Checking intersection of two shapes of type Graphics java AWT

[Zayaan Khan]

Hi. I am making a game where there is a character that the snake (player controls this) and an enemy. What I am trying to achieve is that the program should detect collisions between the snake and the enemy . However, I have drawn both the snake and the enemy using fillRect() and fillOval() respectively (using Graphics library java AWT) and my current collision detection code is not functioning.

I am wondering if there is a way to check for collisions between two java AWT Graphics objects. I will show my code which includes the current state of collision detection in my program. I have also included a screenshot image of the current state of collision detection in my program.

Code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.Random;
import java.util.List;

public class Panel extends JPanel implements ActionListener {

    static final int SCREEN_WIDTH = 600;
    static final int SCREEN_HEIGHT = 600;
    Dimension dimension = new Dimension(SCREEN_WIDTH, SCREEN_HEIGHT);
    static final int UNIT_SIZE = 25;
    static final int GAME_UNITS = (SCREEN_WIDTH * SCREEN_HEIGHT) / UNIT_SIZE;
    final int[] x = new int[GAME_UNITS];
    final int[] y = new int[GAME_UNITS];
    int bodyParts = 6;
    int applesEaten = 0;
    int appleX;
    int appleY;
    char direction = 'R';
    boolean running = false;
    Timer timer;
    final int DELAY = 75;
    Random random;

    // enemy
    final int[] enemyX = new int[GAME_UNITS];
    final int[] enemyY = new int[GAME_UNITS];
    int enemyBody = 3;
    char enemyDirection = 'D';

    // button
    JButton retryButton;
    JButton exitButton;
    int timeAlive = 0;


    Panel() {
        super();

        // button
/*        retryButton = new JButton("Try Again");
        retryButton.setFont(new Font("Monaco", Font.PLAIN, 20));
        retryButton.setBounds(50, (SCREEN_HEIGHT / 2) + 200, 200, 50);
        retryButton.setFocusable(false);
        retryButton.setVisible(true);
        retryButton.setEnabled(true);*/

        exitButton = new JButton("Exit");
        exitButton.setFont(new Font("Monaco", Font.PLAIN, 20));
        exitButton.setBounds((SCREEN_WIDTH / 2 ) + 50, (SCREEN_HEIGHT / 2) + 200, 200, 50);
        exitButton.setFocusable(false);
        exitButton.setVisible(true);
        exitButton.setEnabled(true);

        random = new Random();
        this.setPreferredSize(dimension);
        this.setBackground(Color.BLACK);
        this.setOpaque(true);
       // this.setBounds(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT); // same size as window  -> white bg but grid displayed
        this.setFocusable(true);
        this.addKeyListener(new MyKeyAdapter());
        this.addKeyListener(new KeyClicked());

        startGame();

        this.setVisible(true);
    }

    public void startGame() {
        newApple();
        running = true;
        timer = new Timer(DELAY, this);
        timer.start();
    }
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        draw(g);
    }
    public void draw(Graphics g) {
        if (running) {
            for (int i = 0; i < SCREEN_WIDTH / UNIT_SIZE; i++) {
                g.drawLine(0, i * UNIT_SIZE, SCREEN_WIDTH, i * UNIT_SIZE);

                for (int j = 0; j < SCREEN_HEIGHT / UNIT_SIZE; j++) {
                    g.drawLine(j * UNIT_SIZE, 0, j * UNIT_SIZE, SCREEN_HEIGHT);
                }
            }
            g.setColor(Color.RED);
            g.fillOval(appleX, appleY, UNIT_SIZE, UNIT_SIZE);

            // drawing snake
            for (int i = 0; i <= bodyParts; i++) {
                if (i == 0) {
                    g.setColor(Color.BLUE);
                    g.fillRect(x[i], y[i], UNIT_SIZE, UNIT_SIZE);
                } else {
                    g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255)));
                }
            }
            // drawing enemy
            for (int i = 0; i < enemyBody; i++) {
                if (i == 0) {
                    g.setColor(new Color(47, 152, 47));
                    //g.fillOval(enemyX[i], enemyY[i], UNIT_SIZE, UNIT_SIZE);
                    g.fillOval(SCREEN_WIDTH / 2 , enemyY[i], UNIT_SIZE, UNIT_SIZE);


