I'm trying to write a Pong applet in Java. When the user holds down either up or down, their paddle should move smoothly, but this isn't the case. It moves, then pauses, then starts moving again. Is there a way to stop this short pause from happening?
Main Class:
public class Main extends JApplet {
public DrawPanel dp = new DrawPanel(400, 400);
public void init(){
add(dp);
setSize(400, 400);
requestFocusInWindow();
Action moveDown = new AbstractAction(){
public void actionPerformed(ActionEvent e){
dp.player.y += 10;
dp.repaint();
}
};
dp.getInputMap().put(KeyStroke.getKeyStroke("pressed DOWN"), "move down");
dp.getActionMap().put("move down", moveDown);
}
}
DrawPanel Class:
public class DrawPanel extends JPanel {
public Paddle player;
public Paddle opponent;
public DrawPanel(int height, int width){
int y = (height / 2) - (height / 10);
int w = 15;
int h = height / 5;
player = new Paddle(2, y, 15, h, Color.white);
opponent = new Paddle(width - (w+2), y, 15, h, Color.white);
}
public void paintComponent(Graphics g){
super.paintComponent(g);
this.setBackground(Color.BLACK);
g.setColor(player.color);
g.fillRect(player.x, player.y, player.width, player.height);
g.setColor(opponent.color);
g.fillRect(opponent.x, opponent.y, opponent.width, opponent.height);
}
}
Paddle Class:
public class Paddle {
public int x, y, width, height;
public Color color;
public Paddle(int _x_, int _y_, int w, int h, Color c){
x = _x_;
y = _y_;
width = w;
height = h;
color = c;
}
}
The underlying issue is an impedance mismatch between the "instance" notion of a keyPressed and the "duration" notion of the movement.
Instead of trying to smooth that over in the view (which shouldn't have anything to do with the details of the game logic anyway), enhance the game model with api that's a better fit. F.i. add start/stop logic and bind those methods to keyPressed/keyReleased:
public class Paddle {
public void startMoveDown() {
// here goes the logic, f.i. starting a timer
// in the actionPerformed of that timer:
... moveUnitDown();
}
public void stopMoveDown() {
//...
}
protected void moveUnitDown() {
y+=unit;
// ideally, have listeners and notify them the change of y
}
}
// in the view:
Action startMoveDown = new AbstractAction(){
public void actionPerformed(ActionEvent e){
player.startMoveDown();
}
};
dp.getInputMap().put(KeyStroke.getKeyStroke("pressed DOWN"), "start move down");
dp.getActionMap().put("start move down", startMoveDown);
// in the view:
Action stopMoveDown = new AbstractAction(){
public void actionPerformed(ActionEvent e){
player.stopMoveDown();
}
};
dp.getInputMap().put(KeyStroke.getKeyStroke("released DOWN"), "stop move down");
dp.getActionMap().put("stop move down", stopMoveDown);
Related
I am making Conways Game of Life. In the mouse listener I want the cell to appear/disappear on the screen when I click once. I use a 40x40 boolean array (gameState) of 20x20 pixel cells. I want to paint the squares in my paint method using the co-ordinates of my mouse which i get in its clicked method. However, I am getting a null-pointer exception at line 71 and do not know what to do to solve it.
