Looping and Fade-away: Lesson 2

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

Hope you found the last tutorial of some use. I know I did. This will be a real quick and easy tutorial. It won't get too much more complicated at this point.

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

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 Lesson2 {
  /** Buffers hold sound data. */
  IntBuffer buffer = BufferUtils.createIntBuffer(1);

  /** Sources are points emitting sound. */
  IntBuffer source = BufferUtils.createIntBuffer(1);

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

  /** Velocity of the source sound. */
  FloatBuffer sourceVel = BufferUtils.createFloatBuffer(3).put(new float[] { 0.0f, 0.0f, 0.1f });

  /** 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 });

There is only one change in the code since the last tutorial in this first section. It is that we altered the sources velocity. It's 'z' field is now 0.1.

  /**
   * 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("Footsteps.wav");
    AL10.alBufferData(buffer.get(0), waveFile.format, waveFile.data, waveFile.samplerate);
    waveFile.dispose();

    // Bind the buffer with the source.
    AL10.alGenSources(source);

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

    AL10.alSourcei(source.get(0), AL10.AL_BUFFER,   buffer.get(0) );
    AL10.alSourcef(source.get(0), AL10.AL_PITCH,    1.0f          );
    AL10.alSourcef(source.get(0), AL10.AL_GAIN,     1.0f          );
    AL10.alSource (source.get(0), AL10.AL_POSITION, sourcePos     );
    AL10.alSource (source.get(0), AL10.AL_VELOCITY, sourceVel     );
    AL10.alSourcei(source.get(0), AL10.AL_LOOPING,  AL10.AL_TRUE  );

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

    return AL10.AL_FALSE;

Two changes in this section. First we are loading the file "Footsteps.wav". We are also explicitly setting the sources 'AL_LOOPING' value to 'AL_TRUE'. What this means is that when the source is prompted to play it will continue to play until stopped. It will play over again after the sound clip has ended.

  /**
   * 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);
  }

Nothing has changed here.

  public static void main(String[] args) {
    new Lesson2().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();

    // Loop.
    long time = Sys.getTime();
    long elapse = 0;

    while (!kbhit()) {
    	elapse += Sys.getTime() - time;
    	time += elapse;

    	if (elapse > 5000) {
    		elapse = 0;

    		sourcePos.put(0, sourcePos.get(0) + sourceVel.get(0));
    		sourcePos.put(1, sourcePos.get(1) + sourceVel.get(1));
    		sourcePos.put(2, sourcePos.get(2) + sourceVel.get(2));

    		AL10.alSource(source.get(0), AL10.AL_POSITION, sourcePos);
    	}
    }
    killALData();
  }
}

The only thing that has changed in this code is the loop. Instead of playing and stopping the audio sample it will slowly get quieter as the sources position grows more distant. We do this by slowly incrementing the position by it's velocity over time. The time is sampled by checking the system clock which gives us a tick count. It shouldn't be necessary to change this, but if the audio clip fades too fast you might want to change 5000 to some higher number. Pressing return key will end the loop.

Download source code and resources for this lesson here.