====== bullet碰撞检测 ======
===== 调用方法 =====
**别听网上的乱分析**。bullet一共有4种碰撞检测，分别是单体检测，全体检测，射线检测，扫描检测
==== 单体检测 ====
检测与一个物体碰撞的所有物体
==== 全体检测 ====
检测碰撞世界中发生的所有碰撞
==== 射线检测 ====
检测与一根线碰撞的所有物体
==== 扫描检测 ====
假定一个物体向前移动一段距离，检测路上发生的碰撞
===== 底层原理 =====
==== 粗碰撞阶段 ====
	btVector3 aabbMin,aabbMax;
	colObj->getCollisionShape()->getAabb(colObj->getWorldTransform(),aabbMin,aabbMax);
	btSingleContactCallback	contactCB(colObj,this,resultCallback);
	
	m_broadphasePairCache->aabbTest(aabbMin,aabbMax,contactCB);//底层是层次包围盒
==== 精确碰撞阶段 ====
	virtual bool	process(const btBroadphaseProxy* proxy)
	{
		btCollisionObject*	collisionObject = (btCollisionObject*)proxy->m_clientObject;
		if (collisionObject == m_collisionObject)
			return true;
    
		//only perform raycast if filterMask matches
		if(m_resultCallback.needsCollision(collisionObject->getBroadphaseHandle())) 
		{
			btCollisionObjectWrapper ob0(0,m_collisionObject->getCollisionShape(),m_collisionObject,m_collisionObject->getWorldTransform(),-1,-1);
			btCollisionObjectWrapper ob1(0,collisionObject->getCollisionShape(),collisionObject,collisionObject->getWorldTransform(),-1,-1);//获取形状
    
			btCollisionAlgorithm* algorithm = m_world->getDispatcher()->findAlgorithm(&ob0,&ob1,0, BT_CLOSEST_POINT_ALGORITHMS);//查找针对这两个形状的精确碰撞接口
			if (algorithm)
			{
				btBridgedManifoldResult contactPointResult(&ob0,&ob1, m_resultCallback);
				//discrete collision detection query
				
				algorithm->processCollision(&ob0,&ob1, m_world->getDispatchInfo(),&contactPointResult);//调用接口
    
				algorithm->~btCollisionAlgorithm();
				m_world->getDispatcher()->freeCollisionAlgorithm(algorithm);
			}
		}
		return true;
	}