Comparison of Direct3D and OpenGL
Encyclopedia
Direct3D and OpenGL are competing application programming interface
s (APIs) which can be used in applications to render 2D and 3D computer graphics
, taking advantage of hardware acceleration when available. Modern graphics processing unit
(GPUs) may implement a particular version of one or both of these APIs.
platform. The OpenGL API is available under an open source
license, and implementations exist for a wide variety of platforms.
In more detail, the two computer graphics APIs are:
Note that many essential OpenGL
extensions and methods, although documented, are actually patented, thus imposing serious legal troubles to implement them (see issues with Mesa).
OpenGL and Direct3D are both implemented in the display driver
. The following compares the two APIs, structured around various considerations mostly relevant to game development.
family of video game console
s and Sega
's Dreamcast. Several mostly functional ports of the Direct3D API have been made by Wine
, a project to port common Windows APIs to Unix-like
operating systems, and Cedega, a proprietary fork of Wine, but this is impeded due to the interdependence of DirectX
on many other components of Windows, and because Direct3D's proprietary nature requires reverse engineering
, a difficult process.
OpenGL has implementations available across many platforms including Microsoft Windows, Unix
-based systems such as Mac OS X
, GNU/Linux
. It is a myth that variants of OpenGL are used on Nintendo and Sony platforms, as they have developed their own libraries. The PlayStation 3
game console has an OpenGL implementation, but it remains unused by most developers due to performance issues. A subset of OpenGL was chosen as the main graphics library for Android, iOS, and Symbian
in the OpenGL ES
form.
Microsoft's OpenGL driver provides no hardware acceleration; support was dropped in Windows XP, not long after they failed to deliver Fahrenheit Low Level support for a OpenGL/DirectX merger in the late 1990s. OpenGL hardware acceleration on Windows is achieved by users first installing installable client drivers (ICDs) developed by GPU
manufacturers. These ICDs are, in virtually all cases, bundled with the standard driver download package from the hardware vendor
(IHV), so installing recent graphics drivers is sufficient to provide hardware OpenGL support.
file in which he urged Microsoft to abandon Direct3D in favor of OpenGL. Chris Hecker
made a similar request in an "Open Letter to Microsoft" in the April–May 1997 issue of Game Developer Magazine.
Version 5 (the second version, named to reflect its release as part of DirectX 5) replaced execute buffers with the new DrawPrimitive API, but it was still considered cumbersome. Chris Hecker's "Open Letter to Microsoft" referred to DrawPrimitive as "an immature and poorly-designed clone of OpenGL that's missing some of the architectural decisions that make OpenGL fast."
Despite the controversy, Microsoft continued to evolve the API. A detailed history of releases and added features is given on the Microsoft Direct3D web pages.
Some former critics of Direct3D acknowledge that now Direct3D is as good if not better than OpenGL in terms of abilities and ease of use. In January 2007, John Carmack said that "…DX9 is really quite a good API
level. Even with the Direct3D
side of things, where I know I have a long history of people thinking I'm antagonistic against it. Microsoft has done a very, very good job of sensibly evolving it at each step—they're not worried about breaking backwards compatibility—and it's a pretty clean API. I especially like the work I'm doing on the 360, and it's probably the best graphics API as far as a sensibly designed thing that I've worked with."
Some design features of Direct3D have remained unchanged since version one, most notably its reliance on Microsoft's COM
. One advantage of using COM is that the API can be used in any COM-aware language, notably Delphi
, and Microsoft Visual C++
, C#, and Visual Basic .NET
.
, though it can use other programming language
s. It is built on the concept of a state machine, though more recent OpenGL versions have transformed it into much more of an object-based system. As an API, OpenGL depends on no particular language feature, and can be made callable from almost any programming language with the proper bindings. Such bindings exist for Ada
, BASIC
(BlitzMax
(often used to program games), PureBasic
, Visual Basic
), C#, Delphi
, Fortran
, Haskell
, Java
, Lisp, Lua, Pascal
, Perl
, Python
, and Ruby
to name some.
As such, there are functional differences in how the two APIs work. Direct3D expects the application to manage hardware resources; OpenGL makes the implementation do it. This tradeoff for OpenGL decreases difficulty in developing for the API, while at the same time increasing the complexity of creating an implementation (or driver) that performs well. With Direct3D, the developer must manage hardware resources independently; however, the implementation is simpler, and developers have the flexibility to allocate resources in the most efficient way possible for their application.
Until about 2005, another functional difference between the APIs was the way they handled rendering to textures. The Direct3D method (SetRenderTarget) is convenient, while prior versions of OpenGL required manipulating pixel buffers (P-buffers). This was cumbersome and risky: if the programmer's codepath was different from that anticipated by the driver maker, the code would have fallen back to software rendering, causing a substantial performance drop. However, widespread support for the "frame buffer objects" extension, which provided an OpenGL equivalent of the Direct3D method, successfully addressed this shortcoming, and the "render target" feature of OpenGL brought OpenGL up to par with Direct3D in this respect.
Outside of a few minor functional differences which have mostly been addressed over the years, the two APIs provide nearly the same level of function. Hardware and software makers generally respond rapidly to changes in DirectX
, e.g. pixel processor and shader requirements in DirectX 9 to stream processors in DirectX 10, while new features in OpenGL
are mainly implemented first by vendors and afterward retroactively applied to the standard.
and SGI
engaged in what has been called the "API
Wars". Much of the argument revolved around which API offered superior performance. This question was relevant due to the very high cost of graphics accelerators
during this time, which meant the consumer market was using software renderers implemented by Microsoft for both Direct3D and OpenGL.
business software such as AutoCAD
and DOS games such as id Software
's Doom originally had to be optimized to run on many different graphics chipsets. When hardware manufacturers such as 3Dlabs
(member of the OpenGL Architecture Review Board
) made OpenGL compatible graphics accelerators (e.g., GLint chip), developers such as John Carmack of id Software optimized their products for OpenGL. As multitasking user environments such as Microsoft Windows
on the PC and the X Window system (X11) on Unix-like
systems became prevalent, the relevance of this hardware faded.
