unity官方资源包CarController理解

    最近要写汽车的控制，发现比人物控制难很多，涉及到汽车的很多知识，自己写了一点不忍直视，各种bug，然后被告知untiy官方资源包里有控制脚本，就去学习了一下，然后借鉴了网上的一些教程，在这里表示衷心感谢，为了方面自己和他人，免得自己弄丢，然后贴在这里：

using System;
using UnityEngine;

namespace UnityStandardAssets.Vehicles.Car//此处可改成自己的car名字
{
    internal enum CarDriveType
    {
        FrontWheelDrive,//前驱
        RearWheelDrive,//后驱
        FourWheelDrive//四驱
    }

    internal enum SpeedType
    {
        MPH,//英里
        KPH//千米/h
    }

    public class CarController : MonoBehaviour
    {
        //[SerializeField]是为了成员变量可以在检视面板上显示
        [SerializeField] private CarDriveType m_CarDriveType = CarDriveType.FourWheelDrive; //四驱
        [SerializeField] private WheelCollider[] m_WheelColliders = new WheelCollider[4]; //存放轮子的数组
        [SerializeField] private GameObject[] m_WheelMeshes = new GameObject[4]; //车轮模型
        [SerializeField] private WheelEffects[] m_WheelEffects = new WheelEffects[4];//存放特效数组，粒子，音效等
        [SerializeField] private Vector3 m_CentreOfMassOffset;//车的重心
        [SerializeField] private float m_MaximumSteerAngle;//最大可转角度
        [Range(0, 1)] [SerializeField] private float m_SteerHelper; // 0 is raw physics , 1 the car will grip in the direction it is facing//初始化为0，1是车被控制面对的方向
        [Range(0, 1)] [SerializeField] private float m_TractionControl; // 0 is no traction control, 1 is full interference///0没有牵引力控制系统,1是完整的干扰
     //所有车轮的扭矩  扭矩越大，加速性能越好；扭矩越小，加速性能越差
     //如某车的1挡齿比（齿轮的齿数比，本质就是齿轮的半径比）是3，尾牙为4，轮胎半径为0.3米，原扭矩是200Nm的话，最后在轮轴的扭矩就变成200×3×4=2400Nm，
     //再除以轮胎半径0.3米后，轮胎与地面摩擦的部分就有2400Nm/0.3m=8000N，即800公斤力的驱动力，这就足以驱动汽车了

        //驱动力公式：驱动力=扭矩×变速箱齿比×主减速器速比×机械效率÷轮胎半径
        [SerializeField] private float m_FullTorqueOverAllWheels;//所有轮胎的扭矩
        [SerializeField] private float m_ReverseTorque;//反向扭矩
        [SerializeField] private float m_MaxHandbrakeTorque;//最大刹车扭矩
        [SerializeField] private float m_Downforce = 100f;//下压力
        [SerializeField] private SpeedType m_SpeedType;//速度类型
        [SerializeField] private float m_Topspeed = 200;//最大速度
        [SerializeField] private static int NoOfGears = 5;//档位数
        [SerializeField] private float m_RevRangeBoundary = 1f;//最大滑动距离
        [SerializeField] private float m_SlipLimit;//轮胎下滑给定的阈值
        [SerializeField] private float m_BrakeTorque;//刹车扭矩

        private Quaternion[] m_WheelMeshLocalRotations;//四元数组存储车轮本地转动数据
        private Vector3 m_Prevpos, m_Pos;
        private float m_SteerAngle; //转向角
        private int m_GearNum;//档位数
        private float m_GearFactor;//挡位因子
        private float m_OldRotation;//用于转动计算
        private float m_CurrentTorque;//当前扭矩
        private Rigidbody m_Rigidbody;//刚体
        private const float k_ReversingThreshold = 0.01f; //反转阈值

        //角色信息访问控制，对外接口
        public bool Skidding { get; private set; }
        public float BrakeInput { get; private set; }
        public float CurrentSteerAngle{ get { return m_SteerAngle; }}//当前车轮角度
        public float CurrentSpeed{ get { return m_Rigidbody.velocity.magnitude*2.23693629f; }}//当前速度
        public float MaxSpeed{get { return m_Topspeed; }}//最大速度
        public float Revs { get; private set; }//转速属性
        public float AccelInput { get; private set; } //加速输入

        // Use this for initialization
        //初始化
        private void Start()
        {
            m_WheelMeshLocalRotations = new Quaternion[4]; //获得车轮的四元数的角度信息
            for (int i = 0; i < 4; i++)
            {
                m_WheelMeshLocalRotations[i] = m_WheelMeshes[i].transform.localRotation;
            }
            m_WheelColliders[0].attachedRigidbody.centerOfMass = m_CentreOfMassOffset;

            m_MaxHandbrakeTorque = float.MaxValue;

            m_Rigidbody = GetComponent();

