qt-everywhere-src-5.15.1/qtcharts/examples/charts/audio/xyseriesiodevice.cpp

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#include "xyseriesiodevice.h"

#include <QtCharts/QXYSeries>

XYSeriesIODevice::XYSeriesIODevice(QXYSeries *series, QObject *parent) :
    QIODevice(parent),
    m_series(series)
{
}

qint64 XYSeriesIODevice::readData(char *data, qint64 maxSize)
{
    Q_UNUSED(data)
    Q_UNUSED(maxSize)
    return -1;
}

qint64 XYSeriesIODevice::writeData(const char *data, qint64 maxSize)
{
    static const int resolution = 4;

    if (m_buffer.isEmpty()) {
        m_buffer.reserve(sampleCount);
        for (int i = 0; i < sampleCount; ++i)
            m_buffer.append(QPointF(i, 0));
    }

    int start = 0;
    const int availableSamples = int(maxSize) / resolution;
    if (availableSamples < sampleCount) {
        start = sampleCount - availableSamples;
        for (int s = 0; s < start; ++s)
            m_buffer[s].setY(m_buffer.at(s + availableSamples).y());
    }

    for (int s = start; s < sampleCount; ++s, data += resolution)
        m_buffer[s].setY(qreal(uchar(*data) -128) / qreal(128));

    m_series->replace(m_buffer);
    return (sampleCount - start) * resolution;
}