Sensing hover over outer edge of a Path2D circle in JPanel

Question

So, I have a program that draws Path2D circles onto JPanel. What I am trying to do is resize the circle when the user clicks and drags the bottom right of the circle. So, what I want is to detect when they are on the bottom-right outer edge of the circle, not the bottom-right of the bounds around the circle. Basically, I need to figure out how to do something like this:

enter image description here

I know how to do this with rectangles using getBounds() but when you use getBounds() on a circle, it will return the square around the circle and not the bounds of the actual circle. Any ideas on how I can get this to work? Thanks!

Here is a shortened, runnable version of my program:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Panel;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Path2D;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Editor {

    public static void main(String[] args) {

        JFrame frame = new UMLWindow();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setBounds(30, 30, 1000, 700);
        frame.getContentPane().setBackground(Color.white);
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

class UMLWindow extends JFrame {
    Shapes shapeList = new Shapes();
    Panel panel;

    private static final long serialVersionUID = 1L;

    public UMLWindow() {
        addMenus();
        panel = new Panel();
    }

    public void addMenus() {

        getContentPane().add(shapeList);

        setSize(300, 200);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        shapeList.addCircle(100, 100);
    }
}

// Shapes class, used to draw the shapes on the panel
// as well as implements the MouseListener for dragging
class Shapes extends JPanel {
    private static final long serialVersionUID = 1L;

    private List<Path2D> shapes = new ArrayList<Path2D>();
    int currentIndex;

    public Shapes() {
        MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
        addMouseListener(myMouseAdapter);
        addMouseMotionListener(myMouseAdapter);
    }

    public void addCircle(int width, int height) {
        Path2D circ = new Path2D.Double();
        circ.append(new Ellipse2D.Double(442, 269, width, height), true);
        shapes.add(circ);
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        Graphics2D g2 = (Graphics2D) g;
        g2.setStroke(new BasicStroke(2));
        for (Path2D shape : shapes) {
            g2.draw(shape);
        }
    }

    class MyMouseAdapter extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent e) {

        }

        @Override
        public void mouseDragged(MouseEvent e) {
        }

        @Override
        public void mouseReleased(MouseEvent e) {
        }
    }
}

You'll probably want to brush up on your trig, but you might be able to use a `PathIterator` — MadProgrammer, Oct 19 '14 at 23:11
@MadProgrammer I was hoping you didn't mention having to use trig. Will check out PathIterator, though — Harry, Oct 19 '14 at 23:15

score 2 · Answer 1 · answered Oct 19 '14 at 23:19

2

Not sure if this will work but you can try something like:

Create a Shape circle that is a couple of pixels smaller than your original Shape
Create a Shape circle that is a couple of pixels larger than your original Shape
Create an Area object using the larger Shape
Create an Area object using the smaller Shape and subtract this Area from the larger Area
Use the contains(...) method to determine if the mouse point is within this Area.

answered Oct 19 '14 at 23:19

camickr

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*"Not sure if this will work.."* I'm sure it *will* work. – Andrew Thompson Oct 20 '14 at 05:26
@AndrewThompson, thanks for the vote of confidence :) – camickr Oct 20 '14 at 19:13

MadProgrammer · Accepted Answer · 2014-10-19T23:44:42.143

You'll want to brush up your trig (or google search like I did ;)). The basic concept is "relatively" easy, but I created a nice method to all the work for me...

This method...

public Point2D getPointOnEdge(float angel, Rectangle bounds) {

    float radius = Math.max(bounds.width, bounds.height) / 2;

    float x = radius;
    float y = radius;

    double rads = Math.toRadians((angel + 90));

    // Calculate the outter point of the line
    float xPosy = (float) (x + Math.cos(rads) * radius);
    float yPosy = (float) (y + Math.sin(rads) * radius);

    return new Point2D.Float(xPosy + bounds.x, yPosy + bounds.y);

}

Will calculate the x/y point that a given angle will appear on a circle, remember, this will ONLY work for circles!

I then use another method...

public Rectangle2D getActiveBounds(float angel, Rectangle bounds) {

    Point2D p = getPointOnEdge(angel, bounds);

    return new Rectangle2D.Double(p.getX() - 4, p.getY() - 4, 8, 8);

}

To calculate the "mouse zone" in which I would consider to be the bottom/right area, cause a single pixel is hard to find and simply use Rectangle#contains, passing it the current mouse location...

Mouse Hover

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Panel;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Path2D;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import static javax.swing.JFrame.EXIT_ON_CLOSE;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Editor {

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

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

                JFrame frame = new UMLWindow();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setBounds(30, 30, 1000, 700);
                frame.getContentPane().setBackground(Color.white);
                frame.setVisible(true);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public static class UMLWindow extends JFrame {

        Shapes shapeList = new Shapes();
        Panel panel;

        private static final long serialVersionUID = 1L;

        public UMLWindow() {
            addMenus();
            panel = new Panel();
        }

        public void addMenus() {

            getContentPane().add(shapeList);

            setSize(300, 200);
            setLocationRelativeTo(null);
            setDefaultCloseOperation(EXIT_ON_CLOSE);

            shapeList.addCircle(100, 100);
        }
    }

// Shapes class, used to draw the shapes on the panel
// as well as implements the MouseListener for dragging
    public static class Shapes extends JPanel {

        private static final long serialVersionUID = 1L;

        private List<Path2D> shapes = new ArrayList<Path2D>();
        int currentIndex;

        private Point mousePoint;

        public Shapes() {
            MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
            addMouseListener(myMouseAdapter);
            addMouseMotionListener(myMouseAdapter);
        }

        public void addCircle(int width, int height) {
            Path2D circ = new Path2D.Double();
            circ.append(new Ellipse2D.Double(442, 269, width, height), true);
            shapes.add(circ);
            repaint();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Graphics2D g2 = (Graphics2D) g;
            g2.setStroke(new BasicStroke(2));
            for (Path2D shape : shapes) {
                g2.setColor(Color.BLACK);
                g2.draw(shape);

                g2.setColor(Color.RED);
                Rectangle2D bottomRight = getActiveBounds(-45, shape.getBounds());

                g2.draw(bottomRight);
                if (mousePoint != null) {

                    if (bottomRight.contains(mousePoint)) {
                        g2.fill(bottomRight);
                    }

                }

            }
        }

        public Rectangle2D getActiveBounds(float angel, Rectangle bounds) {

            Point2D p = getPointOnEdge(angel, bounds);

            return new Rectangle2D.Double(p.getX() - 4, p.getY() - 4, 8, 8);

        }

        public Point2D getPointOnEdge(float angel, Rectangle bounds) {

            float radius = Math.max(bounds.width, bounds.height) / 2;

            float x = radius;
            float y = radius;

            double rads = Math.toRadians((angel + 90));

            // Calculate the outter point of the line
            float xPosy = (float) (x + Math.cos(rads) * radius);
            float yPosy = (float) (y + Math.sin(rads) * radius);

            return new Point2D.Float(xPosy + bounds.x, yPosy + bounds.y);

        }

        class MyMouseAdapter extends MouseAdapter {

            @Override
            public void mouseMoved(MouseEvent e) {
                mousePoint = e.getPoint();
                repaint();
            }

        }
    }

}

This example does all the work within the paint method, because I wanted to see the "area of effect", you can easily use the same logic to change the mouse cursor within the MouseMoitionListener

Sensing hover over outer edge of a Path2D circle in JPanel

2 Answers2

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