GPU Pro 5

82 II Lighting and Shading

n

r

p

C

α

Figure 1.13. Visualization of cone of specular importance sampling.

We successfully applied this method to various specular models such as Phong,

Blinn-Phong, Beckmann and GGX [Walter et al. 07]. However, it is worth noting

that a cone shape is a relaxed bound on the actual distribution 3D shape, the

complexity of which varies over different BRDF. Therefore, the cone shape is

only approximate. In the case of Phong, the cone is actually a perfect match.

However, in the case of Blinn-Phong, due to the use of the half vector, a pyramid

with an ellipse base or even more complex shape would provide tighter, more

accurate b