Dragging a Triangle on Screen

Question

I need help in dragging the vertex of a triangle or just dragging a triangle when the user clicks on it . The code to draw the triangle is as follows. I have used a Polygon and LIne2D with Point2D to draw the lines on screen.
Please Help as i have to have this and more stuff done asap.
The code to draw the triangle on screen is as follows
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import java.awt.geom.*;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
* @author  Kripa Bhojwani
public class Triangle extends javax.swing.JPanel {
    /** Creates new form Triangle */
    public Triangle() {
        initComponents();
      Polygon triangle = new Polygon(3);
    public void paintComponent(Graphics gfx) {
        super.paintComponent(gfx); // standard setup
        Graphics2D g = (Graphics2D) gfx;
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
        RenderingHints.VALUE_ANTIALIAS_ON);
        Polygon triangle = new Polygon(3);
        triangle.add(new Point2D.Double(150,300));
        triangle.add(new Point2D.Double(300,450));
        triangle.add(new Point2D.Double(300,300));
        g.setPaint(Color.BLACK);
        triangle.draw(g);
        // define the elements we will draw
Ellipse2D.Double e1 = new Ellipse2D.Double(p1.x-r1,p1.y-r1, 4*r1, 5*r1 );
        g.fill(e1);
        g.draw(e1);
        Point2D.Double p1 = new Point2D.Double(900, 750);
        Point2D.Double p2 = new Point2D.Double(450, 300    );
        Point2D.Double p3 = new Point2D.Double(300,300);
       /* Ellipse2D.Double e1 = new Ellipse2D.Double(p1.x-r1,p1.y-r1, 4*r1, 5*r1 );
        g.fill(e1);
        g.draw(e1);
        Line2D.Double line = new Line2D.Double(p1, p2);
        Line2D.Double line1 = new Line2D.Double(p2, p3);
        Line2D.Double line2 = new Line2D.Double(p1, p3);
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    private void initComponents() {
        setLayout(new java.awt.BorderLayout());
    // Variables declaration - do not modify
    // End of variables declaration
}the Main Application code is on my JFrame and is as follows:
import javax.swing.*;
* @author  Kripa Bhojwani
public class GUI extends javax.swing.JFrame {
    /** Creates new form GUI */
    public GUI() {
        initComponents();
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    private void initComponents() {
        jScrollPane1 = new javax.swing.JScrollPane();
        triangle1 = new Triangle();
        jMenuBar1 = new javax.swing.JMenuBar();
        jMenu1 = new javax.swing.JMenu();
        jMenuItem1 = new javax.swing.JMenuItem();
        jSeparator1 = new javax.swing.JSeparator();
        jMenuItem2 = new javax.swing.JMenuItem();
        jSeparator2 = new javax.swing.JSeparator();
        jMenuItem3 = new javax.swing.JMenuItem();
        addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
            public void mouseDragged(java.awt.event.MouseEvent evt) {
                formMouseDragged(evt);
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(java.awt.event.WindowEvent evt) {
                exitForm(evt);
        triangle1.setBackground(new java.awt.Color(51, 204, 255));
        triangle1.setPreferredSize(new java.awt.Dimension(500, 500));
        triangle1.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                triangle1MouseClicked(evt);
            public void mouseEntered(java.awt.event.MouseEvent evt) {
                triangle1MouseEntered(evt);
            public void mouseExited(java.awt.event.MouseEvent evt) {
                triangle1MouseExited(evt);
        triangle1.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
            public void mouseDragged(java.awt.event.MouseEvent evt) {
                triangle1MouseDragged(evt);
            public void mouseMoved(java.awt.event.MouseEvent evt) {
                triangle1MouseMoved(evt);
        jScrollPane1.setViewportView(triangle1);
        getContentPane().add(jScrollPane1, java.awt.BorderLayout.CENTER);
        jMenuBar1.setBackground(new java.awt.Color(102, 153, 255));
        jMenu1.setBackground(new java.awt.Color(204, 204, 255));
        jMenu1.setText("File");
        jMenuItem1.setBackground(new java.awt.Color(255, 204, 255));
        jMenuItem1.setText("Open");
        jMenuItem1.setToolTipText("Open");
        jMenu1.add(jMenuItem1);
        jMenu1.add(jSeparator1);
        jMenuItem2.setText("Save");
        jMenuItem2.setToolTipText("Save");
        jMenu1.add(jMenuItem2);
        jMenu1.add(jSeparator2);
        jMenuItem3.setText("Exit");
        jMenuItem3.setToolTipText("X");
        jMenuItem3.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jMenuItem3ActionPerformed(evt);
        jMenu1.add(jMenuItem3);
        jMenuBar1.add(jMenu1);
        setJMenuBar(jMenuBar1);
        pack();
    private void jMenuItem3ActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
