Bug: Incorrect handling of negative indices

Author: einarf

pywavefront/obj.py

@@ -217,7 +217,11 @@ def consume_faces(self):
             has_vn = True
 
         # Are we referencing vertex with color info?
-        vertex = self.vertices[int(parts[0]) - 1]
+        vindex = int(parts[0])
+        if vindex < 0:
+            vindex += len(self.vertices) + 1
+
+        vertex = self.vertices[vindex]
         has_colors = len(vertex) == 6
 
         # Prepare vertex format string
@@ -253,13 +257,13 @@ def consume_faces(self):
 
                 # Resolve negative index lookups
                 if v_index < 0:
-                    v_index += len(self.vertices) - 1
+                    v_index += len(self.vertices) + 1
 
                 if has_vt and t_index < 0:
-                    t_index += len(self.tex_coords) - 1
+                    t_index += len(self.tex_coords) + 1
 
                 if has_vn and n_index < 0:
-                    n_index += len(self.normals) - 1
+                    n_index += len(self.normals) + 1
 
                 pos = self.vertices[v_index][0:3] if has_colors else self.vertices[v_index]
                 color = self.vertices[v_index][3:] if has_colors else ()

test/simple_negative_indices.obj

@@ -0,0 +1,26 @@
+# Comment
+mtllib simple.mtl
+o Simple
+v 0.01 0.02 0.03
+v 0.04 0.05 0.06
+v 0.07 0.08 0.09
+v 0.11 0.12 0.13
+vt 10 11
+vt 12 13
+vt 14 15
+vt 16 17
+vn 20 21 22
+usemtl Material.simple
+f -3/-2/-1 -4/-3/-1 -2/-4/-1
+o SimpleB
+v 1.0 0.0 1.0
+v -1.0 0.0 1.0
+v 1.0 0.0 -1.0
+v -1.0 0.0 -1.0
+vt 0.0 1.0
+vt 0.0 0.0
+vt 1.0 0.0
+vt 1.0 1.0
+vn 0.0 1.0 -0.0
+usemtl Material2.simple
+f -3/-2/-1 -4/-3/-1 -2/-4/-1

test/test_parser.py

@@ -44,6 +44,14 @@ def testObjMaterials(self):
         self.assertEqual(material1.name, 'Material.simple')
         self.assertEqual(material2.name, 'Material2.simple')
 
+class NegativeIndices(TestParsers):
+    """Run all tests with negative indices"""
+    def setUp(self):
+        # Append current path to locate files
+        meshes = pywavefront.Wavefront(prepend_dir('simple_negative_indices.obj'))
+        self.mesh1 = meshes.mesh_list[0]
+        self.mesh2 = meshes.mesh_list[1]
+
 
 class TestParserGz(TestParsers):
     """Run all tests is TestParsers for gzip file as well"""