StaticBatchingUtility combine meshes in runtime

I have AssetBundle and I instantiate an object from it in runtime. Now I need to combine all already created instances of the object with the new instance into a static butch. here how I do it:

GameObject go = (GameObject)Instantiate(gameObjectObj, Vector3.right * 4 + Vector3.left * 2 * l, Quaternion.LookRotation(Vector3.up, Vector3.forward));
go.isStatic = true;
go.transform.parent = root.transform;
gosList.Add(go);
gos = gosList.ToArray();            

StaticBatchingUtility.Combine(gos, root);

As the result I have game object is batching by pairs. For example

  • Objects 1 2 3 4 5 6
  • Drawcall 1 1 2 2 3 3
  • Batching 0 2 2 4 4 6

The question is why the objects are combinig only by pairs?
If I made 10 instances at once and combine them I’ll get 1 drawcall and 10 butches
Here is the code that work fine

for (int i = 0; i < 10; i++){
    GameObject go = (GameObject)Instantiate(gameObjectObj, Vector3.right * 4 + Vector3.left * 2 * l, Quaternion.LookRotation(Vector3.up, Vector3.forward));
    go.isStatic = true;
    go.transform.parent = root.transform;
    gosList.Add(go);
    gos = gosList.ToArray();            
}
    StaticBatchingUtility.Combine(gos, root);

Hi. Combine() is limited to only affect meshes not already batched. This means it is not possible to add more meshes to a previously created batch. Instead, a new batch will be created (and this is why you see them combining only by pairs).

In practice, this implies that, to get the best results, you need to call Combine() only once per desired batch, after all meshes were added to the scene. Or if not possible, at least try to call it as few times as possible, as every call will likely result in one batch added.