fix(loader): Preserves collection hierarchies when importing them fro…

…m blend file

blenderproc/python/loader/BlendLoader.py

@@ -65,8 +65,10 @@ def load_blend(path: str, obj_types: Optional[Union[List[str], str]] = None, nam
  for obj in getattr(data_to, data_block):
  # Check that the object type is desired
  if obj.type.lower() in obj_types:
- # Link objects to the scene
- bpy.context.collection.objects.link(obj)
+ # If object does not yet belong to a imported collection
+ if len(obj.users_collection) == 0:
+ # Link objects to the scene collection
+ bpy.context.collection.objects.link(obj)
  loaded_objects.append(convert_to_entity_subclass(obj))
 
  # If a camera was imported
@@ -89,6 +91,17 @@ def load_blend(path: str, obj_types: Optional[Union[List[str], str]] = None, nam
  # Remove object again if its type is not desired
  bpy.data.objects.remove(obj, do_unlink=True)
  print("Selected " + str(len(loaded_objects)) + " of the loaded objects by type")
+ elif data_block == "collections":
+ # Build up mapping of possible parent-child collection relationships
+ collection_parents = {}
+ for collection in getattr(data_to, data_block):
+ for child in collection.children:
+ collection_parents[child.name] = collection
+
+ # Add all collections to scene collection which do not yet belong to any other collection
+ for collection in getattr(data_to, data_block):
+ if collection.name not in collection_parents:
+ bpy.context.collection.children.link(collection)
  else:
  loaded_objects.extend(getattr(data_to, data_block))