Question

So I’m creating a side scroller and I’m trying to draw an image at the point of another image.

I have my background image which is 5000 x 500 and lets say I want to draw an image that’s 25×25 at 500, 50 of the background image. How would I do that?

So far I’ve tried:

Coins c = new Coins(img.getWidth(this) - 4500, img.getHeight(this) - 250);

But this just draws it at 500, 50 of the frame so it “moves” across the image as I scroll to the right. I want, after scroll once to the right, the coin image to draw at 500,50 of the image still so 495, 50 of the frame.

I could also use getGraphics of the background image and draw the smaller image onto it, but I think because I set the point it’s being draw at during the creation of the object, I can’t do that.

The character doesn’t move, besides up and down, just the background scrolls so I want the coin to move as the background does.

PICTURES:
(can’t embed it because i don’t have 10 rep points)
http://dl.dropbox.com/u/47632315/char.png http://dl.dropbox.com/u/47632315/coin.png http://dl.dropbox.com/u/47632315/sideScrollerBG.png

And the SSCCE:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.awt.image.ImageObserver;
import java.io.IOException;
import javax.imageio.ImageIO;

public class SideScroller extends JPanel implements KeyListener {

    public static void main(String args[]) throws Exception {
        SideScroller f = new SideScroller("Side Scroller");
    }

    JFrame f = new JFrame();
    int x = 0;
    int y = 0;
    int k = 10;
    int j = 50;
    int characterY = 351;
    boolean canJump = true;
    boolean keyPressed[] = new boolean[3];

    Image img;
    Image character;

    Coins c = new Coins(x + 500, y + 350);

    public SideScroller(String s) throws MalformedURLException, IOException {
        img = ImageIO.read(new URL("http://dl.dropbox.com/u/47632315/sideScrollerBG.png"));
        character = ImageIO.read(new URL("http://dl.dropbox.com/u/47632315/char.png"));

        f.setTitle(s);
        // don't use 'magic numbers' when descriptive constants are defined!
        //f.setDefaultCloseOperation(3);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setResizable(false);
        // Better to ask when loaded.
        //setPreferredSize(new Dimension(1000, 500));
        setPreferredSize(new Dimension(1000, img.getHeight(this)));
        f.add(this);
        f.pack();
        // usually harmful, rarely necessary.
//      f.setLayout(null);
        // Looks like a splash screen
        //f.setLocationRelativeTo(null);
        // located by platform default, best.
        f.setLocationByPlatform(true);
        f.addKeyListener(this);
        getKeys();

        // should be done last
        f.setVisible(true);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(img, x, y, this);
        g.drawImage(character, 50, characterY, this);
        c.paint(g, this);
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }

    @Override
    public void keyPressed(KeyEvent e) {
        int keyCode = e.getKeyCode();
        if (keyCode == KeyEvent.VK_ESCAPE) {
            System.exit(0);
        }
        if (keyCode == KeyEvent.VK_RIGHT) {
            keyPressed[0] = true;
        }
        if (keyCode == KeyEvent.VK_LEFT) {
            keyPressed[1] = true;
        }
        if (canJump) {
            if (keyCode == KeyEvent.VK_SPACE) {
                // better to use a javax.swing.Timer here
                new Thread(new Runnable() {
                    public void run() {
                        canJump = false;
                        for (double i = 0; i <= 5.1; i += .2) {
                            characterY = (int) (k * i * i - j * i + 351);
                            f.repaint();
                            System.out.println(characterY);
                            System.out.println(canJump);
                            try {
                                Thread.sleep(25);
                            } catch (InterruptedException e) {
                                System.err.println(e);
                            }
                        }
                        repaint();
                        canJump = true;
                    }
                }).start();
            }
        }
    }

    @Override
    public void keyReleased(KeyEvent e) {
        int keyCode = e.getKeyCode();
        if (keyCode == KeyEvent.VK_RIGHT) {
            keyPressed[0] = false;
        }
        if (keyCode == KeyEvent.VK_LEFT) {
            keyPressed[1] = false;
        }
    }

    public void getKeys() {
        new Thread(new Runnable() {
            public void run() {
                while (true) {
                    if (keyPressed[0]) {
                        x -= 5;
                        repaint();
                    }
                    if (keyPressed[1]) {
                        if (x != 0) {
                            x += 5;
                            repaint();
                        }
                    }
                    try {
                        Thread.sleep(25);
                    } catch (InterruptedException e) {
                        System.err.println(e);
                    }
                }
            }
        }).start();
    }
}

class Coins extends pickUpObject {

    Image coin; 

    public Coins(int x, int y) throws MalformedURLException, IOException{
        super(x, y);
        super.x = x;
        super.y = y;
        coin = ImageIO.read(new URL("http://dl.dropbox.com/u/47632315/coin.png"));
    }

    public void paint(Graphics g, ImageObserver o){
        g.drawImage(coin, x, y, o);
    }
}

abstract class pickUpObject {

    int x, y;

    public pickUpObject(int x, int y){
    }

    public abstract void paint(Graphics g, ImageObserver o);
}

Answer 1

One way is to stamp the Graphics out to a Graphics2D then translate it.

