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, 12 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index c00a403d5e9..833e6f882f1 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -260,6 +260,10 @@ static void object_copy_data(Main *bmain, ID *id_dst, const ID *id_src, const in
   else {
     ob_dst->preview = nullptr;
   }
+
+  if (ob_src->lightgroup) {
+    ob_dst->lightgroup = (LightgroupMembership *)MEM_dupallocN(ob_src->lightgroup);
+  }
 }
 
 static void object_free_data(ID *id)
@@ -310,6 +314,8 @@ static void object_free_data(ID *id)
   }
 
   BKE_previewimg_free(&ob->preview);
+
+  MEM_SAFE_FREE(ob->lightgroup);
 }
 
 static void library_foreach_modifiersForeachIDLink(void *user_data,
@@ -584,6 +590,10 @@ static void object_blend_write(BlendWriter *writer, ID *id, const void *id_addre
   BLO_write_struct_list(writer, LinkData, &ob->pc_ids);
 
   BKE_previewimg_blend_write(writer, ob->preview);
+
+  if (ob->lightgroup) {
+    BLO_write_struct(writer, LightgroupMembership, ob->lightgroup);
+  }
 }
 
 /* XXX deprecated - old animation system */
@@ -800,6 +810,8 @@ static void object_blend_read_data(BlendDataReader *reader, ID *id)
 
   BLO_read_data_address(reader, &ob->preview);
   BKE_previewimg_blend_read(reader, ob->preview);
+
+  BLO_read_data_address(reader, &ob->lightgroup);
 }
 
 /* XXX deprecated - old animation system */