Question

Next semester we have a module in making Java applications in a team. The requirement of the module is to make a game. Over the Christmas holidays I’ve been doing a little practice, but I can’t figure out the best way to draw graphics.

I’m using the Java Graphics2D object to paint shapes on screen, and calling repaint() 30 times a second, but this flickers terribly. Is there a better way to paint high performance 2D graphics in Java?

Answer 1

What you want to do is to create a canvas component with a BufferStrategy and render to that, the code below should show you how that works, I’ve extracted the code from my self written Engine over here.

Performance solely depends on the stuff you want to draw, my games mostly use images. With around 1500 of them I’m still above 200 FPS at 480×480. And with just 100 images I’m hitting 6k FPS when disabling the frame limiting.

A small game (this one has around 120 images at once at the screen) I’ve created can be found here (yes the approach below also works fine as an applet.)

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsEnvironment;
import java.awt.Toolkit;
import java.awt.Transparency;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;

import javax.swing.JFrame;
import javax.swing.WindowConstants;

public class Test extends Thread {
    private boolean isRunning = true;
    private Canvas canvas;
    private BufferStrategy strategy;
    private BufferedImage background;
    private Graphics2D backgroundGraphics;
    private Graphics2D graphics;
    private JFrame frame;
    private int width = 320;
    private int height = 240;
    private int scale = 1;
    private GraphicsConfiguration config =
            GraphicsEnvironment.getLocalGraphicsEnvironment()
                .getDefaultScreenDevice()
                .getDefaultConfiguration();

    // create a hardware accelerated image
    public final BufferedImage create(final int width, final int height,
            final boolean alpha) {
        return config.createCompatibleImage(width, height, alpha
                ? Transparency.TRANSLUCENT : Transparency.OPAQUE);
    }

    // Setup
    public Test() {
        // JFrame
        frame = new JFrame();
        frame.addWindowListener(new FrameClose());
        frame.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
        frame.setSize(width * scale, height * scale);
        frame.setVisible(true);

        // Canvas
        canvas = new Canvas(config);
        canvas.setSize(width * scale, height * scale);
        frame.add(canvas, 0);

        // Background & Buffer
        background = create(width, height, false);
        canvas.createBufferStrategy(2);
        do {
            strategy = canvas.getBufferStrategy();
        } while (strategy == null);
        start();
    }

    private class FrameClose extends WindowAdapter {
        @Override
        public void windowClosing(final WindowEvent e) {
            isRunning = false;
        }
    }

    // Screen and buffer stuff
    private Graphics2D getBuffer() {
        if (graphics == null) {
            try {
                graphics = (Graphics2D) strategy.getDrawGraphics();
            } catch (IllegalStateException e) {
                return null;
            }
        }
        return graphics;
    }

    private boolean updateScreen() {
        graphics.dispose();
        graphics = null;
        try {
            strategy.show();
            Toolkit.getDefaultToolkit().sync();
            return (!strategy.contentsLost());

        } catch (NullPointerException e) {
            return true;

        } catch (IllegalStateException e) {
            return true;
        }
    }

    public void run() {
        backgroundGraphics = (Graphics2D) background.getGraphics();
        long fpsWait = (long) (1.0 / 30 * 1000);
        main: while (isRunning) {
            long renderStart = System.nanoTime();
            updateGame();

            // Update Graphics
            do {
                Graphics2D bg = getBuffer();
                if (!isRunning) {
                    break main;
                }
                renderGame(backgroundGraphics); // this calls your draw method
                // thingy
                if (scale != 1) {
                    bg.drawImage(background, 0, 0, width * scale, height
                            * scale, 0, 0, width, height, null);
                } else {
                    bg.drawImage(background, 0, 0, null);
                }
                bg.dispose();
            } while (!updateScreen());

            // Better do some FPS limiting here
            long renderTime = (System.nanoTime() - renderStart) / 1000000;
            try {
                Thread.sleep(Math.max(0, fpsWait - renderTime));
            } catch (InterruptedException e) {
                Thread.interrupted();
                break;
            }
            renderTime = (System.nanoTime() - renderStart) / 1000000;

        }
        frame.dispose();
    }

    public void updateGame() {
        // update game logic here
    }

    public void renderGame(Graphics2D g) {
        g.setColor(Color.BLACK);
        g.fillRect(0, 0, width, height);
    }

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