v -1 1 1
v 1 1 -1
v 1 -1 1
v -1 -1 -1

# This is a textureless tetrahedron, but define a 
# point anyway just in case
vt 0 0

# simple 4 faces. the tetrahedron doesn't face the camera in any
# meaningful way; it'll be up to you to make that work
f 1/1 3/1 2/1
f 2/1 3/1 4/1
f 1/1 4/1 3/1
f 1/1 2/1 4/1