        System.exit(0);
    private void triangle1MouseMoved(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
         setTitle("Mouse is at [" + evt.getX()  + "," + evt.getY() + "]");
    private void triangle1MouseExited(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
        setTitle("Mouse out of Application Window");
    private void triangle1MouseDragged(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
        setTitle("Mouse Dragged at [" + evt.getX()  + "," + evt.getY() + "]");
    private void triangle1MouseEntered(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
                setTitle("Mouse is in Application Window");
    private void triangle1MouseClicked(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
         setTitle("Mouse clicked at [" + evt.getX()  + "," + evt.getY() + "]");
    private void formMouseDragged(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here
         //setTitle("Mouse is at [" + evt.getX()  + "," + evt.getY() + "]");
    /** Exit the Application */
    private void exitForm(java.awt.event.WindowEvent evt) {
        System.exit(0);
     * @param args the command line arguments
    public static void main(String args[]) {
        new GUI().show();
        JFrame GUI = new JFrame("GUI");
        Triangle tri = new Triangle();
        GUI.getContentPane().add(tri);
    // Variables declaration - do not modify
    private javax.swing.JMenu jMenu1;
    private javax.swing.JMenuBar jMenuBar1;
    private javax.swing.JMenuItem jMenuItem1;
    private javax.swing.JMenuItem jMenuItem2;
    private javax.swing.JMenuItem jMenuItem3;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JSeparator jSeparator1;
    private javax.swing.JSeparator jSeparator2;
    private Triangle triangle1;
    // End of variables declaration
}Any help on how to drag the triangle would be greatly appreciated.
After this i need to stretch the vertex of the triangle such that i can increase the size of it.
Thanks a lot
Sharan

Answer 1

Hi ... I have finally managed to draw and stretch a triangle on screen as well as Increase its size on screen.
I have drawn a Right angle Triangle on screen or so it appears by the constraints set out to draw it.
Then I have enabled dragging only when the user clicks on the Left Cordinates of the BASE. (PRECISELY ON THOSE POINTS)
And stretching any side is possible only when the user clicks on the TOP or the RIght Hand side cordinates of the base.
The problem is that as and when i stretch the triangle or drag the triangle for that matter it redraws itself a number of times i.e. i can c the entire triangle moving on screen and hence it overlaps and redraws itself on screen.
Besides finding the exact cordinates of the triangle to DRAG it i.e. 300,300 for the base is difficult coz as of now thats the way i could work it out.
The code for my program is below and i would appreciate if you could sort my problems out and tellme how to drag the triangle when the user just clicks within the area of the triangle and stretches it in a way that it does not redraw the entire triangle..
Thanks...
This is my main Class
import java.awt.*;
import java.util.*;
import javax.swing.*;
import java.awt.Graphics.*;
import java.awt.geom.Point2D;
* @author  Kripa Bhojwani
public class Geometry extends javax.swing.JFrame  {
    /** Creates new form Geometry */
    public Geometry() {
        JFrame Geometry = new JFrame("Geometry");
           initComponents();
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    private void initComponents() {
        addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
            public void mouseDragged(java.awt.event.MouseEvent evt) {
                formMouseDragged(evt);
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(java.awt.event.WindowEvent evt) {
                exitForm(evt);
        pack();
    private void formMouseDragged(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
    /** Exit the Application */
    private void exitForm(java.awt.event.WindowEvent evt) {
        System.exit(0);
     * @param args the command line arguments
    public static void main(String args[]) {
         TriangleModel tri = new TriangleModel(300,150,450,300,300,300);
        View view  = new View(tri);   // view takes in model
         JFrame Geometry = new JFrame("Geometry");
        Geometry.setSize(500,500);
         Geometry.setContentPane(view);
        Geometry.setVisible(true);
        Geometry.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       // new Geometry().show();
    // Variables declaration - do not modify
    // End of variables declaration
This is my triangleModel class ---  the Model
* TriangleModel.java
* Created on 02 December 2004, 20:27
import java.awt.geom.*;
import javax.swing.*;
import java.util.*;
import java.awt.Graphics;
import java.awt.Point;
* @author  Kripa Bhojwani
