Cycles: Add support for light groups

Light groups are a type of pass that only contains lighting from a subset of light sources.
They are created in the View layer, and light sources (lamps, objects with emissive materials
and/or the environment) can be assigned to a group.

Currently, each light group ends up generating its own version of the Combined pass.
In the future, additional types of passes (e.g. shadowcatcher) might be getting their own
per-lightgroup versions.

The lightgroup creation and assignment is not Cycles-specific, so Eevee or external render
engines could make use of it in the future.

Note that Lightgroups are identified by their name - therefore, the name of the Lightgroup
in the View Layer and the name that's set in an object's settings must match for it to be
included.
Currently, changing a Lightgroup's name does not update objects - this is planned for the
future, along with other features such as denoising for light groups and viewing them in
preview renders.

Original patch by Alex Fuller (@mistaed), with some polishing by Lukas Stockner (@lukasstockner97).

Differential Revision: https://developer.blender.org/D12871

1 files changed, 5 insertions, 0 deletions

diff --git a/intern/cycles/kernel/light/light.h b/intern/cycles/kernel/light/light.h
index fb637008ca4..1df1615ed99 100644
--- a/intern/cycles/kernel/light/light.h
+++ b/intern/cycles/kernel/light/light.h
@@ -23,6 +23,7 @@ typedef struct LightSample {
   int prim;       /* primitive id for triangle/curve lights */
   int shader;     /* shader id */
   int lamp;       /* lamp id */
+  int group;      /* lightgroup */
   LightType type; /* type of light */
 } LightSample;
 
@@ -52,6 +53,7 @@ ccl_device_inline bool light_sample(KernelGlobals kg,
   ls->lamp = lamp;
   ls->u = randu;
   ls->v = randv;
+  ls->group = lamp_lightgroup(kg, lamp);
 
   if (in_volume_segment && (type == LIGHT_DISTANT || type == LIGHT_BACKGROUND)) {
     /* Distant lights in a volume get a dummy sample, position will not actually
@@ -413,6 +415,7 @@ ccl_device bool light_sample_from_distant_ray(KernelGlobals kg,
   ls->P = -ray_D;
   ls->Ng = -ray_D;
   ls->D = ray_D;
+  ls->group = lamp_lightgroup(kg, lamp);
 
   /* compute pdf */
   float invarea = klight->distant.invarea;
@@ -441,6 +444,7 @@ ccl_device bool light_sample_from_intersection(KernelGlobals kg,
   ls->t = isect->t;
   ls->P = ray_P + ray_D * ls->t;
   ls->D = ray_D;
+  ls->group = lamp_lightgroup(kg, lamp);
 
   if (type == LIGHT_SPOT) {
     const float3 center = make_float3(klight->co[0], klight->co[1], klight->co[2]);
@@ -706,6 +710,7 @@ ccl_device_forceinline void triangle_light_sample(KernelGlobals kg,
   ls->lamp = LAMP_NONE;
   ls->shader |= SHADER_USE_MIS;
   ls->type = LIGHT_TRIANGLE;
+  ls->group = object_lightgroup(kg, object);
 
   float distance_to_plane = fabsf(dot(N0, V[0] - P) / dot(N0, N0));