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846 lines
33 KiB
Text
846 lines
33 KiB
Text
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<chapter id="alc">
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<title>AL Contexts and the ALC API</title>
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<para>
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This section of the AL specification describes ALC, the AL Context API.
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ALC is a portable API for managing &AL; contexts, including
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resource sharing, locking, and unlocking. Within the core AL API the
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existence of a Context is implied, but the Context is not exposed. The
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Context encapsulates the state of a given intance of the AL state machine.
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</para>
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<para>
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To avoid confusion with the AL related prefixes implied throughout
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this document, the "alc" and "ALC_" prefixes have been made explicit
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in the ALC related sections.
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</para>
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<para>
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ALC defines the following objects: Contexts.
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</para>
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<![ %Annote [
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<note><title>Annotation (ALC entry points)</title><para>
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While the actual ALC implemention might be supplied
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as a separate library, or as part of a server or
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daemon, the specification requires that the AL library
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provides the actual ALC entry points.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (ALC OS independend)</title><para>
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ALC is meant to be OS-independent. OS specifics are
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expected to be adressed by defining proper device
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specifiers strings, and configuration attributes.
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In this, ALC differs from GLX/WGL, which (due to the
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tighter coupling with the window manager and
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operating system) attempt to abstract OS specifics
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to a much lesser degree.
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</para></note>
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]]>
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<![ %RFC [
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<note id="rfc-bk001024-02"><title>RFC/ Issues </title><para>
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Hardware init/deinit, mapping many processes with
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multiple contexts to many devices, sharing resources
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among processes.
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</para></note>
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]]>
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<sect1>
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<title>Managing Devices</title>
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<para>
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ALC introduces the notion of a Device. A Device can be,
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depending on the implementation, a hardware device, or
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a daemon/OS service/actual server. This mechanism also
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permits different drivers (and hardware) to coexist
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within the same system, as well as allowing several
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applications to share system resources for audio, including
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a single hardware output device. The details are left
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to the implementation, which has to map the available
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backends to uniq7ue device specifiers (represented as
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strings).
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</para>
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<![ %Annote [
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<note><title>Annotation (Network transparency)</title><para>
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&AL; is meant for interoperability with &OGL;. Some
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implementations of &OGL; bindings (e.g. GLX) are network
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transparent. The Device API theoretically allows for
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a network transparent AL implementation. No wire protocol
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is specified, no specification or implementation is planned.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Device Enumeration)</title><para>
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At this time, ALC does not provide mechanism to query
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for available devices, and request device enumerations.
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This might be added at a later time, depending on demand
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and the ability to abstract OS and configuration specifics.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (X11 Audio)</title><para>
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The ALC API intentionally mimicks XOpenDisplay
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and XCloseDisplay. There is no X Audio standard,
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although proposals have been made in the past.
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The ALC API design accounts for this possibility
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in a minimal way.
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</para></note>
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]]>
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<sect2>
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<title>Connecting to a Device</title>
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<para>
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The alcOpenDevice function allows the application (i.e. the
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client program) to connect to a device (i.e. the server).
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<funcsynopsis><funcprototype>
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<funcdef> &device; * <function>alcOpenDevice</function></funcdef>
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<paramdef> const &ubyte;* <parameter>deviceSpecifier</parameter></paramdef>
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</funcprototype></funcsynopsis>
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If the function returns NULL, then no sound driver/device has
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been found. The argument is a null terminated string that requests
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a certain device or device configuration. If NULL is specified,
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the implementation will provide an implementation specific default.
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</para>
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<![ %Annote [
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<note><title>Annotation (Operating system dependencies)</title><para>
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At this point, system specific configuration, and operating system
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specific details, are handled by leaving the details of the
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string specifier to the implementation. The application coder
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has to determine how he wants to obtain this information from the
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OS or the user. If, at a later point, device enumeration and
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configuration requests are supported through ALC, the resulting
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string might still be operating system and implementation specific.
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</para></note>
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]]>
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</sect2>
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<sect2>
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<title>Disconnecting from a Device</title>
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<para>
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The alcCloseDevice function allows the application (i.e. the
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client program) to disconnect from a device (i.e. the server).
