What is actually done by the deferred rendering pipeline in this context?

Question

I have been reading a student's thesis regarding deferred rendering and have stumbled across a piece of his work that I couldn't quite understand.

The thesis; in chapter 1.3 it says:

Stalker (see Figure 02) for example is using only deferred lighting to calculate their light accumulation due to complex lighting conditions in the environment, while the rest of the engine still runs in forward rendering

Could someone possibly explain what he means by this? What is the deferred pipeline actually being used for?

Answer 1

It says right in the quote: to calculate the effect of lights in the scene (how much light falls on a particular fragment, what color is it, et cetera).

Computing the effects of more and more light sources is something that forward rendering handles badly; it scales very inefficiently. Deferred rendering alleviates a lot of that computational pressure, making it significantly easier to throw a ton of lights into the scene ("lots of lights" is probably, at least in part, what is meant by "complex lighting conditions").

One reason to mix deferred and traditional rendering pipelines in this fashion was to allow the use of the deferred pipeline for what it was good for (lights, lights, lights) and the forward pipeline for what it was good for (transparency, which is not readily accomplished with a deferred system, especially early on in the technology's use).