Develop Reference

Java Applet - Stop other threads from changing Graphics color

as part of a school project we have to create a little game using Applets. I'm working on some tests right now but there's one thing I can't quite figure out:
I want to have multiple objects flying on my screen at the same time on my Applet screen. The animation effect is created by drawing the object, deleting it then moving it after a while.
Here's my code:
Robotworld class
package core;
import items.Obstacle;
import java.applet.Applet;
import java.awt.*;
import java.util.ArrayList;
public class Roboterwelt extends Applet {
private ArrayList<Obstacle> obstacles = new ArrayList<>();
#Override
public void init() {
setSize(600, 600);
Graphics g = getGraphics();
g.setColor(Color.BLACK);
for(int x = 0; x < 5; x++) {
Obstacle h = new Obstacle((x+1)*100, 100, g, this);
obstacles.add(h);
Thread t = new Thread(h);
t.start();
}
}
#Override
public void paint(Graphics g) {
for(Obstacle o : obstacles) {
o.draw();
}
}
}
Obstacle class
package items;
import java.applet.Applet;
import java.awt.*;
public class Obstacle implements Runnable {
private int x;
private int y;
private Graphics g;
public Hindernis(int x, int y, Graphics g) {
this.x = x;
this.y = y;
this.g = g;
}
public void draw() {
g.drawOval(x, y, 50, 50); //Draw obstacle
}
//Deleting the obstacle by covering it with a white circle
public void delete() {
g.setColor(Color.WHITE); //Change the color to white
g.fillOval(x-5,y-5,60,60); //Making it a bit bigger than the obstacle to fully cover it
g.setColor(Color.BLACK); //Reset the color to black
}
#Override
public void run() {
try {
while(y < 600) {
delete();
y += 10;
draw();
Thread.sleep(1000);
}
} catch(InterruptedException e) {
e.printStackTrace();
}
}
}
The problem is the part where I change the color of the Graphics object to cover the circle in white. When I have multiple threads running to represent the multiple obstacles on my screen and redrawing AND deleting happens concurrently, a thread gets interrupted after changing the color to white and draws a filled oval with the Graphics object which color was set to black by another thread that ran the delete() method to the end.
How can I force the program to not interrupt the delete() method between the color change to white and the drawing of the filled oval shape?

Disclaimer
Applet is deprecated, it is no longer supported by browsers, Oracle or the community. It would be unprofessional of me to try and encourage you to keep using them.
I appreciate that this is a "school" assignment, but perhaps it's time your instructor caught up with the rest of the world and started using something which doesn't actual cause more issues then it solves (hint JavaFX) - IMHO
Answer...
Don't use getGraphics, this is not how custom painting should be done. Painting should be done within the confines of the paint methods. Take a look at Painting in AWT and Swing for details. Apart from solving your immediate issue, your current approach risks been "wiped" clean when the applet repaints itself.
Overriding paint of the top level containers like Applet is a bad idea. Apart from locking you into a single use case, they aren't double buffered, which will cause flickering when painting occurs. The simplest solution is to start with a JPanel, which is double buffered and which can be added to what ever container you want to use.
You don't need multiple threads. Thread is a bit of an art form. More threads doesn't always mean more work gets done and can actually degrade the performance of the system. In your case you want to "update" the state in a single pass and then schedule a paint pass, so that the operations are synchronised in a single step and you don't end up with "dirty" updates
The following example simple makes use of Swing, which is based on AWT. It uses a JFrame instead of an Applet, but the concept is easily transferable, because the core functionality is based on a JPanel, so you can add it to what ever you want.
It makes use of a Swing Timer, which basically schedules a callback on a regular bases, but does it in away which makes it safe to update the state of the UI from (this replaces your Thread).
By using paintComponent to paint the Obstacles, we get two things for free.
Double buffering, so no more flickering
The Graphics context is automatically prepared for us, we don't need to "delete" the objects first, we simply paint the current state
The example also removes the Obstacle once it passes the edge of the panel, so you don't waste time trying to move/paint it when it's no longer visible.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private List<Obstacle> obstacles;
public TestPane() {
Color[] colors = new Color[]{Color.RED, Color.GREEN, Color.BLUE, Color.MAGENTA, Color.YELLOW};
obstacles = new ArrayList<>(10);
int y = 0;
for (int index = 0; index < 5; index++) {
y += 55;
Obstacle obstacle = new Obstacle(y, 0, colors[index]);
obstacles.add(obstacle);
}
Timer timer = new Timer(5, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
Iterator<Obstacle> it = obstacles.iterator();
while (it.hasNext()) {
Obstacle ob = it.next();
if (ob.move(getSize())) {
it.remove();
}
}
repaint();
}
});
timer.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
Iterator<Obstacle> it = obstacles.iterator();
while (it.hasNext()) {
Obstacle ob = it.next();
ob.paint(g2d);
}
g2d.dispose();
}
}
public class Obstacle {
private int x, y;
private Color color;
public Obstacle(int x, int y, Color color) {
this.x = x;
this.y = y;
this.color = color;
}
public void paint(Graphics2D g2d) {
g2d.setColor(color);
g2d.fillRect(x, y, 50, 50);
}
public boolean move(Dimension size) {
y += 1;
return y > size.height;
}
}
}
But all the Obstacles move at the same rate!
Yeah, that's because you used a single delta. If you want the Obstacles to move at different rates, then change the deltas, for example...
public static class Obstacle {
private static Random RND = new Random();
private int x, y;
private Color color;
private int yDelta;
public Obstacle(int x, int y, Color color) {
this.x = x;
this.y = y;
this.color = color;
yDelta = RND.nextInt(5) + 1;
}
public void paint(Graphics2D g2d) {
g2d.setColor(color);
g2d.fillRect(x, y, 50, 50);
}
public boolean move(Dimension size) {
y += yDelta;
return y > size.height;
}
}

