NeHe OpenGL教程第三十九课，DancingWind翻译

class Mass
{
public:
	float m;									// 质量
	Vector3D pos;								// 位置
	Vector3D vel;								// 速度
	Vector3D force;								// 力

	Mass(float m)								// 构造函数
	{
		this->m = m;
	}

	...

	void applyForce(Vector3D force)
	{
		this->force += force;						// 增加一个力
	}

	void init()								// 初始时设为0
	{
		force.x = 0;
		force.y = 0;
		force.z = 0;
	}

	...

	void simulate(float dt)
	{
		vel += (force / m) * dt;					// 更新速度
								

		pos += vel * dt;						// 更新位置
										
	}

class Simulation
{
public:
	int numOfMasses;								// 物体的个数
	Mass** masses;								// 指向物体结构的指针

	Simulation(int numOfMasses, float m)						// 构造函数
	{
		this->numOfMasses = numOfMasses;

		masses = new Mass*[numOfMasses];				

		for (int a = 0; a < numOfMasses; ++a)				
			masses[a] = new Mass(m);			
	}

	virtual void release()							// 释放所有的物体
	{
		for (int a = 0; a < numOfMasses; ++a)				
		{
			delete(masses[a]);
			masses[a] = NULL;
		}

		delete(masses);
		masses = NULL;
	}

	Mass* getMass(int index)
	{
		if (index < 0 || index >= numOfMasses)				// 返回第i个物体
			return NULL;						

		return masses[index];						
	}

...

	(class Simulation continued)

	virtual void init()							// 初始化所有的物体
	{
		for (int a = 0; a < numOfMasses; ++a)				
			masses[a]->init();					
	}

	virtual void solve()							//虚函数，在具体的应用中设置各个施加给各个物体的力 
	{
									
	}

	virtual void simulate(float dt)						//让所有的物体模拟一步
	{
		for (int a = 0; a < numOfMasses; ++a)				
			masses[a]->simulate(dt);				
	}

	...

	(class Simulation continued)

	virtual void operate(float dt)						//  完整的模拟过程
	{
		init();								// 设置力为0
		solve();								// 应用力
		simulate(dt);							// 模拟
	}
};

void Update (DWORD milliseconds)						// 执行模拟

void Update (DWORD milliseconds)
{
	...
	...
	...

	float dt = milliseconds / 1000.0f;					// 转化为秒

	dt /= slowMotionRatio;						// 除以模拟系数

	timeElapsed += dt;							// 更新流失的时间

	...

	...

	float maxPossible_dt = 0.1f;					// 设置模拟间隔
									

  	int numOfIterations = (int)(dt / maxPossible_dt) + 1;			//计算在流失的时间里模拟的次数
	if (numOfIterations != 0)					
		dt = dt / numOfIterations;					

	for (int a = 0; a < numOfIterations; ++a)				// 模拟它们	
	{
		constantVelocity->operate(dt);					
		motionUnderGravitation->operate(dt);				
		massConnectedWithSpring->operate(dt);				
	}
}

class ConstantVelocity : public Simulation
{
public:
	ConstantVelocity() : Simulation(1, 1.0f)				 
	{
		masses[0]->pos = Vector3D(0.0f, 0.0f, 0.0f);			// 初始位置为0
		masses[0]->vel = Vector3D(1.0f, 0.0f, 0.0f);			// 向右运动
	}
};

class MotionUnderGravitation : public Simulation
{
	Vector3D gravitation;							// 加速度

	MotionUnderGravitation(Vector3D gravitation) : Simulation(1, 1.0f)		//  构造函数
	{									
		this->gravitation = gravitation;					// 设置加速度
		masses[0]->pos = Vector3D(-10.0f, 0.0f, 0.0f);			// 设置位置为左边-10处
		masses[0]->vel = Vector3D(10.0f, 15.0f, 0.0f);			// 设置速度为右上
	}

	...

	virtual void solve()							// 设置当前的力
	{
		for (int a = 0; a < numOfMasses; ++a)				
			masses[a]->applyForce(gravitation * masses[a]->m);	
	}

class MassConnectedWithSpring : public Simulation
{
public:
	float springConstant;							// 弹性系数
	Vector3D connectionPos;							// 连接方向

	MassConnectedWithSpring(float springConstant) : Simulation(1, 1.0f)		// 构造函数
	{
		this->springConstant = springConstant;				

		connectionPos = Vector3D(0.0f, -5.0f, 0.0f);		

		masses[0]->pos = connectionPos + Vector3D(10.0f, 0.0f, 0.0f);	
		masses[0]->vel = Vector3D(0.0f, 0.0f, 0.0f);		
	}

	...

virtual void solve()								// 设置当前的力
{
	for (int a = 0; a < numOfMasses; ++a)					
	{
		Vector3D springVector = masses[a]->pos - connectionPos;		
		masses[a]->applyForce(-springVector * springConstant);		
	}
}