Microsoft had marketed Direct3D as faster based on in-house performance comparisons of these two software libraries. The performance deficit was blamed on the rigorous specification and conformance required of OpenGL. This perception was changed at the 1996 Special Interest Group on GRAPHics and Interactive Techniques (SIGGRAPH
) conference. At that time, SGI
challenged Microsoft with their own optimized Windows software implementation of OpenGL called CosmoGL which in various demos matched or exceeded the performance of Direct3D. For SGI, this was a critical milestone as it showed that OpenGL's poor software rendering performance was due to Microsoft's reference OpenGL implementation, and not due to alleged design flaws in OpenGL itself.
On the other hand, software rendering by the 3D API was largely irrelevant for both Direct3D and OpenGL applications. Not many DirectX applications used Direct3D's software rendering, preferring to perform their own software rendering using DirectDraw
's facilities to access the display hardware. As for OpenGL applications, hardware support was expected, and the hardware was so much faster that software fallback by the OpenGL application constituted a rude surprise to the OpenGL developer.
In any case, by the time SGI had demonstrated that OpenGL software rendering performance could be competitive with that of Direct3D, software rendering was fast becoming irrelevant due to the widespread availability of inexpensive 3D graphics hardware. By 1998, even the S3 ViRGE
graphics accelerator was substantially faster than the fastest Pentium II
running Direct3D's MMX rasterizer
.
drivers are kernel-mode drivers installed into the operating system. The user-mode portion of the API is handled by the DirectX runtime provided by Microsoft. Under OpenGL however, the IHV driver is broken into two parts: a user-mode portion that implements the OpenGL API, and a kernel-mode driver that is called by the user-mode portion.
This is an issue because calling kernel-mode operations from user-mode requires performing a system call
(i.e. making the CPU switch to kernel mode). This is a slow operation, taking on the order of microsecond
s to complete. During this time, the CPU is unable to perform any operations. As such, minimizing the number of times this switching operation must be performed would optimize performance. For example, if the GPU's command buffer is full of rendering data, the API could simply store the requested rendering call in a temporary buffer and, when the command buffer is close to being empty, it can perform a switch to kernel-mode and add a number of stored commands all at once. This is known as marshalling
.
Because Direct3D IHV drivers are kernel-mode, and the user-mode code is out of the IHV's hand, there is no chance for such optimizations to occur. Because the Direct3D runtime, the user-mode portion that implements the API, cannot have explicit knowledge of the driver's inner workings, it cannot effectively support marshalling. This means that every Direct3D call that sends commands to the hardware must perform a kernel-mode switch, which again, takes time in the order of microseconds to complete. This has led to a number of behaviors regarding use of Direct3D, the most important being the need for submitting large batches of triangles in one function call.
Since OpenGL's IHV drivers have a user-mode component to them, IHVs have the ability to implement marshalling, thus improving performance. There is still kernel-mode switching, but the theoretical maximum number of switches under OpenGL implementations is simply equal to the Direct3D standard behavior.
Direct3D 10, the release included with Windows Vista
, allows portions of drivers to run in user-mode, making it possible for IHVs to implement marshalling, thus bringing the two back into relative performance parity. Mac OS X
's OpenGL system is very similar, where IHVs implement a simpler version of the OpenGL API (with both user and kernel mode components), and Apple's additions to the runtime provide the direct interface to the user code, and some basic work to make IHVs' jobs easier.
rendering and the "imaging subset", that were generally considered of limited utility for games - although stereoscopic gaming has drawn a lot more interest as of 2011. The API as a whole contains about 250 calls, but only a subset of perhaps 100 are useful for game development. However, no official gaming-specific subset was ever defined. MiniGL, released by 3Dfx as a stopgap measure to support glQuake, might have served as a starting point, but additional features like stencil were soon adopted by games, and support for the entire OpenGL standard continued. Today, workstations and consumer machines use the same architectures and operating systems, and so modern incarnations of the OpenGL standard still include these features, although only special workstation-class video cards accelerate them.
(ARB), and some are made a core part of future OpenGL revisions.
On the other hand, Direct3D is specified by one vendor only (Microsoft
), leading to a more consistent API, but denying access to vendor-specific features. NVIDIA
's UltraShadow technology, for instance, is not available in the stock Direct3D APIs at the time of writing. It should be noted that Direct3D does support texture format extensions (via FourCC
). These were once little-known and rarely used, but are now used for S3 Texture Compression
.
When graphics cards added support for pixel shaders (known on OpenGL as "fragment programs"), Direct3D provided one "Pixel Shader 1.1" (PS1.1) standard with which the GeForce
3 and up, and Radeon
8500 and up, advertised compatibility. Under OpenGL the same functions were accessed through a variety of custom extensions.
In theory, the Microsoft approach allows one code path to support both brands of card, whereas under OpenGL, programmers must write two separate systems. In reality, though, because of the limits on pixel processing of those early cards, Pixel Shader 1.1 was nothing more than a pseudo-assembly language version of the NVIDIA-specific OpenGL extensions. For the most part, the only cards that claimed PS 1.1 functionality were by NVIDIA, and that is because they were built for it natively. When the Radeon 8500 was released, Microsoft released an update to Direct3D that included Pixel Shader 1.4, which was nothing more than a pseudo-assembly language version of the ATI
-specific OpenGL extensions. The only cards that claimed PS 1.4 support were ATI cards because they were designed with the precise hardware needed to make that functionality happen.
This situation existed only for a short time under both APIs. Second-generation pixel shading cards functioned far more similarly, with each architecture evolving toward the same kind of pixel processing conclusion. As such, Pixel Shader 2.0 allowed a unified code path under Direct3D. Around the same time OpenGL introduced its own ARB-approved vertex and pixel shader extensions (GL_ARB_vertex_program and GL_ARB_fragment_program), and both sets of cards supported this standard also.
, for example.
At one point many professional graphics cards only supported OpenGL, now virtually all professional cards which work on the Windows platform will also support Direct3D. Part of this has been a change in the professional graphics market from largely Unix-based hardware like SGIs and Suns to less expensive PC-based systems, leading to the growth of Windows in this market segment, while at the same time providing a new market for OpenGL software in Unix-based consumer systems running Linux or Apple OS X.
