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, 24 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_object.c b/source/blender/makesrna/intern/rna_object.c
index e4495df36f1..f995ee3383e 100644
--- a/source/blender/makesrna/intern/rna_object.c
+++ b/source/blender/makesrna/intern/rna_object.c
@@ -2292,6 +2292,21 @@ static int rna_Object_mesh_symmetry_yz_editable(PointerRNA *ptr, const char **UN
   return PROP_EDITABLE;
 }
 
+void rna_Object_lightgroup_get(PointerRNA *ptr, char *value)
+{
+  BKE_lightgroup_membership_get(((Object *)ptr->owner_id)->lightgroup, value);
+}
+
+int rna_Object_lightgroup_length(PointerRNA *ptr)
+{
+  return BKE_lightgroup_membership_length(((Object *)ptr->owner_id)->lightgroup);
+}
+
+void rna_Object_lightgroup_set(PointerRNA *ptr, const char *value)
+{
+  BKE_lightgroup_membership_set(&((Object *)ptr->owner_id)->lightgroup, value);
+}
+
 #else
 
 static void rna_def_vertex_group(BlenderRNA *brna)
@@ -3775,6 +3790,15 @@ static void rna_def_object(BlenderRNA *brna)
   RNA_def_property_editable_func(prop, "rna_Object_mesh_symmetry_yz_editable");
   RNA_def_property_ui_text(prop, "Z", "Enable mesh symmetry in the Z axis");
 
+  /* Lightgroup Membership */
+  prop = RNA_def_property(srna, "lightgroup", PROP_STRING, PROP_NONE);
+  RNA_def_property_string_funcs(prop,
+                                "rna_Object_lightgroup_get",
+                                "rna_Object_lightgroup_length",
+                                "rna_Object_lightgroup_set");
+  RNA_def_property_flag(prop, PROP_EDITABLE);
+  RNA_def_property_ui_text(prop, "Lightgroup", "Lightgroup that the object belongs to");
+
   RNA_define_lib_overridable(false);
 
   /* anim */