public class TriangleModel extends Observable {
    private int cx, cy, x1,x2,x3, y1,y2,y3;
    private int _transx;
    private int _transy;
    /** Creates a new instance of TriangleModel */
    public TriangleModel(int x1, int y1, int x2, int y2, int x3, int y3) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
        this.x3 = x3;
        this.y3 = y3;
        setChanged();
        notifyObservers();
    public void setTop(int x1, int y1){
        this.y1= y1;
        setChanged();
        notifyObservers();
    public void setRight(int x2, int y2){
        this.x2 = x2;     
        setChanged();
        notifyObservers();
    public void setLeft(int x3, int y3){
        _transx = x3 - this.x3;
        _transy = y3 - this.y3;
        this.x3 += _transx;
        this.y3 += _transy;
        this.y2 += _transy;
        this.x2 += _transx;
        this.x1 += _transx;
        this.y1 += _transy;
        setChanged();
        notifyObservers();
    public Point getTop(){
        Point p = new Point(x1,y1);
        return p;
    public Point getRight(){
        Point p1 = new Point(x2,y2);
        return p1;
    public Point getLeft(){
        Point p3 = new Point(x3,y3);
        return p3;
This is the Controller and View
import java.awt.*;
import java.util.*;
import javax.swing.*;
import java.awt.Graphics.*;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.awt.event.*;
import java.awt.Graphics2D;
* @author  Kripa Bhojwani
public class View extends javax.swing.JPanel implements Observer, MouseMotionListener, MouseListener{
    private TriangleModel model;
    private Polygon triangle;
    private boolean pressed = false;
    private boolean pressT = false;
    private boolean pressR = false;
    /** Creates new form View */
    public View(TriangleModel model) {
        this.model = model;
        model.addObserver(this);
        addMouseListener(this);
        addMouseMotionListener(this);
        // initComponents();
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    private void initComponents() {
        setLayout(new java.awt.BorderLayout());
    public void paintComponent(Graphics gfx) {
        Graphics2D g = (Graphics2D) gfx;
        //  g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
        //RenderingHints.VALUE_ANTIALIAS_ON);
        //        Polygon triangle = new Polygon(3);
        Point tc = model.getTop();
        Point lc = model.getLeft();
        Point rc = model.getRight();
        //        triangle.add(new Point2D.Double(tc.getX(), tc.getY()));
        //        triangle.add(new Point2D.Double(lc.getX(), lc.getY()));
        //        triangle.add(new Point2D.Double(rc.getX(), rc.getY()));
        Point2D.Double p1 = new Point2D.Double(tc.getX(),tc.getY());
        Point2D.Double p2 = new Point2D.Double(lc.getX(),lc.getY());
        Point2D.Double p3 = new Point2D.Double(rc.getX(),rc.getY());
        Line2D.Double line = new Line2D.Double(p1, p2);
        Line2D.Double line1 = new Line2D.Double(p2, p3);
        Line2D.Double line2 = new Line2D.Double(p1, p3);
        // g.setPaint(Color.BLACK);
        // triangle.draw(g);
        g.draw(line);
        g.draw(line2);
        g.draw(line1);
    public void update(Observable o, Object arg) {
        repaint();
    public void mouseClicked(java.awt.event.MouseEvent e) {
    public void mouseDragged(java.awt.event.MouseEvent e) {
        if(pressed == true){
            model.setLeft(e.getX() ,  e.getY());
        else if(pressT == true){
            model.setTop(e.getX() , e.getY());
        else if (pressR == true){
            model.setRight(e.getX(), e.getY());
        else {
            pressed = false;
            pressT= false;
    public void mouseEntered(java.awt.event.MouseEvent e) {
    public void mouseExited(java.awt.event.MouseEvent e) {
    public void mouseMoved(java.awt.event.MouseEvent e) {
        System.out.println(""+e.getX() + e.getY());
    public void mousePressed(java.awt.event.MouseEvent e) {
        if (model.getLeft().getX()== e.getX() && model.getLeft().getY()== e.getY()){
            pressed = true;
        else if (model.getTop().getX()==e.getX() && model.getTop().getY()==e.getY()){
            pressT = true;
        else if(model.getRight().getX() == e.getX() && model.getRight().getY()==e.getY()){
            pressR = true;
        else {
            pressed =false;
            pressT = false;
            pressR = false;
    public void mouseReleased(java.awt.event.MouseEvent e) {
        if(pressed == true){
            model.setLeft(e.getX(),e.getY());
        else if (pressT ==true ){
            model.setTop(e.getX(), e.getY());
        else if(pressR ==true){
            model.setTop(e.getX(),e.getY());
        else{
            pressed = false;
            pressT = false;
            pressR = false;
    // Variables declaration - do not modify
    // End of variables declaration
Thanks again
code]