Write The Case Study Of Open Gl

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Write the case study of Open GL(Graphics Library)

OpenGL (Open Graphics Library) is a standard specification defining a crosslanguage cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL was developed by Silicon Graphics Inc. (SGI) in 1992[1] and is widely used in CAD, virtual reality, scientific visualization, information visualization, flight simulation. It is also used in video games, where it competes with Direct3D on Microsoft Windows platforms Specification At its most basic level, OpenGL is a specification, meaning it is simply a document that describes a set of functions and the precise behaviours that they must perform. From this specification, hardware vendors create implementations — libraries of functions created to match the functions stated in the OpenGL specification, making use of hardware acceleration where possible. Hardware vendors have to meet specific tests to be able to qualify their implementation as an OpenGL implementation. Efficient vendor-supplied implementations of OpenGL (making use of graphics acceleration hardware to a greater or lesser extent) exist for Mac OS, Windows, Linux, many Unix platforms, and PlayStation 3. Various software implementations exist, bringing OpenGL to a variety of platforms that do not have vendor support. Notably, the free software/open source library Mesa 3D is a fully software-based graphics API which is code-compatible with OpenGL. However to avoid licensing costs associated with formally calling itself an OpenGL implementation, it claims merely to be a "very similar" API. The OpenGL specification was revised by OpenGL Architecture Review Board (ARB) founded in 1992. The ARB was formed by a set of companies interested in the creation of a consistent and widely available API. Microsoft, one of the founding members, left the project in 2003. On 21 September 2006, control of OpenGL passed to the Khronos Group.[2] This was done in order to improve the marketing of OpenGL, and to remove barriers between the development of OpenGL and OpenGL ES.[3] The subgroup of Khronos that manages OpenGL was called the OpenGL ARB Working Group,[4] for historical reasons. There is a list of members which make up the OpenGL ARB Working Group at section Members of Khronos Group. OpenGL is a general purpose API with lots of different possibilities because of the great number of companies with different interests which have made up the old ARB and the current group too. Mark Segal and Kurt Akeley authored the original OpenGL specification. Chris Frazier edited version 1.1. Jon Leech edited versions 1.2 through the present version 2.1. Jon Leech has retired as secretary of the old ARB, and Barthold Lichtenbelt has taken his place as Khronos OpenGL ARB Steering Group Chair. Design

OpenGL serves two main purposes: • •

To hide the complexities of interfacing with different 3D accelerators, by presenting the programmer with a single, uniform API. To hide the differing capabilities of hardware platforms, by requiring that all implementations support the full OpenGL feature set (using software emulation if necessary).

OpenGL's basic operation is to accept primitives such as points, lines and polygons, and convert them into pixels. This is done by a graphics pipeline known as the OpenGL state machine. Most OpenGL commands either issue primitives to the graphics pipeline, or configure how the pipeline processes these primitives. Prior to the introduction of OpenGL 2.0, each stage of the pipeline performed a fixed function and was configurable only within tight limits. OpenGL 2.0 offers several stages that are fully programmable using GLSL. OpenGL is a low-level, procedural API, requiring the programmer to dictate the exact steps required to render a scene. This contrasts with descriptive (aka scene graph or retained mode) APIs, where a programmer only needs to describe a scene and can let the library manage the details of rendering it. OpenGL's low-level design requires programmers to have a good knowledge of the graphics pipeline, but also gives a certain amount of freedom to implement novel rendering algorithms. OpenGL has historically been influential on the development of 3D accelerators, promoting a base level of functionality that is now common in consumer-level hardware: •

Rasterised points, lines and polygons as basic primitives

Simplified version of the Graphics Pipeline Process; excludes a number of features like blending, VBOs and logic ops • • • •

