Matrices in MTLVertexDescriptor

Question

I'm trying to write vertex descriptor for my vertex shader which takes following struct as stage_in input.

struct VertexIn {
      float2x2 foo;
}

vertex float4 vertexShader(const VertexIn in [[stage_in]]) {...}

Now when defining vertex descriptor's attribute what should be the MTLVertexFormat? vertexDescriptor.attributes[0].format = ???

I went through the documentation, I didn't find any enum case for Matrices. Is it fine if say set format as float2 and give size 2 * size of float2?

Answer 1

According The Metal Feature Set Tables:

---

You can declare only one argument of the vertex, fragment, or kernel function with the [[stage_in]] attribute. For a user-defined structure declared with the [[stage_in]] attribute, the members of the structure can be:

• A scalar integer or floating-point value.
• A vector of integer or floating-point values.
• An interpolant<T,P> value for fragment function input.

You cannot use the stage_in attribute to declare members of the structure that are packed vectors, matrices, structures, bitfields, references or pointers to a type, or arrays of scalars, vectors, or matrices.

---