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OpenAL Tutorials from DevMaster.net. Reprinted with Permission.<br>
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<td width="47%" height="12" valign="middle"><p><b><font color="#FFFFFF">OpenAL
Tutorials</font></b></p></td>
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<p class="ArticleTitle"><font size="5">Sources Sharing Buffers<br>
</font><strong><font size="4">Lesson 5</font></strong></p>
<p align="right" class="ArticleAuthor">Author: <a href="mailto:lightonthewater@hotmail.com">Jesse
Maurais<br>
</a>Adapted For Java By: <a href="athomas@dev.java.net">Athomas
Goldberg </a></p>
<p>At this point in the OpenAL series I will show one method of having your buffers
be shared among many sources. This is a very logical and natural step, and it
is so easy that some of you may have already done this yourself. If you have
you may just skip this tutorial in total and move on. But for those keeners
who want to read all of the info I've got to give, you may find this interesting.
Plus, we will be implementing the Alc layer directly so that we can use some
of that knowledge gained in lesson 4. On top of that we will create a program
you might even use!</p>
<p>Well, here we go. I've decided to only go over bits of the code that are significant,
since most of the code has been repeated so far in the series. Check out the
full source code in the download.</p>
<pre class=code><span class=codeComment><font color="#0000FF">static</font> ALC alc;
<font color="#0000FF">static</font> AL al;<font color="#006600">
// These index the buffers.</font></span>
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> THUNDER = 0;
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> WATERDROP = 1;
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> STREAM = 2;
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> RAIN = 3;
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> CHIMES = 4;
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> OCEAN = 5;
<span class=codeKeyword><font color="#0000FF">public static final int</font></span> NUM_BUFFERS = 6;
<font color="#006600"><span class=codeComment>// Buffers hold sound data.</span>
</font><font color="#0000FF">static int</font>[] buffers = <font color="#0000FF">new int</font>[NUM_BUFFERS];
<span class=codeComment><font color="#006600">// A vector list of sources for multiple emissions.</font></span>
Vector sources = <font color="#0000FF">new </font>Vector();
</pre>
<p>First I've written out a few macros that we can use to index the buffer array.
We will be using several wav files so we need quite a few buffers here. Instead
of using an array for storing the sources we will use a Vector. We chose to
do this because it allows us to have a dynamic number of sources. We can just
keep adding sources to the scene until OpenAL runs out of them. This is also
the first tutorial where we will deal with sources as being a resource that
will run out. And yes, they will run out; they are finite.</p>
<pre class=code><font color="#0000FF">static int </font>initOpenAL() {
ALC.Device device;
ALC.Context context;
String deviceSpecifier;
String deviceName = "DirectSound3D";
<span class=codeComment><font color="#006600">// Get handle to device.</font></span>
device = alc.alcOpenDevice(deviceName);
<font color="#006600"><span class=codeComment>// Get the device specifier.</span></font>
deviceSpecifier = alc.alcGetString(device, ALC.ALC_DEVICE_SPECIFIER);
System.out.println("Using device " + deviceSpecifier);
<span class=codeComment><font color="#006600">// Create audio context.</font></span>
context = alc.alcCreateContext(device, <font color="#0000FF">null</font>);
<span class=codeComment><font color="#006600">// Set active context.</font></span>
alc.alcMakeContextCurrent(context);
<span class=codeComment><font color="#006600">// Check for an error.</font></span>
<span class=codeKeyword><font color="#0000FF">if </font></span>(alc.alcGetError() != ALC.ALC_NO_ERROR)
<span class=codeKeyword><font color="#0000FF">return</font></span> AL.AL_FALSE;
<span class=codeKeyword><font color="#0000FF">return</font></span> AL.AL_TRUE;
}
</pre>
<p>This is some sample code from what we learned in the last tutorial. We get
a handle to the device "DirectSound3D", and then obtain a rendering
context for our application. This context is set to current and the function
