Sound.OpenAL.ALC.Device

This module corresponds to section 6.1 (Managing Devices) of the OpenAL Specification and Reference (version 1.1).

ALC introduces the notion of a device. A device can be, depending on the implementation, a hardware device, or a daemon/OS service/actual server. This mechanism also permits different drivers (and hardware) to coexist within the same system, as well as allowing several applications to share system resources for audio, including a single hardware output device. The details are left to the implementation, which has to map the available backends to unique device specifiers.

Documentation

data Device

The abstract device type.

Instances

Eq Device

Ord Device

Show Device

openDevice :: Maybe String -> IO (Maybe Device)

openDevice allows the application (i.e. the client program) to connect to a device (i.e. the server). If the function returns Nothing, then no sound driver/device has been found. The argument to openDevice specifies a certain device or device configuration. If it is Nothing, the implementation will provide an implementation specific default, see defaultDeviceSpecifier. Otherwise it is Just an implementation-dependent string. You can use allDeviceSpecifiers to get a list of the known OpenAL devices.

Notes for Windows: There are 3 possible device strings, each having a deprecated equivalent for legacy applications only:

• "Generic Hardware" (legacy string: "DirectSound3D")
• "Generic Software" (legacy string: "DirectSound")
• "Generic Software Fallback" (legacy string: "MMSYSTEM")

Notes for Linux\*nix:/ If an .openalrc file is present in the user's home directory, it is loaded first, otherwise /etc/openalrc is tried. The bindings (if any) of devices, direction, sampling-rate, and speaker-num (see below) after loading one of these files take precedence over any bindings done via the argument to openDevice.

The syntax of these files is lisp-based and a sequence of expressions, where an expression is one the following:

• A boolean value of the form #f or #t, which evaluate to false and true, respectively.
• An non-negative integer value, i.e. a sequence of decimal digits, evaluating to itself.
• A (signed) floating point value, as recoginzed by C's atof(), evaluating to itself.
• A pointer value of the form #pnum, where num can be an octal, decimal or hexadecimal value, as recoginzed by C`s strtol(), evaluating to itself. This kind of expression is currently unused.
• A string, i.e. a sequence of printable/whitespace characters between double quotes, evaluating to itself.
• A symbol, i.e. a sequence of almost all characters which don't form a simple expression like the ones mentioned below, e.g. foo, bar1, 3baz, ... The symbol evaluates to the value currently bound to it.
• A function application of the form (symbol expression...). The function bound to the symbol is applied to the evaluated arguments.
• A quotation of the form (quote expression) or 'expression, evaluating to the unevaluated expression itself.
• A definition of the form (define symbol expression), binding symbol to the value of expression. The whole expression evaluates to the value of expression, too.
• A conjunction of boolean expressions of the form (and expression...). Each expression is evaluated in turn, and if one of them evaluates to false, the value of the whole expression is false. Otherwise the value is true.
• An extension loading mechanism of the form (load-extension libraryName), where libraryName has to evaluate to a string. This tries to load the dynamic library with up to 3 special entry points: alExtension_03282000 (pointing to a mandatory NULL-terminated sequence of pairs of pointers to names and extension functions), alExtInit_03282000 (an optional initialization function), and alExtFini_03282000 (an optional cleanup function). If the extension could be loaded successfully, the whole expression evaluates to true, otherwise to false.

Some symbols have a special meaning for OpenAL:

devices

Has the form (devspec...), where devspec is either a symbol/string specifying a device or (device device-param...), specifying a device with additional parameters. These optional device parameters are stored in a variable device-params, but are currently unused. The first device which can successfully opened is used.

direction

Type string or symbol: "read" specifies that the device should be an input device, everything else means output device (default).

sampling-rate

Type integer or float: Specifies the internal mixing frequency, default is 44.1kHz.

speaker-num

Type integer or float: Specifies the number of speakers, which can be 1, 2 (default), or 4.

alsa-device

Type string, alsa backend only: Specifies both alsa-out-device and alsa-in-device, default "plughw:0,0".

alsa-out-device

Type string, alsa backend only: Specifies the ALSA output device, defaults to the value of alsa-device.

alsa-in-device

Type string, alsa backend only: Specifies the ALSA input device, defaults to the value of alsa-device.

native-in-device

Type string, native backend on IRIX only.

native-out-device

Type string, native backend on IRIX only.

native-rear-out-device

Type string, native backend on IRIX only.

native-use-select

Type boolean, native backend on Linux only: If #t, wait up to 0.8sec for the device to become ready for writing. If #f, just try to write and hope it won't hang forever. The latter might be necessary for some drivers which don't implement select() , like some Aureal drivers.

lin-dsp-path

Type string, native backend on Linux only: Path to DSP device for writing, tried before /dev/sound/dsp and /dev/sound if set.

lin-dsp-read-path

Type string, native backend on Linux only: Path to DSP device for reading, tried before /dev/sound/dsp and /dev/sound if set. Defaults to the value of lin-dsp-path.

native-backend-debug

Type boolean, native backend on Darwin only: If set to #f, be a bit verbose on stderr about what's going on in the backend.

source-rolloff-factor

Type integer or float: Value of the initial rolloff factor for sources, default is 1.0.

listener-position

List of 3 integers or floats: Value of the initial listener position, default is (0 0 0).

listener-velocity

List of 3 integers or floats: Value of the initial listener velocity, default is (0 0 0).

listener-orientation

List of 6 integers or floats: Value of the initial listener orientation (at/up), default is (0 0 -1 0 1 0).

The string given to openDevice has to be of the form '((symbol expression) ...), which means basically a sequence of define expressions. Example:

 "'((sampling-rate 8000) (native-backend-debug #f))"

Note: The information above has been reverse-engineered from the OpenAL SI and could be inaccurate. Any corrections and/or additions are highly welcome.

closeDevice :: Device -> IO Bool

closeDevice allows the application (i.e. the client program) to disconnect from a device (i.e. the server). It returns True for success and False for failure. Once closed, the Device is invalid.

Note: Older OpenAL implementations will always report a success!

defaultDeviceSpecifier :: GettableStateVar (Maybe String)

Contains Just the specifier string for the default device or Nothing if there is no sound support at all.

deviceSpecifier :: Device -> GettableStateVar String

Contains the specifier string for the given device.

allDeviceSpecifiers :: GettableStateVar [String]

Contains a list of specifiers for all available devices.