Unity基础（6）--资源管理（3）小赛车竞技

namespace UnityStandardAssets.Vehicles.Car
{
    //汽车驱动类型
    internal enum CarDriveType
    {
        //四驱
        FrontWheelDrive,
        //后驱
        RearWheelDrive,
        //前驱
        FourWheelDrive
    }
    //速度类型
    internal enum SpeedType
    {
        //英里每小时
        MPH,
        //千米每小时
        KPH
    }

    public class CarController : MonoBehaviour
    {
        [SerializeField] private CarDriveType m_CarDriveType = CarDriveType.FourWheelDrive;
        [SerializeField] private WheelCollider[] m_WheelColliders = new WheelCollider[4];
        [SerializeField] private GameObject[] m_WheelMeshes = new GameObject[4];
        [SerializeField] private WheelEffects[] m_WheelEffects = new WheelEffects[4];
        //重心位置
        [SerializeField] private Vector3 m_CentreOfMassOffset;
        //最大可转角度
        [SerializeField] private float m_MaximumSteerAngle;
        [Range(0, 1)] [SerializeField] private float m_SteerHelper; // 0 is raw physics , 1 the car will grip in the direction it is facing
        [Range(0, 1)] [SerializeField] private float m_TractionControl; // 0 is no traction control, 1 is full interference
        //所有轮胎的扭矩
        [SerializeField] private float m_FullTorqueOverAllWheels;
        //反向扭矩
        [SerializeField] private float m_ReverseTorque;
        //最大刹车扭矩
        [SerializeField] private float m_MaxHandbrakeTorque;
        //最大下压力
        [SerializeField] private float m_Downforce = 100f;
        //速度单位
        [SerializeField] private SpeedType m_SpeedType;
        //最高速度
        [SerializeField] private float m_Topspeed = 200;
        //档位总数
        [SerializeField] private static int NoOfGears = 5;
        //
        [SerializeField] private float m_RevRangeBoundary = 1f;
        //最大滑动距离
        [SerializeField] private float m_SlipLimit;
        //刹车扭矩
        [SerializeField] private float m_BrakeTorque;

        private Quaternion[] m_WheelMeshLocalRotations;
        private Vector3 m_Prevpos, m_Pos;
        private float m_SteerAngle;
        //当前档位
        private int m_GearNum;
        //档位因子
        private float m_GearFactor;
        //上一帧汽车方向
        private float m_OldRotation;
        //当前扭矩
        private float m_CurrentTorque;
        private Rigidbody m_Rigidbody;
        private const float k_ReversingThreshold = 0.01f;

        public bool Skidding { get; private set; }
        public float BrakeInput { get; private set; }
        public float CurrentSteerAngle{ get { return m_SteerAngle; }}
        public float CurrentSpeed{ get { if(m_Rigidbody == null) return 0;return m_Rigidbody.velocity.magnitude*2.23693629f; }}
        public float MaxSpeed{get { return m_Topspeed; }}
        public float Revs { get; private set; }
        public float AccelInput { get; private set; }
        public Rigidbody CarRigidbody { get{return m_Rigidbody;}}
        // Use this for initialization
        private void Start()
        {
            //四个轮胎的自转方向
            m_WheelMeshLocalRotations = new Quaternion[4];
            for (int i = 0; i < 4; i++)
            {
                m_WheelMeshLocalRotations[i] = m_WheelMeshes[i].transform.localRotation;
            }
            //设置重心
            m_WheelColliders[0].attachedRigidbody.centerOfMass = m_CentreOfMassOffset;
            //设置最大手刹扭矩
            m_MaxHandbrakeTorque = float.MaxValue;

            m_Rigidbody = GetComponent<Rigidbody>();
            //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。
            m_CurrentTorque = m_FullTorqueOverAllWheels - (m_TractionControl*m_FullTorqueOverAllWheels);
        }

