Thread: My first Java 2D Game won't work

Hi there.

I'm new on java.

I'm following Zephyr Java 2D Game video tutorials on youtube.

Problem :

It should move the screen when i pressing W,A,S,D keys, but won't work. Please have look at the below classes.

Game.java

package ca.hamed.game;
 
import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;
 
import javax.swing.JFrame;
 
import ca.hamed.game.gfx.Screen;
import ca.hamed.game.gfx.SpriteSheet;
 
public class Game extends Canvas implements Runnable {
 
	private static final long serialVersionUID = 1L;
 
	public static final int WIDTH = 160;
	public static final int HEIGHT = WIDTH / 12 * 9;
	public static final int SCALE = 3;
	public static final String NAME = "Game";
 
	private JFrame frame;
 
	public boolean running = false;
	public int tickCount = 0;
 
	private BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
	private int[] pixels = ((DataBufferInt) image.getRaster().getDataBuffer()).getData();
 
	private Screen screen;
 
	public InputHandler input;
 
	public Game() {
		setMinimumSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
		setMaximumSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
		setPreferredSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
 
		frame = new JFrame(NAME);
 
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setLayout(new BorderLayout());
		frame.add(this, BorderLayout.CENTER);
		frame.pack();
 
		frame.setResizable(false);
		frame.setLocationRelativeTo(null);
		frame.setVisible(true);
	}
 
	public void init() {
		screen = new Screen(WIDTH, HEIGHT, new SpriteSheet("/sprite_sheet.png"));
		input = new InputHandler(this);
	}
 
	public synchronized void start() {
		running = true;
		new Thread(this).start();
	}
 
	public synchronized void stop() {
		running = false;
	}
 
	public void tick() {
		tickCount++;
		if (input.up.isPressed()) {
			screen.yOffset--;
		}
		if (input.down.isPressed()) {
			screen.yOffset++;
		}
		if (input.left.isPressed()) {
			screen.xOffset--;
		}
		if (input.right.isPressed()) {
			screen.xOffset++;
		}
	}
 
	public void render() {
		BufferStrategy bs = getBufferStrategy();
		if (bs == null) {
			createBufferStrategy(3);
			return;
		}
 
		screen.render(pixels, 0, WIDTH);
 
		Graphics g = bs.getDrawGraphics();
		g.setColor(Color.black);
		g.drawRect(0, 0, getWidth(), getHeight());
		g.drawImage(image, 0, 0, getWidth(), getHeight(), null);
		g.dispose();
 
		bs.show();
	}
 
	public void run() {
		long lastTime = System.nanoTime();
		double nsPerTick = 1000000000D / 60D;
 
		int ticks = 0;
		int frames = 0;
 
		long lastTimer = System.currentTimeMillis();
		double delta = 0;
 
		init();
 
		while (running) {
			long now = System.nanoTime();
			delta += (now - lastTime) / nsPerTick;
			lastTime = now;
			boolean shouldRender = true;
 
			while (delta >= 1) {
				ticks++;
				tick();
				delta -= 1;
				shouldRender = true;
			}
			try {
				Thread.sleep(2);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			if (shouldRender) {
				frames++;
				render();
			}
 
			if (System.currentTimeMillis() - lastTimer >= 1000) {
				lastTimer += 1000;
				System.out.println(ticks + " ticks , " + frames + " frames");
				frames = 0;
				ticks = 0;
			}
		}
	}
 
	public static void main(String[] args) {
		new Game().start();
	}
 
}

SpriteSheet.java

package ca.hamed.game.gfx;
 
import java.awt.image.BufferedImage;
import java.io.IOException;
 
import javax.imageio.ImageIO;
 
public class SpriteSheet {
	public String path;
	public int width;
	public int height;
 
	public int[] pixels;
 
	public SpriteSheet(String path) {
		BufferedImage image = null;
		try {
			image = ImageIO.read(SpriteSheet.class.getResourceAsStream(path));
		} catch (IOException e) {
			e.printStackTrace();
		}
		if (image == null) {
			return;
		}
		this.path = path;
		this.width = image.getWidth();
		this.height = image.getHeight();
 
		pixels = image.getRGB(0, 0, width, height, null, 0, width);
 
		for (int i = 0; i < pixels.length; i++) {
			pixels[i] = (pixels[i] & 0xff) / 64;
		}
	}
}

