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

12 files changed, 110 insertions, 13 deletions

diff --git a/intern/cycles/scene/background.cpp b/intern/cycles/scene/background.cpp
index 1c3a9f9358d..bffc8895bfd 100644
--- a/intern/cycles/scene/background.cpp
+++ b/intern/cycles/scene/background.cpp
@@ -32,6 +32,8 @@ NODE_DEFINE(Background)
 
   SOCKET_NODE(shader, "Shader", Shader::get_node_type());
 
+  SOCKET_STRING(lightgroup, "Light Group", ustring());
+
   return type;
 }
 
@@ -101,6 +103,15 @@ void Background::device_update(Device *device, DeviceScene *dscene, Scene *scene
       kbackground->surface_shader |= SHADER_EXCLUDE_CAMERA;
   }
 
+  /* Light group. */
+  auto it = scene->lightgroups.find(lightgroup);
+  if (it != scene->lightgroups.end()) {
+    kbackground->lightgroup = it->second;
+  }
+  else {
+    kbackground->lightgroup = LIGHTGROUP_NONE;
+  }
+
   clear_modified();
 }
 
diff --git a/intern/cycles/scene/background.h b/intern/cycles/scene/background.h
index bbffce6e30a..50b4368d708 100644
--- a/intern/cycles/scene/background.h
+++ b/intern/cycles/scene/background.h
@@ -30,6 +30,8 @@ class Background : public Node {
 
   NODE_SOCKET_API(float, volume_step_size)
 
+  NODE_SOCKET_API(ustring, lightgroup)
+
   Background();
   ~Background();
 
diff --git a/intern/cycles/scene/film.cpp b/intern/cycles/scene/film.cpp
index e17c839d60b..c3b126544c4 100644
--- a/intern/cycles/scene/film.cpp
+++ b/intern/cycles/scene/film.cpp
@@ -175,6 +175,7 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
   kfilm->pass_volume_direct = PASS_UNUSED;
   kfilm->pass_volume_indirect = PASS_UNUSED;
   kfilm->pass_shadow = PASS_UNUSED;
+  kfilm->pass_lightgroup = PASS_UNUSED;
 
   /* Mark passes as unused so that the kernel knows the pass is inaccessible. */
   kfilm->pass_denoising_normal = PASS_UNUSED;
@@ -189,6 +190,7 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
   bool have_cryptomatte = false;
   bool have_aov_color = false;
   bool have_aov_value = false;
+  bool have_lightgroup = false;
 
   for (size_t i = 0; i < scene->passes.size(); i++) {
     const Pass *pass = scene->passes[i];
@@ -223,6 +225,15 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
       assert(pass->get_type() <= PASS_CATEGORY_BAKE_END);
     }
 
+    if (pass->get_lightgroup() != ustring()) {
+      if (!have_lightgroup) {
+        kfilm->pass_lightgroup = kfilm->pass_stride;
+        have_lightgroup = true;
+      }
+      kfilm->pass_stride += pass->get_info().num_components;
+      continue;
+    }
+
     switch (pass->get_type()) {
       case PASS_COMBINED:
         kfilm->pass_combined = kfilm->pass_stride;
@@ -414,6 +425,26 @@ int Film::get_aov_offset(Scene *scene, string name, bool &is_color)
   return -1;
 }
 
+bool Film::update_lightgroups(Scene *scene)
+{
+  map<ustring, int> lightgroups;
+  int i = 0;
+  foreach (const Pass *pass, scene->passes) {
+    ustring lightgroup = pass->get_lightgroup();
+    if (!lightgroup.empty()) {
+      if (!lightgroups.count(lightgroup)) {
+        lightgroups[lightgroup] = i++;
+      }
+    }
+  }
+  if (scene->lightgroups != lightgroups) {
+    scene->lightgroups = lightgroups;
+    return true;
+  }
+
+  return false;
+}
+
 void Film::update_passes(Scene *scene, bool add_sample_count_pass)
 {
   const Background *background = scene->background;
@@ -580,11 +611,19 @@ void Film::remove_auto_passes(Scene *scene)
 
