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, 19 insertions, 0 deletions

diff --git a/source/blender/makesdna/DNA_layer_types.h b/source/blender/makesdna/DNA_layer_types.h
index 7b6fe3773f8..d5f7e25bb80 100644
--- a/source/blender/makesdna/DNA_layer_types.h
+++ b/source/blender/makesdna/DNA_layer_types.h
@@ -124,6 +124,21 @@ typedef struct ViewLayerAOV {
    * matches `eViewLayerAOVType` */
   int type;
 } ViewLayerAOV;
+
+/* Lightgroup Renderpass definition. */
+typedef struct ViewLayerLightgroup {
+  struct ViewLayerLightgroup *next, *prev;
+
+  /* Name of the Lightgroup */
+  char name[64];
+} ViewLayerLightgroup;
+
+/* Lightgroup membership information. */
+typedef struct LightgroupMembership {
+  /* Name of the Lightgroup */
+  char name[64];
+} LightgroupMembership;
+
 typedef struct ViewLayer {
   struct ViewLayer *next, *prev;
   /** MAX_NAME. */
@@ -164,6 +179,10 @@ typedef struct ViewLayer {
   ListBase aovs;
   ViewLayerAOV *active_aov;
 
+  /* List containing the 'ViewLayerLightgroup`s */
+  ListBase lightgroups;
+  ViewLayerLightgroup *active_lightgroup;
+
   /* Runtime data */
   /** ViewLayerEngineData. */
   ListBase drawdata;