// gets nearby objects using CullingGroup
// Assign this script to some gameobject, that the distance is measured from

using UnityEngine;

namespace UnityLibrary
{
    public class CullingGroupExample : MonoBehaviour
    {
        // just some dummy prefab to spawn (use default sphere for example)
        public GameObject prefab;

        // distance to search objects from
        public float searchDistance = 3;

        public bool colorInvisibleObjects = false;

        int objectCount = 5000;

        // collection of objects
        Renderer[] objects;
        CullingGroup cullGroup;
        BoundingSphere[] bounds;

        void Start()
        {
            // create culling group
            cullGroup = new CullingGroup();
            cullGroup.targetCamera = Camera.main;

            // measure distance to our transform
            cullGroup.SetDistanceReferencePoint(transform);

            // search distance "bands" starts from 0, so index=0 is from 0 to searchDistance
            cullGroup.SetBoundingDistances(new float[] { searchDistance, float.PositiveInfinity });

            bounds = new BoundingSphere[objectCount];

            // spam random objects
            objects = new Renderer[objectCount];
            for (int i = 0; i < objectCount; i++)
            {
                var pos = Random.insideUnitCircle * 30;
                var go = Instantiate(prefab, pos, Quaternion.identity);
                objects[i] = go.GetComponent<Renderer>();

                // collect bounds for objects
                var b = new BoundingSphere();
                b.position = go.transform.position;

                // get simple radius..works for our sphere
                b.radius = go.GetComponent<MeshFilter>().mesh.bounds.extents.x;
                bounds[i] = b;
            }

            // set bounds that we track
            cullGroup.SetBoundingSpheres(bounds);
            cullGroup.SetBoundingSphereCount(objects.Length);

            // subscribe to event
            cullGroup.onStateChanged += StateChanged;
        }

        // object state has changed in culling group
        void StateChanged(CullingGroupEvent e)
        {
            if (colorInvisibleObjects == true && e.isVisible == false)
            {
                objects[e.index].material.color = Color.gray;
                return;
            }

            // if we are in distance band index 0, that is between 0 to searchDistance
            if (e.currentDistance == 0)
            {
                objects[e.index].material.color = Color.green;
            }
            else // too far, set color to red
            {
                objects[e.index].material.color = Color.red;
            }
        }

        // cleanup
        private void OnDestroy()
        {
            cullGroup.onStateChanged -= StateChanged;
            cullGroup.Dispose();
            cullGroup = null;
        }

    }
}