How to Check Mouse Click in 2D Graphics java.

Question

I need to make a code that will Draw a triangle. then user will click the inside or outside the triangle. and A dialogue box will be shown that "Click is inside the triangle" if it is.

I have code to draw triangle, here is the code, now what to do. i dont know. if any one help then please.

I have tried axis base but i did not come up with required result.

public void paintComponent(Graphics g)  
        {  
            Graphics2D g2 = (Graphics2D) g;  
            g2.draw(new Line2D.Double (150, 200, 200, 100)); 
            g2.draw(new Line2D.Double (100, 100, 150, 200));           
            g2.draw(new Line2D.Double (100, 100, 200, 100)); 
        }

Output is here. enter image description here

This should help: http://stackoverflow.com/questions/2049582/how-to-determine-a-point-in-a-triangle — lwi, Dec 28 '14 at 17:18

Mshnik · Accepted Answer · 2014-12-28T17:45:03.463

The Shape class is what you want to use. Instead of drawing the triangle by hand (with individual draw statements for each line), create a Shape object representing the triangle. A Polygon will suffice for creating triangles.

Instead of changing the painting of the JFrame, it's a better idea to have a custom painted panel and add that to the frame.

public class YourFrame extends JFrame { //Replace with your class name, obviously

    public YourFrame(){
        //Create and add trianglePanel
        setLayout(new BorderLayout());
        add(new TrianglePanel(), BorderLayout.CENTER);
        pack();
        repaint();
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    class TrianglePanel extends JPanel implements MouseListener{
        private Polygon triangle;

        public TrianglePanel(){
            //Create triangle
            triangle = new Polygon();
            triangle.addPoint(150, 200);
            triangle.addPoint(100, 100);
            triangle.addPoint(200, 100);

            //Add mouse Listener
            addMouseListener(this);

            //Set size to make sure that the whole triangle is shown
            setPreferredSize(new Dimension(300, 300));
        }

        /** Draws the triangle as this frame's painting */
        public void paintComponent(Graphics g){
            Graphics2D g2d = (Graphics2D)g;
            g2d.draw(triangle);
        }

        //Required methods for MouseListener, though the only one you care about is click
        public void mousePressed(MouseEvent e) {}
        public void mouseReleased(MouseEvent e) {}
        public void mouseEntered(MouseEvent e) {}
        public void mouseExited(MouseEvent e) {}

        /** Called whenever the mouse clicks.
          * Could be replaced with setting the value of a JLabel, etc. */
        public void mouseClicked(MouseEvent e) {
            Point p = e.getPoint();
            if(triangle.contains(p)) System.out.println("Triangle contains point");
            else System.out.println("Triangle Doesn't contain point");
        }
    }
}

I did not got it but let me try. then i will ask if i had some trouble. Thanks — Adnan Ali, Dec 28 '14 at 17:30
Changed to paint triangle as a panel. This is how I would do it if I were coding it. — Mshnik, Dec 28 '14 at 17:35
these lines have error There is no addPoint Function.... triangle.addPoint(150, 200); triangle.addPoint(100, 100); triangle.addPoint(200, 100); — Adnan Ali, Dec 28 '14 at 17:43
Ah, right. Dumb mistake on my part. Changed static type of `triangle` to Polygon. — Mshnik, Dec 28 '14 at 17:44
this code works fine. but now how to add it in frame ? Can u please guide ? — Adnan Ali, Dec 28 '14 at 17:54
The code in the `YourFrame()` constructor creates and adds a panel (that draws as a triangle) to the center of the frame. So look at those lines. — Mshnik, Dec 28 '14 at 17:56
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/67804/discussion-between-adnan-ali-and-mshnik). — Adnan Ali, Dec 28 '14 at 18:13

score 0 · Answer 2 · answered Dec 28 '14 at 18:32

Final code with the help of @Mshink

 public class Triangle_shape extends JFrame {
        /**
         * @param args the command line arguments
         */
        public Triangle_shape(){
            //Create and add trianglePanel

          //  setVisible(true);
        //    setDefaultCloseOperation(EXIT_ON_CLOSE);
        }
      public static void main(String[] args) {

            // TODO code application logic here
          TrianglePanel t= new TrianglePanel();
        JFrame frame = new JFrame ();  
        final int FRAME_WIDTH = 500;  
        final int FRAME_HEIGHT = 500;

        frame.setSize (FRAME_WIDTH, FRAME_HEIGHT);           

        frame.setLayout(new BorderLayout());
          frame.add(t);
        //    frame.add(new TrianglePanel(), BorderLayout.CENTER);
            frame.pack();
            frame.repaint();
            frame.setTitle("A Test Frame");  
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
        frame.setVisible(true);  

