From 9acdd67b831f2d3d9db249b1c46d42139024cebf Mon Sep 17 00:00:00 2001
From: Jeremy Reizenstein <reizenstein@meta.com>
Date: Fri, 13 Sep 2024 02:00:49 -0700
Subject: [PATCH] fix obj material indexing bug #1368

Summary:
Make the negative index actually not an error

fixes https://github.com/facebookresearch/pytorch3d/issues/1368

Reviewed By: das-intensity

Differential Revision: D62177991

fbshipit-source-id: e5ed433bde1f54251c4d4b6db073c029cbe87343
---
 pytorch3d/io/obj_io.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pytorch3d/io/obj_io.py b/pytorch3d/io/obj_io.py
index 32083a5f..3cc29794 100644
--- a/pytorch3d/io/obj_io.py
+++ b/pytorch3d/io/obj_io.py
@@ -649,8 +649,7 @@ def _load_obj(
         # Create an array of strings of material names for each face.
         # If faces_materials_idx == -1 then that face doesn't have a material.
         idx = faces_materials_idx.cpu().numpy()
-        face_material_names = np.array(material_names)[idx]  # (F,)
-        face_material_names[idx == -1] = ""
+        face_material_names = np.array([""] + material_names)[idx + 1]  # (F,)
 
         # Construct the atlas.
         texture_atlas = make_mesh_texture_atlas(