当cube和sphere的距离大于2m sphere会主动跟着cube前进 小于2m以后sphere会原地不动

要在Unity中实现这样的功能，你需要结合C#脚本、物理引擎和碰撞检测。首先，给Sphere添加一个Rigidbody组件，然后编写如下的C#代码：

using UnityEngine;
using System.Collections;

public class SphereFollowCube : MonoBehaviour
{
    public GameObject cube; // Cube游戏对象引用
    private float distanceThreshold = 2f; // 距离阈值
    private Rigidbody sphereRigidbody; // 球的Rigidbody实例

    void Start()
    {
        sphereRigidbody = GetComponent<Rigidbody>();
    }

    void FixedUpdate()
    {
        Vector3 directionToCube = cube.transform.position - transform.position;
        float currentDistance = Vector3.Distance(transform.position, cube.transform.position);

        if (currentDistance > distanceThreshold)
        {
            sphereRigidbody.velocity = directionToCube.normalized * movementSpeed;
        }
        else
        {
            sphereRigidbody.velocity = Vector3.zero; // 当距离小于2米，停止移动
        }
    }

    [SerializeField] private float movementSpeed = 10f; // 移动速度

    // 在这里添加OnCollisionStay事件处理，如果球撞到立方体，检查是否超出2米范围
    void OnCollisionStay(Collision collision)
    {
        if (collision.gameObject == cube)
        {
            currentDistance = Vector3.Distance(transform.position, cube.transform.position);
            if (currentDistance <= distanceThreshold)
                sphereRigidbody.velocity = Vector3.zero;
        }
    }