CullChildObjects

using System;
using System.Collections.Generic;
using UnityEngine;
using System.Collections;

/// <summary>
/// This culls all the objects which are child objects of the current object, that have a mesh renderer.
/// This is much more efficient than attaching a cullObject to each individual object.
/// </summary>
public class CullChildObjects : MonoBehaviour
{
    private MeshRenderer[] meshes;
    private Camera playerCamera;

    private bool outOfDistanceLastFrame;

    void Start ()
    {
        // attempt to get the camera controlled by the player
        playerCamera = GameObject.FindGameObjectWithTag ("MainCamera").GetComponent<Camera> ();
        if (playerCamera == null)
            print ("The main camera was not found inside CulledObject script.");

        meshes = GetComponentsInChildren<MeshRenderer> ();

        // attempt to get the meshRenderer component on the child objects
        if (meshes == null || meshes.Length == 0) {
            print (tag);
            print ("CullChildObjects require a mesh component on child objects, in order to enable and disable the objects.");
        }
    }

    void Update ()
    {
        // calculate the absolute distance between the camera and this object
        var distance = Math.Abs (Vector3.Distance (transform.position, playerCamera.transform.position));

        // if the distance between the objects is above the render distance
        if (distance > CulledObject.RenderDistance && !outOfDistanceLastFrame)
            OnObjectOutOfDistance ();
        else if (distance < CulledObject.RenderDistance && outOfDistanceLastFrame) // if we're in distance and we were not last frame
            OnObjectInDistance ();
    }

    /// <summary>
    /// Called when the object is out of the distance of the camera - and it was in distance last frame.
    /// </summary>
    void OnObjectOutOfDistance ()
    {
        outOfDistanceLastFrame = true;

        for (int i = 0; i < meshes.Length; i++)
            if (meshes [i] != null && meshes [i].enabled)
                meshes [i].enabled = false;
    }

    /// <summary>
    /// Called when the object is in distance of the camera - and it was not in distance last frame.
    /// </summary>
    void OnObjectInDistance ()
    {
        outOfDistanceLastFrame = false;

        for (int i = 0; i < meshes.Length; i++)
            if (meshes [i] != null && !meshes [i].enabled)
                meshes [i].enabled = true;
    }
}