The principle historical reason for OpenGL's dominance in the professional market was performance. Many professional graphics applications (for example, Softimage
|3D, Alias
PowerAnimator
) were originally written in IRIS GL
for high-end SGI workstations, which were far more capable, both graphically and in raw CPU power, than the PCs of the time. Later, many of these were ported to OpenGL, even as the personal computer was evolving into a system powerful enough to run some professional graphics applications. Users were able to run Maya, for example, the successor to Alias
on either SGIs or Windows-based personal computers (and today on Linux, Mac OS X, and Windows). Price competition eventually broke SGI's dominance in the market, but the established base of OpenGL software engineers and the broadening user base for OpenGL in Apple, Linux, and other operating systems, has resulted in a market where both DirectX and OpenGL are viable, widespread APIs.
The other reason for OpenGL's historical advantage was marketing and design. DirectX is a set of APIs that were not marketed towards professional graphics applications. Indeed, they were not even designed with those applications in mind. DirectX was an API designed for low-level, high-performance access to broadly available, lower-performance, consumer-priced graphics hardware for the purpose of game development. OpenGL is a much more general purpose 3D API, targeting a full range of graphics hardware from low-end commodity graphics cards up to professional and scientific graphics visualization well out of the range of the average consumer, and providing features that are not necessarily exclusive towards any particular kind of user.
Gaming developers typically haven't demanded as wide an API as professional graphics system developers. Many games don't need overlay planes, stencils, and so on, although this hasn't prevented some game developers from using them when available. In particular, game designers are rarely interested in the pixel invariance demanded in certain parts of the OpenGL standards, which are conversely highly useful to film and computer-aided modeling.
An attempt was once made to merge OpenGL and DirectX by SGI and Microsoft. The Fahrenheit graphics API
was intended to bring together both the high end capability of OpenGL with the broad low-level support of DirectX. Microsoft eventually retreated from the project, having never allocated sufficient resources to produce its portion of the rendering engine, in a move widely held to be to ensure lock-in of developers to the Window/DirectX platform, which would be lost if the Fahrenheit API became the world de-facto standard graphics API. However, Fahrenheit lead to a number of improvements in DirectX, and the primary architect of Fahrenheit now works at Microsoft on DirectX.
In the console world proprietary native APIs are dominant, with some consoles (e.g. the PS3) providing OpenGL wrappers. The original Xbox supports Direct3D 8.1 as its native API while the Xbox 360 supports a modified version of Direct3D 9.0c as its native API. Most console developers prefer to use the native APIs for each console in order to maximize performance, making OpenGL and Direct3D comparisons primarily relevant for PC platforms.
(also known as OpenGL ES) is a subset of the OpenGL 3D graphics API designed for embedded devices. Various versions of smartphone
operating systems
support OpenGL ES, such as Android, iOS (iPad
, iPhone
, iPod Touch
), Maemo
(Nokia N900
), and Symbian
.
OpenGL ES is available in 3 variants, OpenGL ES 1.0, 1.1, and 2.0. Starting with the release of 2.0, backwards compatibility with older variants was removed, due to the extensive programmable pipeline functions available in GL ES 2.0, over the fixed-pipeline functions of GL ES 1.0 and 1.1.
Direct3D Mobile, a derivative from Direct3D , is supported by Windows CE
. Currently all Windows Phone 7
devices use a .NET Framework
UI accelerated by Direct3D Mobile 9 on Adreno 200 integrated GPUs by Qualcomm.
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
s (APIs) which can be used in applications to render 2D and 3D computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
, taking advantage of hardware acceleration when available. Modern graphics processing unit
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
(GPUs) may implement a particular version of one or both of these APIs.
Availability
Direct3D application development generally targets the Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
platform. The OpenGL API is available under an open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
license, and implementations exist for a wide variety of platforms.
| Direct3D | OpenGL | |
|---|---|---|
| Platform | Microsoft Windows | Cross-platform |
| Mobile Platforms | Direct3D Mobile | OpenGL for Embedded Systems (OpenGL ES OpenGL ES OpenGL for Embedded Systems is a subset of the OpenGL 3D graphics application programming interface designed for embedded systems such as mobile phones, PDAs, and video game consoles. OpenGL ES is managed by the not-for-profit technology consortium, the Khronos Group, Inc.- Versions :Several... ) |
| License | Proprietary | Open source or trademark |
In more detail, the two computer graphics APIs are:
- Direct3D is a proprietaryProprietary softwareProprietary software is computer software licensed under exclusive legal right of the copyright holder. The licensee is given the right to use the software under certain conditions, while restricted from other uses, such as modification, further distribution, or reverse engineering.Complementary...
APIApplication programming interfaceAn application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
that provides functions to render three dimensional graphics, and uses hardware acceleration if it is available on the graphics card. It was designed by Microsoft Corporation for use on the WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
platform. It can also be used on other operating systems through special software such as WineWine (software)Wine is a free software application that aims to allow computer programs written for Microsoft Windows to run on Unix-like operating systems. Wine also provides a software library, known as Winelib, against which developers can compile Windows applications to help port them to Unix-like...
, although the subset of features provided is not as complete as the reference implementation. - OpenGLOpenGLOpenGL is a standard specification defining a cross-language, 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...
is an open standardOpen standardAn open standard is a standard that is publicly available and has various rights to use associated with it, and may also have various properties of how it was designed . There is no single definition and interpretations vary with usage....
API that provides a number of functions to render 2D and 3D graphics, and is available on most modern operating systemOperating systemAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s including but not limited to WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, Mac OS XMac OS XMac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
and GNU/LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
.
Note that many essential OpenGL
OpenGL
OpenGL is a standard specification defining a cross-language, 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...
extensions and methods, although documented, are actually patented, thus imposing serious legal troubles to implement them (see issues with Mesa).
OpenGL and Direct3D are both implemented in the display driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
. The following compares the two APIs, structured around various considerations mostly relevant to game development.
