delphi截圖問題

這個源碼是截屏目的.但我想截指定的窗口,比如 計算器 窗口.我應該改哪裏?謝謝

var

Fullscreen: Tbitmap;

FullscreenCanvas: TCanvas;

dc: HDC;

begin

Fullscreen := TBitmap.Create; //創建壹個BITMAP來存放圖象

Fullscreen.Width := 100;

Fullscreen.Height := 100;

DC := GetDC(0); //取得屏幕的 DC，參數0指的是屏幕

FullscreenCanvas := TCanvas.Create; //創建壹個CANVAS對象

FullscreenCanvas.Handle := DC;

Fullscreen.Canvas.CopyRect

(Rect(0, 0, screen.Width, screen.Height), fullscreenCanvas,

Rect(0, 0, Screen.Width, Screen.Height));

//把整個屏幕復制到BITMAP中

FullscreenCanvas.Free; //釋放CANVAS對象

ReleaseDC(0, DC); //釋放DC

image1.picture.Bitmap := fullscreen; //拷貝下的圖象賦給IMAGE對象

image1.Width := fullscreen.Width;

image1.Height := fullscreen.Height;

fullscreen.free; //釋放bitmap

form1.WindowState := wsNormal; //復原窗口狀態

end;