Fix T76897: Lamp Power Not Updating from Driver

Lamps were not tagged with `ID_RECALC_SHADING` when they were updated
from drivers. As a result, Cycles considered the lamp as unchanged. This
is resolved by having a (seemingly non-functional) callback in a new
`LIGHT_UPDATE` depsgraph node.

This patch unconditionally adds the `LIGHT_UPDATE` node + the relation
from the lamp's PARAMETERS node.

Differential Revision: https://developer.blender.org/D7822

Reviewed by: brecht

4 files changed, 17 insertions, 1 deletions

diff --git a/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc b/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
index 0e84494b2b7..6f4333ee81d 100644
--- a/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
+++ b/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
@@ -83,6 +83,7 @@ extern "C" {
 #include "BKE_key.h"
 #include "BKE_lattice.h"
 #include "BKE_layer.h"
+#include "BKE_light.h"
 #include "BKE_mask.h"
 #include "BKE_material.h"
 #include "BKE_mball.h"
@@ -1452,6 +1453,12 @@ void DepsgraphNodeBuilder::build_light(Light *lamp)
   build_parameters(&lamp->id);
   /* light's nodetree */
   build_nodetree(lamp->nodetree);
+
+  Light *lamp_cow = get_cow_datablock(lamp);
+  add_operation_node(&lamp->id,
+                     NodeType::SHADING,
+                     OperationCode::LIGHT_UPDATE,
+                     function_bind(BKE_light_eval, _1, lamp_cow));
 }
 
 void DepsgraphNodeBuilder::build_nodetree(bNodeTree *ntree)
diff --git a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
index 9bad796c541..9cd150fb8df 100644
--- a/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
+++ b/source/blender/depsgraph/intern/builder/deg_builder_relations.cc
@@ -2246,14 +2246,20 @@ void DepsgraphRelationBuilder::build_light(Light *lamp)
   build_idproperties(lamp->id.properties);
   build_animdata(&lamp->id);
   build_parameters(&lamp->id);
+
+  ComponentKey lamp_parameters_key(&lamp->id, NodeType::PARAMETERS);
+
   /* light's nodetree */
   if (lamp->nodetree != nullptr) {
     build_nodetree(lamp->nodetree);
-    ComponentKey lamp_parameters_key(&lamp->id, NodeType::PARAMETERS);
     ComponentKey nodetree_key(&lamp->nodetree->id, NodeType::SHADING);
     add_relation(nodetree_key, lamp_parameters_key, "NTree->Light Parameters");
     build_nested_nodetree(&lamp->id, lamp->nodetree);
   }
+
+  /* For allowing drivers on lamp properties. */
+  ComponentKey shading_key(&lamp->id, NodeType::SHADING);
+  add_relation(lamp_parameters_key, shading_key, "Light Shading Parameters");
 }
 
 void DepsgraphRelationBuilder::build_nodetree(bNodeTree *ntree)
diff --git a/source/blender/depsgraph/intern/node/deg_node_operation.cc b/source/blender/depsgraph/intern/node/deg_node_operation.cc
index 1e03d51f557..1a73d81d053 100644
--- a/source/blender/depsgraph/intern/node/deg_node_operation.cc
+++ b/source/blender/depsgraph/intern/node/deg_node_operation.cc
@@ -173,6 +173,8 @@ const char *operationCodeAsString(OperationCode opcode)
       return "SHADING";
     case OperationCode::MATERIAL_UPDATE:
       return "MATERIAL_UPDATE";
+    case OperationCode::LIGHT_UPDATE:
+      return "LIGHT_UPDATE";
     case OperationCode::WORLD_UPDATE:
       return "WORLD_UPDATE";
     /* Movie clip. */
diff --git a/source/blender/depsgraph/intern/node/deg_node_operation.h b/source/blender/depsgraph/intern/node/deg_node_operation.h
index 2faf139ec93..214f5e8b094 100644
--- a/source/blender/depsgraph/intern/node/deg_node_operation.h
+++ b/source/blender/depsgraph/intern/node/deg_node_operation.h
@@ -170,6 +170,7 @@ enum class OperationCode {
   /* Shading. ------------------------------------------------------------- */
   SHADING,
   MATERIAL_UPDATE,
+  LIGHT_UPDATE,
   WORLD_UPDATE,
 
   /* Batch caches. -------------------------------------------------------- */