Track Box with Floating Legend

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

A box that horizontally centers around the x data value nearest to the mouse cursor.
A floating legend box that moves with the mouse cursor, displaying the data values at the x data value nearest to the mouse cursor.

On the server side, the code draws the chart as usual, and outputs both the image and the Javascript Chart Model of the chart.

The trackBoxLegend Javascript function is the routine that draws the track cursor. Its key elements are:

The trackBoxLegend Javascript function is the routine that draws the track cursor. Its key elements are:

The code first uses JsChartViewer.hideObj to clear the previous track cursor, if any.
The nearest x data value is obtained using JsXYChart.getNearestXValue.
The code draws a rectangle that horizontally spans from (x - 0.5) to (x + 0.5) with JsChartViewer.showTextBox. The +/- 0.5 offset is the suitable value to use for a label based x-axis (that is, for axis set up with Axis.setLabels or Axis.setLabels2). For this type of axis, the label distance is assumed to be 1 x-axis unit irrespective of what are the labels, so an offset of 0.5 refers to the middle position between two labels.
The code then iterates through all data sets in all layers to find all the data points at the nearest x data value. For each of these points, it formats a legend entry for the point, which consists of a colored square as the icon (creating using JsChartViewer.htmlRect), data set name (obtained using JsDataSet.getDataName), and the data value (obtained using JsDataSet.getValue).
Finally, the code combines all the legend entries into a legend box and draws it near the mouse cursor using JsChartViewer.showTextBox.

[JSP Version] jspdemo/trackbox.jsp

<%@page import="ChartDirector.*, java.util.*" %>
<%
// The data for the bar chart
double[] data0 = {100, 125, 245, 147, 67};
double[] data1 = {85, 156, 179, 211, 123};
double[] data2 = {97, 87, 56, 267, 157};
String[] labels = {"Mon", "Tue", "Wed", "Thur", "Fri"};

// Create a XYChart object of size 540 x 375 pixels
XYChart c = new XYChart(540, 375);

// Add a title to the chart using 18pt Times Bold Italic font
c.addTitle("Average Weekly Network Load", "Times New Roman Bold Italic", 18);

// Set the plotarea at (50, 55) and of 440 x 280 pixels in size. Use a vertical gradient color from
// light blue (f9f9ff) to blue (6666ff) as background. Set border and grid lines to white (ffffff).
c.setPlotArea(50, 55, 440, 280, c.linearGradientColor(0, 55, 0, 335, 0xf9f9ff, 0x6666ff), -1,
    0xffffff, 0xffffff);

// Add a legend box at (50, 28) using horizontal layout. Use 10pt Arial Bold as font, with
// transparent background.
c.addLegend(50, 28, false, "Arial Bold", 10).setBackground(Chart.Transparent);

// Set the x axis labels
c.xAxis().setLabels(labels);

// Draw the ticks between label positions (instead of at label positions)
c.xAxis().setTickOffset(0.5);

// Set axis label style to 8pt Arial Bold
c.xAxis().setLabelStyle("Arial Bold", 8);
c.yAxis().setLabelStyle("Arial Bold", 8);

// Set axis line width to 2 pixels
c.xAxis().setWidth(2);
c.yAxis().setWidth(2);

// Add axis title
c.yAxis().setTitle("Throughput (MBytes Per Hour)");

// Add a multi-bar layer with 3 data sets
BarLayer layer = c.addBarLayer2(Chart.Side);
layer.addDataSet(data0, 0xff0000, "Server #1");
layer.addDataSet(data1, 0x00ff00, "Server #2");
layer.addDataSet(data2, 0xff8800, "Server #3");

// Set bar border to transparent. Use glass lighting effect with light direction from left.
layer.setBorderColor(Chart.Transparent, Chart.glassEffect(Chart.NormalGlare, Chart.Left));

// Configure the bars within a group to touch each others (no gap)
layer.setBarGap(0.2, Chart.TouchBar);

// Create the WebChartViewer object
WebChartViewer viewer = new WebChartViewer(request, "chart1");

// Output the chart
viewer.setChart(c, Chart.SVG);

