Use the collider of multiple objects as one collider

Question

In my fps level (Unity), targets spawn at a random position. I want to make sure targets can't spawn behind objects or inside objects.

To make sure they don't spawn behind an object, I've made a raycast going from the player to the target. If it's obstructed I recalculate the spawn point. This works fine, but, since the targets are spheres the raycast won't be obstructed when a target is 50% inside an object, for example the floor. I don't want that, obviously.

To determine whether or not the target is in the bounds of another object, I tried using OnCollisionEnter and OnCollisionExit. While this works when simply moving a target inside another object, it seems to be unreliable when one script's Update cycle is recalculating the spawn position while the target's Update cycle is keeping track of the Collision.

So I looked for a different approach. Here's what I came up with (from the Unity docs):

m_Collider2 = spawnpoints[i].GetComponent<Collider>();
m_Collider = world.GetComponentInChildren<Collider>();
if (m_Collider.bounds.Intersects(m_Collider2.bounds))
{
    Debug.Log("Bounds intersecting");
}

The Game Object world is the parent in which I put all the objects of my gaming world.

The problem is that he only takes into account the collider of the first object. I basically want to use one big collider, which is composed by all the level objects.

Is this possible? Or does anyone know a different approach on how I can achieve this?

Answer 1

You should use the GetComponentsInChildren method instead of GetComponentInChildren, so that you can get from it an array of colliders on which you can execute a foreach to check if the bounds are intersecting.

I.E.:

m_Collider2 = spawnpoints [i].GetComponent<Collider>();
m_Collider = world.GetComponentsInChildren<Collider>();
foreach(Collider objCollider in m_Collider) {
    if (objCollider.bounds.Intersects(m_Collider2.bounds))
    {
        Debug.Log("Bounds intersecting");
        break;
    }
}

But, this way of doing things is very heavy for the CPU, since GetComponent methods are really slow, so their use should be limited inside Awake and Start methods if possible.

Another approach to the problem would be to create a List<Collider> at the start, and add to it the starting children of your World game object. If another one is instantiated, just Add it to your list, if it's destroyed, just Remove it.

Then, just before instantiation, you can check the bounds by looping inside the List with a foreach, the check will be a lot more faster.

==================================

EDIT:

Ok, here's the deal. First of all, add these lines to your World game object script (I guess you called the class World):

using UnityEngine;
using System.Collections.Generic; //Namespace needed to use the List type

public class World : MonoBehaviour {

    //The list which will hold references to the children game objects colliders
    public List<Collider> childrenColliders;

    private void Start() {
        //Code used to populate the list at start
        childrenColliders = new List<Collider>(GetComponentsInChildren<Collider>());
    }

Now, since in the script which spawns a new object has already a world variable which holds a reference to the World class:

foreach(Collider coll in world.childrenColliders) {
    if (coll.bounds.Intersects(m_Collider2.bounds))
    {
        Debug.Log("Bounds intersecting");
        break;
    }
}

And, of course, as I said before remember to add a newly spawned game object's collider to the list with:

void AddNewGameObject() {
    // spawnPoint is the transform.position Vector3 you'll use for the new game object
    var newGameObject = Instantiate(yourObjectPrefab, spawnPoint, Quaternion.identity, world.transform);
    world.childrenColliders.Add(newGameObject.GetComponent<Collider>());
}

That's pretty much it. ;)