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Core OpenGL, or CGL, is Apple Inc.'s Macintosh Quartz windowing system interface to the OS X implementation of the OpenGL specification. CGL is analogous to GLX, which is the X11 interface to OpenGL, as well as WGL, which is the Microsoft Windows interface to OpenGL.
All windowing system interfaces to OpenGL arose out of the migration of Silicon Graphics proprietary 3D graphics application programming interface (API) IrisGL to its current open standard form OpenGL. When the decision was made to make IrisGL an open standard, the primary required design change was to make this graphics standard API windowing system agnostic. All window system specific logic was therefore removed from IrisGL when moving to OpenGL. Window system logic includes any event mechanism for gathering input from devices such as keyboards and mice, as well as any window ordering or sizing logic used when drawing to a modern windowed user interface. Further, all internal management of window memory buffers, sometimes referred to as surfaces, was also removed from IrisGL to create OpenGL.
With OpenGL windowing system agnostic, companies such as Apple must shoulder the burden of configuring and managing the surfaces used as a destination for OpenGL rendering.
On OS X, CGL is the foundation layer of windowing system interfaces to OpenGL. Both AGL (Apple Graphics Library) and the Cocoa (API) (or AppKit) have interfaces to OpenGL and are logical software layers and depend on CGL for their behavior. CGL and AGL interoperate freely. CGL and Cocoa may be used together, however Cocoa classes may implicitly make changes to CGL state. Function calls from AGL and Cocoa should not be mixed.
Configuration of these surfaces is done through a pixel format selection process where different compatible layers of rendering information are combined to form a framebuffer. Examples of such layers are color buffers, transparency buffers (alpha), stencil buffers, and depth buffers. The CGL function CGLChoosePixelFormat is used to perform this buffer compatibility check. CGLChoosePixelFormat will, based on input parameters and their scoring policy, choose a pixel format that represents a compatible buffer configuration that is supported by the underlying renderer that will be used to process graphics commands. Renderers may be either hardware based, such that they correspond to graphics cards installed in the system or they may be software based, where the main CPU of the system handles all of the graphics command processing and final rasterization work.
On Mac OS X, CGL is also responsible for handling the heterogeneous nature of graphics device installations and configuration on Macintosh systems. Macintosh computers may have any number of displays and graphics cards installed in them. In these configurations, the user's desktop may be virtualized (extended) or mirrored across multiple displays which are connected to multiple graphics cards which may or may not be from the same graphics vendor.
When users configure their Macintosh to use a virtualized desktop, and they drag windows from one display to another, CGL handles the management of OpenGL graphics state that must be shadowed between devices to provide command processing consistency between them. Dragging a window across a Macintosh desktop between two different displays that are supported by two different renderers is known as a "Virtual Screen Change".
CGL also provides a mechanism to obtain information about the renderer that is currently in use. The primary data structure that maintains OpenGL state on Mac OS X is a CGLContextObj. These CGL contexts can be retrieved at any time using a call to CGLGetCurrentContext. The CGLContextObj may then be queried for specifics about the renderer that is associated with it.
Also included is Apple's in-house OpenGL software renderer. Originally, this was a simple integer package, in 10.3 a new floating point one was introduced which ultimately replaced it. The software renderer, though slow, is fast enough for basic applications and kept feature-complete Archived January 8, 2014, at the Wayback Machine with OS X's OpenGL implementation for development purposes.
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The OpenGL Utility Toolkit (GLUT) is a library of utilities for OpenGL programs, which primarily perform system-level I/O with the host operating system. Functions performed include window definition, window control, and monitoring of keyboard and mouse input. Routines for drawing a number of geometric primitives are also provided, including cubes, spheres and the Utah teapot. GLUT also has some limited support for creating pop-up menus.
OpenGL is a cross-language, cross-platform application programming interface (API) for rendering 2D and 3D vector graphics. The API is typically used to interact with a graphics processing unit (GPU), to achieve hardware-accelerated rendering.
GNUstep is a free software implementation of the Cocoa Objective-C frameworks, widget toolkit, and application development tools for Unix-like operating systems and Microsoft Windows. It is part of the GNU Project.
Carbon was one of two primary C-based application programming interfaces (APIs) developed by Apple for the macOS operating system. Carbon provided a good degree of backward compatibility for programs that ran on Mac OS 8 and 9. Developers could use the Carbon APIs to port (“carbonize”) their “classic” Mac applications and software to the Mac OS X platform with little effort, compared to porting the app to the entirely different Cocoa system, which originated in OPENSTEP. With the release of macOS 10.15 Catalina, the Carbon API was officially discontinued and removed, leaving Cocoa as the sole primary API for developing macOS applications.