A transform and lighting pipeline Z-buffering Texture mapping Alpha blending

A brief description of the process in the graphics pipeline could be:[5] 1. Evaluation, if necessary, of the polynomial functions which define certain inputs, like NURBS surfaces, approximating curves and the surface geometry. 2. Vertex operations, transforming and lighting them depending on their material. Also clipping non visible parts of the scene in order to produce the viewing volume. 3. Rasterisation or conversion of the previous information into pixels. The polygons are represented by the appropriate colour by means of interpolation algorithms. 4. Per-fragment operations, like updating values depending on incoming and previously stored depth values, or colour combinations, among others. 5. At last, fragments are inserted into the Frame buffer. Many modern 3D accelerators provide functionality far above this baseline, but these new features are generally enhancements of this basic pipeline rather than radical reinventions of it. Example This example will draw a green square on the screen. OpenGL has several ways to accomplish this task, but this is the easiest to understand. glClear( GL_COLOR_BUFFER_BIT ); This statement clears the color buffer, so that the screen will start blank. glMatrixMode( GL_PROJECTION ); /* Subsequent matrix commands will affect the projection matrix */ glLoadIdentity(); /* Initialise the projection matrix to identity */ glFrustum( -1, 1, -1, 1, 1, 1000 ); /* Apply a perspective-projection matrix */ These statements initialize the projection matrix, setting a 3d frustum matrix that represents the viewable area. This matrix transforms objects from camerarelative space to OpenGL's projection space. glMatrixMode( GL_MODELVIEW ); /* Subsequent matrix commands will affect the modelview matrix */ glLoadIdentity(); /* Initialise the modelview to identity */ glTranslatef( 0, 0, -3 ); /* Translate the modelview 3 units along the Z axis */ These statements initialize the modelview matrix. This matrix defines a transform from model-relative coordinates to camera space. The combination of the modelview matrix and the projection matrix transforms objects from model-relative space to projection screen space. glBegin( GL_POLYGON ); /* Begin issuing a polygon */ glColor3f( 0, 1, 0 ); /* Set the current color to green */ glVertex3f( -1, -1, 0 ); /* Issue a vertex */ glVertex3f( -1, 1, 0 ); /* Issue a vertex */ glVertex3f( 1, 1, 0 ); /* Issue a vertex */ glVertex3f( 1, -1, 0 ); /* Issue a vertex */ glEnd(); /* Finish issuing the polygon */ These commands draw a green square in the XY plane. Documentation

OpenGL's popularity is partially due to the excellence of its official documentation. The OpenGL ARB released a series of manuals along with the specification which have been updated to track changes in the API. These are almost universally known by the colors of their covers: •

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The Red Book – OpenGL Programming Guide, 5th edition. ISBN 0-321-33573-2 A readable tutorial and reference book – this is a 'must have' book for OpenGL programmers. The first edition is available online here and here. The Blue Book – OpenGL Reference manual, 4th edition. ISBN 0-321-17383-X Essentially a hard-copy printout of the man pages for OpenGL. Includes a postersized fold-out diagram showing the structure of an idealised OpenGL implementation. It is available here . The Green Book – OpenGL Programming for the X Window System. ISBN 0201-48359-9 A book about X11 interfacing and GLUT. The Alpha Book (which actually has a white cover) – OpenGL Programming for Windows 95 and Windows NT. ISBN 0-201-40709-4 A book about interfacing OpenGL with Microsoft Windows.Then, for OpenGL 2.0 and beyond: The Orange Book – The OpenGL Shading Language. ISBN 0-321-33489-2 A readable tutorial and reference book for GLSL

Extensions The OpenGL standard allows individual vendors to provide additional functionality through extensions as new technology is created. Extensions may introduce new functions and new constants, and may relax or remove restrictions on existing OpenGL functions. Each vendor has an alphabetic abbreviation that is used in naming their new functions and constants. For example, NVIDIA's abbreviation (NV) is used in defining their proprietary function glCombinerParameterfvNV() and their constant GL_NORMAL_MAP_NV. It may happen that more than one vendor agrees to implement the same extended functionality. In that case, the abbreviation EXT is used. It may further happen that the Architecture Review Board "blesses" the extension. It then becomes known as a standard extension, and the abbreviation ARB is used. The first ARB extension was GL_ARB_multitexture, introduced in version 1.2.1. Following the official extension promotion path, multitexturing is no longer an optionally implemented ARB extension, but has been a part of the OpenGL core API since version 1.3. Before using an extension a program must first determine its availability, and then obtain pointers to any new functions the extension defines. The mechanism for doing this is platform-specific and libraries such as GLEW and GLEE exist to simplify the process. Specifications for nearly all extensions can be found at the official extension registry Associated utility libraries Several libraries are built on top of or beside OpenGL to provide features not available in OpenGL itself. Libraries such as GLU can always be found with OpenGL

