For typical computer displays, three-dimensional is a misnomer—their displays are two-dimensional. Semantically, however, most graphical user interfaces use three dimensions – in addition to height and width, they offer a third dimension of layering or stacking screen elements over one another. This may be represented visually on screen through an illusionary transparent effect, which offers the advantage that information in background windows may still be read, if not interacted with. Or the environment may simply hide the background information, possibly making the distinction apparent by drawing a drop shadow effect over it.
Some environments use the methods of 3D graphics to project virtual three dimensional user interface objects onto the screen. These are often shown in use in sci-fi films (see below for examples). As the processing power of computer graphics hardware increases, this becomes less of an obstacle to a smooth user experience.
Three-dimensional graphics are currently mostly used in computer games, art and computer-aided design (CAD). A three-dimensional computing environment could also be useful in other scenarios, like molecular graphics and aircraft design.
Several attempts have been made to create a multi-user three-dimensional environment, including the Croquet Project and Sun's Project Looking Glass.
The use of three-dimensional graphics has become increasingly common in mainstream operating systems, from creating attractive interfaces - eye candy to functional purposes only possible using three dimensions. For example, user switching is represented by rotating a cube whose faces are each user's workspace, and window management is represented via a Rolodex-style flipping mechanism in Windows Vista (see Windows Flip 3D). In both cases, the operating system transforms windows on-the-fly while continuing to update the content of those windows.