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OpenGL functions are blocks of code used to draw, manipulate, and render 3D scenes. They have a strict naming convention consisting of a prefix, name, number of parameters, and data type. This convention ensures standardization and ease of use.
An OpenGL® function is a block of executable code that is called from within a computer program using the function name and any associated parameters. A function parameter is a variable or piece of information that must be added after the OpenGL® function name to direct the action that will be taken. OpenGL® has a wide range of functions that are used to draw, manipulate and render a three-dimensional (3D) scene and to change the values of various variables that can affect the appearance or speed of rendering. All functions in the OpenGL® function library use a strict naming convention that describes what parameters are expected and in which library the function is contained.
The naming convention for an OpenGL® function consists of four parts that form the actual name of a function. The first part is called the prefix and indicates the library to which the function belongs. For core functions, this prefix is “gl”, which stands for “graphics library”. Other prefixes include “excess” for “graphics library utility tools” and two-letter codes representing graphics hardware manufacturers that require special features for their specific cards to access features not available for other devices.
The second part of an OpenGL® function name is the name itself. This can directly refer to a value to change or an action to take. Examples of part of a function name include “color”, “vertex”, “clear” and “deleteTextures”. The name immediately follows the prefix and is usually capitalized to distinguish it from the prefix and make the code more readable.
The third element of an OpenGL® function name is the number of parameters accepted by the function. These can also be called arguments. This is simply a number. So a function that takes three arguments will have the number 3 in this position, right after the function name.
The final element of an OpenGL® function name is the data type of the variable expected as a parameter. This is a shorthand that helps remind the programmer what data is expected, and also allows a single function to have multiple predictable variations that take arguments of a different data type. Examples of this are “f” for a floating point number, “i” for an integer, or “b” for a byte.
Based on these rules, a fully qualified OpenGL® function name for creating a vertex point at a 3D location defined in floating point numbers would be “glVertex3f”. The function can be logically changed to accept integers by simply changing the last part to read glVertex3i. Part of OpenGL®’s success is its strict adherence to standards such as function naming conventions.
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