private void doPhysics() {
world.step(Gdx.graphics.getDeltaTime(), 6, 2);
List<Contact> contactList = world.getContactList();
for (int i = 0; i < contactList.size(); i++) {
Contact contact = contactList.get(i);
if (contact.isTouching()) {
Object a = contact.getFixtureA().getBody().getUserData();
Object b = contact.getFixtureB().getBody().getUserData();
if (a instanceof CannonBall && b instanceof EnemyShip) {
if(((CannonBall) a).life < 10) {
// TODO send enemy hit packet
// ((EnemyShip) b).life -= 1;