Cirkel i OpenGl?

Kode 

procedure TForm1.FormPaint(Sender: TObject);
var
  I, Antal : Integer;
begin
  glClearColor(0,0,0,0);
  glClear(gl_Color_Buffer_Bit);

  glBegin(GL_Polygon);
  Antal := 1000;
  for I := 0 to Antal do
  begin
    glVertex3f(cos(i*PI/Antal)/5,sin(i*PI/Antal)/5,0);
    glVertex3f(cos(i*PI/Antal)/5,sin(i*PI/Antal)/5,0.2);
    glVertex3f(cos(i*PI/Antal)/5,0,0.2);
    glVertex3f(cos(i*PI/Antal)/5,0,0);
  end;
  glEnd;

  SwapBuffers(Context.DeviceContext);
end;