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Source code

void PlottingGraph::draw()
{
	m_time++;
	memmove(m_y, &m_y[1], 99 * sizeof(double));
	m_y[99] = 10000 * sin((double)m_time / 360 * 3.1415 * 10) + rand() % 4000 - 2000;//m_y[99] = 100 * sin((double)m_time / 360 * 3.1415 * 10) + rand() % 400 - 200;
	for (int i = 0; i < 100; i++)
            m_x[i]++;
	if (!m_curve)
	{      
        qreal left = int(rect.left()) - (int(rect.left()) % gridSize);
        qreal top = int(rect.top()) - (int(rect.top()) % gridSize);
        QVarLengthArray<QLineF, 100> lines;
        for (qreal x = left; x < rect.right(); x += gridSize)
        lines.append(QLineF(x, rect.top(), x, rect.bottom()));
        for (qreal y = top; y < rect.bottom(); y += gridSize)
        lines.append(QLineF(rect.left(), y, rect.right(), y));
        qDebug() << lines.size();
        painter->drawLines(lines.data(), lines.size());

		        m_curve = new QwtPlotCurve();
                m_curve->setPen(QPen(Qt::blue));//setPen(QPen(QColor::fromRgb(255, 255, 0), 3));
                m_curve->setData(m_x, m_y, 100);
		        m_curve->attach(myPlot);
	}
    m_curve->setData(m_x, m_y, 100);
    myPlot->setAxisScale(QwtPlot::xBottom, m_time, m_time + 100); // auto replots 
}