Performance

A fundamental consideration in interactive 3D graphics is performance. Numerous calculations are required to render a 3D scene of even modest complexity, and in an interactive application, a scene must generally be redrawn several times per second. An API for use in interactive 3D applications must therefore provide efficient access to the capabilities of the graphics hardware of which it makes use. But different graphics subsystems provide different capabilities, so a common interface must be found.

The interface must also provide a means to switch on and off various rendering features. This is required both because some hardware may not provide support for some features and so cannot provide those features with acceptable performance, and also because even with hardware support, enabling certain features or combinations of features may decrease performance significantly. Slow rendering may be acceptable, for instance, when producing a final image of a scene, but interactive rates are normally required when manipulating objects within the scene or adjusting the viewpoint. In such cases the performance-degrading features may be desirable for the final image, but undesirable during scene manipulation.