2个多边形，其中一个包围另一个，如何将中间的环带区域涂成红色？

Question

如题

Answer 1

procedure TForm1.Button1Click(Sender: TObject);begin
   with Canvas do
   begin
     Rectangle(100,100,300,300);
     Rectangle(150,150,250,250);
     Brush.Color := clRed;
     FillRect(rect(150,150,250,250));
   end;
end;

Answer 2

先创建出HRGH的区域，再用CombineRgn获取环带的区域，之后填充：var a, b, c: HRGN;
    hbr: HBRUSH;
begin
  //  Canvas.Rectangle(100,200,400,400);
  //  Canvas.RoundRect(120,220,300,350,100,100);
  hbr := CreateSolidBrush(clRed);
  a:=CreateRectRgn(100,200,400,400);
  b:=CreateRoundRectRgn(120,220,300,350,100,100);
  c:=CreateRectRgn(0,0,1,1);
  CombineRgn(c, a, b, RGN_DIFF);
  FillRgn(Canvas.Handle,c, hbr);
end;