In computing, a windowing system is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the WIMP paradigm for a user interface.
GLX is an extension to the X Window System core protocol providing an interface between OpenGL and the X Window System as well as extensions to OpenGL itself. It enables programs wishing to use OpenGL to do so within a window provided by the X Window System. GLX distinguishes two "states": indirect state and direct state.
Direct3D and OpenGL are competing application programming interfaces (APIs) which can be used in applications to render 2D and 3D computer graphics. As of 2005, graphics processing units (GPUs) almost always implement one version of both of these APIs. Examples include: DirectX 9 and OpenGL 2 circa 2004; DirectX 10 and OpenGL 3 circa 2008; and most recently, DirectX 11 and OpenGL 4 circa 2011. GPUs that support more recent versions of the standards are backward compatible with applications that use the older standards; for example, one can run older DirectX 9 games on a more recent DirectX 11-certified GPU.
Quartz Compositor is the display server in macOS. It is responsible for presenting and maintaining rasterized, rendered graphics from the rest of the Core Graphics framework and other renderers in the Quartz technologies family.
In Apple's macOS operating system, Quartz is the Quartz 2D and Quartz Compositor part of the Core Graphics framework. Quartz includes both a 2D renderer in Core Graphics and the composition engine that sends instructions to the graphics card. Because of this vertical nature, Quartz is often synonymous with Core Graphics.
OpenGL for Embedded Systems is a subset of the OpenGL computer graphics rendering application programming interface (API) for rendering 2D and 3D computer graphics such as those used by video games, typically hardware-accelerated using a graphics processing unit (GPU). It is designed for embedded systems like smartphones, tablet computers, video game consoles and PDAs. OpenGL ES is the "most widely deployed 3D graphics API in history".
Xgl is an obsolete display server implementation supporting the X Window System protocol designed to take advantage of modern graphics cards via their OpenGL drivers, layered on top of OpenGL. It supports hardware acceleration of all X, OpenGL and XVideo applications and graphical effects by a compositing window manager such as Compiz or Beryl. The project was started by David Reveman of Novell and first released on January 2, 2006. It was removed from the X.org server in favor of AIGLX on June 12, 2008.
Desktop Window Manager is the compositing window manager in Microsoft Windows since Windows Vista that enables the use of hardware acceleration to render the graphical user interface of Windows.
The architecture of macOS describes the layers of the operating system that is the culmination of Apple Inc.'s decade-long research and development process to replace the classic Mac OS.
Accelerated Indirect GLX ("AIGLX") is an open source project founded by Red Hat and the Fedora community, led by Kristian Høgsberg, to allow accelerated indirect GLX rendering capabilities to the X.Org Server and DRI drivers. This allows remote X clients to get fully hardware accelerated rendering over the GLX protocol; coincidentally, this development was required for OpenGL compositing window managers to function with hardware acceleration.
VirtualGL is an open-source software package that redirects the 3D rendering commands from Unix and Linux OpenGL applications to 3D accelerator hardware in a dedicated server and sends the rendered output to a (thin) client located elsewhere on the network. On the server side, VirtualGL consists of a library that handles the redirection and a wrapper program that instructs applications to use this library. Clients can connect to the server either using a remote X11 connection or using an X11 proxy such as a VNC server. In case of an X11 connection some client-side VirtualGL software is also needed to receive the rendered graphics output separately from the X11 stream. In case of a VNC connection no specific client-side software is needed other than the VNC client itself.
WGL or Wiggle is an API between OpenGL and the windowing system interface of Windows. WGL is analogous to EGL, which is an interface between rendering APIs such as OpenCL, OpenGL, OpenGL ES or OpenVG and the native platform, as well as to CGL, which is the OS X interface to OpenGL.
Wayland is a communication protocol that specifies the communication between a display server and its clients, as well as a C library implementation of that protocol. A display server using the Wayland protocol is called a Wayland compositor, because it additionally performs the task of a compositing window manager.
EGL is an interface between Khronos rendering APIs and the underlying native platform windowing system. EGL handles graphics context management, surface/buffer binding, rendering synchronization, and enables "high-performance, accelerated, mixed-mode 2D and 3D rendering using other Khronos APIs." EGL is managed by the non-profit technology consortium Khronos Group.
Pixel buffer or pBuffer is a feature in OpenGL and OpenGL ES platform interfaces which allows for off-screen rendering. It is specified as an extension to WGL API, and a core feature of GLX & EGL.