 static bool compare_pass_order(const Pass *a, const Pass *b)
 {
+  /* On the highest level, sort by number of components.
+   * Within passes of the same component count, sort so that all non-lightgroup passes come first.
+   * Within that group, sort by type. */
   const int num_components_a = a->get_info().num_components;
   const int num_components_b = b->get_info().num_components;
 
   if (num_components_a == num_components_b) {
-    return (a->get_type() < b->get_type());
+    const int is_lightgroup_a = !a->get_lightgroup().empty();
+    const int is_lightgroup_b = !b->get_lightgroup().empty();
+    if (is_lightgroup_a == is_lightgroup_b) {
+      return (a->get_type() < b->get_type());
+    }
+    return is_lightgroup_b;
   }
 
   return num_components_a > num_components_b;
diff --git a/intern/cycles/scene/film.h b/intern/cycles/scene/film.h
index 43597b0fc79..f1e3237eb9e 100644
--- a/intern/cycles/scene/film.h
+++ b/intern/cycles/scene/film.h
@@ -68,6 +68,8 @@ class Film : public Node {
 
   int get_aov_offset(Scene *scene, string name, bool &is_color);
 
+  bool update_lightgroups(Scene *scene);
+
   /* Update passes so that they contain all passes required for the configured functionality.
    *
    * If `add_sample_count_pass` is true then the SAMPLE_COUNT pass is ensured to be added. */
diff --git a/intern/cycles/scene/light.cpp b/intern/cycles/scene/light.cpp
index 85a7f37994c..5e311d3051f 100644
--- a/intern/cycles/scene/light.cpp
+++ b/intern/cycles/scene/light.cpp
@@ -134,6 +134,8 @@ NODE_DEFINE(Light)
 
   SOCKET_NODE(shader, "Shader", Shader::get_node_type());
 
+  SOCKET_STRING(lightgroup, "Light Group", ustring());
+
   return type;
 }
 
@@ -902,6 +904,14 @@ void LightManager::device_update_points(Device *, DeviceScene *dscene, Scene *sc
     klights[light_index].tfm = light->tfm;
     klights[light_index].itfm = transform_inverse(light->tfm);
 
+    auto it = scene->lightgroups.find(light->lightgroup);
+    if (it != scene->lightgroups.end()) {
+      klights[light_index].lightgroup = it->second;
+    }
+    else {
+      klights[light_index].lightgroup = LIGHTGROUP_NONE;
+    }
+
     light_index++;
   }
 
diff --git a/intern/cycles/scene/light.h b/intern/cycles/scene/light.h
index 25190f6fb63..5b852f210fc 100644
--- a/intern/cycles/scene/light.h
+++ b/intern/cycles/scene/light.h
@@ -71,6 +71,8 @@ class Light : public Node {
   NODE_SOCKET_API(int, max_bounces)
   NODE_SOCKET_API(uint, random_id)
 
+  NODE_SOCKET_API(ustring, lightgroup)
+
   void tag_update(Scene *scene);
 
   /* Check whether the light has contribution the scene. */
diff --git a/intern/cycles/scene/object.cpp b/intern/cycles/scene/object.cpp
index 9b19169880a..55d89fc3673 100644
--- a/intern/cycles/scene/object.cpp
+++ b/intern/cycles/scene/object.cpp
@@ -98,6 +98,8 @@ NODE_DEFINE(Object)
 
   SOCKET_FLOAT(ao_distance, "AO Distance", 0.0f);
 
