Tony Barrera Anders Hast Ewert Bengtsson Faster Shading by Equal Angle Interpolation of Vectors. 217-223 2004 10 IEEE Trans. Vis. Comput. Graph. 2 http://doi.ieeecomputersociety.org/10.1109/TVCG.2004.1260773 db/journals/tvcg/tvcg10.html#BarreraHB04