如何判断Delphi控件当前是否可见？

{----------------------------------------------------------}
function IsMyFormCovered(const MyForm: TForm): Boolean;
var
   MyRect: TRect;
   MyRgn,TempRgn: HRGN;
   RType: Integer;
   hw: HWND;
begin
  MyRect := MyForm.BoundsRect;            // screen coordinates
  MyRgn := CreateRectRgnIndirect(MyRect); // MyForm not overlapped region
  hw := GetTopWindow(0);                  // currently examined topwindow
  RType := SIMPLEREGION;                  // MyRgn type

// From topmost window downto MyForm,build the not overlapped portion of MyForm
  while (hw<>0) and (hw <> MyForm.handle) and (RType <> NULLREGION) do
  begin
    // nothing to do if hidden window
    if IsWindowVisible(hw) then
    begin
      GetWindowRect(hw,MyRect);
      TempRgn := CreateRectRgnIndirect(MyRect);// currently examined window region
      RType := CombineRgn(MyRgn,MyRgn,TempRgn,RGN_DIFF); // diff intersect
      DeleteObject( TempRgn );
    end; {if}
    if RType <> NULLREGION then // there's a remaining portion
      hw := GetNextWindow(hw,GW_HWNDNEXT);
  end; {while}

  DeleteObject(MyRgn);
  Result := RType = NULLREGION;
end;

function IsMyFormVisible(const MyForm : TForm): Boolean;
begin
  Result:= MyForm.visible and
           isWindowVisible(MyForm.Handle) and
           not IsMyFormCovered(MyForm);
end;