/*                    g.translate(SCREEN_WIDTH / 2, SCREEN_HEIGHT / 2);*/
                } else {
                    g.setColor(new Color(47, 152, 47));
               //     g.fillOval(enemyX[i], enemyY[i], UNIT_SIZE, UNIT_SIZE);
                    g.fillOval(SCREEN_WIDTH / 2 , enemyY[i], UNIT_SIZE, UNIT_SIZE);
/*                    g.translate(SCREEN_WIDTH / 2, SCREEN_HEIGHT / 2);*/
                }
            }
        }
        else {
            gameOver(g);
        }
    }
    public void newApple() {
        appleX = random.nextInt((int) (SCREEN_WIDTH / UNIT_SIZE)) * UNIT_SIZE;
        appleY = random.nextInt((int) (SCREEN_HEIGHT / UNIT_SIZE)) * UNIT_SIZE;
    }
    public void move() {
        for (int i = bodyParts; i > 0; i--) {
            x[i] = x[i-1];
            y[i] = y[i-1];
        }
        switch (direction) {
            case 'U': y[0] = y[0] - UNIT_SIZE; break;
            case 'D': y[0] = y[0] + UNIT_SIZE; break;
            case 'L': x[0] = x[0] - UNIT_SIZE; break;
            case 'R': x[0] = x[0] + UNIT_SIZE;
        }
        // enemy movement
        for (int j = enemyBody; j > 0; j--) {
            enemyY[j] = enemyY[j-1];
            if (enemyY[j] == SCREEN_HEIGHT) {
                enemyY[j] = enemyY[j+1];
            }
        }
        // enemy direction
        switch (enemyDirection) {
            case 'U': enemyY[0] = enemyY[0] - UNIT_SIZE;
            if (enemyY[0] == 0)
                enemyDirection = 'D';
            break;
            case 'D': enemyY[0] = enemyY[0] + UNIT_SIZE;
            if (enemyY[0] == SCREEN_HEIGHT)
                enemyDirection = 'U';
            break;
            case 'L': enemyX[0] = enemyX[0] - UNIT_SIZE; break;
            case 'R': enemyX[0] = enemyX[0] + UNIT_SIZE;
        }
    }
    public void checkApple() {
        if ((x[0] == appleX) && (y[0] == appleY)) {
            applesEaten++;
            bodyParts++;
            newApple();
        }
    }
    public static boolean getIntersection(int[] arr1, int[] arr2) {
        List<Integer> list = new ArrayList<Integer>();
        for (int i = arr1.length - 1 ; i > 0; i--) {
            for (int j = arr2.length - 1; j > 0; j--) {
                if (arr1[i] == arr2[j]) {
                    return true;
                }
                else {
                    return false;
                }
            }
        }
        return false;
    }

    public void checkCollisions() {
        // check if head touches body
        for (int i = bodyParts; i > 0; i--) {
            if ((x[0] == x[i]) && (y[0] == y[i])) {
                running = false;
                break;
            }
        }
        // check if head touches borders
        if (x[0] < 0) {
            running = false; // if touches left border
        }
        if (x[0] > SCREEN_WIDTH) { // if touches right border
            running = false;
        }
        if (y[0] < 0) { // if touches top border
            running = false;
        }
        if (y[0] > SCREEN_HEIGHT) { // if touches bottom border
            running = false;
        }
/*        for (int i = bodyParts; i > 0; i--) {
            for (int z = enemyBody; z > 0; z--) {
                if (((x[0] == enemyX[0]) && (y[0] == enemyY[0])) || ((x[i] == enemyX[z]) && (y[i] == enemyY[z]))) {
                    running = false;
                    break;
                }
            }
        }*/
        if (getIntersection(x, enemyX) && getIntersection(y, enemyY)) {
            running = false;
        }
    }
}

I have taken out some misc code to attempt to shorten the post

the image below shows how collision detection is currently not working between the snake and the enemy (green)

[Norm Radder]

I have taken out some misc code to attempt to shorten the post

Could you fix the code so that it compiles and executes for testing?

