Thread: Collision Detection between Sprites and Images?

Hello everyone

I am creating a small game and have come to the point where I need to use collision detection. The problem is, I do not exactly know how to create basic collision with rectangles. I now it requires you to import java.awt.Rectangle but thats about it as far as what has worked for me.

package outrun;
 
import java.awt.Image;
import javax.swing.ImageIcon;
 
public class Cobblestone {
 
	private String cobblestone = "/resources/cobblestone_outrun.png";
 
private Image image;
 
 
	public Cobblestone() {
		ImageIcon i = new ImageIcon(this.getClass().getResource(cobblestone));
		image = i.getImage();
		}
 
		 public Image getImage() {
		    	return image;
		    }
 
}

This is my cobblestone class. The image is 20x20 pixels, I need collision for this.

package outrun;
 
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.Rectangle;
 
import javax.swing.ImageIcon;
 
public class Person {
 
	private String person = "/resources/person_outrun.png";
 
	private int dx;
	private int dy;
	private int x;
	private int y;
	private Image image;
 
	public Person() {
		ImageIcon i = new ImageIcon(this.getClass().getResource(person));
		image = i.getImage();
 
		x = 31;
	    y = 175;	
	}
 
	public void move() {
		x += dx;
		y += dy;
	}
 
    public int getX() {
    	return x;
    }
 
    public int getY() {
    	return y;
 
    }
 
    public Image getImage() {
    	return image;
    }
 
    public void KeyPressed(KeyEvent e) {
 
        int key = e.getKeyCode();
 
    	if (key == KeyEvent.VK_RIGHT) {
    		dx = 1;
    	}
 
        if (key == KeyEvent.VK_LEFT) {
        	dx = -1;
        }
 
        if (key == KeyEvent.VK_UP) {
        	dy = -1;
        }
 
        if (key == KeyEvent.VK_DOWN) {
        	dy = 1;
        }
    }
 
    public void KeyReleased(KeyEvent e) {
    	int key = e.getKeyCode();
 
    	if (key == KeyEvent.VK_RIGHT) {
    		dx = 0;
    	}
 
        if (key == KeyEvent.VK_LEFT) { 
        	dx = 0;
        }
 
        if (key == KeyEvent.VK_UP) {
        	dy = 0;
        }
 
        if (key == KeyEvent.VK_DOWN) {
        	dy = 0;
        }
    }
}

This is my person class, I also need collision for this.

Do I determine the collision method in my board.class? What I wish to happen is if the person intersects the cobblestone, the person stops (dx = 0 and dy = 0). How would I go about doing this? Thanks! Any help would be greatly appreciated!

Oh yes, but how would I go about creating a rectangle for the person, it moves? The parameters consist of x and y values. How would I be able to create one if the person is moving, hence constantly changing x and y values? I am confused as to how to use the rectangle class.

The person has width and height, it is an image I created. Would I need to use getWidth() and getHeight() and assign them to two new variables?

Ok I will work on that, Eclipse somehow does not want to open my files stating that the files do not exist. I will resume work once I get that sorted from someone.

Ok, so I have made rectangle classes for both cobblestone.java and person.java (the images I wish to intersect.) Now I am actually determining the collision in my board.java:

public void checkCollisions() {
 
    	Rectangle r1 = person.getBounds();
    	Rectangle r2 = cobblestone.getBounds();
 
   	 if (r1.intersects(r2)) {
   	 }
    }

The problem is I do not know what to put within my if statement. dx and dy control the 'speed' or translation of the person in my person class through coordinates. In other words, they control the movement of my person. How do I implement these variables in my board.java?

I know what I want to happen, I just don't know how to show it. If they both collide, I want the variables dx and dy to be equal to zero. The trouble is those two variables are in the person class, not the board class, where I want them to be uses also. How would I be able to do that?

What I meant by was if they both collide with each other, sorry, I wasn't to clear! I do not want to change the variables. I want to use the variable dx and dy from board.java in person.java though I do not know how to do that.

package outrun;
 
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.Rectangle;
 
import javax.swing.ImageIcon;
 
public class Person {
 
	private String person = "/resources/person_outrun.png";
 
	private int dx;
	private int dy;
	private int x;
	private int y;
	private int width;
	private int height;
	private Image image;
 
	public Person() {
 
		ImageIcon i = new ImageIcon(this.getClass().getResource(person));
		image = i.getImage();
		width = image.getWidth(null);
		height = image.getHeight(null);
 
		x = 31;
	    y = 175;	
	}
 
	public void move() {
		x += dx;
		y += dy;
	}
 
    public int getX() {
    	return x;
    }
 
    public int getY() {
    	return y;
 
