save normals from Meshes, Pointclouds to PLY

Summary: Save existing vertex normals when a mesh is saved to PLY, and existing normals when a point cloud is saved to PLY.

Reviewed By: theschnitz

Differential Revision: D27765257

fbshipit-source-id: fa0aae4c0f100f7e5eb742f48fc3dfc87435deba

pytorch3d/io/ply_io.py

@@ -1238,10 +1238,14 @@ def save(
         if not endswith(path, self.known_suffixes):
             return False
 
-        # TODO: normals are not saved. We only want to save them if they already exist.
         verts = data.verts_list()[0]
         faces = data.faces_list()[0]
 
+        if data.has_verts_normals():
+            verts_normals = data.verts_normals_list()[0]
+        else:
+            verts_normals = None
+
         if isinstance(data.textures, TexturesVertex):
             mesh_verts_colors = data.textures.verts_features_list()[0]
             n_colors = mesh_verts_colors.shape[1]
@@ -1261,7 +1265,7 @@ def save(
                 verts=verts,
                 faces=faces,
                 verts_colors=verts_colors,
-                verts_normals=None,
+                verts_normals=verts_normals,
                 ascii=binary is False,
                 decimal_places=decimal_places,
             )
@@ -1304,13 +1308,14 @@ def save(
 
         points = data.points_list()[0]
         features = data.features_packed()
+        normals = data.normals_packed()
 
         with _open_file(path, path_manager, "wb") as f:
             _save_ply(
                 f=f,
                 verts=points,
                 verts_colors=features,
-                verts_normals=None,
+                verts_normals=normals,
                 faces=None,
                 ascii=binary is False,
                 decimal_places=decimal_places,