public void UpdateAsteroid(Asteroid a, float elapsed)
 {
     a.Position.Y += a.Velocityy * elapsed;
     a.Position.X += a.Velocityx * elapsed;
     a.boundingBox = new Rectangle((int)a.Position.X, (int)a.Position.Y, (int)(textura.Width * a.Escala), (int)(textura.Height * a.Escala));
 }
 public void DrawAsteroid(SpriteBatch spriteBatch, Asteroid a)
 {
     spriteBatch.Draw(textura, a.Position, null,
                      Color.White, 0f, new Vector2(textura.Width / 2, textura.Height / 2), a.Escala, SpriteEffects.None, 0f);
 }