Portability
Direct3D is officially implemented only on Microsoft's Windows family of operating systems, including embedded versions used in the XboxXbox
The Xbox is a sixth-generation video game console manufactured by Microsoft. It was released on November 15, 2001 in North America, February 22, 2002 in Japan, and March 14, 2002 in Australia and Europe and is the predecessor to the Xbox 360. It was Microsoft's first foray into the gaming console...
family of video game console
Video game console
A video game console is an interactive entertainment computer or customized computer system that produces a video display signal which can be used with a display device to display a video game...
s and Sega
Sega
, usually styled as SEGA, is a multinational video game software developer and an arcade software and hardware development company headquartered in Ōta, Tokyo, Japan, with various offices around the world...
's Dreamcast. Several mostly functional ports of the Direct3D API have been made by Wine
Wine (software)
Wine is a free software application that aims to allow computer programs written for Microsoft Windows to run on Unix-like operating systems. Wine also provides a software library, known as Winelib, against which developers can compile Windows applications to help port them to Unix-like...
, a project to port common Windows APIs to Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems, and Cedega, a proprietary fork of Wine, but this is impeded due to the interdependence of DirectX
DirectX
Microsoft DirectX is a collection of application programming interfaces for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay,...
on many other components of Windows, and because Direct3D's proprietary nature requires reverse engineering
Reverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...
, a difficult process.
OpenGL has implementations available across many platforms including Microsoft Windows, Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
-based systems such as Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
, GNU/Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
. It is a myth that variants of OpenGL are used on Nintendo and Sony platforms, as they have developed their own libraries. The PlayStation 3
PlayStation 3
The is the third home video game console produced by Sony Computer Entertainment and the successor to the PlayStation 2 as part of the PlayStation series. The PlayStation 3 competes with Microsoft's Xbox 360 and Nintendo's Wii as part of the seventh generation of video game consoles...
game console has an OpenGL implementation, but it remains unused by most developers due to performance issues. A subset of OpenGL was chosen as the main graphics library for Android, iOS, and Symbian
Symbian
Symbian is a mobile operating system and computing platform designed for smartphones and currently maintained by Accenture. The Symbian platform is the successor to Symbian OS and Nokia Series 60; unlike Symbian OS, which needed an additional user interface system, Symbian includes a user...
in the OpenGL ES
OpenGL ES
OpenGL for Embedded Systems is a subset of the OpenGL 3D graphics application programming interface designed for embedded systems such as mobile phones, PDAs, and video game consoles. OpenGL ES is managed by the not-for-profit technology consortium, the Khronos Group, Inc.- Versions :Several...
form.
Microsoft's OpenGL driver provides no hardware acceleration; support was dropped in Windows XP, not long after they failed to deliver Fahrenheit Low Level support for a OpenGL/DirectX merger in the late 1990s. OpenGL hardware acceleration on Windows is achieved by users first installing installable client drivers (ICDs) developed by GPU
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
manufacturers. These ICDs are, in virtually all cases, bundled with the standard driver download package from the hardware vendor
Independent hardware vendor
An independent hardware vendor is a business term for companies specializing in making or selling computer hardware, usually for niche markets.-See also:*Independent software vendor*Software company...
(IHV), so installing recent graphics drivers is sufficient to provide hardware OpenGL support.
Direct3D
The first version of Direct3D elicited widespread criticism because even simple operations, such as state changes, required creating and submitting objects called "execute buffers". In contrast, in OpenGL most state changes can be performed with one function call. The Direct3D model frustrated many programmers. The most famous complaint was probably made by high-profile game developer John D. Carmack in the .planFinger protocol
In computer networking, the Name/Finger protocol and the Finger user information protocol are simple network protocols for the exchange of human-oriented status and user information.-Name/Finger protocol:...
file in which he urged Microsoft to abandon Direct3D in favor of OpenGL. Chris Hecker
Chris Hecker
-Biography:Hecker was a student at the Parsons School of Design in New York City, studying the fine arts towards work as an illustrator. An article in Byte Magazine sold him on programming and he dropped out of school to begin work on graphics and games....
made a similar request in an "Open Letter to Microsoft" in the April–May 1997 issue of Game Developer Magazine.
Version 5 (the second version, named to reflect its release as part of DirectX 5) replaced execute buffers with the new DrawPrimitive API, but it was still considered cumbersome. Chris Hecker's "Open Letter to Microsoft" referred to DrawPrimitive as "an immature and poorly-designed clone of OpenGL that's missing some of the architectural decisions that make OpenGL fast."
Despite the controversy, Microsoft continued to evolve the API. A detailed history of releases and added features is given on the Microsoft Direct3D web pages.
Some former critics of Direct3D acknowledge that now Direct3D is as good if not better than OpenGL in terms of abilities and ease of use. In January 2007, John Carmack said that "…DX9 is really quite a good API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
level. Even with the Direct3D
Direct3D
Direct3D is part of Microsoft's DirectX application programming interface . Direct3D is available for Microsoft Windows operating systems , and for other platforms through the open source software Wine. It is the base for the graphics API on the Xbox and Xbox 360 console systems...
side of things, where I know I have a long history of people thinking I'm antagonistic against it. Microsoft has done a very, very good job of sensibly evolving it at each step—they're not worried about breaking backwards compatibility—and it's a pretty clean API. I especially like the work I'm doing on the 360, and it's probably the best graphics API as far as a sensibly designed thing that I've worked with."
Some design features of Direct3D have remained unchanged since version one, most notably its reliance on Microsoft's COM
Component Object Model
Component Object Model is a binary-interface standard for software componentry introduced by Microsoft in 1993. It is used to enable interprocess communication and dynamic object creation in a large range of programming languages...
. One advantage of using COM is that the API can be used in any COM-aware language, notably Delphi
Object Pascal
Object Pascal refers to a branch of object-oriented derivatives of Pascal, mostly known as the primary programming language of Embarcadero Delphi.-Early history at Apple:...
, and Microsoft Visual C++
Visual C++
Microsoft Visual C++ is a commercial , integrated development environment product from Microsoft for the C, C++, and C++/CLI programming languages...
