Sound.OpenAL.ALC.Context

This module corresponds to section 6.2 (Managing Rendering Contexts) of the OpenAL Specification and Reference (version 1.1).

All operations of the AL core API affect a current AL context. Within the scope of AL, the ALC is implied - it is not visible as a handle or function parameter. Only one AL Context per process can be current at a time. Applications maintaining multiple AL Contexts, whether threaded or not, have to set the current context accordingly. Applications can have multiple threads that share one more or contexts. In other words, AL and ALC are threadsafe.

Documentation

type Frequency = Float

Frequency, specified in samples per second, i.e. units of Hertz [Hz]. Note that the underlying OpenAL API currently uses integral frequencies only, but we want to mirror physical reality here more closely.

data ContextAttribute

The application can choose to specify certain attributes for a context at context-creation time. Attributes not specified explicitly are set to implementation dependent defaults.

Constructors

Frequency Frequency

Frequency for mixing output buffer, in units of Hz

Refresh Frequency

Refresh intervals, in units of Hz

Sync Bool

Flag, indicating a synchronous context

MonoSources Int

A hint indicating how many sources should be capable of supporting mono data

StereoSources Int

A hint indicating how many sources should be capable of supporting stereo data

Instances

Eq ContextAttribute

Ord ContextAttribute

Show ContextAttribute

data Context

The abstract context type.

Instances

Eq Context

Ord Context

Show Context

createContext :: Device -> [ContextAttribute] -> IO (Maybe Context)

Create a context for a given device and given attributes. Context creation will fail in the following cases: a) if the application requests attributes that, by themselves, can not be provided b) if the combination of specified attributes can not be provided c) if a specified attribute, or the combination of attributes, does not match the default values for unspecified attributes If context creation fails, Nothing will be returned, otherwise Just the new context. Note that createContext does not set the current context, this must be done separately via currentContext.

currentContext :: StateVar (Maybe Context)

Contains Just the current context with respect to OpenAL operation, or Nothing if there is no current context. Setting it to the latter is useful when shutting OpenAL down. The state variable applies to the device that the context was created for. For each OS process (usually this means for each application), only one context can be current at any given time. All AL commands apply to the current context. Commands that affect objects shared among contexts (e.g. buffers) have side effects on other contexts.

processContext :: Context -> IO ()

The current context is the only context accessible to state changes by AL commands (aside from state changes affecting shared objects). However, multiple contexts can be processed at the same time. To indicate that a context should be processed (i.e. that internal execution state like offset increments are supposed to be performed), the application has to use processContext. Repeated calls to processContext are legal, and do not affect a context that is already marked as processing. The default state of a context created by createContext is that it is processing.

suspendContext :: Context -> IO ()

The application can suspend any context from processing (including the current one). To indicate that a context should be suspended from processing (i.e. that internal execution state like offset increments is not supposed to be changed), the application has to use suspendContext. Repeated calls to suspendContext are legal, and do not affect a context that is already marked as suspended.

destroyContext :: Context -> IO ()

Destroy the given context. Note that the the correct way to destroy a context is to first release it by setting currentContext to Nothing. Applications should not attempt to destroy a current context, doing so will not work and will result in an ALCInvalidOperation error.

contextsDevice :: Context -> GettableStateVar (Maybe Device)

Contains Just the device of the given context or Nothing if the context is invalid.

allAttributes :: Device -> GettableStateVar [ContextAttribute]

Contains the attribute list for the current context of the specified device.