public class ParabolaPath
{
    
    
    /// <summary> 初始化抛物线运动轨迹 </summary>
    /// <param name="start">起点</param>
    /// <param name="end">终点</param>
    /// <param name="height">高度(相对于两个点的最高位置 高出多少)</param>
    /// <param name="gravity">重力加速度(负数)</param>
    /// <returns></returns>
    public ParabolaPath(Vector3 start, Vector3 end, float height = 10, float gravity = -9.8f)
    {
    
    
        Init(start, end, height, gravity);
    }

    /// <summary> 初始化抛物线运动轨迹 </summary>
    /// <param name="start">起点</param>
    /// <param name="end">终点</param>
    /// <param name="height">高度(相对于两个点的最高位置 高出多少)</param>
    /// <param name="gravity">重力加速度(负数)</param>
    /// <returns></returns>
    public void Init(Vector3 start, Vector3 end, float height = 10, float gravity = -9.8f)
    {
    
    
        // 求出最高点

        float topY = Mathf.Max(start.y, end.y) + height;

        // 上升阶段的竖直距离

        float d1 = topY - start.y;

        // 下降阶段的竖直距离

        float d2 = topY - end.y;

        float g2 = 2 / -gravity;

        // 利用公式 h = g * t * t / 2 来算出上升阶段的时间

        float t1 = Mathf.Sqrt(g2 * d1);

        // 利用公式 h = g * t * t / 2 来算出下降阶段的时间

        float t2 = Mathf.Sqrt(g2 * d2);

        // 抛物线运行的总时间

        float t = t1 + t2;

        // 计算出在水平方向上的两个轴的移动速度 vX vZ (同时也是水平方向的初始速度)

        float vX = (end.x - start.x) / t;

        float vZ = (end.z - start.z) / t;

        // 计算出竖直方向上的初速度 vY

        float vY = -gravity * t1;

        // 到这里初始速度的3个分量都计算完毕

        m_start = start;

        m_end = end;

        m_gravity = gravity;

        m_totalTime = t;

        m_velocityStart = new Vector3(vX, vY, vZ);

        m_position = m_start;

        m_time = 0;
    }

    /// <summary>
    /// 初始位置
    /// </summary>
    public Vector3 start
    {
    
    
        get {
    
     return m_start; }
    }

    /// <summary>
    /// 结束位置
    /// </summary>
    public Vector3 end
    {
    
    
        get {
    
     return m_end; }
    }

    /// <summary>
    /// 总时间
    /// </summary>
    public float totalTime
    {
    
    
        get {
    
     return m_totalTime; }
    }

    /// <summary>
    /// 初始速度
    /// </summary>
    public Vector3 velocityStart
    {
    
    
        get {
    
     return m_velocityStart; }
    }

    /// <summary>
    /// 当前位置
    /// </summary>
    public Vector3 position
    {
    
    
        get {
    
     return m_position; }
    }

    /// <summary>
    /// 当前速度
    /// </summary>
    public Vector3 velocity
    {
    
    
        get {
    
     return GetVelocity(m_time); }
    }

    /// <summary>
    /// 当前时间
    /// </summary>
    public float time
    {
    
    
        get {
    
     return m_time; }

        set
        {
    
    
            value = Mathf.Clamp(value, 0, m_totalTime);

            m_time = value;

            m_position = GetPosition(value);
        }
    }

    /// <summary>
    /// 获取某个时间点的位置
    /// </summary>
    /// <param name="time"></param>
    /// <returns></returns>
    public Vector3 GetPosition(float time)
    {
    
    
        if (time == 0)
        {
    
    
            return m_start;
        }

        if (time == m_totalTime)
        {
    
    
            return m_end;
        }

        float dY = 0.5f * m_gravity * time * time;

        return m_start + m_velocityStart * time + new Vector3(0, dY, 0);
    }

    /// <summary>
    /// 获取某个时间点的速度
    /// </summary>
    /// <param name="time"></param>
    /// <returns></returns>
    public Vector3 GetVelocity(float time)
    {
    
    
        if (time == 0)
        {
    
    
            return m_velocityStart;
        }

        return m_velocityStart + new Vector3(0, m_velocityStart.y + m_gravity * time, 0);
    }


    private Vector3 m_start;

    private Vector3 m_end;

    private float m_gravity;

    private float m_totalTime;

    private Vector3 m_velocityStart;

    private Vector3 m_position;

    private float m_time;
}