            //当前扭矩=全部扭矩-（牵引系数【0-1】*全部扭矩）
            //设置当前扭矩，初始化的扭矩值跟m_TractionControl大小有关，m_TractionControl决定是否有牵引力，如果m_TractionControl
            //值为0，则当前扭矩直接就是最大值，如果该值为1，则初始扭矩为0，然后汽车启动慢慢增加扭矩力。建议m_TractionControl数值为0.5
            m_CurrentTorque = m_FullTorqueOverAllWheels - (m_TractionControl*m_FullTorqueOverAllWheels);//
        }

        //变档函数
        private void GearChanging()
        {
            float f = Mathf.Abs(CurrentSpeed/MaxSpeed);
            float upgearlimit = (1/(float) NoOfGears)*(m_GearNum + 1);
            float downgearlimit = (1/(float) NoOfGears)*m_GearNum;

            if (m_GearNum > 0 && f < downgearlimit)
            {
                m_GearNum--;
            }

            if (f > upgearlimit && (m_GearNum < (NoOfGears - 1)))
            {
                m_GearNum++;
            }
        }

        //在0-1范围内为值添加一个曲线偏向1的简单函数
        // simple function to add a curved bias towards 1 for a value in the 0-1 range
        private static float CurveFactor(float factor)
        {
            return 1 - (1 - factor)*(1 - factor);
        }

        //松开插值的版本，允许值超出范围
        // unclamped version of Lerp, to allow value to exceed the from-to range
        private static float ULerp(float from, float to, float value)
        {
            return (1.0f - value)*from + value*to;
        }

        //计算齿轮因素/档位因子
        private void CalculateGearFactor()
        {
            float f = (1/(float) NoOfGears);
            // gear factor is a normalised representation of the current speed within the current gear's range of speeds.
            // We smooth towards the 'target' gear factor, so that revs don't instantly snap up or down when changing gear.
            //齿轮因素是在当前齿轮的速度范围的正常表示。我们顺利走向“目标”装备因素,所以转速时不要立即调节或向下改变齿轮。
            //目标齿轮数=（当前速度/最大速度）*最大齿轮数-当前齿轮数
            //我们要让值平滑地想着目标移动，以保证转速不会在变换档位时突然地上高或者降低
            //反向差值，通过当前速度的比例值，找当前速度在当前档位的比例位置，得到的值将是一个0~1范围内的值。
            var targetGearFactor = Mathf.InverseLerp(f*m_GearNum, f*(m_GearNum + 1), Mathf.Abs(CurrentSpeed/MaxSpeed));//反插值，计算比例值（5，10，8）=（8-5）/（10-5）=3/5
            m_GearFactor = Mathf.Lerp(m_GearFactor, targetGearFactor, Time.deltaTime*5f);   //从当前档位因子向目标档位因子做平滑差值
        }

        //计算引擎转速(显示/声音)
        private void CalculateRevs()
        {
            // calculate engine revs (for display / sound)
            // (this is done in retrospect - revs are not used in force/power calculations)
            CalculateGearFactor();
            var gearNumFactor = m_GearNum/(float) NoOfGears;
            var revsRangeMin = ULerp(0f, m_RevRangeBoundary, CurveFactor(gearNumFactor));
            var revsRangeMax = ULerp(m_RevRangeBoundary, 1f, gearNumFactor);
            Revs = ULerp(revsRangeMin, revsRangeMax, m_GearFactor);
        }

        //运动函数，最重要
        public void Move(float steering, float accel, float footbrake, float handbrake)
        {
            //保持当前轮胎网格跟随wheelcolliders转动
            for (int i = 0; i < 4; i++)
            {
                Quaternion quat;//四元数quat,用于旋转
                Vector3 position;
                m_WheelColliders[i].GetWorldPose(out position, out quat);//获取wheelcolliders的姿势，位置和转向角
                //设置网格物体的位置和转向角
                m_WheelMeshes[i].transform.position = position;
                m_WheelMeshes[i].transform.rotation = quat;
            }

            //clamp input values
            steering = Mathf.Clamp(steering, -1, 1);//限制steering的值在-1和1之间，以下同上
            AccelInput = accel = Mathf.Clamp(accel, 0, 1);
            BrakeInput = footbrake = -1*Mathf.Clamp(footbrake, -1, 0);
            handbrake = Mathf.Clamp(handbrake, 0, 1);