Screen.java

package ca.hamed.game.gfx;
 
public class Screen {
	public static final int MAP_WIDTH = 64;
	public static final int MAP_WIDTH_MASK = MAP_WIDTH - 1;
 
	public int[] tiles = new int[MAP_WIDTH * MAP_WIDTH];
	public int[] colours = new int[MAP_WIDTH * MAP_WIDTH * 4];
 
	public int xOffset = 0;
	public int yOffset = 0;
 
	public int width;
	public int height;
 
	public SpriteSheet sheet;
 
	public Screen(int width, int height, SpriteSheet sheet) {
		this.width = width;
		this.height = height;
		this.sheet = sheet;
 
		for (int i = 0; i < MAP_WIDTH * MAP_WIDTH; i++) {
			colours[i * 4 + 0] = 0xff00ff;
			colours[i * 4 + 1] = 0x00ffff;
			colours[i * 4 + 2] = 0x00ffff;
			colours[i * 4 + 3] = 0xffffff;
		}
	}
 
	public void render(int[] pixels, int offset, int row) {
		for (int yTile = yOffset >> 3; yTile <= (yOffset + height) >> 3; yTile++) {
			int yMin = yTile * 8 - yOffset;
			int yMax = yMin + 8;
 
			if (yMin < 0) yMin = 0;
			if (yMax > height) yMax = height;
 
			for (int xTile = xOffset >> 3; xTile <= (xOffset + width) >> 3; xTile++) {
				int xMin = xTile * 8 - xOffset;
				int xMax = xMin + 8;
 
				if (xMin < 0) xMin = 0;
				if (xMax > width) xMax = width;
 
				int tileIndex = (xTile & (MAP_WIDTH_MASK)) + (yTile & (MAP_WIDTH_MASK)) * MAP_WIDTH;
 
				for (int y = yMin; y < yMax; y++) {
					int sheetPixel = ((y + yOffset) & 7) * sheet.width + ((xMin + xOffset) & 7);
					int tilePixel = offset + xMin + y * row;
					for (int x = xMin; x < xMax; x++) {
						int colour = tileIndex * 4 + sheet.pixels[sheetPixel++];
						pixels[tilePixel++] = colours[colour];
					}
				}
			}
		}
	}
}

InputHandler.java

package ca.hamed.game;
 
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.List;
 
public class InputHandler implements KeyListener {
 
	public InputHandler(Game game) {
		game.addKeyListener(this);
	}
 
	public class Key {
		private boolean pressed = false;
 
		public boolean isPressed() {
			return pressed;
		}
 
		public void toggle(boolean isPressed) {
			pressed = isPressed;
		}
	}
 
	public List<Key> keys = new ArrayList<Key>();
 
	public Key up = new Key();
	public Key down = new Key();
	public Key left = new Key();
	public Key right = new Key();
 
	public void keyPressed(KeyEvent e) {
		toggleKey(e.getKeyCode(), true);
	}
 
	public void keyReleased(KeyEvent e) {
		toggleKey(e.getKeyCode(), false);
	}
 
	public void keyTyped(KeyEvent e) {
 
	}
 
	public void toggleKey(int keyCode, boolean isPressed) {
		if (keyCode == KeyEvent.VK_W) {
			up.toggle(true);
		}
		if (keyCode == KeyEvent.VK_S) {
			down.toggle(true);
		}
		if (keyCode == KeyEvent.VK_A) {
			left.toggle(true);
		}
		if (keyCode == KeyEvent.VK_D) {
			right.toggle(true);
		}
	}
}

Any helps would be great awesome.

Originally Posted by Norm

Have you tried to debug the code to see where the problem is? For example: Add some println statements to the key listeners methods to see if they are being called.

It run successfully. There is a logical problem

I mean it does not have any syntax errors. It runs without any problems. But when the screen shows up it must move through W,A,S,D keys but won't work.
I can't explain more...

So are W, A, S, and D key presses being seen by the key listeners, firing an action? Add some code to the key listener methods to see what is happening or not happening. If you find the key presses aren't being seen and acted upon, trace it back further and keep tracing it back until you find the break in logic. If there is no break in the logic that you can find, then make sure you've implemented the key listening mechanism correctly.

This is basic debugging stuff you should learn how to do.

Thank you. I found it, the problem was right there :

public void toggleKey(int keyCode, boolean isPressed) {
		if (keyCode == KeyEvent.VK_W) {
			up.toggle(true);
		}
		if (keyCode == KeyEvent.VK_S) {
			down.toggle(true);
		}
		if (keyCode == KeyEvent.VK_A) {
			left.toggle(true);
		}
		if (keyCode == KeyEvent.VK_D) {
			right.toggle(true);
		}
	}

Should change to :

public void toggleKey(int keyCode, boolean isPressed) {
		if (keyCode == KeyEvent.VK_W) {
			up.toggle(isPressed);
		}
		if (keyCode == KeyEvent.VK_S) {
			down.toggle(isPressed);
		}
		if (keyCode == KeyEvent.VK_A) {
			left.toggle(isPressed);
		}
		if (keyCode == KeyEvent.VK_D) {
			right.toggle(isPressed);
		}
	}

Cheers