fixed back facing specular highlight
fixed back facing specular highlight

JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,JianpingCAI/libigl,JianpingCAI/libigl