There has been a lot of research around ways to efficiently capture some of the feel and realism of a movie-quality global illumination simulation without the extra overhead, and one of the most popular approaches is known as ambient occlusion (AO). This is much more efficient but also much less realistic. The single largest shortcut is to disregard global illumination when calcuating lighting in the scene and instead only look at local, direct lighting. Traditional 3D pipelines take a number of shortcuts when simulating lighting in a scene in order to get realtime performance. How do we get movie-quality lighting in real time?
