Fix save_ply with noncontiguous faces

Summary: As noted in #710, save_ply was failing with some values of the faces tensor. It was assuming the faces were contiguous in using view() to change them. Here we avoid doing that.

Reviewed By: patricklabatut

Differential Revision: D29159655

fbshipit-source-id: 47214a7ce915bab8d81f109c2b97cde464fd57d8

Author: bottler

pytorch3d/io/ply_io.py

@@ -1154,9 +1154,14 @@ def _save_ply(
             if ascii:
                 np.savetxt(f, faces_array, "3 %d %d %d")
             else:
-                # rows are 13 bytes: a one-byte 3 followed by three four-byte face indices.
-                faces_uints = np.full((len(faces_array), 13), 3, dtype=np.uint8)
-                faces_uints[:, 1:] = faces_array.astype(np.uint32).view(np.uint8)
+                faces_recs = np.zeros(
+                    len(faces_array),
+                    dtype=[("count", np.uint8), ("vertex_indices", np.uint32, 3)],
+                )
+                faces_recs["count"] = 3
+                faces_recs["vertex_indices"] = faces_array
+                faces_uints = faces_recs.view(np.uint8)
+
                 if isinstance(f, BytesIO):
                     f.write(faces_uints.tobytes())
                 else:

tests/test_io_ply.py

@@ -353,6 +353,11 @@ def test_normals_save(self):
         save_ply(file, verts=verts, faces=faces, verts_normals=normals)
         file.close()
 
+    def test_contiguity_unimportant(self):
+        verts = torch.rand(32, 3)
+        self._test_save_load(verts, torch.randint(30, size=(10, 3)))
+        self._test_save_load(verts, torch.randint(30, size=(3, 10)).T)
+
     def test_empty_save_load(self):
         # Vertices + empty faces
         verts = torch.tensor([[0.1, 0.2, 0.3]])