How to create a box collider that surrounds an object and its children?

Question

I have a car that needs a box collider.

If the car were 1 single mesh, I would only need to call:

        boxCol = gameObject.AddComponent<BoxCollider>();

and it would create a BoxCollider that perfectly fits my car, based on my car's mesh.

Now I have a car which consists of many different parts in the transformation hierarchy. (For example: the body of the car is the parent of the 4 doors. Every door is a separate game object, and has a doorknob child, etc.)

Now I need a script that changes the BoxCollider so that its box surrounds the whole car, including all of these parts.

I found this pose on Unity Answers, but it just doesn't get me the right collider.

Here is the code I'm using:

using UnityEngine;
using UnityEditor;
using System.Collections;

public class ColliderToFit : MonoBehaviour
{

    [MenuItem("My Tools/Collider/Fit to Children")]
    static void FitToChildren()
    {
        foreach (GameObject rootGameObject in Selection.gameObjects)
        {
            if (!(rootGameObject.GetComponent<Collider>()  is BoxCollider))
                continue;

            bool hasBounds = false;
            Bounds bounds = new Bounds(Vector3.zero, Vector3.zero);

            for (int i = 0; i < rootGameObject.transform.childCount; ++i)
            {
                Renderer childRenderer = rootGameObject.transform.GetChild(i).GetComponent<Renderer>();
                if (childRenderer != null)
                {
                    if (hasBounds)
                    {
                        bounds.Encapsulate(childRenderer.bounds);
                    }
                    else
                    {
                        bounds = childRenderer.bounds;
                        hasBounds = true;
                    }
                }
            }

            BoxCollider collider = (BoxCollider)rootGameObject.GetComponent<Collider>();
            collider.center = bounds.center - rootGameObject.transform.position;
            collider.size = bounds.size;
        }
    }

}

Answer 1

I found out that the Boxcollider I get from the solution above was only expanding the bounds of all the children while leaving out the gameObject itself aswell as all other descendants, and it only delivered the right solution for position and rotation 0, and scale 1, which confused me at first.

here is the code that will surround the gameobject and every descendant: (keep in mind that you need to set the position and the rotation to 0 and the localScale to 1 and to get the right Collider. Just store the old transform variables somewhere and then set them to 0 (and scale to 1) , then change the collider (call this script), then set the transform variables back again) . Have fun!

public void addBoundsToAllChildren()
{
    if (boxCol == null)
    {
        boxCol = gameObject.GetComponent(typeof(BoxCollider)) as BoxCollider;
        if (boxCol == null)
        {
            boxCol = gameObject.AddComponent<BoxCollider>();
        }
    }
    Bounds bounds = new Bounds(Vector3.zero, Vector3.zero);
    Renderer thisRenderer = transform.GetComponent<Renderer>();
    bounds.Encapsulate(thisRenderer.bounds);
    boxCol.offset = bounds.center - transform.position;
    boxCol.size = bounds.size;

    allDescendants = gameObject.GetComponentsInChildren<Transform>();
    foreach (Transform desc in allDescendants)
    {
        Renderer childRenderer = desc.GetComponent<Renderer>();
        if (childRenderer != null)
        {
           bounds.Encapsulate(childRenderer.bounds);
        }
        boxCol.offset = bounds.center - transform.position;
        boxCol.size = bounds.size;
    }
}

Answer 2

A modified version of @OC_RaizW answer for BoxCollider2D (only children taken into account, not self):

public void addBoundsToAllChildren()
{

    var boxCol = gameObject.GetComponent<BoxCollider2D>();
    if (boxCol == null)
    {
        boxCol = gameObject.AddComponent<BoxCollider2D>();
    }

    Bounds bounds = new Bounds(transform.position, Vector3.zero);

    var allDescendants = gameObject.GetComponentsInChildren<Transform>();
    foreach (Transform desc in allDescendants)
    {
        Renderer childRenderer = desc.GetComponent<Renderer>();
        if (childRenderer != null)
        {
            bounds.Encapsulate(childRenderer.bounds);
        }
        boxCol.offset = bounds.center - transform.position;
        boxCol.size = bounds.size;
    }
}

Answer 3

I had the same issue, hopefully, this will help somebody someday.

First, get all possible mesh renderers:

var renderers = gameObject.GetComponentsInParent<Renderer>().ToList();
renderers.AddRange(gameObject.GetComponentsInChildren<Renderer>());

Set the center of initial bounds to the position of the parent object and size to zero, and then encapsulate every mesh:

var bounds = new Bounds(transform.position, Vector3.zero);
foreach (var r in renderers)
{
    bounds.Encapsulate(r.bounds);
}

Add the collider to the parent object and set the size and center for the collider, keep in mind the assumption here is that the position of the object is 0:

var spaceCollider = gameObject.AddComponent<BoxCollider>();
var c = spaceCollider.center;
spaceCollider.center = new Vector3(c.x, c.y + bounds.size.y / 2, c.z);
spaceCollider.size = bounds.size;
spaceCollider.isTrigger = true;

Answer 4

Maybe I'm misunderstanding the question, but why don't you just go into Unity and create the Box Collider and make it the right size you want? As opposed to trying to create it in code. As long as all the other components are a part of the car, it will surround them too.