窗体上打个矩形的洞

procedure MakeRectHole(Ctrl:TWinControl;Form:TForm);
var
  Rgn1, Rgn2: HRGN;
begin
  Rgn1 := CreateRectRgn(0,0, Form.Width, Form.Height);
  Rgn2 := CreateRectRgn(Ctrl.Left, Ctrl.Top,Ctrl.Left+ Ctrl.Width,Ctrl.Top+ Ctrl.Height);
  CombineRgn(Rgn1, Rgn1, Rgn2, RGN_DIFF);
  SetWindowRgn(Form.Handle, Rgn1, TRUE);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
     MakeRectHole(Panel1,Form1);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
       BorderStyle:=BsNone;
       WindowState:= wsMaximized;
end;