ToneGenerator.h

Go to the documentation of this file.

// Copyright 2015 - 2026, GIBIS-UNIFESP and the wiRedPanda contributors
// SPDX-License-Identifier: GPL-3.0-or-later

 
#pragma once
 
#include <cmath>
#include <cstring>
 
#include <QAudioFormat>
#include <QIODevice>

class ToneGenerator : public QIODevice
{
    Q_OBJECT
 
public:
    explicit ToneGenerator(QObject *parent = nullptr)
        : QIODevice(parent)
    {
    }

    static QAudioFormat format()
    {
        QAudioFormat fmt;
        fmt.setSampleRate(SampleRate);
        fmt.setChannelCount(1);
        fmt.setSampleFormat(QAudioFormat::Int16);
        return fmt;
    }

    void setFrequency(double hz) { m_frequency = hz; }

    double frequency() const { return m_frequency; }

    bool isSequential() const override { return true; }

    qint64 bytesAvailable() const override { return SampleRate * BytesPerSample; }

    bool start()
    {
        m_phase = 0.0;
        return open(QIODevice::ReadOnly);
    }
 
protected:
    qint64 readData(char *data, qint64 maxSize) override
    {
        constexpr double twoPi = 2.0 * M_PI;
        const double increment = m_frequency / SampleRate;
 
        const qint64 samples = maxSize / BytesPerSample;
 
        for (qint64 i = 0; i < samples; ++i) {
            // data is Qt's raw QIODevice buffer — no alignment guarantee, so a
            // reinterpret_cast<qint16*> store is a -Wcast-align violation on
            // armhf/riscv64 (issue #453). memcpy of a compile-time-constant 2
            // bytes inlines to a single (possibly unaligned) store at -O2, so
            // this has no measurable cost in the real-time audio path.
            const qint16 sample = static_cast<qint16>(Amplitude * std::sin(twoPi * m_phase));
            std::memcpy(data + i * BytesPerSample, &sample, sizeof(sample));
            m_phase += increment;
            if (m_phase >= 1.0) {
                m_phase -= 1.0;
            }
        }
 
        return samples * BytesPerSample;
    }

    qint64 writeData(const char *, qint64) override { return -1; }
 
private:
    static constexpr int SampleRate = 44100;
    static constexpr int BytesPerSample = sizeof(qint16);
    static constexpr double Amplitude = 28000.0;
 
    double m_frequency = 1047.0; // C6 default
    double m_phase = 0.0;
};