Nodes: refactor node tree update handling

Goals of this refactor:
* More unified approach to updating everything that needs to be updated
  after a change in a node tree.
* The updates should happen in the correct order and quadratic or worse
  algorithms should be avoided.
* Improve detection of changes to the output to avoid tagging the depsgraph
  when it's not necessary.
* Move towards a more declarative style of defining nodes by having a
  more centralized update procedure.

The refactor consists of two main parts:
* Node tree tagging and update refactor.
  * Generally, when changes are done to a node tree, it is tagged dirty
    until a global update function is called that updates everything in
    the correct order.
  * The tagging is more fine-grained compared to before, to allow for more
    precise depsgraph update tagging.
* Depsgraph changes.
  * The shading specific depsgraph node for node trees as been removed.
  * Instead, there is a new `NTREE_OUTPUT` depsgrap node, which is only
    tagged when the output of the node tree changed (e.g. the Group Output
    or Material Output node).
  * The copy-on-write relation from node trees to the data block they are
    embedded in is now non-flushing. This avoids e.g. triggering a material
    update after the shader node tree changed in unrelated ways. Instead
    the material has a flushing relation to the new `NTREE_OUTPUT` node now.
  * The depsgraph no longer reports data block changes through to cycles
    through `Depsgraph.updates` when only the node tree changed in ways
    that do not affect the output.

Avoiding unnecessary updates seems to work well for geometry nodes and cycles.
The situation is a bit worse when there are drivers on the node tree, but that
could potentially be improved separately in the future.

Avoiding updates in eevee and the compositor is more tricky, but also less urgent.
* Eevee updates are triggered by calling `DRW_notify_view_update` in
  `ED_render_view3d_update` indirectly from `DEG_editors_update`.
* Compositor updates are triggered by `ED_node_composite_job` in `node_area_refresh`.
  This is triggered by calling `ED_area_tag_refresh` in `node_area_listener`.

Removing updates always has the risk of breaking some dependency that no
one was aware of. It's not unlikely that this will happen here as well. Adding
back missing updates should be quite a bit easier than getting rid of
unnecessary updates though.

Differential Revision: https://developer.blender.org/D13246

6 files changed, 15 insertions, 0 deletions

diff --git a/source/blender/depsgraph/intern/node/deg_node.cc b/source/blender/depsgraph/intern/node/deg_node.cc
index 8bc03d8b736..075bfd35ec1 100644
--- a/source/blender/depsgraph/intern/node/deg_node.cc
+++ b/source/blender/depsgraph/intern/node/deg_node.cc
@@ -116,6 +116,8 @@ const char *nodeTypeAsString(NodeType type)
       return "VISIBILITY";
     case NodeType::SIMULATION:
       return "SIMULATION";
+    case NodeType::NTREE_OUTPUT:
+      return "NTREE_OUTPUT";
 
     /* Total number of meaningful node types. */
     case NodeType::NUM_TYPES:
@@ -174,6 +176,7 @@ eDepsSceneComponentType nodeTypeToSceneComponent(NodeType type)
     case NodeType::CACHE:
     case NodeType::PROXY:
     case NodeType::SIMULATION:
+    case NodeType::NTREE_OUTPUT:
       return DEG_SCENE_COMP_PARAMETERS;
 
     case NodeType::VISIBILITY:
@@ -251,6 +254,7 @@ eDepsObjectComponentType nodeTypeToObjectComponent(NodeType type)
     case NodeType::DUPLI:
     case NodeType::SYNCHRONIZATION:
     case NodeType::SIMULATION:
+    case NodeType::NTREE_OUTPUT:
     case NodeType::UNDEFINED:
     case NodeType::NUM_TYPES:
       return DEG_OB_COMP_PARAMETERS;
diff --git a/source/blender/depsgraph/intern/node/deg_node.h b/source/blender/depsgraph/intern/node/deg_node.h
index 7e093ab8765..ef58a35afb2 100644
--- a/source/blender/depsgraph/intern/node/deg_node.h
+++ b/source/blender/depsgraph/intern/node/deg_node.h
@@ -147,6 +147,8 @@ enum class NodeType {
   SYNCHRONIZATION,
   /* Simulation component. */
   SIMULATION,
+  /* Node tree output component. */
+  NTREE_OUTPUT,
 
