Convert Mesh.SetVertices() to Mesh.SetVertexBufferParams() and Mesh.SetVertexBufferData()-CodePudding

I'm trying to improve the performance of some mesh generation, and so I'd like to change from using SetVertices() to the SetVertexBufferParam/Data pattern. This is what I have:

// verts is a NativeArray<float3>
// numVerts is the length of verts
Mesh mesh = new Mesh();

// this works and creates a series of flat faces
mesh.SetVertices(verts);

// this creates a mesh but it's very wrong
mesh.SetVertexBufferParams(numVerts,
  new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32, 3),
  new VertexAttributeDescriptor(VertexAttribute.Normal, VertexAttributeFormat.Float32, 3));
mesh.SetVertexBufferData(verts, 0, 0, numVerts);

// afterwards I set indices, norms, etc.

Desired result vs result using SetVertexBufferData:

What did I do wrong?

CodePudding user response：

See Mesh.SetVertexBufferData and in particular also VertexAttributeDescriptor

Usually you use your own Vertex struct. You are passing a layout

new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32, 3),
new VertexAttributeDescriptor(VertexAttribute.Normal, VertexAttributeFormat.Float32, 3)

which would expect an input struct like e.g.

[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public struct YourVertex
{
    public Vector3 position;
    public Vector3 normal;
}

but actually you only provide the float3 data which is only enough for

new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32, 3)

In the native array you basically just get

float, float, float, float, float, float, float, float, float, float, ...

so since you tell the layout to expect a 3 x Float32 position a 3x Float32 normal it is trying to apply always 3 floats to the position and 3 floats to the normal

=> these 3 floats belonging actually to the next vertex get kinda "lost" / applied incorrectly as normal