procedure TForm1.FormCreate(Sender: TObject);
var LParticles : TGorillaRainParticleEmitter;
begin
  LParticles := TGorillaRainParticleEmitter.Create(FGorilla);
  LParticles.Parent := FGorilla;
  LParticles.Camera := FCamera;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  // on some constellations you will need an interval to update the viewport
  FGorilla.Invalidate();
end;