Problems with BufferedImage in Java

I am making a game (like Civilization) that has different tile types that I want to render as images. I have 9 different 16x16 png images to load in (called Con1, Con2, etc.), and here is my image loading code: (img[] is my BufferedImage array)
public void loadImages(){
for(int i = 0; i < 9; i++){
try {
img[i] = ImageIO.read(this.getClass().getResource("Con"+i+".png"));
}catch (Exception ex) {
System.out.println("Missing Image");
ex.printStackTrace();
}
}
}
I then paint these images with this code: (t[][] is my tile type array)
public void paint(Graphics g){
if(loop){
BufferedImage B = new BufferedImage(this.getWidth(), this.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics r = B.getGraphics();
for (int x = 0; x < WIDTH; x++){
for (int y = 0; y < HEIGHT; y++){
if(i[x][y] == 0){
if (t[x][y] == 0){
g.drawImage(img[0], x, y, this);
}
else if(t[x][y] == 1){
g.drawImage(img[1], x, y, this);
}
else if(t[x][y] == 3){
g.drawImage(img[3], x, y, this);
}
else if(t[x][y] == 4){
g.drawImage(img[4], x, y, this);
}
else if(t[x][y] == 5){
g.drawImage(img[5], x, y, this);
}
}
r.fillRect(x*SCALE, y*SCALE, SCALE, SCALE);
}
}
g.drawImage(B, 0, 22, this);
}
}
My problem is that it doesn't show up correctly when I run it. I get this image:
that flashes on and off in the top-left corner of the window. What I am supposed to see is an image similar to the top-left portion of the above one (landmasses surrounded by ocean) except large enough to fill the window. Here is some runnable code: (I don't think the code will run without the required images but I would appreciate some help with getting the images to you all.)
//imports
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
public class MCVCon extends JFrame implements KeyListener, MouseListener{
//setting up variables
public BufferedImage[] img = new BufferedImage[9];
private final int WIDTH = 50, HEIGHT = 50;
private boolean loop = false;
private int SCALE = 16;
int t[][] = new int[WIDTH][HEIGHT]; //terrain type (since I took out the terrain generation it is set to 0 or ocean)
public MCVCon(){
//creating the window
super("Conqueror");
setSize(SCALE*WIDTH, SCALE*HEIGHT+22);
setVisible(true);
requestFocusInWindow();
setDefaultCloseOperation(EXIT_ON_CLOSE);
loadImages();
loop = true;
while(true){
this.repaint();
//delay for repaint
try{
Thread.sleep(50);
}
catch(Exception ex){
ex.printStackTrace();
}
}
}
//load images
public void loadImages(){
for(int i = 0; i < 9; i++){
try {
img[i] = ImageIO.read(this.getClass().getResource("Con"+i+".png"));
}catch (Exception ex) {
System.out.println("Missing Image");
ex.printStackTrace();
}
}
}
//paint the images
public void paint(Graphics g){
if(loop){
BufferedImage B = new BufferedImage(this.getWidth(), this.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics r = B.getGraphics();
for (int x = 0; x < WIDTH; x++){
for (int y = 0; y < HEIGHT; y++){
if (t[x][y] == 0){
g.drawImage(img[0], x, y, this);
}
else if(t[x][y] == 1){
g.drawImage(img[1], x, y, this);
}
r.fillRect(x*SCALE, y*SCALE, SCALE, SCALE);
}
}
g.drawImage(B, 0, 22, this);
}
}
//run the program
public static void main(String[] args) {
new MCVCon();
}
//necessary overrides
#Override
public void keyTyped(KeyEvent e) {
}
#Override
public void keyPressed(KeyEvent e) {
}
#Override
public void keyReleased(KeyEvent e) {
}
#Override
public void mouseClicked(MouseEvent e) {
}
#Override
public void mousePressed(MouseEvent e) {
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
}
I was wondering what the problem might be. Thanks in advance.

