SRCCOPY);
Bitmap:=TBitmap.Create;
Bitmap.Handle:=BHandle;
BitMap.SaveToStream(BmpStream);
BmpStream.Position:=0;
LeftSize:=BmpStream.Size;
Bitmap.Free;
DeleteDC(DestDC);
ReleaseDC(Bhandle,SourceDC);
end;
存为“C:/VClient/ClnUnit.pas”和“C:/VClient/VClient.dpr”，
并编译。

　　第二步，编制VServer.exe文件。新建Delphi工程，将窗体的Name属性设为“Server”。
加入TNMUDP控件，Name属性设为“SUDP”；LocalPort属性设为“2222”，让控件SUDP监视
主控机的2222端口，当有数据发送到该口时，触发控件SUDP的OnDataReceived事件；RemotePort
属性设为“1111”，当控件SUDP发送数据时，将数据发到受控机的1111口。加入控件Image1，
Align属性设为“alClient”；加入控件Button1，Caption属性设为“截屏”；加入控件Label1，
Caption属性设为“左：上：右：下”；加入控件Edit1，Text属性设为“0:0:100:100”；
加入控件Label2，Caption属性设为“受控机IP地址”；加入控件Edit2，Text属性设为“127.0.0.1”；
在implementation后面加入变量定义
const BufSize=2048;
var
RsltStream,TmpStream:TMemoryStream;

为Server的OnCreate事件添加代码：
procedure TServer.FormCreate(Sender: TObject);
begin
RsltStream:=TMemoryStream.Create;
TmpStream:=TMemoryStream.Create;
end;

为Client的OnDestroy事件添加代码：
procedure TServer.FormDestroy(Sender: TObject);
begin
RsltStream.Free;
TmpStream.Free;
end;

为控件Button1的OnClick事件添加代码：
procedure TServer.Button1Click(Sender: TObject);
var ReqCode:array[0..29] of char;ReqCodeStr:string;
begin
ReqCodeStr:='show'+Edit1.Text;
StrpCopy(ReqCode,ReqCodeStr);
TmpStream.Clear;
RsltStream.Clear;
SUDP.RemoteHost:=Edit2.Text;
SUDP.SendBuffer(ReqCode,30);
end;

为控件SUDP的OnDataReceived事件添加代码：
procedure TServer.SUDPDataReceived(Sender: TComponent;
NumberBytes: Integer; FromIP: String);
var ReqCode:array[0..29] of char;ReqCodeStr:string;
begin
ReqCodeStr:='show'+Edit1.text;
StrpCopy(ReqCode,ReqCodeStr);
SUDP.ReadStream(TmpStream);
RsltStream.CopyFrom(TmpStream,NumberBytes);
if NumberBytes< BufSize then { 数据已读完 }
begin
RsltStream.Position:=0;
Image1.Picture.Bitmap.LoadFromStream(RsltStream);
TmpStream.Clear;
RsltStream.Clear;
end
else
begin
TmpStream.Clear;
ReqCode:='show';
SUDP.RemoteHost:=Edit2.Text;
SUDP.SendBuffer(ReqCode,30);
end;
end;