+  SOCKET_STRING(lightgroup, "Light Group", ustring());
+
   return type;
 }
 
@@ -393,7 +395,8 @@ static float object_volume_density(const Transform &tfm, Geometry *geom)
 
 void ObjectManager::device_update_object_transform(UpdateObjectTransformState *state,
                                                    Object *ob,
-                                                   bool update_all)
+                                                   bool update_all,
+                                                   const Scene *scene)
 {
   KernelObject &kobject = state->objects[ob->index];
   Transform *object_motion_pass = state->object_motion_pass;
@@ -532,6 +535,15 @@ void ObjectManager::device_update_object_transform(UpdateObjectTransformState *s
   if (geom->geometry_type == Geometry::HAIR) {
     state->have_curves = true;
   }
+
+  /* Light group. */
+  auto it = scene->lightgroups.find(ob->lightgroup);
+  if (it != scene->lightgroups.end()) {
+    kobject.lightgroup = it->second;
+  }
+  else {
+    kobject.lightgroup = LIGHTGROUP_NONE;
+  }
 }
 
 void ObjectManager::device_update_prim_offsets(Device *device, DeviceScene *dscene, Scene *scene)
@@ -618,7 +630,7 @@ void ObjectManager::device_update_transforms(DeviceScene *dscene, Scene *scene,
                [&](const blocked_range<size_t> &r) {
                  for (size_t i = r.begin(); i != r.end(); i++) {
                    Object *ob = state.scene->objects[i];
-                   device_update_object_transform(&state, ob, update_all);
+                   device_update_object_transform(&state, ob, update_all, scene);
                  }
                });
 
diff --git a/intern/cycles/scene/object.h b/intern/cycles/scene/object.h
index 561ecd4e7e9..c41f1416180 100644
--- a/intern/cycles/scene/object.h
+++ b/intern/cycles/scene/object.h
@@ -66,6 +66,8 @@ class Object : public Node {
 
   NODE_SOCKET_API(float, ao_distance)
 
+  NODE_SOCKET_API(ustring, lightgroup)
+
   /* Set during device update. */
   bool intersects_volume;
 
@@ -169,7 +171,8 @@ class ObjectManager {
  protected:
   void device_update_object_transform(UpdateObjectTransformState *state,
                                       Object *ob,
-                                      bool update_all);
+                                      bool update_all,
+                                      const Scene *scene);
   void device_update_object_transform_task(UpdateObjectTransformState *state);
   bool device_update_object_transform_pop_work(UpdateObjectTransformState *state,
                                                int *start_index,
diff --git a/intern/cycles/scene/pass.cpp b/intern/cycles/scene/pass.cpp
index 41730cb189d..5f5b19e710d 100644
--- a/intern/cycles/scene/pass.cpp
+++ b/intern/cycles/scene/pass.cpp
@@ -124,6 +124,7 @@ NODE_DEFINE(Pass)
   SOCKET_ENUM(mode, "Mode", *pass_mode_enum, static_cast<int>(PassMode::DENOISED));
   SOCKET_STRING(name, "Name", ustring());
   SOCKET_BOOLEAN(include_albedo, "Include Albedo", false);
+  SOCKET_STRING(lightgroup, "Light Group", ustring());
 
   return type;
 }
@@ -134,7 +135,7 @@ Pass::Pass() : Node(get_node_type()), is_auto_(false)
 
 PassInfo Pass::get_info() const
 {
-  return get_info(type, include_albedo);
+  return get_info(type, include_albedo, !lightgroup.empty());
 }
 
 bool Pass::is_written() const
@@ -142,7 +143,7 @@ bool Pass::is_written() const
   return get_info().is_written;
 }
 
-PassInfo Pass::get_info(const PassType type, const bool include_albedo)
+PassInfo Pass::get_info(const PassType type, const bool include_albedo, const bool is_lightgroup)
 {
   PassInfo pass_info;
 
