I need to dynamically display about 30,000 DAQ points. The x-axis display range is [0,1000]. When I select the graph, the width of the pen is set to 2. At this time, the spectrogram drawing is stuck.
The main code:

QVector<double> m_x, m_y;
void ChartTest::timerEvent(QTimerEvent *evt)
{
     Q_UNUSED(evt)
     for (int i = 0; i < m_chart->graphCount(); ++i){
         auto pG = m_chart->graph(i);
         generateTestData(50000, &m_x, &m_y);
         pG->setData(m_x, m_y);
     }
     m_chart->replot();
}
void ChartTest::generateTestData(int n, QVector<double> *x, QVector<double> *y)
{
    x->resize(n);
    y->resize(n);

    double yScale = (rand()/(double)RAND_MAX + 0.5)*2;

    double r1 = (rand()/(double)RAND_MAX - 0.5)*2;
    double r2 = (rand()/(double)RAND_MAX - 0.5)*2;
    double r3 = (rand()/(double)RAND_MAX - 0.5)*2;
    double r4 = (rand()/(double)RAND_MAX - 0.5)*2;

    double xStep = 1000.0 / n;
    for (int i=0; i<n; i++)
    {
        x->data()[i] = i * xStep;
        y->data()[i] = (qSin(x->data()[i]*r1*5)*qSin(qCos(x->data()[i]*r2)*r4*3)+
                        r3*qCos(qSin(x->data()[i])*r4*2))*yScale;
    }
}

When the x-axis range is small, such as [0,100],[-5,5], even if the line width is 2 and the amount of data is equal, it will not freeze.
Does the drawing range of the X axis affect the drawing speed?
I want the line width to be 2 when selected, but I can't stand the drawing lag. Can anyone give me advice?