Volumetric Lighting
The first tech is volumetric lighting, first seen in Fallout 4 under the "God Rays" setting. The technique uses hardware tessellation to add atmospheric lighting to the environment. It's easiest to show a few slides that demonstrate how volumetric lighting works:
Starting with the base rendered scene, using a directional light with shadow mapping, light volumes are computed by extruding geometry, which gives the third image showing the scattered lighting. This is combined with the original shadow mapped image to create a final product, which looks far better (IMO), but the performance hit can be rather severe.
Nvidia noted a 5% drop in performance for Fallout 4 by turning on God Rays at the low setting, with a far more substantial 40% drop in performance when using the ultra setting. That might sound horrible, but when you compare Nvidia's off vs. low and the ultra vs. low, you can see that nearly all of the gains can be had using the low setting. One thing to note here is that the above scenes are a great use case for volumetric lighting, but there are many situations where volumetric lighting wouldn't show nearly as noticeable a change.
