glTF importer: fix regression for skinned mesh normals not being renormalized

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, 3, 42),
+    "version": (1, 3, 43),
     'blender': (2, 90, 0),
     'location': 'File > Import-Export',
     'description': 'Import-Export as glTF 2.0',

io_scene_gltf2/blender/imp/gltf2_blender_mesh.py

@@ -540,6 +540,7 @@ def skin_into_bind_pose(gltf, skin_idx, vert_joints, vert_weights, locs, vert_no
     if len(vert_normals) != 0:
         vert_normals[:] = mul_mats_vecs(skinning_mats_3x3, vert_normals)
         # Don't translate normals!
+        normalize_vecs(vert_normals)
 
 
 def mul_mats_vecs(mats, vecs):
@@ -547,6 +548,11 @@ def mul_mats_vecs(mats, vecs):
     return np.matmul(mats, vecs.reshape(len(vecs), 3, 1)).reshape(len(vecs), 3)
 
 
+def normalize_vecs(vectors):
+    norms = np.linalg.norm(vectors, axis=1, keepdims=True)
+    np.divide(vectors, norms, out=vectors, where=norms != 0)
+
+
 def merge_duplicate_verts(vert_locs, vert_normals, vert_joints, vert_weights, sk_vert_locs, loop_vidxs, edge_vidxs):
     # This function attempts to invert the splitting done when exporting to
     # glTF. Welds together verts with the same per-vert data (but possibly