Fast Near Phong-Quality Software Shading

Quadratic shading has been proposed as a technique giving better results than Gouraud shading, but which is substantially faster than Phong shading. Several techniques for fitting a second order surface to six points have been proposed. We show in this paper how an approximation of the mid-edge samples can be done in a very efficient way. An approximation of the mid-edge vectors are derived. Several advantages are apparent when these vectors are put into the original formulation. First of all it will only depend on the vertex vectors. Moreover, it will simplify the setup and no extra square roots are necessary for normalizing the mid-edge vectors. The setup will be about three times faster than previous approaches. This makes quadratic shading very fast for interpolation of both diffuse and specular light, which will make it suitable for near Phong quality software renderings.