, C#, and Visual Basic .NET
Visual Basic .NET
Visual Basic .NET , is an object-oriented computer programming language that can be viewed as an evolution of the classic Visual Basic , which is implemented on the .NET Framework...
.
OpenGL
OpenGL is a specification implemented in the C languageC (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, though it can use other programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
s. It is built on the concept of a state machine, though more recent OpenGL versions have transformed it into much more of an object-based system. As an API, OpenGL depends on no particular language feature, and can be made callable from almost any programming language with the proper bindings. Such bindings exist for Ada
Ada (programming language)
Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages...
, BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
(BlitzMax
Blitz BASIC
Blitz BASIC refers to the programming language dialect that was interpreted by the first Blitz compilers, devised by New Zealand-based developer Mark Sibly. Being derived from BASIC, Blitz syntax was designed to be easy to pick-up for beginners first learning to program...
(often used to program games), PureBasic
PureBasic
PureBasic is a commercially distributed procedural computer programming language and integrated development environment based on BASIC and developed by Fantaisie Software for Windows 32/64-bit, Linux 32/64-bit, and Mac OS X. An Amiga version is available, although it has been discontinued and...
, Visual Basic
Visual Basic
Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model...
), C#, Delphi
Object Pascal
Object Pascal refers to a branch of object-oriented derivatives of Pascal, mostly known as the primary programming language of Embarcadero Delphi.-Early history at Apple:...
, Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
, Haskell
Haskell (programming language)
Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the...
, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
, Lisp, Lua, Pascal
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
, Perl
Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
, Python
Python (programming language)
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
, and Ruby
Ruby (programming language)
Ruby is a dynamic, reflective, general-purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto...
to name some.
Comparison
In general, Direct3D is designed to virtualize 3D hardware interfaces. Direct3D frees the game programmer from accommodating the graphics hardware. OpenGL, on the other hand, is designed to be a 3D hardware-accelerated rendering system that may be emulated in software. These two APIs are fundamentally designed under two separate modes of thought.As such, there are functional differences in how the two APIs work. Direct3D expects the application to manage hardware resources; OpenGL makes the implementation do it. This tradeoff for OpenGL decreases difficulty in developing for the API, while at the same time increasing the complexity of creating an implementation (or driver) that performs well. With Direct3D, the developer must manage hardware resources independently; however, the implementation is simpler, and developers have the flexibility to allocate resources in the most efficient way possible for their application.
Until about 2005, another functional difference between the APIs was the way they handled rendering to textures. The Direct3D method (SetRenderTarget) is convenient, while prior versions of OpenGL required manipulating pixel buffers (P-buffers). This was cumbersome and risky: if the programmer's codepath was different from that anticipated by the driver maker, the code would have fallen back to software rendering, causing a substantial performance drop. However, widespread support for the "frame buffer objects" extension, which provided an OpenGL equivalent of the Direct3D method, successfully addressed this shortcoming, and the "render target" feature of OpenGL brought OpenGL up to par with Direct3D in this respect.
Outside of a few minor functional differences which have mostly been addressed over the years, the two APIs provide nearly the same level of function. Hardware and software makers generally respond rapidly to changes in DirectX
DirectX
Microsoft DirectX is a collection of application programming interfaces for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay,...
, e.g. pixel processor and shader requirements in DirectX 9 to stream processors in DirectX 10, while new features in OpenGL
OpenGL
OpenGL is a standard specification defining a cross-language, 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...
are mainly implemented first by vendors and afterward retroactively applied to the standard.
Performance
Shortly after the establishment of both Direct3D and OpenGL as viable graphics libraries (circa 1995), MicrosoftMicrosoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
and SGI
Silicon Graphics
Silicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...
engaged in what has been called the "API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
Wars". Much of the argument revolved around which API offered superior performance. This question was relevant due to the very high cost of graphics accelerators
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
during this time, which meant the consumer market was using software renderers implemented by Microsoft for both Direct3D and OpenGL.
Early debate
DOSDOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
business software such as AutoCAD
AutoCAD
AutoCAD is a software application for computer-aided design and drafting in both 2D and 3D. It is developed and sold by Autodesk, Inc. First released in December 1982, AutoCAD was one of the first CAD programs to run on personal computers, notably the IBM PC...
and DOS games such as id Software
Id Software
Id Software is an American video game development company with its headquarters in Richardson, Texas. The company was founded in 1991 by four members of the computer company Softdisk: programmers John Carmack and John Romero, game designer Tom Hall, and artist Adrian Carmack...
's Doom originally had to be optimized to run on many different graphics chipsets. When hardware manufacturers such as 3Dlabs
3Dlabs
3DLABS was the name of the fabless semiconductor company that originally developed the GLINT and PERMEDIA high-end graphics chip technology that was used on many of the worlds leading computer graphics cards in the CAD and DCC markets, including its own Wildcat and Oxygen cards.In 2006 the company...
(member of the OpenGL Architecture Review Board
OpenGL Architecture Review Board
The OpenGL Architecture Review Board is an industry consortium that governed the OpenGL specification.It was formed in 1992, and defined the conformance tests, approved the OpenGL specification and advanced the standard...
) made OpenGL compatible graphics accelerators (e.g., GLint chip), developers such as John Carmack of id Software optimized their products for OpenGL. As multitasking user environments such as Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
on the PC and the X Window system (X11) on Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
systems became prevalent, the relevance of this hardware faded.
Microsoft had marketed Direct3D as faster based on in-house performance comparisons of these two software libraries. The performance deficit was blamed on the rigorous specification and conformance required of OpenGL. This perception was changed at the 1996 Special Interest Group on GRAPHics and Interactive Techniques (SIGGRAPH
SIGGRAPH
SIGGRAPH is the name of the annual conference on computer graphics convened by the ACM SIGGRAPH organization. The first SIGGRAPH conference was in 1974. The conference is attended by tens of thousands of computer professionals...
) conference. At that time, SGI
Silicon Graphics
Silicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...
challenged Microsoft with their own optimized Windows software implementation of OpenGL called CosmoGL which in various demos matched or exceeded the performance of Direct3D. For SGI, this was a critical milestone as it showed that OpenGL's poor software rendering performance was due to Microsoft's reference OpenGL implementation, and not due to alleged design flaws in OpenGL itself.
