ChartDirector 6.0 (C++ Edition)

Track Line with Legend (QT)

NOTE: This section describes Track Line with Legend for QT only. For MFC, please refer to Track Line with Legend (MFC).

This sample program demonstrates a track cursor programmed with the following features:

The code first draws the chart, and sets the track cursor to the right side of the plot area. This ensures the chart initially has a legend that reflects the latest data values. In the QChartViewer.mouseMovePlotArea signal handler, the track cursor is updated to reflect the mouse position.

The trackLineLegend method is the routine that draws the track cursor. Its key elements are:

Source Code Listing

The following is the main source code of this demo. The complete QT project is in "qtdemo/tracklegend".

[File: qtdemo/tracklegend/tracklegend.cpp]
#include <QApplication>
#include "tracklegend.h"
#include <vector>
#include <sstream>

using namespace std;

int main(int argc, char *argv[])
    QApplication app(argc, argv);
    app.setStyleSheet("* {font-family:arial;font-size:11px}");
    TrackLegend demo;;
    return app.exec();

TrackLegend::TrackLegend(QWidget *parent) :
    setWindowTitle("Track Line with Legend");

    // Create the QChartViewer and draw the chart
    m_ChartViewer = new QChartViewer(this);

    // Set the window to be of the same size as the chart
    setFixedSize(m_ChartViewer->width(), m_ChartViewer->height());

    // Set up the mouseMovePlotArea handler for drawing the track cursor
    connect(m_ChartViewer, SIGNAL(mouseMovePlotArea(QMouseEvent*)),

    delete m_ChartViewer->getChart();

// Draw the chart and display it in the given viewer
void TrackLegend::drawChart(QChartViewer *viewer)
    // Data for the chart as 3 random data series
    RanSeries r(127);
    DoubleArray data0 = r.getSeries(100, 100, -15, 15);
    DoubleArray data1 = r.getSeries(100, 150, -15, 15);
    DoubleArray data2 = r.getSeries(100, 200, -15, 15);
    DoubleArray timeStamps = r.getDateSeries(100, Chart::chartTime(2011, 1, 1), 86400);

    // Create a XYChart object of size 640 x 400 pixels
    XYChart *c = new XYChart(640, 400);

    // Add a title to the chart using 18 pts Times New Roman Bold Italic font
    c->addTitle("    Product Line Global Revenue", "timesbi.ttf", 18);

    // Set the plotarea at (50, 55) with width 70 pixels less than chart width, and height 90 pixels
    // less than chart height. Use a vertical gradient from light blue (f0f6ff) to sky blue (a0c0ff)
    // as background. Set border to transparent and grid lines to white (ffffff).
    c->setPlotArea(50, 55, c->getWidth() - 70, c->getHeight() - 90, c->linearGradientColor(0, 55, 0,
        c->getHeight() - 35, 0xf0f6ff, 0xa0c0ff), -1, Chart::Transparent, 0xffffff, 0xffffff);

    // Set legend icon style to use line style icon, sized for 8pt font

    // Set axis label style to 8pts Arial Bold
    c->xAxis()->setLabelStyle("arialbd.ttf", 8);
    c->yAxis()->setLabelStyle("arialbd.ttf", 8);

    // Set the axis stem to transparent

    // Configure x-axis label format
    c->xAxis()->setMultiFormat(Chart::StartOfYearFilter(), "{value|mm/yyyy} ",
        Chart::StartOfMonthFilter(), "{value|mm}");

    // Add axis title using 10pts Arial Bold Italic font
    c->yAxis()->setTitle("USD millions", "arialbi.ttf", 10);

    // Add a line layer to the chart using a line width of 2 pixels.
    LineLayer *layer = c->addLineLayer();

    // Add 3 data series to the line layer
    layer->addDataSet(data0, 0xff3333, "Alpha");
    layer->addDataSet(data1, 0x008800, "Beta");
    layer->addDataSet(data2, 0x3333cc, "Gamma");

    // Include track line with legend for the latest data values
    trackLineLegend(c, c->getPlotArea()->getRightX());

    // Set the chart image to the QChartViewer

// Draw track cursor when mouse is moving over plotarea
void TrackLegend::onMouseMovePlotArea(QMouseEvent *)
    trackLineLegend((XYChart *)m_ChartViewer->getChart(), m_ChartViewer->getPlotAreaMouseX());

// Draw the track line with legend
void TrackLegend::trackLineLegend(XYChart *c, int mouseX)
    // Clear the current dynamic layer and get the DrawArea object to draw on it.
    DrawArea *d = c->initDynamicLayer();

    // The plot area object
    PlotArea *plotArea = c->getPlotArea();

    // Get the data x-value that is nearest to the mouse, and find its pixel coordinate.
    double xValue = c->getNearestXValue(mouseX);
    int xCoor = c->getXCoor(xValue);

    // Draw a vertical track line at the x-position
    d->vline(plotArea->getTopY(), plotArea->getBottomY(), xCoor, d->dashLineColor(0x000000, 0x0101));

    // Container to hold the legend entries
    vector<string> legendEntries;

    // Iterate through all layers to build the legend array
    for (int i = 0; i < c->getLayerCount(); ++i) {
        Layer *layer = c->getLayerByZ(i);

        // The data array index of the x-value
        int xIndex = layer->getXIndexOf(xValue);

        // Iterate through all the data sets in the layer
        for (int j = 0; j < layer->getDataSetCount(); ++j) {
            DataSet *dataSet = layer->getDataSetByZ(j);

            // We are only interested in visible data sets with names
            const char *dataName = dataSet->getDataName();
            int color = dataSet->getDataColor();
            if (dataName && *dataName && (color != (int)Chart::Transparent)) {
                // Build the legend entry, consist of the legend icon, name and data value.
                double dataValue = dataSet->getValue(xIndex);
                ostringstream legendEntry;
                legendEntry << "<*block*>" << dataSet->getLegendIcon() << " " << dataName << ": " <<
                    ((dataValue == Chart::NoValue) ? "N/A" : c->formatValue(dataValue, "{value|P4}"))
                    << "<*/*>";

                // Draw a track dot for data points within the plot area
                int yCoor = c->getYCoor(dataSet->getPosition(xIndex), dataSet->getUseYAxis());
                if ((yCoor >= plotArea->getTopY()) && (yCoor <= plotArea->getBottomY())) {
                    d->circle(xCoor, yCoor, 4, 4, color, color);

    // Create the legend by joining the legend entries
    ostringstream legendText;
    legendText << "<*block,maxWidth=" << plotArea->getWidth() << "*><*block*><*font=arialbd.ttf*>["
        << c->xAxis()->getFormattedLabel(xValue, "mmm dd, yyyy") << "]<*/*>";
    for (int i = ((int)legendEntries.size()) - 1; i >= 0; --i)
        legendText << "        " << legendEntries[i];

    // Display the legend on the top of the plot area
    TTFText *t = d->text(legendText.str().c_str(), "arial.ttf", 8);
    t->draw(plotArea->getLeftX() + 5, plotArea->getTopY() - 3, 0x000000, Chart::BottomLeft);