How to create a mesh in a background process

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Hello everyone,

I'm trying to create a mesh from a text file at running.

My script is based on this url : http://www.kamend.com/2014/05/rendering-a-point-cloud-inside-unity/ I'm using the same shader and I change the "CreateMesh" function in order to be able to show more than 60 000 points.

My problem is that creating a mesh with a lot of points takes a lot of time and I didn't succeed to move the CreateMesh method into an IEnumerator. (I have to show an object with more than 4 000 000 points or several object of 800 000 points each)

The way I created the IEnumerator was like this:

 IEnumerator createMesh(){
       yield return null;
       <create the mesh>
 }

This way the IEnumerator is meaningless. (and IEnumerator are run in the main thread)

Could you please tell me how can I create my mesh in a background process (for not blocking the Augmented Reality part and other stuff)? (The best would be to be able to show the 3d model progressively) The target platforms are iOS and Android.

PS: I know there is an asset which manage more than 20 million points (https://www.assetstore.unity3d.com/jp/#!/content/16019) but my company is not interested in buying this asset for several reason (not about money)

I really thank you in advance for your help

Answer 1

Best Answer

Answer by Bunny83 · Jul 13, 2016 at 10:31 AM

I see several problems here:

First of all a mesh in Unity can only have 65k vertices since the used index buffer is a 16bit buffer so you can't address more vertices. That means you have to split your mesh into seperate meshes. 4 000 000 vertices would mean you need 60+ seperate meshes.
You can't use the Mesh class from a different thread than the main thread. You can prepare the vertex / index arrays in a background thread, but the actual mesh creation / assignment of the arrays has to be done on the main thread.

There are ways to workaround those limitations, but they require you to write native code plugins which manually create VBOs (OpenGL) or VertexBuffers(D3D) in order to use 32 bit index buffers. This is not that trivial. That's why such ready-to-use solutions usually aren't free.

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ludokun · Jul 13, 2016 at 01:26 PM 0

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Thank you for your reply.

You're right, a mesh can only have 65k vertices, that's why I've improved the code from the url on my post in order to create automatically enough GameObject with MeshFilter and MeshRenderer for displaying my full object.

Concerning the second point, that's ok if I can't show my model progressively, but at which point of the creation process, I have to run it on the main thread? when running the mesh.SetIndices() method?

Bunny83 ludokun · Jul 13, 2016 at 04:09 PM 0

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Everything that involves the Mesh class directly has to be done on the main thread. So when you call the setter for the vertex positions / colors / uvs / normals / ... as well as setting the indices. Those are all methods that run engine core functions which can only be used from the main thread.

So what you can do in a background thread is the allocation of your arrays and the actual generation of the mesh data. However the assignment to the Mesh class has to be done on the main thread.

ludokun Bunny83 · Jul 14, 2016 at 06:14 AM 0

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Thank you for your reply.

I've succeeded to create a thread for retrieving all vertices, colors and indices and set them on the main thread (not glad the way I manage it though...)

Everything works the way I expected :) thank you very much

Answer 2

Answer by LiamMitchell · Dec 17, 2019 at 06:02 AM

You can use UInt32 for the index.

         if (Vertices.Length >= ushort.MaxValue)
         {
             mesh.indexFormat = UnityEngine.Rendering.IndexFormat.UInt32;
         }
         else if (Vertices.Length >= uint.MaxValue)
         {
             Debug.Log("Too many vertices for Unitys limit per mesh. Suggest to chunk it up into multiple meshes.");
         }

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How to create a mesh in a background process

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