// Output Javascript chart model to the browser to support tracking cursor
viewer.setChartModel(c.getJsChartModel());
%>
<!DOCTYPE html>
<html>
<head>
    <title>Track Box with Floating Legend</title>
    <script type="text/javascript" src="cdjcv.js"></script>
</head>
<body style="margin:5px 0px 0px 5px">
<script type="text/javascript">

//
// Use the window load event to set up the MouseMovePlotArea event handler
//
JsChartViewer.addEventListener(window, 'load', function() {
    var viewer = JsChartViewer.get('<%=viewer.getId()%>');

    // Draw track cursor when mouse is moving over plotarea. Hide it when mouse leaves plot area.
    viewer.attachHandler(["MouseMovePlotArea", "TouchStartPlotArea", "TouchMovePlotArea", "ChartMove"],
    function(e) {
        this.preventDefault(e);   // Prevent the browser from using touch events for other actions
        trackBoxLegend(viewer, viewer.getPlotAreaMouseX(), viewer.getPlotAreaMouseY());
        viewer.setAutoHide("all", ["MouseOutPlotArea", "TouchEndPlotArea"]);
    });
});

//
// Draw track box with legend
//
function trackBoxLegend(viewer, mouseX, mouseY)
{
    // Remove all previously drawn tracking object
    viewer.hideObj("all");

    // The chart and its plot area
    var c = viewer.getChart();
    var plotArea = c.getPlotArea();

    // Get the data x-value that is nearest to the mouse
    var xValue = c.getNearestXValue(mouseX);

    // Compute the position of the box. This example assumes a label based x-axis, in which the labeling spacing
    // is one x-axis unit. So the left and right sides of the box is 0.5 unit from the central x-value.
    var boxLeft = Math.min(c.getXCoor(xValue - 0.5), c.getXCoor(xValue + 0.5));
    var boxWidth = Math.max(0, Math.abs(c.getXCoor(xValue + 0.5) - c.getXCoor(xValue - 0.5)) - 1);
    var boxTop = plotArea.getTopY();
    var boxHeight = Math.max(0, plotArea.getHeight() - 2);

    // Draw the track box
    viewer.showTextBox("trackBox", boxLeft, boxTop, JsChartViewer.TopLeft, "",
        "width:" + boxWidth + "px;height:" + boxHeight + "px;border:solid 1px black;");

    // Array to hold the legend entries
    var legendEntries = [];

    // Iterate through all layers to build the legend array
    for (var i = 0; i < c.getLayerCount(); ++i)
    {
        var layer = c.getLayerByZ(i);

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

        // Iterate through all the data sets in the layer
        for (var j = 0; j < layer.getDataSetCount(); ++j)
        {
            var dataSet = layer.getDataSetByZ(j);

            // Build the legend entry, consist of a colored square box, the name and the data value.
            var dataColor = dataSet.getDataColor();
            var dataValue = dataSet.getValue(xIndex);
            if ((dataValue != null) && (dataColor != null))
            {
                legendEntries.push("<nobr>" + viewer.htmlRect(7, 7, dataColor) + " " +
                    dataSet.getDataName() + ": " + dataValue.toPrecision(4) + "</nobr> ");
            }
        }
    }

    // Create the legend by joining the legend entries
    if (legendEntries.length > 0)
    {
        var legend = "<u>" + c.xAxis().getFormattedLabel(xValue) + "</u><br />" + legendEntries.reverse().join("<br />");

        // Display the legend at the bottom-right side of the mouse cursor
        viewer.showTextBox("legend", mouseX + 16, mouseY + 16, JsChartViewer.TopLeft, legend,
            "border:solid 1px black;background:#ffffcc;padding:3px;font:bold 11px Arial;-webkit-text-size-adjust:100%;");
    }
}

</script>
<div style="font-size:18pt; font-family:verdana; font-weight:bold">
    Track Box with Floating Legend
</div>
<hr style="border:solid 1px #000080" />
<div style="font-size:10pt; font-family:verdana; margin-bottom:1.5em">
    <a href="viewsource.jsp?file=<%=request.getServletPath()%>">View Source Code</a>
</div>
<!-- ****** Here is the chart image ****** -->
<%=viewer.renderHTML(response)%>
</body>
</html>