History
Performer came about in 1991 when a group from SGI's Open Inventor project, then known as IRIS Inventor, decided to focus on performance rather than ease of programmability. Whereas Inventor delivered easy-to-use objects and various UI elements to interact with them, Performer focused on a scene graph system that could be re-arranged on the fly for performance reasons, allowing the various passes of a rendering task to be performed in parallel in multiple threads. Performer allowed the scene to describe levels of detail with hysteresis bands and fade capabilities. Frame rate and statistics were monitored and a 'stress' factor was calculated. This could be used to further weight the level of detail in the scene eliminating detail to maintain a target frame rate.
Other key features of Performer were the use of symmetric multi-processing capabilities, support multiple graphics pipes and the ability to utilize the scalable resources of high end systems. In this regard Performer was actually simple to use given the underlying complexity. Application culling and rendering could be running in different threads locked to different physical processors. In a multi-pipe (multiple graphics subsystems) configuration rendering to each graphics pipe would have a dedicated thread and similarly culling would also have a dedicated processor. Advanced features like database paging, texture paging and point light source management (for flight simulation) and intersection testing for collision detection would also have dedicated processors allowing asynchronous I/O and processing to occur without negatively impacting graphics performance. Most of this complexity was hidden beneath a simpler scene graph API with relatively high level configuration calls which could be made to set up the threads and inter-process communication.
Performer did not have a native file format, merely plugin loaders from 3rd parties such as MultiGen's OpenFlight format loader. Similarly there was no default runtime, there was sample code and the often used and often modified 'perfly' sample application. This probably contributed to its reputation for being difficult to use.
By the mid-1990s it started to become clear that there was no reason that Inventor and Performer could not be combined. This led to the Cosmo 3D project that SGI was intending to build both Inventor and Performer (now essentially API shims) out of, as well as promote as a new and higher-level standardized API for future work on the SGI platform. However, after the first beta release of Cosmo 3D, SGi joined with Intel and IBM (and later DEC) to create OpenGL++, essentially a cleaned up version of Cosmo. This project died when SGI turned their attention to an almost identical project with Microsoft known as Fahrenheit, which was also killed. Today Inventor and Performer remain separate products, and none of the combined versions ever saw the light of day.
Features
Performer consists primarily of two libraries: the lower-level libpr and the higher-level libpf. The libpr library provides an object-oriented interface to high-speed rendering functions based on the concept of a pfGeoSet and a pfGeoState. A pfGeoSet is a collection of graphics primitives, such as polygons or lines. A pfGeoState encapsulates properties pertaining to a given pfGeoSet such as lighting, transparency, and texturing.
The libpf library includes functions for the generation and manipulation of hierarchical scene graphs, scene processing (simulation, intersection, culling, and drawing tasks), level-of-detail management, asynchronous database paging, dynamic coordinate systems, environment models, light points, and so on. This library also provides transparent support for multiple viewports spread across multiple graphics pipelines.
Other Performer libraries--libpfutil, libpfdb, libpfui, etc.--provide functions for generating optimized geometry, database conversion, device input (such as for interfacing with external flyboxes and MIL-STD-1553 mux busses), motion models, collision models, and a format-independent database interface that supports common data formats such as Open Inventor, OpenFlight, Designer's Workbench, Medit, and Wavefront.
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.
Direct3D is a graphics application programming interface (API) for Microsoft Windows. Part of DirectX, Direct3D is used to render three-dimensional graphics in applications where performance is important, such as games. Direct3D uses hardware acceleration if it is available on the graphics card, allowing for hardware acceleration of the entire 3D rendering pipeline or even only partial acceleration. Direct3D exposes the advanced graphics capabilities of 3D graphics hardware, including Z-buffering, W-buffering, stencil buffering, spatial anti-aliasing, alpha blending, color blending, mipmapping, texture blending, clipping, culling, atmospheric effects, perspective-correct texture mapping, programmable HLSL shaders and effects. Integration with other DirectX technologies enables Direct3D to deliver such features as video mapping, hardware 3D rendering in 2D overlay planes, and even sprites, providing the use of 2D and 3D graphics in interactive media ties.
