CODEWITHSUNDEEP
metalmetalkit
Nikola Bozhkov
Nikola Bozhkov

Reputation: 76

When to use setVertexBytes/setVertexBuffer when dealing with small data in Metal?

The documentation for setVertexBytes says:

Use this method for single-use data smaller than 4 KB. Create a MTLBuffer object if your data exceeds 4 KB in length or persists for multiple uses.

What exactly does single-use mean?

For example, if I have a uniforms struct which is less than 4KB(and is updated every frame), is it better to use a triple buffer technique or simply use setVertexBytes?

From what I understand using setVertexBytes would copy the data every time into a MTLBuffer that Metal manages. This sounds slower than using triple buffering.

But then if I have different objects, each with its own uniforms, I would have to triple buffer everything, since it's dynamically updated. And if I have a material that updates rarely but is passed to the shader every frame, would it be better to keep it in a buffer or pass it as a pointer using setVertexBytes?

Upvotes: 3

Views: 1438

Answers (1)

warrenm
warrenm

Reputation: 31782

It's not necessarily the case that Metal manages a distinct resource into which this data is written. As user Columbo notes in their comment, some hardware allows constant data to be recorded directly into command buffer memory, from which it can be subsequently read by a shader.

As always, you should profile in order to find the difference between the two approaches on your target hardware, but if the amount of data you're pushing per draw call is small, you might very well find that using setVertexBytes:... is faster than writing into a buffer and calling setVertexBuffer:....

For data that doesn't vary every frame (your slow-varying material use case), it may indeed be more efficient to keep that data in a buffer (double- or triple-buffered) rather than using setVertexBytes:....

Upvotes: 5

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