So, I had a look at your code, there's no easy way to say, but it's a mess, with compounding issues which would make it very difficult to isolate the origin of any one problem, other than to say, they all feed into each other.
Let's start with the painting...
You're painting directly to the frame. This is generally discouraged for a number of reasons.
Let's start with the fact that JFrame isn't a single component, it's made up of a number compounding components
This makes it inherently dangerous to paint directly to, as any one of the child components could be painted without the frame's paint method been called.
Painting directly to a frame also means you're painting without consideration to the frame's borders/decorations, which are added into the visible area of the window, but wait...
setSize(SCALE*WIDTH, SCALE*HEIGHT+22);
suggests that you've tried to compensate for this, but this is "guess" work, as the decorations could take up more or less space depending on the configuration of the system
And, finally, top level containers aren't actually double buffered.
"But I'm painting to my own buffer" you say - but you're not
You create a BufferdImage and assign it's Graphics context t r
BufferedImage B = new BufferedImage(this.getWidth(), this.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics r = B.getGraphics();
But when you paint anything, you're using g, which is the Graphics context passed to the paint method
g.drawImage(img[0], x, y, this);
This is also woefully inefficient, as you're creating a new BufferedImage each time paint is called, which takes time to create, takes up memory and puts extra strain on the garbage collection process as the local object becomes eligible for disposal almost immediately
Don't even get me started on the "main paint loop"
The next problem you have, is you have no concept of virtual and real world space.
You make a virtual map of your world using t, which maintains information about which tile should be used for a given x/y coordinate, but you never map this to the real world, instead, you paint each tile exactly at the same pixel x/y position, which means they now overlap, tiles have width and height, which means they need to be offset when painted onto the real world.
And finally, which I think is your actually question, is about scaling. There are a number of ways you could apply scaling, you could pre-scale the tiles when you load them, this gives you a lot of control over "how" they are scaled, but locks you into a single scale.
You could instead maintain a list of the scaled tiles, generated from a master list, which can be updated if the scale changes
Or you could simply scale the Graphics context directly.
Now, I've create a simple example, based on your code, correcting for most of the above. It creates a series of randomly colored rectangles at 10x10 pixels, instead of tiles, but the concept is the same.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class MCVCon extends JFrame {
//setting up variables
public MCVCon() {
//creating the window
super("Conqueror");
add(new GamePane());
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
MCVCon frame = new MCVCon();
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
//necessary overrides
public class GamePane extends JPanel {
public BufferedImage[] img = new BufferedImage[9];
private final int width = 5, height = 5;
private int scale = 16;
int t[][] = new int[width][height]; //terrain type (since I took out the terrain generation it is set to 0 or ocean)
Color[] colors = new Color[]{
Color.RED,
Color.BLUE,
Color.CYAN,
Color.DARK_GRAY,
Color.GRAY,
Color.GREEN,
Color.LIGHT_GRAY,
Color.MAGENTA,
Color.ORANGE,
Color.PINK,
Color.YELLOW
};
int tileHeight = 10;
int tileWidth = 10;
public GamePane() {
loadImages();
Random rnd = new Random();
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
int value = rnd.nextInt(9);
System.out.println(value + "- " + colors[value]);
t[x][y] = value;
}
}
Timer timer = new Timer(50, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
repaint();
}
});
timer.start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(width * tileWidth * scale, height * tileHeight * scale);
}
public void loadImages() {
for (int i = 0; i < 9; i++) {
try {
img[i] = new BufferedImage(tileWidth, tileHeight, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = img[i].createGraphics();
g2d.setColor(colors[i]);
g2d.fill(new Rectangle(0, 0, tileWidth, tileHeight));
g2d.dispose();
} catch (Exception ex) {
System.out.println("Missing Image");
ex.printStackTrace();
}
}
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setTransform(AffineTransform.getScaleInstance(scale, scale));
for (int x = 0; x < width; x++) {
for (int y = 0; y < height; y++) {
g2d.drawImage(img[t[x][y]], x * tileWidth, y * tileHeight, this);
}
}
g2d.dispose();
}
}
}

timer.schedule() in not working at all (in Java)

