One major issue with
deferred rendering is that it does not allow for
translucency; the scene is placed into a single flat image and there is no way to express the fact that an object is to be overlaid on top of another object. This can be a problem when implementing systems such as
level-of-detail (or
LOD) switching. A basic requirement for an LOD system is that when the viewer moves a certain distance away from an object, that object should be replaced with a lower-polygon version in order to reduce rendering costs. Switching from a high polygon version to a low polygon version in one frame can be visually jarring, however, so it is usually desirable to fade out one version of the object whilst fading in another version over the course of a few frames. This presents an immediate problem: It is not possible to implement traditional alpha translucency fading in a deferred rendering system, as described above.