Fixed size array support

[sselecirPyM]

As far as I know, hlsl supports fixed-size arrays. Are there any plans to support the use of fixed-size arrays in shaders?

[Sergio0694]

This is something I want to add, but need support for fixed size arrays added to C# first.
They've prototyped it in last year's hackathon, but hasn't made it to an official C# release yet.
Unfortunately I don't see this happening before at least C# 13. Will leave this open to track it though 🙂

[sselecirPyM]

You can support only new T[constant] statements. Or Span variable= stackalloc T[constant].

[harrison314]

You can support only new T[constant] statements. Or Span variable= stackalloc T[constant].

Or use Hlsl intrinsics eg. float[] array = Hlsl.AllocConstSizeFloatArray(32);

[rickbrew]

Could also permit InlineArray-esque syntax, e.g.

[HlslArray(100)]
private struct Float4Len100 { public float4 element0; }

public float4 Execute()
{
    Float4Len100 array = default;
    for (int i = 0; i < 100; ++i) { array[i] = (float4)i; }
    ...
}

It's kind of ugly, but this way we don't have to wait 5 years for whatever support might be hopefully added to C#. And if/when the right syntax does come along, just switch over to that and nuke the old syntax.

This would unlock a lot of potential, the lack of this is currently limiting what I can do quite severely!

[luoluo39]

Could also permit InlineArray-esque syntax, e.g.

I can see no reason not to support System.Runtime.CompilerServices.InlineArray, which already met our needs.
implement something similar by ourselves will bring some syntax noise and a lot of extra work to do.

[rickbrew]

I can see no reason not to support System.Runtime.CompilerServices.InlineArray,

As @Sergio0694 explained it to me on Discord, it will still require an additional attribute so that the source generator knows when to kick in. So it would be

[InlineArray(100)]
[HlslArray]
private struct Float4Len100 { public float4 element0; }

And there is quite a bit of work in the generator that would be needed to enable all of this. Don't worry, I've been lobbying @Sergio0694 for this quite a bit -- he definitely knows how important this is :)

There's also the matter of how to unify this across other arrays in other contexts, or other array-like-things such as groupshared and RWStructuredBuffer<T> (e.g. resource textures). Or if that's even necessary / important.

[Sergio0694]

Could you folks link any shaders here that do use fixed size arrays? I'm thinking about the implementation here, and I'd like to double check that against some real world code to make sure that it work work fine in those scenarios. Thank you! :)