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<chapter id="arts-apis">
<title>&arts; Application Programming Interfaces</title>
<sect1 id="api-overview">
<title>Overview</title>
<para>
aRts is not only a piece of software, it also provides a variety of APIs
for a variety of purposes. In this section, I will try to describe the "big
picture", a brief glance what those APIs are supposed to do, and how they
interact.
</para>
<para>
There is one important distinction to make: most of the APIs are <emphasis>
language and location independant</emphasis> because they are specified as
<emphasis>mcopidl</emphasis>.
That is, you can basically use the services they offer from any language,
implement them in any language, and you will not have to care whether you
are talking to local or remote objects. Here is a list of these first:
</para>
<variablelist>
<varlistentry>
<term>core.idl</term>
<listitem><para>
Basic definitions that form the core of the MCOP functionality, such as
the protocol itself, definitions of the object, the trader, the flow
system and so on.
</para></listitem>
</varlistentry>
<varlistentry>
<term>artsflow.idl</term>
<listitem><para>
These contain the flow system you will use for connecting audio streams, the
definition of <emphasis>Arts::SynthModule</emphasis> which is the base for
any interface that has streams, and finally a few useful audio objects
</para></listitem>
</varlistentry>
<varlistentry>
<term>kmedia2.idl</term>
<listitem><para>
Here, an object that can play a media, <emphasis>Arts::PlayObject</emphasis>
gets defined. Media players such as the KDE media player noatun will be able
to play any media for which a PlayObject can be found. So it makes sense to
implement PlayObjects for various formats (such as mp3, mpg video, midi, wav,
...) on that base, and there are a lot already.
</para></listitem>
</varlistentry>
<varlistentry>
<term>soundserver.idl</term>
<listitem><para>
Here, an interface for the system wide sound server artsd is defined. The
interface is called <emphasis>Arts::SoundServer</emphasis>, which implements
functionality like accepting streams from the network, playing samples,
creating custom other aRts objects and so on. Network transparency is
implied due to the use of MCOP (as for everything else here).
</para></listitem>
</varlistentry>
<varlistentry>
<term>artsbuilder.idl</term>
<listitem><para>
This module defines basic flow graph functionality, that is, combining
simpler objects to more complex ones, by defining a graph of them. It defines
the basic interface <emphasis>Arts::StructureDesc</emphasis>,
<emphasis>Arts::ModuleDesc</emphasis> and <emphasis>Arts::PortDesc</emphasis>
which contain a description of a structure, module, and port. There is also
a way to get a "living network of objects" out of these connection and value
descriptions, using a factory.
</para></listitem>
</varlistentry>
<varlistentry>
<term>artsmidi.idl</term>
<listitem><para>
This module defines basic midi functionality, like objects that produce
midi events, what is a midi event, an <emphasis>Arts::MidiManager</emphasis>
to connect the producers and consumers of midi events, and so on. As always
network transparency implied.
</para></listitem>
</varlistentry>
<varlistentry>
<term>artsmodules.idl</term>
<listitem><para>
Here are various additional filters, oscillators, effects, delays and
so on, everything required for real useful signal processing, and to
build complex instruments and effects out of these basic building blocks.
</para></listitem>
</varlistentry>
<varlistentry>
<term>artsgui.idl</term>
<listitem><para>
This cares about visual objects. It defines the basic type <emphasis>
Arts::Widget</emphasis> from which all GUI modules derive. This will produce
toolkit independency, and ... visual GUI editing, and serializable GUIs.
Also, as the GUI elements have normal attributes, their values can be
straight forward connected to some signal processing modules. (I.e. the
value of a slider to the cutoff of a filter). As always: network transparent.
</para></listitem>
</varlistentry>
</variablelist>
<para>
Where possible, aRts itself is implemented using IDL. On the other hand, there
are some <emphasis>language specific</emphasis> APIs, using either plain C++ or
plain C. It is usually wise to use IDL interfaces where possible, and the
other APIs where necessary. Here is a list of language specific APIs:
</para>
<variablelist>
<varlistentry>
<term>KNotify, KAudioPlayer (included in libkdecore)</term>
<listitem><para>
These are convenience KDE APIs for the simple and common common case, where
you just want to play a sample. The APIs are plain C++, Qt/KDE optimized,
and as easy as it can get.
</para></listitem>
</varlistentry>
<varlistentry>
<term>libartsc</term>
<listitem><para>
Plain C interface for the sound server. Very useful for porting legacy
applications.
</para></listitem>
</varlistentry>
<varlistentry>
<term>libmcop</term>
<listitem><para>
Here all magic for MCOP happens. The library contains the basic things you
need to know for writing a simple MCOP application, the dispatcher, timers,
iomanagement, but also the internals to make the MCOP protocol itself work.