I made a simple program in Java which draws a rectangle on a canvas. And then the rectangle starts moving along X-axis, from left to right.
But the timer.schedule() function is not working. Following is the code:-
package firstanimation;
import java.awt.*;
import java.util.Timer;
public class FirstAnimation {
public static void main(String[] args) {
Frame frame = new Frame("SomeRandomName");
frame.setBounds(50, 50, 700, 500);
frame.setBackground(Color.red);
MyCanvas canvas = new MyCanvas();
frame.add(canvas);
frame.setVisible(true);
Graphics graph = frame.getGraphics();
Timer timer = new Timer();
Task task = new Task(canvas, graph);
timer.schedule(task, 1000,1000);
}
}
package firstanimation;
import java.awt.*;
public class MyCanvas extends Canvas{
public int x,y,width,height;
public MyCanvas()
{
x = 0;
y = 0;
width = 50;
height = 50;
}
#Override
public void paint(Graphics g) {
g.setColor(Color.LIGHT_GRAY);
g.fillRect(x, y, width, height);
}
#Override
public void update(Graphics g) {
x+=10;
g.fillRect(x, y, width, height);
}
}
package firstanimation;
import java.util.TimerTask;
import java.awt.Graphics;
public class Task extends TimerTask{
private MyCanvas canvas;
private Graphics graphics;
public Task(MyCanvas can, Graphics g)
{
super();
canvas = can;
graphics = g;
canvas.paint(g);
}
#Override
public void run() {
canvas.update(graphics);
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
}
But the strange thing is... Every time i'm maximizing and restoring the frame, the box is moving.
Why is this happening?

"But the strange thing is... Every time i'm maximizing and restoring the frame, the box is moving. Why is this happening?"
Because repaint() is called when you resize which update the graphics, which you should be doing, instead of trying to call paint.
But...
Still many things wrong.
Seeing as this is your first animation (package firstanimation;), let me get you started in the right direction.
Don't use Canvas. Use JPanel or JComponent instead. When you do, don't override paint but paintComponent instead. Also make sure you call super.paintComponent so you aren't let with any paint artifact during the animation.
public class MyCanvas extends JPanel {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
//painting code
}
}
Never use getGraphics on a component to do any painting.
You shouldn't ever have to explicitly call paint. The paint[Component] method will be implicitly called for you. A simple call to repaint() will repaint the component.
I just realized you're using all AWT components. Don't use them, they're out-dated. Instead use Swing component. The majority of them are just prefixed with a J, like Frame -> JFrame. They are in the javax.swing.* package.
For animation use a javax.swing.Timer. You can see more at How to Use Timers. The basic construct is
Timer ( int delayInMillis, ActionListener listener )
where delayInMillis is the time to delay between ticks(in this case animations) and the ActionListener listens for "ticks". Each tick, the actionPerformed of the ActionListener is called. There, you can put the code to update any variables you use for animation.
I suggest you read the tutorials Performing Custom Painting to see the proper way to paint.
Here's a simple example with all the points above mentioned
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class AnimateBall extends JPanel {
private static final int D_W = 500;
private static final int D_H = 300;
private Ball ball;
public AnimateBall() {
Random rand = new Random();
int randX = rand.nextInt(D_W);
int randY = rand.nextInt(D_H);
ball = new Ball(randX, randY);
Timer timer = new Timer(15, new ActionListener() {
public void actionPerformed(ActionEvent e) {
ball.animate();
repaint();
}
});
timer.start();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
ball.drawBall(g);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(D_W, D_H);
}
public class Ball {
int x = 0;
int y = 0; // Current ball position
int dx = 4; // Increment on ball's x-coordinate
int dy = 4; // Increment on ball's y-coordinate
int radius = 15; // Ball radius
public Ball(int x, int y) {
this.x = x;
this.y = y;
}
Color color = new Color((int) (Math.random() * 256),
(int) (Math.random() * 256), (int) (Math.random() * 256));
public void drawBall(Graphics g) {
g.setColor(color);
g.fillOval(x - radius, y - radius, radius * 2, radius * 2);
}
public void animate() {
if (x < 0 || x > getWidth()) {
dx = -dx;
}
if (y < 0 || y > getHeight()) {
dy = -dy;
}
// Adjust ball position
x += dx;
y += dy;
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame();
frame.add(new AnimateBall());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
}

Java using Graphics in a Method

Hi guys I'm super new to Java; I've looked around and haven't been able to find an answer to this question. Any chance you could help me?
Here is an example of what I'm trying to achieve.
public class FrameWork extends JFrame implements MouseListener {
... //Irrelevant to the question code
public void mouseClicked(MouseEvent e){
int x = e.getX();
int y = e.getY();
if (x==1 && y==1){
// This is where and when I want to draw GFXDice
}
}}
Now the other class, all imports left out for readability.
public class Board extends JPanel{
Image GFXDice1;
public Board() {
ImageIcon Dice1;
Dice1 = new ImageIcon(this.getClass().getResource("GFX/Dice1"));
GFXDice1 = Dice1.getImage();
}
Now the graphics part
public void paint(Graphics g){
Graphics2D g2d = (Graphics2D) g;
g2d.drawImage(GFXDice, 100, 100, null);
}
Now for the question - I want to use the method paint from the Class Board in the Class FrameWork - But can't get it to work - any ideas ? I'm offering a bazillion units of good karma to anyone who has an idea.

