We mentioned forward rendering briefly in the last section, but what exactly does forward rendering mean? Forward rendering is one of the two main high-level rendering methods used by Unity; for the most part, you'll probably be using forward rendering for VR development, but it's still good to know the advantages and disadvantages of both methods.
In forward rendering, lighting is calculated for each geometry fragment, or visible pixel of an object, regardless of whether another object will ultimately obscure any fragments that would otherwise be seen. Each individual light in the scene requires its own calculations, so if you have a complex scene with a lot of geometry and more than a few lights, you're going to hit a performance bottleneck pretty quickly.
The best way to get around this issue is to bake your lights instead of actually rendering them. By using the same light baking method we used in Chapter 2, Stepping into Virtual Reality...