ChartDirector 6.0 (C++ Edition)

Crosshair with Axis Labels (QT)

NOTE: This section describes Crosshair with Axis Labels for QT only. For MFC, please refer to Crosshair with Axis Labels (MFC).

This sample program demonstrates a track cursor programmed as a crosshair cursor with axis labels.

The code first draws the chart. Then in the QChartViewer.mouseMovePlotArea signal handler, the track cursor is drawn to reflect the mouse position. The track cursor is configured to automatically hide itself when the mouse leaves the plot area.

The crossHair 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/crosshair".

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

using namespace std;

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

CrossHair::CrossHair(QWidget *parent) :
    setWindowTitle("Crosshair with Axis Labels");

    // 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 CrossHair::drawChart(QChartViewer *viewer)
    // The XY data of the first data series
    double dataX[] = {50, 55, 37, 24, 42, 49, 63, 72, 83, 59};
    double dataY[] = {3.6, 2.8, 2.5, 2.3, 3.8, 3.0, 3.8, 5.0, 6.0, 3.3};
    int noOfPoints = (int)(sizeof(dataX) / sizeof(*dataX));

    // Create a XYChart object of size 520 x 490 pixels
    XYChart *c = new XYChart(520, 490);

    // Set the plotarea at (60, 40) and of size 450 x 400 pixels, with white background and a light
    // grey border (0xc0c0c0). Turn on both horizontal and vertical grid lines with light grey color
    // (0xc0c0c0)
    c->setPlotArea(60, 40, 450, 400, 0xffffff, -1, 0xc0c0c0, 0xc0c0c0, -1);

    // Add a title to the chart using 18 point Times Bold Itatic font.
    c->addTitle("      Chemical X Thermal Conductivity", "timesbi.ttf", 18);

    // Add titles to the axes using 12 pts Arial Bold Italic font
    c->yAxis()->setTitle("Thermal Conductivity (W/K)", "arialbi.ttf", 12);
    c->xAxis()->setTitle("Concentration (g/liter)", "arialbi.ttf", 12);

    // Set the axes line width to 3 pixels

    // Add a scatter layer using (dataX, dataY)
    ScatterLayer *scatterLayer = c->addScatterLayer(DoubleArray(dataX, noOfPoints), 
        DoubleArray(dataY, noOfPoints), "", Chart::GlassSphereShape, 13, 0xcc0000);

    // Tooltip for the scatter layer
    scatterLayer->setHTMLImageMap("", "",
        "title='Concentration: {x} g/liter, Conductivity: {value} W/K'");

    // Add a trend line layer for (dataX, dataY)
    TrendLayer *trendLayer = c->addTrendLayer(DoubleArray(dataX, noOfPoints), 
        DoubleArray(dataY, noOfPoints), 0xcc0000);

    // Set the line width to 3 pixels

    // Add a 95% confidence band for the line
    trendLayer->addConfidenceBand(0.95, 0x806666ff);

    // Add a 95% confidence band (prediction band) for the points
    trendLayer->addPredictionBand(0.95, 0x8066ff66);

    // Tool tip for the trend layer
    trendLayer->setHTMLImageMap("", "", "title='Trend Line: y = {slope|P4} x + {intercept|P4}'");

    // Add a legend box at (60, 35) (top of the chart) with horizontal layout. Use 10 pts Arial Bold
    // Italic font. Set the background and border color to Transparent and use line style legend
    // icons.
    LegendBox *legendBox = c->addLegend(60, 35, false, "arialbi.ttf", 9);

    // Add entries to the legend box
    legendBox->addKey("95% Line Confidence", 0x806666ff);
    legendBox->addKey("95% Point Confidence", 0x8066ff66);

    ostringstream trendLegend;
    trendLegend << "Trend Line: y = " << c->formatValue(trendLayer->getSlope(), "{value|4}") << " x";
    trendLegend << " + " << c->formatValue(trendLayer->getIntercept(), "{value|4}");
    legendBox->addKey(trendLegend.str().c_str(), 0xcc0000, 3);

    // Set the chart image to the QChartViewer

    // Include tool tip for the chart

// Draw track cursor when mouse is moving over plotarea
void CrossHair::onMouseMovePlotArea(QMouseEvent *)
    crosshair((XYChart *)m_ChartViewer->getChart(), m_ChartViewer->getPlotAreaMouseX(),
    // Hide the track cursor when the mouse leaves the plot area

// Draw cross hair cursor with axis labels
void CrossHair::crosshair(XYChart *c, int mouseX, int mouseY)
    // 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();

    // Draw a vertical line and a horizontal line as the cross hair
    d->vline(plotArea->getTopY(), plotArea->getBottomY(), mouseX, d->dashLineColor(0x000000, 0x0101));
    d->hline(plotArea->getLeftX(), plotArea->getRightX(), mouseY, d->dashLineColor(0x000000, 0x0101));

    // Draw y-axis label
    ostringstream ylabel;
    ylabel << "<*block,bgColor=FFFFDD,margin=3,edgeColor=000000*>" << c->formatValue(c->getYValue(
        mouseY, c->yAxis()), "{value|P4}") << "<*/*>";
    TTFText *t = d->text(ylabel.str().c_str(), "arialbd.ttf", 8);
    t->draw(plotArea->getLeftX() - 5, mouseY, 0x000000, Chart::Right);

    // Draw x-axis label
    ostringstream xlabel;
    xlabel << "<*block,bgColor=FFFFDD,margin=3,edgeColor=000000*>" << c->formatValue(c->getXValue(
        mouseX), "{value|P4}") << "<*/*>";
    t = d->text(xlabel.str().c_str(), "arialbd.ttf", 8);
    t->draw(mouseX, plotArea->getBottomY() + 5, 0x000000, Chart::Top);