            //Set the steer on the front wheels.
            //Assuming that wheels 0 and 1 are the front wheels.
            //设置前轮转向角，0，1为前轮，汽车行驶时也只是控制前轮转向
            m_SteerAngle = steering*m_MaximumSteerAngle;
            m_WheelColliders[0].steerAngle = m_SteerAngle;
            m_WheelColliders[1].steerAngle = m_SteerAngle;
            //调用角度辅助助手
            SteerHelper();
            //设置加速/刹车信息到WheelCollider
            ApplyDrive(accel, footbrake);
            //检查速度范围
            CapSpeed();

            //Set the handbrake.设置手刹
            //Assuming that wheels 2 and 3 are the rear wheels.2，3代表后轮
            if (handbrake > 0f)
            {
                //设置手刹值到后轮，达到减速目的
                var hbTorque = handbrake*m_MaxHandbrakeTorque;
                m_WheelColliders[2].brakeTorque = hbTorque;
                m_WheelColliders[3].brakeTorque = hbTorque;
            }

            //计算转速，用来供外部调用转速属性Revs来播放引擎声音等
            CalculateRevs();
            //改变档位
            GearChanging();
            //施加下压力
            AddDownForce();
            //检查轮胎
            CheckForWheelSpin();
            //牵引力控制系统
            TractionControl();
        }

        //检查速度范围
        private void CapSpeed()
        {
            float speed = m_Rigidbody.velocity.magnitude;//将标量速度赋予speed
            //判断速度类型，
            switch (m_SpeedType)
            {
                case SpeedType.MPH:

                    speed *= 2.23693629f;
                    if (speed > m_Topspeed)
                        m_Rigidbody.velocity = (m_Topspeed/2.23693629f) * m_Rigidbody.velocity.normalized;//速度归一化
                    break;

                case SpeedType.KPH:
                    speed *= 3.6f;
                    if (speed > m_Topspeed)
                        m_Rigidbody.velocity = (m_Topspeed/3.6f) * m_Rigidbody.velocity.normalized;
                    break;
            }
        }

        //设置加速/刹车信息到WheelCollider
        private void ApplyDrive(float accel, float footbrake)
        {

            float thrustTorque;
            switch (m_CarDriveType)
            {
                case CarDriveType.FourWheelDrive:
                    thrustTorque = accel * (m_CurrentTorque / 4f);
                    for (int i = 0; i < 4; i++)
                    {
                        m_WheelColliders[i].motorTorque = thrustTorque;
                    }
                    break;

                case CarDriveType.FrontWheelDrive:
                    thrustTorque = accel * (m_CurrentTorque / 2f);
                    m_WheelColliders[0].motorTorque = m_WheelColliders[1].motorTorque = thrustTorque;
                    break;

                case CarDriveType.RearWheelDrive:
                    thrustTorque = accel * (m_CurrentTorque / 2f);
                    m_WheelColliders[2].motorTorque = m_WheelColliders[3].motorTorque = thrustTorque;
                    break;

            }

            for (int i = 0; i < 4; i++)
            {
                if (CurrentSpeed > 5 && Vector3.Angle(transform.forward, m_Rigidbody.velocity) < 50f)
                {
                    m_WheelColliders[i].brakeTorque = m_BrakeTorque*footbrake;
                }
                else if (footbrake > 0)
                {
                    m_WheelColliders[i].brakeTorque = 0f;
                    m_WheelColliders[i].motorTorque = -m_ReverseTorque*footbrake;
                }
            }
        }

        //此函数时move函数用于转向角
        private void SteerHelper()
        {
            for (int i = 0; i < 4; i++)
            {
                WheelHit wheelhit;
                m_WheelColliders[i].GetGroundHit(out wheelhit);
                if (wheelhit.normal == Vector3.zero)
                    return; // wheels arent on the ground so dont realign the rigidbody velocity 车轮离地，则不用调整汽车角度了。
            }

            // this if is needed to avoid gimbal lock problems that will make the car suddenly shift direction
            //使用四元数避免万向锁的问题
            //假如上一次车体Y方向角度比这次小于十度，就根据相差的度数乘以系数m_SteerHelper，得出需要旋转的度数
            //根据这个度数算出四元数，然后将刚体速度直接旋转这个偏移度数
            if (Mathf.Abs(m_OldRotation - transform.eulerAngles.y) < 10f)
            {
                var turnadjust = (transform.eulerAngles.y - m_OldRotation) * m_SteerHelper;
                Quaternion velRotation = Quaternion.AngleAxis(turnadjust, Vector3.up);
                m_Rigidbody.velocity = velRotation * m_Rigidbody.velocity;
            }
            m_OldRotation = transform.eulerAngles.y;
        }


