How to set background image in Java?

How to set background image in Java? - java

I am developing a simple platform game using Java using BlueJ as the IDE. Right now I have player/enemy sprites, platforms and other items in the game drawn using polygons and simple shapes. Eventually I hope to replace them with actual images.
For now I would like to know what is the simplest solution to setting an image (either URL or from local source) as the 'background' of my game window/canvas?
I would appreciate it if it isn't something long or complex as my programming skills aren't very good and I want to keep my program as simple as possible. Kindly provide example codes with comments to elaborate on their function, and also if it's in its own class, how to call on relevant methods used by it on other classes.
Thank you very much.

The answer will vary slightly depending on whether the application or applet is using AWT or Swing.
（Basically, classes that start with J such as JApplet and JFrame are Swing, and Applet and Frame are AWT.)
In either case, the basic steps would be:
Draw or load an image into a Image object.
Draw the background image in the painting event of the Component you want to draw the background in.
Step 1. Loading the image can be either by using the Toolkit class or by the ImageIO class.
The Toolkit.createImage method can be used to load an Image from a location specified in a String:
Image img = Toolkit.getDefaultToolkit().createImage("background.jpg");
Similarly, ImageIO can be used:
Image img = ImageIO.read(new File("background.jpg");
Step 2. The painting method for the Component that should get the background will need to be overridden and paint the Image onto the component.
For AWT, the method to override is the paint method, and use the drawImage method of the Graphics object that is handed into the paint method:
public void paint(Graphics g)
{
// Draw the previously loaded image to Component.
g.drawImage(img, 0, 0, null);
// Draw sprites, and other things.
// ....
}
For Swing, the method to override is the paintComponent method of the JComponent, and draw the Image as with what was done in AWT.
public void paintComponent(Graphics g)
{
　　　　// Draw the previously loaded image to Component.
　　　　g.drawImage(img, 0, 0, null);
　　　　// Draw sprites, and other things.
　　　　// ....
}
Simple Component Example
Here's a Panel which loads an image file when instantiated, and draws that image on itself:
class BackgroundPanel extends Panel
{
// The Image to store the background image in.
Image img;
public BackgroundPanel()
{
// Loads the background image and stores in img object.
img = Toolkit.getDefaultToolkit().createImage("background.jpg");
}
public void paint(Graphics g)
{
// Draws the img to the BackgroundPanel.
g.drawImage(img, 0, 0, null);
}
}
For more information on painting:
Painting in AWT and Swing
Lesson: Performing Custom Painting from The Java Tutorials may be of help.

Firstly create a new class that extends the WorldView class. I called my new class Background. So in this new class import all the Java packages you will need in order to override the paintBackground method. This should be:
import city.soi.platform.*;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.image.ImageObserver;
import javax.swing.ImageIcon;
import java.awt.geom.AffineTransform;
Next after the class name make sure that it says extends WorldView. Something like this:
public class Background extends WorldView
Then declare the variables game of type Game and an image variable of type Image something like this:
private Game game;
private Image image;
Then in the constructor of this class make sure the game of type Game is in the signature of the constructor and that in the call to super you will have to initialise the WorldView, initialise the game and initialise the image variables, something like this:
super(game.getCurrentLevel().getWorld(), game.getWidth(), game.getHeight());
this.game = game;
bg = (new ImageIcon("lol.png")).getImage();
Then you just override the paintBackground method in exactly the same way as you did when overriding the paint method in the Player class. Just like this:
public void paintBackground(Graphics2D g)
{
float x = getX();
float y = getY();
AffineTransform transform = AffineTransform.getTranslateInstance(x,y);
g.drawImage(bg, transform, game.getView());
}
Now finally you have to declare a class level reference to the new class you just made in the Game class and initialise this in the Game constructor, something like this:
private Background image;
And in the Game constructor:
image = new Background(this);
Lastly all you have to do is add the background to the frame! That's the thing I'm sure we were all missing. To do that you have to do something like this after the variable frame has been declared:
frame.add(image);
Make sure you add this code just before frame.pack();.
Also make sure you use a background image that isn't too big!
Now that's it! Ive noticed that the game engines can handle JPEG and PNG image formats but could also support others. Even though this helps include a background image in your game, it is not perfect! Because once you go to the next level all your platforms and sprites are invisible and all you can see is your background image and any JLabels/Jbuttons you have included in the game.

