Basics of Java 2D games tutorial

Basics

In this part of the Java 2D games tutorial, we will write about some basics needed to create games. We will create a skeleton of a game. Paint a donut and display a picture.

About

This is Java 2D games tutorial. It is aimed at beginners. This tutorial will teach you basics of programming 2D games in Java programming language and Swing GUI toolkit. All images used in this tutorial can be downloaded here.

Skeleton

We will show the skeleton of each of our Java 2D games.

Board.java

package skeleton;

import javax.swing.JPanel;

public class Board extends JPanel {
    public Board() {
    }
}

The Board is a panel, where the game takes place.

Skeleton.java

package skeleton;

import javax.swing.JFrame;

public class Skeleton extends JFrame {

    public Skeleton() {
        add(new Board());
        setTitle("Skeleton");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(300, 280);
        setLocationRelativeTo(null);
        setVisible(true);
        setResizable(false);
    }
    public static void main(String[] args) {
        new Skeleton();
    }
}

This is the entry point of the game. Here we have the main method.

add(new Board());

Here we put the Board to the center of the JFrame component.

setDefaultCloseOperation(EXIT_ON_CLOSE);

This will close the application when we click on the close button. It is not the default behaviour.

setSize(300, 280);

This line sets the size for our window.

setLocationRelativeTo(null);

We center the window.

setVisible(true);

Show the window on the screen.

setResizable(false);

Make the window unresizable.

Figure: Skeleton

Donut

The objects on the Board are either images or are drawn with the painting tools provided by the Java 2D API. In the next example, we draw a Donut. We use the painting API.

Board.java

package donut;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.AffineTransform;
import java.awt.geom.Ellipse2D;

import javax.swing.JPanel;


public class Board extends JPanel{

    public void paint(Graphics g)
    {
      super.paint(g);

      Graphics2D g2 = (Graphics2D) g;

      RenderingHints rh =
            new RenderingHints(RenderingHints.KEY_ANTIALIASING,
                               RenderingHints.VALUE_ANTIALIAS_ON);

      rh.put(RenderingHints.KEY_RENDERING,
             RenderingHints.VALUE_RENDER_QUALITY);

      g2.setRenderingHints(rh);

      Dimension size = getSize();
      double w = size.getWidth();
      double h = size.getHeight();

      Ellipse2D e = new Ellipse2D.Double(0, 0, 80, 130);
      g2.setStroke(new BasicStroke(1));
      g2.setColor(Color.gray);


      for (double deg = 0; deg < 360; deg += 5) {
          AffineTransform at =
              AffineTransform.getTranslateInstance(w / 2, h / 2);
          at.rotate(Math.toRadians(deg));
          g2.draw(at.createTransformedShape(e));
        }
    }
}

The painting is done inside the paint() method.

Graphics2D g2 = (Graphics2D) g;

The Graphics2D object provides a sophisticated control over painting.

RenderingHints rh =
    new RenderingHints(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
rh.put(RenderingHints.KEY_RENDERING,
    RenderingHints.VALUE_RENDER_QUALITY);
g2.setRenderingHints(rh);

The rendering hints are used to make the drawing smooth.

Dimension size = getSize();
double w = size.getWidth();
double h = size.getHeight();

We get the height and the width of the window.

Ellipse2D e = new Ellipse2D.Double(0, 0, 80, 130);
g2.setStroke(new BasicStroke(1));
g2.setColor(Color.gray);

Here we create the ellipse.

for (double deg = 0; deg < 360; deg += 5) {
    AffineTransform at =
    AffineTransform.getTranslateInstance(w / 2, h / 2);
    at.rotate(Math.toRadians(deg));
    g2.draw(at.createTransformedShape(e));
}

Here the ellispse is rotated 72 times to create a "donut".

Donut.java

package donut;

import javax.swing.JFrame;


public class Donut extends JFrame {


    public Donut() {

        add(new Board());

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(360, 310);
        setLocationRelativeTo(null);
        setTitle("Donut");
        setVisible(true);
    }

    public static void main(String[] args) {
        new Donut();
    }
}

This is the main class.

Figure: Donut

Image

When we create computer games, we often work with images. In the next example we load an image and display it on the Board.

Board.java

package bardejov;

import java.awt.Graphics;
import java.awt.Graphics2D;

import java.awt.Image;

import javax.swing.ImageIcon;
import javax.swing.JPanel;

public class Board extends JPanel {

    Image bardejov;

    public Board() {
        ImageIcon ii = new ImageIcon(this.getClass().getResource("bardejov.jpg"));
        bardejov = ii.getImage();
    }

    public void paint(Graphics g) {

        Graphics2D g2d = (Graphics2D) g;
        g2d.drawImage(bardejov, 10, 10, null); 
    }
}

We display an image of a town on the Board. The image is drawn inside the paint() method.

ImageIcon ii = new ImageIcon(this.getClass().getResource("bardejov.jpg"));

We create an ImageIcon.

bardejov = ii.getImage();

We get an Image out of the ImageIcon.

g2d.drawImage(bardejov, 10, 10, null); 

We draw the image on the window.

Image.java

package bardejov;

import javax.swing.JFrame;


public class Image extends JFrame {

    public Image() {

        add(new Board());

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(280, 240);
        setLocationRelativeTo(null);
        setTitle("Bardejov");
        setVisible(true);
    }

    public static void main(String[] args) {
        new Image();
    }
}

This is the main class of the example.

Figure: Image

In this chapter, we have covered some basics of Java game programming.