Path tracing

A Monte Carlo method for estimating light transport through random paths of successive surface interactions. A sampled continuation contributes its scattering response and cosine divided by its sampling probability density function. Next-event estimation makes direct source connections explicit, including connections to ideal point lights.

Explicit light-source sampling at a surface interaction: connect to a sampled source and use a shadow ray to test visibility. It avoids relying solely on a randomly continued path to hit an emitter; this is essential for ordinary continuous direction sampling with ideal point lights.