Or try this ;)
try {
this.setContentPane(
new JLabel(new ImageIcon(ImageIO.read(new File("your_file.jpeg")))));
} catch (IOException e) {};

The Path is the only thing you really have to worry about if you are really new to Java.
You need to drag your image into the main project file, and it will show up at the very bottom of the list.
Then the file path is pretty straight forward. This code goes into the constructor for the class.
img = Toolkit.getDefaultToolkit().createImage("/home/ben/workspace/CS2/Background.jpg");
CS2 is the name of my project, and everything before that is leading to the workspace.

<script>
function SetBack(dir) {
document.getElementById('body').style.backgroundImage=dir;
}
SetBack('url(myniftybg.gif)');
</script>

Related

Java Applet - Drawing Polygons - Reading RGB

I am trying to write a Java Applet that has the ability to draw polygons on a canvas. So far so good.
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class DrawingLines2 extends Applet implements ItemListener {
DrawCanvas canvas;
public void init() {
// Create components and lay out the applet
canvas = new DrawCanvas();
...
}
}
class DrawCanvas extends Canvas implements ActionListener, MouseListener{
...
}
However, I would then like the program to be able to get the current visible canvas and loop through each pixel, collecting its color.
However, it does not appear that there is a method within the Canvas class that lets me get the color of a pixel in the canvas at a specified point (x,y).
Is there another way of achieving this?

One approach might be to use Robot#getPixelColor, but you will need to convert the pixel position from the component space to the screen space. This might be rather slow and you could also have issues creating the Robot instance due to the tight security restrictions that applets operate under.
Another option might be to create a BufferedImage the same size as the DrawCanvas and using its Graphics context, call print on the DrawCanvas
Something like...
class DrawCanvas extends Canvas implements ActionListener, MouseListener{
//...
public Color getRGBAt(int x, int y) {
BufferedImage img = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_TYPE_INT_ARGB);
Graphics2D g2d = img.createGraphics();
paint(g2d);
g2d.dispose();
return new Color(img.getRGB(x, y), true);
}
Now, personally, I'd strongly discourage you from using AWT based components and encourage you to use the Swing API instead, as AWT is rather antiquated and not many developers are using it actively, making it difficult to find support for problems you might have. I'd also encourage you not to use applets if you can avoid it, while you are learning; they have a bunch of their own issues which just complicate the whole process, without much gain.

Create a BufferedImage, do your drawings on that BufferedImage then copy the content of BufferedImage to the Canvas using drawImage().
Use getData() or getRGB() from BufferedImage to get the pixel color.

JPanel: What is the simplest way to display an image?

I am working on a project and I need to display an image that I have already drawn. I need a background image and several foreground images that I can move around. What is the easiest way to do this? I haven't been able to find a clear answer.
ImageIcon image = new ImageIcon("imagename.jpg");
JLabel label = new JLabel("", image, JLabel.CENTER);
JPanel panel = new JPanel(new BorderLayout());
panel.add( label, BorderLayout.CENTER );
return panel;

The answer depends. Do you want to resize the background image to meet the requirements of the client are or not? If so, do you want to "fill" or "fit" the image to the area.
Take a look at Java: maintaining aspect ratio of JPanel background image for a lengthier discussion on the topic.
The next question you need to ask, is do you want to paint the animation on the surface or use existing components and move them instead...
You could check out...
Swing animation running extremely slow
https://stackoverflow.com/questions/15858623/how-to-use-a-swing-timer-to-animate/15859932#15859932
Drawing 2 Balls to move in different direction on Java but one disappeared
Java Bouncing Ball
Multiple bouncing balls thread issue
I am trying to make ball gradually move
the images are not loading
Which uses the paintComponent or direct paint method.
This approach is relatively common and easy to control. The problem is if you want to perform sub animation (ie animate the actually element separately from the main animation...think walking or spinning), then it becomes more difficult.
Check out
Java ball object doesn't bounce off of drawn rectangles like it's supposed to.
Which uses components instead. This method is good if you want to provide sub animation, but has the complexity of requiring you to size and position the components within the container.
Just as a side note. JLabel is a container ;)

