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, 6 insertions, 2 deletions

diff --git a/intern/cycles/scene/pass.h b/intern/cycles/scene/pass.h
index c12df007b5d..e0689eba688 100644
--- a/intern/cycles/scene/pass.h
+++ b/intern/cycles/scene/pass.h
@@ -53,6 +53,7 @@ class Pass : public Node {
   NODE_SOCKET_API(PassMode, mode)
   NODE_SOCKET_API(ustring, name)
   NODE_SOCKET_API(bool, include_albedo)
+  NODE_SOCKET_API(ustring, lightgroup)
 
   Pass();
 
@@ -72,7 +73,9 @@ class Pass : public Node {
   static const NodeEnum *get_type_enum();
   static const NodeEnum *get_mode_enum();
 
-  static PassInfo get_info(PassType type, const bool include_albedo = false);
+  static PassInfo get_info(PassType type,
+                           const bool include_albedo = false,
+                           const bool is_lightgroup = false);
 
   static bool contains(const vector<Pass *> &passes, PassType type);
 
@@ -80,7 +83,8 @@ class Pass : public Node {
   static const Pass *find(const vector<Pass *> &passes, const string &name);
   static const Pass *find(const vector<Pass *> &passes,
                           PassType type,
-                          PassMode mode = PassMode::NOISY);
+                          PassMode mode = PassMode::NOISY,
+                          const ustring &lightgroup = ustring());
 
   /* Returns PASS_UNUSED if there is no corresponding pass. */
   static int get_offset(const vector<Pass *> &passes, const Pass *pass);