# Unity 计算导弹抛物线弹道和转向

### 代码实现

``````// 求导弹初始速度
public void InitVelocity(Vector3 start, Vector3 end, float height = 10, float gravity = -9.8f)
float topY = Mathf.Max(start.y, end.y) + height;
float d1 = topY - start.y;
float d2 = topY - end.y;
float g2 = 2 / -gravity;
float t1 = Mathf.Sqrt(g2 * d1);
float t2 = Mathf.Sqrt(g2 * d2);
float t = t1 + t2;
float vX = (end.x - start.x) / t;
float vZ = (end.z - start.z) / t;
float vY = -gravity * t1;
Vector3 v0 = new Vector3(vX, vY, vZ);
return v0;
}

// 求下一帧导弹的位置：
public static Vector3 NextPosition(Vector3 position, Vector3 velocity, float gravity, float time) {
float dY = 0.5f * gravity * time * time;
return position + velocity * time + new Vector3(0, dY, 0);
}``````

``````using UnityEngine;

/// <summary>
/// 抛物线运动轨迹
/// ZhangYu 2019-04-28
/// <param>blog:https://segmentfault.com/a/1190000018336439</param>
/// </summary>
public class ParabolaPath {

/// <summary> 是否夹紧起点和终点 </summary>
public bool isClampStartEnd;
private Vector3 m_start;
private Vector3 m_end;
private float m_height;
private float m_gravity;
private float m_upTime;
private float m_downTime;
private float m_totalTime;
private Vector3 m_velocityStart;
private Vector3 m_position;
private float m_time;

/// <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) {
float topY = Mathf.Max(start.y, end.y) + height;
float d1 = topY - start.y;
float d2 = topY - end.y;
float g2 = 2 / -gravity;
float t1 = Mathf.Sqrt(g2 * d1);
float t2 = Mathf.Sqrt(g2 * d2);
float t = t1 + t2;
float vX = (end.x - start.x) / t;
float vZ = (end.z - start.z) / t;
float vY = -gravity * t1;
m_start = start;
m_end = end;
m_height = height;
m_gravity = gravity;
m_upTime = t1;
m_downTime = t2;
m_totalTime = t;
m_velocityStart = new Vector3(vX, vY, vZ);
m_position = m_start;
m_time = 0;
}

/// <summary> 起点 </summary>
public Vector3 start { get { return m_start; } }
/// <summary> 终点 </summary>
public Vector3 end { get { return m_end; } }
/// <summary> 目标高度 </summary>
public float height { get { return m_height; } }
/// <summary> 重力加速度 </summary>
public float gravity { get { return m_gravity; } }
/// <summary> 上升时间 </summary>
public float upTime { get { return m_upTime; } }
/// <summary> 下降时间 </summary>
public float downTime { get { return m_downTime; } }
/// <summary> 总运动时间 </summary>
public float totalTime { get { return m_totalTime; } }
/// <summary> 顶点 </summary>
public Vector3 top { get { return GetPosition(m_upTime); } }
/// <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 {
if (isClampStartEnd) 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>
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>
public Vector3 GetVelocity(float time) {
if (time == 0) return m_velocityStart;
return m_velocityStart + new Vector3(0, m_velocityStart.y + m_gravity * time, 0);
}

}``````

``````using UnityEngine;

/// <summary>
/// 抛物线导弹
/// <para>计算弹道和转向</para>
/// <para>ZhangYu 2019-02-27</para>
/// </summary>
public class Missile : MonoBehaviour {

public Transform target;        // 目标
public float height = 16f;      // 高度
public float gravity = -9.8f;   // 重力加速度
private ParabolaPath path;      // 抛物线运动轨迹

private void Start() {
path = new ParabolaPath(transform.position, target.position, height, gravity);
path.isClampStartEnd = true;
transform.LookAt(path.GetPosition(path.time + Time.deltaTime));
}

private void Update() {
// 计算位移
float t = Time.deltaTime;
path.time += t;
transform.position = path.position;

// 计算转向
transform.LookAt(path.GetPosition(path.time + t));

// 简单模拟一下碰撞检测
if (path.time >= path.totalTime) enabled = false;
}

}``````

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