Selecting Circle Segements

Question

I am creating a wheel / dial selector in windows using java, that would popup on a button press for the user to select one of the different segments to do what ever they have specified previously on creation of that segment.

I am stuck with how to select different segments of a circle, currently I have JLabels created around the circle using a custom layout but their interactive area is limited to a rectangle around the text.

How can I change this area to a triangle / pi segment?

Is there a better way to achieve this?

Here is an image where segment 4 has the area (highlighted in blue) that I want to achieve.

Answer 1

If jfreechchart is acceptable, a PiePlot may serve. Starting from PieChartDemo1, included in the distribution, the following changes produce the plot shown below. A ChartMouseListener highlights the indicated section as the mouse is moved.

public static JPanel createDemoPanel() {
    …
    PiePlot plot = (PiePlot) chart.getPlot();
    PieDataset data = plot.getDataset();
    panel.addChartMouseListener(new ChartMouseListener() {
        @Override
        public void chartMouseMoved(ChartMouseEvent e) {
            ChartEntity ce = e.getEntity();
            if (ce instanceof PieSectionEntity) {
                for (int i = 0; i < data.getItemCount(); i++) {
                    plot.setExplodePercent(data.getKey(i), 0);
                }
                PieSectionEntity item = (PieSectionEntity) ce;
                plot.setExplodePercent(item.getSectionKey(), 0.25);
            }
        }
        @Override
        public void chartMouseClicked(ChartMouseEvent e) {}
    });
    return panel;
}

Answer 2

To be honest, there are any number of ways you might do this. One of the simplest ways I can think of is to take advantage of the 2D Graphics Shape API.

The following example simply uses a Arc2D for simplicity, but the general concept should work for Path based shapes as well (if you want to get that complicated)

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Arc2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Arc2D segment;

        private Arc2D selected = null;

        public TestPane() {
            segment = new Arc2D.Double(0, 0, 190, 190, -11.75, 23.5, Arc2D.PIE);
            addMouseMotionListener(new MouseAdapter() {
                @Override
                public void mouseMoved(MouseEvent e) {
                    Point p = e.getPoint();
                    p.translate(-5, -5);
                    selected = null;
                    if (segment.contains(e.getPoint())) {
                        selected = segment;
                    }
                    repaint();
                }
            });
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.translate(5, 5);
            if (selected != null) {
                g2d.setColor(Color.BLUE);
                g2d.fill(selected);
            }
            g2d.setColor(Color.RED);
            g2d.draw(segment);
            g2d.dispose();
        }

    }

}

Have a look at Working with Geometry for more details