mixer.h

/*
 * This file is part of libsidplayfp, a SID player engine.
 *
 * Copyright 2011-2015 Leandro Nini <drfiemost@users.sourceforge.net>
 * Copyright 2007-2010 Antti Lankila
 * Copyright (C) 2000 Simon White
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
 
#ifndef MIXER_H
#define MIXER_H
 
#include "sidcxx11.h"
 
#include <stdint.h>
#include <cstdlib>
 
#include <vector>
 
namespace libsidplayfp
{
 
class sidemu;
 
class Mixer
{
public:
    static const unsigned int MAX_SIDS = 3;
 
    static const int_least32_t SCALE_FACTOR = 1 << 16;
#ifdef HAVE_CXX11
    static constexpr double SQRT_0_5 = 0.70710678118654746;
#else
#  define SQRT_0_5 0.70710678118654746
#endif
    static const int_least32_t C1 = static_cast<int_least32_t>(1.0 / (1.0 + SQRT_0_5) * SCALE_FACTOR);
    static const int_least32_t C2 = static_cast<int_least32_t>(SQRT_0_5 / (1.0 + SQRT_0_5) * SCALE_FACTOR);
 
private:
    typedef int_least32_t (Mixer::*mixer_func_t)() const;
 
public:
    static const int_least32_t VOLUME_MAX = 1024;
 
private:
    std::vector<sidemu*> m_chips;
    std::vector<short*> m_buffers;
 
    std::vector<int_least32_t> m_iSamples;
    std::vector<int_least32_t> m_volume;
 
    std::vector<mixer_func_t> m_mix;
 
    int oldRandomValue;
    int m_fastForwardFactor;
 
    // Mixer settings
    short         *m_sampleBuffer;
    uint_least32_t m_sampleCount;
    uint_least32_t m_sampleIndex;
 
    bool m_stereo;
 
private:
    void updateParams();
 
    int triangularDithering()
    {
        const int prevValue = oldRandomValue;
        oldRandomValue = rand() & (VOLUME_MAX-1);
        return oldRandomValue - prevValue;
    }
 
    /*
     * Channel matrix
     *
     *   C1
     * L 1.0
     * R 1.0
     *
     *   C1   C2
     * L 1.0  0.0
     * R 0.0  1.0
     *
     *   C1       C2           C3
     * L 1/1.707  0.707/1.707  0.0
     * R 0.0      0.707/1.707  1/1.707
     * 
     * FIXME
     * it seems that scaling down the summed signals is not the correct way of mixing, see:
     * http://dsp.stackexchange.com/questions/3581/algorithms-to-mix-audio-signals-without-clipping
     * maybe we should consider some form of soft/hard clipping instead to avoid possible overflows
     */
 
    // Mono mixing
    template <int Chips>
    int_least32_t mono() const
    {
        int_least32_t res = 0;
        for (int i = 0; i < Chips; i++)
            res += m_iSamples[i];
        return res / Chips;
    }
 
    // Stereo mixing
    int_least32_t stereo_OneChip() const { return m_iSamples[0]; }
 
    int_least32_t stereo_ch1_TwoChips() const { return m_iSamples[0]; }
    int_least32_t stereo_ch2_TwoChips() const { return m_iSamples[1]; }
 
    int_least32_t stereo_ch1_ThreeChips() const { return (C1*m_iSamples[0] + C2*m_iSamples[1]) / SCALE_FACTOR; }
    int_least32_t stereo_ch2_ThreeChips() const { return (C2*m_iSamples[1] + C1*m_iSamples[2]) / SCALE_FACTOR; }
 
public:
    Mixer() :
        oldRandomValue(0),
        m_fastForwardFactor(1),
        m_sampleCount(0),
        m_stereo(false)
    {
        m_mix.push_back(&Mixer::mono<1>);
    }
 
    void doMix();
 
    void clockChips();
 
    void resetBufs();
 
    void begin(short *buffer, uint_least32_t count);
 
    void clearSids();
 
    void addSid(sidemu *chip);
 
    sidemu* getSid(unsigned int i) const { return (i < m_chips.size()) ? m_chips[i] : nullptr; }
 
    bool setFastForward(int ff);
 
    void setVolume(int_least32_t left, int_least32_t right);
 
    void setStereo(bool stereo);
 
    bool notFinished() const { return m_sampleIndex != m_sampleCount; }
 
    uint_least32_t samplesGenerated() const { return m_sampleIndex; }
};
 
}
 
#endif // MIXER_H