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<funcsynopsis><funcprototype>
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<funcdef> &void; <function>alcCloseDevice</function></funcdef>
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<paramdef> &device; * <parameter>deviceHandle</parameter></paramdef>
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</funcprototype></funcsynopsis>
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If deviceHandle is NULL or invalid, an ALC_INVALID_DEVICE error
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will be generated. Once closed, a deviceHandle is invalid.
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</para>
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</sect2>
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</sect1>
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<sect1>
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<title>Managing Rendering Contexts</title>
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<para>
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All operations of the AL core API affect a current AL context.
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Within the scope of AL, the ALC is implied - it is not visible as
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a handle or function parameter. Only one AL Context per INprocess
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can be current at a time. Applications maintaining multiple
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AL Contexts, whether threaded or not, have to set the current
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context accordingly. Applications can have multiple threads
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that share one more or contexts. In other words, AL and ALC are
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threadsafe.
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</para>
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<para>
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The default AL Context interoperates with a hardware device driver.
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The application manages hardware and driver resources by
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communicating through the ALC API, and configures and uses
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such Contexts by issuing AL API calls. A default AL Context
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processes AL calls and sound data to generate sound output.
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Such a Context is called a Rendering Context. There might
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be non-rendering contexts in the future.
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</para>
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<para>
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The word "rendering" was chosen intentionally to emphasize the
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primary objective of the AL API - spatialized sound - and the
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underlying concept of AL as a sound synthesis pipeline that
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simulates sound propagation by specifying spatial arrangements
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of listeners, filters, and sources. If used in describing an
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application that uses both &OGL; and &AL;, "sound rendering
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context" and "graphics rendering context" should be used for
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clarity. Throughout this document, "rendering" is used
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to describe spatialized audio synthesis (avoiding ambiguous
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words like "processing", as well as proprietary and restrictive
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terms like "wavetracing").
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</para>
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<sect2>
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<title>Context Attributes</title>
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<para>
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The application can choose to specify certain attributes for
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a context. Attributes not specified explicitely are set to
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implementation dependend defaults.
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</para>
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<para>
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<table>
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<title>Context Attributes</title>
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<tgroup cols="2" align="left" colsep=1 rowsep=1>
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<colspec colname=c1>
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<colspec colname=c2>
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<thead>
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<row>
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<entry>Name</>
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<entry>Description</>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>ALC_FREQUENCY</>
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<entry>Frequency for mixing output buffer, in units of Hz.</>
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</row>
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<row>
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<entry>ALC_REFRESH</>
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<entry>Refresh intervalls, in units of Hz.</>
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</row>
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<row>
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<entry>ALC_SYNC</>
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<entry>Flag, indicating a synchronous context.</>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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<![ %Annote [
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<note><title>Annotation (Refresh Control)</title><para>
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Applications might have a fixed, or bounded, schedule for
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state changes (e.g. synchronously with the GL framerate).
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In this case it is desirable to specify the mixahead
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interval (milliseconds), or refresh rate (Hz), for the
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mixing thread. This is especially important for a synchronous
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context, where the application has to specify the refresh
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interval it intends to keep.
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</para></note>
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]]>
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<![ %RFC [
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<note id="rfc-bk001026-05"><title>RFC / Mixing Buffer Configuration </title><para>
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ALC_RESOLUTION was originally used to specify the accuracy of the
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mixing output buffer. For the time being this is not supported, but
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could be added if mixing path and result accuracy control is desirable
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to scale resource requirements.
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A full ALC_FORMAT (including channel and other attributes) does not
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make sense for rendering contexts, but will be necessary for PBuffers
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(mix to memory).
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</para></note>
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]]>
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<![ %RFC [
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<note id="rfc-bk001026-01"><title>RFC / LOKI extensions </title><para>
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<programlisting>
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ALC_SOURCES_HINT_LOKI, /* # of sources to pre-allocate */
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ALC_BUFFERS_HINT_LOKI, /* # of buffers to pre-allocate */
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ALC_CD_LOKI, /* demand CD/DVD control */
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</programlisting>
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</para></note>
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]]>
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</sect2>
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<sect2>
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<title>Creating a Context</title>
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<para>
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A context is created using alcCreateContext. The device parameter
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has to be a valid device. The attribute list can be NULL,
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or a zero terminated list of integer pairs composed of valid
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ALC attribute tokens and requested values.