        //档位更新
        private void GearChanging()
        {
            //这里其实相当于将所有速度进行了划分，f就是指的目前速度处于最大速度的几分之几
            //如果NoOfGears是5，那么就把速度分成5段
            //1档就是0/5 ~ 1/5,
            //2档就是1/5 ~ 2/5，
            //3档就是2/5 ~ 3/5,
            //4档就是3/5 ~ 4/5，
            //5档就是4/5 ~ 5/5,
            //每次先看当前档位是几档，然后看当前速度是否匹配当前档位，如果匹配当前档位没啥事，如果不匹配则看当前速度如果小于当前档位
            //最小速度则减档，如果大于当前档位最大速度则，加档；
            float f = Mathf.Abs(CurrentSpeed/MaxSpeed);
            //计算当前档位的速度上限
            float upgearlimit = (1/(float) NoOfGears)*(m_GearNum + 1);
            //计算当前档位的速度下限
            float downgearlimit = (1/(float) NoOfGears)*m_GearNum;
            //如果当前档位大于0， 则看当前速度是否小于当前档位，如果小于，则果断降档
            if (m_GearNum > 0 && f < downgearlimit)
            {
                m_GearNum--;
            }
            //如果当前档位小于最大档位-1档，且当前速度大于当前档位上限，则果断加档
            //这里我好奇的是，为什么条件不是"if(f>upgearlimit&&(m_GearNum < NoOfGears))"，干嘛要减一？
            //我觉得原因可能是因为这个5档，只是理论速度，故意不达到。。。就像一般汽车为了汽车性能稳定，速度设定可以上200码一样，但是没有人上过。。
            if (f > upgearlimit && (m_GearNum < (NoOfGears - 1)))
            {
                m_GearNum++;
            }
        }


        // 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);
        }


        // unclamped version of Lerp, to allow value to exceed the from-to range
        //非限制版本的插值函数，我刚开始没发现他有啥特别之处，“非限制”怎么体现？直到我发现他的value没有限制0~1的范围才瞬间明白。
        private static float ULerp(float from, float to, float value)
        {
            return (1.0f - value)*from + value*to;
        }

        //计算档位因子
        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.
            //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));
            //从当前档位因子向目标档位因子做平滑差值
            m_GearFactor = Mathf.Lerp(m_GearFactor, targetGearFactor, Time.deltaTime*5f);
        }

        //计算转速
        private void CalculateRevs()
        {
            // calculate engine revs (for display / sound)
            //计算引擎转速（只用于显示和声音）
            // (this is done in retrospect - revs are not used in force/power calculations)
            //（我的个人理解：）这个计算是回溯的转速，不能用于力的计算。
            //计算在当前档位上的转速因子（决定在当前档位上的转速）
            CalculateGearFactor();
            //档位因子
            var gearNumFactor = m_GearNum/(float) NoOfGears;
            //计算在当前档位下的最小速度
            var revsRangeMin = ULerp(0f, m_RevRangeBoundary, CurveFactor(gearNumFactor));
            //计算在当前档位下的最大速度
            var revsRangeMax = ULerp(m_RevRangeBoundary, 1f, gearNumFactor);
            //根据当前的转速因子，计算当前的转速
            Revs = ULerp(revsRangeMin, revsRangeMax, m_GearFactor);
        }

        //外部调用的汽车移动控制函数
        public void Move(float steering, float accel, float footbrake, float handbrake)
        {
            Debug.Log ("***************************: " + footbrake + " " + handbrake);
            //保持当前的轮胎网格跟随WheelCollider转动
            for (int i = 0; i < 4; i++)
            {
                Quaternion quat;
                Vector3 position;
                m_WheelColliders[i].GetWorldPose(out position, out quat);
                m_WheelMeshes[i].transform.position = position;
                m_WheelMeshes[i].transform.rotation = quat;
            }
            //clamp input values
            //限定输入值范围
            steering = Mathf.Clamp(steering, -1, 1);
            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.
            //设置前轮转角
            //Assuming that wheels 0 and 1 are the front wheels.
            //wheels下标为0、1的就是前轮
            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.
            //Wheel下标是2、3就是后轮
            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
            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();
        }

