Since it is desirable to be able to turn features on and off, it should be the case that doing so has few or no side effects on other features. If, for instance, it is desired that each polygon be drawn with a single color rather than interpolating colors across its face, doing so should not affect how lighting or texturing is applied. Similarly, enabling or disabling any single feature should not engender an inconsistent state in which rendering results would be undefined. These kinds of feature independence are necessary to allow a programmer to easily manipulate features without having to generate tests for particular illegal or undesirable feature combinations that may require changing the state of apparently unrelated features. Another benefit of feature independence is that features may be combined in useful ways that may have been unforseen when the interface was designed.