bullet3 三种碰撞检测及实现
Bullet 物理引擎是一个专业的开放源码的碰撞检测,刚体和柔体动力学库。Bullet 物理引擎目标是实时和交互使用在游戏,电影和机器人的视觉效果。自由zlib授权的商业使用库。
bullet3的三种碰撞检测
以下三种方式都是可以达到碰撞检测的效果:
btCollisionWorld::contactTest
检测指定对象是否与场景发生碰撞;btCollisionWorld::performDiscreteCollisionDetection
检测场景中所有的碰撞;btDynamicsWorld::stepSimulation
模拟运动。
还有一种射线检测,但是与这里的物体碰撞稍微有些区别,这里就不展开来讲了。
0. 准备工作
先创建一个场景,增加一个地板(box)
btDefaultCollisionConfiguration* g_colConfig;
btCollisionDispatcher* g_dispatcher;
btBroadphaseInterface* g_broadInterface;
btSequentialImpulseConstraintSolver* g_solver;
btDynamicsWorld* g_world; // 场景信息,退出的时候需要deleteg_colConfig = new btDefaultCollisionConfiguration();
g_dispatcher = new btCollisionDispatcher(g_colConfig);
g_broadInterface = new btDbvtBroadphase();
g_solver = new btSequentialImpulseConstraintSolver;
g_world = new btDiscreteDynamicsWorld(g_dispatcher, g_broadInterface, g_solver, g_colConfig);g_world->setGravity(btVector3(0,-10,0)); // 设置重力加速度// add a test box
{btCollisionShape* shape = new btBoxShape(btVector3(btScalar(1000.),btScalar(10.),btScalar(1000.)));btTransform trans;trans.setIdentity();trans.setOrigin(btVector3(0, -10, 0));btScalar mass=0.f;btVector3 localInertia(0, 0, 0);bool isDynamic = (mass != 0.f);if (isDynamic)shape->calculateLocalInertia(mass, localInertia);btDefaultMotionState* myMotionState = new btDefaultMotionState(trans);btRigidBody::btRigidBodyConstructionInfo cInfo(mass, myMotionState, shape, localInertia);btRigidBody* body = new btRigidBody(cInfo);g_world->addRigidBody(body);
}
1. btCollisionWorld::contactTest
完整函数内容为
void btCollisionWorld::contactTest(btCollisionObject * colObj, ContactResultCallback & resultCallback)
contactTest
会对确定的colObj对象与btCollisionWorld
中的所有对象进行接触检测,并调用ContactResultCallBack
回调。
其实这个函数不算碰撞检测,只是算接触检测,如果距离为0,是会触发回调的。
1.1. 继承回调的结构体
ContactResultCallback
结构体有一个名为addSingleResult
的纯虚函数,在继承的时候一定要实现addSingleResult
函数。这个也是碰撞的时候执行的回调函数。是这个结构体的核心。碰撞信息会存储在btManifoldPoint & cp
中,使用方法也比较简单,可以参考API文档的接口。其它地方的碰撞,也是用这个对象存储,处理方法是一样的。
// 碰撞检测回调
struct MyColCallBack : btCollisionWorld::ContactResultCallback
{public:btScalar addSingleResult(btManifoldPoint & cp,const btCollisionObjectWrapper * colObj0Wrap,int partId0,int index0,const btCollisionObjectWrapper * colObj1Wrap,int partId1,int index1){btVector3 posA = cp.getPositionWorldOnA();btVector3 posB = cp.getPositionWorldOnB();printf("col pos for A {%f, %f, %f}\n", posA.getX(), posA.getY(), posA.getZ());printf("col pos for B {%f, %f, %f}\n", posB.getX(), posB.getY(), posB.getZ());return btScalar(0.f);};
};
1.2. 碰撞检测
// 创建一个球体,并加入到场景中
btCollisionShape* shape = new btSphereShape(btScalar(1.f));
btTransform trans;
trans.setIdentity();
trans.setOrigin(btVector3(0, 1, 0));btScalar mass=1.f;
btVector3 localInertia(0, 0, 0);
bool isDynamic = (mass != 0.f);