The easiest way i've found is to create an entirely new class and extend JPanel like so:
import javax.swing.*;
import javax.imageio.*;
import java.io.*;
import java.awt.*;
public class Background extends JPanel {
private Image image;
public Background(){
this.setPreferredSize(new Dimension(width,height));
image =Toolkit.getDefaultToolkit().getImage("your_image.jpg");;
}
public void paintComponent(Graphics g) {
//paints the background image
super.paintComponent(g);
do{
}while(g.drawImage(image, 0, 0, null)==false);
}
}
To instantiate this class simply call this:
Background b= new Background();
From your main program.
Remember that b now acts as a Jpanel so you can simply call b.add(element)
If you don't understand what i've talked about and shown you, view this document on extending classes:
Extending Classes

is it possible to add background image to jdesktop pane

I am trying to create virtual desktop. I complete successfully.But i am not able to set background image for jdesktoppane. I want to set background image and After adding image also the desktop pane work normally.Is anyone know means just tell me
Thanks

From this thread at coderanch, a possible solution is to paint in the paintComponent method of your subclass of the JDesktopPane (or in your renderer for this class, which could be better).

You can extend JDeskTopPane class with another member as image and then in constructor set the background to that image.
public ExtendedJDesktopPane(Image image) {
super();
this.image = image;
}
protected void paintComponent(Graphics g) {
g.drawImage(scaledImage, 0, 0, this);
}
EDIT:
This is similar to the link provided below by Riduidel.. i just got late writing it.

Pictures in a JPanel

I'm trying to write an application where I want to add different pictures on a Jpanel. Everything works fine except for the JPG format which displays very bad quality images.
This is how I do the drawing :
class draw extends Canvas
{
Dimension canvasSize = new Dimension(400, 400);
String fileName;
public void paint(Graphics g)
{
if(this.fileName!=null)
{
Toolkit toolkit = Toolkit.getDefaultToolkit();
Image img = toolkit.getImage(fileName);
g.drawImage(img, 0, 0, this);
}
}
public void setFileName(String name)
{
this.fileName=name;
}
public Dimension getMinimumSize()
{
return canvasSize;
}
public Dimension getPreferredSize()
{
return canvasSize;
}
}
Is there a way such that JPG format is covered ?

This is probably because you're stretching (or compressing) the image to the size of the canvas. JPEG images don't look great when you scale them, particularly if you're scaling up. Try an image that's the same size as (or close to) your canvas. You can also get the height and width of the JPEG from the Image class and display it in its original dimensions. Sun's Drawing an Image tutorial shows how to do this.

The posted code indicates that the OP is painting the image at its original size. So my comments about the code:
a) You say you want to add the image to a JPanel, yet for some reason you are extending Canvas. Stick with Swing components. Then if you need to do custom painting you would override the paintComponent() method NOT the paint method.
b) When you do use custom painting, you should never read the image in the painting method. This method can be called numerous times. It possible that the image has not been completely read into memory. I know Swing will automatically repaint as more of the image is read, I'm not sure how the AWT Canvas works.
c) Also, when overriding paint methods don't forget to invoke super.paint(), super.paintComponent() or you may get unexpected results.
d) However, based on the posted code there is no need to even do custom painting (since you are drawing the image at its actual size). Just create an ImageIcon from the image and add the Icon to a JLabel. Then you just add the label to the GUI.
I suggest you read the section from the Swing tutorial on How to Use Icons. If the image quality is poor then the problem is probably with your image because now you are using standard code, not custom code.

How to add an image to a JPanel?

I have a JPanel to which I'd like to add JPEG and PNG images that I generate on the fly.
All the examples I've seen so far in the Swing Tutorials, specially in the Swing examples use ImageIcons.
I'm generating these images as byte arrays, and they are usually larger than the common icon they use in the examples, at 640x480.
Is there any (performance or other) problem in using the ImageIcon class to display an image that size in a JPanel?
What's the usual way of doing it?
How to add an image to a JPanel without using the ImageIcon class?
Edit: A more careful examination of the tutorials and the API shows that you cannot add an ImageIcon directly to a JPanel. Instead, they achieve the same effect by setting the image as an icon of a JLabel. This just doesn't feel right...

