auto contactListener = EventListenerPhysicsContact::create();
contactListener->onContactBegin = CC_CALLBACK_1(PhysicsContactTest::onContactBegin, this);
_eventDispatcher->addEventListenerWithSceneGraphPriority(contactListener, this);
bool PhysicsContactTest::onContactBegin(PhysicsContact& contact)
{
// 碰撞的回调函数， 怎么获取碰撞的坐标点呢？？？
return true;
}