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<p align="center" class="title"><span class="title"><font size="5">Single Static
Source</font></span><font size="4"><br>
<b>Lesson 1</b></font></p>
<p align="center" class="title"><b><font size="4">from <a href="http://www.devmaster.net">DevMaster.net</a></font></b></p>
<p align="center" class="title"> <span class="author">Author: <a href="mailto:lightonthewater@hotmail.com"><font color="#888888">Jesse
Maurais</font></a> </span><br>
Adapted for Java by: <a href="mailto:athomas@dev.java.net"><font color="#888888">Athomas Goldberg</font></a></p>
<p>Welcome to the exciting world of OpenAL! OpenAL
is still in a stage of growth, and even though there is an ever larger following
to the API it still hasn't reached it's full potential. One of the big reasons
for this is that there is still not yet hardware acceleration built in for
specific cards. However, Creative Labs is a major contributor to the OpenAL
project and also happens to be one of the largest soundcard manufacturers. So
there is a promise of hardware accelerated features in the near future. OpenAL's
only other major contributor, Loki, has gone the way of the dinosaur. So the
future of OpenAL on Linux platforms is uncertain. You can still obtain the Linux
binaries on some more obscure websites.</p>
<p>OpenAL has also not been seen in many major
commercial products, which may have also hurt it's growth. As far as I know the
only pc game to use OpenAL has been Metal Gear 2 (although recently I've
discovered that Unreal 2 does as well). The popular modeling program, Blender3D,
was also known to use OpenAL for all it's audio playback. Aside from these
however the only other OpenAL uses have been in the sdk examples and a few
obscure tutorials on the internet.</p>
<p>But lets face it, OpenAL has a lot of
potential. There are many other audio libraries that claim to work with the
hardware on a lower level (and this may be true), but the designers of OpenAL
did several things in it's design which make it a superior API. First of all
they emulated the OpenGL API which is one of the best ever designed. The API
style is flexible, so different coding methods and hardware implementations will
take advantage of this. People who have had a lot of experience with OpenGL will
be able to pick up OpenAL quite fast. OpenAL also has the advantage of creating
3D surround sound which a lot of other API's cannot boast. On top of all of that
it also has the ability to extend itself into EAX and AC3 flawlessly. To my
knowledge no other audio library has that capability.</p>
<p>If you still haven't found a reason here to use
OpenAL then here's another. It's just cool. It's a nice looking API and will
integrate well into your code. You will be able to do many cool sound effects
with it. But before we do that we have to learn the basics.</p>
<p>So let's get coding!</p>
<pre class=code><font color="#0000FF">import</font> net.java.games.joal.*;
<font color="#0000FF">import</font> net.java.games.joal.util.*;
<font color="#0000FF">import</font> java.io.*;
<font color="#0000FF">import</font> java.nio.ByteBuffer;</pre>
<pre class=code><font color="#0000FF">public</font> <font color="#0000FF">class</font> SingleStaticSource {
<font color="#0000FF"><span class=codeComment>static</span></font><span class=codeComment> AL al = ALFactory.getAL();
<font color="#006600">// Buffers hold sound data.</font></span>
<font color="#0000FF">static int</font>[] buffer = new <font color="#0000FF">int</font>[1];;
<span class=codeComment> <font color="#006600">// Sources are points emitting sound.</font></span>
<font color="#0000FF">static int</font>[] source = <font color="#0000FF">new</font> <font color="#0000FF">int</font>[1];
</pre>
<p>Those familiar with OpenGL know that it uses "texture objects" (or "texture
names") to handle textures used by a program. OpenAL does a similar thing with
audio samples. There are essentially 3 kinds of objects in OpenAL. A buffer
which stores all the information about how a sound should be played and the
sound data itself, and a source which is a point in space that emits a sound.