if (isDynamic)shape->calculateLocalInertia(mass, localInertia);btDefaultMotionState* myMotionState = new btDefaultMotionState(trans);
btRigidBody::btRigidBodyConstructionInfo cInfo(mass, myMotionState, shape, localInertia);
btRigidBody* g_body = new btRigidBody(cInfo);
g_world->addRigidBody(g_body);// 创建回调并碰撞检测
MyColCallBack callBack;
g_world->contactTest(g_body, callBack);// todo delete
运行结果:
2. btCollisionWorld::performDiscreteCollisionDetection
performDiscreteCollisionDetection
会对场景中的所有物体进行一次碰撞检测。而contactTest
是对确定的物体进行碰撞检测。
g_world->performDiscreteCollisionDetection();list<btCollisionObject*> m_collisionObjects;
int numManifolds = g_world->getDispatcher()->getNumManifolds();for(int i=0; i<numManifolds; i++)
{btPersistentManifold* contactManifold = g_world->getDispatcher()->getManifoldByIndexInternal(i);btCollisionObject* obA = (btCollisionObject*)(contactManifold->getBody0());btCollisionObject* obB = (btCollisionObject*)(contactManifold->getBody1());int numContacts = contactManifold->getNumContacts();for(int j=0; j<numContacts; j++){btManifoldPoint& pt = contactManifold->getContactPoint(j);if(pt.getDistance()<=0.f){m_collisionObjects.push_back(obA);m_collisionObjects.push_back(obB);btVector3 posA = pt.getPositionWorldOnA();btVector3 posB = pt.getPositionWorldOnB();printf("%d A -> {%f, %f, %f}\n", i, posA.getX(), posA.getY(), posA.getZ()); // 碰撞点printf("%d B -> {%f, %f, %f}\n", i, posB.getX(), posB.getY(), posB.getZ());}}
}
这里需要注意一下,多个物体两两碰撞的时候,列表m_collisionObjects
内是存在重复的可能的,往往需要去重一下。
m_collisionObjects.sort();
m_collisionObjects.unique();
运行结果:
这里我多加了一个半径为1,位置为{1,1,0}的求,然后基本上两个球和地板发生了两两碰撞。
3. btDynamicsWorld::stepSimulation
完整的函数内容为:
virtual int btDynamicsWorld::stepSimulation(btScalar timeStep,int maxSubSteps = 1,btScalar fixedTimeStep = btScalar(1.)/btScalar(60.))
stepSimulation
其实不是用来做碰撞检测的,而是用来做物理运动模拟的。既然能做运动模拟,那肯定也能够做碰撞检测了。
3.1. 模拟运动
设置场景的重力加速为btVector3(0,-10,0)
,增加一个半径为1,位置为{0,100,0}的球体,并设置其质量为1,冲量为{2,0,0},即球体会以x轴速度为2,Y轴以-10的加速度做抛物线运动。
// 设置重力加速度
g_world->setGravity(btVector3(0,-10,0)); // 创建一个球体,并加入到场景中
btCollisionShape* shape = new btSphereShape(btScalar(1.f));
btTransform trans;
trans.setIdentity();
trans.setOrigin(btVector3(0, 100, 0));btScalar mass=1.f;
btVector3 localInertia(0, 0, 0);
bool isDynamic = (mass != 0.f);
if (isDynamic)shape->calculateLocalInertia(mass, localInertia);btDefaultMotionState* myMotionState = new btDefaultMotionState(trans);
btRigidBody::btRigidBodyConstructionInfo cInfo(mass, myMotionState, shape, localInertia);
btRigidBody* g_body = new btRigidBody(cInfo);
g_body->applyCentralImpulse(btVector3(2,0,0)); // 设置冲量
g_world->addRigidBody(g_body);for (i=0;i<10;i++)
{g_world->stepSimulation(1.f/60.f,10); // 模拟运动trans = g_body->getWorldTransform();printf("world pos = %f,%f,%f\n", trans.getOrigin().getX(), trans.getOrigin().getY(),trans.getOrigin().getZ());}
}
执行结果