2D On screen && off screen view C#

Hello guys can someone help me out?
I used c# script that clamps GUITexture to edge of screen if object is not in it.
But how can i make the GUITexture disabled if camera can see the object? and enabled again if not in view?


Code i found is :

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. [RequireComponent (typeof (GUITexture))]
5. public class ObjectLabel : MonoBehaviour {
6.  
7.     public Transform target;  // Object that this label should follow
8.     public Vector3 offset = Vector3.up;    // Units in world space to offset; 1 unit above object by default
9.     public bool clampToScreen = false;  // If true, label will be visible even if object is off screen
10.     public float clampBorderSize = 0.05f;  // How much viewport space to leave at the borders when a label is being clamped
11.     public bool useMainCamera = true;   // Use the camera tagged MainCamera
12.     public Camera cameraToUse ;   // Only use this if useMainCamera is false
13.     Camera cam ;
14.     Transform thisTransform;
15.     Transform camTransform;
16.     public string tag = "";
17.     GUITexture gui;
18.  
19.     public bool onscreen = true;
20.  
21.     void Start ()
22.     {
23.         gui = GetComponent<GUITexture>();
24.         thisTransform = transform;
25.         if (useMainCamera)
26.             cam = Camera.main;
27.         else
28.             cam = cameraToUse;
29.         camTransform = cam.transform;
30.         target = GameObject.FindWithTag(tag).transform;
31.     }
32.  
33.  
34.     public Transform targetPoint;
35.     public float holdGazeTimeInSeconds = 2;
36.  
37.     private float currentGazeTimeInSeconds = 0;
38.  
39.  
40.  
41.     void Update()
42.     {
43.         //Part i don't know
44.  
45.         if(/*OBJECT IS IN CAMERA VIEW*/)
46.         {
47.         Debug.Log("Found it");
48.         gui.enabled = false; //Disable gui while i can see it!
49.         }
50.          else
51.         {
52.         Debug.Log("Not Found");
53.         gui.enabled = true; //Eneble gui when i can't see it!
54.         }
55.  
56.  
57.         //Till here i need help
58.    
59.         if ( clampToScreen ) {
60.                
61.                 Vector3 relativePosition = camTransform.InverseTransformPoint (target.position + offset);
62.                 relativePosition.z = Mathf.Max (relativePosition.z, 1.0f);
63.                 thisTransform.position = cam.WorldToViewportPoint (camTransform.TransformPoint (relativePosition));
64.                 thisTransform.position = new Vector3 (Mathf.Clamp (thisTransform.position.x, clampBorderSize, 1.0f - clampBorderSize),
65.                     Mathf.Clamp (thisTransform.position.y, clampBorderSize, 1.0f - clampBorderSize),
66.                     thisTransform.position.z);
67.         }
68.         else
69.         {
70.             thisTransform.position = cam.WorldToViewportPoint(target.position + offset);
71.  
72.         }
73.     }
74. }

 

Do a bit of searching, there's many posts about this:

http://answers.unity3d.com/questions/8003/how-can-i-know-if-a-gameobject-is-seen-by-a-partic.html