Make a polygon hole on a form

Make a polygon hole on a form

type
  PtsType = array [0..15, 0..1] of Integer;

const
  Pts: PtsType = ((0, 0), (800, 0), (800, 600),
    (200, 600), (200, 220), (300, 280),
    (265, 205), (350, 117), (205, 170),
    (120, 90), (130, 200), (60, 350), (200, 220),
    (200, 600), (0, 600), (0, 0));

procedure TForm1.Button1Click(Sender: TObject);
var
  HRegion1: THandle;
begin
  HRegion1 := CreatePolygonRgn(Pts, SizeOf(Pts) div 8, alternate);
  SetWindowRgn(Handle, HRegion1, True);
end;