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, 11 insertions, 7 deletions

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;
   }