NeHe OpenGL教程第四十课，DancingWind翻译

class Spring									
{										
public:
	Mass* mass1;								// 质点1
	Mass* mass2;								// 质点2

	float springConstant;							// 弹性系数
	float springLength;							//弹簧长度 
	float frictionConstant;							//摩擦系数

	Spring(Mass* mass1, Mass* mass2,
		// 构造函数
		float springConstant, float springLength, float frictionConstant)
	{
		this->springConstant = springConstant;			
		this->springLength = springLength;				
		this->frictionConstant = frictionConstant;			

		this->mass1 = mass1;						
		this->mass2 = mass2;						
	}

	void solve()								// 计算各个物体的受力
	{
		Vector3D springVector = mass1->pos - mass2->pos;		
		
		float r = springVector.length();					// 计算两个物体之间的距离

		Vector3D force;							
		
		if (r != 0)							// 计算力
			force += -(springVector / r) * (r - springLength) * springConstant;
		...

		force += -(mass1->vel - mass2->vel) * frictionConstant;		// 加上摩擦力
		mass1->applyForce(force);						// 给物体1施加力
		mass2->applyForce(-force);						// 给物体2施加力
	}									

class RopeSimulation : public Simulation					//绳索类
{
public:
	Spring** springs;							// 弹簧类结构的数组的指针

	Vector3D gravitation;						// 万有引力

	Vector3D ropeConnectionPos;						// 绳索的连接点
	
	Vector3D ropeConnectionVel;						//连接点的速度，我们使用这个移动绳子

	float groundRepulsionConstant;					//地面的反作用力
	
	float groundFrictionConstant;					//地面的摩擦系数
	
	float groundAbsorptionConstant;					//地面的缓冲力
	
	float groundHeight;						//地面高度

	float airFrictionConstant;						//空气的摩擦系数

	RopeSimulation(								
		int numOfMasses,					
		float m,							
		float springConstant,					
		float springLength,						
		float springFrictionConstant,					
		Vector3D gravitation,						
		float airFrictionConstant,				
		float groundRepulsionConstant,				
		float groundFrictionConstant,				
		float groundAbsorptionConstant,				
		float groundHeight						
		) : Simulation(numOfMasses, m)			
	{
		this->gravitation = gravitation;
		
		this->airFrictionConstant = airFrictionConstant;

		this->groundFrictionConstant = groundFrictionConstant;
		this->groundRepulsionConstant = groundRepulsionConstant;
		this->groundAbsorptionConstant = groundAbsorptionConstant;
		this->groundHeight = groundHeight;

		for (int a = 0; a < numOfMasses; ++a)				// 设置质点位置
		{
			masses[a]->pos.x = a * springLength;			
			masses[a]->pos.y = 0;					
			masses[a]->pos.z = 0;					
		}

		springs = new Spring*[numOfMasses - 1];			
		
		for (a = 0; a < numOfMasses - 1; ++a)				//创建各个质点之间的模拟弹簧
		{
			springs[a] = new Spring(masses[a], masses[a + 1], 
				springConstant, springLength, springFrictionConstant);
		}
	}

	void solve()								// 计算施加给各个质点的力
	{
		for (int a = 0; a < numOfMasses - 1; ++a)			// 弹簧施加给各个物体的力
		{
			springs[a]->solve();					
		}

		for (a = 0; a < numOfMasses; ++a)				// 计算各个物体受到的其它的力
		{
			masses[a]->applyForce(gravitation * masses[a]->m);	// 万有引力
			// 空气的摩擦力
			masses[a]->applyForce(-masses[a]->vel * airFrictionConstant);

			if (masses[a]->pos.y < groundHeight)			// 计算地面对质点的作用
			{
				Vector3D v;					

				v = masses[a]->vel;				// 返回速度
				v.y = 0;					// y方向的速度为0

		// 计算地面给质点的力
				masses[a]->applyForce(-v * groundFrictionConstant);

				v = masses[a]->vel;				
				v.x = 0;					
				v.z = 0;					

				if (v.y < 0)					// 计算地面的缓冲力

					masses[a]->applyForce(-v * groundAbsorptionConstant);
				
				// 计算地面的反作用力
				Vector3D force = Vector3D(0, groundRepulsionConstant, 0) * 
					(groundHeight - masses[a]->pos.y);

				masses[a]->applyForce(force);			// 施加地面对质点的力
			}
		}
	}

	void simulate(float dt)						// 模拟一次
	{
		Simulation::simulate(dt);					// 调用基类的模拟函数

		ropeConnectionPos += ropeConnectionVel * dt;			// 计算绳子的连接点

		if (ropeConnectionPos.y < groundHeight)				
		{
			ropeConnectionPos.y = groundHeight;
			ropeConnectionVel.y = 0;
		}

		masses[0]->pos = ropeConnectionPos;				// 更新绳子的连接点和速度
		masses[0]->vel = ropeConnectionVel;				
	}

	void setRopeConnectionVel(Vector3D ropeConnectionVel)			
	{
		this->ropeConnectionVel = ropeConnectionVel;
	}

RopeSimulation* ropeSimulation =
	new RopeSimulation(
		80,								// 80 质点
		0.05f,								// 每个质点50g
		10000.0f,								// 弹性系数
		0.05f,								// 质点之间的距离
		0.2f,								// 弹簧的内摩擦力
		Vector3D(0, -9.81f, 0),						// 万有引力
		0.02f,								// 空气摩擦力
		100.0f,								// 地面反作用系数
		0.2f,								// 地面摩擦系数
		2.0f,								// 地面缓冲系数
		-1.5f);								// 地面高度

float dt = milliseconds / 1000.0f;						// 经过的秒数

float maxPossible_dt = 0.002f;						// 模拟间隔

int numOfIterations = (int)(dt / maxPossible_dt) + 1;				// 模拟次数
if (numOfIterations != 0)							
	dt = dt / numOfIterations;						

for (int a = 0; a < numOfIterations; ++a)					// 执行模拟
	ropeSimulation->operate(dt);