It's important to understand that a source is not itself an audio sample. A
source only plays back sound data from a buffer bound to it. The source is also
given special properties like position and velocity. </p>
<p>The third object which I have not mentioned yet is the listener. There is
only one listener which represents where 'you' are, the user. The listener
properties along with the source properties determine how the audio sample will
be heard. For example their relative positions will determine the intensity of
the sound.</p>
<pre class=code>
<span class=codeComment><font color="#006600"> // Position of the source sound.</font></span>
<font color="#0000FF"> static float</font>[] sourcePos = { 0.0f, 0.0f, 0.0f };
<font color="#006600">
<span class=codeComment> // Velocity of the source sound.</span></font>
<font color="#0000FF"> static float</font>[] sourceVel = { 0.0f, 0.0f, 0.0f };
<span class=codeComment> <font color="#006600">// Position of the listener.</font></span>
<font color="#0000FF">static float</font>[] listenerPos = { 0.0f, 0.0f, 0.0f };
<span class=codeComment> <font color="#006600">// Velocity of the listener.</font></span>
<font color="#0000FF">static float</font>[] listenerVel = { 0.0f, 0.0f, 0.0f };
<span class=codeComment> <font color="#006600">// Orientation of the listener. (first 3 elements are "at", second 3 are "up")</font></span>
<font color="#0000FF">static float</font>[] listenerOri = { 0.0f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f };
</pre>
<p>In the above code we specify the position and velocity of the source and listener
objects. These arrays are vector based Cartesian coordinates. You could easily
build a structure or class to do the same thing. In this example I used arrays
for simplicity.</p>
<p>Here we will create a function that loads all of our sound data from a file.
</p>
<pre class=code> <font color="#0000FF">static int</font> LoadALData() {
<span class=codeComment> <font color="#006600">// variables to load into</font>
<font color="#0000FF">int</font>[] format = <font color="#0000FF">new int</font>[1];<br> <font color="#0000FF">int</font>[] size = <font color="#0000FF">new int</font>[1];<br> ByteBuffer[] data = <font color="#0000FF">new</font> ByteBuffer[1];<br> <font color="#0000FF">int</font>[] freq = new <font color="#0000FF">int</font>[1];
<font color="#0000FF">int</font>[] loop = new <font color="#0000FF">int</font>[1];<br></span>
<font color="#006600">// Load wav data into a buffer.</font>
al.alGenBuffers(1, buffer);
<span class=codeKeyword>if</span> (al.alGetError() != AL.AL_NO_ERROR)
<span class=codeKeyword> return</span> AL.AL_FALSE;
ALut.alutLoadWAVFile("wavdata/FancyPants.wav", format, data, size, freq, loop);
al.alBufferData(buffer[0], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0],data[0],size[0],freq[0]);
</pre>
<p>The function 'alGenBuffers' will create the buffer objects and store them in
the variable we passed it. It's important to do an error check to make sure
everything went smoothly. There may be a case in which OpenAL could not generate
a buffer object due to a lack of memory. In this case it would set the error
bit.</p>
<p>The ALut is very helpful here. It opens up the file for us and gives us all
the information we need to create the buffer. And after we have attached all
this data to the buffer it will help use dispose of the data. It all works in
a clean and efficient manner.</p>
<pre class=code>
<span class=codeComment><font color="#006600">// Bind buffer with a source.</font></span>
al.alGenSources(1, source);
<span class=codeKeyword>if</span> (al.alGetError() != AL.AL_NO_ERROR)
<span class=codeKeyword>return</span> AL.AL_FALSE;
al.alSourcei (source[0], AL.AL_BUFFER, buffer[0] );
al.alSourcef (source[0], AL.AL_PITCH, 1.0f );
al.alSourcef (source[0], AL.AL_GAIN, 1.0f );
al.alSourcefv(source[0], AL.AL_POSITION, sourcePos);
al.alSourcefv(source[0], AL.AL_VELOCITY, sourceVel);
al.alSourcei (source[0], AL.AL_LOOPING, loop[0] );</pre>
<p>We generate a source object in the same manner we generated the buffer object.
