Java optimizing painting a background image for a game

Question

I'm working on recreating "Legend of Zelda a Link to the Past" as part of an assignment.

And I've got the following problem, the game world is a BufferedImage of which I subImage() the part I need for the current location of the player. The game works but uses 80 / 110 percent of the CPU. A profile revealed that the culprit is the drawing of the image.

So I figured I put the background in a separate JPanel from the Player, enemies etc JPanel. Render them on top off each other (JLayeredPane) and repaint the background panel far less often.

But how do I do this how do I tell swing to draw one panel x times a sec and the other y times? If you have a better way of optimizing let me know.

Here's what I've got at the moment:

public class Main extends JFrame
{
    private ZeldaGame game = new ZeldaGame();
    private View view = new View(game);
    private BackgroundView bckView = new BackgroundView(game);
    private Controller ctl = new Controller(game, view, bckView, this);

    public Main()
    {
        setLayout(null);

        view.setBounds(0, 0, game.getWidth(), game.getHeight());
        bckView.setBounds(0, 0, game.getWidth(), game.getHeight());

        JLayeredPane pane = new JLayeredPane();
        pane.add(bckView, 1);
        pane.add(view, 0);

        setLayeredPane(pane);

        setSize(game.getWidth(), game.getHeight());
        setResizable(false);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setVisible(true);
    }

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

Thank You.

Answer 1

It's not really possible to have different render times because of the way the framebuffer works -- what the result would be is loads of nasty flickering. What you need to do is using Canvas instead of JPanel and JLayeredPane and you can either override the paint() method of the canvas or use bi.getGraphics() and blit the background and the characters on a loop using either of these methods in the correct order. I'd advise using a thin engine like GTGE which will abstract from all the messy details of optimisation. These high level components you're using seriously aren't designed for games, and you shouldn't be using them at all.

Answer 2

Ok I've found the error of my ways. I was using passive rendering while I should have used active rendering. Active rendering basically shuts down the automatic repaints by calling setIgnoreRepaint(true); on the frame and do the loop yourself.

And as an added bonus I don't need to use JPanels.