Handle header has no newline or space after OFF. (#665)

Summary:
Allow a line like `OFF10 10 10` as the start of an OFF file. Such things apparently occur in ModelNet40.

This resolves https://github.com/facebookresearch/pytorch3d/issues/663.

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/665

Test Plan: New test

Reviewed By: nikhilaravi

Differential Revision: D28180006

Pulled By: bottler

fbshipit-source-id: 7f474c6a262e32da012217e09f76e8672a7f0278

pytorch3d/io/off_io.py

@@ -6,6 +6,9 @@
 """
 This module implements utility functions for loading and saving
 meshes as .off files.
+
+This format is introduced, for example, at
+http://www.geomview.org/docs/html/OFF.html .
 """
 import warnings
 from pathlib import Path
@@ -226,15 +229,17 @@ def _load_off_stream(file) -> dict:
         faces_colors: FloatTensor of shape (F, C), where C is 3 or 4.
     """
     header = file.readline()
-    if header.lower() in (b"off\n", b"off\r\n", "off\n"):
-        header = file.readline()
 
     while _is_line_empty(header):
         header = file.readline()
 
-    items = header.split(b" ")
-    if len(items) and items[0].lower() in ("off", b"off"):
-        items = items[1:]
+    if header[:3].lower() == b"off":
+        header = header[3:]
+
+    while _is_line_empty(header):
+        header = file.readline()
+
+    items = header.split()
     if len(items) < 3:
         raise ValueError("Invalid counts line: %s" % header)
 
@@ -247,7 +252,7 @@ def _load_off_stream(file) -> dict:
     except ValueError:
         raise ValueError("Invalid counts line: %s" % header)
 
-    if (len(items) > 3 and not items[3].startswith("#")) or n_verts < 0 or n_faces < 0:
+    if (len(items) > 3 and not items[3].startswith(b"#")) or n_verts < 0 or n_faces < 0:
         raise ValueError("Invalid counts line: %s" % header)
 
     verts, verts_colors = _read_verts(file, n_verts)

tests/test_io_off.py

@@ -254,6 +254,11 @@ class TestMeshOffIO(TestCaseMixin, unittest.TestCase):
         lines2[0] = "OFF " + lines[0]
         load(lines2)
 
+        # OFF line can be merged in to the first line with no space
+        lines2 = lines.copy()
+        lines2[0] = "OFF" + lines[0]
+        load(lines2)
+
         with self.assertRaisesRegex(ValueError, "Not enough face data."):
             load(lines[:-1])