ChartDirector 6.0 (C++ Edition)

Track Line with Axis Labels (QT)




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

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

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 trackLineAxis 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/trackaxis".

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

using namespace std;


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


TrackAxis::TrackAxis(QWidget *parent) :
    QDialog(parent)
{
    setWindowTitle("Track Line with Axis Labels");

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

    // 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*)),
        SLOT(onMouseMovePlotArea(QMouseEvent*)));
}

TrackAxis::~TrackAxis()
{
    delete m_ChartViewer->getChart();
}

//
// Draw the chart and display it in the given viewer
//
void TrackAxis::drawChart(QChartViewer *viewer)
{
    // Data for the chart as 2 random data series
    RanSeries r(127);
    DoubleArray data0 = r.getSeries(180, 10, -1.5, 1.5);
    DoubleArray data1 = r.getSeries(180, 150, -15, 15);
    DoubleArray timeStamps = r.getDateSeries(180, Chart::chartTime(2011, 1, 1), 86400);

    // Create a XYChart object of size 670 x 400 pixels
    XYChart *c = new XYChart(670, 400);

    // Add a title to the chart using 18 pts Times New Roman Bold Italic font
    c->addTitle("Plasma Stabilizer Energy Usage", "timesbi.ttf", 18);

    // Set the plotarea at (50, 55) with width 100 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() - 100, c->getHeight() - 90, c->linearGradientColor(0, 55, 0,
        c->getHeight() - 35, 0xf0f6ff, 0xa0c0ff), -1, Chart::Transparent, 0xffffff, 0xffffff);

    // Add a legend box at (50, 25) using horizontal layout. Use 10pts Arial Bold as font. Set the
    // background and border color to Transparent.
    c->addLegend(50, 25, false, "arialbd.ttf", 10)->setBackground(Chart::Transparent);

    // Set axis label style to 8pts Arial Bold
    c->xAxis()->setLabelStyle("arialbd.ttf", 8);
    c->yAxis()->setLabelStyle("arialbd.ttf", 8);
    c->yAxis2()->setLabelStyle("arialbd.ttf", 8);

    // Set the axis stem to transparent
    c->xAxis()->setColors(Chart::Transparent);
    c->yAxis()->setColors(Chart::Transparent);
    c->yAxis2()->setColors(Chart::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("Power Usage (Watt)", "arialbi.ttf", 10);
    c->yAxis2()->setTitle("Effective Load (kg)", "arialbi.ttf", 10);

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

    // Add 2 data series to the line layer
    layer->setXData(timeStamps);
    layer->addDataSet(data0, 0xcc0000, "Power Usage");
    layer->addDataSet(data1, 0x008800, "Effective Load")->setUseYAxis2();

    // Set the chart image to the QChartViewer
    viewer->setChart(c);
}

//
// Draw track cursor when mouse is moving over plotarea
//
void TrackAxis::onMouseMovePlotArea(QMouseEvent *)
{
    trackLineAxis((XYChart *)m_ChartViewer->getChart(), m_ChartViewer->getPlotAreaMouseX());
    m_ChartViewer->updateDisplay();
    
    // Hide the track cursor when the mouse leaves the plot area
    m_ChartViewer->removeDynamicLayer("mouseLeavePlotArea");
}

//
// Draw track line with axis labels
//
void TrackAxis::trackLineAxis(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);

    // The vertical track line is drawn up to the highest data point (the point with smallest
    // y-coordinate). We need to iterate all datasets in all layers to determine where it is.
    int minY = plotArea->getBottomY();

    // Iterate through all layers to find the highest data point
    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);

            double dataPoint = dataSet->getPosition(xIndex);
            if ((dataPoint != Chart::NoValue) && (dataSet->getDataColor() != (int)Chart::Transparent))
                minY = min(minY, c->getYCoor(dataPoint, dataSet->getUseYAxis()));
        }
    }

    // Draw a vertical track line at the x-position up to the highest data point.
    d->vline(max(minY, plotArea->getTopY()), plotArea->getBottomY() + 6, xCoor, d->dashLineColor(
        0x000000, 0x0101));

    // Draw a label on the x-axis to show the track line position
    ostringstream xlabel;
    xlabel << "<*font,bgColor=000000*> " << c->xAxis()->getFormattedLabel(xValue, "mmm dd, yyyy")
        << " <*/font*>";
    TTFText *t = d->text(xlabel.str().c_str(), "arialbd.ttf", 8);
    t->draw(xCoor, plotArea->getBottomY() + 6, 0xffffff, Chart::Top);
    t->destroy();

    // 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);

            // The positional value, axis binding, pixel coordinate and color of the data point.
            double dataPoint = dataSet->getPosition(xIndex);
            Axis *yAxis = dataSet->getUseYAxis();
            int yCoor = c->getYCoor(dataPoint, yAxis);
            int color = dataSet->getDataColor();

            // Draw the axis label only for visible data points of named data sets
            if ((dataPoint != Chart::NoValue) && (color != (int)Chart::Transparent) && (yCoor >=
                plotArea->getTopY()) && (yCoor <= plotArea->getBottomY())) {
                // The axis label consists of 3 parts - a track dot for the data point, an axis label,
                // and a line joining the track dot to the axis label.

                // Draw the line first. The end point of the line at the axis label side depends on
                // whether the label is at the left or right side of the axis (that is, on whether the
                // axis is on the left or right side of the plot area).
                int xPos = yAxis->getX() + ((yAxis->getAlignment() == Chart::Left) ? -4 : 4);
                d->hline(xCoor, xPos, yCoor, d->dashLineColor(color, 0x0101));

                // Draw the track dot
                d->circle(xCoor, yCoor, 4, 4, color, color);

                // Draw the axis label. If the axis is on the left side of the plot area, the labels
                // should right aligned to the axis, and vice versa.
                ostringstream axisLabel;
                axisLabel << "<*font,bgColor=" << hex << color << "*> "
                    << c->formatValue(dataPoint, "{value|P4}")    << " <*/font*>";
                t = d->text(axisLabel.str().c_str(), "arialbd.ttf", 8);
                t->draw(xPos, yCoor, 0xffffff,
                    ((yAxis->getAlignment() == Chart::Left) ? Chart::Right : Chart::Left));
                t->destroy();
            }
        }
    }
}