Add Collection Export Centering options

addons/io_scene_gltf2/__init__.py

@@ -638,10 +638,23 @@ class ExportGLTF2_Base(ConvertGLTF2_Base):
     )
 
     # Not starting with "export_", as this is a collection only option
-    at_collection_center: BoolProperty(
-        name="Export at Collection Center",
-        description="Export at Collection center of mass of root objects of the collection",
-        default=False,
+    collection_center_mode: EnumProperty(
+        name="Collection Center",
+        description="Scene origin of exported collection",
+        items=(
+            ('WORLD_ORIGIN', 'World Origin',
+             'Export at world origin as scene origin'),
+            ('CENTER_MASS', 'Center of Mass',
+             'Export at Collection center of mass of root objects of the collection'),
+            ('OBJECT_POSITION', 'Object Position',
+             'Export at object position as scene origin')),
+        default='WORLD_ORIGIN'
+    )
+
+    collection_center_object: StringProperty(
+        name="Center Object",
+        description="Object to use as exported scene origin",
+        default=""
     )
 
     export_extras: BoolProperty(
@@ -1195,7 +1208,9 @@ def execute(self, context):
             export_settings['gltf_active_collection_with_nested'] = False
         export_settings['gltf_active_scene'] = self.use_active_scene
         export_settings['gltf_collection'] = self.collection
-        export_settings['gltf_at_collection_center'] = self.at_collection_center
+        export_settings['gltf_collection_center_mode'] = self.collection_center_mode
+        if self.collection_center_mode == 'OBJECT_POSITION':
+            export_settings['gltf_collection_center_object'] = context.scene.objects.get(self.collection_center_object)
 
         export_settings['gltf_selected'] = self.use_selection
         export_settings['gltf_layers'] = True  # self.export_layers
@@ -1402,7 +1417,7 @@ def draw(self, context):
         is_file_browser = context.space_data.type == 'FILE_BROWSER'
 
         export_main(layout, operator, is_file_browser)
-        export_panel_collection(layout, operator, is_file_browser)
+        export_panel_collection(layout, operator, is_file_browser, context)
         export_panel_include(layout, operator, is_file_browser)
         export_panel_transform(layout, operator)
         export_panel_data(layout, operator)
@@ -1432,14 +1447,16 @@ def export_main(layout, operator, is_file_browser):
         layout.prop(operator, 'will_save_settings')
 
 
-def export_panel_collection(layout, operator, is_file_browser):
+def export_panel_collection(layout, operator, is_file_browser, context):
     if is_file_browser:
         return
 
     header, body = layout.panel("GLTF_export_collection", default_closed=True)
     header.label(text="Collection")
     if body:
-        body.prop(operator, 'at_collection_center')
+        body.prop(operator, 'collection_center_mode')
+        if operator.collection_center_mode == 'OBJECT_POSITION':
+            body.prop_search(operator, 'collection_center_object', context.scene, 'objects')
 
 
 def export_panel_include(layout, operator, is_file_browser):

addons/io_scene_gltf2/blender/exp/gather.py

@@ -23,7 +23,7 @@
 from . import tree as gltf2_blender_gather_tree
 from .animation.sampled.object.keyframes import get_cache_data
 from .animation.animations import gather_animations
-
+from mathutils import Vector
 
 def gather_gltf2(export_settings):
     """
@@ -103,9 +103,18 @@ def __gather_scene(blender_scene, export_settings):
     # We need to calculate the collection center,
     # In order to set the scene center to the collection center
     # Using object center barycenter for now (another option could be to use bounding box center)
-    if export_settings['gltf_collection'] and export_settings['gltf_at_collection_center']:
-        vtree.calculate_collection_center()
-
+    if export_settings['gltf_collection']:
+        match export_settings['gltf_collection_center_mode']:
+            case 'WORLD_ORIGIN':
+                pass
+            case 'CENTER_MASS':
+                vtree.calculate_collection_center_barycenter()
+            case 'OBJECT_POSITION':
+                center_object = export_settings['gltf_collection_center_object']
+                if center_object:
+                    export_settings['gltf_collection_center'] = center_object.matrix_world.translation
+                else:
+                    export_settings['gltf_collection_center'] = Vector((0.0, 0.0, 0.0))
     vtree.variants_reset_to_original()
 
     export_user_extensions('vtree_after_filter_hook', export_settings, vtree)

addons/io_scene_gltf2/blender/exp/nodes.py

@@ -458,14 +458,11 @@ def __init__(self, name):
 
 def __gather_trans_rot_scale(vnode, export_settings):
     if vnode.parent_uuid is None:
-        # No parent, so matrix is world matrix, except if we export a collection
-        if export_settings['gltf_collection'] and export_settings['gltf_at_collection_center']:
+        # No parent, so matrix is world matrix, except if we export a collection        
+        trans, rot, sca = vnode.matrix_world.decompose()
+        if export_settings['gltf_collection'] and export_settings['gltf_collection_center_mode'] != 'WORLD_ORIGIN':
             # If collection, we need to take into account the collection offset
-            trans, rot, sca = vnode.matrix_world.decompose()
             trans -= export_settings['gltf_collection_center']
-        else:
-            # No parent, so matrix is world matrix
-            trans, rot, sca = vnode.matrix_world.decompose()
     else:
         # calculate local matrix
         if export_settings['vtree'].nodes[vnode.parent_uuid].skin is None:

addons/io_scene_gltf2/blender/exp/tree.py

@@ -1046,7 +1046,7 @@ def check_if_we_can_remove_armature(self):
                     "We can't remove armature object because some armatures have multiple root bones.")
                 break
 
-    def calculate_collection_center(self):
+    def calculate_collection_center_barycenter(self):
         # Because we already filtered the tree, we can use all objects
         # to calculate the center of the scene
         # Are taken into account all objects that are direct root in the exported collection