Code:

class Test {public:int run(const std::vector<std::string>& args);void updateCallback(RenderContext& renderContext, float time); // called every frameprivate:btBroadphaseInterface* m_broadphase;btCollisionConfiguration* m_collisionConfiguration;btCollisionDispatcher* m_dispatcher;btConstraintSolver* m_solver;btDynamicsWorld* m_world;std::vector<btDefaultMotionState*>m_motionStates;std::vector<std::shared_ptr<Node>>m_boxNodes;};

Code:

int Test::run(const vector<string>& args) {// <make a window, make a scene, set callbacks>// init bulletm_collisionConfiguration = new btDefaultCollisionConfiguration();m_dispatcher = new btCollisionDispatcher(m_collisionConfiguration);m_broadphase = new btDbvtBroadphase();m_solver = new btSequentialImpulseConstraintSolver();m_world = new btDiscreteDynamicsWorld(m_dispatcher, m_broadphase, m_solver, m_collisionConfiguration);// create falling boxes{constexpr unsigned OBJECT_ARRAY_SIZE_X = 2;constexpr unsigned OBJECT_ARRAY_SIZE_Y = 4;constexpr unsigned OBJECT_ARRAY_SIZE_Z = 2;constexpr unsigned SPACING = 1.0;constexpr unsigned DROP_HEIGHT = 40.0;for (int k=0; k<OBJECT_ARRAY_SIZE_Y; ++k) {for (int i=0;i <OBJECT_ARRAY_SIZE_X; ++i) {for(int j = 0; j<OBJECT_ARRAY_SIZE_Z; ++j) {vec3 position = {SPACING * i - (OBJECT_ARRAY_SIZE_X / 2.0),DROP_HEIGHT + SPACING * k - (OBJECT_ARRAY_SIZE_Y / 2.0),SPACING * j  - (OBJECT_ARRAY_SIZE_Z / 2.0) };// create bullet model{btBoxShape* boxShape = new btBoxShape(btVector3(1.0f/2.0, 1.0f/2.0, 1.0f/2.0));// (makes no difference)//boxShape->setMargin(0);btTransform transform;transform.setIdentity();transform.setOrigin(btVector3(position.x, position.y, position.z));btDefaultMotionState* motionState = new btDefaultMotionState(transform);m_motionStates.push_back(motionState);float mass = 2.0;btVector3 localInertia = {0, 0, 0};boxShape->calculateLocalInertia(mass, localInertia);btRigidBody::btRigidBodyConstructionInfo rbInfo(mass, motionState, boxShape, localInertia);rbInfo.m_friction = 0.25;rbInfo.m_rollingFriction = 0.25;rbInfo.m_restitution = 0.25;btRigidBody* rigidBody = new btRigidBody(rbInfo);m_world->addRigidBody(rigidBody);}// create visual model{auto node = Node::GeometryNode(make_shared<Box>(1.0, 1.0, 1.0));node->position(position);m_boxNodes.push_back(node);scene->rootNode()->addChild(node);}}}}}// create ground box{constexpr float GROUND_DIM = 50.0;// create bullet model{btBoxShape* groundShape = new btBoxShape(btVector3(GROUND_DIM/2.0, 0.25/2.0, GROUND_DIM/2.0));// (makes no difference)//groundShape->setMargin(0);btTransform transform;transform.setIdentity();transform.setOrigin(btVector3(0, 0, 0));btDefaultMotionState* motionState = new btDefaultMotionState(transform);btVector3 localInertia = {0, 0, 0};groundShape->calculateLocalInertia(0, localInertia);btRigidBody::btRigidBodyConstructionInfo rbInfo(0, motionState, groundShape, localInertia);rbInfo.m_mass = 0;rbInfo.m_friction = 1.0;rbInfo.m_rollingFriction = 1.0;rbInfo.m_restitution = 0.1;btRigidBody* rigidBody = new btRigidBody(rbInfo);m_world->addRigidBody(rigidBody);}// create visual model{auto groundNode = make_shared<Node>("Box");groundNode->geometry(make_shared<Box>(GROUND_DIM, 0.25, GROUND_DIM));auto gridImage = TestImageNamed("grid10");auto planeDiffuseProperty = make_shared<MaterialProperty>(gridImage);planeDiffuseProperty->wrapS(WRAP_MODE::REPEAT);planeDiffuseProperty->wrapT(WRAP_MODE::REPEAT);planeDiffuseProperty->maxAnisotropy(16);planeDiffuseProperty->minificationFilter(FILTER_MODE::LINEAR_MIPMAP_LINEAR);planeDiffuseProperty->magnificationFilter(FILTER_MODE::LINEAR);auto planeMaterial = make_shared<Material>(nullptr, planeDiffuseProperty, nullptr);planeMaterial->uvScale(GROUND_DIM/10.0);planeMaterial->doubleSided(true);groundNode->geometry()->addMaterial(planeMaterial);groundNode->position({0, 0, 0});scene->rootNode()->addChild(groundNode);}}// <set background, lights, etc>m_window->display(); // blocks until closed by the callback belowreturn 0;}void Test::updateCallback(RenderContext& renderContext, float time) { // called every framestatic float previousSeconds = time;float deltaSeconds = time - previousSeconds;previousSeconds = time;// step the simulation{m_world->stepSimulation(deltaSeconds, 10, 1.0/120.0);}// update visual model{for (unsigned i=0; i<m_motionStates.size(); ++i) {auto motionState = m_motionStates[i];auto boxNode = m_boxNodes[i];btTransform btWorldTransform;btWorldTransform.setIdentity();motionState->getWorldTransform(btWorldTransform);mat4 worldMat;btWorldTransform.getOpenGLMatrix(value_ptr(worldMat));boxNode->transform(worldMat);}}}

Code:

glm::mat4 bulletToGlm(const btTransform& t){glm::mat4 m(0);const btMatrix3x3& basis = t.getBasis();// rotationfor (int r = 0; r < 3; r++){for (int c = 0; c < 3; c++){m[c][r] = basis[r][c];}}// traslationbtVector3 origin = t.getOrigin();m[3][0] = origin.getX();m[3][1] = origin.getY();m[3][2] = origin.getZ();// unit scalem[0][3] = 0.0f;m[1][3] = 0.0f;m[2][3] = 0.0f;m[3][3] = 1.0f;return m;}

Code:

simTime = glfwGetTime();dynamicsWorld->stepSimulation(deltaTime, 20, 1./100);dynamicsWorld->synchronizeMotionStates();  //if I remember correctly this was for the btRaycastVehicle's wheelsif (drawDebug){dynamicsWorld->debugDrawWorld();}simTime = (glfwGetTime() - simTime);