        }
       public static class TrianglePanel extends JPanel implements MouseListener{
            private Polygon triangle;

            public TrianglePanel(){
                //Create triangle
                triangle = new Polygon();
                triangle.addPoint(150, 200);
                triangle.addPoint(100, 100);
                triangle.addPoint(200, 100);

                //Add mouse Listener
                addMouseListener(this);

                //Set size to make sure that the whole triangle is shown
                setPreferredSize(new Dimension(300, 300));
            }

            /** Draws the triangle as this frame's painting */
            public void paintComponent(Graphics g){
                Graphics2D g2d = (Graphics2D)g;
                g2d.draw(triangle);
            }

            //Required methods for MouseListener, though the only one you care about is click
            public void mousePressed(MouseEvent e) {}
            public void mouseReleased(MouseEvent e) {}
            public void mouseEntered(MouseEvent e) {}
            public void mouseExited(MouseEvent e) {}

            /** Called whenever the mouse clicks.
              * Could be replaced with setting the value of a JLabel, etc. */
            public void mouseClicked(MouseEvent e) {
                Point p = e.getPoint();
                if(triangle.contains(p)) System.out.println("Triangle contains point");
                else System.out.println("Triangle Doesn't contain point");
            }




        }
    }

score -1 · Answer 3 · answered Dec 28 '14 at 17:44

This should do the job. It's not the best option, nor the one with the best performance, but it works.

// The main class which makes the frame and adds the necessary stuff
class Mainclass {
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setSize(400,400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        CPanel panel = new CPanel();

        // I like colours
        panel.setBackground(new Color(255,255,255,255));
        frame.add(panel);

        frame.addMouseListener(new Mouse(panel));

        frame.setVisible(true);
    }
}

// The MouseListener which checks if the mouse is clicked
class Mouse implements MouseListener {

    CPanel panel;

    public Mouse(CPanel panel) {
        this.panel=panel;
    }


    @Override
    public void mouseClicked(MouseEvent e) {
        int x=e.getX();
        int y=e.getY();

        boolean inside=false;

        ArrayList<Integer> Ys = panel.coordinates.get(x);
        if(Ys != null) {
            if(panel.coordinates.get(x).contains(y)) {
                inside=true;
            }
        }

        if(inside) {
            System.out.println("You clicked in the triangle");
        } else {
            System.out.println("You clicked out of the triangle");
        }

    }

    @Override   public void mousePressed  (MouseEvent e) {}
    @Override   public void mouseReleased (MouseEvent e) {}
    @Override   public void mouseEntered  (MouseEvent e) {}
    @Override   public void mouseExited   (MouseEvent e) {}
}

// The panel
class CPanel extends JPanel {

    public int minX=100;
    public int maxX=200;
    public int minY=100;
    public int maxY=200;

    // All the pixels in the triangle
    HashMap<Integer, ArrayList<Integer>> coordinates = new HashMap<Integer, ArrayList<Integer>>();


    public void paintComponent(Graphics G) {
        super.paintComponent(G);

        /** For that one downvoter: I made it G2D, even though it makes no difference **/
        Graphics2D g = (Graphics2D) G;

        // Drawing a centered triangle
        int xCen=(int)Math.round((minX+maxX)/2.0);

        // I like colours
        g.setColor(new Color(0,0,255,128));

        for(int y=0; y<=maxY-minY; y++) {

            int x0=xCen-y;
            int x1=xCen+y;

            int y0=y+minY;

            for(int x=x0; x<=x1; x++) {
                // Adding all pixels in this row to 'coordinates'
                ArrayList<Integer> Ys = coordinates.get(x);

                if(Ys==null) {
                    coordinates.put(x, new ArrayList<Integer>());
                    Ys = coordinates.get(x);
                }

                Ys.add(y0);
                coordinates.put(x, Ys);
            }

            // Draw the row
            g.drawLine(x0,y0,x1,y0);
        }

        // Output the coordinates for debugging purposes
        System.out.println(coordinates);
    }
}

Again, if you want something with better performance, don't use this.

Triangle drawing code, How it works ? I need to make about 27 triangles (Sierpinski triangle). loop will not be a good option to draw... — Adnan Ali, Dec 28 '14 at 17:48
@AdnanAli That's what I said twice, it's not the one with best performance, but you get the idea on how to do it. — Charlie, Dec 28 '14 at 17:49

How to Check Mouse Click in 2D Graphics java.

3 Answers3