Physically Based Rendering, 3rd Edition

14.2.2: Sampling shapes

In pbrt, area lights are defined by attaching an emission profile to a Shape. Therefore, in order to sample incident illumination from such light sources, it is useful to be able to generate samples over the surface of shapes. To make this possible, we will add sampling methods to the Shape class that sample points on their surfaces. The AreaLight sampling methods to be defined shortly will in turn call these methods.

There are two shape sampling methods, both named Shape::Sample(). The first chooses points on the surface of the shape using a sampling distribution with respect to surface area and returns the local geometric information about the sampled point in an Interaction. In addition to initializing the position ...