Java Graphics drawImage消耗多少？

Question

I was making an application in Java, and noticed after doing this:

g.drawImage(ImageIO.read(...)....);

that it consumed a lot more CPU and frames, so I started to wonder and if there were any other better ways to draw an image.

Thanks!

Answer 1

It's not the drawImage that's taking up a lot of CPU, it's the ImageIO.read(…) ! Opening streams is expensive and thus should only be done once; when you first need to load the images. The best way to draw an image is to pre-load it into a BufferedImage (or if you manipulate the pixels a VolatileImage ).

BufferedImage imageToDraw = ImageIO.read(getClass().getResource("path/To/Image.png"));

That path starts in the directory of your .java files. So, you'll want to add a folder containing your image(s). There are many different ways to load images, more of which are discussed here .

Then you can draw it just like you did before.

g.drawImage(imageToDraw, x, y, null);

This should be much faster. If you are still having problems with speed then this question might be useful.

Answer 2

One possibility is using visualvm: http://visualvm.java.net . I've used it with some success.

Quick steps:

• start your app locally
• start visualvm
• Tools > Options > Profiling > Misc (bottom) > Reset calibration data: Ok
• in VVM, connect to your app ie, in left-hand frame, double-click on pkg.YourMainClass (pid 2112)
• Profiler tab, then click on Memory.

after initial baseline profiling is complete, you see a histogram of live objects.

You can take snapshots and compare them, set filters on packages, etc. See http://visualvm.java.net/docindex.html

Answer 3

If you're reading the image rather than holding it as an instance of Image, you will be taking way too much memory up.

I highly, HIGHLY suggest to store the image as an instance of Image with ImageIO.read(params) rather than drawing it and reading it every single loop pass-through.

You'd most likely do it like this in your Canvas/JPanel/Swing Component class:

private Image myImage;

//Assume other code here

public void loadImages() {
     myImage = ImageIO.read(params);
     //load any other images
}

public void paint(Graphics g) {
     g.drawImage(myImage, x, y, null);
}

Just like any other application, resources (images, data, etc) are all loaded at the start-up.