事情是这样的，我想实现一个功能，就是点击正方体的正面，就在正面的方向在生成一个正方体，在点击侧面，又在侧面生成一个正方体，研究一下午了，求指导，在线等

一个方法，仅仅针对楼主所说的正方形
using UnityEngine;
using System.Collections;
public class test : MonoBehaviour {
public GameObject obj;
public float distance = 1;
// Use this for initialization
void Start () {
if (!obj)
{
Debug.LogError("obj对象为null");
}
if (obj.GetComponent<Collider>())
{
Destroy(obj.GetComponent<Collider>());
}
}
// Update is called once per frame
void Update () {
Ray ray;
if (Input.GetMouseButtonDown(0))
{
ray = Camera.main.ScreenPointToRay(Input.mousePosition);
RaycastHit hit;
if (Physics.Raycast(ray, out hit, 1000))
{
Vector3 orign=hit.collider.bounds.center;
Vector3 hitPoint = hit.point;
Vector3 hitPointLocal = hit.collider.gameObject.transform.InverseTransformPoint(hitPoint);
float x = Mathf.Abs(hitPointLocal.x);
float y = Mathf.Abs(hitPointLocal.y);
float z = Mathf.Abs(hitPointLocal.z);
if (x < 0.5) { hitPointLocal = new Vector3(0,hitPointLocal.y,hitPointLocal.z); }
if (y < 0.5) { hitPointLocal = new Vector3(hitPointLocal.x, 0,hitPointLocal.z); }
if (z < 0.5) { hitPointLocal = new Vector3(hitPointLocal.x, hitPointLocal.y,0); }
hitPoint = hit.collider.gameObject.transform.TransformPoint(hitPointLocal);
Vector3 direction =Vector3.Normalize(hitPoint - orign);
Vector3 spwanPoint = hitPoint + direction * distance;
Instantiate(obj,spwanPoint,hit.collider.gameObject.transform.rotation);
}
}
}
}

原理：
获取点击在物体上的点。
将改点坐标转化为相对于物体的坐标。
将该点坐标校正到对应面中心点。
将该点转化为世界坐标。

明显小白不适合做这个功能。看楼上

射线检测就能做，hit 的信息是正面反面写判断就行了