Develop Reference

MouseListener not giving accurate mouse location

I am attempting to have a circle appear on the screen and follow the mouse around. (Eventually I'm going to turn it into a game with ray casting) I am using a MouseMotionListener and am trying to use the mouseMoved method to get accurate mouse location within my JPanel. The problem is though that the farther I move my mouse down the screen, the less accurate it becomes. By the time my mouse gets to the bottom, it is drawing circles about 20 pixels above. It is not a lagging thing because it never catches up, it is always a few pixels above where it should be.
I've tried using different methods that call from MouseEvents and have tried using MousePointerInfo but none work correctly. It does seem to work when I have the JFrame set to undecorated, but obviously that does not look good for a program and thus I want to avoid that.
public class Driver {
public static void main(String[] args) {
JFrame frame = new JFrame("Moonlight");
frame.setSize(700, 700);
frame.setLocation(350, 50);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setContentPane(new MoonlightPanel());
frame.setVisible(true);
}
}
public class Panel extends JPanel {
private BufferedImage myImage;
private Graphics myBuffer;
private Timer t;
public Panel () {
myImage = new BufferedImage(700, 700, BufferedImage.TYPE_INT_RGB);
myBuffer = myImage.getGraphics();
t = new Timer(0, new Listener());
t.start();
addMouseMotionListener(new Mouse());
}
private class Listener implements ActionListener {
public void actionPerformed(ActionEvent e) {
drawBackground();
/*try {
Point pos = getMousePosition();
myBuffer.setColor(Color.WHITE);
myBuffer.fillOval(pos.x - 10, pos.y - 10, 20, 20);
}
catch(NullPointerException en) {}*/
repaint();
}
}
private class Mouse implements MouseMotionListener {
public void mouseMoved(MouseEvent e) {
Point pos = new Point(e.getX(), e.getY());
System.out.println(pos);
myBuffer.setColor(Color.BLUE);
myBuffer.fillOval(pos.x - 10, pos.y - 10, 20, 20);
}
public void mouseDragged(MouseEvent e) {}
}
public void drawBackground() {
setBackground(Color.BLACK);
}
public void paintComponent(Graphics g) {
g.drawImage(myImage, 0, 0, getWidth(), getHeight(), null);
}
}

Your code is much more complex than it needs to be. The Panel class members are unnecessary. All you need to do is save the mouse location in the mouseMoved() method - in a class member variable - and reference it in the paintComponent() method to draw your blue circle. The below code is a stripped-down version which displays a blue circle that follows the mouse pointer around on the screen.
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MoonLite extends JPanel implements MouseMotionListener {
private Point pt;
public MoonLite() {
setBackground(Color.BLACK);
setForeground(Color.BLUE);
addMouseMotionListener(this);
}
public void mouseMoved(MouseEvent e) {
pt = e.getPoint();
repaint();
}
public void mouseDragged(MouseEvent e) {
// Do nothing.
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
if (pt != null) {
g.fillOval(pt.x - 10, pt.y - 10, 20, 20);
}
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame("Moonlight");
frame.setSize(700, 700);
frame.setLocation(350, 50);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setContentPane(new MoonLite());
frame.setVisible(true);
}
});
}
}

Figure drawn without function call?

I am getting a problem in java program for moving a circle. The program has 2 basic buttons:
START: used for moving the circle
STOP: used for exiting the program
My problem is that the circle appears before I press the start button. However I make the call to move only when START Button is pressed which makes the call to repaint and then the circle should appear. But it appears by default. I have no problem in moving the circle. Here is my source code:
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
class Moving extends JFrame implements ActionListener
{
JButton start,stop;Move mypanel;
Moving()
{
setTitle("Moving circle");
setLayout(new BorderLayout());
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(800,600);
start=new JButton("START");
stop=new JButton("STOP");
start.addActionListener(this);stop.addActionListener(this);
JPanel p=new JPanel();
p.setLayout(new FlowLayout());
p.add(start);p.add(stop);
getContentPane().add(p,BorderLayout.SOUTH);
mypanel=new Move();
getContentPane().add(mypanel,BorderLayout.CENTER);
}
public void actionPerformed(ActionEvent e)
{
String s=e.getActionCommand();
if(s.equals("STOP"))
System.exit(0);
else if(s.equals("START"))
mypanel.move();
}
public static void main(String []args)
{
Moving obj=new Moving();
obj.setVisible(true);
}
}
class Move extends JPanel
{ static int x=80, cv=0;
public void move()
{
repaint();
}
public void paintComponent(Graphics g)
{
setBackground(Color.green);
super.paintComponent(g);
g.setColor(Color.red);
if(x<500&&cv==0)
{g.fillOval(x, 80, 100, 100);this.inc();}
else if((x>=500||cv==1)&&x>=80)
{
cv=1;g.fillOval(x, 80, 100, 100);this.dec();
}
else cv=0;
}
public void inc()
{
x+=10;
}
public void dec()
{
x-=10;
}
}

