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, 2 insertions, 0 deletions

diff --git a/intern/cycles/blender/shader.cpp b/intern/cycles/blender/shader.cpp
index 224cbea85f3..d3527567b96 100644
--- a/intern/cycles/blender/shader.cpp
+++ b/intern/cycles/blender/shader.cpp
@@ -1532,6 +1532,8 @@ void BlenderSync::sync_world(BL::Depsgraph &b_depsgraph, BL::SpaceView3D &b_v3d,
   background->set_use_shader(view_layer.use_background_shader ||
                              viewport_parameters.use_custom_shader());
 
+  background->set_lightgroup(ustring(b_world ? b_world.lightgroup() : ""));
+
   background->tag_update(scene);
 }