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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>JOAL OpenAL Tutorials from DevMaster.net Lesson 6: Advanced Loading and Error Handles</title>
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OpenAL Tutorials from DevMaster.net. Reprinted with Permission.<br>
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<p class="ArticleTitle"><font size="5">Advanced Loading and Error Handles<br>
</font><font color="#000000" size="4"><strong>Lesson 6</strong></font></p>
<p align="right" class="ArticleAuthor">Author: <a href="mailto:lightonthewater@hotmail.com">Jesse
Maurais</a><br>
Adapted For Java By: <a href="mailto:athomas@dev.java.net">Athomas Goldberg</a></p>
<p align="justify">We've been doing some pretty simple stuff up until now that
didn't require us to be very precise in the way we've handled things. The reason
for this is that we have been writing code for simplicity in order to learn
easier, rather that for robustness. Since we are going to move into some advanced
stuff soon we will take some time to learn the proper ways. Most importantly
we will learn a more advanced way of handling errors. We will also reorganize
the way we have been loading audio data. There wasn't anything wrong with our
methods in particular, but we will need a more organized and flexible approach
to the process.</p>
<p align="justify">We will first consider a few functions that will help us out
a lot by the time we have finished.</p>
<pre class=code><font color="#0000FF"><span class=codeComment><font color="#006600">/**
* 1) Identify the error code.
* 2) Return the error as a string.
*/</font></span>
public</font> <font color="#0000FF">static</font> String getALErrorString(<font color="#0000FF">int</font> err);
<span class=codeComment><font color="#006600">/**
* 1) Identify the error code.
* 2) Return the error as a string.
*/</font></span>
<font color="#0000FF">public</font> <font color="#0000FF">static</font> String getALCErrorString(<font color="#0000FF">int</font> err);
<font color="#0000FF"><span class=codeComment><font color="#006600">/**
* 1) Creates a buffer.
* 2) Loads a wav file into the buffer.
* 3) Returns the buffer id.
*/</font></span>
public static int </font>loadALBuffer(String path) <font color="#0000FF">throws</font> IOException;
<span class=codeComment><font color="#006600">/**
* 1) Checks if file has already been loaded.
* 2) If it has been loaded already, return the buffer id.
* 3) If it has not been loaded, load it and return buffer id.
*/</font></span>
<font color="#0000FF">public static int </font>getLoadedALBuffer(String path) <font color="#0000FF">throws</font> IOException;
<font color="#0000FF"><span class=codeComment><font color="#006600">/**
* 1) Creates a source.
* 2) Calls 'GetLoadedALBuffer' with 'path' and uses the
* returned buffer id as it's sources buffer.
* 3) Returns the source id.
*/
</font></span>public static int </font>loadALSample(String path, <span class=codeKeyword><font color="#0000FF">boolean</font></span> loop) <font color="#0000FF">throws</font> IOException;
<span class=codeKeyword>
</span><span class=codeComment><font color="#006600">/**
* 1) Releases temporary loading phase data.
*/</font></span>
<span class=codeKeyword><font color="#0000FF">public static void</font></span><font color="#0000FF"> </font>killALLoadedData();
<span class=codeKeyword>
</span><span class=codeComment><font color="#006600">/**
* 1) Loads all buffers and sources for the application.
*/</font></span>
<span class=codeKeyword><font color="#0000FF">public static boolean</font></span><font color="#0000FF"> </font>loadALData();
<span class=codeKeyword>
</span><span class=codeComment><font color="#006600">/**
* 1) Releases all buffers.
* 2) Releases all sources.
