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, 21 insertions, 1 deletions

diff --git a/source/blender/editors/include/ED_node.h b/source/blender/editors/include/ED_node.h
index 5bac452c7c9..db1ba80dd3c 100644
--- a/source/blender/editors/include/ED_node.h
+++ b/source/blender/editors/include/ED_node.h
@@ -100,7 +100,7 @@ void ED_node_socket_draw(struct bNodeSocket *sock,
                          float scale);
 void ED_node_tree_update(const struct bContext *C);
 void ED_node_tag_update_id(struct ID *id);
-void ED_node_tag_update_nodetree(struct Main *bmain, struct bNodeTree *ntree, struct bNode *node);
+
 /**
  * Sort nodes by selection: unselected nodes first, then selected,
  * then the active node at the very end. Relative order is kept intact.
@@ -152,6 +152,26 @@ void ED_node_set_active(struct Main *bmain,
                         bool *r_active_texture_changed);
 
 /**
+ * Call after one or more node trees have been changed and tagged accordingly.
+ *
+ * This function will make sure that other parts of Blender update accordingly. For example, if the
+ * node group interface changed, parent node groups have to be updated as well.
+ *
+ * Additionally, this will send notifiers and tag the depsgraph based on the changes. Depsgraph
+ * relation updates have to be triggered by the caller.
+ *
+ * \param C: Context if available. This can be null.
+ * \param bmain: Main whose data-blocks should be updated based on the changes.
+ * \param ntree: Under some circumstances the caller knows that only one node tree has
+ *   changed since the last update. In this case the function may be able to skip scanning #bmain
+ *   for other things that have to be changed. It may still scan #bmain if the interface of the
+ *   node tree has changed.
+ */
+void ED_node_tree_propagate_change(const struct bContext *C,
+                                   struct Main *bmain,
+                                   struct bNodeTree *ntree);
+
+/**
  * \param scene_owner: is the owner of the job,
  * we don't use it for anything else currently so could also be a void pointer,
  * but for now keep it an 'Scene' for consistency.