Fix for broken collider when parenting to rigidbody

Hello World!

Today I ran into a problem when trying to clone prefabs (ship parts) and parent them to a space ship. The problem was the physics broke, resulting in all clones colliders got stuck where they were instansiated, instead of the standard behavior of them following the object.

After a quick discussion on IRC, we managed to find a solution. Just before you add the clone to the parent through clone.transform.parent = ship.transform;, you temporarily disable the clone. After the transform binding is done, you can activate it again. This worked for me, if you are having trouble please make a reply about it.

Here is working code from my project that creates 10 rockets to a ship.

This script is intended to be placed on an empty game object that simply creates a few rockets on a ship when you start the game.

Variables:
ship - Any game object that acts as your base object to attach stuff to. It should have a rigid body and a collider.
rocketPrefab - Any prefab you want to instansiate around ship. It should not have any rigid body, but it should have a collider.

Note the scales on the transforms; new prefabs are placed 1 unit away from the ship. This will cause problems if your parts or ship is too large because of overlapping.

Code (csharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class ShipBuilderTest : MonoBehaviour
5. {
6.     public GameObject ship;
7.     public GameObject rocketPrefab;
8.    
9.     void Start()
10.     {
11.         float piDouble = Mathf.PI * 2;
12.         float step = piDouble / 10; // Create 10 objects
13.  
14.         for (float angle = 0; angle < piDouble; angle += step)
15.         {
16.             float cos = Mathf.Cos(angle);
17.             float sin = Mathf.Sin(angle);
18.  
19.             Vector3 offset = new Vector3(cos, sin);
20.             Vector3 position = Vector3.zero;
21.             Quaternion rotation = Quaternion.identity;
22.  
23.             GameObject clone = Instantiate(rocketPrefab, position, rotation) as GameObject;
24.             clone.active = false; // WORKAROUND FIX
25.             clone.transform.parent = ship.transform;
26.             clone.transform.localPosition = position + offset;
27.             clone.transform.localRotation = rotation;
28.             clone.active = true; // WORKAROUND FIX
29.         }
30.     }
31. }
32.  

I hope that this will help other people with the same problem. I have sent a problem report to the developers so that it will be addressed in the future.

Note: This works for me in Version 2.5.0f5 (21627).

 

Thanks for posting your discovery!