By default setVisible would be true. So, if you don't won't to show panel on load then make it false on constructor.
And then make it visible when you hit Start.
See below:
class Move extends JPanel {
static int x = 80, cv = 0;
Move(){
setVisible(false); <-- Make it false here
}
public void move() {
this.setVisible(true); <----- make it visible here when you click start
repaint();
}
public void paintComponent(Graphics g) {
setBackground(Color.green);
..... REMAINING CODE
}
}

My suggestion is that if you do not want to show your circle before the pressing of the start button you have to remove drawing of the circle from the paintComponent method.
You can achieve the above by declaring a new method in your Move class say drawCircle like this:
public void drawCircle(Graphics g){
g.setColor(Color.red);
if(x<500&&cv==0)
{g.fillOval(x, 80, 100, 100);this.inc();}
else if((x>=500||cv==1)&&x>=80)
{
cv=1;g.fillOval(x, 80, 100, 100);this.dec();
}
else cv=0;
}
now in your Move class introduce a new boolean variable say circleShowing and intialise to false. This is declared so that the paintComponent method of the Move class can decide whether the circle should be drawn or not. You can do it like this:
public void paintComponent(Graphics g){
setBackground(Color.green);
super.paintComponent(g);
if(circleShowing){
drawCircle(g);
}
}
Now finally in the actionPerformed method of your Moving class you in the else if block you could write the following:
mypanel.circleShowing = true;
mypanel.move();
I hope if you make these changes this will work as you wish.

what is Alternative of Paint and repaint function?

Is there any function which can be replaced with paint() and repaint()in java.
I have a scenario.
There is a triangle (Triangle 1). when user will click in triangle another triangle (Triangle 2) will appear and 1st (Triangle 1) will be removed from screen. (coded using JFrame, paint() and repaint())
I have achieved it so far. but problem is when I minimize or change size of window with mouse the output window, it just paint again Triangle 1 rather than Triangle 2. OR Clear the whole screen if i call g2d.clearRect(0, 0, 1000, 1000);
triangle.reset();
Note: These both functions are to remove previous triangle (Triangle 1).
Is there any function that state should not be changed on minimize or when window size changed ?
or can we override repaint() or anything helping according to scenario.
Here is the Working code. Execute it, Click in triangle then minimize and see again. You will get the problem more clearly.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Triangle_shape extends JFrame implements ActionListener {
public static JButton btnSubmit = new JButton("Submit");
public Triangle_shape() {
}
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.setLayout(new BorderLayout());
frame.add(new TrianglePanel(), BorderLayout.CENTER);
frame.add(btnSubmit, BorderLayout.PAGE_END);
frame.pack();
frame.repaint();
frame.setTitle("A Test Frame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e) {
throw new UnsupportedOperationException("Not supported yet.");
}
public static class TrianglePanel extends JPanel implements MouseListener {
private Polygon triangle, triangle2;
public TrianglePanel() {
//Create triangle
triangle = new Polygon();
triangle.addPoint(400, 550); //left
triangle.addPoint(600, 550); //right
triangle.addPoint(500, 350); //top
//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
*/
#Override
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) {
Graphics2D g2d = (Graphics2D) this.getGraphics();
Point p = e.getPoint();
if (triangle.contains(p)) {
System.out.println("1");
g2d.clearRect(0, 0, 1000, 1000);
triangle.reset();
g2d.setColor(Color.MAGENTA);
triangle2 = new Polygon();
triangle2.addPoint(600, 550); // left
triangle2.addPoint(700, 350); //top
triangle2.addPoint(800, 550); //right
g2d.draw(triangle2);
} else {
System.out.println("Triangle dont have point");
}
}
}
}