The general way to do most Swing drawing is via passive graphics. This means:
Do the drawing itself in the paintComponent(Graphics g) method of a JPanel or JComponent.
In your MouseListener change the state of some of the fields of the class. In your mouseClicked method you are setting the state of some local variables, and I recommend that you instead make your x and y fields, not local.
Then when the mouse listener is done making changes, call repaint() on the JPanel.
Then in the paintComponent method, use those fields that were changed in the mouse listener to do your drawing.
Don't forget to call the super's paintComponent method in your paintComponent override.
Don't forget to read tutorials on Swing Graphics to get the fine points.
Edit
For example, please have a look at a small graphics program that I created for an answer to another recent question.
The drawing occurs in the main class, SpaceShip, which extends JPanel. I add an anonymous inner MouseAdapter class for my Mouse Listener, and inside of the MouseAdapter, I call a method called moveIt, passing in the MouseEvent object.
MouseAdapter myMouseAdapter = new MouseAdapter() {
public void mousePressed(MouseEvent evt) {
moveIt(evt);
count = count + 1;
}
#Override
public void mouseDragged(MouseEvent evt) {
moveIt(evt);
}
};
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
All moveIt(MouseEvent evt) does is to change the state of two fields, myX and myY, and then calls repaint() on the current class:
public void moveIt(MouseEvent evt) {
myY = evt.getY() - sprite.getHeight() / 2;
myX = evt.getX() - sprite.getWidth() / 2;
repaint();
}
And then in the class's paintComponent method, I first call the super's paintComponent to allow it to erase any previous old out of date images, then I paint a background image, background, then I draw a sprite that uses the myX and myY variables to tell it where to draw, then I draw some yellow rectangles at locations that are determined by the JPanel's size:
protected void paintComponent(Graphics g) {
super.paintComponent(g);
font1 = new Font("Serif", Font.BOLD, 36);
g.drawImage(background, 0, 0, this);
g.drawImage(sprite, myX, myY, this);
g.setColor(Color.yellow);
int rectCount = 10;
int height = getHeight() / rectCount;
int width = 272;
int x = getWidth() - width;
for (int i = 0; i < rectCount; i++) {
int y = i * height;
g.drawRect(x, y, width, height);
}
g.setFont(font1);
g.drawString(Integer.toString(count), 500, 100);
}
The whole thing looks like this:
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.awt.Graphics;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.io.IOException;
import java.net.URL;
import java.lang.String;
import java.awt.Font;
#SuppressWarnings("serial")
public class SpaceShip extends JPanel {
private static final String BACKGROUND_PATH = "http://www.thatsreallypossible.com/"
+ "wp-content/uploads/2012/12/Space-Colonialisation.jpg";
private static final String SPRITE_PATH = "http://www.pd4pic.com/"
+ "images250_/ufo-flying-saucer-spacecraft-spaceship-alien.png";
private Font font1;
int myX = 100;
int myY = 400;
int count = 0;
private BufferedImage background;
private BufferedImage sprite;
public SpaceShip() throws IOException {
URL backgroundUrl = new URL(BACKGROUND_PATH);
URL spriteUrl = new URL(SPRITE_PATH);
background = ImageIO.read(backgroundUrl);
sprite = ImageIO.read(spriteUrl);
MouseAdapter myMouseAdapter = new MouseAdapter() {
public void mousePressed(MouseEvent evt) {
moveIt(evt);
count = count + 1;
}
#Override
public void mouseDragged(MouseEvent evt) {
moveIt(evt);
}
};
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
#Override
public Dimension getPreferredSize() {
if (background != null) {
return new Dimension(background.getWidth(), background.getHeight());
}
return super.getPreferredSize();
}
public void moveIt(MouseEvent evt) {
myY = evt.getY() - sprite.getHeight() / 2;
myX = evt.getX() - sprite.getWidth() / 2;
repaint();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
font1 = new Font("Serif", Font.BOLD, 36);
g.drawImage(background, 0, 0, this);
g.drawImage(sprite, myX, myY, this);
g.setColor(Color.yellow);
int rectCount = 10;
int height = getHeight() / rectCount;
int width = 272;
int x = getWidth() - width;
for (int i = 0; i < rectCount; i++) {
int y = i * height;
g.drawRect(x, y, width, height);
}
g.setFont(font1);
g.drawString(Integer.toString(count), 500, 100);
}
public static void main(String[] args) {
JFrame frame = new JFrame("Basic Game");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
SpaceShip ex;
try {
ex = new SpaceShip();
frame.getContentPane().add(ex);
frame.pack();
frame.setResizable(false);
frame.setVisible(true);
ex.requestFocus();
} catch (IOException e) {
e.printStackTrace();
}
}
}

