OpenGL® class libraries provide an object-oriented implementation of the OpenGL® API. They offer advantages such as encapsulation and inheritance, but can be confusing for some developers. These libraries encapsulate basic OpenGL® functions and divide them into different classes, including a scene graph. Most OpenGL® libraries have been translated into an object-oriented form, making it easier for developers to keep OpenGL® current across existing devices.
An OpenGL® class can refer to an object-oriented implementation of parts of the OpenGL® abstract programming interface (API) or a class that uses OpenGL® function calls within its code. The nature of the OpenGL® library meant that there really wasn’t any support for an object-oriented version of the API, and most programs called functions as they were written, outside of a class. As object-oriented languages became more prevalent, several OpenGL® class libraries appeared to act as wrapper objects for the main library. There are advantages to using an OpenGL® class that has been fully realized instead of just the collection of functions provided in the library, including encapsulation and a way to derive new functional classes through inheritance while protecting the base implementation. Not all developers use an OpenGL® class library, because it can be confusing to switch to fully object-oriented programming paradigms.
In object-oriented programming, a class is a collection of data, variables, and functions, called methods, that modify the information it contains. OpenGL®’s origins as a library of functions for the C programming language, which was not an object-oriented language, meant that some of the programming methodologies and practices it developed were not suited to object-oriented programming. As some operating systems and other devices began to rely more on object-oriented languages, several OpenGL® class libraries arose.
Some of the OpenGL® class libraries simply encapsulate basic OpenGL® functions. This provided a secure and compatible framework for programming. While this type of class was required for some languages, it still required the helper classes to be turned into a functional application. Truly organized libraries divide OpenGL® functions into a number of classes, each of which handles a different element of the library, such as rendering.
A number of OpenGL® class libraries have begun to expand on the base OpenGL® engine and have begun to include more functionality. This mainly included a special class for handling objects in a scene, called a scene graph. These classes acted as a wrapper around the core libraries providing a logical framework upon which a program could be built that did more than render a scene and exit without having to invent a new OpenGL® framework each time.
Almost all OpenGL® libraries, including utility libraries, have been translated in one way or another into an object-oriented form. This has, in some cases, made it easier for developers to keep OpenGL® current across existing devices, forming a mostly uniform blueprint on how to implement OpenGL® in an object-oriented environment. With the addition of object-oriented development tools, it has also made it possible to drag and drop an OpenGL® class into a program that supports visual development, simplifying some of the more complicated aspects.
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