Bullet(Cocos2dx)之封装PhysicsWorld3D

Bullet3之封装PhysicsWorld3D

根据bullet3 HelloWorld程序去封装一个PhysicsWorld3D，

首先应该去创建一个物理世界，而对于一个物理世界，默认都有重力，提供一个创建

世界的静态方法（重力默认为(0, -10, 0）)

static PhysicsWorld3D* create(const btVector3& gravity = btVector3(0, -10, 0));

负责创建世界，同时对世界初始化

这里创建一个btDiscreteDynamicsWorld

直接复制bullet3 HelloWorld对世界的初始化，并修改

_collisionConfiguration,_dispatcher, _solver, _overlappingPairCache, _drawer均为成员变量，

具体使用参照Bullet的文档

PhysicsWorld3D* PhysicsWorld3D::create(const btVector3& gravity){auto world = new PhysicsWorld3D;if (world && world->initWorld(gravity)){return world;}delete world;return nullptr;}bool PhysicsWorld3D::initWorld(const btVector3& gravity){_collisionConfiguration = new btDefaultCollisionConfiguration();_dispatcher = newbtCollisionDispatcher(_collisionConfiguration);_overlappingPairCache = new btDbvtBroadphase();_solver = new btSequentialImpulseConstraintSolver;_world = new btDiscreteDynamicsWorld(_dispatcher, _overlappingPairCache, _solver, _collisionConfiguration);if (_world == nullptr){return false;}_world->setGravity(gravity);return true;}

销毁一个物理世界

void PhysicsWorld3D::destroy(){this->clear();delete _collisionConfiguration;delete _dispatcher;delete _solver;delete _overlappingPairCache;delete _world;delete this;}void PhysicsWorld3D::clear(){int i;//remove the rigidbodies from the dynamics world and delete themfor (i = _world->getNumCollisionObjects() - 1; i >= 0; i--){btCollisionObject* obj = _world->getCollisionObjectArray()[i];btRigidBody* body = btRigidBody::upcast(obj);if (body && body->getMotionState()){delete body->getMotionState();delete body->getCollisionShape();}_world->removeCollisionObject(body);delete obj;}}

创建一些简单的body

由于每种body都有自己的材质信息

btRigidBodyConstructionInfo是构造一个刚体信息的结构体,

 

我们只需关心几个参数，

friction; // 摩擦系数

rollingFriction; // 滚动摩擦系数

restitution; // 恢复系数(弹性系数)

mass;   // 质量

自己去实现一个简单的材质结构体

struct PhysicsMaterial3D{btScalar friction;btScalar rollingFriction;btScalar restitution;btScalar mass;PhysicsMaterial3D() :friction(0.0f),rollingFriction(0.f),restitution(0.f),mass(0.f){}PhysicsMaterial3D(btScalar aMass, btScalar aFriction, btScalar aRestitution, btScalar aRollingFriction) :friction(aFriction),rollingFriction(aRollingFriction),restitution(aRestitution),mass(aMass){}};

并提供一个默认的材质信息

const PhysicsMaterial3D PHYSICS_MATERIAL3D_DEFAULT(1.f, 0.5f, 0.5f, 0.0f); 

实现构造3个基本物体，如下声明

btRigidBody* addPlane(const btVector3& normal, const btVector3& position, const PhysicsMaterial3D& material = PHYSICS_MATERIAL3D_DEFAULT);btRigidBody* addSphere(btScalar radius, const btVector3& position, const PhysicsMaterial3D& material = PHYSICS_MATERIAL3D_DEFAULT);btRigidBody* addBox(const btVector3& halfSize, const btVector3& position, const PhysicsMaterial3D& material = PHYSICS_MATERIAL3D_DEFAULT);

对于一个无限的平面，需要一个法向量决定Plane的朝向，同时position决定plane的位置，当然还有材质，但是mass必须为0

对于一个球体（Sphere）半径，位置，材质

对于一个盒子（Box）尺寸, 位置，材质

btRigidBody* PhysicsWorld3D::addPlane(const btVector3& normal, const btVector3& position, const PhysicsMaterial3D& material){CCAssert(material.mass == 0.f, "plane's mass must be 0."); // 特殊处理，保证mass为0btCollisionShape* groundShape = new btStaticPlaneShape(normal, 0.f);auto body = getBody(groundShape, position, material);_world->addRigidBody(body);return body;}btRigidBody* PhysicsWorld3D::addSphere(btScalar radius, const btVector3& position, const PhysicsMaterial3D& material){btCollisionShape* colShape = new btSphereShape(radius);auto body = getBody(colShape, position, material);_world->addRigidBody(body);return body;}btRigidBody* PhysicsWorld3D::addBox(const btVector3& size, const btVector3& position, const PhysicsMaterial3D& material){btCollisionShape* colShape = new btBoxShape(size * 0.5f); // halfSizeauto body = getBody(colShape, position, material);_world->addRigidBody(body);return body;}

构造一个刚体包含一些共同的步骤collisionShape, position, material

由于Plane，Sphere，Box collisionShape类型不同，所以单独实现，

其他的公共步骤可以抽离出来

btRigidBody* getBody(btCollisionShape* colShape, const btVector3& position, const PhysicsMaterial3D& material);

仿照HelloWorld构造body的方法

btRigidBody* PhysicsWorld3D::getBody(btCollisionShape* colShape, const btVector3& position, const PhysicsMaterial3D& material){/// Create Dynamic ObjectsbtTransform startTransform;startTransform.setIdentity();//rigidbody is dynamic if and only if mass is non zero, otherwise staticbool isDynamic = (material.mass != 0.f);btVector3 localInertia(0,0,0);if (isDynamic)colShape->calculateLocalInertia(material.mass, localInertia); // 计算物体惯性startTransform.setOrigin(position); // 设置物体位置//using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objectsbtDefaultMotionState* myMotionState = new btDefaultMotionState(startTransform);btRigidBody::btRigidBodyConstructionInfo rbInfo(material.mass, myMotionState,colShape,localInertia);// 使用自定义的材质rbInfo.m_restitution = material.restitution;rbInfo.m_friction = material.friction;rbInfo.m_rollingFriction = material.rollingFriction;// 创建bodybtRigidBody* body = new btRigidBody(rbInfo);return body;}

不要忘了物理世界的更新

void PhysicsWorld3D::update(float dt){_world->stepSimulation(dt);}

完整源码