A scene graph is a general data structure commonly used by vector-based graphics editing applications and modern computer games, which arranges the logical and often spatial representation of a graphical scene. It is a collection of nodes in a graph or tree structure. A tree node may have many children but only a single parent, with the effect of a parent applied to all its child nodes; an operation performed on a group automatically propagates its effect to all of its members. In many programs, associating a geometrical transformation matrix at each group level and concatenating such matrices together is an efficient and natural way to process such operations. A common feature, for instance, is the ability to group related shapes and objects into a compound object that can then be manipulated as easily as a single object.
Fahrenheit was an effort to create a unified high-level API for 3D computer graphics to unify Direct3D and OpenGL. It was designed primarily by Microsoft and SGI and also included work from an HP-MS joint effort.
X3D is a royalty-free ISO/IEC standard for declaratively representing 3D computer graphics. File format support includes XML, ClassicVRML, Compressed Binary Encoding (CBE) and a draft JSON encoding. X3D became the successor to the Virtual Reality Modeling Language (VRML) in 2001. X3D features extensions to VRML, the ability to encode the scene using an XML syntax as well as the Open Inventor-like syntax of VRML97, or binary formatting, and enhanced application programming interfaces (APIs).
OpenGL++ was a graphics library written in C++ that supported object-oriented data structures on top of the OpenGL 3D graphics system. The project started as the result of a partnership between SGI, IBM and Intel, and later, Digital Equipment Corporation. It was intended to provide a higher level API than the "bare metal" support of OpenGL, as well as being an implementation for Java3D. Work on OpenGL++ ended when SGI decided to partner with Microsoft instead, leading to the Fahrenheit project, which also died.
Open Inventor, originally IRIS Inventor, is a C++ object oriented retained mode 3D graphics toolkit designed by SGI to provide a higher layer of programming for OpenGL. Its main goals are better programmer convenience and efficiency. Open Inventor exists as both proprietary software and free and open-source software, subject to the requirements of the GNU Lesser General Public License (LGPL), version 2.1.
QuickDraw 3D, or QD3D for short, is a 3D graphics API developed by Apple Inc. starting in 1995, originally for their Macintosh computers, but delivered as a cross-platform system.
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.
The Khronos Group, Inc. is an American non-profit member-funded industry consortium based in Beaverton, Oregon, focused on the creation of open standard, royalty-free application programming interfaces (APIs) for authoring and accelerated playback of dynamic media on a wide variety of platforms and devices. Khronos members may contribute to the development of Khronos API specifications, vote at various stages before public deployment, and accelerate delivery of their platforms and applications through early access to specification drafts and conformance tests.
PHIGS is an application programming interface (API) standard for rendering 3D computer graphics, considered to be the 3D graphics standard for the 1980s through the early 1990s. Subsequently, a combination of features and power led to the rise of OpenGL, which became the most popular professional 3D API of the mid to late 1990s.
Java 3D is a scene graph-based 3D application programming interface (API) for the Java platform. It runs on top of either OpenGL or Direct3D until version 1.6.0, which runs on top of Java OpenGL (JOGL). Since version 1.2, Java 3D has been developed under the Java Community Process. A Java 3D scene graph is a directed acyclic graph (DAG).
OpenSceneGraph is an open-source 3D graphics application programming interface, used by application developers in fields such as visual simulation, computer games, virtual reality, scientific visualization and modeling.
Retained mode in computer graphics is a major pattern of API design in graphics libraries, in which
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.
OpenSG is a scene graph system to create real-time graphics programs, e.g. for virtual reality applications. It is developed following Open Source principles, LGPL licensed, and can be used freely. It runs on Windows, Linux, Solaris and OS X and is based on OpenGL.
Oak3D is a free JavaScript library for 3D graphics development based on the HTML5 WebGL standard, dedicated in realizing the Web3D applications with GPU acceleration for all the front-end developers in an easy and efficient way.
This is a glossary of terms relating to computer graphics.