</para></listitem>
</varlistentry>
<varlistentry>
<term>libartsflow</term>
<listitem><para>
Besides the implementation of artsflow.idl, some useful utilities like
sampling rate conversion.
</para></listitem>
</varlistentry>
<varlistentry>
<term>libqiomanager</term>
<listitem><para>
Integration of MCOP into the Qt event loop, when you write Qt applications
using MCOP.
</para></listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1 id="knotify">
<title>knotify</title>
<para>
</para>
</sect1>
<sect1 id="kaudioplayer">
<title>kaudioplayer</title>
<para>
</para>
</sect1>
<sect1 id="libkmid">
<title>libkmid</title>
<para>
</para>
</sect1>
<sect1 id="kmedia2">
<title>kmedia2</title>
<para>
</para>
</sect1>
<sect1 id="soundserver">
<title>sound server</title>
<para>
</para>
</sect1>
<sect1 id="artsflow">
<title>artsflow</title>
<para>
</para>
</sect1>
<sect1 id="capi">
<title>C <acronym>API</acronym></title>
<sect2 id="capiintro">
<title>Introduction</title>
<para> The &arts; C <acronym>API</acronym> was designed to make it easy to
writing and port plain C applications to the &arts; sound server. It provides
streaming functionality (sending sample streams to
<application>artsd</application>), either blocking or non-blocking. For most
applications you simply remove the few system calls that deal with your audio
device and replace them with the appropriate &arts; calls.</para>
<para>I did two ports as a proof of concept: <application>mpg123</application>
and <application>quake</application>. You can get the patches from <ulink
url="http://space.twc.de/~stefan/kde/download/artsc-patches.tar.gz">here</ulink>.
Feel free to submit your own patches to the maintainer of &arts; or of
multimedia software packages so that they can integrate &arts; support into
their code.</para>
</sect2>
<sect2 id="capiwalkthru">
<title>Quick Walkthrough</title>
<para>Sending audio to the sound server with the <acronym>API</acronym> is very
simple:</para>
<procedure>
<step><para>include the header file using <userinput>#include
<artsc.h></userinput></para></step>
<step><para>initialize the <acronym>API</acronym> with
<function>arts_init()</function></para></step>
<step><para>create a stream with
<function>arts_play_stream()</function></para></step>
<step><para>configure specific parameters with
<function>arts_stream_set()</function></para></step>
<step><para>write sampling data to the stream with
<function>arts_write()</function></para></step>
<step><para>close the stream with
<function>arts_close_stream()</function></para></step>
<step><para>free the <acronym>API</acronym> with
<function>arts_free()</function></para></step>
</procedure>
<para>Here is a small example program that illustrates this:</para>
<programlisting>
#include <stdio.h>
#include <artsc.h>
int main()
{
arts_stream_t stream;
char buffer[8192];
int bytes;
int errorcode;
errorcode = arts_init();
if (errorcode < 0)
{
fprintf(stderr, "arts_init error: %s\n", arts_error_text(errorcode));
return 1;
}
stream = arts_play_stream(44100, 16, 2, "artsctest");
while((bytes = fread(buffer, 1, 8192, stdin)) > 0)
{
errorcode = arts_write(stream, buffer, bytes);
if(errorcode < 0)
{
fprintf(stderr, "arts_write error: %s\n", arts_error_text(errorcode));
return 1;
}
}
arts_close_stream(stream);
arts_free();
return 0;
}
</programlisting>
</sect2>
<sect2 id="capiartscconfig">
<title>Compiling and Linking: <application>artsc-config</application></title>
<para>To easily compile and link programs using the &arts; C
<acronym>API</acronym>, the <application>artsc-config</application> utility is
provided which knows which libraries you need to link and where the includes
are. It is called using</para>
<screen>
<userinput><command>artsc-config</command> <option>--libs</option></userinput>
</screen>
<para>to find out the libraries and </para>
<screen>
<userinput><command>artsc-config</command> <option>--cflags</option></userinput>
</screen>
<para>to find out additional C compiler flags. The example above could have been
compiled using the command line:</para>
<screen>
<userinput><command>cc</command> <option>-o artsctest artsctest.c `artsc-config --cflags` `artsc-config --libs`</option></userinput>
<userinput><command>cc</command> <option>-o artsctest</option> <option>artsctest.c</option> <option>`artsc-config --cflags`</option> <option>`artsc-config --libs`</option></userinput>
</screen>
</sect2>
<sect2 id="c-api-reference">
<title>Library Reference</title>
<para>
[TODO: generate the documentation for artsc.h using kdoc]
</para>
</sect2>
</sect1>
</chapter>
