Substrate Adaptive GBuffer: HWRT Hit Lighting drops indirect lighting from lights with a Light Function (GI / Reflections)

The Light Function variant of the hit lighting miss shader is compiled as the Light Function material, so MATERIAL_IS_SUBSTRATE=1. This makes it read the ray hit surface from the payload incorrectly:

• This shader permutation has SUBSTRATE_INLINE_SHADING=1 and SUBSTRATE_DEFERRED_SHADING=0, the header/BSDF unpack from the payload is compiled out.
• SubstrateGetBSDFSharedBasis takes the inline path and returns the zero-initialized SharedLocalBases, so the hit normal is 0 and the light contribution is 0.
• The LF material's SUBSTRATE_FASTPATH / SINGLEPATH / CLAMPED_CLOSURE_COUNT and the default SUBSTRATE_USES_FORCED_COMPLEXITY=1 also drive how the hit surface is unpacked (the payload writer RayTracingMaterialHitShaders.usf:16-19 uses SUBSTRATE_USES_FORCED_COMPLEXITY 0).

Here is a work around:

[Link Removed]

1. Download the repro project from additional info URL
   • Project already sets r.Substrate=1, r.Substrate.ProjectGBufferFormat=1, Lumen HWRT with Hit Lighting, r.RayTracing.LightFunction=1.
2. Move to the two rooms in the level and compare the light with and without a Light Function
   You can use following BugItGo commands
   1. GI: BugItGo 404.234184 1526.353047 230.520925 -8.400000 -183.399997 0.000000
   2. Reflection: BugItGo -323.400190 -1497.680129 164.879523 -4.600000 -185.199997 0.000000

Result: The lights with Light Functions do not contribute to indirect lighting (GI) or reflections