will check if everything went smoothly before we return success.</p>
<pre class=code><span class=codeKeyword><font color="#0000FF">static void</font></span> exitOpenAL() {
ALC.Context curContext;
ALC.Device curDevice;
<font color="#006600"><span class=codeComment>// Get the current context.</span></font>
curContext = alc.alcGetCurrentContext();
<span class=codeComment><font color="#006600">// Get the device used by that context.</font></span>
curDevice = alc.alcGetContextsDevice(curContext);
<font color="#006600"> <span class=codeComment>// Reset the current context to NULL.</span>
</font> alc.alcMakeContextCurrent(<font color="#0000FF">null</font>);
<font color="#006600"> <span class=codeComment>// Release the context and the device.</span>
</font> alc.alcDestroyContext(curContext);
alc.alcCloseDevice(curDevice);
}
</pre>
<p>This will do the opposite we did in the previous code. It retrieves the context
and device that our application was using and releases them. It also sets the
current context to null (the default) which will suspend the processing of any
data sent to OpenAL. It is important to reset the current context to null or
else you will have an invalid context trying to process data. The results of
doing this can be unpredictable.</p>
<p>If you are using a multi-context application you may need to have a more advanced
way of dealing with initialization and shutdown. I would recommend making all
devices and contexts global and closing them individually, rather than retrieving
the current context.</p>
<pre class=code><font color="#0000FF">static int </font>loadALData() {
<font color="#006600"><span class=codeComment>// Variables to load into.</span></font>
<font color="#0000FF">int</font>[] format = new <font color="#0000FF">int</font>[1];
<font color="#0000FF">int</font>[] size = new <font color="#0000FF">int</font>[1];
ByteBuffer[] data = new ByteBuffer[1];
<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];
<span class=codeComment><font color="#006600">// Load wav data into buffers.</font></span>
al.alGenBuffers(NUM_BUFFERS, buffers);
<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_FALSE;
ALut.alutLoadWAVFile("wavdata/thunder.wav", format, data, size, freq, loop);
al.alBufferData(buffers[THUNDER], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
ALut.alutLoadWAVFile("wavdata/waterdrop.wav", format, data, size, freq, loop);
al.alBufferData(buffers[WATERDROP], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
ALut.alutLoadWAVFile("wavdata/stream.wav", format, data, size, freq, loop);
al.alBufferData(buffers[STREAM], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
ALut.alutLoadWAVFile("wavdata/rain.wav", format, data, size, freq, loop);
al.alBufferData(buffers[RAIN], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
ALut.alutLoadWAVFile("wavdata/ocean.wav", format, data, size, freq, loop);
al.alBufferData(buffers[OCEAN], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
ALut.alutLoadWAVFile("wavdata/chimes.wav", format, data, size, freq, loop);
al.alBufferData(buffers[CHIMES], format[0], data[0], size[0], freq[0]);
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
<font color="#006600"> <span class=codeComment>// Do another error check and return.</span>
</font><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_FALSE;
<span class=codeKeyword><font color="#0000FF">return</font></span> AL.AL_TRUE;
}
</pre>
<p>We've totally removed the source generation from this function. That's because
from now on we will be initializing the sources separately.</p>
<pre class=code><span class=codeKeyword><font color="#0000FF">static void</font></span><font color="#0000FF"> </font>addSource(int type) {
<font color="#0000FF">int[]</font> source = <font color="#0000FF">new int</font>[1];
al.alGenSources(1, source);
<span class=codeKeyword><font color="#0000FF">if</font> </span>(al.alGetError() != AL.AL_NO_ERROR) {
System.err.println("Error generating audio source.");
System.exit(1);
}
al.alSourcei (source[0], AL.AL_BUFFER, buffers[type]);
al.alSourcef (source[0], AL.AL_PITCH, 1.0 );
al.alSourcef (source[0], AL.AL_GAIN, 1.0 );
al.alSourcefv(source[0], AL.AL_POSITION, sourcePos );
al.alSourcefv(source[0], AL.AL_VELOCITY, sourceVel );
al.alSourcei (source[0], AL.AL_LOOPING, AL.AL_TRUE );
al.alSourcePlay(source);
sources.put(new Integer(source[0]));
}
</pre>
