Modifying vertices using advanced mesh API

I need some help with the new mesh api. The documentation is so sparse it's hard to find anything useful yet.I create my mesh using:

Code (CSharp):

1. mesh.SetVertexBufferParams(vertices.Length, new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32));            
2. mesh.SetVertexBufferData(vertices, 0, 0, vertices.Length);                    
3.  
4. mesh.SetIndexBufferParams(triangles.Length, IndexFormat.UInt32);            
5. mesh.SetIndexBufferData(triangles, 0, 0, triangles.Length);            
6.  
7. mesh.SetSubMesh(0, new SubMeshDescriptor(0, triangles.Length));

Then, I need to modify said mesh's vertices. Modifying the NativeArray directly does nothing, and calling SetVertexBufferData again results in https://imgur.com/ArFNUzB (before calling SetVertexBufferData again it looks like it's supposed to: https://imgur.com/jvpJTgW).

What's the proper way to modify vertices using advanced mesh API? Is it even possible, without allocating an extra array for modified vertices?

 

Not to resurrect this but as MostNimbus said, it doesn't work like that (see his first screenshot of what happens if you attempt what you're suggesting.) If it does work like that and you omitted some important step, then I'd love to see a barebones, fully functional example.

E.g. I have a method that initializes the mesh after I fill the NativeArray:

Code (CSharp):

1.     private void InitializeMesh()
2.     {
3.         _mesh.SetVertexBufferParams(_mvertices.Length,
4.             new VertexAttributeDescriptor(VertexAttribute.Position, dimension: 3),
5.             new VertexAttributeDescriptor(VertexAttribute.Normal, dimension: 3),
6.             new VertexAttributeDescriptor(VertexAttribute.TexCoord0, dimension: 2)
7.         );
8.         _mesh.SetVertexBufferData(_mvertices, 0, 0, _mvertices.Length, 0);
9.  
10.         _mesh.SetIndexBufferParams(_indices.Length, IndexFormat.UInt32);
11.         _mesh.SetIndexBufferData(_indices, 0, 0, _indices.Length);
12.        
13.         _mesh.subMeshCount = 1;
14.         _mesh.SetSubMesh(0, new SubMeshDescriptor(0, _indices.Length, MeshTopology.Triangles)
15.         {
16.             firstVertex = 0,
17.             vertexCount = _mvertices.Length
18.         }, MeshUpdateFlags.DontRecalculateBounds | MeshUpdateFlags.DontValidateIndices | MeshUpdateFlags.DontNotifyMeshUsers);
19.         _mesh.bounds = new Bounds(Vector3.zero, Vector3.one * 1000);
20.     }
21.  

Which results in this:



Then, any time I modify the NativeArray, I have to call InitializeMesh() again. I.e.:

Code (CSharp):

1.             _mvertices[0] = new MeshVertex()
2.             {
3.                 vertex = new float3(0, 10, 0),
4.                 normal = new float3(0, 0, 1),
5.                 uv = new float2(0, 0),
6.             };
7.  
8.             InitializeMesh();

That works, of course, it results in this:



But if I attempt what you suggested... i.e.:

Code (CSharp):

1.             _mvertices[0] = new MeshVertex()
2.             {
3.                 vertex = new float3(0, 10, 0),
4.                 normal = new float3(0, 0, 1),
5.                 uv = new float2(0, 0),
6.             };
7.        
8.             _mesh.SetVertexBufferData(_mvertices, 0, 0, _mvertices.Length, 0);
9.  

...it results in incredibly broken geometry, like this:



I'm using a height-based color effect for my custom wireframe shader. So it looks to me like the GPU is reading that absurdly incorrect vertex position correctly. Also note I turned on Unity's shaded wireframe to see if the editor could make sense of that geometry, which unsurprisingly it can't.

All that said, if there's an actual proper way to update the vertices in this mesh API without having to re-set all the other data that it should already have, I would definitely love to hear it.