Main
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferStrategy;
public class mainApplication extends JFrame implements Runnable, MouseListener {
private static final Dimension windowsize = new Dimension(80, 600);
private BufferStrategy strategy;
private Graphics offscreenGraphics;
private static boolean isGraphicsInitialised = false;
private static int rows = 40;
private static int columns = 40;
private static int height = windowsize.height;
private static int width = windowsize.width;
private static Cells cells;
private int xArrayElement,yArrayElement, xPosition, yPosition;
private static boolean gameState[][] = new boolean[rows][columns];
public mainApplication() {
System.out.println(System.getProperty("user.dir"));
setDefaultCloseOperation(EXIT_ON_CLOSE);
Dimension screensize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
int x = screensize.width / 2 - windowsize.width / 2;
int y = screensize.height / 2 - windowsize.height / 2;
setBounds(x, y, screensize.width, screensize.height);
setVisible(true);
createBufferStrategy(2);
strategy = getBufferStrategy();
offscreenGraphics = strategy.getDrawGraphics();
isGraphicsInitialised = true;
// MouseEvent mouseEvent = new MouseEvent();
addMouseListener(this);
// addMouseMotionListener(MouseEvent);
Thread t = new Thread(this);
t.start();
}
public void mousePressed(MouseEvent e) { }
public void mouseReleased(MouseEvent e) { }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) { }
public void mouseClicked(MouseEvent e) {
if(e.getClickCount() == 1){
xPosition = e.getX();
yPosition = e.getY();
cells.setPosition(xPosition,yPosition);
xArrayElement = (xPosition/20);
yArrayElement = (yPosition/20);
if(gameState[xArrayElement][yArrayElement]){
gameState[xArrayElement][yArrayElement] = false;
}
else if (!gameState[xArrayElement][yArrayElement]) {
gameState[xArrayElement][yArrayElement] = true;
}
}
}
#Override
public void run() {
while (true) {
try { //threads entry point
Thread.sleep(20); //forces us to catch exception
}
catch (InterruptedException e) {
}
}
}
public void paint(Graphics g) {
if (isGraphicsInitialised) {
g = strategy.getDrawGraphics();
g.setColor(Color.BLACK);
g.fillRect(0, 0, 800, 800);
if (gameState[xArrayElement][yArrayElement]) {
g.setColor(Color.WHITE);
cells.paint(g);
}
else if (!gameState[xArrayElement][yArrayElement]) {
g.setColor(Color.BLACK);
g.fillRect(xPosition, yPosition, 20, 20);
}
strategy.show();
}
}
public static void main(String[]args){
mainApplication test = new mainApplication();
}
}
Cells class
import java.awt.*;
public class Cells {
int x;
int y;
public Cells(){
}
public void setPosition(int xi, int xj){
x = xi;
y = xi;
System.out.println(xi);
System.out.println("sjdkgffdjv" + y);
}
public boolean cellState(boolean visible){
return visible;
}
public void paint(Graphics g){
g.drawRect(x, y, 20,20);
}
}
It's because you haven't initialized your cells variable in Main class..
So try this
private static Cells cells = new Cells();
As #nullPointer has pointed out (sorry, dad joke) you're getting a NPE because you haven't initialized the class member Cells. There are also a few other points to make that might unrelated to the question.
Don't create that thread
Swing already uses a thread to handle UI events and drawing so creating another thread is dangerous.
Make Cells immutable
Cells should be immutable. At no point should you need to set the position of a cell. If you need to change where a Cell is at, just dispose of the object and create a new one at that position.
I'm trying to create a circle around the mouse constantly in a JFrame, i.e the circle follows the mouse around the screen. To do this, I'm trying to use repaint() coupled with a timer, so that the circle continuously updates its location. For now, I have the program repainting the circle every second.
class MouseJFrame extends JFrame implements MouseListener{
int circleXcenter;
int circleYcenter;
int circleRadius = 25;
boolean show = false;
int delay = 1000;
// listen for and respond to mouse events
public MouseJFrame(){
new Timer(delay, taskPerformer).start();
addMouseListener(this);
}
// paints a circle
public void paint(Graphics g){
super.paint(g);
if(show){
g.drawOval(circleXcenter,circleYcenter,
circleRadius*2,circleRadius*2);
}
}
// getX and getY return the location of the mouse
ActionListener taskPerformer = new ActionListener() {
public void mouseDragged(MouseEvent e){
int xLocation = e.getX();
int yLocation = e.getY();
show = true;
circleXcenter = xLocation-circleRadius;
circleYcenter = yLocation-circleRadius;
repaint();
}
public void mouseMoved(MouseEvent e){
int xLocation = e.getX();
int yLocation = e.getY();
show = true;
circleXcenter = xLocation-circleRadius;
circleYcenter = yLocation-circleRadius;
repaint();
}
};
// class to create MouseJFrame object
public class TestMouseJFrame{
public static void main(String[] a){
MouseJFrame myMouseJFrame = new MouseJFrame ();
myMouseJFrame.setSize(200, 200);
myMouseJFrame.setVisible(true);
}
}
However, I get an error message regarding the ActionListener. When I try to fix this I get a load of other errors.
What can I do to get my program to run as intended?
It always works with images but rectangles and ovals never buffer right. I have a basic game loop in my gamepanel class that draws the player repeatedly. It doesn't remove the rectangle, just leaves a trace. I want to use a rectangle instead of an image for learning purposes. I tried using repaint in the game loop, but it flickered like crazy and still didn't work. I looked at another tutorial on this in this website but they used opengl witch is foreign to me and I don't want to take the time to figure it out.