On the other hand, software rendering by the 3D API was largely irrelevant for both Direct3D and OpenGL applications. Not many DirectX applications used Direct3D's software rendering, preferring to perform their own software rendering using DirectDraw
DirectDraw
DirectDraw is part of Microsoft's DirectX API. DirectDraw is used to render graphics in applications where top performance is important. DirectDraw also allows applications to run fullscreen or embedded in a window such as most other MS Windows applications. DirectDraw uses hardware acceleration if...
's facilities to access the display hardware. As for OpenGL applications, hardware support was expected, and the hardware was so much faster that software fallback by the OpenGL application constituted a rude surprise to the OpenGL developer.
In any case, by the time SGI had demonstrated that OpenGL software rendering performance could be competitive with that of Direct3D, software rendering was fast becoming irrelevant due to the widespread availability of inexpensive 3D graphics hardware. By 1998, even the S3 ViRGE
S3 ViRGE
The S3 Virtual Reality Graphics Engine graphics chipset was one of the first 2D/3D accelerators designed for the mass market.-Introduction:...
graphics accelerator was substantially faster than the fastest Pentium II
Pentium II
The Pentium II brand refers to Intel's sixth-generation microarchitecture and x86-compatible microprocessors introduced on May 7, 1997. Containing 7.5 million transistors, the Pentium II featured an improved version of the first P6-generation core of the Pentium Pro, which contained 5.5 million...
running Direct3D's MMX rasterizer
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...
.
Mode switching (on Microsoft Windows)
A more substantive and modern performance difference arises because of the structure of the hardware drivers provided by hardware developers. Under DirectX, IHVIndependent hardware vendor
An independent hardware vendor is a business term for companies specializing in making or selling computer hardware, usually for niche markets.-See also:*Independent software vendor*Software company...
drivers are kernel-mode drivers installed into the operating system. The user-mode portion of the API is handled by the DirectX runtime provided by Microsoft. Under OpenGL however, the IHV driver is broken into two parts: a user-mode portion that implements the OpenGL API, and a kernel-mode driver that is called by the user-mode portion.
This is an issue because calling kernel-mode operations from user-mode requires performing a system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
(i.e. making the CPU switch to kernel mode). This is a slow operation, taking on the order of microsecond
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
s to complete. During this time, the CPU is unable to perform any operations. As such, minimizing the number of times this switching operation must be performed would optimize performance. For example, if the GPU's command buffer is full of rendering data, the API could simply store the requested rendering call in a temporary buffer and, when the command buffer is close to being empty, it can perform a switch to kernel-mode and add a number of stored commands all at once. This is known as marshalling
Marshalling (computer science)
In computer science, marshalling is the process of transforming the memory representation of an object to a data format suitable for storage or transmission...
.
Because Direct3D IHV drivers are kernel-mode, and the user-mode code is out of the IHV's hand, there is no chance for such optimizations to occur. Because the Direct3D runtime, the user-mode portion that implements the API, cannot have explicit knowledge of the driver's inner workings, it cannot effectively support marshalling. This means that every Direct3D call that sends commands to the hardware must perform a kernel-mode switch, which again, takes time in the order of microseconds to complete. This has led to a number of behaviors regarding use of Direct3D, the most important being the need for submitting large batches of triangles in one function call.
Since OpenGL's IHV drivers have a user-mode component to them, IHVs have the ability to implement marshalling, thus improving performance. There is still kernel-mode switching, but the theoretical maximum number of switches under OpenGL implementations is simply equal to the Direct3D standard behavior.
Direct3D 10, the release included with Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
, allows portions of drivers to run in user-mode, making it possible for IHVs to implement marshalling, thus bringing the two back into relative performance parity. Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
's OpenGL system is very similar, where IHVs implement a simpler version of the OpenGL API (with both user and kernel mode components), and Apple's additions to the runtime provide the direct interface to the user code, and some basic work to make IHVs' jobs easier.
Structure
OpenGL, originally designed for then-powerful SGI workstations, includes a number of features, like stereoStereoscopy
Stereoscopy refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the brain to give the perception of 3-D depth...
rendering and the "imaging subset", that were generally considered of limited utility for games - although stereoscopic gaming has drawn a lot more interest as of 2011. The API as a whole contains about 250 calls, but only a subset of perhaps 100 are useful for game development. However, no official gaming-specific subset was ever defined. MiniGL, released by 3Dfx as a stopgap measure to support glQuake, might have served as a starting point, but additional features like stencil were soon adopted by games, and support for the entire OpenGL standard continued. Today, workstations and consumer machines use the same architectures and operating systems, and so modern incarnations of the OpenGL standard still include these features, although only special workstation-class video cards accelerate them.
Extensions
The OpenGL extension mechanism is probably the most heavily disputed difference between the two APIs. OpenGL includes a mechanism where any driver can advertise its own extensions to the API, thus introducing new functions such as blend modes, new ways to transfer data to GPUs, or different texture wrapping parameters. This allows new functions to be exposed quickly, but can lead to confusion if different vendors implement similar extensions with different APIs. Many of these extensions are periodically standardized by the OpenGL Architecture Review BoardOpenGL Architecture Review Board
The OpenGL Architecture Review Board is an industry consortium that governed the OpenGL specification.It was formed in 1992, and defined the conformance tests, approved the OpenGL specification and advanced the standard...
(ARB), and some are made a core part of future OpenGL revisions.
On the other hand, Direct3D is specified by one vendor only (Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
), leading to a more consistent API, but denying access to vendor-specific features. NVIDIA
NVIDIA
Nvidia is an American global technology company based in Santa Clara, California. Nvidia is best known for its graphics processors . Nvidia and chief rival AMD Graphics Techonologies have dominated the high performance GPU market, pushing other manufacturers to smaller, niche roles...
's UltraShadow technology, for instance, is not available in the stock Direct3D APIs at the time of writing. It should be noted that Direct3D does support texture format extensions (via FourCC
FourCC
A FourCC is a sequence of four bytes used to uniquely identify data formats.The concept originated in the OSType scheme used in the Macintosh system software and was adopted for the Amiga/Electronic Arts Interchange File Format and derivatives...
