CODEWITHSUNDEEP
javaswingawt
soapergem
soapergem

Reputation: 10029

How can I load images in the background in a Swing application?

I've got a simple Swing/AWT application that runs in full screen mode on Windows. I have a couple of different PNG files that it loads as its own background image depending on context.

It loads them like this:

BufferedImage bufferedImage;
bufferedImage = ImageIO.read(getClass().getResource("/bg1.png"));
Image bgImage1 = bufferedImage.getScaledInstance(width, height, Image.SCALE_SMOOTH);
bufferedImage = ImageIO.read(getClass().getResource("/bg2.png"));
Image bgImage2 = bufferedImage.getScaledInstance(width, height, Image.SCALE_SMOOTH);
bufferedImage = ImageIO.read(getClass().getResource("/bg3.png"));
Image bgImage3 = bufferedImage.getScaledInstance(width, height, Image.SCALE_SMOOTH);

And later draws them like this:

window.repaint();
graphics.drawImage(bgImage1, 0, 0, null);
// draw some other stuff too, like text

And just to be thorough, window is a JWindow variable, and graphics is a Graphics2D variable.

The problem I'm running into happens when I switch out one of the background images for another. The first time I do the switch, calling something like this:

window.repaint();
graphics.drawImage(bgImage2, 0, 0, null);
// draw some other stuff too, like text

...the entire screen goes white for about a second. And then it does successfully show the image, but that flicker is really annoying. My guess is that because the images are relatively large and high resolution (2560x1440), it needs about a second to load them and scale them to the appropriate size.

How can I get it to load those images silently? As in... how do I avoid drawing a blank white screen for a second, that first time it displays a new background image? All subsequent times are already instantaneous, probably because it's truly grabbed them into memory at that point. But simply calling getScaledInstance apparently isn't enough to put things into memory, because it doesn't actually flicker until I call drawImage down the line.

Upvotes: 0

Views: 181

Answers (2)

Radiodef
Radiodef

Reputation: 37875

ImageIcon will load in the background as a feature.

You can also accomplish this fairly easily with a background thread e.g.:

final String path = "/example.png";
new SwingWorker<BufferedImage, Void>() {
    @Override
    public BufferedImage doInBackground() throws IOException {
        return ImageIO.read(ClassName.class.getResource(path));
    }
    @Override
    public void done() {
        try {
            BufferedImage img = get();
            // put img somewhere
        } catch(InterruptedException ignored) {
        } catch(ExecutionException ex) {
            ex.printStackTrace(System.err);
        }
    }
}.execute();

Also,

window.repaint();
graphics.drawImage(bgImage2, 0, 0, null);

This worries me a little bit. In general we do not need to ask for a repaint of an entire top-level container. You should also not be using getGraphics() to paint.

Non-top-level Swing components are double-buffered but if you are painting outside of the paint structure you do not get this. It will result in flickering.

Two good sources for correct custom painting are:

Painting should be done passively by overriding paintComponent on a JComponent. A JLabel can also display an ImageIcon as a feature so you do not necessarily have to do custom painting if you just want to display an image.

Upvotes: 2

Passero
Passero

Reputation: 222

I notice that the scaling takes a lot of time, not the loading of the images. Because of this, I usually store a scaled image so I can use it later on so I only have to scale once.

Upvotes: 0

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