Unity C# 3D世界坐标转2D屏幕坐标

让2D UI跟随3D物体移动或指示3D物体的位置该怎么做呢?
关键代码:
Camera.main.WorldToScreenPoint(target.position) + new Vector3(-Screen.width / 2, -Screen.height / 2);
测试脚本:Position3DTo2DTest.cs
using UnityEngine;

/// <summary>
/// 3D物体转2D屏幕坐标测试
/// ZhangYu 2019-03-20
/// </summary>
public class Position3DTo2DTest : MonoBehaviour {

public Transform target; // 3D目标
public Transform ui; // 2D UI
private Vector3 originOff; // 当前UI系统(0,0)点 相对于屏幕左下角(0, 0)点的偏移量

private void Start () {
originOff = new Vector3(-Screen.width / 2, -Screen.height / 2);
Reposition();
}

private void Update () {
// 需要性能优化 仅在物体移动或相机移动后调用即可
Reposition();
}

// 根据目标物体 重定位UI
private void Reposition() {
Vector3 position = Camera.main.WorldToScreenPoint(target.position) + originOff;
position.z = 0;
ui.localPosition = position;
}

}
实现效果：血条UI悬浮在人物头顶
当摄像机旋转角度时 依然有效