*/</font></span>
<font color="#0000FF"><span class=codeKeyword>public </span>static <span class=codeKeyword>void</span> </font>killALData();
<font color="#0000FF">private static</font> Vector loadedFiles = <font color="#0000FF">new</font> Vector(); <span class=codeComment><font color="#006600">// Holds loaded file paths temporarily.</font></span>
<font color="#0000FF">private static</font> Vector buffers = <font color="#0000FF">new</font> Vector(); <span class=codeComment><font color="#006600">// Holds all loaded buffers.</font></span><font color="#006600">
</font><font color="#0000FF">private static</font> Vector sources<font color="#006600"> = <font color="#0000FF">new</font> </font>Vector();<font color="#006600"> <span class=codeComment>// Holds all validated sources.</span></font>
</pre>
<p align="justify">Take a close look at the functions and try to understand what
we are going to be doing. Basically what we are trying to create is a system
in which we no longer have to worry about the relationship between buffers and
sources. We can call for the creation of a source from a file and this system
will handle the buffer's creation on it's own so we don't duplicate a buffer
(have two buffers with the same data). This system will handle the buffers as
a limited resource, and will handle that resource efficiently.</p>
<pre class=code><font color="#0000FF">public</font> String getALErrorString(<font color="#0000FF">int</font> err) {
<span class=codeKeyword><font color="#0000FF">switch</font></span>(err) {
<span class=codeKeyword><font color="#0000FF">case</font></span> AL.AL_NO_ERROR: <span class=codeKeyword><font color="#0000FF">return</font></span> "AL_NO_ERROR";
<span class=codeKeyword><font color="#0000FF">case</font></span> AL.AL_INVALID_NAME: <span class=codeKeyword><font color="#0000FF">return</font></span> "AL_INVALID_NAME";
<span class=codeKeyword><font color="#0000FF">case</font></span> AL.AL_INVALID_ENUM: <span class=codeKeyword><font color="#0000FF">return</font></span> "AL_INVALID_ENUM";
<span class=codeKeyword><font color="#0000FF">case</font></span> AL.AL_INVALID_VALUE: <span class=codeKeyword><font color="#0000FF">return</font></span> "AL_INVALID_VALUE";
<span class=codeKeyword><font color="#0000FF">case</font></span> AL.AL_INVALID_OPERATION: <span class=codeKeyword><font color="#0000FF">return</font></span> "AL_INVALID_OPERATION";
<span class=codeKeyword><font color="#0000FF">case</font></span> AL.AL_OUT_OF_MEMORY: <span class=codeKeyword><font color="#0000FF">return</font></span> "AL_OUT_OF_MEMORY";
<font color="#0000FF">default</font>: <font color="#0000FF">return</font> <font color="#0000FF">null</font>;
}
}
</pre>
<p align="justify">This function will convert an OpenAL error code to a string
so it can be read on the console (or some other device). The OpenAL sdk says
that the only exception that needs be looked for in the current version is the
'AL_OUT_OF_MEMORY' error. However, we will account for all the errors so that
our code will be up to date with later versions.</p>
<pre class=code><font color="#0000FF">public</font> String getALCErrorString(<font color="#0000FF">int</font> err) {
<span class=codeKeyword><font color="#0000FF">switch</font></span>(err) {
<span class=codeKeyword><font color="#0000FF">case</font></span> ALC_NO_ERROR: <span class=codeKeyword><font color="#0000FF">return</font></span> "ALC_NO_ERROR";
<span class=codeKeyword> <font color="#0000FF">case</font></span> ALC_INVALID_DEVICE: <span class=codeKeyword><font color="#0000FF">return</font></span> "ALC_INVALID_DEVICE";
<span class=codeKeyword> <font color="#0000FF">case</font></span> ALC_INVALID_CONTEXT: <span class=codeKeyword><font color="#0000FF">return</font></span> "ALC_INVALID_CONTEXT";
<span class=codeKeyword> <font color="#0000FF">case</font></span> ALC_INVALID_ENUM: <span class=codeKeyword><font color="#0000FF">return</font></span> "ALC_INVALID_ENUM";
<span class=codeKeyword> <font color="#0000FF">case</font></span> ALC_INVALID_VALUE: <span class=codeKeyword><font color="#0000FF">return</font></span> "ALC_INVALID_VALUE";
<span class=codeKeyword> <font color="#0000FF">case</font></span> ALC_OUT_OF_MEMORY: <span class=codeKeyword><font color="#0000FF">return</font></span> "ALC_OUT_OF_MEMORY";
<font color="#0000FF">default</font>: <font color="#0000FF">return</font> <font color="#0000FF">null</font>;
}
}
</pre>
<p align="justify">This function will perform a similar task as the previous one
accept this one will interpret Alc errors. OpenAL and Alc share common id's,
but not common enough and not dissimilar enough to use the same function for
both.</p>
<p align="justify">One more note about the function 'alGetError': The OpenAL sdk
defines that it only holds a single error at a time (i.e. there is no stacking).
When the function is invoked it will return the first error that it has received,
and then clear the error bit to 'AL_NO_ERROR'. In other words an error will
only be stored in the error bit if no previous error is already stored there.</p>
<pre class=code><font color="#0000FF">public int</font> loadALBuffer(String path) <font color="#0000FF">throws</font> IOException {
<span class=codeComment><font color="#006600">// Variables to store data which defines the buffer.</font></span>
<font color="#0000FF">int</font>[] format = <font color="#0000FF">new int</font>[1];
<font color="#0000FF">int</font>[] size = <font color="#0000FF">new int</font>[1];
ByteBuffer[] data = <font color="#0000FF">new</font> ByteBuffer[1];
<font color="#0000FF">int</font>[] freq = <font color="#0000FF">new int</font>[1];
<font color="#0000FF">int</font>[] loop = <font color="#0000FF">new int</font>[1];
<font color="#006600"><span class=codeComment>// Buffer id and error checking variable.</span></font>
<font color="#0000FF">int</font>[] buffer = <font color="#0000FF">new int</font>[1];
int result;
<span class=codeComment><font color="#006600">// Generate a buffer. Check that it was created successfully.</font></span>
al.alGenBuffers(1, buffer);
<span class=codeKeyword><font color="#0000FF">if</font> </span>((result = al.alGetError()) != AL.AL_NO_ERROR)
<span class=codeKeyword><font color="#0000FF">throw</font></span><font color="#0000FF"> new</font> IOException(getALErrorString(result));
<span class=codeComment><font color="#006600">// Read in the wav data from file. Check that it loaded correctly.</font></span><font color="#006600">
</font>
ALut.alutLoadWAVFile(path, format, data, size, freq, loop);
<span class=codeKeyword><font color="#0000FF">if</font> </span>((result = al.alGetError()) != AL.AL_NO_ERROR)
<span class=codeKeyword><font color="#0000FF">throw</font></span><font color="#0000FF"> new </font>IOException(getALErrorString(result));
<span class=codeComment><font color="#006600">// Send the wav data into the buffer. Check that it was received properly.</font></span>
al.alBufferData(buffer[1], format[0], data[0], size[0], freq[0]);
<span class=codeKeyword><font color="#0000FF">if</font> </span>((result = al.alGetError()) != AL.AL_NO_ERROR)
<span class=codeKeyword><font color="#0000FF">throw</font></span> new IOException(getALErrorString(result));
<font color="#006600"> <span class=codeComment>// Get rid of the temporary data.</span>
</font>
ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);
<span class=codeKeyword><font color="#0000FF">if</font> </span>((result = al.alGetError()) != AL.AL_NO_ERROR)
<span class=codeKeyword><font color="#0000FF">throw</font></span> new IOException(getALErrorString(result));
<font color="#006600"> <span class=codeComment>// Return the buffer id.</span>
</font> <span class=codeKeyword><font color="#0000FF">return</font></span> buffer[0];
}
</pre>
<p align="justify">As you can see we do an error check at every possible phase
of the load. Any number of things can happen at this point which will cause
an error to be thrown. There could be no more system memory either for the buffer
creation or the data to be loaded, the wav file itself may not even exist, or
an invalid value can be passed to any one of the OpenAL functions which will
generate an error.</p>
<pre class=code><font color="#0000FF">public int </font>getLoadedALBuffer(String path) <font color="0000ff">throws</font> IOException {
<span class=codeKeyword><font color="#0000FF">int</font></span> count = 0; <span class=codeComment><font color="#006600">// 'count' will be an index to the buffer list.</font></span>
<font color="#0000FF">int</font> buffer; <span class=codeComment><font color="#006600">// Buffer id for the loaded buffer.</font></span>
<span class=codeComment>// Iterate through each file path in the list.</span>
Iterator iter = loadedFiles.iterator();
<font color="#0000FF">int i = 0;
while</font>(iter.hasNext()) {
String str = (String)iter.next();
if(str.equals(path)) {
<font color="#0000FF">return</font> ((Integer)buffers.get(i)).intValue();
}
i++;
}
<span class=codeComment><font color="#006600">// If we have made it this far then this file is new and we will create a buffer for it.</font></span>
buffer = loadALBuffer(path);
<span class=codeComment><font color="#006600">// Add this new buffer to the list, and register that this file has been loaded already.</font></span>
buffers.add(new Integer(buffer));
loadedFiles.add(path);
<span class=codeKeyword><font color="#0000FF">return</font></span> buffer;
}
</pre>
<p align="justify">This will probably be the piece of code most people have trouble
with, but it's really not that complex. We are doing a search through a list
which contains the file paths of all the wav's we have loaded so far. If one
of the paths matches the one we want to load, we will simply return the id to
the buffer we loaded it into the first time. This way as long as we consistently
load our files through this function, we will never have buffers wasted due
to duplication. Every file loaded this way must also be kept track of with it's
own list. The 'buffers' list is parallel to the 'loadedFiles' list. What I mean
by this is that every buffer in the index of 'buffers', is the same path of
the index in 'loadedFiles' from which that buffer was created.</p>
<pre class=code><font color="#0000FF">public static int </font>loadALSample(String path, <span class=codeKeyword><font color="#0000FF">boolean</font></span> loop) <font color="0000ff">throws</font> IOException {
<font color="#0000FF">int</font>[] source = <font color="0000ff">new int</font>[1];
<font color="0000ff">int</font> buffer;
<font color="0000ff">int</font> result;
<span class=codeComment><font color="006600">// Get the files buffer id (load it if necessary).</font></span>
buffer = getLoadedALBuffer(path);
<span class=codeComment><font color="006600">// Generate a source.</font></span>
al.alGenSources(1, source);
<span class=codeKeyword><font color="000066">if</font> </span>((result = al.alGetError()) != AL.AL_NO_ERROR)
<span class=codeKeyword><font color="0000ff">throw</font></span> new IOException(getALErrorString(result));
<font color="#006600"><span class=codeComment>// Setup the source properties.</span></font>
al.alSourcei (source[0], AL.AL_BUFFER, buffer );
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 ? AL.AL_TRUE : AL.AL_FALSE );
<span class=codeComment>// Save the source id.</span>
sources.add(new Integer(source[0]));
<span class=codeComment>// Return the source id.</span>
<span class=codeKeyword><font color="0000ff">return</font></span> source[0];
}
</pre>
<p align="justify">Now that we have created a system which will handle the buffers
for us, we just need an extension to it that will get the sources. In this code
we obtain the result of a search for the file, which is the buffer id that the
file was loaded into. This buffer is bound to the new source. We save the source
id internally and also return it.</p>
<pre class=code><span class=codeKeyword><font color="#0000FF">public static void</font></span><font color="#0000FF"> </font>killALLoadedData() {
loadedFiles.clear();
}
</pre>
<p>The global vector loadedFiles' stored the file path of every wav file that
was loaded into a buffer. It doesn't make sense to keep this data lying around
after we have loaded all of our data, so we will dispose of it.</p>
<pre class=code><span class=codeComment><font color="#006600">// Source id's.</font></span>
<font color="#0000FF">int</font> phaser1;
<font color="#0000FF">int</font> phaser2;
<span class=codeKeyword><font color="#0000FF">public static void</font></span><font color="#0000FF"> </font>loadALData() <font color="#0000FF">throws</font> IOException {
<font color="#006600"><span class=codeComment>// Anything for your application here. No worrying about buffers.</span></font>
phaser1 = loadALSample("wavdata/phaser.wav", <span class=codeKeyword><font color="#0000FF">false</font></span>);
phaser2 = loadALSample("wavdata/phaser.wav", <span class=codeKeyword><font color="#0000FF">true</font></span>);
killLoadedALData();
}
</pre>
<p align="justify">We have seen the function in previous tutorials. It will represent
the part of a program which loads all wav's used by the program. In it we can
see why our system is useful. Even though we have made a call to load the same
wav file into two distinct sources, the buffer for the file 'phaser.wav' will
only be created once, and the sources 'gPhaser1' and 'gPhaser2' will both use
that buffer for playback. There is no more concern for handling buffers because
the system will handle them automatically.</p>
<pre class=code><span class=codeKeyword><font color="#0000FF">public static void</font></span><font color="#0000FF"> </font>killALData()
{
<font color="006600"> <span class=codeComment>// Release all buffer data.</span>
</font> Iterator iter = buffers.iterator();
<span class=codeKeyword><font color="#0000FF">while</font>(iter.hasNext()) {</span>
al.alDeleteBuffers(1, new int[] { ((Integer)iter.next()).intValue());
}
<font color="006600"> <span class=codeComment>// Release all source data.</span>
</font> iter = sources.iterator();<font color="006600">
</font> <span class=codeKeyword><font color="#0000FF">while</font>(iter.hasNext()) {</span>
al.alDeleteSources(1, new int[] { ((Integer)iter.next()).intValue());
}<font color="006600">
<span class=codeComment>// Destroy the lists.</span></font>
buffers.clear();
sources.clear();
}
</pre>
<p align="justify">All along we have been storing the buffer and source id's into
stl vectors. We free all the buffers and sources by going through them and releasing
them individually. After which we destroy the lists themselves. All we need
to do now is catch the OpenAL errors that we have thrown.</p>
<pre class=code> <span class=codeKeyword><font color="#0000FF">try</font></span> {
initOpenAL();
loadALData();
} <span class=codeKeyword><font color="#0000FF">catch</font></span>(IOException err){
err.printStackTrace();
}
</pre>
<p align="justify">If something has gone wrong during the course of the load we
will be notified of it right away. When we catch the error it will be reported
on the console. We can use this for debugging or general error reporting. </p>
<p align="justify">That's it. A more advanced way of reporting errors, and a more
robust way of loading your wav files. We may find we need to do some modifications
in the future to allow for more flexibility, but for now we will be using this
source for basic file loading in future tutorials. Expect future tutorials to
expand on this code.</p>
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