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

1 files changed, 2 insertions, 9 deletions

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index a7ed16f5086..500d8e2e0ac 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -501,16 +501,13 @@ void ntreeFreeLocalTree(struct bNodeTree *ntree);
 struct bNode *ntreeFindType(const struct bNodeTree *ntree, int type);
 bool ntreeHasType(const struct bNodeTree *ntree, int type);
 bool ntreeHasTree(const struct bNodeTree *ntree, const struct bNodeTree *lookup);
-void ntreeUpdateTree(struct Main *main, struct bNodeTree *ntree);
 void ntreeUpdateAllNew(struct Main *main);
-/**
- * \param tree_update_flag: #eNodeTreeUpdate enum.
- */
-void ntreeUpdateAllUsers(struct Main *main, struct ID *id, int tree_update_flag);
+void ntreeUpdateAllUsers(struct Main *main, struct ID *id);
 
 void ntreeGetDependencyList(struct bNodeTree *ntree,
                             struct bNode ***r_deplist,
                             int *r_deplist_len);
+void ntreeUpdateNodeLevels(struct bNodeTree *ntree);
 
 /**
  * XXX: old trees handle output flags automatically based on special output
@@ -833,10 +830,6 @@ void nodeClearActive(struct bNodeTree *ntree);
 void nodeClearActiveID(struct bNodeTree *ntree, short idtype);
 struct bNode *nodeGetActiveTexture(struct bNodeTree *ntree);
 
-void nodeUpdate(struct bNodeTree *ntree, struct bNode *node);
-bool nodeUpdateID(struct bNodeTree *ntree, struct ID *id);
-void nodeUpdateInternalLinks(struct bNodeTree *ntree, struct bNode *node);
-
 int nodeSocketIsHidden(const struct bNodeSocket *sock);
 void ntreeTagUsedSockets(struct bNodeTree *ntree);
 void nodeSetSocketAvailability(struct bNodeTree *ntree,