        //控制车速
        private void CapSpeed()
        {
            float speed = m_Rigidbody.velocity.magnitude;
            switch (m_SpeedType)
            {
                case SpeedType.MPH:
                    //将速度m/s转换为mile/h，以便比较
                    speed *= 2.23693629f;
                    if (speed > m_Topspeed)
                        m_Rigidbody.velocity = (m_Topspeed/2.23693629f) * m_Rigidbody.velocity.normalized;
                    break;

                case SpeedType.KPH:
                //将速度m/s转换为km/h，以便比较
                    speed *= 3.6f;
                    if (speed > m_Topspeed)
                        m_Rigidbody.velocity = (m_Topspeed/3.6f) * m_Rigidbody.velocity.normalized;
                    break;
            }
        }


        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;
                }
            }
        }


        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
                //假如轮子离地，就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
            //这个是为了避免万向锁问题的，万向锁问题会导致汽车突然变换方向（我直到万向锁问题，但不理解下面是怎么避免问题的，我只知道四元数的使用
            //就是为了避免万向锁问题）
            //下面这个If函数的效果就是，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
            //计算出这个偏移角度的四元数，然后将刚体速度直接旋转这个偏倚度数，
            //根据代码开头m_SteerHelper的定义，这个做法相当于做了一个角度辅助，不完全凭借WheelCollider物理效果
            //而直接操控速度方向，对车角度进行调整。
            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
        private void AddDownForce()
        {
            m_WheelColliders[0].attachedRigidbody.AddForce(-transform.up*m_Downforce*
                                                         m_WheelColliders[0].attachedRigidbody.velocity.magnitude);
        }


        // checks if the wheels are spinning and is so does three things
        //检查轮胎是否旋转
        // 1) emits particles
        //检查是否发射尾气粒子
        // 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WheelEffects类控制的
        private void CheckForWheelSpin()
        {
            // loop through all wheels
            for (int i = 0; i < 4; i++)
            {
                WheelHit wheelHit;
                m_WheelColliders[i].GetGroundHit(out wheelHit);

                // is the tire slipping above the given threshhold
                //轮胎滑行距离是否超出阈值
                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
                    //避免四个轮胎都同时播放滑行声音
                    // if they do it can lead to some strange audio artefacts
                    //如果那样的话会导致某些奇怪的音效
                    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();
            }
        }

        // crude traction control that reduces the power to wheel if the car is wheel spinning too much
        //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
        private void TractionControl()
        {
            WheelHit wheelHit;
            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;
            }
        }


        private void AdjustTorque(float forwardSlip)
        {
            //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。
            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;
                }
            }
        }


        private bool AnySkidSoundPlaying()
        {
            for (int i = 0; i < 4; i++)
            {
                if (m_WheelEffects[i].PlayingAudio)
                {
                    return true;
                }
            }
            return false;
        }

        void Update()
        {
            //这两段If分别用来控制汽车X轴/Z轴上汽车不会过度翻转，导致汽车游戏性差。
            if (transform.rotation.eulerAngles.x > 60 && transform.rotation.eulerAngles.x < 300) {
                Quaternion temp = transform.rotation;
                if (transform.rotation.eulerAngles.x < 180) {
                    temp.eulerAngles = new Vector3(60f, transform.rotation.eulerAngles.y, transform.rotation.eulerAngles.z);
                }
                else {
                    temp.eulerAngles = new Vector3(300f, transform.rotation.eulerAngles.y, transform.rotation.eulerAngles.z);
                }
                transform.rotation = temp;
            }
            if (transform.rotation.eulerAngles.z > 25 && transform.rotation.eulerAngles.z < 335) {
                Quaternion temp = transform.rotation;
                if (transform.rotation.eulerAngles.z < 180) {
                    temp.eulerAngles = new Vector3(transform.rotation.eulerAngles.x, transform.rotation.eulerAngles.y, 25);

                }
                else
                {
                    temp.eulerAngles = new Vector3(transform.rotation.eulerAngles.x, transform.rotation.eulerAngles.y, 335);

                }
                transform.rotation = temp;
            }
        }
    }
}