JFrame:
import javax.swing.JFrame;
public class Game {
public static void main(String[] args) {
JFrame f = new JFrame();
f.setTitle("OMG I MADE A GAME");
f.setResizable(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(new Panel());
f.pack();
f.setVisible(true);
}
}
JPanel Class:
import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.event.*;
import javax.swing.JPanel;
import com.game.entity.Player;
public class Panel extends JPanel implements Runnable, KeyListener{
private static final long serialVersionUID = -5122190028751177848L;
// dimensions
public static final int WIDTH = 320;
public static final int HEIGHT = 240;
public static final int SCALE = 2;
// game thread
private Thread thread;
private boolean running;
// image
private BufferedImage image;
private Graphics2D g;
private Player p;
public Panel() {
super();
setPreferredSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
setFocusable(true);
requestFocus();
}
// DRAWS PANEL TO FRAME
public void addNotify() {
super.addNotify();
if(thread == null) {
thread = new Thread(this);
addKeyListener(this);
thread.start();
}
}
private void init() {
image = new BufferedImage(
WIDTH, HEIGHT,
BufferedImage.TYPE_INT_RGB );
g = (Graphics2D) image.getGraphics();
p = new Player(100, 100);
running = true;
}
public void run() {
init();
// game loop
while(running) {
update();
draw();
drawToScreen();
System.out.println("ELAPSED :" + System.nanoTime()/ 1000000 + " Seconds");
try {
Thread.sleep(10);
}
catch(Exception e) {
e.printStackTrace();
}
}
}
private void update() {
p.update();
}
private void draw(){
// NAME (remember it loops)
String name = "2014 Jay H.";
g.setFont(new Font("Name", 0, 12));
g.setColor(Color.WHITE);
g.drawString(name, 0, 10);
g.setColor(Color.BLUE);
g.fillRect( 0, 10, 65, 5);
//TITLE looks sexy :D
g.setColor(Color.GREEN);
g.setFont(new Font("Title", 0, WIDTH/ 10));
g.drawString("JAY'S GAME", WIDTH/ 5, 100);
//DRAW PLAYER
p.draw(g);
}
// SCREEN IMAGE (dont have to use. Just use this^)
private void drawToScreen() {
Graphics g2 = getGraphics();
g2.drawImage(image, 0, 0,
WIDTH * SCALE, HEIGHT * SCALE,null);
g2.dispose();
}
public void keyTyped(KeyEvent key) {}
// PUBLIC KEYRELEASES
public void keyPressed(KeyEvent key) {
int KeyCode = key.getKeyCode();
//EXIT SYSTEM
if(KeyCode == KeyEvent.VK_Q) {System.exit(0);
} //UP
if(KeyCode == KeyEvent.VK_W){p.setDY(-2);}
}
// PUBLIC KEYRELEASES
public void keyReleased(KeyEvent key) {
int KeyCode = key.getKeyCode();
//UP
if(KeyCode == KeyEvent.VK_W) {p.setDY(0);}
}
}
Player Class:
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import javax.swing.ImageIcon;
//FOR NOW THE PLAYER IS A RECTANGLE
public class Player {
// PLAYER CORDINATES AND VELOCITY
int x,y,dx,dy;
public Player(int x, int y) {
//NEEDED TO USE THE X AND Y
this.x =x;
this.y = y;
}
public void update() {
x += dx;
y += dy;
}
// DRAW TO PANEL CLASS
public void draw(Graphics2D g) {
//BODY
g.setColor(Color.PINK);
g.fillRect(x, y, 20, 20);
//EYES
g.setColor(Color.BLACK);
g.fillRect(x+3, y+2, 5, 10);
g.fillRect(x+ 12, y+2, 5, 10);
//EYERIS
g.setColor(Color.WHITE);
g.fillRect(x+3, y+2, 2, 10);
g.fillRect(x+15, y+2, 2, 10);
//NOSE
g.setColor(Color.MAGENTA);
g.fillRect(x+5, y+13, 10, 5);
//NOSTRILLS
g.setColor(Color.red);
g.fillRect(x+6, y+15, 2, 2);
g.fillRect(x+12, y+15, 2, 2);
}
//GET METHODS FOR CORDINATES AND VELOCITY (Unused for now... i think)
public int getX() {return x;}
public int getY() {return y;}
public int getDX() {return dx;}
public int getDY() {return dy;}
//SET METHODS TO CHANGE
public void setX(int x) {this.x = x;}
public void setY(int y) {this.y = y;}
public void setDX(int dx) {this.dx = dx;}
public void setDY(int dy) {this.dy = dy;}
}
You need to "reset" the background of the buffer before you paint to it.
Remember, painting is accumilitive, that is, what ever you painted previously, will remain. You will need to rebuild each frame from scratch each time you paint to it
Flickering will occur for two reasons...
You are using AWT based components, which aren't double buffered
You are overriding paint of a top level container like JFrame, which isn't double buffered.