). These were once little-known and rarely used, but are now used for S3 Texture Compression
S3 Texture Compression
S3 Texture Compression is a group of related lossy texture compression algorithms originally developed by Iourcha et al. of S3 Graphics, Ltd. for use in their Savage 3D computer graphics accelerator...
.
When graphics cards added support for pixel shaders (known on OpenGL as "fragment programs"), Direct3D provided one "Pixel Shader 1.1" (PS1.1) standard with which the GeForce
GeForce
GeForce is a brand of graphics processing units designed by Nvidia. , there have been eleven iterations of the design. The first GeForce products were discrete GPUs designed for use on add-on graphics boards, intended for the high-margin PC gaming market...
3 and up, and Radeon
Radeon
Radeon is a brand of graphics processing units and random access memory produced by Advanced Micro Devices , first launched in 2000 by ATI Technologies, which was acquired by AMD in 2006. Radeon is the successor to the Rage line. There are four different groups, which can be differentiated by...
8500 and up, advertised compatibility. Under OpenGL the same functions were accessed through a variety of custom extensions.
In theory, the Microsoft approach allows one code path to support both brands of card, whereas under OpenGL, programmers must write two separate systems. In reality, though, because of the limits on pixel processing of those early cards, Pixel Shader 1.1 was nothing more than a pseudo-assembly language version of the NVIDIA-specific OpenGL extensions. For the most part, the only cards that claimed PS 1.1 functionality were by NVIDIA, and that is because they were built for it natively. When the Radeon 8500 was released, Microsoft released an update to Direct3D that included Pixel Shader 1.4, which was nothing more than a pseudo-assembly language version of the ATI
Ati
As a word, Ati may refer to:* Ati, a town in Chad* Ati, a Negrito ethnic group in the Philippines* Ati-Atihan Festival, an annual celebration held in the Philippines* Ati, a queen of the fabled Land of Punt in Africa...
-specific OpenGL extensions. The only cards that claimed PS 1.4 support were ATI cards because they were designed with the precise hardware needed to make that functionality happen.
This situation existed only for a short time under both APIs. Second-generation pixel shading cards functioned far more similarly, with each architecture evolving toward the same kind of pixel processing conclusion. As such, Pixel Shader 2.0 allowed a unified code path under Direct3D. Around the same time OpenGL introduced its own ARB-approved vertex and pixel shader extensions (GL_ARB_vertex_program and GL_ARB_fragment_program), and both sets of cards supported this standard also.
Professional graphics
OpenGL has always seen more use in the professional graphics market than DirectX, while DirectX is used mostly for computer games. (The term professional is used here to refer to the professional production and display of graphics, such as in computer animated films and scientific visualisation, as opposed to games where the graphics produced are for the end user's personal, rather than professional, use.). Currently both OpenGL and DirectX have a large enough overlap in functionality that either could be used for most common purposes, with the operating system itself often being the primary criterion dictating which is used, with DirectX the common choice on Windows, and OpenGL being used on nearly everything else. Some esoteric applications still divide the applicability of the two APIs: doing accelerated 3D across a network connection is only directly supported by OpenGL with GLXGLX
GLX provides the interface connecting OpenGL and the X Window System: it enables programs wishing to use OpenGL to do so within a window provided by the X Window System.-History:...
, for example.
At one point many professional graphics cards only supported OpenGL, now virtually all professional cards which work on the Windows platform will also support Direct3D. Part of this has been a change in the professional graphics market from largely Unix-based hardware like SGIs and Suns to less expensive PC-based systems, leading to the growth of Windows in this market segment, while at the same time providing a new market for OpenGL software in Unix-based consumer systems running Linux or Apple OS X.
The principle historical reason for OpenGL's dominance in the professional market was performance. Many professional graphics applications (for example, Softimage
Softimage
Softimage, Co. was a company located in Montreal, Quebec, Canada that produced 3D animation software. Their flagship products, Softimage 3D and Softimage XSI, are used in the creation of computer animation for films, television advertisement, and video games...
|3D, Alias
Alias Systems Corporation
Alias Systems Corporation , headquartered in Toronto, Ontario, Canada, was a software company that produced high-end 3D graphics software. The company was formed in 1995 when Silicon Graphics bought Alias Research, which was founded in 1983, and Wavefront Technologies, founded in 1984, then merged...
PowerAnimator
PowerAnimator
PowerAnimator and Animator, also referred to simply as "Alias", the precursor to what is now Maya and StudioTools, was a highly-integrated industrial 3D modeling, animation, and visual effects suite. It has had a long track record, starting with Terminator 2: Judgment Day in 1991 and ending in Star...
) were originally written in IRIS GL
IRIS GL
IRIS GL was a proprietary graphics API created by Silicon Graphics for producing 2D and 3D computer graphics on their IRIX-based IRIS graphical workstations...
for high-end SGI workstations, which were far more capable, both graphically and in raw CPU power, than the PCs of the time. Later, many of these were ported to OpenGL, even as the personal computer was evolving into a system powerful enough to run some professional graphics applications. Users were able to run Maya, for example, the successor to Alias
Alias Systems Corporation
Alias Systems Corporation , headquartered in Toronto, Ontario, Canada, was a software company that produced high-end 3D graphics software. The company was formed in 1995 when Silicon Graphics bought Alias Research, which was founded in 1983, and Wavefront Technologies, founded in 1984, then merged...
on either SGIs or Windows-based personal computers (and today on Linux, Mac OS X, and Windows). Price competition eventually broke SGI's dominance in the market, but the established base of OpenGL software engineers and the broadening user base for OpenGL in Apple, Linux, and other operating systems, has resulted in a market where both DirectX and OpenGL are viable, widespread APIs.
The other reason for OpenGL's historical advantage was marketing and design. DirectX is a set of APIs that were not marketed towards professional graphics applications. Indeed, they were not even designed with those applications in mind. DirectX was an API designed for low-level, high-performance access to broadly available, lower-performance, consumer-priced graphics hardware for the purpose of game development. OpenGL is a much more general purpose 3D API, targeting a full range of graphics hardware from low-end commodity graphics cards up to professional and scientific graphics visualization well out of the range of the average consumer, and providing features that are not necessarily exclusive towards any particular kind of user.
