unity3d中2d自上而下射击游戏的旋转控制出现问题

我试图让我的角色面对鼠标在y轴上旋转。它稍微旋转了一下，但不面向鼠标。摄像机的位置在玩家的正上方，我看到许多其他的自上而下射击游戏的例子，几乎和我的一模一样，所以我不知道是什么问题，请帮忙，谢谢。

using UnityEngine;
using System.Collections;
public class playermovementscript : MonoBehaviour { 
public float movementspeed = 5f; 
public float bulletspeed  = 10f;
public GameObject bullet; 
public GameObject shooter;  
public Vector3 target;  
public Camera camera;
// Use this for initialization
void Start () {  
    //refrence to main camera
    Camera camera;
}
// Update is called once per frame
void Update () {
    //call movement function in every frame
    movement (); 
    // cheek for input of f in every frame if true execute shoot function
    if (Input.GetKeyDown (KeyCode.F)) {
        shoot();
    } 
 } 


void movement(){
    // makes refrence to gameobjects rigidbody and makes its velocity varible to equal values of axis x and y
    gameObject.GetComponent<Rigidbody>().velocity = new Vector3(Input.GetAxisRaw("Horizontal")*movementspeed,0,Input.GetAxisRaw("Vertical")*movementspeed); 
// makes vector 3 type target equall to mouse position on pixial cordinates converted in to real world coordniates
    target = camera.ViewportToWorldPoint (new Vector3(Input.mousePosition.x,Input.mousePosition.y,camera.transform.position.y - transform.position.y)); 
    //target.x -= transform.position.x; 
    //target.z -= transform.position.z;
    // states the vector 3 values of target 
    Debug.Log (target);  
    // makes object local z face target and iniziates up axis
    transform.LookAt (target,Vector3.up);
}