procedure TForm1.Button1Click(Sender: TObject);

begin

  canvas.Font.Name := 'Times New Roman';

  canvas.Font.size := 72;

  canvas.Font.style := [fsItalic,fsBold];

  beginpath(canvas.handle);

    SetBkMode(Canvas.Handle, TRANSPARENT ); //试验一下不用这行语句，会得到很有意思的结果

    canvas.Polygon([Point(0,0),Point(Width,0),

                    Point(Width,Height),Point(0,Height),

                    Point(0,0)]); //试验不用该语句看看结果如何

    canvas.TextOut(20,40,'Hello');

  endpath(canvas.handle);

  SetWindowRgn( Handle, PathToRegion(canvas.Handle), true );

end;