paint() and repaint() work fine, but you are not using them as they are designed to be used. The window system doesn't keep a persistent image of what a component looks like. It expects your component to be able to repaint its entire appearance on demand (such as when the window is resized or un-minimized).
If you grab a Graphics object with getGraphics() and draw something on the component, the stuff you draw will indeed be lost if/when the entire component needs to be repainted. So you should not do that, but instead make sure your paintComponent method has all the information it needs to completely repaint the component.
If you only want one triangle on the screen at once, do not create a separate variable triangle2. Just replace the one triangle you have by altering your mouse click handler as follows:
public void mouseClicked(MouseEvent e) {
Point p = e.getPoint();
if (triangle.contains(p)) {
triangle = new Polygon();
triangle.addPoint(600, 550); // left
triangle.addPoint(700, 350); //top
triangle.addPoint(800, 550); //right
repaint();
} else {
System.out.println("Point not in triangle");
}
}
Your paintComponent method should call super.paintComponent to ensure the background is painted, but otherwise you do not need to change it:
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
g2d.draw(triangle);
}
Alternatively if you are trying to keep multiple triangles on the screen, for example, to add a new one at every click, you should add them into a list of shapes which will be drawn whenever the component needs to be repainted:
private final List<Shape> shapes = new ArrayList<>();
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
for (Shape s : shapes)
g2d.draw(s);
}
Then to control the set of shapes that is on screen, manipulate the contents of the list, and call repaint();.
For instance, to add a new shape to the ones on screen:
Polygon triangle = new Polygon();
triangle.addPoint(200, 300);
triangle.addPoint(200, 200);
triangle.addPoint(300, 200);
shapes.add(triangle);
repaint();
To remove all shapes from the screen:
shapes.clear();
repaint();
You should also make sure that you switch to the Swing thread at the start of the program, because it is not safe to interact with Swing components from the main thread. In main:
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame();
.
.
.
frame.setVisible(true);
}
});
}

Your mouseClicked method should not create a new Triangle object. After resetting triangle just add new points to it. Also don't draw in this method but call repaint:
public void mouseClicked(MouseEvent e) {
Point p = e.getPoint();
if (triangle.contains(p)) {
System.out.println("1");
triangle.reset(); // change the current triangle
triangle.addPoint(600, 550); // new left
triangle.addPoint(700, 350); // new top
triangle.addPoint(800, 550); // new right
repaint(); // force repainting
} else {
System.out.println("Triangle dont have point");
}
}
Now if you want many triangles you should have a collection of Polygons. Like this :
public static class TrianglePanel extends JPanel implements MouseListener {
private Vector<Polygon> triangles;
public TrianglePanel() {
n = 0;
// Create an empty collection
triangles = new Vector<Polygon>();
//Create first triangle
Polygon triangle = new Polygon();
triangle.addPoint(400, 550); //left
triangle.addPoint(600, 550); //right
triangle.addPoint(500, 350); //top
// Add the triangle to the collection
triangles.add(triangle);
//Add mouse Listener
addMouseListener(this);
//Set size to make sure that the whole triangle is shown
setPreferredSize(new Dimension(300, 300));
}
/**
* Draws the triangles as this frame's painting
*/
#Override
public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
for (Polygon p : triangles) // Draw all triangles in the collection
g2d.draw(p);
}
//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) {
Graphics2D g2d = (Graphics2D) this.getGraphics();
Point p = e.getPoint();
// Do what you want with p and the collection
// For example : remove all triangles that contain the point p
ListIterator<Polygon> li = triangles.listIterator();
while (li.hasNext()) {
if (li.next().contains℗) li.remove();
}
// Do what you want to update the list
// For example: Add a new triangle...
Polygon triangle = new Polygon();
triangle.addPoint(600+n, 550); // left
triangle.addPoint(700+n, 350); //top
triangle.addPoint(800+n, 550); //right
triangles.add(triangle); // add the new triangle to the list
n += 10; // next new triangle will be "moved" right
repaint();
}
private int n;
}

Repaint() doesn't clear the frame

public class Graphics2DTest extends JPanel implements ActionListener{
private Timer time = new Timer(5,(ActionListener) this);
int x = 0,y = 0;
public void paintComponent(Graphics g){
Graphics2D gui = (Graphics2D) g;
Rectangle2D rectangle = new Rectangle2D.Double(x,y,100,150);
gui.setPaint(Color.GREEN);
gui.fill(rectangle);
time.start();
}
public void actionPerformed(ActionEvent arg0) {
x++;
y++;
repaint();
}
}
The problem is repaint() is supposed to clear the frame and draw the rectangle in the position, but the previously painted rectangle remains. So, how to do it? Please explain your answers.

