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, 28 insertions, 0 deletions

diff --git a/release/scripts/startup/bl_ui/properties_view_layer.py b/release/scripts/startup/bl_ui/properties_view_layer.py
index 4dee7b73faf..83e797583ad 100644
--- a/release/scripts/startup/bl_ui/properties_view_layer.py
+++ b/release/scripts/startup/bl_ui/properties_view_layer.py
@@ -187,6 +187,33 @@ class VIEWLAYER_PT_layer_passes_cryptomatte(ViewLayerCryptomattePanel, Panel):
     COMPAT_ENGINES = {'BLENDER_EEVEE'}
 
 
+class ViewLayerLightgroupsPanel(ViewLayerButtonsPanel, Panel):
+    bl_label = "Light Groups"
+
+    def draw(self, context):
+        layout = self.layout
+
+        layout.use_property_split = True
+        layout.use_property_decorate = False
+
+        view_layer = context.view_layer
+
+        row = layout.row()
+        col = row.column()
+        col.template_list("UI_UL_list", "lightgroups", view_layer,
+                          "lightgroups", view_layer, "active_lightgroup_index", rows=2)
+
+        col = row.column()
+        sub = col.column(align=True)
+        sub.operator("scene.view_layer_add_lightgroup", icon='ADD', text="")
+        sub.operator("scene.view_layer_remove_lightgroup", icon='REMOVE', text="")
+
+
+class VIEWLAYER_PT_layer_passes_lightgroups(ViewLayerLightgroupsPanel):
+    bl_parent_id = "VIEWLAYER_PT_layer_passes"
+    COMPAT_ENGINES = {'CYCLES'}
+
+
 classes = (
     VIEWLAYER_PT_layer,
     VIEWLAYER_PT_layer_passes,
@@ -195,6 +222,7 @@ classes = (
     VIEWLAYER_PT_eevee_layer_passes_effects,
     VIEWLAYER_PT_layer_passes_cryptomatte,
     VIEWLAYER_PT_layer_passes_aov,
+    VIEWLAYER_PT_layer_passes_lightgroups,
     VIEWLAYER_UL_aov,
 )