Where are the locations of the two objects stored?

[Carey Brown]

if( x[i] == enemyX[i] && y[i] == enemyY[i] )

Would this work?

[Rob Camick]

I am wondering if there is a way to check for collisions between two java AWT Graphics objects.

Don't paint graphics objects.

Instead paint Shape objects using the Graphics2D.fill( Shape ) method.

Then you can use the Shape.intersects(...) method to check for collisions.

Check out Playhing With Shapes for some general information on using a Shape object.

An example of playing with shapes that you can create and drag around a panel:

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;

public class ShapePanel extends JPanel
{
	private ArrayList<ColoredShape> coloredShapes = new ArrayList<ColoredShape>();

	public ShapePanel()
	{
		DragListener dl = new DragListener();
		addMouseListener(dl);
		addMouseMotionListener(dl);
	}

	@Override
	protected void paintComponent(Graphics g)
	{
		super.paintComponent(g);

		Graphics2D g2 = (Graphics2D) g;
		g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

		for (ColoredShape cs : coloredShapes)
		{
			g2.setColor( cs.getForeground() );
			g2.fill( cs.getShape() );
		}
	}

	@Override
	public Dimension getPreferredSize()
	{
		return new Dimension(600, 500);
	}

	public void addShape(Shape shape, Color color)
	{
		// Convert the Shape to a GeneralPath so the Shape can be translated
		// to a new location when dragged

		ColoredShape cs = new ColoredShape(color, new GeneralPath(shape));
		coloredShapes.add( cs );
		repaint();
	}

	class ColoredShape
	{
		private Color foreground;
		private GeneralPath shape;

		public ColoredShape(Color foreground, GeneralPath shape)
		{
			this.foreground = foreground;
			this.shape = shape;
		}

		public Color getForeground()
		{
			return foreground;
		}

		public void setForeground(Color foreground)
		{
			this.foreground = foreground;
		}

		public GeneralPath getShape()
		{
			return shape;
		}
	}

	class DragListener extends MouseAdapter
	{
		private GeneralPath dragShape;
		private Point pressed;

		@Override
		public void mousePressed(MouseEvent e)
		{
			//  the clicked Shape will be moved to the end of the List
			//  so it is painted on top of all other shapes.

			if (SwingUtilities.isLeftMouseButton(e))
			{
				pressed = e.getPoint();

				for (int i = coloredShapes.size() - 1; i >= 0; i--)
				{
					ColoredShape cs = coloredShapes.get(i);

					if (cs.getShape().contains( pressed ))
					{
						coloredShapes.remove(i);
						coloredShapes.add(cs);
						repaint();
						dragShape = cs.getShape();
						break;
					}
				}
			}
		}

		@Override
		public void mouseDragged(MouseEvent e)
		{
			if (dragShape != null)
			{
				int deltaX = e.getX() - pressed.x;
				int deltaY = e.getY() - pressed.y;

				dragShape.transform(AffineTransform.getTranslateInstance(deltaX, deltaY));

				pressed = e.getPoint();
				repaint();
			}
		}

		@Override
		public void mouseReleased(MouseEvent e)
		{
			dragShape = null;
		}
	}

	private static void createAndShowGUI()
	{
		ShapePanel shapePanel = new ShapePanel();

		GeneralPath barBell = new GeneralPath();
		barBell.append(new Ellipse2D.Double(100, 100, 75, 100), true);
		barBell.append(new Rectangle2D.Double(150, 125, 175, 50), true);
		barBell.append(new Ellipse2D.Double(300, 100, 75, 100), true);
		shapePanel.addShape(barBell, Color.RED);

		Rectangle2D rect = new Rectangle2D.Double(100, 300, 75, 150);
		shapePanel.addShape(rect, Color.BLUE);

