Unity C#重力计算函数返回NaN值的原因排查求助

问题场景 #

使用以下脚本计算天体间引力时，场景中两个物体均触发Input force is { NaN, NaN, NaN }错误，已确认无明显除零情况，需要排查原因。

脚本代码 #

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Gravity : MonoBehaviour
{
    public const float gravity = 10;
    public float mass = 10f;
    public bool active = true;
    public Rigidbody rigidbody;
    public Transform transform;
    GameObject[] otherObjs;
    Gravity[] otherGravities;

    void Start () {
        rigidbody = gameObject.GetComponent<Rigidbody>();
        transform = gameObject.transform;
        otherObjs = GameObject.FindGameObjectsWithTag("Body");
        otherGravities = new Gravity[otherObjs.Length];
        for (int i = 0; i < otherObjs.Length; i++)
        {
            otherGravities[i] = otherObjs[i].GetComponent<Gravity>();
        }
    }

    void FixedUpdate () {
        rigidbody.AddForce(CalculateGravity());
    }

    Vector3 CalculateGravity () {
        Vector3 finalGravity = new Vector3(0, 0, 0);
        foreach (Gravity current in otherGravities) {
            float distance = Vector3.Distance(transform.position, current.transform.position);
            Vector3 unNormalDirection = transform.position - current.transform.position;
            Vector3 direction = unNormalDirection.normalized;
            Vector3 gravitationalPull = ((mass * current.mass) / (distance * distance)) * direction;
            finalGravity += gravitationalPull;
        }
        return finalGravity;
    }
}

错误信息 #

rigidbody.force assign attempt for 'Sun' is not valid. Input force is { NaN, NaN, NaN }.
UnityEngine.Rigidbody:AddForce (UnityEngine.Vector3)
Gravity:FixedUpdate () (at Assets/Scripts/Gravity.cs:27)

排查思路 #

• 排除自身对象遍历：GameObject.FindGameObjectsWithTag("Body")会将挂载该脚本的自身（如果标签为Body）也加入数组。当遍历到自身时，Vector3.Distance返回0，此时对零向量执行normalized操作会直接得到(NaN, NaN, NaN)，最终导致引力计算结果为NaN。需在遍历前添加判断跳过自身：

  foreach (Gravity current in otherGravities) {
      if (current == this) continue; // 跳过自身
      // 剩余计算逻辑
  }
  

• 校验数组元素有效性：若场景中存在标签为Body但未挂载Gravity脚本的物体，otherGravities数组会包含null元素。遍历到null时访问current.transform会引发空引用，虽不一定直接导致NaN，但会破坏计算逻辑。建议在Start方法中筛选有效组件，改用List存储：

  List<Gravity> validGravities = new List<Gravity>();
  foreach (var obj in otherObjs)
  {
      Gravity comp = obj.GetComponent<Gravity>();
      if (comp != null && comp != this)
      {
          validGravities.Add(comp);
      }
  }
  otherGravities = validGravities.ToArray();
  

• 检查质量与距离的合法性：

  1. 确认所有物体的mass值未被设置为NaN或无穷大，可在CalculateGravity中添加日志输出mass和current.mass的值验证。
  2. 即使排除了自身，若两物体位置完全重合（距离为0），零向量归一化仍会产生NaN。需添加距离阈值判断，跳过极近距离的计算：

     float distance = Vector3.Distance(transform.position, current.transform.position);
     if (distance < 0.001f) continue; // 跳过极近距离，避免异常
     

• 修正引力方向逻辑：当前代码中unNormalDirection = transform.position - current.transform.position得到的是远离对方的方向，与引力“相互吸引”的逻辑相反。虽不会导致NaN，但会引发物理行为异常，建议修正为：

  Vector3 unNormalDirection = current.transform.position - transform.position;
  

• 确认常量gravity的使用：脚本中定义了gravity常量但未参与计算，实际引力公式缺少引力系数，需补全：

  Vector3 gravitationalPull = (gravity * mass * current.mass) / (distance * distance) * direction;
  

内容的提问来源于stack exchange，提问作者Ninju4821