Manually combining meshes per frame

Unity Engine
1

This question follows from http://forum.unity3d.com/threads/207914-Batching-draw-calls

I have 80 gems of different colours, and I’m trying to get them all to render in the same draw call.

I discovered that any form of batching fails because my shader has 2 passes.

So now I am trying to combine the meshes of all 80 children into the parent.

So I turn off the renderer in each of the children (well, in the prefab from which all children are cloned), and put this code in the parent:

	void Update( )
	{
                Component[] meshFilters = GetComponentsInChildren<MeshFilter>();
                CombineInstance[] combine = new CombineInstance[meshFilters.Length];

		for (int i = 0; i < meshFilters.Length; i++ ) 
		{
			MeshFilter M_i = (MeshFilter)meshFilters[ i ];
			
			combine[i].mesh = M_i.mesh;
			combine[i].transform = M_i.transform.localToWorldMatrix;
			
                        //M_i.gameObject.active = false;
                }
        
                transform.GetComponent< MeshFilter >().mesh = new Mesh();
        transform.GetComponent< MeshFilter >().mesh.CombineMeshes( combine ); // count <= std::numeric_limits<UInt16>::max()

                transform.gameObject.active = true;
	}

This has been adapted from Unity - Scripting API: Mesh.CombineMeshes

Code on that page wouldn’t run out of the box.

So this appears to work for a few seconds, but the triangle count goes through the roof and unity crashes. I’ve also been warned on the channel that using CombineMeshes every frame is a really bad idea.

EDIT: Note the error

       // count <= std::numeric_limits<UInt16>::max()
        transform.GetComponent< MeshFilter >().mesh.CombineMeshes( combine );

How to do this properly?

I’ve been told that the right way to do this would be to create the uber-mesh initially, and then each frame copy all of the child meshes into it Vertex by Vertex, Triangle by Triangle

How do I do this? Could someone point me towards some code?

EDIT: I may be able to adapt http://wiki.unity3d.com/index.php?title=MeshMerger

2

Sounds like you’ve got a memory leak with all the Meshes you’re creating. Unity’s garbage collector doesn’t automatically destroy your dynamically created meshes, you have to manage this yourself.

Currently what your code is doing is allocating memory for a new Mesh every frame with

 transform.GetComponent< MeshFilter >().mesh = new Mesh();

but never deleting with the old ones! Hence the eventual Editor crash from running out of memory. Infact you shouldn’t need this problematic line in your Update loop anyway; just make sure your MeshFilter component has a Mesh allocated to it in the Start() function.

Also, you should be caching the references to those MeshFilters in the child objects. Calls like ‘GetComponentsInChildren()’ are quite expensive, and you definitely don’t want to be doing them every frame if you can avoid it. Have a “Component[ ] meshFilters” class variable, and initialise it in the Start() function.

Hope this helps!

3

Thanks, you were right on the money. It works nicely now! π