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

2 files changed, 12 insertions, 6 deletions

diff --git a/intern/cycles/integrator/pass_accessor.cpp b/intern/cycles/integrator/pass_accessor.cpp
index 0be3cf6860b..05318b7545b 100644
--- a/intern/cycles/integrator/pass_accessor.cpp
+++ b/intern/cycles/integrator/pass_accessor.cpp
@@ -18,7 +18,11 @@ CCL_NAMESPACE_BEGIN
  */
 
 PassAccessor::PassAccessInfo::PassAccessInfo(const BufferPass &pass)
-    : type(pass.type), mode(pass.mode), include_albedo(pass.include_albedo), offset(pass.offset)
+    : type(pass.type),
+      mode(pass.mode),
+      include_albedo(pass.include_albedo),
+      is_lightgroup(!pass.lightgroup.empty()),
+      offset(pass.offset)
 {
 }
 
@@ -127,7 +131,8 @@ bool PassAccessor::get_render_tile_pixels(const RenderBuffers *render_buffers,
 
   const PassType type = pass_access_info_.type;
   const PassMode mode = pass_access_info_.mode;
-  const PassInfo pass_info = Pass::get_info(type, pass_access_info_.include_albedo);
+  const PassInfo pass_info = Pass::get_info(
+      type, pass_access_info_.include_albedo, pass_access_info_.is_lightgroup);
   int num_written_components = pass_info.num_components;
 
   if (pass_info.num_components == 1) {
@@ -215,8 +220,8 @@ void PassAccessor::init_kernel_film_convert(KernelFilmConvert *kfilm_convert,
                                             const Destination &destination) const
 {
   const PassMode mode = pass_access_info_.mode;
-  const PassInfo &pass_info = Pass::get_info(pass_access_info_.type,
-                                             pass_access_info_.include_albedo);
+  const PassInfo &pass_info = Pass::get_info(
+      pass_access_info_.type, pass_access_info_.include_albedo, pass_access_info_.is_lightgroup);
 
   kfilm_convert->pass_offset = pass_access_info_.offset;
   kfilm_convert->pass_stride = buffer_params.pass_stride;
@@ -279,8 +284,8 @@ bool PassAccessor::set_render_tile_pixels(RenderBuffers *render_buffers, const S
     return false;
   }
 
-  const PassInfo pass_info = Pass::get_info(pass_access_info_.type,
-                                            pass_access_info_.include_albedo);
+  const PassInfo pass_info = Pass::get_info(
+      pass_access_info_.type, pass_access_info_.include_albedo, pass_access_info_.is_lightgroup);
 
   const BufferParams &buffer_params = render_buffers->params;
 
diff --git a/intern/cycles/integrator/pass_accessor.h b/intern/cycles/integrator/pass_accessor.h
index 7de1d03961b..683d3a35272 100644
--- a/intern/cycles/integrator/pass_accessor.h
+++ b/intern/cycles/integrator/pass_accessor.h
@@ -28,6 +28,7 @@ class PassAccessor {
     PassType type = PASS_NONE;
     PassMode mode = PassMode::NOISY;
     bool include_albedo = false;
+    bool is_lightgroup = false;
     int offset = -1;
 
     /* For the shadow catcher matte pass: whether to approximate shadow catcher pass into its