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<funcsynopsis><funcprototype>
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<funcdef> &context; * <function> alcCreateContext </function></funcdef>
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<paramdef> const &device; * <parameter> deviceHandle </parameter></paramdef>
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<paramdef> ∫ * <parameter> attrList </parameter></paramdef>
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</funcprototype></funcsynopsis>
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Context creation will fail
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if the application requests attributes that, by themselves,
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can not be provided. Context creation will fail if the
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combination of specified attributes can not be provided.
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Context creation will fail if a specified attribute, or
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the combination of attributes, does not match the default
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values for unspecified attributes.
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</para>
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</sect2>
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<sect2>
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<title>Selecting a Context for Operation</title>
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<para>
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To make a Context current with respect to AL Operation (state
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changes by issueing commands), alcMakeContextCurrent is used.
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The context parameter can be NULL or a valid context pointer.
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The operation will apply to the device that the context was
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created for.
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<funcsynopsis><funcprototype>
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<funcdef> &bool; <function> alcMakeContextCurrent </function></funcdef>
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<paramdef> &context; * <parameter> context </parameter></paramdef>
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</funcprototype></funcsynopsis>
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For each OS process (usually this means for each application), only
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one context can be current at any given time. All AL commands apply
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to the current context. Commands that affect objects shared among
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contexts (e.g. buffers) have side effects on other contexts.
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</para>
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<![ %Annote [
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<note><title>Annotation (No Explicit Device)</title><para>
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An ALC context is bound to the device it was created for.
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The context carries this information, thus removing the
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need to specify the device explicitely. Contexts can not
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be made current for any other device aside from the one
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they were created for.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (No Multiple Current)</title><para>
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There is only one current context per process, even
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in multithreaded applications, even if multiple
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devices are used.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Current NULL)</title><para>
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The implementation is encouraged to exploit optimizations
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possible if the application sets the current context
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to NULL, indicating that no state changes are intended
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for the time being. The application should not set the
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current context to NULL if more state changes are
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pending on the most recent, or another context created
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for the same device.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Shared Objects)</title><para>
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Buffers are shared among contexts. As mutiple contexts
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can exist at the same time, the state of shared objects
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is also shared among contexts.
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</para></note>
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]]>
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<![ %RFC [
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<note id="rfc-bk001026-06"><title>RFC / Buffer Deletion </title><para>
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Buffers that have not yet been processed in another context
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can not be deleted from any other context.
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</para></note>
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]]>
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</sect2>
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<sect2>
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<title>Initiate Context Processing</title>
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<para>
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The current context is the only context accessible to state
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changes by AL commands (aside from state changes affecting
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shared objects). However, multiple contexts can be processed
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at the same time. To indicate that a context should be
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processed (i.e. that internal execution state like offset
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increments are supposed to be performed), the application
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has to use alcProcessContext.
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<funcsynopsis><funcprototype>
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<funcdef> &void; <function>alcProcessContext</function></funcdef>
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<paramdef> &context; * <parameter> context </parameter></paramdef>
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</funcprototype></funcsynopsis>
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Repeated calls to alcProcessContext are legal, and do not
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affect a context that is already marked as processing. The
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default state of a context created by alcCreateContext is
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that it is not marked as processing.
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</para>
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<![ %Annote [
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<note><title>Annotation (Sync and async implementations)</title><para>
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Unfortunately, the exact semantics of alcProcessContext is
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not independend of the implementation. Ideally it should be completely
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transparent to the application whether the sound driver is threaded or
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synced. Unfortunately a synced context has to have its execution
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initiated by the application, which requires calls of
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alcProcessContext timed in accordance to the drivers mixahead,
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or the rendering buffer will underflow. For a threaded driver,
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the implementation is free to consider alcProcessContext
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a NOP once the context has been marked as processing.
