How to add background image using Graphics in Java

Question

private void render() {
    BufferStrategy bufferStrat = this.getBufferStrategy();
    
    if(bufferStrat == null) {
        createBufferStrategy(3);
        return;
    }
     
    Graphics g = bufferStrat.getDrawGraphics();
    
    g.drawImage(image, 0,0, getWidth(), getHeight(), this);
    
    g.dispose();
    bufferStrat.show();
}

This gives a black background (which is right technically).

So how would I add a background image from my windows computer to replace the black background in my JFrame?

Answer 1

Simple example based on the example in the BufferStrategy JavaDocs

import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Test {

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

    public Test() {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends Canvas {

        private volatile boolean keepRendering = true;
        private BufferedImage background;
        private Thread renderThread;

        public TestPane() {
            try {
                background = ImageIO.read(getClass().getResource("/images/Background.jpg"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            if (background == null) {
                return new Dimension(200, 200);
            }
            return new Dimension(background.getWidth(), background.getHeight());
        }

        @Override
        public void addNotify() {
            super.addNotify();
            if (renderThread != null) {
                keepRendering = false;
                try {
                    renderThread.join();
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }
            }

            keepRendering = true;
            renderThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    render();
                    try {
                        Thread.sleep(16);
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    }
                }
            });
            renderThread.start();
        }

        @Override
        public void removeNotify() {
            super.removeNotify();
            if (renderThread == null) {
                return;
            }
            keepRendering = false;
            try {
                renderThread.join();
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }

        protected void render() {
            BufferStrategy strategy = getBufferStrategy();
            if (strategy == null) {
                createBufferStrategy(2);
            }
            // Just in case
            strategy = getBufferStrategy();
            if (strategy == null) {
                return;
            }
            while (keepRendering) {

                // Prepare for rendering the next frame
                // ...
                // Render single frame
                do {
                    // The following loop ensures that the contents of the drawing buffer
                    // are consistent in case the underlying surface was recreated
                    do {
                        // Get a new graphics context every time through the loop
                        // to make sure the strategy is validated
                        Graphics graphics = strategy.getDrawGraphics();

                        if (background != null) {
                            int x = (getWidth() - background.getWidth()) / 2;
                            int y = (getHeight() - background.getHeight()) / 2;
                            graphics.drawImage(background, y, y, this);
                        }

                        // Render to graphics
                        // ...
                        // Dispose the graphics
                        graphics.dispose();

                        // Repeat the rendering if the drawing buffer contents
                        // were restored
                    } while (strategy.contentsRestored());

                    // Display the buffer
                    strategy.show();

                    // Repeat the rendering if the drawing buffer was lost
                } while (strategy.contentsLost());
            }
        }

    }
}