如何在Unity中显示FPS

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour
{
    public float updateInterval = 0.5F;
    private double lastInterval;
    private int frames = ;
    private float fps;
    void Start()
    {
        lastInterval = Time.realtimeSinceStartup;
        frames = ;
    }
    void OnGUI()
    {
        GUILayout.Label(" " + fps.ToString("f2"));
    }
    void Update()
    {
        ++frames;
        float timeNow = Time.realtimeSinceStartup;
        if (timeNow > lastInterval + updateInterval)
        {
            fps = (float)(frames / (timeNow - lastInterval));
            frames = ;
            lastInterval = timeNow;
        }
    }
}