Pad a struct so its size is a multiple of 16 bytes

Question

I'm trying to have my C# struct match up some complex padding and packing rules.

• Fields should be aligned on 4 byte boundaries.
• The entire struct should be a multiple of 16 bytes

Using the StructLayout attribute I can make sure that fields are aligned on 4 byte boundaries.

[StructLayout(LayoutKind.Sequential, Pack=4)]
struct Foo
{
    float a;
    float b;
}

But looking at the other options for the StructLayout attribute I see no options for padding the struct to multiples of 16 bytes. Is there no option for that in C#?

The only option I see is manually set the right size, using the Size property of the StructLayout attribute. But that seems brittle to me. As every time somebody adds a field to this struct they should take care not to forget to update the size.

Answer 1

After more searching, it indeed does look like I have to manually set the Size and FieldOffset to get to the right packing rules for Constant Buffers in DirectX/HLSL/C# interop code.

In my own project this is even a bit more complex. Since I use source generators to create these structs. But in the end I was able to figure it out. For those interested the source code can be found here.