Absolute Positioning Graphic JPanel Inside JFrame Blocked by Blank Sections

I'm trying to improve my understanding of Java, particularly Java GUI, by making a puzzle program. Currently the user selects an image, which is cut up into a specified number of pieces. The pieces are drawn randomly to the screen but they seem to be covered by blank portions of other pieces, and not all of them show up, but I can print out all the coordinates. I am using absolute positioning because a LayoutManager didn't seem to work. I briefly tried layeredPanes but they confused me and didn't seem to solve the problem. I would really appreciate some help.
Here are the 2 relevant classes:
import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
public class PuzzlePieceDriver extends JFrame
{
private static Dimension SCREENSIZE = Toolkit.getDefaultToolkit().getScreenSize();
private static final int HEIGHT = SCREENSIZE.height;
private static final int WIDTH = SCREENSIZE.width;
public static int MY_WIDTH;
public static int MY_HEIGHT;
private static BufferedImage image;
private int xPieces = PuzzleMagicDriver.getXPieces();
private int yPieces = PuzzleMagicDriver.getYPieces();
private PuzzlePiece[] puzzle = new PuzzlePiece[xPieces*yPieces];
public Container pane = this.getContentPane();
private JLayeredPane layeredPane = new JLayeredPane();
public PuzzlePieceDriver(ImageIcon myPuzzleImage)
{
MY_WIDTH = myPuzzleImage.getIconWidth()+(int)myPuzzleImage.getIconHeight()/2;
MY_HEIGHT = myPuzzleImage.getIconHeight()+(int)myPuzzleImage.getIconHeight()/2;
setTitle("Hot Puzz");
setSize(MY_WIDTH,MY_HEIGHT);
setLocationByPlatform(true);
pane.setLayout(null);
image = iconToImage(myPuzzleImage); //pass image into bufferedImage form
puzzle = createClip(image);
//pane.add(layeredPane);
setVisible(true);
}//end constructor
public static BufferedImage iconToImage(ImageIcon icon)
{
Image img = icon.getImage();
int w = img.getWidth(null);
int h = img.getHeight(null);
BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
Graphics g = image.createGraphics();
// Paint the image onto the buffered image
g.drawImage(img, 0, 0, null);
g.dispose();
return image;
}//end BufferedImage
protected int randomNumber(int min, int max)
{
int temp =
min + (int)(Math.random() * ((max - min) + 1));
return temp;
}//end randomNumber
private PuzzlePiece[] createClip(BufferedImage passedImage)
{
int cw, ch;
int w,h;
w = image.getWidth(null);
h = image.getHeight(null);
cw = w/xPieces;
ch = h/yPieces;
int[] cells=new int[xPieces*yPieces];
int dx, dy;
BufferedImage clip = passedImage;
//layeredPane.setPreferredSize(new Dimension(w,h));
for (int x=0; x<xPieces; x++)
{
int sx = x*cw;
for (int y=0; y<yPieces; y++)
{
int sy = y*ch;
int cell = cells[x*xPieces+y];
dx = (cell / xPieces) * cw;
dy = (cell % yPieces) * ch;
clip= passedImage.getSubimage(sx, sy, cw, ch);
int myX = randomNumber(0,(int)w);
int myY = randomNumber(0,(int)h);
PuzzlePiece piece=new PuzzlePiece(clip,myX,myY);
puzzle[x*xPieces+y]=piece;
piece.setBounds(myX,myY,w,h);
//layeredPane.setBounds(myX,myY,w,h);
//layeredPane.add(piece,new Integer(x*xPieces+y));
pane.add(piece);
piece.repaint();
}//end nested for
}//end for
return puzzle;
}//end createClip
}//end class
Sorry if the spacing is a little messed up!
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
public class PuzzlePiece extends JPanel
{
private Point imageCorner; //the image's top-left corner location
private Point prevPt; //mouse location for previous event
private Boolean insideImage =false;
private BufferedImage image;
public PuzzlePiece(BufferedImage clip, int x, int y)
{
image = clip;
imageCorner = new Point(x,y);
//repaint();
}//end constructor
public void paintComponent(Graphics g)
{
super.paintComponent(g);
g.drawImage(image, (int)getImageCornerX(),(int)getImageCornerY(), this);
System.out.println("paint "+getImageCornerX()+" "+getImageCornerY());
//repaint();
//g.dispose();
}//end paintComponent
public Point getImageCorner()
{
return imageCorner;
}//end getImageCorner
public double getImageCornerY()
{
return imageCorner.getY();
}//end getImageCornerY
public double getImageCornerX()
{
return imageCorner.getX();
}//end getPoint
}//end class PuzzlePiece
Any help would be appreciated, I've gotten really stuck! Thanks!!

I was really intrigued by this idea, so I made another example, using a custom layout manager.
public class MyPuzzelBoard extends JPanel {
public static final int GRID_X = 4;
public static final int GRID_Y = 4;
private BufferedImage image;
public MyPuzzelBoard(BufferedImage image) {
setLayout(new VirtualLayoutManager());
setImage(image);
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
if (e.getClickCount() == 2) {
removeAll();
generatePuzzel();
} else {
Component comp = getComponentAt(e.getPoint());
if (comp != null && comp != MyPuzzelBoard.this) {
setComponentZOrder(comp, 0);
invalidate();
revalidate();
repaint();
}
}
}
});
}
public void setImage(BufferedImage value) {
if (value != image) {
image = value;
removeAll();
generatePuzzel();
}
}
public BufferedImage getImage() {
return image;
}
protected float generateRandomNumber() {
return (float) Math.random();
}
protected void generatePuzzel() {
BufferedImage image = getImage();
if (image != null) {
int imageWidth = image.getWidth();
int imageHeight = image.getHeight();
int clipWidth = imageWidth / GRID_X;
int clipHeight = imageHeight / GRID_Y;
for (int x = 0; x < GRID_X; x++) {
for (int y = 0; y < GRID_Y; y++) {
float xPos = generateRandomNumber();
float yPos = generateRandomNumber();
Rectangle bounds = new Rectangle((x * clipWidth), (y * clipHeight), clipWidth, clipHeight);
MyPiece piece = new MyPiece(image, bounds);
add(piece, new VirtualPoint(xPos, yPos));
}
}
}
invalidate();
revalidate();
repaint();
}
public class VirtualPoint {
private float x;
private float y;
public VirtualPoint(float x, float y) {
this.x = x;
this.y = y;
}
public float getX() {
return x;
}
public float getY() {
return y;
}
public void setX(float x) {
this.x = x;
}
public void setY(float y) {
this.y = y;
}
}
public class VirtualLayoutManager implements LayoutManager2 {
private Map<Component, VirtualPoint> mapConstraints;
public VirtualLayoutManager() {
mapConstraints = new WeakHashMap<>(25);
}
#Override
public void addLayoutComponent(Component comp, Object constraints) {
if (constraints instanceof VirtualPoint) {
mapConstraints.put(comp, (VirtualPoint) constraints);
}
}
#Override
public Dimension maximumLayoutSize(Container target) {
return new Dimension(Integer.MAX_VALUE, Integer.MAX_VALUE);
}
#Override
public float getLayoutAlignmentX(Container target) {
return 0.5f;
}
#Override
public float getLayoutAlignmentY(Container target) {
return 0.5f;
}
#Override
public void invalidateLayout(Container target) {
}
#Override
public void addLayoutComponent(String name, Component comp) {
}
#Override
public void removeLayoutComponent(Component comp) {
mapConstraints.remove(comp);
}
#Override
public Dimension preferredLayoutSize(Container parent) {
return new Dimension(400, 400);
}
#Override
public Dimension minimumLayoutSize(Container parent) {
return preferredLayoutSize(parent);
}
#Override
public void layoutContainer(Container parent) {
int width = parent.getWidth();
int height = parent.getHeight();
for (Component comp : parent.getComponents()) {
VirtualPoint p = mapConstraints.get(comp);
if (p != null) {
int x = Math.round(width * p.getX());
int y = Math.round(height * p.getY());
Dimension size = comp.getPreferredSize();
x = Math.min(x, width - size.width);
y = Math.min(y, height - size.height);
comp.setBounds(x, y, size.width, size.height);
}
}
}
}
}
Basically, this uses a "virtual" coordinate system, where by rather then supply absolute x/y positions in pixels, you provide them as percentage of the parent container. Now, to be honest, it wouldn't take much to convert back to absolute positioning, just this way, you also get layout scaling.
The example also demonstrates Z-reording (just in case) and the double click simple re-randomizes the puzzel
Oh, I also made the piece transparent (opaque = false)
Oh, one thing I should mention, while going through this example, I found that it was possible to have pieces placed off screen (completely and partially).
You may want to check your positioning code to make sure that the images when they are laid out aren't been moved off screen ;)

Try using setBorder(new LineBorder(Color.RED)) in your puzzle piece constructor to see where the bounds of your puzzle pieces are. If they are where you'd expect them to be, it's likely that your positioning is wrong. Also make your puzzle pieces extend JComponent instead, or use setOpaque(false) if you're extending JPanel.