If you are using JPanels, then are probably working with Swing. Try this:
BufferedImage myPicture = ImageIO.read(new File("path-to-file"));
JLabel picLabel = new JLabel(new ImageIcon(myPicture));
add(picLabel);
The image is now a swing component. It becomes subject to layout conditions like any other component.

Here's how I do it (with a little more info on how to load an image):
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JPanel;
public class ImagePanel extends JPanel{
private BufferedImage image;
public ImagePanel() {
try {
image = ImageIO.read(new File("image name and path"));
} catch (IOException ex) {
// handle exception...
}
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image, 0, 0, this); // see javadoc for more info on the parameters
}
}

Fred Haslam's way works fine. I had trouble with the filepath though, since I want to reference an image within my jar. To do this, I used:
BufferedImage wPic = ImageIO.read(this.getClass().getResource("snow.png"));
JLabel wIcon = new JLabel(new ImageIcon(wPic));
Since I only have a finite number (about 10) images that I need to load using this method, it works quite well. It gets file without having to have the correct relative filepath.

I think there is no need to subclass of anything. Just use a Jlabel. You can set an image into a Jlabel. So, resize the Jlabel then fill it with an image. Its OK. This is the way I do.

You can avoid rolling your own Component subclass completely by using the JXImagePanel class from the free SwingX libraries.
Download

JLabel imgLabel = new JLabel(new ImageIcon("path_to_image.png"));

You can subclass JPanel - here is an extract from my ImagePanel, which puts an image in any one of 5 locations, top/left, top/right, middle/middle, bottom/left or bottom/right:
protected void paintComponent(Graphics gc) {
super.paintComponent(gc);
Dimension cs=getSize(); // component size
gc=gc.create();
gc.clipRect(insets.left,insets.top,(cs.width-insets.left-insets.right),(cs.height-insets.top-insets.bottom));
if(mmImage!=null) { gc.drawImage(mmImage,(((cs.width-mmSize.width)/2) +mmHrzShift),(((cs.height-mmSize.height)/2) +mmVrtShift),null); }
if(tlImage!=null) { gc.drawImage(tlImage,(insets.left +tlHrzShift),(insets.top +tlVrtShift),null); }
if(trImage!=null) { gc.drawImage(trImage,(cs.width-insets.right-trSize.width+trHrzShift),(insets.top +trVrtShift),null); }
if(blImage!=null) { gc.drawImage(blImage,(insets.left +blHrzShift),(cs.height-insets.bottom-blSize.height+blVrtShift),null); }
if(brImage!=null) { gc.drawImage(brImage,(cs.width-insets.right-brSize.width+brHrzShift),(cs.height-insets.bottom-brSize.height+brVrtShift),null); }
}

There shouldn't be any problem (other than any general problems you might have with very large images).
If you're talking about adding multiple images to a single panel, I would use ImageIcons. For a single image, I would think about making a custom subclass of JPanel and overriding its paintComponent method to draw the image.
(see 2)

JPanel is almost always the wrong class to subclass. Why wouldn't you subclass JComponent?
There is a slight problem with ImageIcon in that the constructor blocks reading the image. Not really a problem when loading from the application jar, but maybe if you're potentially reading over a network connection. There's plenty of AWT-era examples of using MediaTracker, ImageObserver and friends, even in the JDK demos.

