Allow `NodeTree`s to be reused in the `pre_export` phase.

Logic trees can be shared, so it is conceivable that a logic tree might
be pre-exported more than once. They can already be created by artists
and referenced from multiple Advanced Logic modifiers, so this is good
for consistency.

korman/exporter/convert.py

@@ -510,8 +510,12 @@ class Exporter:
 
         @handle_temporary.register(bpy.types.NodeTree)
         def _(temporary, parent):
+            # NodeTrees are reuseable, so make sure we haven't already encountered it.
+            if not temporary.name in self.want_node_trees:
                 self.exit_stack.enter_context(TemporaryObject(temporary, bpy.data.node_groups.remove))
                 log_msg(f"'{parent.name}' generated NodeTree '{temporary.name}'")
+            else:
+                log_msg(f"'{parent.name}' reused NodeTree '{temporary.name}'")
             if temporary.bl_idname == "PlasmaNodeTree":
                 parent_so = self.mgr.find_create_object(plSceneObject, bl=parent)
                 self.want_node_trees[temporary.name].add((parent, parent_so))

korman/properties/modifiers/base.py

@@ -181,19 +181,23 @@ class PlasmaModifierProperties(bpy.types.PropertyGroup):
 
 class PlasmaModifierLogicWiz:
     def convert_logic(self, bo, **kwargs):
-        """Creates, converts, and returns an unmanaged NodeTree for this logic wizard. If the wizard
+        """Attempts to look up an already existing logic tree matching the name provided and returns
-           fails during conversion, the temporary tree is deleted for you. However, on success, you
+           it, if found. If not, creates, converts, and returns an unmanaged NodeTree for this wizard.
-           are responsible for removing the tree from Blender, if applicable."""
+           If the wizard fails during conversion, the temporary tree is deleted for you. However, on
+           success, you are responsible for removing the tree from Blender, if applicable."""
         name = kwargs.pop("name", self.key_name)
         assert not "tree" in kwargs
-        tree = bpy.data.node_groups.new(name, "PlasmaNodeTree")
+
+        node_groups = bpy.data.node_groups
+        tree = node_groups.get(name)
+        if tree is None:
+            tree = node_groups.new(name, "PlasmaNodeTree")
             kwargs["tree"] = tree
             try:
                 self.logicwiz(bo, **kwargs)
             except:
                 bpy.data.node_groups.remove(tree)
                 raise
-        else:
         return tree
 
     def _create_python_file_node(self, tree, filename: str, attributes: Dict[str, Any]) -> bpy.types.Node: