JFreeChart StackedXYAreaRenderer causes “crimp” in chart

I'm using JFreeChart to show a stacked line chart of two sets of data over time, in this example dogs and cats.

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.JFrame;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.DateAxis;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.StackedXYAreaRenderer;
import org.jfree.data.time.Minute;
import org.jfree.data.time.TimeTableXYDataset;

public class ChartTest {

    public ChartTest() throws ParseException{

        TimeTableXYDataset chartData = createChartData();
        JFreeChart chart = createChart(chartData);
        ChartPanel chartPanel = new ChartPanel(chart);  

        JFrame frame = new JFrame("Chart Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(chartPanel);
        frame.setSize(500,  500);

        frame.setVisible(true);
    }

    private TimeTableXYDataset createChartData() throws ParseException {

        int[] dogs = {14, 81, 99, 89, 151, 263, 396, 548, 822, 1410, 2180, 3134, 4065, 5016, 6019, 7648, 9323, 11059, 12252, 13432, 15238, 17559, 19796, 21853, 23971, 26414, 28694, 31371, 34233, 37353, 40451, 44081, 47978, 52040, 56024, 60486, 64881, 69663, 74320, 79391, 84840, 91228, 96383, 102061, 107832, 114244, 119992, 126207, 132894, 139146, 144727, 150896, 156503, 161960, 167724, 174172, 180121, 185929, 191375, 196050, 200768, 205208, 208727, 212329, 216439, 221102, 224284, 226944, 230307, 233075, 234814, 236220, 237733, 239158, 240311, 241267};
        int[] cats = {244, 360, 363, 644, 1075, 1516, 2241, 3160, 3591, 4661, 5633, 6990, 7889, 9059, 10510, 11743, 12506, 13540, 14557, 15705, 16969, 18350, 20197, 21659, 23160, 24840, 26394, 28109, 29742, 31428, 33021, 34514, 35822, 37339, 38784, 40258, 41568, 42921, 44180, 45454, 46710, 48084, 49418, 50712, 51920, 53014, 53923, 54830, 55756, 56573, 57554, 58352, 59064, 59874, 60933, 61948, 62762, 63299, 63772, 64243, 64789, 65206, 65693, 66016, 66391, 66859, 67432, 67919, 68400, 68677, 68944, 69211, 69511, 69786, 69990, 70279};

        final TimeTableXYDataset chartData = new TimeTableXYDataset();

        long start = new SimpleDateFormat("MM/dd/yyyy HH:mm").parse("11/08/2016 08:00").getTime();

        for (int t = 0; t < dogs.length; t++) {
            Minute m = new Minute(new Date(start + 15*t*60*1000));
            chartData.add(m, dogs[t], "Dogs");
            chartData.add(m, cats[t], "Cats");
        }

        return chartData;
    }

    private JFreeChart createChart(TimeTableXYDataset chartData) {

        JFreeChart chart = ChartFactory.createStackedXYAreaChart("Dogs and Cats", "Time", "Count", chartData, PlotOrientation.VERTICAL, false, true, false);

        StackedXYAreaRenderer chartRenderer = new StackedXYAreaRenderer(); 
        XYPlot plot = (XYPlot)chart.getPlot();
        plot.setRenderer(chartRenderer);

        DateAxis dateAxis = new DateAxis();
        dateAxis.setDateFormatOverride(new SimpleDateFormat("HH:mm"));
        dateAxis.setTickLabelFont(dateAxis.getTickLabelFont().deriveFont(20f));

        plot.setDomainAxis(dateAxis);

        return chart;
    }

    public static void main(String... args) throws ParseException{
        new ChartTest();
    }
}

However, this results in a "crimp" in the cats section of the chart:

I've looked my data over, and it doesn't contain negative values or anything strange that might throw the chart off.

Through some shotgun debugging, I realized that if I remove this section of code from the createChart() function:

    StackedXYAreaRenderer chartRenderer = new StackedXYAreaRenderer(); 
    XYPlot plot = (XYPlot)chart.getPlot();
    plot.setRenderer(chartRenderer);

    DateAxis dateAxis = new DateAxis();
    dateAxis.setDateFormatOverride(new SimpleDateFormat("HH:mm"));
    dateAxis.setTickLabelFont(dateAxis.getTickLabelFont().deriveFont(20f));

    plot.setDomainAxis(dateAxis);

Then I get a more reasonable stacked line chart:

But then I lose my nicely formatted dates.

My questions are:

What is causing the "crimp" in the cats section of the chart, and the space between the two stacks?
Is there a different way to format the dates that doesn't cause this behavior?

trashgod

ChartFactory.createStackedXYAreaChart() instantiates StackedXYAreaRenderer2 to avoid this problem. Your example replaces it with an instance of StackedXYAreaRenderer. Either,

Use the factory's renderer and a custom DateAxis.

private JFreeChart createChart(TimeTableXYDataset chartData) {
    JFreeChart chart = ChartFactory.createStackedXYAreaChart(
        "Dogs and Cats", "Time", "Count", chartData,
        PlotOrientation.VERTICAL, false, true, false);
    DateAxis dateAxis = new DateAxis();
    dateAxis.setDateFormatOverride(new SimpleDateFormat("HH:mm"));
    dateAxis.setTickLabelFont(dateAxis.getTickLabelFont().deriveFont(20f));
    XYPlot plot = (XYPlot) chart.getPlot();
    plot.setDomainAxis(dateAxis);
    return chart;
}

Recapitulate the factory, as shown here, in your createChart() method.

private JFreeChart createChart(TimeTableXYDataset chartData) {
    DateAxis dateAxis = new DateAxis("Time");
    dateAxis.setDateFormatOverride(new SimpleDateFormat("HH:mm"));
    dateAxis.setTickLabelFont(dateAxis.getTickLabelFont().deriveFont(20f));
    NumberAxis yAxis = new NumberAxis("Count");
    XYToolTipGenerator toolTipGenerator = new StandardXYToolTipGenerator();
    StackedXYAreaRenderer2 renderer = new StackedXYAreaRenderer2(
        toolTipGenerator, null);
    renderer.setOutline(true);
    XYPlot plot = new XYPlot(chartData, dateAxis, yAxis, renderer);
    plot.setOrientation(PlotOrientation.VERTICAL);
    plot.setRangeAxis(yAxis);  // forces recalculation of the axis range
    JFreeChart chart = new JFreeChart("Dogs and Cats",
        JFreeChart.DEFAULT_TITLE_FONT, plot, false);
    new StandardChartTheme("JFree").apply(chart);
    return chart;
}

Can you expand a little bit on why the StackedXYRenderer causes that crimp?

The author writes, "StackedXYAreaRenderer2 uses a different drawing approach, calculating a polygon for each data point and filling that." In contrast, StackedXYAreaRenderer appears to close a single Shape by connecting the endpoints with a straight line.

来源：https://stackoverflow.com/questions/40495286/jfreechart-stackedxyarearenderer-causes-crimp-in-chart

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