   /* Total number of meaningful node types. */
   NUM_TYPES,
diff --git a/source/blender/depsgraph/intern/node/deg_node_component.cc b/source/blender/depsgraph/intern/node/deg_node_component.cc
index b716877902c..4c430904e44 100644
--- a/source/blender/depsgraph/intern/node/deg_node_component.cc
+++ b/source/blender/depsgraph/intern/node/deg_node_component.cc
@@ -351,6 +351,7 @@ DEG_COMPONENT_NODE_DEFINE(Armature, ARMATURE, 0);
 DEG_COMPONENT_NODE_DEFINE(GenericDatablock, GENERIC_DATABLOCK, 0);
 DEG_COMPONENT_NODE_DEFINE(Visibility, VISIBILITY, 0);
 DEG_COMPONENT_NODE_DEFINE(Simulation, SIMULATION, 0);
+DEG_COMPONENT_NODE_DEFINE(NTreeOutput, NTREE_OUTPUT, ID_RECALC_NTREE_OUTPUT);
 
 /** \} */
 
@@ -385,6 +386,7 @@ void deg_register_component_depsnodes()
   register_node_typeinfo(&DNTI_GENERIC_DATABLOCK);
   register_node_typeinfo(&DNTI_VISIBILITY);
   register_node_typeinfo(&DNTI_SIMULATION);
+  register_node_typeinfo(&DNTI_NTREE_OUTPUT);
 }
 
 /** \} */
diff --git a/source/blender/depsgraph/intern/node/deg_node_component.h b/source/blender/depsgraph/intern/node/deg_node_component.h
index 9f108af8012..8fd28dfc497 100644
--- a/source/blender/depsgraph/intern/node/deg_node_component.h
+++ b/source/blender/depsgraph/intern/node/deg_node_component.h
@@ -222,6 +222,7 @@ DEG_COMPONENT_NODE_DECLARE_GENERIC(Armature);
 DEG_COMPONENT_NODE_DECLARE_GENERIC(GenericDatablock);
 DEG_COMPONENT_NODE_DECLARE_NO_COW(Visibility);
 DEG_COMPONENT_NODE_DECLARE_GENERIC(Simulation);
+DEG_COMPONENT_NODE_DECLARE_GENERIC(NTreeOutput);
 
 /* Bone Component */
 struct BoneComponentNode : public ComponentNode {
diff --git a/source/blender/depsgraph/intern/node/deg_node_operation.cc b/source/blender/depsgraph/intern/node/deg_node_operation.cc
index eaae5d2d5dc..2d0d6854851 100644
--- a/source/blender/depsgraph/intern/node/deg_node_operation.cc
+++ b/source/blender/depsgraph/intern/node/deg_node_operation.cc
@@ -182,6 +182,9 @@ const char *operationCodeAsString(OperationCode opcode)
       return "LIGHT_UPDATE";
     case OperationCode::WORLD_UPDATE:
       return "WORLD_UPDATE";
+    /* Node Tree. */
+    case OperationCode::NTREE_OUTPUT:
+      return "NTREE_OUTPUT";
     /* Movie clip. */
     case OperationCode::MOVIECLIP_EVAL:
       return "MOVIECLIP_EVAL";
diff --git a/source/blender/depsgraph/intern/node/deg_node_operation.h b/source/blender/depsgraph/intern/node/deg_node_operation.h
index 31cbb9702ba..4abdc014946 100644
--- a/source/blender/depsgraph/intern/node/deg_node_operation.h
+++ b/source/blender/depsgraph/intern/node/deg_node_operation.h
@@ -177,6 +177,9 @@ enum class OperationCode {
   LIGHT_UPDATE,
   WORLD_UPDATE,
 
+  /* Node Tree. ----------------------------------------------------------- */
+  NTREE_OUTPUT,
+
   /* Batch caches. -------------------------------------------------------- */
   GEOMETRY_SELECT_UPDATE,