【C++】Bullet3代码存档

        之前试了一下Bullet3物理引擎，但在linux上编译失败，于是放弃了。令我不满的还有另外一个原因，下载的发行包竟然有500M。C++的Bullet3代码根本用不了，大部分教程实际都是用的老版本。而且此项目还整了python版本，各种蹭人工智能的热度，感觉后面的维护者越来越不靠谱了。

        于是我准备换用ode引擎，下面对bullet3的简单使用记录一下。

一、配置

# bullet3
# 3实际上没有教程，似乎已经弃坑（这里使用2的版本）
# https://github.com/bulletphysics/bullet3/issues/4002
include_directories(${CMAKE_SOURCE_DIR}/third/bullet3/src)
target_link_libraries(${PROJECT_NAME} PRIVATE LinearMath)
target_link_libraries(${PROJECT_NAME} PRIVATE BulletCollision)
target_link_libraries(${PROJECT_NAME} PRIVATE BulletDynamics)

        在CMakePresets.json里需要加入以下变量到cacheVariables，关闭其他东西的构建：

"BUILD_EXTRAS": false,
"BUILD_UNIT_TESTS": false 

二、使用

/**
* @file		dl_physics.h
* @brief	3d物理，基于Bullet3
*
*
* @version	1.0
* @author	lveyou
* @date		22-10-28
*
* @note
*/
#pragma once

#include 

#include 

#include "dl_type.h"
#include "math/dl_transform.h"
#include "dl_time.h"
#include "dl_rigid_body.h"


//Extras / BulletMultiThreaded 拥有多线程版本 碰撞调度和 解算器

namespace dl
{

inline btVector3 toBtVector3(const Position3& v)
{
	return btVector3(v[0], v[1], v[2]);
}

class RigidBodyImp
{
public:
	btRigidBody* _rigidBody;
	btMotionState* _motion;//运动状态，可选 动态物体才有
	size_t _idShape;//形状id
};

class Physics
{
public:
	btDefaultCollisionConfiguration* _collConfig;//碰撞配置
	btCollisionDispatcher* _collDispatcher;//碰撞调度
	btBroadphaseInterface* _broadphase;//broad-phase
	btSequentialImpulseConstraintSolver* _solver;//解算器
	btDiscreteDynamicsWorld* _world;//世界

	std::vector _allShape;//所有形状

	Physics()
	{
		_collConfig = new btDefaultCollisionConfiguration;
		_collDispatcher = new btCollisionDispatcher(_collConfig);
		_broadphase = new btDbvtBroadphase;
		_solver = new btSequentialImpulseConstraintSolver;
		_world = new btDiscreteDynamicsWorld(_collDispatcher, _broadphase, _solver, _collConfig);
		_world->setGravity(btVector3(0, 0, -Numbers::GRAVITY));

		btCollisionShape* shape = new btBoxShape(
			btVector3(1, 1, 1));

		_allShape.push_back(shape);
	}

	/**
	* @brief 创建刚体
	* @param[in] shape_id 形状id
	* @param[in] trans 变换
	* @param[in] mass 质量
	* @retval 失败返回nullptr
	*/
 	RigidBody* CreateRigidBody(size_t shape_id, Transform* trans, Float mass)
	{
		if (shape_id >= _allShape.size())
		{
			log_err0("shape id越界！");
			return nullptr;
		}
		RigidBody* ret = new RigidBody;
		RigidBodyImp* body = ret->GetImp();
		//形状
		body->_idShape = shape_id;
		btCollisionShape* shape = _allShape[shape_id];
		//运动状态
		btTransform bt_trans;
		bt_trans.setIdentity();
		Position3 pos = trans->GetTranslation();
		bt_trans.setOrigin(toBtVector3(pos));

		body->_motion = new btDefaultMotionState(bt_trans);
		//质量和惯性
		btScalar bt_mass{ mass };
		btVector3 local_inertia(0, 0, 0);
		if (bt_mass)
			shape->calculateLocalInertia(bt_mass, local_inertia);
		//创建刚体
		body->_rigidBody = new btRigidBody(bt_mass, body->_motion, shape);
		//加入世界
		_world->addRigidBody(body->_rigidBody);
		return ret;
	}

	//! 创建默认刚体
	RigidBody* CreateRigidBodyDefault(Transform* trans)
	{
		return CreateRigidBody(0, trans, 1);
	}

	//! 创建形状 box
	size_t CreateShapeBox(const Position3& box)
	{
		size_t id = _allShape.size();
		btCollisionShape* shape = new btBoxShape(toBtVector3(box));
		_allShape.push_back(shape);
		return id;
	}

	void Update()
	{
		_world->stepSimulation(g_time->GetDelta());

		//更新位置
		/*for (int j = _world->getNumCollisionObjects() - 1; j >= 0; j--)
		{
			btCollisionObject* obj = _world->getCollisionObjectArray()[j];
			btRigidBody* body = btRigidBody::upcast(obj);

			btTransform trans;
			if (body && body->getMotionState())
			{
				body->getMotionState()->getWorldTransform(trans);
			}
			else
			{
				trans = obj->getWorldTransform();
			}
			trans.getOpenGLMatrix()
			printf("world pos object %d = %f,%f,%f\n", j, float(trans.getOrigin().getX()), float(trans.getOrigin().getY()), float(trans.getOrigin().getZ()));
		}*/
	}

	void UpdateRigidBody(RigidBodyImp* body, Transform* trans)
	{
		btTransform bt_trans;
		btRigidBody* bt_body = body->_rigidBody;

		if (bt_body->getMotionState())
		{
			bt_body->getMotionState()->getWorldTransform(bt_trans);
		}
		else
		{
			bt_trans = bt_body->getWorldTransform();
		}
		const btVector3& pos = bt_trans.getOrigin();
		trans->SetTranslation({pos.getX(), pos.getY(), pos.getZ()});
	}

	~Physics()
	{
		//反向删除
		for (int i = _world->getNumCollisionObjects() - 1; i >= 0; --i)
		{
			btCollisionObject* obj = _world->getCollisionObjectArray()[i];
			btRigidBody* body = btRigidBody::upcast(obj);
			if (body && body->getMotionState())
			{
				delete body->getMotionState();
			}
			_world->removeCollisionObject(obj);
			delete obj;
		}

		for (auto& iter : _allShape)
		{
			delete iter;
		}

		delete _world;
		delete _solver;
		delete _broadphase;
		delete _collDispatcher;
		delete _collConfig;
	}
};

extern Physics* g_physics;

}