    // here we 'translate' the graphics 2D object to a separate location  
    g2d.translate(x,0);

Screenhsot

In this image, the character has moved to the right and is jumping. The coin has shifted left according to the distance the character has moved right.

Full code

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.awt.image.ImageObserver;
import java.io.IOException;
import javax.imageio.ImageIO;

public class SideScroller extends JPanel implements KeyListener {

    public static void main(String args[]) throws Exception {
        SideScroller f = new SideScroller("Side Scroller");
    }

    JFrame f = new JFrame();
    int x = 0;
    int y = 0;
    int k = 10;
    int j = 50;
    int characterY = 351;
    boolean canJump = true;
    boolean keyPressed[] = new boolean[3];

    Image img;
    Image character;

    Coins c = new Coins(x + 500, y + 350);

    public SideScroller(String s) throws MalformedURLException, IOException {
        img = ImageIO.read(new URL("http://dl.dropbox.com/u/47632315/sideScrollerBG.png"));
        character = ImageIO.read(new URL("http://dl.dropbox.com/u/47632315/char.png"));

        f.setTitle(s);
        // don't use 'magic numbers' when descriptive constants are defined!
        //f.setDefaultCloseOperation(3);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setResizable(false);
        // Better to ask when loaded.
        //setPreferredSize(new Dimension(1000, 500));
        setPreferredSize(new Dimension(1000, img.getHeight(this)));
        f.add(this);
        f.pack();
        // usually harmful, rarely necessary.
//      f.setLayout(null);
        // Looks like a splash screen
        //f.setLocationRelativeTo(null);
        // located by platform default, best.
        f.setLocationByPlatform(true);
        f.addKeyListener(this);
        getKeys();

        // should be done last
        f.setVisible(true);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(img, x, y, this);
        g.drawImage(character, 50, characterY, this);
        Graphics2D g2d = (Graphics2D)g;
        // here we 'translate' the graphics object to a separate location  
        g2d.translate(x,0);
        c.paint(g2d, this);
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }

    @Override
    public void keyPressed(KeyEvent e) {
        int keyCode = e.getKeyCode();
        if (keyCode == KeyEvent.VK_ESCAPE) {
            System.exit(0);
        }
        if (keyCode == KeyEvent.VK_RIGHT) {
            keyPressed[0] = true;
        }
        if (keyCode == KeyEvent.VK_LEFT) {
            keyPressed[1] = true;
        }
        if (canJump) {
            if (keyCode == KeyEvent.VK_SPACE) {
                // better to use a javax.swing.Timer here
                new Thread(new Runnable() {
                    public void run() {
                        canJump = false;
                        for (double i = 0; i <= 5.1; i += .2) {
                            characterY = (int) (k * i * i - j * i + 351);
                            f.repaint();
                            System.out.println(characterY);
                            System.out.println(canJump);
                            try {
                                Thread.sleep(25);
                            } catch (InterruptedException e) {
                                System.err.println(e);
                            }
                        }
                        repaint();
                        canJump = true;
                    }
                }).start();
            }
        }
    }

    @Override
    public void keyReleased(KeyEvent e) {
        int keyCode = e.getKeyCode();
        if (keyCode == KeyEvent.VK_RIGHT) {
            keyPressed[0] = false;
        }
        if (keyCode == KeyEvent.VK_LEFT) {
            keyPressed[1] = false;
        }
    }

    public void getKeys() {
        new Thread(new Runnable() {
            public void run() {
                while (true) {
                    if (keyPressed[0]) {
                        x -= 5;
                        repaint();
                    }
                    if (keyPressed[1]) {
                        if (x != 0) {
                            x += 5;
                            repaint();
                        }
                    }
                    try {
                        Thread.sleep(25);
                    } catch (InterruptedException e) {
                        System.err.println(e);
                    }
                }
            }
        }).start();
    }
}

class Coins extends pickUpObject {

    Image coin; 

    public Coins(int x, int y) throws MalformedURLException, IOException{
        super(x, y);
        super.x = x;
        super.y = y;
        coin = ImageIO.read(new URL("http://dl.dropbox.com/u/47632315/coin.png"));
    }

    public void paint(Graphics g, ImageObserver o){
        g.drawImage(coin, x, y, o);
    }
}

abstract class pickUpObject {

    int x, y;

    public pickUpObject(int x, int y){
    }

    public abstract void paint(Graphics g, ImageObserver o);
}