There are lots of suggestions I'd like to make, but first...
The way you choose a random position is off...
int myX = randomNumber(0,(int)w);
int myY = randomNumber(0,(int)h);
This allows duplicate position's to be generated (and overlaying cells)
UPDATES (using a layout manager)
Okay, so this is a slight shift in paradigm. Rather then producing a clip and passing it to the piece, I allowed the piece to make chooses about how it was going to render the the piece. Instead, I passed it the Rectangle it was responsible for.
This means, you could simply use something like setCell(Rectangle) to make a piece change (unless you're hell bent on drag'n'drop ;))
I ended up using Board panel due to some interesting behavior under Java 7, but that's another question ;)
package puzzel;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.*;
public class PuzzlePieceDriver extends JFrame {
public PuzzlePieceDriver(ImageIcon myPuzzleImage) {
setTitle("Hot Puzz");
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLayout(new BorderLayout());
add(new Board(myPuzzleImage));
pack();
setVisible(true);
}//end constructor
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
} catch (InstantiationException ex) {
} catch (IllegalAccessException ex) {
} catch (UnsupportedLookAndFeelException ex) {
}
ImageIcon image = new ImageIcon(PuzzlePieceDriver.class.getResource("/issue459.jpg"));
PuzzlePieceDriver driver = new PuzzlePieceDriver(image);
driver.setLocationRelativeTo(null);
driver.setVisible(true);
}
});
}
}//end class
A piece panel...
The panel overrides the preferred and minimum size methods...while it works for this example, it's probably better to use setPreferredSize and setMiniumumSize instead ;)
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package puzzel;
import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
public class PuzzlePiece extends JPanel {
private BufferedImage masterImage;
private Rectangle pieceBounds;
private BufferedImage clip;
public PuzzlePiece(BufferedImage image, Rectangle bounds) {
masterImage = image;
pieceBounds = bounds;
// Make sure the rectangle fits the image
int width = Math.min(pieceBounds.x + pieceBounds.width, image.getWidth() - pieceBounds.x);
int height = Math.min(pieceBounds.y + pieceBounds.height, image.getHeight() - pieceBounds.y);
clip = image.getSubimage(pieceBounds.x, pieceBounds.y, width, height);
}//end constructor
#Override
public Dimension getPreferredSize() {
return pieceBounds.getSize();
}
#Override
public Dimension getMinimumSize() {
return getPreferredSize();
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
int x = 0;
int y = 0;
g.drawImage(clip, x, y, this);
g.setColor(Color.RED);
g.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
}//end paintComponent
}//end class PuzzlePiece
The board panel...used mostly because of some interesting issues I was having with Java 7...Implements a MouseListener, when you run the program, click the board, it's fun ;)
package puzzel;
import java.awt.Graphics;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;
import javax.swing.ImageIcon;
import javax.swing.JPanel;
/**
*
* #author shane
*/
public class Board extends JPanel {
public static final int X_PIECES = 4;
public static final int Y_PIECES = 4;
private PuzzlePiece[] puzzle = new PuzzlePiece[X_PIECES * Y_PIECES];
private static BufferedImage image;
public Board(ImageIcon myPuzzleImage) {
image = iconToImage(myPuzzleImage); //pass image into bufferedImage form
puzzle = createClip();
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
removeAll();
invalidate();
createClip();
// doLayout();
invalidate();
revalidate();
repaint();
}
});
}
public static BufferedImage iconToImage(ImageIcon icon) {
Image img = icon.getImage();
int w = img.getWidth(null);
int h = img.getHeight(null);
BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
Graphics g = image.createGraphics();
// Paint the image onto the buffered image
g.drawImage(img, 0, 0, null);
g.dispose();
return image;
}//end BufferedImage
protected int randomNumber(int min, int max) {
int temp = min + (int) (Math.random() * ((max - min) + 1));
return temp;
}//end randomNumber
private PuzzlePiece[] createClip() {
int cw, ch;
int w, h;
w = image.getWidth(null);
h = image.getHeight(null);
cw = w / X_PIECES;
ch = h / Y_PIECES;
// Generate a list of cell bounds
List<Rectangle> lstBounds = new ArrayList<>(25);
for (int y = 0; y < h; y += ch) {
for (int x = 0; x < w; x += cw) {
lstBounds.add(new Rectangle(x, y, cw, ch));
}
}
BufferedImage clip = image;
setLayout(new GridBagLayout());
for (int x = 0; x < X_PIECES; x++) {
for (int y = 0; y < Y_PIECES; y++) {
// Get a random index
int index = randomNumber(0, lstBounds.size() - 1);
// Remove the bounds so we don't duplicate any positions
Rectangle bounds = lstBounds.remove(index);
PuzzlePiece piece = new PuzzlePiece(clip, bounds);
puzzle[x * X_PIECES + y] = piece;
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridx = x;
gbc.gridy = y;
gbc.fill = GridBagConstraints.BOTH;
add(piece, gbc);
piece.invalidate();
piece.repaint();
}//end nested for
}//end for
invalidate();
repaint();
return puzzle;
}//end createClip
}
Now I know you eventually going to ask about how to move a piece, GridBagLayout has this wonderful method called getConstraints which allows you to retrieve the constraints used to layout the component in question. You could then modify the gridx and gridy values and use setConstraints to update it (don't forget to call invalidate and repaint ;))
I'd recommend having a read of How to Use GridBagLayout for more information ;)
Eventually, you'll end up with something like: