LWJGL 2 - Lightweight Java Game Library
Other Articles in the Series
· Lesson 1: Single Static Source
· Lesson 2: Looping and Fade-away
· Lesson 3: Multiple Sources
· Lesson 4: A Closer Look at ALC
· Lesson 5: Sources Sharing Buffers
· Lesson 6: Advanced Loading and Error Handles
· Lesson 7: The Doppler Effect

Multiple Sources: Lesson 3

Author: Jesse Maurais | From: devmaster.net
Modified for LWJGL by: Brian Matzon

Hello. It's been a while since my last tutorial. But better late than never I guess. Since I'm sure your all impatient to read the latest tutorial, I'll just jump right into it. What we hope to accomplish with this one is to be able to play more that one audio sample at a time. Very intense games have all kinds of stuff going on usually involving different sound clips. It won't be hard to implement any of this though. Doing multiple sounds is similar to doing just one.

import java.io.IOException;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.util.Random;

import org.lwjgl.BufferUtils;
import org.lwjgl.LWJGLException;
import org.lwjgl.openal.AL;
import org.lwjgl.openal.AL10;
import org.lwjgl.util.WaveData;

public class Lesson3 {
  /** Maximum data buffers we will need. */
  public static final int NUM_BUFFERS = 3;

  /** Maximum emissions we will need. */
  public static final int NUM_SOURCES = 3;

  /** Index of battle sound */
  public static final int BATTLE = 0;

  /** Index of gun 1 sound */
  public static final int GUN1 = 1;

  /** Index of gun 2 sound */
  public static final int GUN2 = 2;

  /** Buffers hold sound data. */
  IntBuffer buffer = BufferUtils.createIntBuffer(NUM_BUFFERS);

  /** Sources are points emitting sound. */
  IntBuffer source = BufferUtils.createIntBuffer(NUM_BUFFERS);

  /** Position of the source sound. */
  FloatBuffer sourcePos = BufferUtils.createFloatBuffer(3*NUM_BUFFERS);

  /** Velocity of the source sound. */
  FloatBuffer sourceVel = BufferUtils.createFloatBuffer(3*NUM_BUFFERS);

  /** Position of the listener. */
  FloatBuffer listenerPos = BufferUtils.createFloatBuffer(3).put(new float[] { 0.0f, 0.0f, 0.0f });

  /** Velocity of the listener. */
  FloatBuffer listenerVel = BufferUtils.createFloatBuffer(3).put(new float[] { 0.0f, 0.0f, 0.0f });

  /** Orientation of the listener. (first 3 elements are "at", second 3 are "up") */
  FloatBuffer listenerOri =
      BufferUtils.createFloatBuffer(6).put(new float[] { 0.0f, 0.0f, -1.0f,  0.0f, 1.0f, 0.0f });

I guess this little piece of source code will be familiar to a lot of you who've read the first two tutorials. The only difference is that we now have 3 different sound effects that we are going to load into the OpenAL sound system.

  /**
   * boolean LoadALData()
   *
   *  This function will load our sample data from the disk using the Alut
   *  utility and send the data into OpenAL as a buffer. A source is then
   *  also created to play that buffer.
   */
  int loadALData() {

    // Load wav data into a buffer.
    AL10.alGenBuffers(buffer);

    if(AL10.alGetError() != AL10.AL_NO_ERROR)
      return AL10.AL_FALSE;

    WaveData waveFile = WaveData.create("Battle.wav");
    AL10.alBufferData(buffer.get(BATTLE), waveFile.format, waveFile.data, waveFile.samplerate);
    waveFile.dispose();

    waveFile = WaveData.create("Gun1.wav");
    AL10.alBufferData(buffer.get(GUN1), waveFile.format, waveFile.data, waveFile.samplerate);
    waveFile.dispose();

    waveFile = WaveData.create("Gun2.wav");
    AL10.alBufferData(buffer.get(GUN2), waveFile.format, waveFile.data, waveFile.samplerate);
    waveFile.dispose();

    // Bind buffers into audio sources.
    AL10.alGenSources(source);

    if (AL10.alGetError() != AL10.AL_NO_ERROR)
      return AL10.AL_FALSE;

    AL10.alSourcei(source.get(BATTLE), AL10.AL_BUFFER,   buffer.get(BATTLE));
    AL10.alSourcef(source.get(BATTLE), AL10.AL_PITCH,    1.0f          );
    AL10.alSourcef(source.get(BATTLE), AL10.AL_GAIN,     1.0f          );
    AL10.alSource (source.get(BATTLE), AL10.AL_POSITION, (FloatBuffer) sourcePos.position(BATTLE*3));
    AL10.alSource (source.get(BATTLE), AL10.AL_VELOCITY, (FloatBuffer) sourceVel.position(BATTLE*3));
    AL10.alSourcei(source.get(BATTLE), AL10.AL_LOOPING,  AL10.AL_TRUE  );

    AL10.alSourcei(source.get(GUN1), AL10.AL_BUFFER,   buffer.get(GUN1));
    AL10.alSourcef(source.get(GUN1), AL10.AL_PITCH,    1.0f          );
    AL10.alSourcef(source.get(GUN1), AL10.AL_GAIN,     1.0f          );
    AL10.alSource (source.get(GUN1), AL10.AL_POSITION, (FloatBuffer) sourcePos.position(GUN1*3));
    AL10.alSource (source.get(GUN1), AL10.AL_VELOCITY, (FloatBuffer) sourceVel.position(GUN1*3));
    AL10.alSourcei(source.get(GUN1), AL10.AL_LOOPING,  AL10.AL_FALSE );

    AL10.alSourcei(source.get(GUN2), AL10.AL_BUFFER,   buffer.get(GUN2));
    AL10.alSourcef(source.get(GUN2), AL10.AL_PITCH,    1.0f          );
    AL10.alSourcef(source.get(GUN2), AL10.AL_GAIN,     1.0f          );
    AL10.alSource (source.get(GUN2), AL10.AL_POSITION, (FloatBuffer) sourcePos.position(GUN2*3));
    AL10.alSource (source.get(GUN2), AL10.AL_VELOCITY, (FloatBuffer) sourceVel.position(GUN2*3));
    AL10.alSourcei(source.get(GUN2), AL10.AL_LOOPING,  AL10.AL_FALSE );

    // Do another error check and return.
    if (AL10.alGetError() == AL10.AL_NO_ERROR)
      return AL10.AL_TRUE;

    return AL10.AL_FALSE;

This code looks quite a bit different at first, but it isn't really. Basically we load the file data into our 3 buffers, then lock the 3 buffers to our 3 sources relatively. The only other difference is that the "Battle.wav" (Source index 0) is looping while the rest are not.

NOTE: Notice how the buffers position is changed. Since we know a vector in the buffer consists of 3 floats, we use this knowledge to index into the buffer and position us precisely where the next vector begins. We could have used multiple buffers, but this is quicker, and takes up less code - at a slight cost of added complexity.

  /**
   * void setListenerValues()
   *
   *  We already defined certain values for the Listener, but we need
   *  to tell OpenAL to use that data. This function does just that.
   */
  void setListenerValues() {
    AL10.alListener(AL10.AL_POSITION,    listenerPos);
    AL10.alListener(AL10.AL_VELOCITY,    listenerVel);
    AL10.alListener(AL10.AL_ORIENTATION, listenerOri);
  }

  /**
   * void killALData()
   *
   *  We have allocated memory for our buffers and sources which needs
   *  to be returned to the system. This function frees that memory.
   */
  void killALData() {
    AL10.alDeleteSources(source);
    AL10.alDeleteBuffers(buffer);
  }

I don't think we changed anything in this code.

  public static void main(String[] args) {
    new Lesson3().execute();
  }

  /**
   *  Check for keyboard hit
   */
  private boolean kbhit() {
    try {
    	return (System.in.available() != 0);
    } catch (IOException ioe) {
    }
    return false;
  }

  public void execute() {
    // Initialize OpenAL and clear the error bit.
    try{
    	AL.create();
    } catch (LWJGLException le) {
    	le.printStackTrace();
      return;
    }
    AL10.alGetError();

    // Load the wav data.
    if(loadALData() == AL10.AL_FALSE) {
      System.out.println("Error loading data.");
      return;
    }

    setListenerValues();

    // Begin the battle sample to play.
    AL10.alSourcePlay(source.get(BATTLE));

    // Go through all the sources and check that they are playing.
    // Skip the first source because it is looping anyway (will always be playing).
    int play;
    Random random = new Random();


    while (!kbhit()) {
      for (int i=1; iif (play != AL10.AL_PLAYING) {
        double theta = (double) (random.nextInt() % 360) * 3.14 / 180.0;

        sourcePos.put(i*3+0, -(float) (Math.cos(theta)));
        sourcePos.put(i*3+1, -(float) (random.nextInt()%2));
        sourcePos.put(i*3+2, -(float) (Math.sin(theta)));

        AL10.alSource(source.get(i), AL10.AL_POSITION, (FloatBuffer) sourcePos.position(i*3));
        AL10.alSourcePlay(source.get(i));
      }
    }
    killALData();
  }
}

Here is the interesting part of this tutorial. We go through each of the sources to make sure it's playing. If it is not then we set it to play but we select a new point in 3D space for it to play (just for kicks). And bang! We are done. As most of you have probably seen, you don't have to do anything special to play more than one source at a time. OpenAL will handle all the mixing features to get the sounds right for their respective distances and velocities. And when it comes right down to it, isn't that the beauty of OpenAL? You know that was a lot easier than I thought. I don't know why I waited so long to write it. Anyway, if anyone reading wants to see something specific in future tutorials (not necessarily pertaining to OpenAL, I have quite an extensive knowledge base) drop me a line at lightonthewater@hotmail.com I plan to do tutorials on sharing buffers and the Doppler effect in some later tutorial unless there is request for something else.

Have fun with the code!

Download source code and resources for this lesson here.

 
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