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, 4 insertions, 2 deletions

diff --git a/intern/cycles/session/buffers.cpp b/intern/cycles/session/buffers.cpp
index f9893ed1e1c..3bbc205ca7a 100644
--- a/intern/cycles/session/buffers.cpp
+++ b/intern/cycles/session/buffers.cpp
@@ -49,6 +49,7 @@ NODE_DEFINE(BufferPass)
   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());
 
   SOCKET_INT(offset, "Offset", -1);
 
@@ -64,13 +65,14 @@ BufferPass::BufferPass(const Pass *scene_pass)
       type(scene_pass->get_type()),
       mode(scene_pass->get_mode()),
       name(scene_pass->get_name()),
-      include_albedo(scene_pass->get_include_albedo())
+      include_albedo(scene_pass->get_include_albedo()),
+      lightgroup(scene_pass->get_lightgroup())
 {
 }
 
 PassInfo BufferPass::get_info() const
 {
-  return Pass::get_info(type, include_albedo);
+  return Pass::get_info(type, include_albedo, !lightgroup.empty());
 }
 
 /* --------------------------------------------------------------------