JFreeChart 简单图（抛物线）

Question

我使用 JFreeChart 写了一个简单的抛物线图。

package parabolademo;

import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartMouseEvent;
import org.jfree.chart.ChartMouseListener;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.data.function.Function2D;
import org.jfree.data.function.PolynomialFunction2D;
import org.jfree.data.general.DatasetUtilities;
import org.jfree.data.xy.XYDataset;
import org.jfree.ui.ApplicationFrame;
import org.jfree.ui.RefineryUtilities;


public class ParabolaDemo extends ApplicationFrame {

/*
 * @param title  the frame title.
 */
public ParabolaDemo(final String title) {

    super(title);
    double[] a = {0.0, 0.0, 3.0};
    Function2D p = new PolynomialFunction2D(a);
    XYDataset dataset = DatasetUtilities.sampleFunction2D(p, -20.0, 20.0, 100, "Function");
    final JFreeChart chart = ChartFactory.createXYLineChart(
        "Parabola",
        "X", 
        "Y", 
        dataset,
        PlotOrientation.VERTICAL,
        true,
        true,
        false
    );

    final ChartPanel chartPanel = new ChartPanel(chart);
    chartPanel.addChartMouseListener(new ChartMouseListener() {

        @Override
        public void chartMouseClicked(ChartMouseEvent cme) {
            Point2D po = chartPanel.translateScreenToJava2D(cme.getTrigger().getPoint());
            Rectangle2D plotArea = chartPanel.getScreenDataArea();
            XYPlot plot = (XYPlot) chart.getPlot(); // your plot
            double chartX = plot.getDomainAxis().java2DToValue(po.getX(), plotArea, plot.getDomainAxisEdge());
            double chartY = plot.getRangeAxis().java2DToValue(po.getY(), plotArea, plot.getRangeAxisEdge());
            System.out.println("Clicked!");
            System.out.println("X:" + chartX + ", Y:" + chartY);
        }

        @Override
        public void chartMouseMoved(ChartMouseEvent cme) {

        }
    });
    chartPanel.setPreferredSize(new java.awt.Dimension(500, 270));
    setContentPane(chartPanel);
}

public static void main(final String[] args) {

    final ParabolaDemo demo = new ParabolaDemo("Parabola Plot Demo");
    demo.pack();
    RefineryUtilities.centerFrameOnScreen(demo);
    demo.setVisible(true);
}

}

如何获取 FUNCTION PLOT 点的坐标（我的 chartMouseListener 获取窗口中任意点的坐标）？用户移动鼠标并释放鼠标按钮后如何接收点坐标？ 我希望当单击鼠标时，绘图点跟随鼠标，因此绘图将被重建（为此，有必要再次计算系数，知道该坐标并采用任何其他 2 个坐标）。怎么做？如何用新系数重建绘图？

Answer 1

给定一个名为cmd 的ChartMouseEvent，忽略XYItemEntity 以外的任何类型其他 的实体。一旦你知道了实体，就不要插值——只需查询数据集。

ChartEntity ce = cme.getEntity();
if (ce instanceof XYItemEntity) {
    XYItemEntity e = (XYItemEntity) ce;
    XYDataset d = e.getDataset();
    int s = e.getSeriesIndex();
    int i = e.getItem();
    System.out.println("X:" + d.getX(s, i) + ", Y:" + d.getY(s, i));
}

还可以考虑在绘图的渲染器上调用 setBaseShapesVisible(true)。