Source/WebCore/Modules/webaudio/PeriodicWave.h

/*
 * Copyright (C) 2012 Google Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
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 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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#pragma once

#include "AudioArray.h"
#include <JavaScriptCore/Float32Array.h>
#include <memory>
#include <wtf/RefCounted.h>
#include <wtf/Vector.h>

namespace WebCore {

class PeriodicWave : public RefCounted<PeriodicWave> {
public:
    static Ref<PeriodicWave> createSine(float sampleRate);
    static Ref<PeriodicWave> createSquare(float sampleRate);
    static Ref<PeriodicWave> createSawtooth(float sampleRate);
    static Ref<PeriodicWave> createTriangle(float sampleRate);

    // Creates an arbitrary wave given the frequency components (Fourier coefficients).
    static Ref<PeriodicWave> create(float sampleRate, Float32Array& real, Float32Array& imag);

    // Returns pointers to the lower and higher wave data for the pitch range containing
    // the given fundamental frequency. These two tables are in adjacent "pitch" ranges
    // where the higher table will have the maximum number of partials which won't alias when played back
    // at this fundamental frequency. The lower wave is the next range containing fewer partials than the higher wave.
    // Interpolation between these two tables can be made according to tableInterpolationFactor.
    // Where values from 0 -> 1 interpolate between lower -> higher.
    void waveDataForFundamentalFrequency(float, float* &lowerWaveData, float* &higherWaveData, float& tableInterpolationFactor);

    // Returns the scalar multiplier to the oscillator frequency to calculate wave table phase increment.
    float rateScale() const { return m_rateScale; }

    unsigned periodicWaveSize() const { return m_periodicWaveSize; }
    float sampleRate() const { return m_sampleRate; }

private:
    enum class Type {
        Sine,
        Square,
        Sawtooth,
        Triangle,
    };

    explicit PeriodicWave(float sampleRate);

    void generateBasicWaveform(Type);

    float m_sampleRate;
    unsigned m_periodicWaveSize;
    unsigned m_numberOfRanges;
    float m_centsPerRange;

    // The lowest frequency (in Hertz) where playback will include all of the partials.
    // Playing back lower than this frequency will gradually lose more high-frequency information.
    // This frequency is quite low (~10Hz @ 44.1KHz)
    float m_lowestFundamentalFrequency;

    float m_rateScale;

    unsigned numberOfRanges() const { return m_numberOfRanges; }

    // Maximum possible number of partials (before culling).
    unsigned maxNumberOfPartials() const;

    unsigned numberOfPartialsForRange(unsigned rangeIndex) const;

    // Creates tables based on numberOfComponents Fourier coefficients.
    void createBandLimitedTables(const float* real, const float* imag, unsigned numberOfComponents);
    Vector<std::unique_ptr<AudioFloatArray>> m_bandLimitedTables;
};

} // namespace WebCore