给定一个圆心，如何画出同心圆。犹如圆型雷达一样！

var

  i:Integer;

  rect:TRect;

begin

  Self.Canvas.Pen.Style := psSolid;

  Self.Canvas.Pen.Color := clRed;

  rect.Left := 100;

  rect.Right := 500;

  rect.Bottom := 500;

  rect.Top := 100;

  for i := 0 to 3 do

  begin

    rect.Left := rect.Left + i*20;

    rect.Right := rect.Right - i*20;

    rect.Top := rect.Top + i*20;

    rect.Bottom := rect.Bottom - i*20;

    Self.Canvas.Ellipse(rect);

  end;

end;