|Maintainer||Sven Panne <email@example.com>|
A convenience module, combining the Haskell bindings for AL and ALC.
A Brief History of OpenAL
The first discussions about implementing OpenAL as an audio API complimentary to OpenGL started around 1998. There were a few aborted attempts at creating the headers and a specification, but by late 1999 Loki Entertainment Software was in need for an API of exactly this type and pursued both a specification and a Linux implementation. At around that time, Loki started talking with Creative Labs about standardizing the API and expanding platform support. The OpenAL 1.0 specification was released in early 2000 and compliant OpenAL libraries were released in the same year for Linux, MacOS 8/9, Windows, and BeOS. Loki Entertainment also shipped several games using OpenAL in 2000: Heavy Gear 2 and Heretic 2 (both under Linux). In 2001, Creative Labs released the first hardware-accelerated OpenAL libraries. The libraries supported the SoundBlaster Live on MacOS 8/9 and Windows.
Since 2001, there has been continuous improvement in OpenAL. Some platforms are less relevant than in 2000 (BeOS and MacOS 8/9 for instance), but more platforms have been added as well (BSD, Solaris, IRIX, Mac OS X, and the popular console gaming platforms). Hardware support is enabled for many Creative and NVIDIA audio devices under Windows as well.
In terms of product support, OpenAL has been used in a large number of titles over the years, on many platforms (for a list of many of the titles, see http://www.openal.org/titles.html).
What is the OpenAL Audio System?
OpenAL (for Open Audio Library) is a software interface to audio hardware. The interface consists of a number of functions that allow a programmer to specify the objects and operations in producing high-quality audio output, specifically multichannel output of 3D arrangements of sound sources around a listener.
The OpenAL API is designed to be cross-platform and easy to use. It resembles the OpenGL API in coding style and conventions. OpenAL uses a syntax resembling that of OpenGL where applicable. For more information on OpenGL, see http://www.opengl.org/ and the Graphics.Rendering.OpenGL module.
OpenAL is foremost a means to generate audio in a simulated three-dimensional space. Consequently, legacy audio concepts such as panning and left/right channels are not directly supported. OpenAL does include extensions compatible with the IA-SIG 3D Level 1 and Level 2 rendering guidelines to handle sound-source directivity and distancerelated attenuation and Doppler effects, as well as environmental effects such as reflection, obstruction, transmission, reverberation. For more information on IA-SIG 3D, see http://www.iasig.org/wg/closed/3dwg/3dwg.shtml.
Like OpenGL, the OpenAL core API has no notion of an explicit rendering context, and operates on an implied current OpenAL Context. Unlike the OpenGL specification, the OpenAL specification includes both the core API (the actual OpenAL API, see Sound.OpenAL.AL) and the operating system bindings of the ALC API (the Audio Library Context, see Sound.OpenAL.ALC). Unlike OpenGL's GLX, WGL and other OS-specific bindings, the ALC API is portable across platforms as well.
Different Views of OpenAL
Programmer's View of OpenAL
To the programmer, OpenAL is a set of commands that allow the specification of sound sources and a listener in three dimensions, combined with commands that control how these sound sources are rendered into the output buffer. The effect of OpenAL commands is not guaranteed to be immediate, as there are latencies depending on the implementation, but ideally such latency should not be noticeable to the user.
A typical program that uses OpenAL begins with calls to open a sound device which is used to process output and play it on attached hardware (speakers or headphones). Then, calls are made to allocate an AL context and associate it with the device. Once an AL context is allocated, the programmer is free to issue AL commands. Some calls are used to render sources (point and directional sources, looping or not), while others affect the rendering of these sources including how they are attenuated by distance and relative orientation.
Implementor's View of OpenAL
To the implementor, OpenAL is a set of commands that affect the operation of CPU and sound hardware. If the hardware consists only of an addressable output buffer, then OpenAL must be implemented almost entirely on the host CPU. In some cases audio hardware provides DSP-based and other acceleration in various degrees. The OpenAL implementor's task is to provide the CPU software interface while dividing the work for each AL command between the CPU and the audio hardware. This division should be tailored to the available audio hardware to obtain optimum performance in carrying out AL calls.
OpenAL maintains a considerable amount of state information. This state controls how the sources are rendered into the output buffer. Some of this state is directly available to the user: he or she can make calls to obtain its value. Some of it, however, is visible only by the effect it has on what is rendered. One of the main goals of the OpenAL specification is to make OpenAL state information explicit, to elucidate how it changes, and to indicate what its effects are.
The Specification's View of OpenAL
The OpenAL specification (see http://www.openal.org/documentation.html) views OpenAL as a state machine that controls a multichannel processing system to synthesize a digital stream, passing sample data through a chain of parametrized digital audio signal processing operations. This model should engender a specification that satisfies the needs of both programmers and implementors. It does not, however, necessarily provide a model for implementation. Any proper implementation must produce results conforming to those produced by the methods specified in the OpenAL specification, but there may be ways to carry out a particular computation that are more efficient than the one specified.
The documentation is more or less based upon the OpenAL 1.1 Specification and Reference, which is in turn based upon the older OpenAL Specification and Reference (1.0), published in June 2000. Both copyright notices are presented below:
Version 1.1: Published June 2005, Copyright (c) 2005 by authors
Version 1.0 Draft Edition: Published June 2000, Copyright (c) 1999-2000 by Loki Software
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the copyright owners.
BeOS is a trademark of PalmSource, Inc. Linux is a trademark of Linus Torvalds. Macintosh and Apple are trademarks of Apple Computer, Inc. OpenAL is a trademark of Creative Labs, Inc. OpenGL is a trademark of Silicon Graphics, Inc. UNIX is a trademark of X/Open Group. Windows is a trademark of Microsoft Corp. X Window System is a trademark of X Consortium, Inc. All other trademarks are property of their respective owners.