You should either use a BufferStrategy or override the paintComponent method of a Swing based component, like JPanel which are double buffered by default
Working on an applet that draws 2 eyes and uses MouseMotionListener to move the they eyes. Also when the mouse exits the content pane, the eyes look straight. The one thing
I'm struggling with is I can't figure out how to restrict the pupils movements to stay within the eye. Any suggestions you guys have would be great.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class WatchMe extends JApplet
{
private int leftMouseX = 130;
private int leftMouseY = 155;
private int rightMouseX = 305;
private int rightMouseY = 155;
private boolean mouseEntered;
//init method
public void init()
{
//set background to green
getContentPane().setBackground(Color.green);
//add mouse listener
addMouseListener(new MyMouseListener());
//add a motion listener
addMouseMotionListener(new MyMouseMotionListener());
}
public void paint(Graphics g)
{
//call superclass paint method
super.paint(g);
//draw left eye
g.setColor(Color.yellow);
g.fillOval(75, 100, 150, 150);
//draw left pupil
g.setColor(Color.black);
g.fillOval(leftMouseX, leftMouseY, 40, 40);
//draw right eye
g.setColor(Color.yellow);
g.fillOval(250, 100, 150, 150);
//draw right pupil
g.setColor(Color.black);
g.fillOval(rightMouseX, rightMouseY, 40, 40);
//checks to see if the mouse is in the pane, if not
//sets the x,y coordinates to look straight
if (! mouseEntered)
{
leftMouseX = 130;
leftMouseY = 155;
rightMouseX = 305;
rightMouseY = 155;
repaint();
}
}
private class MyMouseListener implements MouseListener
{
public void mousePressed(MouseEvent e)
{
}
public void mouseClicked(MouseEvent e)
{
}
public void mouseReleased(MouseEvent e)
{
}
public void mouseEntered(MouseEvent e)
{
mouseEntered = true;
repaint();
}
public void mouseExited(MouseEvent e)
{
mouseEntered = false;
repaint();
}
}
private class MyMouseMotionListener implements MouseMotionListener
{
public void mouseDragged(MouseEvent e)
{
leftMouseX = e.getX();
leftMouseY = e.getY();
rightMouseX = e.getX();
rightMouseY = e.getY();
repaint();
}
public void mouseMoved(MouseEvent e)
{
leftMouseX = e.getX();
leftMouseY = e.getY();
rightMouseX = e.getX();
rightMouseY = e.getY();
repaint();
}
}
}
As a start I would recommend putting your eye dimensions in variables as shown below. This way you reduce the chance of errors when entering the same numbers more than once, and if you later decide to change the eye size or position, you only have to change it once.
public static final int LEFT_X = 75;
public static final int LEFT_Y = 100;
public static final int EYE_SIZE = 150;
We also need the left pupil to be independent of the mouse (so it doesn't follow the mouse out of the eye) so we'll do this:
private leftPupilX = 130;
private leftPupilY = 155;
Next you need to determine whether or not the mouse is currently in the left eye. This is what will restrict the pupil to the bounds of the eye. I've done this in a method for convenience.
public void setLeftEye() {
//Set the X Coord for the pupil
//Mouse is to the left of the eye
if(leftMouseX < LEFT_X) {
leftPupilX = LEFT_X;
//Mouse is to the right of the eye
} else if(leftMouseX > LEFT_X + EYE_SIZE) {
leftPupilX = LEFT_X + EYE_SIZE;
//Mouse is in eye
} else {
leftPupilX = leftMouseX;
}
//Set the Y Coord for the pupil
//Mouse is above the eye
if(leftMouseY < LEFT_Y) {
leftPupilY = LEFT_X;
//Mouse is below the eye
} else if(leftMouseY > LEFT_Y + EYE_SIZE) {
leftPupilY = LEFT_Y + EYE_SIZE;
//Mouse is in eye
} else {
leftPupilY = leftMouseY;
}
}
Finally you'll need to update the code that draws the left pupil to reflect the variable change, and actually call our new method.
