Vulkan-docs: VK_NVX_raytracing does not document structure of the instance buffer

[kennyalive]

vkCmdBuildAccelerationStructureNVX function has VkBuffer instanceData parameter but it seems there is no description of instance buffer data layout in the specification of version 1.1.86.

[kayru]

Presumably, the missing structure is VkInstanceNVX (which is mentioned, but not detailed).

[kayru]

While we wait for the official spec clarification, it's possible to use DXR spec to guess the instance data structure. It is likely to be this:

struct Instance
{
    float transform[12];
    uint32_t instanceID : 24;
    uint32_t instanceMask : 8;
    uint32_t instanceContributionToHitGroupIndex : 24;
    uint32_t flags : 8;
    uint64_t accelerationStructureHandle;
};

Acceleration structure handle should be acquired via vkGetAccelerationStructureHandleNVX.

[dgkoch]

what @kayru wrote is the correct layout -- it is the same as in DXR.

We'll aim to correct this in a future documentation update.

[dgkoch]

VK_NVX_raytracing has now been replaced with VK_NV_ray_tracing which is now published in the 1.1.91 spec (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VK_NV_ray_tracing ). The documentation has also significantly improved and the issues reported here should all be addressed.