I'm doing something very similar in a private project I'm working on. Thus far I've generated images up to 1024x1024 without any problems (except memory) and can display them very quickly and without any performance problems.
Overriding the paint method of JPanel subclass is overkill and requires more work than you need to do.
The way I do it is:
Class MapIcon implements Icon {...}
OR
Class MapIcon extends ImageIcon {...}
The code you use to generate the image will be in this class. I use a BufferedImage to draw onto then when the paintIcon() is called, use g.drawImvge(bufferedImage); This reduces the amount of flashing done while you generate your images, and you can thread it.
Next I extend JLabel:
Class MapLabel extends Scrollable, MouseMotionListener {...}
This is because I want to put my image on a scroll pane, I.e. display part of the image and have the user scroll around as needed.
So then I use a JScrollPane to hold the MapLabel, which contains only the MapIcon.
MapIcon map = new MapIcon ();
MapLabel mapLabel = new MapLabel (map);
JScrollPane scrollPane = new JScrollPane();
scrollPane.getViewport ().add (mapLabel);
But for your scenario (just show the whole image every time). You need to add the MapLabel to the top JPanel, and make sure to size them all to the full size of the image (by overriding the GetPreferredSize()).

This answer is a complement to #shawalli's answer...
I wanted to reference an image within my jar too, but instead of having a BufferedImage, I simple did this:
JPanel jPanel = new JPanel();
jPanel.add(new JLabel(new ImageIcon(getClass().getClassLoader().getResource("resource/images/polygon.jpg"))));

Create a source folder in your project directory, in this case I called it Images.
JFrame snakeFrame = new JFrame();
snakeFrame.setBounds(100, 200, 800, 800);
snakeFrame.setVisible(true);
snakeFrame.add(new JLabel(new ImageIcon("Images/Snake.png")));
snakeFrame.pack();

You can avoid using own Components and SwingX library and ImageIO class:
File f = new File("hello.jpg");
JLabel imgLabel = new JLabel(new ImageIcon(file.getName()));

I can see many answers, not really addressing the three questions of the OP.
1) A word on performance: byte arrays are likely unefficient unless you can use an exact pixel byte ordering which matches to your display adapters current resolution and color depth.
To achieve the best drawing performance, simply convert your image to a BufferedImage which is generated with a type corresponding to your current graphics configuration. See createCompatibleImage at https://docs.oracle.com/javase/tutorial/2d/images/drawonimage.html
These images will be automatically cached on the display card memory after drawing a few times without any programming effort (this is standard in Swing since Java 6), and therefore the actual drawing will take negligible amount of time - if you did not change the image.
Altering the image will come with an additional memory transfer between main memory and GPU memory - which is slow. Avoid "redrawing" the image into a BufferedImage therefore, avoid doing getPixel and setPixel at all means.
For example, if you are developing a game, instead of drawing all the game actors to a BufferedImage and then to a JPanel, it is a lot faster to load all actors as smaller BufferedImages, and draw them one by one in your JPanel code at their proper position - this way there is no additional data transfer between the main memory and GPU memory except of the initial transfer of the images for caching.
ImageIcon will use a BufferedImage under the hood - but basically allocating a BufferedImage with the proper graphics mode is the key, and there is no effort to do this right.
2) The usual way of doing this is to draw a BufferedImage in an overridden paintComponent method of the JPanel. Although Java supports a good amount of additional goodies such as buffer chains controlling VolatileImages cached in the GPU memory, there is no need to use any of these since Java 6 which does a reasonably good job without exposing all of these details of GPU acceleration.
Note that GPU acceleration may not work for certain operations, such as stretching translucent images.
3) Do not add. Just paint it as mentioned above:
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(image, 0, 0, this);
}
"Adding" makes sense if the image is part of the layout. If you need this as a background or foreground image filling the JPanel, just draw in paintComponent. If you prefer brewing a generic Swing component which can show your image, then it is the same story (you may use a JComponent and override its paintComponent method) - and then add this to your layout of GUI components.
4) How to convert the array to a Bufferedimage
Converting your byte arrays to PNG, then loading it is quite resource intensive. A better way is to convert your existing byte array to a BufferedImage.
For that: do not use for loops and copy pixels. That is very very slow. Instead:
learn the preferred byte structure of the BufferedImage (nowadays it is safe to assume RGB or RGBA, which is 4 bytes per pixel)
learn the scanline and scansize in use (e.g. you might have a 142 pixels wide image - but in the real life that will be stored as a 256 pixel wide byte array since it is faster to process that and mask the unused pixes by the GPU hardware)
then once you have an array build according to these principles, the setRGB array method of the BufferedImage can copy your array to the BufferedImage.

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