added some comments regarding future use of MIS, scene takes and intersected ray and gives intersection

Author: keptsecret

include/nbl/builtin/hlsl/path_tracing/concepts.hlsl

@@ -318,32 +318,30 @@ NBL_CONCEPT_END(
 namespace impl
 {
 struct DummyRay {};
+struct DummyIntersect {};
 }
 
 #define NBL_CONCEPT_NAME Scene
 #define NBL_CONCEPT_TPLT_PRM_KINDS (typename)
 #define NBL_CONCEPT_TPLT_PRM_NAMES (T)
 #define NBL_CONCEPT_PARAM_0 (scene, T)
-#define NBL_CONCEPT_PARAM_1 (intersectP, typename T::vector3_type)
-#define NBL_CONCEPT_PARAM_2 (id, typename T::object_handle_type)
-#define NBL_CONCEPT_PARAM_3 (ray, impl::DummyRay)
-NBL_CONCEPT_BEGIN(4)
+#define NBL_CONCEPT_PARAM_1 (id, typename T::object_handle_type)
+#define NBL_CONCEPT_PARAM_2 (ray, impl::DummyRay)
+NBL_CONCEPT_BEGIN(3)
 #define scene NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_0
-#define intersectP NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_1
-#define id NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_2
-#define ray NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_3
+#define id NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_1
+#define ray NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_2
 NBL_CONCEPT_END(
     ((NBL_CONCEPT_REQ_TYPE)(T::vector3_type))
     ((NBL_CONCEPT_REQ_TYPE)(T::object_handle_type))
     ((NBL_CONCEPT_REQ_TYPE)(T::mat_light_id_type))
     ((NBL_CONCEPT_REQ_TYPE)(T::interaction_type))
     ((NBL_CONCEPT_REQ_TYPE_ALIAS_CONCEPT)(MaterialLightID, typename T::mat_light_id_type))
     ((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((scene.getMatLightIDs(id)), ::nbl::hlsl::is_same_v, typename T::mat_light_id_type))
-    ((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((scene.template getInteraction<impl::DummyRay>(id, intersectP, ray)), ::nbl::hlsl::is_same_v, typename T::interaction_type))
+    ((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((scene.template getIntersection<impl::DummyIntersect, impl::DummyRay>(id, ray)), ::nbl::hlsl::is_same_v, impl::DummyIntersect))
 );
 #undef ray
 #undef id
-#undef intersectP
 #undef scene
 #include <nbl/builtin/hlsl/concepts/__end.hlsl>
 

include/nbl/builtin/hlsl/path_tracing/unidirectional.hlsl

@@ -55,7 +55,6 @@ struct Unidirectional
         return hlsl::dot(spectralTypeToLumaCoeffs, col);
     }
 
-    // TODO: will only work with isotropic surfaces, need to do aniso
     bool closestHitProgram(uint16_t depth, uint32_t _sample, NBL_REF_ARG(ray_type) ray, NBL_CONST_REF_ARG(closest_hit_type) intersectData)
     {
         anisotropic_interaction_type interaction = intersectData.getInteraction();
@@ -117,8 +116,13 @@ struct Unidirectional
             bxdf::fresnel::OrientedEtas<monochrome_type> orientedEta = bxdf::fresnel::OrientedEtas<monochrome_type>::create(interaction.getNdotV(), hlsl::promote<monochrome_type>(monochromeEta));
             anisocache_type _cache = anisocache_type::template create<anisotropic_interaction_type, sample_type>(interaction, nee_sample, orientedEta);
 
+            // While NEE or other generators are not supposed to pick up Delta lobes by accident, we need the MIS weights to add up to 1 for the non-delta lobes.
+            // So we need to weigh the Delta lobes as if the MIS weight is always 1, but other areas regularly.
+            // Meaning that eval's pdf should equal quotient's pdf , this way even the diffuse contributions coming from within a specular lobe get a MIS weight near 0 for NEE.
+            // This stops a discrepancy in MIS weights and NEE mistakenly trying to add non-delta lobe contributions with a MIS weight > 0 and creating energy from thin air.
             if (neeContrib.pdf > scalar_type(0.0))
             {
+                // we'll need an `eval_and_mis_weight` and `quotient_and_mis_weight`
                 const scalar_type bsdf_pdf = materialSystem.pdf(matID, nee_sample, interaction, _cache);
                 neeContrib.quotient *= materialSystem.eval(matID, nee_sample, interaction, _cache) * rcpChoiceProb;
                 const scalar_type otherGenOverLightAndChoice = bsdf_pdf * rcpChoiceProb / neeContrib.pdf;