target.position - trans.position 点到目标的向量 赋值给 up（Y轴）

直接改变物体的朝向（任意轴）

Transform target1,target2;

1. 获得target1指向target2的向量

   Vector3 dir = target1.position - target2.position;

2. //让target1指向target2

   target1.up = dir;

3. //y轴指向target2，z轴target1.forward，x轴：target1.right