Have you tried calling super.paintComponent(g) in your paintComponent method? This will clear prior images drawn in your JPanel:
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D gui = (Graphics2D) g;
Rectangle2D rectangle = new Rectangle2D.Double(x,y,100,150);
gui.setPaint(Color.GREEN);
gui.fill(rectangle);
//time.start();
}
Also, don't start a timer or do any program logic within the paintComponent method. First of all you cannot absolutely control when or if the method will be called, and secondly, this method must be concerned only with painting and nothing else, and needs to be as fast as possible.
For instance:
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class Graphics2DTest extends JPanel implements ActionListener {
private Timer time = new Timer(5, (ActionListener) this);
int x = 0, y = 0;
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D gui = (Graphics2D) g;
Rectangle2D rectangle = new Rectangle2D.Double(x, y, 100, 150);
gui.setPaint(Color.GREEN);
gui.fill(rectangle);
//time.start();
}
public void actionPerformed(ActionEvent arg0) {
x++;
y++;
repaint();
}
public Graphics2DTest() {
setPreferredSize(new Dimension(700, 500));
time.start();
}
private static void createAndShowUI() {
JFrame frame = new JFrame("Graphics2DTest");
frame.getContentPane().add(new Graphics2DTest());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
createAndShowUI();
}
});
}
}

You need to repaint the background each time as well. Add code to paint the background before you paint the rectangle.

You need to clear the background first.
A resource is this:
http://java.sun.com/products/jfc/tsc/articles/painting/

Image mapping like feature in Java swing, Points vs GeneralPath

My gaol is to draw several images using 2D graphics in a paintComponent() method. However, I'm not sure how I could add a MouseListener such that each image would know if it was selected.
My solution thus far is too simply record the coordinates of the mouse click, and see if they are contained within the boundaries of each of the images. However this will be difficult with images that have more complex boundaries.
Another option would be too create simple shapes and place them over the images, but again images with more complex boundaries will be difficult. In another discussion on SO found
here, someone mentioned using GeneralPath to draw more complex shapes. I have never played with is, but this seems encouraging.
Of these 2 options, what seems to be the best solution, or are there other recommendations

Are you images painted on top of one another or are they drawn separately.
If they are drawn separately, then you should do the custom painting on a JComponent. Then you can do the drawing by using the GeneralPath. You will also need to implement the contains(...) method by checking if the mouseclick is contained in the GeneralPath. If the contains() method is implemented properly then the MouseListener will respond properly.
Here is a simpler example:
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class RoundButton extends JButton {
public RoundButton(String label) {
super(label);
// These statements enlarge the button so that it
// becomes a circle rather than an oval.
Dimension size = getPreferredSize();
size.width = size.height = Math.max(size.width, size.height);
setPreferredSize(size);
// This call causes the JButton not to paint the background.
// This allows us to paint a round background.
setContentAreaFilled(false);
}
// Paint the round background and label.
protected void paintComponent(Graphics g) {
if (getModel().isArmed()) {
// You might want to make the highlight color
// a property of the RoundButton class.
g.setColor(Color.lightGray);
} else {
g.setColor(getBackground());
}
g.fillOval(0, 0, getSize().width-1, getSize().height-1);
// This call will paint the label and the focus rectangle.
super.paintComponent(g);
}
// Paint the border of the button using a simple stroke.
protected void paintBorder(Graphics g) {
g.setColor(getForeground());
g.drawOval(0, 0, getSize().width-1, getSize().height-1);
}
// Hit detection.
Shape shape;
public boolean contains(int x, int y) {
// If the button has changed size, make a new shape object.
if (shape == null || !shape.getBounds().equals(getBounds())) {
shape = new Ellipse2D.Float(0, 0, getWidth(), getHeight());
}
return shape.contains(x, y);
}
// Test routine.
public static void main(String[] args) {
// Create a button with the label "Jackpot".
JButton button = new RoundButton("Jackpot");
button.setBackground(Color.green);
button.setBounds(0, 0, 100, 100);
JButton button2 = new RoundButton("Jackpot2");
button2.setBackground(Color.red);
button2.setBounds(50, 50, 100, 100);
// Create a frame in which to show the button.
JFrame frame = new JFrame();
frame.getContentPane().setBackground(Color.yellow);
frame.getContentPane().setLayout(null);
frame.getContentPane().add(button);
frame.getContentPane().add(button2);
// frame.getContentPane().setLayout(new FlowLayout());
frame.setSize(200, 200);
frame.setVisible(true);
MouseListener mouseListener = new MouseAdapter() {
public void mouseEntered( MouseEvent e )
{}
public void mouseExited( MouseEvent e )
{}
public void mouseClicked( MouseEvent e )
{
System.out.println( "clicked " );
}
public void mousePressed( MouseEvent e )
{
System.out.println( "pressed " );
}
public void mouseReleased( MouseEvent e )
{
System.out.println( "released " );
}
};
button.addMouseListener( mouseListener );
}
}