@@ -157,9 +158,9 @@ PassInfo Pass::get_info(const PassType type, const bool include_albedo)
       pass_info.num_components = 0;
       break;
     case PASS_COMBINED:
-      pass_info.num_components = 4;
+      pass_info.num_components = is_lightgroup ? 3 : 4;
       pass_info.use_exposure = true;
-      pass_info.support_denoise = true;
+      pass_info.support_denoise = !is_lightgroup;
       break;
     case PASS_DEPTH:
       pass_info.num_components = 1;
@@ -369,13 +370,16 @@ const Pass *Pass::find(const vector<Pass *> &passes, const string &name)
   return nullptr;
 }
 
-const Pass *Pass::find(const vector<Pass *> &passes, PassType type, PassMode mode)
+const Pass *Pass::find(const vector<Pass *> &passes,
+                       PassType type,
+                       PassMode mode,
+                       const ustring &lightgroup)
 {
   for (const Pass *pass : passes) {
-    if (pass->get_type() != type || pass->get_mode() != mode) {
+    if (pass->get_type() != type || pass->get_mode() != mode ||
+        pass->get_lightgroup() != lightgroup) {
       continue;
     }
-
     return pass;
   }
 
diff --git a/intern/cycles/scene/pass.h b/intern/cycles/scene/pass.h
index c12df007b5d..e0689eba688 100644
--- a/intern/cycles/scene/pass.h
+++ b/intern/cycles/scene/pass.h
@@ -53,6 +53,7 @@ class Pass : public Node {
   NODE_SOCKET_API(PassMode, mode)
   NODE_SOCKET_API(ustring, name)
   NODE_SOCKET_API(bool, include_albedo)
+  NODE_SOCKET_API(ustring, lightgroup)
 
   Pass();
 
@@ -72,7 +73,9 @@ class Pass : public Node {
   static const NodeEnum *get_type_enum();
   static const NodeEnum *get_mode_enum();
 
-  static PassInfo get_info(PassType type, const bool include_albedo = false);
+  static PassInfo get_info(PassType type,
+                           const bool include_albedo = false,
+                           const bool is_lightgroup = false);
 
   static bool contains(const vector<Pass *> &passes, PassType type);
 
@@ -80,7 +83,8 @@ class Pass : public Node {
   static const Pass *find(const vector<Pass *> &passes, const string &name);
   static const Pass *find(const vector<Pass *> &passes,
                           PassType type,
-                          PassMode mode = PassMode::NOISY);
+                          PassMode mode = PassMode::NOISY,
+                          const ustring &lightgroup = ustring());
 
   /* Returns PASS_UNUSED if there is no corresponding pass. */
   static int get_offset(const vector<Pass *> &passes, const Pass *pass);
diff --git a/intern/cycles/scene/scene.cpp b/intern/cycles/scene/scene.cpp
index 359e2d8e2c3..b6b53004816 100644
--- a/intern/cycles/scene/scene.cpp
+++ b/intern/cycles/scene/scene.cpp
@@ -251,6 +251,11 @@ void Scene::device_update(Device *device_, Progress &progress)
    * - Lookup tables are done a second time to handle film tables
    */
 
+  if (film->update_lightgroups(this)) {
+    light_manager->tag_update(this, ccl::LightManager::LIGHT_MODIFIED);
+    object_manager->tag_update(this, ccl::ObjectManager::OBJECT_MODIFIED);
+  }
+
   progress.set_status("Updating Shaders");
   shader_manager->device_update(device, &dscene, this, progress);
 
diff --git a/intern/cycles/scene/scene.h b/intern/cycles/scene/scene.h
index e1b36899302..9e3e8d61b80 100644
--- a/intern/cycles/scene/scene.h
+++ b/intern/cycles/scene/scene.h
@@ -197,6 +197,9 @@ class Scene : public NodeOwner {
   /* Optional name. Is used for logging and reporting. */
   string name;
 
+  /* Maps from Light group names to their pass ID. */
+  map<ustring, int> lightgroups;
+
   /* data */
   BVH *bvh;
   Camera *camera;