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, 20 insertions, 0 deletions

diff --git a/intern/cycles/kernel/geom/object.h b/intern/cycles/kernel/geom/object.h
index 86c57c84b47..3faab7fa905 100644
--- a/intern/cycles/kernel/geom/object.h
+++ b/intern/cycles/kernel/geom/object.h
@@ -283,6 +283,26 @@ ccl_device_inline float object_pass_id(KernelGlobals kg, int object)
   return kernel_tex_fetch(__objects, object).pass_id;
 }
 
+/* Lightgroup of lamp */
+
+ccl_device_inline int lamp_lightgroup(KernelGlobals kg, int lamp)
+{
+  if (lamp == LAMP_NONE)
+    return LIGHTGROUP_NONE;
+
+  return kernel_tex_fetch(__lights, lamp).lightgroup;
+}
+
+/* Lightgroup of object */
+
+ccl_device_inline int object_lightgroup(KernelGlobals kg, int object)
+{
+  if (object == OBJECT_NONE)
+    return LIGHTGROUP_NONE;
+
+  return kernel_tex_fetch(__objects, object).lightgroup;
+}
+
 /* Per lamp random number for shader variation */
 
 ccl_device_inline float lamp_random_number(KernelGlobals kg, int lamp)