BasicEmitter.cs

//  
//  Author: John Carruthers (johnc@frag-labs.com)
//  
//  Copyright (C) 2013 John Carruthers
//  
//  Permission is hereby granted, free of charge, to any person obtaining
//  a copy of this software and associated documentation files (the
//  "Software"), to deal in the Software without restriction, including
//  without limitation the rights to use, copy, modify, merge, publish,
//  distribute, sublicense, and/or sell copies of the Software, and to
//  permit persons to whom the Software is furnished to do so, subject to
//  the following conditions:
//   
//  The above copyright notice and this permission notice shall be
//  included in all copies or substantial portions of the Software.
//   
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
//  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
//  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
//  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
//  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
//  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//  

using System;
using System.IO;
using System.Threading;

namespace FragLabs.Audio.Locator
{
    /// <summary>
    /// A basic emitter that plays a single frequency.
    /// </summary>
    public class BasicEmitter : IEmitter
    {
        private readonly Stream _outputAudioStream;
        private readonly TimeSpan _repeatDelay;
        private readonly int _frequency;
        private readonly int _amplitude;
        private readonly int _channels;
        private readonly int _sampleRate;

        private byte[] _emitSoundData;
        private Thread _thread;

        public BasicEmitter(Stream outputAudioStream, TimeSpan repeatDelay, int frequency,
                        int amplitude, int channels, int sampleRate)
        {
            _outputAudioStream = outputAudioStream;
            _repeatDelay = repeatDelay;
            _frequency = frequency;
            _amplitude = amplitude;
            _channels = channels;
            _sampleRate = sampleRate;
            if (outputAudioStream == null) throw new ArgumentNullException("outputAudioStream");
            ProduceEmitSoundData();

            //  todo: replace this with a better mechanism for transmitting
            _thread = new Thread(() =>
                {
                    while (true)
                    {
                        _outputAudioStream.Write(_emitSoundData, 0, _emitSoundData.Length);
                        Thread.Sleep(_repeatDelay);
                    }
                });
            _thread.Start();
        }

        private void ProduceEmitSoundData()
        {
            var duration = TimeSpan.FromMilliseconds(10);
            var sampleCount = Convert.ToInt32(duration.TotalSeconds *
                _sampleRate);
            var samples = new short[sampleCount * _channels];
            var angle = (Math.PI * 2 * _frequency) /
                (_sampleRate * _channels);
            for (var i = 0; i < sampleCount; i++)
            {
                var offset = i * 2;
                samples[offset] = Convert.ToInt16(_amplitude *
                    Math.Sin(angle * i));
                samples[offset + 1] = Convert.ToInt16(_amplitude *
                    Math.Sin(angle * i));
            }
            _emitSoundData = new byte[sampleCount * 2 * _channels];
            for (var i = 0; i < samples.Length; i++)
            {
                var offset = i * 2;
                var sample = BitConverter.GetBytes(samples[i]);
                Buffer.BlockCopy(sample, 0, _emitSoundData, offset, 2);
            }
        }
    }
}