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</para><para>
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One consequence is that an application that was developed
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using a threaded implementation of AL might not work
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properly with a synchronous implementation of AL (on
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the other hand, an AL application that works using a
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synchronous implementation is guaranteed to work with
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a threaded implementation.
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</para><para>
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Enforcing alcProcessContext calls would defeat the purpose
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of a threaded implementation. Permitting the AL implementation
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to e.g. schedule optimizations based on alcProcessContext
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calls would similarly obfuscate the exact semantincs.
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Consequently, the application coder has to accept this
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implementation dependency, and has to rely on the ALC_SYNC
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attribute to explicitely request a synchronous implementation.
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The implementation can expect the application to be aware
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of the additonal constraints imposed on alcProcessContext in
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this case.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Multiple Contexts and SYNC refresh)</title><para>
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The application can request SYNC contexts or threaded contexts,
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however, the implementation is not obliged to provide both, or provide
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a mixture of both on the same device.
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</para></note>
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]]>
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<![ %RFC [
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<note id="rfc-bk001024-03"><title>RFC/ Implications for Networking</title><para>
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What does alcProcessContext imply for networking?
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For AL, will we add alFlush/alFinish?
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</para></note>
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]]>
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</sect2>
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<sect2>
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<title>Suspend Context Processing</title>
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<para>
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The application can suspend any context from processing
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(including the current one). To indicate that a context should be
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suspended from processing (i.e. that internal execution state like
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offset increments is not supposed to be changed), the application
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has to use alcSuspendContext.
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<funcsynopsis><funcprototype>
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<funcdef> &void; <function>alcSuspendContext</function></funcdef>
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<paramdef> &context; * <parameter> context </parameter></paramdef>
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</funcprototype></funcsynopsis>
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Repeated calls to alcSuspendContext are legal, and do not
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affect a context that is already marked as suspended. The
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default state of a context created by alcCreateContext is
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that it is marked as suspended.
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</para>
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<![ %Annote [
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<note><title>Annotation (Sync and async implementations)</title><para>
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Unfortunately, the exact semantics of alcSuspendContext is
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also not independend of the implementation. For a threaded
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implementation, alcSuspendContext is necessary to ensure a context
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is not processed. For a synchronous implementation, omitting
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alcProcessContext calls will ultimately have the same effect,
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but will also generate rendering buffer underflow errors.
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Again, the application coder that requests a synchronous
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context using ALC_SYNC has to make sure that alcSuspendContext
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is used accordingly.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Suspending vs. Muting a context)</title><para>
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By setting Listener GAIN to zero, an application can mute a
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context, and expect the implementation to bypass all rendering.
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However, the context is still processing, and the internal
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execution state is still updated accordingly. Suspending a
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context, whether muted or not, will incidentally suspend rendering
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as well. However, it is the application's responsibility to
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prevent artifacts (e.g. by proper GAIN control to fade in and
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out). It is recommended to mute a context before suspending.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Current Context Suspended)</title><para>
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It is possible to make a suspended context current, or
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suspend the current context. In this case, the implementation
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is still obliged to immediately verify AL commands as they
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are issued, and generate errors accordingly. The implementation
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is permitted to postpone propagating the actual state changes
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until the context is marked for processing again, with the
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exception of dereferencing data (e.g. buffer contents).
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For efficiency reasons (memory usage), most if not all
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AL commands applied to a suspended context will usually
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be applied immediately. State changes will have to be applied
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in the sequence they were requested. It is possible to
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use suspension of a current context as an explicit locking
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(to enforce apparent synchronicity), but execution is still
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guaranteed to be in sequence, and the implementation is not
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expected to optimize this operation. A typical use would
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be setting up the initial configuration while loading a
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scene.
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</para></note>
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]]>
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<![ %Annote [
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<note><title>Annotation (Release of Hardware Resources)</title><para>
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The specification does not guarantee that the implementation
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will release hardware resources used by a suspended context.
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This might well depend on the details of the hardware and driver.
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Neither a muted context nor a suspended context can be expected
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to free device resources. If all contexts for a given device
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are suspended, and no context of this device is current, the
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implementation is expected to release all hardware resources if possible.