Gaming developers typically haven't demanded as wide an API as professional graphics system developers. Many games don't need overlay planes, stencils, and so on, although this hasn't prevented some game developers from using them when available. In particular, game designers are rarely interested in the pixel invariance demanded in certain parts of the OpenGL standards, which are conversely highly useful to film and computer-aided modeling.
An attempt was once made to merge OpenGL and DirectX by SGI and Microsoft. The Fahrenheit graphics API
Fahrenheit graphics API
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. Much of the original Fahrenheit project was abandoned, and Microsoft and SGI...
was intended to bring together both the high end capability of OpenGL with the broad low-level support of DirectX. Microsoft eventually retreated from the project, having never allocated sufficient resources to produce its portion of the rendering engine, in a move widely held to be to ensure lock-in of developers to the Window/DirectX platform, which would be lost if the Fahrenheit API became the world de-facto standard graphics API. However, Fahrenheit lead to a number of improvements in DirectX, and the primary architect of Fahrenheit now works at Microsoft on DirectX.
Gaming
In the earliest days of 3D accelerated gaming, performance and reliability were key benchmarks and several 3D accelerator cards competed against each other for dominance. Software was written specifically for a particular brand of graphics card. However, over the years, OpenGL and Direct3D emerged as software layers above the hardware, mainly because of industry support for a cross-hardware graphics library. Competition between the two rose as each game developer would choose either one or the other.In the console world proprietary native APIs are dominant, with some consoles (e.g. the PS3) providing OpenGL wrappers. The original Xbox supports Direct3D 8.1 as its native API while the Xbox 360 supports a modified version of Direct3D 9.0c as its native API. Most console developers prefer to use the native APIs for each console in order to maximize performance, making OpenGL and Direct3D comparisons primarily relevant for PC platforms.
Mobile phones and other embedded devices
OpenGL for Embedded SystemsOpenGL ES
OpenGL for Embedded Systems is a subset of the OpenGL 3D graphics application programming interface designed for embedded systems such as mobile phones, PDAs, and video game consoles. OpenGL ES is managed by the not-for-profit technology consortium, the Khronos Group, Inc.- Versions :Several...
(also known as OpenGL ES) is a subset of the OpenGL 3D graphics API designed for embedded devices. Various versions of smartphone
Smartphone
A smartphone is a high-end mobile phone built on a mobile computing platform, with more advanced computing ability and connectivity than a contemporary feature phone. The first smartphones were devices that mainly combined the functions of a personal digital assistant and a mobile phone or camera...
operating systems
Mobile operating system
A mobile operating system, also known as a mobile OS, mobile software platform or a handheld operating system, is the operating system that controls a mobile device or information appliance—similar in principle to an operating system such as Windows, Mac OS X, or Linux distributions that controls a...
support OpenGL ES, such as Android, iOS (iPad
IPad
The iPad is a line of tablet computers designed, developed and marketed by Apple Inc., primarily as a platform for audio-visual media including books, periodicals, movies, music, games, and web content. The iPad was introduced on January 27, 2010 by Apple's then-CEO Steve Jobs. Its size and...
, iPhone
IPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...
, iPod Touch
IPod Touch
The iPod Touch is a portable media player, personal digital assistant, handheld game console, and Wi-Fi mobile device designed and marketed by Apple Inc. The iPod Touch adds the multi-touch graphical user interface to the iPod line...
), Maemo
Maemo
Maemo is a software platform developed by the Maemo community for smartphones and Internet tablets. It is based on the Debian Linux distribution, but has no relation to it...
(Nokia N900
Nokia N900
The Nokia N900 is a smartphone made by Nokia. It supersedes the Nokia N810. Its default operating system, Maemo 5, is a Linux-based OS originally developed for the Nokia 770 Internet Tablet. It is the first Nokia device based upon the Texas Instruments OMAP3 microprocessor with the ARM Cortex-A8...
), and Symbian
Symbian
Symbian is a mobile operating system and computing platform designed for smartphones and currently maintained by Accenture. The Symbian platform is the successor to Symbian OS and Nokia Series 60; unlike Symbian OS, which needed an additional user interface system, Symbian includes a user...
.
OpenGL ES is available in 3 variants, OpenGL ES 1.0, 1.1, and 2.0. Starting with the release of 2.0, backwards compatibility with older variants was removed, due to the extensive programmable pipeline functions available in GL ES 2.0, over the fixed-pipeline functions of GL ES 1.0 and 1.1.
Direct3D Mobile, a derivative from Direct3D , is supported by Windows CE
Windows CE
Microsoft Windows CE is an operating system developed by Microsoft for embedded systems. Windows CE is a distinct operating system and kernel, rather than a trimmed-down version of desktop Windows...
. Currently all Windows Phone 7
Windows Phone 7
Windows Phone is a mobile operating system developed by Microsoft, and is the successor to its Windows Mobile platform, although incompatible with it. Unlike its predecessor, it is primarily aimed at the consumer market rather than the enterprise market...
devices use a .NET Framework
.NET Framework
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
UI accelerated by Direct3D Mobile 9 on Adreno 200 integrated GPUs by Qualcomm.
See also
- Direct3D
- Fahrenheit graphics APIFahrenheit graphics APIFahrenheit 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. Much of the original Fahrenheit project was abandoned, and Microsoft and SGI...
- Glide APIGlide APIGlide is a 3D graphics API developed by 3dfx Interactive for their Voodoo Graphics 3D accelerator cards. Although it originally started as a proprietary API, it was later open sourced by 3dfx. It was dedicated to gaming performance, supporting geometry and texture mapping primarily, in data...
- OpenGLOpenGLOpenGL is a standard specification defining a cross-language, 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...
- RRedline
- WebGLWebGLWebGL is a software library that extends the capability of the JavaScript programming language to allow it to generate interactive 3D graphics within any compatible web browser...