How to Capture the Screen Shot of the Active Window

How to Capture the Screen Shot of the Active Window

Need to take a screen shoot from code? No problem ... here's how to capture the Windows desktop or the Active Window's image into a TBitmap object - and display it inside a TImage control.

Drop a TImage on a Form and use the following code:

procedure ScreenShot(activeWindow: bool; destBitmap : TBitmap) ;
var
   w,h : integer;
   DC : HDC;
   hWin : Cardinal;
   r : TRect;
begin
   if activeWindow then
   begin
     hWin := GetForegroundWindow;
     dc := GetWindowDC(hWin) ;
     GetWindowRect(hWin,r) ;
     w := r.Right - r.Left;
     h := r.Bottom - r.Top;
   end
   else
   begin
     hWin := GetDesktopWindow;
     dc := GetDC(hWin) ;
     w := GetDeviceCaps (DC, HORZRES) ;
     h := GetDeviceCaps (DC, VERTRES) ;
   end;

   try
    destBitmap.Width := w;
    destBitmap.Height := h;
    BitBlt(destBitmap.Canvas.Handle,
           0,
           0,
           destBitmap.Width,
           destBitmap.Height,
           DC,
           0,
           0,
           SRCCOPY) ;
   finally
    ReleaseDC(hWin, DC) ;
   end;
end;

Usage:

var
   b:TBitmap;
begin
  b := TBitmap.Create;
  try
    ScreenShot(TRUE, b) ;
    Image1.Picture.Bitmap.Assign(b) ;
  finally
    b.FreeImage;
    FreeAndNil(b) ;
  end;

Note: the first parameter in the TakeShot is a bool value indicating whether to take a screen shot of the active window or to grab what's currently on the desktop window.

For an example application, download the source code.

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