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</para></note>
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]]>
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</sect2>
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<sect2>
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<title>Destroying a Context</title>
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<para>
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<funcsynopsis><funcprototype>
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<funcdef> &void; <function> alcDestroyContext </function></funcdef>
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<paramdef> &context; * <parameter> context </parameter></paramdef>
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</funcprototype></funcsynopsis>
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|
The correct way to destroy a context is to first release it using
|
|
alcMakeCurrent and NULL. Applications should not attempt to destroy
|
|
a current context.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
|
|
|
|
<sect1>
|
|
<title>ALC Queries</title>
|
|
|
|
<sect2>
|
|
<title>Query for Current Context</title>
|
|
<para>
|
|
The application can query for, and obtain an handle to, the current
|
|
context for the application. If there is no current context, NULL is
|
|
returned.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef> &context; * <function>alcGetCurrentContext</function></funcdef>
|
|
<void>
|
|
</funcprototype></funcsynopsis>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Query for a Context's Device</title>
|
|
<para>
|
|
The application can query for, and obtain an handle to, the device
|
|
of a given context.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef> &device; * <function>alcGetContextsDevice</function></funcdef>
|
|
<paramdef> &context; * <parameter> context </parameter></paramdef>
|
|
</funcprototype></funcsynopsis>
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2>
|
|
<title>Query For Extensions</title>
|
|
<para>
|
|
To verify that a given extension is available for the current
|
|
context and the device it is associated with, use
|
|
<funcsynopsis>
|
|
<funcprototype>
|
|
<funcdef>&bool;<function>IsExtensionPresent</function></funcdef>
|
|
<paramdef> const &device; * <parameter>deviceHandle</parameter></paramdef>
|
|
<paramdef>const &ubyte; * <parameter> extName </parameter></paramdef>
|
|
</funcprototype>
|
|
</funcsynopsis>
|
|
A NULL name argument returns FALSE, as do invalid and unsupported string
|
|
tokens. A NULL deviceHandle will result in an INVALID_DEVICE error.
|
|
<![ %Annote [
|
|
<note><title>Annotation (Exlicit Device Parameter)</title><para>
|
|
Certain ALC Extensions might be relevant to context creation
|
|
(like additional attributes, or support for unusual multi-context
|
|
combinations), thus the application might have to query these
|
|
before a context is created. On the other hand, ALC Extensions
|
|
are specific to the device.
|
|
</para></note>
|
|
]]>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Query for Function Entry Addresses</title>
|
|
<para>
|
|
The application is expected to verify the applicability of
|
|
an extension or core function entry point before requesting
|
|
it by name, by use of alcIsExtensionPresent.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef> &void; * <function> alcGetProcAddress</function></funcdef>
|
|
<paramdef> const &device; * <parameter>deviceHandle</parameter></paramdef>
|
|
<paramdef> const &ubyte; * <parameter> funcName </parameter></paramdef>
|
|
</funcprototype></funcsynopsis>
|
|
Entry points can be device specific, but are not context specific.
|
|
Using a NULL device handle does not guarantee that the entry
|
|
point is returned, even if available for one of the available
|
|
devices. Specifying a NULL name parameter will cause an
|
|
ALC_INVALID_VALUE error.
|
|
</para>
|
|
|
|
</sect2>
|
|
<sect2>
|
|
<title>Retrieving Enumeration Values</title>
|
|
<para>
|
|
Enumeration/token values are device independend, but tokens
|
|
defined for extensions might not be present for a given device.
|
|
Using a NULL handle is legal, but only the tokens defined by
|
|
the AL core are guaranteed. Availability of extension tokens
|
|
dependends on the ALC extension.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef> &uint; <function> alcGetEnumValue </function></funcdef>
|
|
<paramdef> const &device; * <parameter>deviceHandle</parameter></paramdef>
|
|
<paramdef> const &ubyte; <parameter> enumName </parameter></paramdef>
|
|
</funcprototype></funcsynopsis>
|
|
Specifying a NULL name parameter will cause an
|
|
ALC_INVALID_VALUE error.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Query for Error Conditions</title>
|
|
<para>
|
|
ALC uses the same conventions and mechanisms as AL for error
|
|
handling. In particular, ALC does not use conventions
|
|
derived from X11 (GLX) or Windows (WGL).
