How to keep an icon in one side of a chart in JFreeChart Java

Question

I have the following chart:

The chart is dynamic and has the capability of make zoom in and zoom out. I want to put an icon that is created as:

BufferedImage triangleIcon = null;
        try {
            triangleIcon = ImageIO.read(getClass().getClassLoader().getResource("Resources/Imagenes/triangulo.png"));
        } catch (IOException e) {
        }

And can be placed in any point as:

xyannotation = new XYImageAnnotation(XValue, YValue, triangleIcon);
this.xyplot.addAnnotation(xyannotation); 

I want to put this icon at any Y value but always next to the left side of the chart, without taking into account the zoom. Something like:

Is it possible?

Answer 1

I looks like you want to annotate "one side of the…chart, ignoring the value of the X axis". Ordinarily, such annotations specify both coordinates in data space. One approach is a custom annotation that extends the abstract parent, AbstractXYAnnotation. Override draw() to transform the vertical data coordinate to the corresponding screen coordinate, while pinning the horizontal screen coordinate to the dataArea of the plot. Pan and zoom to see the effect.

AffineTransform at = new AffineTransform();
…
@Override
public void draw(…) {
    RectangleEdge rangeEdge = plot.getRangeAxisEdge();
    double y = rangeAxis.valueToJava2D(yValue, dataArea, rangeEdge);
    at.setToIdentity();
    at.translate(dataArea.getX() + 1, y);
    …
}

Example code:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.Shape;
import java.awt.Stroke;
import java.awt.geom.AffineTransform;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.annotations.AbstractXYAnnotation;
import org.jfree.chart.axis.ValueAxis;
import org.jfree.chart.plot.PlotRenderingInfo;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.ui.RectangleEdge;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

/**
 * @see https://stackoverflow.com/q/72311226/230513
 * @see https://stackoverflow.com/q/71780485/230513
 */
public class XYShapeTest {

    private static final int N = 18_000;
    private static final int SIZE = 16;
    private final Shape pointer = createPolygon(SIZE);

    private static class AxisAnnotation extends AbstractXYAnnotation {

        private final AffineTransform at = new AffineTransform();
        private final Stroke stroke = new BasicStroke(4f);
        private final Shape shape;
        private final double yValue;

        public AxisAnnotation(Shape shape, double y) {
            this.shape = shape;
            this.yValue = y;
        }

        @Override
        public void draw(Graphics2D g2, XYPlot plot, Rectangle2D dataArea,
            ValueAxis domainAxis, ValueAxis rangeAxis,
            int rendererIndex, PlotRenderingInfo info) {
            RectangleEdge rangeEdge = plot.getRangeAxisEdge();
            double y = rangeAxis.valueToJava2D(yValue, dataArea, rangeEdge);
            at.setToIdentity();
            at.translate(dataArea.getX() + 1, y);
            g2.setStroke(stroke);
            g2.setPaint(Color.BLACK);
            g2.draw(at.createTransformedShape(shape));
        }
    }

    private Shape createPolygon(int size) {
        Polygon p = new Polygon();
        p.addPoint(0, 0);
        p.addPoint(0, 1);
        p.addPoint(2, 0);
        p.addPoint(0, -1);
        AffineTransform at = new AffineTransform();
        at.scale(size, size);
        return at.createTransformedShape(p);
    }

    private XYDataset createDataset() {
        XYSeries series = new XYSeries("Series");
        for (int i = 0; i <= N; i += 1_000) {
            series.add(i / 1_000, i);
        }
        return new XYSeriesCollection(series);
    }

    private JFreeChart createChart(final XYDataset dataset) {
        JFreeChart chart = ChartFactory.createXYLineChart("Test", "X", "Y", dataset);
        XYPlot plot = (XYPlot) chart.getPlot();
        plot.setDomainPannable(true);
        plot.setRangePannable(true);
        plot.addAnnotation(new AxisAnnotation(pointer, 9_000));
        return chart;
    }

    private void display() {
        JFrame f = new JFrame("XYShapeTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new ChartPanel(createChart(createDataset())) {
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(600, 300);
            }
        });
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new XYShapeTest()::display);
    }
}