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OpenGL

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OpenGL, or the Open Graphics Library, is a cross-language and cross-platform application programming interface (API). An API acts as a bridge that allows different software programs to communicate. In this case, OpenGL allows programs to send instructions to a graphics processing unit (GPU). The GPU is specialized hardware designed for hardware-accelerated rendering. This means the hardware does the heavy work of drawing pictures very quickly. OpenGL is essential for rendering 2D and 3D vector graphics. It powers many modern technologies, including video games, virtual reality, and flight simulations. It is also used in scientific visualization and computer-aided design (CAD).

Pipeline OpenGL
Pipeline OpenGL

The mechanism of OpenGL relies on a specific set of functions and named integer constants. A programmer calls these functions to tell the computer what to draw. For example, the constant GL_TEXTURE_2D is used to describe a surface, which corresponds to the decimal number 3553. While these functions look similar to the C programming language, the API is actually language-independent. This means it can be used with many different coding languages. Most of the time, the API uses the GPU to handle the rendering process. However, it is also possible to implement OpenGL using only a central processing unit (CPU). This is known as software rendering.

Glxinfo with glxgears screenshot
Glxinfo with glxgears screenshot

OpenGL is highly flexible because it supports many different environments through language bindings. A binding is a way to connect the API to a specific programming language. One famous example is WebGL, which is a JavaScript binding used for 3D rendering inside web browsers. WebGL is actually based on OpenGL ES 2.0. There are also C bindings like WGL, GLX, and CGL. Mobile devices use different versions, such as the C binding for iOS and the Java and C bindings for Android. It is important to note that OpenGL only handles rendering. It does not manage input from a mouse, audio, or the creation of windows. Developers use other libraries, like GLFW or SDL, to handle those tasks.

Before OpenGL, creating graphics software was an expensive and difficult process. In the 1980s, developers had to write custom drivers for every different piece of hardware. This required a massive amount of repetitive effort. Silicon Graphics, Inc. (SGI) changed this by developing OpenGL in 1991. They released it on June 30, 1992. SGI previously had a system called IRIS GL, which was an industry standard for workstations. To create a public standard, SGI opened a version of IRIS GL to become OpenGL. This allowed applications to use advanced graphics even on low-powered systems by using software implementations for unsupported hardware features.

Pipeline OpenGL
Pipeline OpenGL

The history of OpenGL includes many attempts to unify graphics standards. In 1992, SGI helped form the OpenGL Architecture Review Board (ARB) to manage the specification. In 1996, Microsoft released Direct3D, which became a major competitor. This led to the Fahrenheit project in 1997, a joint effort between Microsoft and SGI to unify their interfaces. However, the project was abandoned in 1999 due to financial constraints and a lack of industry support. In July 2006, the management of OpenGL transferred from the ARB to the Khronos Group. This is a non-profit technology consortium that includes many different companies.

Glxinfo with glxgears screenshot
Glxinfo with glxgears screenshot

Development of OpenGL has changed significantly over the years. Between 2001 and 2014, the specification was updated almost every year. For example, in 2009, versions 3.1 and 3.2 were released. In 2010, three new versions arrived: 3.3, 4.0, and 4.1. The latest version, OpenGL 4.6, was released in 2017 after a three-year break. This version included eleven existing extensions into the core profile. Today, active development for OpenGL has largely stopped. The Khronos Group has moved its focus to a newer API called Vulkan, which was released in 2016. Because of this shift, some modern GPU features like ray tracing are not supported by the standard OpenGL specification.

Despite the rise of newer tools, OpenGL remains a vital part of computer science. It stays relevant because it is cross-platform and works on many different systems. Even though it is an older standard, it can still run efficiently on modern hardware. This is possible through compatibility layers like ANGLE and Zink. These layers allow OpenGL to run on top of newer APIs like Vulkan or Metal. Furthermore, hardware vendors can add new features through extensions. These extensions are added to the OpenGL Registry and allow for custom functionality. This flexibility ensures that OpenGL continues to be used in many professional and creative fields today.

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File:Pipeline OpenGL.svg
Pipeline OpenGL.svg
File:Glxinfo with glxgears screenshot.png
Glxinfo with glxgears screenshot.png
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