How to get the correct Binding Space for Parameter Block?

[LJFYC007]

So I'm using slang + nvrhi + d3d12 now, for example, a slang like this:

struct Vertex
{
    float3 position;
    float2 texCoord;
    float3 normal;
};

struct Scene
{
    RaytracingAccelerationStructure rtAccel;
    StructuredBuffer<Vertex> vertices;
    StructuredBuffer<uint> indices;
};

ConstantBuffer<Camera> gCamera;
RWTexture2D<float4> result;
ParameterBlock<Scene> gScene;

How to get the correct Binding Space we need in the Binding Set of gScene in nvrhi? I'm confusing since I know the correct Binding Space should be 1 for gScene, and should be 0 for gCamera and result, but when I try to use getBindingSpace() it always return 0.

[mkeshavaNV]

The problem is that when you call getBindingSpace() on a parameter block, it's likely returning 0 because it's looking at the wrong resource kind. Parameter blocks in Slang use a special resource kind called SubElementRegisterSpace to manage their binding spaces, which is different from regular parameters. Can you try:
auto space = varLayout->getOffset(LayoutResourceKind::SubElementRegisterSpace);

[LJFYC007]

Thanks a lot!

When I using varLayout->getOffset(slang::ParameterCategory::SubElementRegisterSpace) for gScene varLayout it returns 1 as I wish.

So, here is next problem, do I need to accumulate this offset through the access path like the documentation said? Like what is the problem of directly use getOffset?

[mkeshavaNV]

I suppose you only need to accumulate offsets when dealing with nested parameter blocks or accessing fields within parameter blocks? Otherwise a direct getOffset should be OK I think.

[LJFYC007]

Thanks! Appreciate your help :)