Fix saving / loading empty PLY meshes

Summary:
Similar to D20392526, PLY files without vertices or faces should be allowed:
- a PLY with only vertices can represent a point cloud
- a PLY without any vertex or face is just empty
- a PLY with faces referencing inexistent vertices has invalid data

Reviewed By: gkioxari

Differential Revision: D20400330

fbshipit-source-id: 35a5f072603fd221f382c7faad5f37c3e0b49bb1

tests/test_ply_io.py

@@ -139,6 +139,90 @@ class TestMeshPlyIO(TestCaseMixin, unittest.TestCase):
             ]
             self.assertClose(faces, torch.LongTensor(faces_expected))
 
+    def test_save_ply_invalid_shapes(self):
+        # Invalid vertices shape
+        with self.assertRaises(ValueError) as error:
+            verts = torch.FloatTensor([[0.1, 0.2, 0.3, 0.4]])  # (V, 4)
+            faces = torch.LongTensor([[0, 1, 2]])
+            save_ply(StringIO(), verts, faces)
+        expected_message = (
+            "Argument 'verts' should either be empty or of shape (num_verts, 3)."
+        )
+        self.assertTrue(expected_message, error.exception)
+
+        # Invalid faces shape
+        with self.assertRaises(ValueError) as error:
+            verts = torch.FloatTensor([[0.1, 0.2, 0.3]])
+            faces = torch.LongTensor([[0, 1, 2, 3]])  # (F, 4)
+            save_ply(StringIO(), verts, faces)
+        expected_message = (
+            "Argument 'faces' should either be empty or of shape (num_faces, 3)."
+        )
+        self.assertTrue(expected_message, error.exception)
+
+    def test_save_ply_invalid_indices(self):
+        message_regex = "Faces have invalid indices"
+        verts = torch.FloatTensor([[0.1, 0.2, 0.3]])
+        faces = torch.LongTensor([[0, 1, 2]])
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            save_ply(StringIO(), verts, faces)
+
+        faces = torch.LongTensor([[-1, 0, 1]])
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            save_ply(StringIO(), verts, faces)
+
+    def _test_save_load(self, verts, faces):
+        f = StringIO()
+        save_ply(f, verts, faces)
+        f.seek(0)
+        # raise Exception(f.getvalue())
+        expected_verts, expected_faces = verts, faces
+        if not len(expected_verts):  # Always compare with a (V, 3) tensor
+            expected_verts = torch.zeros(size=(0, 3), dtype=torch.float32)
+        if not len(expected_faces):  # Always compare with an (F, 3) tensor
+            expected_faces = torch.zeros(size=(0, 3), dtype=torch.int64)
+        actual_verts, actual_faces = load_ply(f)
+        self.assertClose(expected_verts, actual_verts)
+        self.assertClose(expected_faces, actual_faces)
+
+    def test_empty_save_load(self):
+        # Vertices + empty faces
+        verts = torch.tensor([[0.1, 0.2, 0.3]])
+        faces = torch.LongTensor([])
+        self._test_save_load(verts, faces)
+
+        faces = torch.zeros(size=(0, 3), dtype=torch.int64)
+        self._test_save_load(verts, faces)
+
+        # Faces + empty vertices
+        message_regex = "Faces have invalid indices"
+        verts = torch.FloatTensor([])
+        faces = torch.LongTensor([[0, 1, 2]])
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            self._test_save_load(verts, faces)
+
+        verts = torch.zeros(size=(0, 3), dtype=torch.float32)
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            self._test_save_load(verts, faces)
+
+        # Empty vertices + empty faces
+        message_regex = "Empty 'verts' and 'faces' arguments provided"
+        verts0 = torch.FloatTensor([])
+        faces0 = torch.LongTensor([])
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            self._test_save_load(verts0, faces0)
+
+        faces3 = torch.zeros(size=(0, 3), dtype=torch.int64)
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            self._test_save_load(verts0, faces3)
+
+        verts3 = torch.zeros(size=(0, 3), dtype=torch.float32)
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            self._test_save_load(verts3, faces0)
+
+        with self.assertWarnsRegex(UserWarning, message_regex):
+            self._test_save_load(verts3, faces3)
+
     def test_simple_save(self):
         verts = torch.tensor(
             [[0, 0, 0], [0, 0, 1], [0, 1, 0], [1, 0, 0]], dtype=torch.float32
@@ -378,6 +462,11 @@ class TestMeshPlyIO(TestCaseMixin, unittest.TestCase):
         lines2.insert(5, "property float z")
         lines2.insert(5, "property float y")
         lines2[-2] = "0 0 0"
+        lines2[-1] = ""
+        with self.assertRaisesRegex(ValueError, "Not enough data for face."):
+            load_ply(StringIO("\n".join(lines2)))
+
+        lines2[-1] = "2 0 0"
         with self.assertRaisesRegex(ValueError, "Faces must have at least 3 vertices."):
             load_ply(StringIO("\n".join(lines2)))