implementations, and others such as GLUT and SDL have grown over time and provide rudimentary cross platform windowing and mouse functionality and if unavailable can easily be downloaded and added to a development environment. Simple graphical user interface functionality can be found in libraries like GLUI or FLTK. Still other libraries like AUX are deprecated and have been superseded by functionality commonly available in more popular libraries, but code using them still exists, particularly in simple tutorials. Other libraries have been created to provide OpenGL application developers a simple means of managing OpenGL extensions and versioning. Examples of these libraries include GLEW (the OpenGL Extension Wrangler Library) and GLEE (the OpenGL Easy Extension Library). In addition to the aforementioned simple libraries, other higher level object oriented scene graph retained mode libraries exist such as PLIB, OpenSG, OpenSceneGraph, and OpenGL Performer. These are available as cross platform free/open source or proprietary programming interfaces written on top of OpenGL and systems libraries to enable the creation of real-time visual simulation applications. Mesa 3D is a free/open source implementation of OpenGL. It supports pure software rendering as well as providing hardware acceleration for several 3D graphics cards under Linux. As of June 22, 2007 it implements the 2.1 standard, and provides some of its own extensions for some platforms. History In the 1980s, developing software that could function with a wide range of graphics hardware was a real challenge. Software developers wrote custom interfaces and drivers for each piece of hardware. This was expensive and resulted in much duplication of effort. By the early 1990s, Silicon Graphics (SGI) was a leader in 3D graphics for workstations. Their IRIS GL API[6] was considered the state of the art and became the de facto industry standard, overshadowing the open standards-based PHIGS. This was because IRIS GL was considered easier to use, and because it supported immediate mode rendering. By contrast, PHIGS was considered difficult to use and outdated in terms of functionality. SGI's competitors (including Sun Microsystems, Hewlett-Packard and IBM) were also able to bring to market 3D hardware, supported by extensions made to the PHIGS standard. This in turn caused SGI market share to weaken as more 3D graphics hardware suppliers entered the market. In an effort to influence the market, SGI decided to turn the IrisGL API into an open standard. SGI considered that the IrisGL API itself wasn't suitable for opening due to licensing and patent issues. Also, the IrisGL had API functions that were not relevant to 3D graphics. For example, it included a windowing, keyboard and mouse API, in part because it was developed before the X Window System and Sun's NeWS systems were developed. In addition, SGI had a large number of software customers; by changing to the OpenGL API they planned to keep their customers locked onto SGI (and IBM)

hardware for a few years while market support for OpenGL matured. Meanwhile, SGI would continue to try to maintain their customers tied to SGI hardware by developing the advanced and proprietary Iris Inventor and Iris Performer programming APIs. As a result, SGI released the OpenGL standard. The OpenGL standardised access to hardware, and pushed the development responsibility of hardware interface programs, sometimes called device drivers, to hardware manufacturers and delegated windowing functions to the underlying operating system. With so many different kinds of graphic hardware, getting them all to speak the same language in this way had a remarkable impact by giving software developers a higher level platform for 3D-software development. In 1992,[7] SGI led the creation of the OpenGL architectural review board (OpenGL ARB), the group of companies that would maintain and expand the OpenGL specification for years to come. OpenGL evolved from (and is very similar in style to) SGI's earlier 3D interface, IrisGL. One of the restrictions of IrisGL was that it only provided access to features supported by the underlying hardware. If the graphics hardware did not support a feature, then the application could not use it. OpenGL overcame this problem by providing support in software for features unsupported by hardware, allowing applications to use advanced graphics on relatively low-powered systems. In 1994 SGI played with the idea of releasing something called "OpenGL++" which included elements such as a scene-graph API (presumably based around their Performer technology). The specification was circulated among a few interested parties – but never turned into a product.[8] Microsoft released Direct3D in 1995, which would become the main competitor of OpenGL. On 17 December 1997[9], Microsoft and SGI initiated the Fahrenheit project, which was a joint effort with the goal of unifying the OpenGL and Direct3D interfaces (and adding a scene-graph API too). In 1998 Hewlett-Packard joined the project.[10] It initially showed some promise of bringing order to the world of interactive 3D computer graphics APIs, but on account of financial constraints at SGI, strategic reasons at Microsoft, and general lack of industry support, it was abandoned in 1999.[11]