Question

I’m planning to write a simple spaceshooter. I have read that the repaint() method is only a request, and it doesn’t execute every time it’s called. I believe I’m noticing the effects of this, as my spaceship tends to lag ever so slightly when I’m moving it. Currently I’m simply drawing my ship in a a JPanel’s paintComponent() method, and keep calling repaint() on regular intervals (my panel’s also Runnable). Seeing as repaint() may potentially screw me over, I’m trying to find a way to work arround it, however I’ve ran out of ideas. The code I have so far:

private void renderGraphics() {
    if (MyImage == null) {
        MyImage = new BufferedImage(getPreferredSize().width,
                getPreferredSize().height, BufferedImage.TYPE_INT_RGB);
    }
    MyGraphics = MyImage.getGraphics();
    MyGraphics.setColor(Color.BLACK);
    MyGraphics.fillRect(0, 0, getPreferredSize().width, getPreferredSize().height);
    MyGraphics.drawImage(ship.getImage(), ship.getCurrentX(), ship.getCurrentY(), null);       
}

The idea was to create my own graphics, and then make the JPanel draw it, and keep calling this instead of repaint() in my run() method, however I have no idea how to do that. I’d appriciate any input on the matter.

Answer 1

There are multiple ways to approach this.

The best is probably to use BufferStrategy and draw to that, of which I have included a code snippet that should work for you.

You can take this one step further and abandon Swing altogether, just using Frame/BufferStrategy. There is a fully working example (from which the code snippet was taken and adapted) in my question here:

AWT custom rendering – capture smooth resizes and eliminate resize flicker

Anyway, here is an implementation BufferStrategy that you should be able to just drop in:

// you should be extending JFrame
public void addNotify() {
    super.addNotify();
    createBufferStrategy(2);
}

private synchronized void render() {
    BufferStrategy strategy = getBufferStrategy();
    if (strategy==null) return;
    sizeChanged = false;
    // 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 {
            MyGraphics draw = strategy.getDrawGraphics();
            draw.setColor(Color.BLACK);
            draw.fillRect(0, 0, getPreferredSize().width, getPreferredSize().height);
            draw.drawImage(ship.getImage(), ship.getCurrentX(), ship.getCurrentY(), null);
            draw.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());
}