|
|
The alcGetError function can be used to query ALC errors.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef>&enum;<function>alcGetError</function></funcdef>
|
|
<paramdef> &device; * <parameter>deviceHandle</parameter></paramdef>
|
|
</funcprototype></funcsynopsis>
|
|
Error conditions are specific to the device.
|
|
</para>
|
|
|
|
<para>
|
|
<table>
|
|
<title>Error Conditions</title>
|
|
<tgroup cols="2" align="left" colsep=1 rowsep=1>
|
|
<colspec colname=c1>
|
|
<colspec colname=c2>
|
|
<thead>
|
|
<row>
|
|
<entry>Name</>
|
|
<entry>Description</>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>ALC_NO_ERROR</>
|
|
<entry>The device handle or specifier does name an accessible driver/server.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_INVALID_DEVICE</>
|
|
<entry>The Context argument does not name a valid context.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_INVALID_CONTEXT</>
|
|
<entry>The Context argument does not name a valid context.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_INVALID_ENUM</>
|
|
<entry>A token used is not valid, or not applicable.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_INVALID_VALUE</>
|
|
<entry>An value (e.g. attribute) is not valid, or not applicable.</>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
|
|
|
|
<![ %Annote [
|
|
<note><title>Annotation (No UNDERFLOW error)</title><para>
|
|
Applications using synchronous (and, depending on CPU
|
|
load, even an asynchronous implementation itself) might
|
|
fail to prevent underflow of the rendering output
|
|
buffer. No ALC error is generated in these cases,
|
|
as it this error condition can not be applied to a
|
|
specific command.
|
|
</para></note>
|
|
]]>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>String Query</title>
|
|
<para>
|
|
The application can obtain certain strings from ALC.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef>const &ubyte; * <function>alcGetString</function></funcdef>
|
|
<paramdef> &device; * <parameter>deviceHandle</parameter></paramdef>
|
|
<paramdef> &enum; <parameter> token </parameter></paramdef>
|
|
</funcprototype></funcsynopsis>
|
|
For some tokens, NULL is is a legal value for the deviceHandle.
|
|
In other cases, specifying a NULL device will generate an
|
|
ALC_INVALID_DEVICE error.
|
|
</para>
|
|
<para>
|
|
<table>
|
|
<title>String Query Tokens</title>
|
|
<tgroup cols="2" align="left" colsep=1 rowsep=1>
|
|
<colspec colname=c1>
|
|
<colspec colname=c2>
|
|
<thead>
|
|
<row>
|
|
<entry>Name</>
|
|
<entry>Description</>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>ALC_DEFAULT_DEVICE_SPECIFIER</>
|
|
<entry>The specifier string for the default device (NULL handle is legal).</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_DEVICE_SPECIFIER</>
|
|
<entry>The specifier string for the device (NULL handle is not legal).</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_EXTENSIONS</>
|
|
<entry>The extensions string for diagnostics and printing.</>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
|
|
<para>
|
|
In addition, printable error message strings are provided for
|
|
all valid error tokens, including ALC_NO_ERROR, ALC_INVALID_DEVICE,
|
|
ALC_INVALID_CONTEXT, ALC_INVALID_ENUM, ALC_INVALID_VALUE.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Integer Query</title>
|
|
<para>
|
|
The application can query ALC for information using an integer
|
|
query function.
|
|
<funcsynopsis><funcprototype>
|
|
<funcdef> &void; <function>alcGetIntegerv</function></funcdef>
|
|
<paramdef> &device; * <parameter>deviceHandle</parameter></paramdef>
|
|
<paramdef> &enum; <parameter> token </parameter></paramdef>
|
|
<paramdef> &sizei; <parameter> size </parameter></paramdef>
|
|
<paramdef> ∫ <parameter> dest </parameter></paramdef>
|
|
</funcprototype></funcsynopsis>
|
|
For some tokens, NULL is a legal deviceHandle. In other
|
|
cases, specifying a NULL device will generate an ALC_INVALID_DEVICE
|
|
error. The application
|
|
has to specify the size of the destination buffer provided.