    }
 
    public Image getImage() {
    	return image;
    }
 
    public Rectangle getBounds() {
        return new Rectangle(x, y, width, height);
    }
 
    public void KeyPressed(KeyEvent e) {
 
        int key = e.getKeyCode();
 
    	if (key == KeyEvent.VK_RIGHT) {
    		dx = 1;
    	}
 
        if (key == KeyEvent.VK_LEFT) {
        	dx = -1;
        }
 
        if (key == KeyEvent.VK_UP) {
        	dy = -1;
        }
 
        if (key == KeyEvent.VK_DOWN) {
        	dy = 1;
        }
    }
 
    public void KeyReleased(KeyEvent e) {
    	int key = e.getKeyCode();
 
    	if (key == KeyEvent.VK_RIGHT) {
    		dx = 0;
    	}
 
        if (key == KeyEvent.VK_LEFT) { 
        	dx = 0;
        }
 
        if (key == KeyEvent.VK_UP) {
        	dy = 0;
        }
 
        if (key == KeyEvent.VK_DOWN) {
        	dy = 0;
        }
    }
}

This is Person.java. It contains the variables dx and dy that I need. However, I want to use the same dx and dy for board.class below:

package outrun;
 
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.Rectangle;
 
import javax.swing.JPanel;
import javax.swing.Timer;
 
public class Board extends JPanel implements ActionListener {
 
	private Timer timer;
 
	private Person person;
	private Cobblestone cobblestone;
 
	public Board() {
 
		addKeyListener(new TAdapter());
		setFocusable(true);
		setBackground(Color.BLACK);
		setDoubleBuffered(true);
 
		setSize(10, 10);
 
		person = new Person();
		cobblestone = new Cobblestone();
		timer = new Timer(5, this);
        timer.start();
	}
 
	public void paint(Graphics g) {
    	super.paint(g);
 
    	Graphics2D m = (Graphics2D)g;
    	m.drawImage(person.getImage(), person.getX(), person.getY(), this);
 
        drawMaze((Graphics2D) g);
 
    }
    private void drawMaze(Graphics2D g){
    	Graphics2D g2 = (Graphics2D)g;
 
            int width = 27; 
            int height = 17;
            int xOffset = 21; 
            int yOffset = 21; 
            int currentX = 10; 
            int currentY = 10; 
                 for(int j = 0; j < height; j++) {
                	 if(j!=8)
                       g2.drawImage(cobblestone.getImage(), currentX, currentY,this);
                       currentY += yOffset;
                       }
                 for(int k = 0; k < width; k++) {
                	 if(k!=13)
                	   g2.drawImage(cobblestone.getImage(), currentX, currentY,this);
                	   currentX += xOffset;
                 }
                 currentY = 10;
            	 currentX = 556;
 
            	 for(int l = 0; l < height; l++) {
            		 if(l!=8)
                	 g2.drawImage(cobblestone.getImage(), currentX, currentY,this);
              	   currentY += yOffset;
                 }
                 currentY = 10;
                 currentX = 10;
 
                 for(int m = 0; m < width; m++) {
                	 if(m!=13)
                	 g2.drawImage(cobblestone.getImage(), currentX, currentY,this);
                	 currentX += xOffset;
 
                     }
 
                 g.setColor(Color.green);
                 g.drawString(" ENV 1 LVL 1", 480, 50);
 
}
 
    public void checkCollisions() {
 
    	Rectangle r1 = person.getBounds();
    	Rectangle r2 = cobblestone.getBounds();
 
   	 if (r1.intersects(r2)) {
   	 }
    }
 
 
  public void actionPerformed(ActionEvent e) {
    	person.move();
    	repaint();
    }
 
    private class TAdapter extends KeyAdapter {
 
    	public void keyReleased(KeyEvent e) {
    		person.KeyReleased(e);
    	}
 
    public void keyPressed(KeyEvent e) {
    	person.KeyPressed(e);
    }
 
    }
 
}

How do I do this?

I need to access them as I want to set dx and dy to zero if both the person and cobblestone intersect each other. How do I make that reference? I have tried person.dx though that does not work.

I tried, but then I come up with many errors stating that the variable could not be resolved. Where in person.java shall I create the method?

public Person(int dx, int dy) {
 
		ImageIcon i = new ImageIcon(this.getClass().getResource(person));
		image = i.getImage();
		width = image.getWidth(null);
		height = image.getHeight(null);
 
		x = 31;
	    y = 175;
	}

I created a new method here. The errors are just errors stating 'dx/dy cannot be resolved into a variable'.

Oh apologies, I posted the wrong code, the errors were already resolved, the interface never refreshed to reflect that yet. Here is my code using the methods:

public int getdx() {
    	return dx;
    }
 
    public int getdy() {
    	return dy;
    }

Now I need to use it for determining collision:

if (r1.intersects(r2)) {
   	 }
     person.getdx()..................
    }

I want dx to equal 0, how do I express that? I will do the same for dy in due course.

I know how to express 'dx = 0;', the problem is dx is not recognized as a variable in board.java. Do I do this? This is in board.class if that helps.

if (r1.intersects(r2)) {
   	 }
     person.getdx()= 0; //This is the problem.
    }