How to use multiple vertex streams with SetVertexBufferData()?

Unity Engine
1

Hello. Hoping an expert in the ‘advanced mesh api’ can offer me some advice.

My question relates to the use of two methods (click for the documentation):

  1. Mesh.SetVertexBufferParams()
  2. Mesh.SetVertexBufferData()

The second of these takes a parameter ‘stream’ which apparently lets us set the vertex data for multiple streams.

I have a test rig working perfectly when just using the default stream (0) but I’m having trouble trying to introduce a second stream.

I assume that I need to set up two separate VertexBufferParams like so:

VertexAttributeDescriptor[] customVertexStream1 = new[] {
      new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32, 3),
};

VertexAttributeDescriptor[] customVertexStream2 = new[] {
      new VertexAttributeDescriptor(VertexAttribute.Normal, VertexAttributeFormat.Float32, 3),
      new VertexAttributeDescriptor(VertexAttribute.TexCoord0, VertexAttributeFormat.Float32, 2),
};

But when I use Mesh.SetVertexBufferParams() there doesn’t appear to be a way to set it for a stream other than the default:

mesh.SetVertexBufferParams(vertexBuffer1.Count, customVertexStream1); // Where's the stream parameter?

There’s no parameter for the stream number like there is for SetVertexBufferData.

Whatever I try, I always get the same exception when trying to call SetVertexBufferData with stream = 1 rather than 0:

SetVertexData() with out-of-bounds arguments; would need to copy 810000 bytes at offset 0 into a 0 byte buffer
This is the same exception you get if you fail to call SetVertexBufferParams() before calling SetVertexBufferData with stream = 0, so I’m pretty sure the issue is the SetVertexBufferParams().

I’ve looked through all the documentation, even the Mesh.cs source code. My question is simple. How do you SetVertexBufferParams() for a stream other than 0?

Just to avoid the obvious questions: I know I can just combine all my data into a single stream. I’ve done that and everything works perfectly. However I would like to try the multiple stream approach because it will open up some potential optimisations with how I generate the vertex buffer data.

Hoping it’s a just a simple step that I’m missing somewhere. Thanks!

2

Stream is part of VertexAttributeDescriptor, so (typing out of my head), it would be like (note I added the last aguments):

VertexAttributeDescriptor[] customVertexStreams = new[] {
      new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32, 3, stream:0),
      new VertexAttributeDescriptor(VertexAttribute.Normal, VertexAttributeFormat.Float32, 3, stream:1),
      new VertexAttributeDescriptor(VertexAttribute.TexCoord0, VertexAttributeFormat.Float32, 2, stream:1),
};
1 Like
3

Doh! Thank you so much for the quick reply. I knew it would be something obvious that I missed. It’s right here in the documentation.

Everything is working beautifully now. :slight_smile:

4

I tried your method, But another SetVertexBufferParams will cover before one, how can i set two stream to transfer data?