Step Line Chart

This example demonstrates joining data points with steps. It also demonstrates irregularly spaced data points on an auto-scaled true date/time axis.

The step line layer is created using XYChart.addStepLineLayer.

Most of the sample charts in this document use enumerated x-axes. In this axis type, the data points are assumed to be evenly spread on the x-direction, so it is not necessary to supply the x values of the data points. The x-axis is treated as a series of text labels using Axis.setLabels or Axis.setLabels2. The labels can be dates/times, numbers, names, or any arbitrary text in any format. Enumerated x-axis is an easy to use yet extremely flexible axis type that is suitable for most charts.

However, for charts with data points not regularly spaced, it is necessary to supply the x values of the data points using Layer.setXData. In this case, ChartDirector can automatically determine the type and scale on the x-axis (auto-scaling).

For date/time axis, in many cases one may need to control the date/time label format. This can be done using Axis.setDateScale3.

[File: phpdemo/stepline.php]

<?php
require_once("../lib/phpchartdir.php");

# The data for the chart
$dataY0 = array(4, 4.5, 5, 5.25, 5.75, 5.25, 5, 4.5, 4, 3, 2.5, 2.5);
$dataX0 = array(chartTime(1997, 1, 1), chartTime(1998, 6, 25), chartTime(1999, 9, 6),
    chartTime(2000, 2, 6), chartTime(2000, 9, 21), chartTime(2001, 3, 4), chartTime(
    2001, 6, 8), chartTime(2002, 2, 4), chartTime(2002, 5, 19), chartTime(2002, 8, 16
    ), chartTime(2002, 12, 1), chartTime(2003, 1, 1));

$dataY1 = array(7, 6.5, 6, 5, 6.5, 7, 6, 5.5, 5, 4, 3.5, 3.5);
$dataX1 = array(chartTime(1997, 1, 1), chartTime(1997, 7, 1), chartTime(1997, 12, 1),
    chartTime(1999, 1, 15), chartTime(1999, 6, 9), chartTime(2000, 3, 3), chartTime(
    2000, 8, 13), chartTime(2001, 5, 5), chartTime(2001, 9, 16), chartTime(2002, 3,
    16), chartTime(2002, 6, 1), chartTime(2003, 1, 1));

# Create a XYChart object of size 500 x 270 pixels, with a pale blue (e0e0ff)
# background, black border, 1 pixel 3D border effect and rounded corners
$c = new XYChart(600, 300, 0xe0e0ff, 0x000000, 1);
$c->setRoundedFrame();

# Set the plotarea at (55, 60) and of size 520 x 200 pixels, with white (ffffff)
# background. Set horizontal and vertical grid lines to grey (cccccc).
$c->setPlotArea(50, 60, 525, 200, 0xffffff, -1, -1, 0xcccccc, 0xcccccc);

# Add a legend box at (55, 32) (top of the chart) with horizontal layout. Use 9 pts
# Arial Bold font. Set the background and border color to Transparent.
$legendObj = $c->addLegend(55, 32, false, "arialbd.ttf", 9);
$legendObj->setBackground(Transparent);

# Add a title box to the chart using 15 pts Times Bold Italic font. The text is white
# (ffffff) on a deep blue (000088) background, with soft lighting effect from the
# right side.
$textBoxObj = $c->addTitle("Long Term Interest Rates", "timesbi.ttf", 15, 0xffffff);
$textBoxObj->setBackground(0x000088, -1, softLighting(Right));

# Set the y axis label format to display a percentage sign
$c->yAxis->setLabelFormat("{value}%");

# Add a red (ff0000) step line layer to the chart and set the line width to 2 pixels
$layer0 = $c->addStepLineLayer($dataY0, 0xff0000, "Country AAA");
$layer0->setXData($dataX0);
$layer0->setLineWidth(2);

# Add a blue (0000ff) step line layer to the chart and set the line width to 2 pixels
$layer1 = $c->addStepLineLayer($dataY1, 0x0000ff, "Country BBB");
$layer1->setXData($dataX1);
$layer1->setLineWidth(2);

# Output the chart
header("Content-type: image/png");
print($c->makeChart2(PNG));
?>