private static void toTangentsWithParity(IrVertex vertex) {
        if (vertex.tang != null && vertex.bitang != null) {
            float wCoord = vertex.norm.cross(vertex.tang).dot(vertex.bitang) < 0f ? -1f : 1f;
            vertex.tang4d = new Vector4f(vertex.tang.x, vertex.tang.y, vertex.tang.z, wCoord);
            vertex.tang = null;
            vertex.bitang = null;
        }
    }
Applies smoothing groups to vertex normals. XXX not implemented!

@param mesh ignored
@return null
jme3-plugins/src/main/java/com/jme3/scene/plugins/IrUtils.java