|
|
A NULL destination or a zero size parameter will cause ALC to ignore
|
|
the query.
|
|
</para>
|
|
|
|
<para>
|
|
<table>
|
|
<title>Integer Query Tokens</title>
|
|
<tgroup cols="2" align="left" colsep=1 rowsep=1>
|
|
<colspec colname=c1>
|
|
<colspec colname=c2>
|
|
<thead>
|
|
<row>
|
|
<entry>Name</>
|
|
<entry>Description</>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>ALC_MAJOR_VERSION</>
|
|
<entry>Major version query.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_MINOR_VERSION</>
|
|
<entry>Minor version query.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_ATTRIBUTES_SIZE</>
|
|
<entry>The size required for the zero-terminated attributes
|
|
list, for the current context. NULL is an invalid
|
|
device. NULL (no current context for the
|
|
specified device) is legal.</>
|
|
</row>
|
|
<row>
|
|
<entry>ALC_ALL_ATTRIBUTES</>
|
|
<entry>Expects a destination of ALC_CURRENT_ATTRIBUTES_SIZE,
|
|
and provides the attribute list for the current
|
|
context of the specified device. NULL is an invalid
|
|
device. NULL (no current context for the
|
|
specified device) will return the default attributes
|
|
defined by the specified device.</>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</para>
|
|
|
|
<![ %Annote [
|
|
<note><title>Annotation (Backward Compatibility)</title><para>
|
|
Backward compatibility is guaranteed only for minor revisions.
|
|
Breaking ABI backwards compatibility will require a issuing
|
|
major revision.
|
|
</para></note>
|
|
]]>
|
|
|
|
<![ %RFC [
|
|
<note id="rfc-bk001026-02"><title>RFC / Version Matching </title><para>
|
|
The ALC version can be different from the AL version.
|
|
The ALC major version has to be identical between
|
|
application and driver (client and server).
|
|
The ALC minor version can differ between client and server,
|
|
and the minimum of the two minor version numbers is returned.
|
|
</para></note>
|
|
]]>
|
|
|
|
<![ %RFC [
|
|
<note id="rfc-bk001027-03"><title>RFC / Device Enumeration </title><para>
|
|
ALC_NUM_DEVICE_SPECIFIERS could be provided as an extension,
|
|
but it requires the number of device configurations to be
|
|
finite and small, as they are to be represented by strings.
|
|
</para></note>
|
|
]]>
|
|
|
|
</sect2>
|
|
</sect1>
|
|
|
|
|
|
|
|
<sect1>
|
|
<title>Shared Objects</title>
|
|
<para>
|
|
For efficiency reasons, certain AL objects are shared across
|
|
ALC contexts. At this time, AL buffers are the only shared
|
|
objects.
|
|
</para>
|
|
|
|
<![ %RFC [
|
|
<note id="rfc-bk001024-01"><title>RFC/ Sharing Sources?</title><para>
|
|
Mike Kelly from Dynamix describes an application scenario with
|
|
multiple camera views of the same scene (implemented using
|
|
several viewports on a single, "split screen", context)
|
|
in which he needs multiple listeners (one per view) to
|
|
preceive the same sources, with the rendering results of
|
|
each listener to mixed for a single output device. As an
|
|
alternative to permitting multiple listeners within a context,
|
|
it might be preferable to introduce a mechanism to explicitely
|
|
share certain AL objects among contexts, at a later time.
|
|
It is not desirable to share Sources by default, especially
|
|
as the more common multi-listener application is expected to
|
|
maintain listeners with disjunct sets of sources.
|
|
</para></note>
|
|
]]>
|
|
<sect2>
|
|
<title>Shared Buffers</title>
|
|
<para>
|
|
Buffers are shared among contexts. The processing state of a buffer
|
|
is determined by the dependencies imposed by all contexts, not just
|
|
the current context. This includes suspended contexts as well as
|
|
contexts that are processing.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
|
|
</chapter>
|