Distance/Height-based fog is an approximation to the fog you would normally see outdoors. Even in the clearest of days, you should be able to see some fog far in the distance. The main benefit of adding the fog effect is that it helps the viewer estimate how far different elements in the scene are based on the amount of fog covering them. In addition to the realism this effect adds, it has the additional benefit of hiding the end of the visible range. Without fog to cover the far plane, it becomes easier to notice when far scene elements are clipped by the cameras far plane.
By tuning the height of the fog you can also add a darker atmosphere to your scene as demonstrated by the following image:
This recipe will demonstrate how distance/height-based fog can be added to our deferred directional light calculation. See the How it works… section for details about adding the effect to other elements of your rendering code.