<p>Here's the function that will generate the sources for us. This function will
generate a single source for any one of the loaded buffers we generated in the
previous source. Given the buffer index 'type', which is one of the macros we
created right from the start of this tutorial. We do an error check to make
sure we have a source to play (like I said, they are finite). If a source cannot
be allocated then the program will exit.</p>
<pre class=code><span class=codeKeyword><font color="#0000FF">static void</font></span><font color="#0000FF"> </font>killALData() {
Iterator iter = sources.iterator();
<span class=codeKeyword><font color="#000000">while</font></span>(iter.hasNext()) {
al.alDeleteSources(1, <font color="#0000FF">new int</font>[] { ((Integer)iter.next()).intValue() });
}
sources.clear();
al.alDeleteBuffers(NUM_BUFFERS, buffers);
exitOpenAL();
}
</pre>
<p>This function has been modified a bit to accommodate the Vector. We have to
delete each source in the list individually and then clear the list which will
effectively destroy it.</p>
<pre class=code><font color="#0000FF"> char</font>[] c = <font color="#0000FF">new char</font>[1];
<font color="#0000FF"> </font><font color="#0000FF">while</font>(c[0] != 'q') {
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF">try</font> {
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>BufferedReader buf =
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF">new</font> BufferedReader(<font color="#0000FF">new</font> InputStreamReader(System.in));
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>System.out.println("Press a key and hit ENTER: " +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\t'w' for Water Drop\n" +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\t't' for Thunder\n" +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\t's' for Stream\n" +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\t'r' for Rain\n" +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\t'o' for Ocean\n" +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\t'c' for Chimes\n" +
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>"\n'q' to Quit\n");
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font>buf.read(c);
<font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF"> </font><font color="#0000FF">switch</font>(c[0]) {
<font color="#0000FF"> case</font> 'w': addSource(WATERDROP); <font color="#0000FF">break</font>;
<font color="#0000FF"></font><font color="#0000FF"> case</font> 't': addSource(THUNDER); <font color="#0000FF">break</font>;
<font color="#0000FF"></font><font color="#0000FF"> case</font> 's': addSource(STREAM); <font color="#0000FF">break</font>;
<font color="#0000FF"></font><font color="#0000FF"> case</font> 'r': addSource(RAIN); <font color="#0000FF">break</font>;
<font color="#0000FF"></font><font color="#0000FF"> case</font> 'o': addSource(OCEAN); <font color="#0000FF">break</font>;
<font color="#0000FF"></font><font color="#0000FF"> case</font> 'c': addSource(CHIMES); <font color="#0000FF">break</font>;
<font color="#0000FF"></font>}
<font color="#0000FF"> </font><font color="#0000FF"> </font>} <font color="#0000FF">catch</font> (IOException e) {
System.exit(1);
<font color="#0000FF"> </font><font color="#0000FF"> </font>}
<font color="#0000FF"> </font>}</pre>
<p>Here is the programs inner loop taken straight out of our main. Basically it
waits for some keyboard input and on certain key hits it will create a new source
of a certain type and add it to the audio scene. Essentially what we have created
here is something like one of those nature tapes that people listen to for relaxation.
Ours is a little better since it allows the user to customize which sounds that
they want in the background. Pretty neat eh? I've been listening to mine while
I code. It's a Zen experience (I'm listening to it right now).</p>
<p>The program can be expanded for using more wav files, and have the added feature
of placing the sources around the scene in arbitrary positions. You could even
allow for sources to play with a given frequency rather than have them loop.
However this would require GUI routines that go beyond the scope of the tutorial.
A full featured "Weathering Engine" would be a nifty program to make
though. ;)</p>
<p>Download the Java Files and Ant build script</p>
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