qcustomplot 绘图 2

这个例子涉及：双坐标，坐标联动、坐标自适应、多线绘制，图形填充，图形缩放

    plot->addGraph();
    plot->graph(0)->setPen(QPen(Qt::blue)); // line color blue for first graph
    plot->graph(0)->setBrush(QBrush(QColor(0, 0, 255, 20))); // first graph will be filled with translucent blue
    plot->addGraph();
    plot->graph(1)->setPen(QPen(Qt::red)); // line color red for second graph
    // generate some points of data (y0 for first, y1 for second graph):
    QVector<double> x(251), y0(251), y1(251);
    for (int i=0; i<251; ++i)
    {
        x[i] = i;
        y0[i] = qExp(-i/150.0)*qCos(i/10.0); // exponentially decaying cosine
        y1[i] = qExp(-i/150.0);              // exponential envelope
    }
    // configure right and top axis to show ticks but no labels:
    // (see QCPAxisRect::setupFullAxesBox for a quicker method to do this)
    plot->xAxis2->setVisible(true);
    plot->xAxis2->setTickLabels(false);
    plot->yAxis2->setVisible(true);
    plot->yAxis2->setTickLabels(false);
    // make left and bottom axes always transfer their ranges to right and top axes:
    connect(plot->xAxis, SIGNAL(rangeChanged(QCPRange)), plot->xAxis2, SLOT(setRange(QCPRange)));
    connect(plot->yAxis, SIGNAL(rangeChanged(QCPRange)), plot->yAxis2, SLOT(setRange(QCPRange)));
    // pass data points to graphs:
    plot->graph(0)->setData(x, y0);
    plot->graph(1)->setData(x, y1);
    // let the ranges scale themselves so graph 0 fits perfectly in the visible area:
    plot->graph(0)->rescaleAxes();
    // same thing for graph 1, but only enlarge ranges (in case graph 1 is smaller than graph 0):
    plot->graph(1)->rescaleAxes(true);
    // Note: we could have also just called customPlot->rescaleAxes(); instead
    // Allow user to drag axis ranges with mouse, zoom with mouse wheel and select graphs by clicking:
    plot->setInteractions(QCP::iRangeDrag | QCP::iRangeZoom | QCP::iSelectPlottables);