mrdoob/three.js — pull request #1000 by netshade (2012-01-01 22:52:03+00:00)
Title: Negative face index in obj models

OBJ model format allows face indexes to be specified w/ negative numbers, indicating a relative lookup of the vertex.

With:
v 0 0 0
v 1 1 1

f -1 0 1 translates to f 1 0 1

This pull request changes the obj converter to recognize this.