diff --git a/src/_impl/vertex_data.py b/src/_impl/vertex_data.py
index c6ebfc9..426b41c 100644
--- a/src/_impl/vertex_data.py
+++ b/src/_impl/vertex_data.py
@@ -49,7 +49,7 @@ def __init__(self, primitive):
                 self._optional_attributes.add(attr.sl_name)
     
     def get_id(self) -> str:
-        return '_'.join(self._optional_attributes)
+        return '_'.join(sorted(self._optional_attributes))
 
     def _generate_vs_in(self, sh):
         with sh.vs_input('VsIn') as VsIn:
diff --git a/src/generate.py b/src/generate.py
index 34ad22b..f0f0412 100644
--- a/src/generate.py
+++ b/src/generate.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import argparse, functools, io, json, os, sys
+import argparse, functools, io, json, os, shutil, sys
 from pathlib import Path
 import multiprocessing as mp
 from typing import List, NamedTuple
@@ -121,7 +121,10 @@ def generate(
     if not gltf_dir_path.is_dir():
         raise NotADirectoryError(gltf_dir_path)
 
-    os.makedirs(out_dir_path, exist_ok = True)
+    # Delete the output directory in order to delete any stale files
+    if os.path.exists(out_dir_path):
+        shutil.rmtree(out_dir_path)
+    os.makedirs(out_dir_path)
 
     shader_dict = dict()
 
diff --git a/tests/ref b/tests/ref
index c2227ae..663c298 160000
--- a/tests/ref
+++ b/tests/ref
@@ -1 +1 @@
-Subproject commit c2227ae720c1e050feb787b38e3f76b12ff83eed
+Subproject commit 663c298311e29a4dafad24f034dca8ede9152140