[delphi.com.ar]

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Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    hRegion: HRGN;
  public

  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  hRegion := CreateEllipticRgn(0, 0, Width, Height);
  SetWindowRgn(Handle, hRegion, True);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  DeleteObject(hRegion);
end;

end.

¡¡Conste que dijiste ovalados o redondos!!