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, 10 insertions, 3 deletions

diff --git a/intern/cycles/kernel/types.h b/intern/cycles/kernel/types.h
index 00b5b007e11..9d9daaa0dda 100644
--- a/intern/cycles/kernel/types.h
+++ b/intern/cycles/kernel/types.h
@@ -46,6 +46,7 @@ CCL_NAMESPACE_BEGIN
 #define LAMP_NONE (~0)
 #define ID_NONE (0.0f)
 #define PASS_UNUSED (~0)
+#define LIGHTGROUP_NONE (~0)
 
 #define INTEGRATOR_SHADOW_ISECT_SIZE_CPU 1024U
 #define INTEGRATOR_SHADOW_ISECT_SIZE_GPU 4U
@@ -1108,6 +1109,7 @@ typedef struct KernelFilm {
 
   int pass_aov_color;
   int pass_aov_value;
+  int pass_lightgroup;
 
   /* XYZ to rendering color space transform. float4 instead of float3 to
    * ensure consistent padding/alignment across devices. */
@@ -1192,8 +1194,10 @@ typedef struct KernelBackground {
 
   int use_mis;
 
+  int lightgroup;
+
   /* Padding */
-  int pad1, pad2, pad3;
+  int pad1, pad2;
 } KernelBackground;
 static_assert_align(KernelBackground, 16);
 
@@ -1372,9 +1376,12 @@ typedef struct KernelObject {
 
   float ao_distance;
 
+  int lightgroup;
+
   uint visibility;
   int primitive_type;
-  int pad[2];
+
+  int pad1;
 } KernelObject;
 static_assert_align(KernelObject, 16);
 
@@ -1427,7 +1434,7 @@ typedef struct KernelLight {
   float random;
   float strength[3];
   int use_caustics;
-  float pad1;
+  int lightgroup;
   Transform tfm;
   Transform itfm;
   union {