		Polygon triangle = new Polygon();
		triangle.addPoint(0, 0);
		triangle.addPoint(100, 0);
		triangle.addPoint(50, 100);
		triangle.translate(400, 250);
		shapePanel.addShape(triangle, Color.GREEN);

		//Shape star = ShapeUtils.radiusShape(10, 30, 12);
		//shapePanel.addShape(star, Color.CYAN);

		JFrame frame = new JFrame("ShapePanel");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.add(shapePanel);
		frame.pack();
		frame.setLocationByPlatform(true);
		frame.setVisible(true);
	}

	public static void main(String[] args)
	{
		java.awt.EventQueue.invokeLater( () -> createAndShowGUI() );
	}
}

Note, the above code converts the Shape objects to a GeneralPath object to make the dragging logic easier. In your case you can just keep the objects a Shape objects.

[Zayaan Khan]

Norm Radder wrote:

I have taken out some misc code to attempt to shorten the post

Could you fix the code so that it compiles and executes for testing?

Where are the locations of the two objects stored?

If you want to test the code, you can use the following link which links to my github project and the code for the main class and panel class is there: https://github.com/zkhan122/snakeboost

[Norm Radder]

Can you post code that demonstrates the problem.  The code from github does not show any collisions when it executes without any interaction from the user.

[Zayaan Khan]

Norm Radder wrote:Can you post code that demonstrates the problem.  The code from github does not show any collisions when it executes without any interaction from the user.

The code on my github repository is the current state of the program. You mentioned "does not show any collisions when it executes without any interaction from the user" and that is the problem I am facing; where when the snake collides with the enemy, there is no feedback which ultimately means that my program is not detecting collisions properly.

[Zayaan Khan]

Carey Brown wrote:

if( x[i] == enemyX[i] && y[i] == enemyY[i] )

Would this work?

What exactly would I iterate over? Because iterating over the variable bodyParts would mean that I am iterating over the snake body but the enemy and snake do not have the same body length. Can you clarify further?

[Norm Radder]

When I execute the code, I do not see any collisions between the two moving bodies.
What do I need to do to make the moving bodies collide?
Can you change the code so that the two bodies collide very soon after the program starts?

How are you debugging the code to see what the x,y values are for both of the moving bodies so you can see what the values are when a collision is missed?   I suggest adding some print statements that print the x,y values for each moving body.

[Carey Brown]

for( int snakeIndex=0 ; snakeIndex < snakeLength ; snakeIndex++ )
    for( int enemyIndex=0 ; enemyIndex < enemyLength ; enemyIndex++ )
        if( x[snakeIndex] == enemyX[enemyIndex] && y[snakeIndex] == enemyY[enemyIndex] )
            // TODO

[Norm Radder]

The code needs lots of debugging to find all the bugs before worrying about the collision logic.
For example,
the enemy body does not reverse when touching all 4 boundaries.
Current code does not use the enemyX and enemyY values for displaying its location.
And more

[Zayaan Khan]

Norm Radder wrote:The code needs lots of debugging to find all the bugs before worrying about the collision logic.
For example,
the enemy body does not reverse when touching all 4 boundaries.
Current code does not use the enemyX and enemyY values for displaying its location.
And more

The enemy body is programmed to just reverse vertically when it touches top border and bottom border (not horizontal borders as you mentioned "4 borders"). Is that not being displayed for you?

[Norm Radder]

There are no comments in  the code saying what directions are valid for the enemy body. Is it only 'U' and D?
Also there are no comments regarding what value of x the enemy should have.  The code appears to use the center column.
 

                  g.fillOval(SCREEN_WIDTH / 2 , enemyY[i], UNIT_SIZE, UNIT_SIZE);

What about my other requests for the code?

When I execute the code, I do not see any collisions between the two moving bodies.
What do I need to do to make the moving bodies collide?
Can you change the code so that the two bodies collide very soon after the program starts?

How are you debugging the code to see what the x,y values are for both of the moving bodies so you can see what the values are when a collision is missed?   I suggest adding some print statements that print the x,y values for each moving body.