        // this is used to add more grip in relation to speed
        //这个是用来增加下压力，这是用来添加更多的速度控制
        private void AddDownForce()
        {
            m_WheelColliders[0].attachedRigidbody.AddForce(-transform.up*m_Downforce*
                                                         m_WheelColliders[0].attachedRigidbody.velocity.magnitude);//Addforce 第一个车轮增加一个力，
        }


        // checks if the wheels are spinning and is so does three things 检查轮胎是否旋转
        // 1) emits particles 是否发射粒子
        // 2) plays tiure skidding sounds 播放滑行音
        // 3) leaves skidmarks on the ground 去掉刹车印
        // these effects are controlled through the WheelEffects class 这些特效都是通过类WheelEffects实现的
        private void CheckForWheelSpin()
        {
            // loop through all wheels 遍历所有车轮
            for (int i = 0; i < 4; i++)
            {
                WheelHit wheelHit;
                m_WheelColliders[i].GetGroundHit(out wheelHit);//获取碰撞信息

                // is the tire slipping above the given threshhold
                //轮胎下滑超过给定的阈值吗
                if (Mathf.Abs(wheelHit.forwardSlip) >= m_SlipLimit || Mathf.Abs(wheelHit.sidewaysSlip) >= m_SlipLimit)
                {
                    //超出则发射烟雾粒子
                    m_WheelEffects[i].EmitTyreSmoke();

                    // avoiding all four tires screeching at the same time
                    // if they do it can lead to some strange audio artefacts
                    //避免四个轮胎都同时播放滑行声音
                    //如果那样的话会导致某些奇怪的音效
                    //函数AnySkidSoundPlaying()是遍历四个轮子，检查是否播放音效，是的返回ture.
                    if (!AnySkidSoundPlaying())
                    {
                        m_WheelEffects[i].PlayAudio();
                    }
                    continue;
                }

                // if it wasnt slipping stop all the audio
                //假如没有超出阈值，还没有停止音效，则停止音效
                if (m_WheelEffects[i].PlayingAudio)
                {
                    m_WheelEffects[i].StopAudio();
                }
                // end the trail generation
                //停止烟雾生成
                m_WheelEffects[i].EndSkidTrail();
            }
        }


        //如果汽车轮胎过度滑转，牵引力系统可以控制减少轮胎动力
        // crude traction control that reduces the power to wheel if the car is wheel spinning too much
        private void TractionControl()//牵引力控制函数
        {
            WheelHit wheelHit;
            //判断驱动类型，四轮，还是前后轮，然后调用AdjustTorque函数
            switch (m_CarDriveType)
            {
                case CarDriveType.FourWheelDrive:
                    // loop through all wheels
                    for (int i = 0; i < 4; i++)
                    {
                        m_WheelColliders[i].GetGroundHit(out wheelHit);

                        AdjustTorque(wheelHit.forwardSlip);
                    }
                    break;

                case CarDriveType.RearWheelDrive:
                    m_WheelColliders[2].GetGroundHit(out wheelHit);
                    AdjustTorque(wheelHit.forwardSlip);

                    m_WheelColliders[3].GetGroundHit(out wheelHit);
                    AdjustTorque(wheelHit.forwardSlip);
                    break;

                case CarDriveType.FrontWheelDrive:
                    m_WheelColliders[0].GetGroundHit(out wheelHit);
                    AdjustTorque(wheelHit.forwardSlip);

                    m_WheelColliders[1].GetGroundHit(out wheelHit);
                    AdjustTorque(wheelHit.forwardSlip);
                    break;
            }
        }

        //当向前滑动距离超过阈值后，就说明轮胎过度滑转，则减少牵引力，以降低转速。上面函数调用
        private void AdjustTorque(float forwardSlip)
        {
            if (forwardSlip >= m_SlipLimit && m_CurrentTorque >= 0)
            {
                m_CurrentTorque -= 10 * m_TractionControl;
            }
            else
            {
                m_CurrentTorque += 10 * m_TractionControl;
                if (m_CurrentTorque > m_FullTorqueOverAllWheels)
                {
                    m_CurrentTorque = m_FullTorqueOverAllWheels;
                }
            }
        }

        //函数AnySkidSoundPlaying()是遍历四个轮子，检查是否播放音效，是的返回ture.上面检查函数调用
        private bool AnySkidSoundPlaying()
        {
            for (int i = 0; i < 4; i++)
            {
                if (m_WheelEffects[i].PlayingAudio)
                {
                    return true;
                }
            }
            return false;
        }
    }
}