glTF exporter: fix collection offset when rotated or scaled

io_scene_gltf2/__init__.py

@@ -15,7 +15,7 @@
 bl_info = {
     'name': 'glTF 2.0 format',
     'author': 'Julien Duroure, Scurest, Norbert Nopper, Urs Hanselmann, Moritz Becher, Benjamin Schmithüsen, Jim Eckerlein, and many external contributors',
-    "version": (1, 5, 15),
+    "version": (1, 5, 16),
     'blender': (2, 91, 0),
     'location': 'File > Import-Export',
     'description': 'Import-Export as glTF 2.0',

io_scene_gltf2/blender/exp/gltf2_blender_gather_nodes.py

@@ -423,8 +423,17 @@ def __gather_trans_rot_scale(blender_object, export_settings):
     sca = __convert_swizzle_scale(sca, export_settings)
 
     if blender_object.instance_type == 'COLLECTION' and blender_object.instance_collection:
-        trans -= __convert_swizzle_location(
+        offset = -__convert_swizzle_location(
             blender_object.instance_collection.instance_offset, export_settings)
+
+        s = Matrix.Diagonal(sca).to_4x4()
+        r = rot.to_matrix().to_4x4()
+        t = Matrix.Translation(trans).to_4x4()
+        o = Matrix.Translation(offset).to_4x4()
+        m = t @ r @ s @ o
+
+        trans = m.translation
+
     translation, rotation, scale = (None, None, None)
     trans[0], trans[1], trans[2] = gltf2_blender_math.round_if_near(trans[0], 0.0), gltf2_blender_math.round_if_near(trans[1], 0.0), \
                                    gltf2_blender_math.round_if_near(trans[2], 0.0)