[Zayaan Khan]

Norm Radder wrote:There are no comments in  the code saying what directions are valid for the enemy body. Is it only 'U' and D?
Also there are no comments regarding what value of x the enemy should have.  The code appears to use the center column.
 

                  g.fillOval(SCREEN_WIDTH / 2 , enemyY[i], UNIT_SIZE, UNIT_SIZE);

What about my other requests for the code?

When I execute the code, I do not see any collisions between the two moving bodies.
What do I need to do to make the moving bodies collide?
Can you change the code so that the two bodies collide very soon after the program starts?

How are you debugging the code to see what the x,y values are for both of the moving bodies so you can see what the values are when a collision is missed?   I suggest adding some print statements that print the x,y values for each moving body.

The body only moves up and down hence the 'U' and 'D'. X value is being treated as 0 as the center is being treated as Y axis (i believe) and it is moving up and down that vertical axis

Also with regards to your request of wanting the "two bodies to collide very soon after the program starts" my problem is the collision itself which I believe I have made clear; my collisions are not working so I need help with that. Others have suggested not to use Graphics g and instead use Rectangles and intersects() which is fine but I want to try my best to do it without intersects() first. If you can provide help with that, it is very much appreciated

[Norm Radder]

my collisions are not working

How do you get a collision?
When I test the program, I would like to see a collision almost immediately after the program starts.
Currently when I execute the program the two bodies do not collide.  One just runs off the screen.

Can you change the code so that the two bodies start near each other and have paths that cross so that there is a collision very soon after the program starts?

How does the code use the enemyX array?  I don't see that it is used when the body is drawn.

[Norm Radder]

Make the game more challenging by having the enemy change directions:
At the class level:

    char[] dirs = {'U','D','L','R'};
    long nbrMoves = 0;  // used to change enemy's direction

In the move method:

      //  change directions every now and then <<<<<<<<<<<
        nbrMoves++;
        if(nbrMoves % 15 == 0) {
            int idx = (int)(Math.random()*dirs.length);
            enemyDirection = dirs[idx];
            System.out.println("dir changed to " + enemyDirection);
        }

[Zayaan Khan]

Norm Radder wrote:

my collisions are not working

How do you get a collision?
When I test the program, I would like to see a collision almost immediately after the program starts.
Currently when I execute the program the two bodies do not collide.  One just runs off the screen.

Can you change the code so that the two bodies start near each other and have paths that cross so that there is a collision very soon after the program starts?

How does the code use the enemyX array?  I don't see that it is used when the body is drawn.

When you say you would like to see a collision, are you referring to how you would like to see the two bodies crossing over each other (perpendicular intersection) as soon as the program starts? Because they can overlap but the program should stop and say "Game over" when it is a perpendicular intersection (any part of snake touching enemy)  or even if the snake head touches any part of enemy.

Also the

enemyX

array was originally being used to draw the enemy but since I wanted the enemy body to start going up and down in the CENTER that is why I replaced

enemyx{i] 

with

SCREEN_WIDTH / 2

. I will try to make the enemy direction randomized as you stated for further upgrade in difficulty.

[Norm Radder]

I replaced ...

Then the code that tests for collisions needs to know and use that so it does not use enemyX.

the program should stop and say "Game over" when ...

The collision never happens.
What does a tester need to do to make a collision happen?  I do not get a collision when I execute the code.

[Zayaan Khan]

Norm Radder wrote:

I replaced ...

Then the code that tests for collisions needs to know and use that so it does not use enemyX.

the program should stop and say "Game over" when ...

The collision never happens.
What does a tester need to do to make a collision happen?  I do not get a collision when I execute the code.

Hi thanks for your help overall I actually managed to get the collision detection working such that when the head of the player snake touches the green enemy then the program detects this and ends the game. I managed to do this by drawing rectangles (as hit boxes) around both sprites and checking if rectangles intersect and also changed my logic for the nested for loop and how it was detecting if the coordinates of both sprites were the same ! (though this is only for the head so I need to do the same for the whole of the player snake body).