Multiple Sources
Lesson 3

Author: Jesse Maurais
Adapted for Java by: Athomas Goldberg

Launch the Demo via Java Web Start

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.nio.ByteBuffer;
import java.util.Random;

import net.java.games.joal.AL;
import net.java.games.joal.ALFactory;
import net.java.games.joal.util.ALut;
  
public class MultipleSources {

    static AL al;

    // Maximum number of buffers we will need.
    static final int NUM_BUFFERS = 3;

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

    // These index the buffers and sources
    static final int BATTLE = 0;
    static final int GUN1   = 1;
    static final int GUN2   = 2;

    // Buffers hold sound data
    static int[] buffers = new int[NUM_BUFFERS];

    // Sources are points of emitting sound
    static int[] sources = new int[NUM_SOURCES];

    // Position of the source sounds.
    static float[][] sourcePos = new float[NUM_SOURCES][3];

    // Velocity of the source sounds
    static float[][] sourceVel = new float[NUM_SOURCES][3];

    // Position of the listener.
    static float[] listenerPos = { 0.0f, 0.0f, 0.0f };

    // Velocity of the listener.
    static float[] listenerVel = { 0.0f, 0.0f, 0.0f };

    // Orientation of the listener. (first 3 elements are "at", second 3 are "up")
    static float[] listenerOri = { 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.

    static int loadALData() {

        //variables to load into

        int[] format = new int[1];
        int[] size = new int[1];
        ByteBuffer[] data = new ByteBuffer[1];
        int[] freq = new int[1];
        int[] loop = new int[1];
        
        // load wav data into buffers

        al.alGenBuffers(NUM_BUFFERS, buffers);
        if (al.alGetError() != AL.AL_NO_ERROR) {
            return AL.AL_FALSE;
        }

        ALut.alutLoadWAVFile(
            "wavdata/Battle.wav",
            format,
            data,
            size,
            freq,
            loop);
        al.alBufferData(
            buffers[BATTLE],
            format[0],
            data[0],
            size[0],
            freq[0]);
        ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);

        ALut.alutLoadWAVFile(
            "wavdata/Gun1.wav",
            format,
            data,
            size,
            freq,
            loop);
        al.alBufferData(
            buffers[GUN1],
            format[0],
            data[0],
            size[0],
            freq[0]);
        ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);

        ALut.alutLoadWAVFile(
            "wavdata/Gun2.wav",
            format,
            data,
            size,
            freq,
            loop);
        al.alBufferData(
            buffers[GUN2],
            format[0],
            data[0],
            size[0],
            freq[0]);
        ALut.alutUnloadWAV(format[0], data[0], size[0], freq[0]);

        // bind buffers into audio sources
        al.alGenSources(NUM_SOURCES, sources);

        al.alSourcei(sources[BATTLE], AL.AL_BUFFER, buffers[BATTLE]);
        al.alSourcef(sources[BATTLE], AL.AL_PITCH, 1.0f);
        al.alSourcef(sources[BATTLE], AL.AL_GAIN, 1.0f);
        al.alSourcefv(sources[BATTLE], AL.AL_POSITION, sourcePos[BATTLE]);
        al.alSourcefv(sources[BATTLE], AL.AL_POSITION, sourceVel[BATTLE]);
        al.alSourcei(sources[BATTLE], AL.AL_LOOPING, AL.AL_TRUE);

        al.alSourcei(sources[GUN1], AL.AL_BUFFER, buffers[GUN1]);
        al.alSourcef(sources[GUN1], AL.AL_PITCH, 1.0f);
        al.alSourcef(sources[GUN1], AL.AL_GAIN, 1.0f);
        al.alSourcefv(sources[GUN1], AL.AL_POSITION, sourcePos[GUN1]);
        al.alSourcefv(sources[GUN1], AL.AL_POSITION, sourceVel[GUN1]);
        al.alSourcei(sources[GUN1], AL.AL_LOOPING, AL.AL_FALSE);

        al.alSourcei(sources[GUN2], AL.AL_BUFFER, buffers[GUN2]);
        al.alSourcef(sources[GUN2], AL.AL_PITCH, 1.0f);
        al.alSourcef(sources[GUN2], AL.AL_GAIN, 1.0f);
        al.alSourcefv(sources[GUN2], AL.AL_POSITION, sourcePos[GUN2]);
        al.alSourcefv(sources[GUN2], AL.AL_POSITION, sourceVel[GUN2]);
        al.alSourcei(sources[GUN2], AL.AL_LOOPING, AL.AL_FALSE);

        // do another error check and return
        if (al.alGetError() != AL.AL_NO_ERROR) {
            return AL.AL_FALSE;
        }

        return AL.AL_TRUE;
    }

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.

    static void setListenerValues() {
        al.alListenerfv(AL.AL_POSITION, listenerPos);
        al.alListenerfv(AL.AL_VELOCITY, listenerVel);
        al.alListenerfv(AL.AL_ORIENTATION, listenerOri);
    }

    static void killAllData() {
        al.alDeleteBuffers(NUM_BUFFERS, buffers);
        al.alDeleteSources(NUM_SOURCES, sources);
        ALut.alutExit();
    }

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

    public static void main(String[] args) {
        al = ALFactory.getAL();

		// Initialize OpenAL and clear the error bit

        ALut.alutInit();
        al.alGetError();
        
		// Load the wav data.

        if(loadALData() == AL.AL_FALSE) {
            System.exit(1);    
        }
        setListenerValues();

		// begin the battle sample to play

        al.alSourcePlay(sources[BATTLE]);
        long startTime = System.currentTimeMillis();
        long elapsed = 0;
        long totalElapsed = 0;
        Random rand = new Random();
        int[] state = new int[1];
        while (totalElapsed < 10000) {
            elapsed = System.currentTimeMillis() - startTime;
            if (elapsed > 50) {
                totalElapsed += elapsed;
                startTime = System.currentTimeMillis();
				
                // pick one of the sources at random and check to see if it is playing.
                // Skip the first source because it is looping anyway (will always be playing).
                
				 int pick = Math.abs((rand.nextInt()) % 2) + 1;
                al.alGetSourcei(sources[pick], AL.AL_SOURCE_STATE, state);
				
                if (state[0] != AL.AL_PLAYING) {
				
				    // pick a random position around the listener to play the source.
				
                    double theta = (rand.nextInt() % 360) * 3.14 / 180.0;
                    sourcePos[pick][0] = - ((float) Math.cos(theta));
                    sourcePos[pick][1] = - ((float) (rand.nextInt() % 2));
                    sourcePos[pick][2] = - ((float) Math.sin(theta));

                    al.alSourcefv(
                        sources[pick],
                        AL.AL_POSITION,
                        sourcePos[pick]);

                    al.alSourcePlay(sources[pick]);
                }
            }
        }
        killAllData();
    }
}

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!