Question

Im working on a game in Java and having an issue (i believe its with the content pane) when rendering. I have a screen class which draws the background and all sprites to an Image. The frame then displays the image using a doubleBuffer. For some odd reason tho the image is rendering off the edge of the frame. You can see in the link below that the image is rendering 3 pixels to the left and 28 pixels above where it should be. Does anyone have any idea what could be causing this?
![enter image description here][1]

http://imageshack.us/photo/my-images/41/weirdg.png/

public class Game extends JFrame implements Runnable{
private static final long serialVersionUID = 1L;

//graphics
public BufferStrategy buffy;
BufferedImage image;
Screen screen;

public Boolean running = false;
public Boolean playerTurn = false;

public InputManager input;
public Level level;
//JButton b;

public static final int HEIGHT = 452;
public static final int WIDTH = 768;

public Game() {
    super("GridWars");
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    JPanel drawPanel = new JPanel();
    drawPanel.setPreferredSize(new Dimension(WIDTH, HEIGHT));
    drawPanel.setLayout(null);
    drawPanel.setOpaque(false);
    //drawPanel.setLocation(50,50);

    setContentPane(drawPanel);
    setResizable(false);
    pack();
    setLocationRelativeTo(null);
    setVisible(true);
    requestFocus();
    createBufferStrategy(2);

    //b = new JButton("this sucks");

    //getContentPane().add(b);
    //b.setBounds(300, 300, 100, 50);


    buffy = getBufferStrategy();
    image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
    screen = new Screen(WIDTH, HEIGHT);
    input = new InputManager(this);
    level = new Level(WIDTH, HEIGHT, input, this);
}

public void start() {
    running = true;
    new Thread(this).start();
}
public void setup(){

}
public void run() {
    final double TICKS = 30.0;
    final double UPDATE_INTERVAL_NS = 1000000000 / TICKS;
    double pastUpdateNS = System.nanoTime();

    int updateCount = 0;
    int frameCount = 0;

    final double FRAPS = 60.0; 
    final double RENDER_INTERVAL_NS = 1000000000 / FRAPS;
    double pastRenderNS = System.nanoTime();

    int pastSecondNS = (int) (pastUpdateNS/1000000000);

    while(running) {
        double nowNS = System.nanoTime();

        if(nowNS - pastUpdateNS >= UPDATE_INTERVAL_NS) {
            update();
            pastUpdateNS += UPDATE_INTERVAL_NS;
            updateCount++;
        }

        float interp = Math.min(1.0f, (float) ((nowNS - pastUpdateNS) / UPDATE_INTERVAL_NS) );
        render(interp);
        pastRenderNS += RENDER_INTERVAL_NS;
        frameCount++;

        int thisSecondNS = (int) (pastUpdateNS/1000000000);
        if (thisSecondNS > pastSecondNS) {
            //System.out.println("TICKS: "+updateCount+" | FRAPS: "+frameCount);
            updateCount = 0;
            frameCount = 0;
            pastSecondNS = thisSecondNS;
        }

        while( nowNS - pastRenderNS < RENDER_INTERVAL_NS && nowNS - pastUpdateNS < UPDATE_INTERVAL_NS) {
            try { Thread.sleep(1); } catch(Exception e) {};
            nowNS = System.nanoTime();
        }
    }
}

public void update() {
    input.update();
    level.update();
}

public void render(float interp) {
    level.render(screen, interp);

    image = screen.getImage();
    Graphics g = buffy.getDrawGraphics();
    g.drawImage(image, 0, 0, null, null);
    //b.repaint();
    g.dispose();
    buffy.show();
}

public static void main(String[] args) {
    Game game = new Game();
    game.start();
}
}

Answer 1

The 0,0 coordinate of Graphics object you obtain from buffy.getDrawGraphics(); is exactly at top left corner of JFrame and it is ignoring frame decorations.

1. UPD I forgot one obvious option. JFrame.getInsets() provides information about decorations. You could simply shift your rendering.

2. You would make frame undecorated (setUndecorated(true)) and render/manage window controls yourself.

3. Or, and i think it is easier way, you would forget about direct rendering on JFrame, place Canvas on it, and use it instead. Canvas also contains createBufferStrategy method, so you need few simple changes.

   JPanel drawPanel = new JPanel();
   drawPanel.setLayout(new BorderLayout());
   Canvas canvas = new Canvas();
   canvas.setPreferredSize(new Dimension(WIDTH, HEIGHT));
   drawPanel.add(canvas, BorderLayout.CENTER);
   
   // some code skipped
   
   canvas.setIgnoreRepaint(true); //important
   canvas.createBufferStrategy(2);
   
   buffy = canvas.getBufferStrategy();
   

I’ve created simple demo with similar render few days ago for another answer. Maybe it will helpful.