Then we define the source properties that it will use when it's in playback. The
most important of these properties is the buffer it should use. This tells the
source which audio sample to playback. In this case we only have one so we bind
it. We also tell the source it's position and velocity which we defined earlier.</p>
<p>One more thing on 'alGenBuffers' and 'alGenSources'. In some example code I
have seen these functions will return an integer value for the number of
buffers/sources created. I suppose this was meant as an error checking feature
that was left out in a later version. If you see this done in other code don't
use it yourself. If you want to do this check, use 'alGetError' instead (like we
have done above).</p>
<pre class=code>
<span class=codeComment><font color="#006600">// Do another error check and return.</font></span>
<span class=codeKeyword><font color="#0000FF">if</font></span> (al.alGetError() == AL.AL_NO_ERROR)
<span class=codeKeyword><font color="#0000FF">return</font></span> AL.AL_TRUE;
<span class=codeKeyword><font color="#0000FF">return</font></span> AL.AL_FALSE;
}
</pre>
<p>To end the function we just do one more check to make sure all is well, then
we return success.</p>
<pre class=code><font color="#0000FF">static <span class=codeKeyword>void</span> </font>setListenerValues() {
al.alListenerfv(AL.AL_POSITION, listenerPos);
al.alListenerfv(AL.AL_VELOCITY, listenerVel);
al.alListenerfv(AL.AL_ORIENTATION, listenerOri);
}
</pre>
<p>We created this function to update the listener properties.</p>
<pre class=code><font color="#0000FF">static <span class=codeKeyword>void</span> </font>killALData() {
al.alDeleteBuffers(1, buffer);
al.alDeleteSources(1, source);
Alut.alutExit();
}
</pre>
<p>This will be our shutdown procedure. It is necessary to call this to release
all the memory and audio devices that our program may be using.</p>
<pre class=code><font color="#0000FF">public static void main</font>(<span class=codeKeyword>String[] args</span>) {
<span class=codeComment><font color="#006600">// Initialize OpenAL and clear the error bit.</font></span>
<span class=codeComment>
ALut.alutInit();</span>
al.alGetError();
</pre>
<p>The function 'alutInit' will setup everything that the Alc needs to do for
us. Basically Alut creates a single OpenAL context through Alc and sets it to
current. On the Windows platform it initializes DirectSound. We also do an
initial call to the error function to clear it. Every time we call 'glGetError'
it will reset itself to 'AL_NO_ERROR'.</p>
<pre class=code>
<span class=codeComment> <font color="#006600">// Load the wav data.</font></span>
<span class=codeKeyword><font color="#0000FF">if</font></span> (loadALData() == AL.AL_FALSE)
<span class=codeKeyword><font color="#0000FF">return</font></span> -1;
setListenerValues();
<span class=codeComment><font color="#006600">// Setup an exit procedure.</font></span>
Runtime runtime = Runtime.getRuntime();
runtime.addShutdownHook(
<font color="#0000FF">new</font> Thread(
<font color="#0000FF">new</font> Runnable() {
<font color="#0000FF">public void</font> run() {
killAllData();
}
}
)
);
</pre>
<p>We will check to see if the wav files loaded correctly. If not we must exit
the program. Then we update the listener values, and finally we set our exit
procedure.</p>
<pre class=code> <font color="#0000FF">char</font>[] c = new <font color="#0000FF">char</font>[1];
<font color="#0000FF">while</font>(c[0] != 'q') {
<font color="#0000FF">try</font> {
BufferedReader buf =
<font color="#0000FF">new</font> BufferedReader(<font color="#0000FF">new</font> InputStreamReader(System.in));
System.out.println("Press a key and hit ENTER: " +
"'p' to play, 's' to stop, 'h' to pause and 'q' to quit");
buf.read(c);
<font color="#0000FF">switch</font>(c[0]) {
<font color="#0000FF">case</font> 'p':
<font color="#006600">// Pressing 'p' will begin playing the sample.</font>
al.alSourcePlay(source[0]);
<font color="#0000FF">break</font>;
<font color="#0000FF">case</font> 's':
<font color="#006600">// Pressing 's' will stop the sample from playing.</font>
alSourceStop(source[0]);
<font color="#0000FF">break</font>;
<font color="#0000FF">case</font> 'h':
<font color="#006600">// Pressing 'n' will pause (hold) the sample.</font>
alSourcePause(source[0]);
<font color="#0000FF">break</font>;
}
} <font color="#0000FF">catch</font> (IOException e) {
System.exit(1);
}
}
}
</pre>
<p>This is the interesting part of the tutorial. It's a very basic loop that
lets us control the playback of the audio sample. Pressing 'p' will replay the
sample, pressing 's' will stop the sample, and pressing 'h' will pause the
sample. Pressing 'q' will exit the program.</p>
<p>Well there it is. Your first delve into OpenAL. I hope it was made simple
enough for you. It may have been a little too simple for the 1337 h4X0r, but we
all got to start somewhere. Things will get more advanced as we go along.</p>
<p> <a href="http://joal-demos.dev.java.net/files/documents/534/256/lesson1.zip">Download
the Java Source and Ant Build File</a></p>
<p>© 2003 <a href="http://www.devmaster.net">DevMaster.net</a> all rights
reserved. </p>
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