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://csdl.computer.org/comp/trans/tg/2004/02/v0217abs.htm db/journals/tvcg/tvcg10.html#BarreraHB04