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

3 files changed, 84 insertions, 0 deletions

diff --git a/source/blender/editors/render/render_intern.hh b/source/blender/editors/render/render_intern.hh
index fc40fb06851..4135a0d97a9 100644
--- a/source/blender/editors/render/render_intern.hh
+++ b/source/blender/editors/render/render_intern.hh
@@ -33,6 +33,8 @@ void SCENE_OT_view_layer_add(struct wmOperatorType *ot);
 void SCENE_OT_view_layer_remove(struct wmOperatorType *ot);
 void SCENE_OT_view_layer_add_aov(struct wmOperatorType *ot);
 void SCENE_OT_view_layer_remove_aov(struct wmOperatorType *ot);
+void SCENE_OT_view_layer_add_lightgroup(struct wmOperatorType *ot);
+void SCENE_OT_view_layer_remove_lightgroup(struct wmOperatorType *ot);
 
 void SCENE_OT_light_cache_bake(struct wmOperatorType *ot);
 void SCENE_OT_light_cache_free(struct wmOperatorType *ot);
diff --git a/source/blender/editors/render/render_ops.cc b/source/blender/editors/render/render_ops.cc
index 1583ce44ee5..f671b2f950d 100644
--- a/source/blender/editors/render/render_ops.cc
+++ b/source/blender/editors/render/render_ops.cc
@@ -39,6 +39,8 @@ void ED_operatortypes_render()
   WM_operatortype_append(SCENE_OT_view_layer_remove);
   WM_operatortype_append(SCENE_OT_view_layer_add_aov);
   WM_operatortype_append(SCENE_OT_view_layer_remove_aov);
+  WM_operatortype_append(SCENE_OT_view_layer_add_lightgroup);
+  WM_operatortype_append(SCENE_OT_view_layer_remove_lightgroup);
 
   WM_operatortype_append(SCENE_OT_render_view_add);
   WM_operatortype_append(SCENE_OT_render_view_remove);
diff --git a/source/blender/editors/render/render_shading.cc b/source/blender/editors/render/render_shading.cc
index f48ac99fe75..07a07b462ef 100644
--- a/source/blender/editors/render/render_shading.cc
+++ b/source/blender/editors/render/render_shading.cc
@@ -1115,6 +1115,86 @@ void SCENE_OT_view_layer_remove_aov(wmOperatorType *ot)
 /** \} */
 
 /* -------------------------------------------------------------------- */
+/** \name View Layer Add Lightgroup Operator
+ * \{ */
+
+static int view_layer_add_lightgroup_exec(bContext *C, wmOperator *UNUSED(op))
+{
+  Scene *scene = CTX_data_scene(C);
+  ViewLayer *view_layer = CTX_data_view_layer(C);
+
+  BKE_view_layer_add_lightgroup(view_layer);
+
+  if (scene->nodetree) {
+    ntreeCompositUpdateRLayers(scene->nodetree);
+  }
+
+  DEG_id_tag_update(&scene->id, 0);
+  DEG_relations_tag_update(CTX_data_main(C));
+  WM_event_add_notifier(C, NC_SCENE | ND_LAYER, scene);
+
+  return OPERATOR_FINISHED;
+}
+
+void SCENE_OT_view_layer_add_lightgroup(wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Add Lightgroup";
+  ot->idname = "SCENE_OT_view_layer_add_lightgroup";
+  ot->description = "Add a Light Group";
+
+  /* api callbacks */
+  ot->exec = view_layer_add_lightgroup_exec;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name View Layer Remove Lightgroup Operator
+ * \{ */
+
+static int view_layer_remove_lightgroup_exec(bContext *C, wmOperator *UNUSED(op))
+{
+  Scene *scene = CTX_data_scene(C);
+  ViewLayer *view_layer = CTX_data_view_layer(C);
+
+  if (view_layer->active_lightgroup == nullptr) {
+    return OPERATOR_FINISHED;
+  }
+
+  BKE_view_layer_remove_lightgroup(view_layer, view_layer->active_lightgroup);
+
+  if (scene->nodetree) {
+    ntreeCompositUpdateRLayers(scene->nodetree);
+  }
+
+  DEG_id_tag_update(&scene->id, 0);
+  DEG_relations_tag_update(CTX_data_main(C));
+  WM_event_add_notifier(C, NC_SCENE | ND_LAYER, scene);
+
+  return OPERATOR_FINISHED;
+}
+
+void SCENE_OT_view_layer_remove_lightgroup(wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Remove Lightgroup";
+  ot->idname = "SCENE_OT_view_layer_remove_lightgroup";
+  ot->description = "Remove Active Lightgroup";
+
+  /* api callbacks */
+  ot->exec = view_layer_remove_lightgroup_exec;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
 /** \name Light Cache Bake Operator
  * \{ */