All the lighting models encountered in Chapter 4, Understanding Lighting Models, were very primitive descriptions of how light behaves. The most important aspect during their making was efficiency. Real-time shading is expensive, and techniques such as Lambertian or BlinnPhong are a compromise between computational cost and realism.
Having a more powerful GPU has allowed us to write progressively more sophisticated lighting models and rendering engines, with the aim of simulating how light actually behaves. This is, in a nutshell, the philosophy behind PBR. As the name suggests, it tries to get as close as possible to the physics behind the processes that give a unique look at each material. Despite this, the term PBR has been widely used in marketing campaigns and is more of a synonym for state-of-the-art rendering rather than a well-defined technique.
Unity implements...