//draw left pupil
setLeftEye();
g.setColor(Color.black);
g.fillOval(leftPupilX, leftPupilY, 40, 40);
These changes should make the left eye track your mouse the way you described. You'll need to do something similar for the right eye, since it has different coordinates. If you have any problems, let me know and I will try to help. :)
I am trying to create a simple animation which draws random rectangles when a button is pressed. So far I managed to create rectangle on the press of a button. I want to further develop the code so that when I press the button, more than multiple random rectangles are created. I tried to create a for loop which asks the inner class to repaint itself but it still didn't work. can anyone help me please.
public class TwoButtonsRandomRec {
JFrame frame;
private int width = 500;
private int height = 500;
private DrawPanel dp;
public int getWidth() {
return width;
}
public void setWidth(int width) {
this.width = width;
}
public int getHeight() {
return height;
}
public void setHeight(int height) {
this.height = height;
}
public static void main (String[] args)
{
TwoButtonsRandomRec test = new TwoButtonsRandomRec();
test.go();
}
public void go()
{
dp = new DrawPanel();
JButton start = new JButton("Start");
start.addActionListener(new startListener());
JButton stop = new JButton("Stop");
stop.addActionListener(new stopListener());
frame = new JFrame();
frame.setSize(getWidth(), getHeight());
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(BorderLayout.NORTH, start);
frame.getContentPane().add(BorderLayout.SOUTH, stop);
}
class startListener implements ActionListener{
public void actionPerformed(ActionEvent event){
frame.getContentPane().add(BorderLayout.CENTER, dp);
frame.repaint();
frame.getRootPane().revalidate();
for(int i=0; i<10; i++){
dp.repaint();
}
}
}
class stopListener implements ActionListener{
public void actionPerformed(ActionEvent event){
System.out.println("stop");
}
}
class DrawPanel extends JPanel{
public void paintComponent(Graphics g){
int w = 5+(int)(Math.random() * width-5);
int h = 5+(int)(Math.random() * height-5);
int maxX = width-w; // diffX & diffY are used to ensure that rectangle is
int maxY = width-h; // draw completely inside the window
int x = (int)(Math.random() * maxX);
int y = (int)(Math.random() * maxY);
Color color = new Color((int) (Math.random()*256), // random red
(int) (Math.random()*256), // random green
(int) (Math.random()*256));// random blue
g.setColor(color);
g.fillRect(x,y,w,h);
}
}
}
repaint() simply tells Swing "when you'll have time, please repaint this area". So if you add rectangles in a loop and call repaint at each iteration, all the rectangles will only appear after the loop has finished, and the action event has been handled.
To have an animation, you need to loop in a separate thread. The easiest way to do that is to use a Swing Timer. When the Start button is started, start a timer which adds a random rectangle and calls repaint() every X milliseconds. When the Stop button is pressed, stop the timer.
What you should do is to put the loop inside paintComponent method and not call repaint in the loop.
So your paintComponent method should look like this:
public void paintComponent(Graphics g){
for (int i = 0; i < 10; i++) {
int w = 5+(int)(Math.random() * width-5);
int h = 5+(int)(Math.random() * height-5);
int maxX = width-w; // diffX & diffY are used to ensure that rectangle is
int maxY = width-h; // draw completely inside the window
int x = (int)(Math.random() * maxX);
int y = (int)(Math.random() * maxY);
Color color = new Color((int) (Math.random()*256), // random red
(int) (Math.random()*256), // random green
(int) (Math.random()*256));// random blue
g.setColor(color);
g.fillRect(x,y,w,h);
}
}
And your action performed should look like this:
public void actionPerformed(ActionEvent event){
frame.getContentPane().add(BorderLayout.CENTER, dp);
frame.repaint();
frame.getRootPane().revalidate();
dp.repaint();
}
Well,here I have done a short EG for you.It displays random rectangles, random times on random screen location.
(You can set your own value of randomization, and the screen location max bound,as per your requirements.)
And also note
int i=(int)(Math.random()*10);
int j=(int)(Math.random()*10);
for(;i<j;i++)
Where at times i may be > than j.So,loop may not work on one or two cliks.Change as per your need.
Here is the working code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SimpleStamper extends JApplet {
public void init() {
Display display = new Display();
setContentPane(display);
}
class Display extends JPanel implements MouseListener {
Display() {
setBackground(Color.black);
addMouseListener(this);
}
public void mousePressed(MouseEvent evt) {
if ( evt.isShiftDown() ) {
repaint();
return;
}
int x = evt.getX();
int y = evt.getY();
Graphics g = getGraphics();
//***MODIFY THE FOLLOWING LINES****//
int i=(int)(Math.random()*10);
int j=(int)(Math.random()*10);
for(;i<j;i++)
{ g.setColor(Color.red);
x=(int)(Math.random()*100);
y=(int)(Math.random()*100);
g.fillRect( x , y , 60, 30 );
g.setColor(Color.black);
g.drawRect(x , y , 60, 30 );}
g.dispose();
}
public void mouseEntered(MouseEvent evt) { }
public void mouseExited(MouseEvent evt) { }
public void mouseClicked(MouseEvent evt) { }
public void mouseReleased(MouseEvent evt) { }
}
}