Distance fog

Distance fog is a technique used in 3D computer graphics to enhance the perception of distance by simulating fog.

Because many of the shapes in graphical environments are relatively simple, and complex shadows are difficult to render, many graphics engines employ a "fog" gradient so objects further from the camera are progressively more obscured by haze and by aerial perspective. This technique simulates the effect of light scattering, which causes more distant objects to appear lower in contrast, especially in outdoor environments.