EngineSound.java

/*
 * GPLv2 or 3, Copyright (c) 2010  Andrzej Zaborowski
 *
 * This class simulates a car engine.  What does a car engine do?  It
 * makes a pc-speaker-like buzz.  The PC Speaker could only emit
 * a (nearly) square wave and we simulate it here for maximum realism.
 */
package wmsturbochallenge;

import java.util.Timer;
import java.util.TimerTask;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.DataLine;
import javax.sound.sampled.SourceDataLine;

class EngineSound {
    public EngineSound() {
        rpm = 0.0;
    }

    public void start() {
        rpm = 0.3;
        speed = 0.0;
        n = 0;

        if (output != null)
            stop();

        AudioFormat output_format =
                new AudioFormat(S_RATE, 16, 1, true, true);
        DataLine.Info info =
                new DataLine.Info(SourceDataLine.class, output_format);

        /* Get the data line, open it and initialise the device */
        try {
            output = (SourceDataLine) AudioSystem.getLine(info);
            output.open(output_format);
            output.start();
            frames_written = 0;
            reschedule(0);
        } catch (Exception e) {
            output = null;
            System.out.println("Audio not available: " +
                    e.getClass().getSimpleName());
        }
    }

    public void stop() {
        rpm = 0.0;
        n = 0;

        if (output == null)
            return;

        tick.cancel();
        tick.purge();

        output.stop();
        output.flush();
        output.close();
        output = null;
    }

    public void set_speed(double speed) {
        /* This engine is equipped with an automatic gear box that
         * switches gears when the RPM becomes too high or too low.  */
        double new_speed = Math.abs(speed);
        double accel = new_speed - this.speed;
        this.speed = new_speed;

        if (accel > 0.05)
            accel = 0.05;
        else if (accel < -0.05)
            accel = -0.05;
        rpm += accel;

        if (accel > 0.0 && rpm > 1.0 + n * 0.2 && speed > 0.0) {
            rpm = 0.3 + n * 0.2;
            n ++;
        } else if (accel < 0.0 && rpm < 0.3) {
            if (n > 0) {
                rpm = 0.7 + n * 0.1;
                n --;
            } else
                rpm = 0.2;
        }
        if (speed < 2.0)
            n = 0;
    }

    public boolean is_on() {
        return output != null;
    }

    protected double speed;
    protected double rpm;
    protected int n;

    protected SourceDataLine output = null;
    protected long frames_written;
    protected Timer tick = new Timer();

    /* Audio parameters.  */
    protected static final int S_RATE = 44100;
    protected static final int MIN_BUFFER = 4096;
    protected static final double volume = 0.3;

    protected class audio_task extends TimerTask {
        @Override
        public void run() {
            if (output == null)
                return;

            /* If more than a two buffers left to play,
             * reschedule and try to wake up closer to the
             * end of already written data.  */
            long frames_current = output.getLongFramePosition();
            if (frames_current < frames_written - MIN_BUFFER * 2) {
                reschedule(frames_current);
                return;
            }

            /* Build a new buffer */
            /* double freq = 20 * Math.pow(1.3, rpm * 5.0); */
            double freq = (rpm - 0.1) * 160.0;
            int wavelen = (int) (S_RATE / freq);
            int bufferlen = MIN_BUFFER - (MIN_BUFFER % wavelen) +
                    wavelen;
            int value = (int) (0x7fff * volume);

            bufferlen *= 2;
            byte[] buffer = new byte[bufferlen];
            for (int b = 0; b < bufferlen; ) {
                int j;
                for (j = wavelen / 2; j > 0; j --) {
                    buffer[b ++] = (byte) (value >> 8);
                    buffer[b ++] = (byte) (value & 0xff);
                }
                value = 0x10000 - value;
                for (j = wavelen - wavelen / 2; j > 0; j --) {
                    buffer[b ++] = (byte) (value >> 8);
                    buffer[b ++] = (byte) (value & 0xff);
                }
                value = 0x10000 - value;
            }

            frames_written +=
                    output.write(buffer, 0, bufferlen) / 2;

            reschedule(frames_current);
        }
    }

    protected void reschedule(long frames) {
        /* Send a new buffer as close to the end of the
         * currently playing buffer as possible (aim at
         * about half into the last frame).  */
        long delay = (frames_written - frames - MIN_BUFFER / 2) *
                1000 / S_RATE;
        if (delay < 0)
            delay = 0;
        tick.schedule(new audio_task(), delay);
    }
}